What does it mean to dump the soil in a pioneer way. Justification of the type of dam and the method of its construction

The most common type of pure gravity platforms are reinforced concrete structures or steel bases ballasted with heavy weights. Reinforced concrete platforms can be a monocon, a columned structure, or a structure with nearly vertical walls. Steel structures, as a rule, have a large number of ballast tanks for receiving water or a weighted composition. A common feature is the presence of voluminous cavities for receiving ballast, which provides greater downforce. Gravity bases are installed in areas where there is an ice situation.

Picture 5 - Steel base on the support mat

Picture 6 - Steel base

Picture 7 - Reinforced concrete base

Flyovers. Stationary platforms with a through support block

The most interesting from the point of view of the development of the resources of the Black and Azov Seas are flyovers and stationary platforms with a through base.

The structures under consideration are primarily united by the permeability for waves and currents of their load-bearing structures supporting the deck with the superstructure. The main structural element of these structures are steel pipes. In addition, the overpasses and the vast majority of support platforms have piled foundations, which provide stability to the entire structure on the seabed.

Flyovers. Overpasses are long structures that provide continuous surface connection of drilling sites with the shore. Drilling rigs and more technological equipment, which is typical for oil and gas fields, are located on the platforms near the trestle. The width of the carriageway of overpasses (usually 3.5 m) allows one-way traffic, therefore, in addition to drilling sites, traveling platforms are arranged along the overpasses. In terms of functionality, overpasses are similar to dams with widenings for drilling sites, but they are built at relatively large depths - about 6-15 m, in some cases, in water areas 20 m or more deep.

The main load-bearing element of the overpass are piles - usually metal pipes with a diameter of 0.3-0.5 m. Reinforced concrete prismatic piles or shell piles are used much less frequently. The supporting element of the overpass consists of two obliquely driven piles connected by a crossbar at a level exceeding the crest of the calculated wave. Piles are also connected by braces to give the structure greater rigidity. Over the crossbars of the supporting elements, bridge structures made of rolled profiles are laid.

As the depth of the sea increases at the construction site of the overpass, the difficulties of mounting flat support blocks increase due to their insufficient rigidity in the direction of the axis of the structures. Therefore, at depths of about 20 m, spatial support blocks are used from two pairs of obliquely driven piles connected by braces in the longitudinal and transverse directions. At the same time, the step of the supports increases, and the span structures instead of the beam structure take the form of spatial trusses.

The first overpasses were built in the oil fields of the Caspian Sea in the 1930s. By the beginning of the 70s. the total length of overpasses in this area reached 360 km. A large number of overpasses were built in the USA during the development of shallow water areas of the shelf in the California region and in the Gulf of Mexico. At shallow depths, the installation of overpasses is carried out in a pioneering way: the next supporting element is installed in the water from an already finished site using a crane. Prismatic or pyramidal support blocks are placed on the bottom using crane ships, fastened with superstructures to the already built part of the overpass and fixed on the bottom by driving piles.

Pile-based platforms. This is the largest group of hydraulic structures on the sea shelf. The first platform was built in 1936 on the Caspian Sea, in 1947 the first platform appeared abroad - in the Gulf of Mexico, at a depth of 6 m. The total number of platforms built around the world since that time is estimated from three to ten thousand.

In the Caspian Sea alone, the number of platforms built (they are called "steel islands") is approaching 1000. Most of the platforms are installed at shallow depths, but about 2000 are operated at depths from 30 to 300 m. structures intended for the development of the shelf.

Since the construction of the first platforms, the ability to conduct installation work at different depths in the open sea, the problems solved on the shelf have changed, and, as a result, the design forms of the platforms have changed. As the depths of the sea, on which the platforms are installed, increase, the proportions, the structure of the supporting blocks and the methods of their construction change.

However, all these changes do not manifest themselves in the form of any qualitative jumps associated with certain depth values ​​or other factors, so the division of platforms into any groups is conditional.

Platforms on several supporting blocks are built mainly at depths of up to 100 m. The first platforms, built in the 50s. at depths up to 30 m, consisted of four to six prismatic or pyramidal blocks of a rectangular shape with a common upper structure. Such structures are still used at depths up to 40 m. . Depending on the depth of the sea, the blocks receive dimensions in plan from 8x16 to 20 x 20 m. Living quarters are arranged, as a rule, on a separate support block, 30-50 m away from the platform for fire safety reasons and connected to it by a walkway. Transportation and installation of blocks are carried out with the help of crane ships. At depths greater than 40 m, the stability of loose prismatic blocks during installation is insufficient. Therefore, the blocks are given a pronounced pyramidal shape, and their total number is reduced to two. As the depth increases and the number of blocks decreases, the dimensions and masses of individual support blocks increase. So, at sea depths of 60-80 m, the mass of one block is 1.2-2.0 thousand tons, and at depths of 100-120 m it reaches 4 thousand tons.

Monoblock platforms. Platforms with a supporting monoblock on a pile foundation are built in the entire range of sea depths on which stationary platforms are operated, i.e. from a few meters to 300 m or more) Starting from a depth of about 100 m, structures with two or more supporting blocks are almost never used . Variants of supporting monoblocks are shown in Figure 9. With access to great depths of the sea, the functions of the supporting block and pile foundation have also changed. In overpasses and multi-block platforms, piles play the main role - they directly perceive loads from the upper structure and carry horizontal loads from waves, currents and ice. Support blocks in such structures only add rigidity to the entire spatial system. For deep-sea platforms on a monoblock, piles and a spatial truss work together. Measures are taken to rigidly connect the support block to the piles (annulus grouting, welding), and as a result, the loads from the topside are perceived by both the piles and the support block. In late built platforms, the piles end at the bottom of the block, and the block posts transfer part of the load directly to the ground.

Support blocks are manufactured on the shore completely or from several sections (tiers). They are transported either on special barges or afloat. During the installation period (before piling), a monoblock placed on the bottom is more stable than individual blocks of a multi-block support structure.

The supporting monoblock of the deep-water platform consists of panels - side flat trusses - and diaphragms connecting them - flat trusses, which stiffen the entire spatial structure. The main element of the panels and the entire support block are racks - metal pipes with a diameter of 1.2-3.0 m (in some cases up to 10 m), with walls 15-50 mm thick. The total number of racks in a block can be different - from 4 to 15. The height of the block racks may have different diameters, and different racks of the same block may differ in diameter. To give buoyancy to the support block, the racks of one of the panels are made much larger in diameter than all the others. The braces of panels and diaphragms are made of tubular elements of smaller diameters than the racks. With an increase in the diameter of the struts, the difficulties in ensuring the stability of the shape of shells that are subjected to significant external hydrostatic pressure increase sharply. How difficult it is to ensure structural rigidity is shown in Figure 11, which shows fragmentary diaphragms, bulkheads and stiffeners inside a rack with a diameter of 8 m.

An increase in the diameter of the props in order to achieve the necessary buoyancy of the support block leads to a significant increase in the metal consumption of the structure. Therefore, in the construction of high support blocks, it is necessary to resort to a stepwise change in the diameter and thickness of the pipes that make up the racks.

An example of this design approach is a drilling platform designed to be installed at a depth of 395 m (Figure 12). The relatively light upper structure of the platform (its mass is 1.5 thousand tons) is supported by a support block, which has a mass 40 times greater (60 thousand tons). In addition, 30,000 tons of steel should be spent on the piles securing the block, and 3,000 tons on risers for a cluster of 24 wells.

The topside structure (modules with process and power equipment, drilling rig, storage and living quarters, helipad) are located on the deck - a metal flooring laid on beams, which* in turn rest on a frame that transfers loads to the support block. Top modules

Figure 11 - Construction of a large diameter support column

buildings are installed in 2-3 tiers. The total mass of the superstructure can be reduced if it is made as a single structure. In this case, due to the own rigidity of the superstructure, the supporting block can also be lightened. However, for installation work in this case, cranes of very large lifting capacity are required. Usually the deck is made separately from the support block and installed on it already in the water area after the block is fixed with piles. In the case when the deck is connected to the support block while still on the shore, it is difficult to tow the structure afloat, but installation work at sea is simplified. The deck flooring must prevent contamination of the water area with drilling fluid, oil and other substances, and therefore has a flare.

The piles that fasten the support block to the ground are steel pipes with a diameter of 0.92 - 2.13 m and walls 3 8 - 64 mm, they are driven into the bottom soil to a depth of 150 m (in some cases even deeper). The main piles are driven inside the supports of the supporting block, their upper end is at the deck level. Piles driven by impacts on the upper end have an open lower end. If the hammer is placed inside the pile (such a solution is more effective, especially if the pile is long), its lower end is muffled. As the pile sinks into the ground, it is increased from above by welding. After the pile is immersed to a predetermined depth, its part protruding above the support block is cut off. At the top, the pile and the block stand are connected by welding, and the space between them is cemented. In some cases, to strengthen the structure in the most vulnerable places - at the level of ice impact and soil entry - one or more pipes are additionally immersed inside the piles and the entire space between them is cemented.

The holding force of the piles driven through the legs of the supporting block may not be sufficient to ensure the stability of the deep water platform from capsizing. In this case, the fringing piles are additionally driven. They can be placed along the contour of the block or concentrated near the racks. It is possible to widen the lower part of the support block in the form of a lattice grillage by fixing it with piles along the entire contour. This solution is of particular interest as it allows the main piles (inside the posts) to be dispensed with, and the fringing piles to be driven vertically. Additional (enclosing) piles are attached to the support block under water directly at the bottom with the help of couplings - guides of short pipe cuts welded at several levels to the support block. After driving the piles to a predetermined depth, the space between them and the couplings is filled with cement mortar (expanding cements are used for this). Large-diameter support posts have a plug at the bottom and rest on the ground, while transferring part of the load from the support block to it. Piles in this case are placed around the racks.

In bearing blocks with posts varying in diameter in steps, only fringing piles, the heads of which are located near the soil surface, can be used. In particular, the support block must be secured with 56 piles, of which 16 are driven through sockets located between the block posts, and the remaining 40 in groups of four around all nine posts.

The scheme of the pile foundation device is shown in Figure 13 . Through couplings - pipes with a diameter of 1.72 m - "short" piles are first driven to a depth of 75 m (they ensure the stability of the block during the initial period of installation work at sea). These piles are made of pipes with a diameter of 1.52 m and walls 25 mm thick. Then, wells are drilled inside the "short" piles and immersed in them to a depth of 135 m below the bottom surface of a pipe with a diameter of 1.22 m. All pipes (couplings and piles) end at a level of 45 m above the bottom surface. The space between all pipes is cemented. Note that at the entrance to the ground, all pipes have inserts of 15 meters in length with thicker walls.

The mass of the support blocks of deep-water platforms significantly exceeds the carrying capacity of floating cranes and crane ships. Therefore, regardless of the method of delivery of the block to the installation site, the operation of placing it on the seabed is always preceded by the position of the block afloat. The buoyancy of the block is achieved not only due to

a significant increase in the diameter of part of the racks, which subsequently leads to large loads on the structure from waves and currents, but also the use of temporary buoyancy - cylindrical tanks or pontoons attached to the block before launching.

The deepest platforms installed after 1975 are operated at oil fields in the Santa Barbara Strait (California) and in the Gulf of Mexico: Hondo (sea depth 260 m), Gervaise (285 m), Cognac (312 In 1988, the Balwinkle platform is to be installed at a depth of 411 m. In the North Sea, since 1975, the Ninian South (138 m), BrentA (140 m), and Thistle platforms have been installed (162m), "Magnus" (186m). Some information about these platforms will be given below. It should be noted that the more severe conditions of the North Sea led to a significantly higher material consumption of the steel platforms installed there. For comparison: the weights of the Gervase and Brent A platforms installed at depths of 285 and 140 m are approximately the same - 39.7 and 33.0 thousand tons. This ratio is also typical for other platforms in these two shelf areas.

/Platforms on a submerged pontoon or shoes. A sharp increase in the cost and labor intensity of the pile foundation with an increase in the depth of the water area makes it necessary to look for such constructive solutions in which piles are not used at all or their role in ensuring the stability of the structure turns out to be secondary. The French company Seatank proposed a platform design with a through support block on a reinforced concrete pontoon, which combines the structural elements of the main types of deep-sea platforms discussed in this and the previous paragraphs.

A through metal support block is fixed on a reinforced concrete pontoon. The pontoon has the same cellular structure as the Kormoran A and Brent C platforms. The cellular pontoon gives buoyancy to the structure during transportation from the shore to the installation site on the bottom, then it is used for ballasting and, finally, for oil storage. In the variant of the platform, designed for production drilling and production at a sea depth of 200 m, the storage capacity of the oil storage is 150 thousand m 3 . The support block must support the topside weighing about 25 thousand tons and has an area of ​​5 thousand m 2. Eight (or other number) cylinders at the corners of the pontoon are used for ballasting and then storing oil.
The reinforced concrete pontoon rests directly on the seabed; its area and mass are determined taking into account the requirements for the stability of the structure from shear and overturning. To increase the shear resistance along the ground, it is possible to immerse metal shells into the ground through special holes in the pontoon. Generally similar structures can be classified as gravitational.

The advantage of the considered design (it is called composite or combined) is that it can be used in cases where piling is impossible (the presence of a rock under a relatively thin layer of soft soils). At the same time, it provides less resistance to wave propagation and flow (like all through support blocks) and makes it possible to successfully solve the problem of storing produced oil.

1 - steel truss of the support block; 2 - ballast tanks with a support shoe (oil storage facilities); 3 - water separating columns; 4 - ballast tanks

Another solution to the problem of ensuring the stability of a through support block without the use of a pile foundation is embodied in the design of the Teknomare platform. The support block is attached to three cylindrical ballast tanks supported by widened and weighted shoes installed directly on the seabed. The configuration of the support block, the dimensions of the tanks and the deck are chosen from the conditions of the area of ​​operation, the purpose of the platform and the depth of the sea.

The first four Teknomare platforms (Figure 14 a) were installed in 1976 at a depth of 86 m in the Congo region. They are designed for an Amy wave and are designed to drill 15 wells (each) and produce oil without storage. Platform erected in 1983 . in the North Sea at a depth of 95 m (Figure 14 b), designed for drilling 24 wells and oil production. It has large-volume ballast tanks, during operation they are used to store 100 thousand m 3 of oil. The diameter of the tanks is 25.7 m. Three shoes with a diameter of 47 m are loaded with solid ballast with a total mass of 51 thousand tons. The tanks of the shoes form a triangle with sides equal to 90 m in plan. The entire structure is made of steel, the total consumption of which is 41.7 thousand tons. This structure is designed for a wave 27 m high. The platform shown in Figure 14c is intended for installation in the Mediterranean Sea at a depth of 200 m.

The advantages of steel gravitational support blocks of this type compared to reinforced concrete ones include the fact that they can be completely manufactured in a pit, since they have a small draft before receiving liquid and solid ballast. The unit is towed in a vertical position, in an area with sufficient great depth it is sunk and takes over the fully assembled topside from the barge, then it is guided to the landing site and ballasted. It is assumed that such structures will find application at sea depths up to 300 - 400 m in areas with a heavy wind regime.

The design of the Mandrill platform (Figure 15) resembles a sliding tripod used to install film or photographic equipment. It is believed that such structures may find application in offshore areas with heavy wind wave conditions, such as the North Sea, and in areas with a depth of 200-500 m. The design option shown in Figure 15 is designed for a depth of 350 m.

Figure - 15. Platform "Mandrill" (a) and options for resting the "legs" of the platform on the ground (b-d)

1 - "legs" forming an A-shaped frame; 2 - folding "leg"; 3 - coupler; 4 - water separating columns; 5 - piles; 6 - couplings for fixing piles; 7 - support shoe

The platform is intended for drilling 56 production wells and oil production, its top structure weighing 55 thousand tons has dimensions of 70 x 120 m in plan and rises 26 m above the water (the estimated wave height is assumed to be 31 m). Spatial supporting structure mounted under water from a flat system of articulated lattice elements assembled on the shore and transported afloat. This system includes: A-shaped rigid connection of two "legs" and struts, a third folding "leg" and two more struts. Three options for supporting the "legs" of the platform on the ground are proposed: with driving of inclined piles (Figure 15b) - steel pipes with a diameter of 2.44, up to 130 m long and weighing up to 450 tons through conductors mounted on inclined "legs"; with driving vertical piles (Figure 15 c), immersed through holes in the support shoes; without driving piles (Figure 15 15 d) - with rigid or hinged fastening to widened shoes. The latter support option is suitable in the presence of sufficiently strong soils.

Platforms with a through support block in the form of a guyed mast. The structures of such platforms are similar to ground structures used as supports for radio, radio relay and television antennas (Figure 16). It is believed that the design can be applied in the depth range of 200 - 700 m. The fundamental difference mast-shaped platform from other deep-water fixed structures is that it does not transmit a bending moment to the subgrade.

The supporting block (underwater mast shaft) is made in the form of a steel pipe truss, its cross section forms a square. Inside the block there are conductors for lowering drill strings. The barrel is held in a vertical position with the help of braces-cables attached to the garlands of arrays lying at the bottom. Guys continue from arrays to pile anchors. Under normal loads on the structure, the garlands of arrays lie on the bottom. Under extreme loads (during a severe storm), the garlands come off the bottom and thereby absorb the jerks transmitted to the braces from the swinging trunk. Calculations and experiments on a large-scale model have shown that the adopted scheme for damping the oscillatory movements of the system provides small (no more than 2%) deviations of the trunk from the vertical.

Two options for resting the trunk on the ground have been developed. In the first, the trunk has a pile foundation. At the same time, part of the piles transfers to the ground all the loads from the upper structure of the platform, i.e. these piles are immersed in the ground through the supports of the support block and are connected to the deck structure with their upper end. This solution is typical for most other structures with a through support block on a pile foundation. The other part of the piles secures the trunk from twisting, and their heads are fixed in the lower end of the trunk. In another version, the pile foundation is not used: the lower end of the shaft is given a conical shape, due to which it sinks 2-15 m into the ground under the weight of the block itself, ballast and due to the vertical component of the tension force of each brace.

The first Lena platform in the form of an underwater guyed mast was installed at a depth of 305 m. Cognac" installed at a depth of 312 m. smaller lengths, used as piles, securing the trunk from twisting. To unfasten the shaft, 20 guys are installed - cables with a diameter of 137 mm and a length of 550 m - with the inclusion of a garland of arrays with a total mass of 200 tons in each of them. The calculated reinforcement in the guy is determined to be 5-6 MN, and the breaking force is 15 MN.

A more daring design decision was made for a platform intended for installation in the Gulf of Mexico at a depth of 700 m. The 40 m wide shaft is fastened by 16 guys with a diameter of 100 mm with garlands of arrays weighing 165 tons. Anchor piles - pipes with a diameter of 1.5 m - are loaded from drilling ships into pre-drilled wells to a depth of 15 m and cemented. The lower cone-shaped end of the trunk is buried in the ground and does not have a pile foundation.

To mount the support block of the deep-sea platform, it is proposed to use the method first used in the construction of the Hondo platform. The support block is manufactured at the shore base in the form of two parts equipped with ballast tanks. one piece afloat. After receiving "ballast (sea water) into the tanks of that part of the block that should be facing down, the block gradually turns and goes into a vertical position without the help of crane equipment. After driving the anchor piles and unfastening the block with braces (first, four two mutually perpendicular directions, and then the rest), all ballast tanks are filled with water, and piles are driven (if any) or the block is immersed in the ground due to its own weight.

The operation of connecting the parts of the block afloat is very complicated, especially since it has to be performed directly above the platform installation site, i.e., in the open sea. Therefore, it is recommended, if possible, to assemble the whole block on the shore. This is exactly what was done during the construction of the Lena platform. The support block was launched from the barge and immediately assumed a vertical position due to the fact that in the lower part it had ballast in the form of iron ore, and in the upper part - inside the block - 12 ballast tanks - buoyancy devices with a diameter of 6 and a length of 36 m.

It is noteworthy that the block was lowered from the barge not through the stern, as usual, but over the side. Inside the block, the main piles (those that should support the upper structure) were placed on the shore. They were built up and hammered with the help of equipment installed on a barge. From the barge, the installation of the deck of the upper structure of the platform was also carried out.

The depth of 700 m is not the limit for this type of fixed platforms.

Assembly and pile work. In the construction of overpasses and platforms in areas with shallow depths, a variety of crane and pile driving equipment is used. Select technological processes that are least dependent on weather conditions.

Initially, floating pile drivers were used to drive piles. Pile work and installation of the flooring could only be carried out in calm weather. The pioneering method of construction has significantly expanded the range of weather conditions for installation and pile work. Numerous modifications of the pioneer method are associated with different technological characteristics of the crane equipment used. Consider, for example, the technology of mounting a flyover.

The parts of the piles located above the crossbar are cut off, all the mounting units are welded, the flooring is installed (d), and then the crane moves forward to the length of the new section. Trestle construction cranes are designed for the construction of trestle sections up to 20 m at depths of about 30 m. Trestle sites are erected in the same pioneering way when working in a direction perpendicular to the axis of the trestle.

Installation of blocks of the support structure of platforms, having a mass of up to 3 thousand tons, is carried out, as a rule, from crane ships, on which the blocks are delivered to a given area. The most responsible operation is tilting - transferring the block to a vertical position. Apply various ways tilting: on the water with the support of the block racks on the ground; through the side of the vessel with support on the bar of a special console; with fastening of the upper part of the block for the deck bollard; blocks that have their own buoyancy in the water, when controlling the reception of ballast into racks.

After landing on the bottom, the block is leveled by various means. Irregularities in the bottom can be eliminated directly under the posts by washing with water supplied through pipes attached to the posts. The leveled block is fixed with metal tubular piles driven through the posts. If the pile driving fails before reaching the calculated immersion depth, a soil plug has to be drilled out to reduce the pile driving resistance. The pipe cavity is then filled with concrete to a level of 5-8 m above the bottom surface. A combination of driven piles with anchoring is possible: the pile is driven to the roof of rocky or semi-rocky soil, then a well is drilled into which the anchor is lowered, and then the well and the cavity of the pile with the anchor rod passed through it are filled with concrete. For increase bearing capacity piles sometimes apply injection cement mortar into the surrounding soil. To do this, the soil plug is completely drilled out of the pile and the solution is fed through the lower end of the pile and holes specially provided for this along its length. Such an operation leads to an increase in the bearing capacity of the pile on the ground by 2-2.5 times. Another way to increase the bearing capacity of a pile is to drill a hole through a driven pile, which is then expanded with sliding device, a reinforcement frame is inserted into the resulting extension and the lower part of the pile and the entire space is poured with concrete.

The manufacturing and installation technology of deep-water platforms differs from that used for flyovers and platforms with several support blocks by a higher degree of industrialization of work and the complexity of individual operations caused by the large dimensions and weight of the support block.

Pipes of small and medium diameters, as well as rolled profiles, are delivered to the enterprise in finished form. Pipes of large diameters (2-10m) and beams of large deck set height (up to 3m) are manufactured directly at the enterprise, equipped for this purpose with semi-automatic production lines.

Assembly of nodes - connections of the supporting parts of the platform and the surface platform, buoyancy tanks, tubular nodes, stiffeners,
floors of intermediate decks, ladders - is carried out in assembly shops equipped with special welding machines and apparatus, lifting and transport mechanisms, assembly devices for various purposes. Manual welding is used only to make seams that are inaccessible to automatic welding. The largest mass of units is determined by the lifting capacity of the crane equipment of assembly shops and usually does not exceed 100 tons.

Intermediate processing of units before sending them to the place of final assembly of the support block consists primarily in the removal of stresses in the material that arise during the welding process. For this, annealing is used in special chambers - furnaces. Intermediate treatment also includes shot blasting of components, degreasing, etching, application protective coatings, galvanization.

The final assembly of the support block is carried out on the slipway, in the dock or in the pit. First, flat panels are assembled. The entire support block is assembled from panels and diaphragms in a horizontal position. The panels are lifted and set in a vertical position with the help of several cranes (up to 6-10) on caterpillar tracks with a total carrying capacity of 200-400 tons. Braces are used to temporarily fix the panels in a vertical position.

Transportation and installation on the bottom of the support blocks of deep-water platforms are carried out using their own buoyancy (when sealing the tubular elements of the block) and ballast tanks or pontoons attached to the racks. Blocks assembled in a pit or dry dock float after the pit floods and are towed afloat to the installation site. Blocks assembled on slipways are launched or moved to special barges. These barges must have decks of considerable size and provide the necessary stability when loaded, taking into account the high position of the center of gravity of the block. In particular, to transport a block 435 m long and weighing 50 thousand tons, intended for the construction of the Balwinkle platform in the Gulf of Mexico at a depth of 411 m, a barge with dimensions of 250 x 62 x 15 m is being built. winches and hydraulic jacks.

The transportation of blocks on barges is more common, despite the fact that during the descent from the barge, special loading conditions of the block arise, requiring the introduction of an additional lattice into the structure of the block. Assembling the block in a pit on pontoons simplifies transport operations, in some cases eliminates the need to deepen the pit and the approach channel. However, blocks transported on pontoons must be designed for waves during the transition period.

The masses and dimensions of the supporting blocks of deep-water platforms are such that the use of crane ships or floating cranes during transportation and installation on the bottom is excluded. Several ways to launch the blocks into the water and move them to a vertical position are shown in Figure 19. The easiest way to set the block to the bottom is when it is towed afloat. By ballasting tanks, internal compartments in racks or pontoons (a), the block gradually turns in the water and acquires a vertical position. After that, it is guided more accurately over the design point of the installation, ballasted and goes to the bottom. The pontoons can then be detached from the block and removed. In another way (b) the block is transported on two pontoons installed across the block. After pulling out - one pontoon, the block turns around the other pontoon and goes down. A method for transporting the block on a barge and pontoon (c) is proposed. Ballasting the pontoon causes the block to pivot around the stern of the barge and slide down at the same time.

The method of launching and installing the block, shown in Figure d, was used during the construction of the "Hondo" platform (water depth 260 m). afloat using specially designed conical grippers mounted on four corner posts.The docking operation was carried out in a protected harbor near the platform installation site.The alignment of the sections on the water was achieved by ballasting the buoyancy in the legs.The docking units with their spring clamps and pneumatic couplings are close to articulated, therefore, after purging the compartments of the racks, welders were lowered into them, who welded the joints from the inside.

Launching long blocks from the barge is dangerous due to surges when the block rests only on the swivel frame at the edge of the barge. In order to avoid damage to the block, an additional lattice is created in it - sprengels. At the stern of the barge intended for lowering long blocks, a double swivel frame (d) is mounted. The loads on the block when leaving the barge are also reduced in the case when the launching is not accompanied by the simultaneous lowering of the block to the bottom (e).

Descent to the bottom from a horizontal position afloat (Figure 20) is considered the most manageable. The unit is brought into a vertical position by ballasting the upright compartments as shown (positions IV and Y).

In world practice, there are examples of assembling the support block of a deep-water platform from three tiers under water. We are talking about the Cognac platform (Figure 22), a block that was divided in height into tiers with dimensions of 47, 97 and 184 m (total block height 328 m, sea depth 312 m). collected in a pit in a vertical position and towed in the same position to the installation site at a distance of 200 km The second and third tiers were assembled in a horizontal position and transported on barges. The dimensions of the block along the bottom were 116 x 122 m.

The development of the transverse descent of the block from the barge (over the side) continues. This method of descent allows you to do without reinforcing the block with shrengels and save up to 10% of metal on this. However, it is difficult to ensure simultaneous overboarding of the entire block, and the list of the barge at this moment reaches 3.0°. Nevertheless, the support block with a length of 330 m and a mass of 27 thousand tons (the Lena platform, which will be discussed later) was lowered entirely over the side of the barge, which has a length of 176 and a width of 49 m. The descent was controlled remotely, while the entire crew removed from the barge.

Pile driving is the most time-consuming stage of installing blocks at the site of operation. Until a certain part of the piles is driven, the structure is not stable, which is especially dangerous in a storm. There are cases when an unfixed block lost stability even in calm - due to erosion of the soil by bottom currents.

How labor-intensive piling is is illustrated by the example of anchoring a bearing block in the North Sea at a depth of 108 m, when it took three weeks to drive 24 piles with a diameter of 1.52 m to a depth of 45 m under quite favorable weather conditions. In view of these difficulties, on another platform in the North Sea, a gradual increase in the holding force of piles was applied: first, piles with a diameter of 1.82 m were immersed to a depth of 30 m, and then piles with a diameter of 1.22 m were driven through them to a depth of 60 m.

One of the circumstances that makes driving piles difficult is that the mass of the piles is commensurate with the mass of the hammer, and the elasticity of a long pile can absorb all the impact energy. In this regard, for driving long piles, hammers are used, which are placed inside the pile - in its lower part. Due to the laboriousness of pile work, the advantages of the method of assembling the support block used in the construction of the Cognac platform are revealed. There, the piles, the main and fringing ones, were hammered until only the lower section of the support block was on the ground. The piles are 190 m long and 2.13 m in diameter with a thickness walls 57 mm and weighing 465 tons were delivered afloat.After receiving the ballast, they were transferred to a vertical position, guided into the guides of the support block and immersed under the action of gravity into the ground by 45 m. cemented with piles and guide sleeves.Pile work continued for 21 days.

A different piling technology was used in the construction of the Hondo platform. The supporting block was strengthened by eight piles with a diameter of 1.22 and a length of up to 380 m, driven through racks, and twelve fringing piles with a diameter of 1.37 and a length of up to 115 m. The piles were delivered on barges in sections 20-70 m and connected by welding as it was lowered inside the posts.To reduce the load on the floating crane that held the pile in the process of its build-up and descent, the sections of the pile were equipped with waterproof partitions.After welding the tenth of the thirteen sections, the pile reached the ground surface, and the waterproof partitions Works on immersion of one pile were carried out within 3.5 days.

The installation of the topside is the final stage in the construction of a deepwater platform. Most of the built platforms have a modular superstructure. Modules weighing 700-1600 tons or more are delivered on transport barges and installed using crane ships. The use of a modular assembly method allows not only to reduce the total duration of work, but also to reduce their cost. It should be borne in mind that similar work on the installation of drilling equipment, carried out at sea, is 8-10 times more expensive than onshore. The high cost of operating crane ships, transport barges and indispensable rescue vessels, their downtime under adverse hydrometeorological conditions can bring the cost of installation of the topside to 30% of the cost of installation of the support block. This explains the trend towards enlargement of the modules of the upper structure.

Stationary ice-resistant platforms

Ice resistance should be provided by structures intended for year-round operation on the shelf of the Arctic and freezing seas, as well as in large water areas of non-freezing seas, where they can be exposed to drifting ice fields and impacts of individual ice floes. Generally speaking, ice-resistant structures should be considered those in which the structural shape and dimensions of the bearing elements are determined primarily by the ice regime. A special approach to the design of ice-resistant platforms is explained not only by the specifics of the main environmental impact, but also by the conditions in which construction should be carried out. This is a very short summer season (2-3 months), when the free or floating ice surface of the sea allows the construction of the facility afloat or on barges to the place of operation. it low temperatures air, contributing to the freezing of the structure and the appearance of brittle cracks in the material, low water temperature, which makes underwater technical work difficult.

The world experience in the construction and operation of ice-resistant platforms is still small. The development of the Arctic regions of the shelf is carried out mostly from artificial islands. However, the need to reach such depths, at which the construction of islands becomes economically unfeasible, encourages the search for structures of ice-resistant platforms. The first ice-resistant platforms were built in the 1960s. Currently, they are operated in several areas of the World Ocean: in the Cook Bay (off the southern coast of Alaska, USA) at depths of 20-40 m, in the Beaufort Sea (on the Canadian section of the shelf) at depths of up to 30 m, in the freezing Sea of ​​Azov at depths up to 8 m. In the future, it will be necessary to develop areas with more severe climatic conditions, in hard-to-reach places and with a wider range of depths. This task is of particular importance for our country, since more than half of the USSR shelf is covered with ice for a long time of the year. In particular, on the shelf of the marginal seas of the Arctic Ocean, only a very small part of the sea surface (the Barents Sea near the Kola Peninsula) is almost always free of ice. Large areas of the Baltic, Black, Caspian and Azov seas are covered with ice. One-
However, the problem of ice resistance of structures in these areas is not paramount, the design and dimensions of the elements are determined by storm conditions. In the Arctic regions, on the other hand, the force impact of usually ice fields 1.5-2 m thick significantly exceeds what is possible during the most severe storms.

The implemented and proposed structures of the supporting bases of ice-resistant platforms are diverse in configuration and methods of construction, and at the same time differ markedly from those designed mainly for the perception of wind wave effects. The specificity of ice-resistant platforms is also manifested in the layout of the topside, since such structures should have greater autonomy, i.e., allow the placement of a sufficient amount of reserves for drilling and other work within 3-6 months (instead of 1 month in areas with a temperate climate), when transport links by water are not possible. Long-term low air temperatures (temperatures below 0 °C last from 7 to 10 months, and minimum temperatures reach -46 °C), frequent stormy winds in winter and snow loads in summer force the protection of all work sites. Water-separating pipes through which wells are being drilled also have to be protected from the effects of ice.

When designing ice-resistant platforms, several basic methods are used to reduce the impact of ice on the structure:

Reducing the number of supporting elements in the area of ​​the waterline or narrowing the structure supporting the topsides;

The device of protective casings around the supports to prevent their damage from the abrasive action of ice;

Giving the outer surface of the support a conical or other shape that facilitates the transition of the ice cover from work in compression to work in bending.

Ice-resistant platforms with a through support block on a pile foundation. They differ from conventional platforms in the absence of braces in the waterline area and the presence of an ice-protective casing on the supporting columns. Such platforms (14 in total) are installed and operated in Cook Inlet, where severe ice conditions are aggravated by semi-diurnal tides up to 12 m high and strong tidal currents up to 4 m/s. Platforms are installed at depths from 19 to 40 m.

A typical design of an ice-resistant platform is shown in Figure 22. The platform support block is made of four columns with a diameter of 4.6 m, connected by braces and horizontal tubular braces only in the underwater part - below the zone exposed to ice. At the top, the columns are connected by a superstructure. Through the columns, 8 piles with a diameter of 0.75 m are sunk into the ground to a depth of 27 m. The piles perceive loads from the upper structure, as well as shearing and overturning forces from the impact of ice on the columns. The annular space in the columns is filled with concrete, and the columns themselves have a protective casing about 15 m high. The platform structures in Cook Inlet are made of high-quality steels with a yield strength of at least 350 MPa. Due to the large diameter of the columns, the support block has its own buoyancy and was delivered to the installation site from the coastal base using tugboats.

AT metal structure ice-resistant support block of a small platform installed at a gas field in the Sea of ​​Azov (figure), there are also no horizontal and inclined connections in the area exposed to ice. This helps to reduce the overall shearing and overturning force from the impact of ice on the columns. In contrast to the design described above, the piles are driven not inside the supporting columns, but through guides mounted on a lattice grillage, which has larger dimensions in plan than the platform deck. The columns are made of three coaxial pipes with a diameter of 1420, 1020 and 630 mm, the annular space is filled with concrete. The platform is designed for a cluster of four wells drilled through strings. Thus, the columns not only support the equipment deck, but also protect the drill pipes from the effects of ice.

A large number of columns and too close arrangement of them in the support block leads to a delay broken ice and the formation of a hummock directly below deck. In connection with this, the design of the support block in the area of ​​the windline should be as permeable as possible to ice fields.

Gravity ice-resistant platforms. Such platforms are held in place mainly by their own weight and ballast. Ice-resistant platforms, with all the variety of structural forms, always have a developed support base, usually round in plan. The platform body can be reinforced concrete or metal. To reduce the force impact of ice on the structure, various methods are used: narrowing the hull in the area of ​​the waterline, giving a cone-shaped shape to the hull and the support column supporting the superstructure in the area of ​​ice impact, the use of movable (floating) cone nozzles on cylindrical columns. Several design options for ice-resistant gravity platforms are shown in Figure 25. The search for optimal solutions continues, since each constructive solution in different conditions exhibits positive or negative properties.

The cylindrical shape of the support column is convenient from the point of view of work, reduces the material consumption of the structure, has a small area over which freezing with ice cover is possible. On the other hand, the cylindrical shape of the obstacle does not contribute to the bending of the ice cover, and the destruction of ice occurs when it reaches the compressive strength in contact with the support.

The conical shape of the support helps to reduce the horizontal component of the ice field pressure on the structure. Ice, creeping onto the support, undergoes bending and breaks when the ultimate tensile strength is reached at some distance from the support (the mechanism of ice field destruction is shown in Section 6.6). The vertical component of the ice pressure on the support, when it is directed downwards, increases the stability of the structure against shear. The disadvantage of the conical shape is the possibility of the formation of hummocks and their freezing when the ice field stops, which is especially likely in shallow water. Freezing of a conical surface with a flat field is also dangerous, since it occurs on a significantly larger area than in the case of a cylindrical support, and at the beginning of the ice field movement can lead to a strong increase in the load on the structure. In addition, the conical shape of the support complicates the work, increases the cost of materials, and makes it difficult for the vessels serving the platform to approach.

Gravity ice-resistant platforms are being developed for operation at relatively shallow depths. The own weight of the platform together with the ballast is not always enough to ensure the stability of the structure from shear under the pressure of ice. In such cases, you have to resort to the help of piles. The use of local materials as ballast brings gravity platforms closer to artificial islands. Sometimes it is difficult to determine what type of ice-resistant structure belongs to. You can be guided by the following feature of the platform - after deballasting and extracting the piles, it can be completely (or divided into a hull and superstructure) moved to another location and reused. The submersible fencing blocks of the artificial island can also be deballasted and transferred to another area, but at the same time, the soil body of the island remains on the seabed. Gravity platforms, unlike islands, have a bottom over the entire area resting on the bottom or bed.

An ice-resistant platform, often referred to as an “ice island”, is shown in Figure 25, d. This platform is designed for drilling operations on the Canadian Arctic shelf at sea depths of up to 22 m. receiving ballast - sea water - into cellular compartments formed by pipes with a diameter of 12 m, the platform sits on the bottom. refrigeration plant the ballast is frozen and gives the structure rigidity and the ability to resist the impact of ice fields up to 1.8 m thick. Four pipes with a diameter of 2.4 m each accommodate 8 conductors for drilling wells. If it is necessary to change the place of operation of the platform, the ballast is melted and pumped out.

The wet method of filling the soil is relatively new. Initially, this method was used only for backfilling loess soils; later it began to be used for filling clay and ordinary sandy soils(sometimes with an admixture of coarse-grained soils and stone).

The wet method has the following advantages over the dry method: a) there is no need to dry or moisten the quarry soil (to the optimum moisture content); b) the soaking of dense clods of cohesive soil, which is laid in the body of the dam, is ensured; c) the duration of the construction season increases due to the possibility of performing work during precipitation, as well as during frosts; d) a high density of the dumped soil is obtained (which is especially important when making clay impervious devices).

The production of work on filling the soil into the water is carried out as follows. The dam is erected in horizontal layers with a thickness of up to 1.5 ... 2.0 m for clay soils and up to 4.0 m for sandy soils. Each planned horizontal soil layer is divided into maps (rectangular in plan), and dams are poured along the borders of the maps in a dry way height equal to approximately the thickness of the layer. The map planned for backfilling with soil is preliminarily filled with water (using pumps). After that, work is carried out on filling the soil into the map according to the scheme in Fig. 2.93. As you can see, filling the map with soil is done in the water in a pioneering way. The water displaced by the soil from the map's pond drains into the adjacent map. The initial compaction of the soil is provided by dump trucks in the process of dumping the brought soil, as well as by bulldozers when they level the surface of the dumped soil layer. No additional compaction is carried out under these conditions.

Overlapping methods and areas of their application

Blocking the river bed during the construction of a river hydroelectric complex is one of the most difficult stages of work in general scheme skip construction costs. The essence of the overlapping process is to switch the flow of water in the river to the drainage tract (various openings, tunnels, channels) prepared in advance at stage I by gradually or instantly blocking the channel with various materials (sand and gravel mixture, rock mass, sorting stone, special concrete elements (cubes , tetranuclei, etc.), (Fig. 2.13).

The channel is blocked by the following methods (Fig. 2.14): frontal backfilling of a stone banquet into flowing water (frontal method); pioneer dumping of a stone banquet into flowing water (pioneer method); alluvium of sandy-gravel soil by means of hydromechanization (alluvial method); instantaneous collapse into the channel of earthen or rock masses (directed explosion method); other special methods (dropping large concrete masses or capsizing them, flooding floating structures, driving sheet piles, immersing wattle or straw mattresses, etc.).

The most common ways of blocking the river bed are the frontal and pioneer methods of backfilling a stone banquet into the water. The complexity of overlapping when applying these methods depends mainly on two factors: the maximum flow velocity in the gap Umax and the maximum specific flow power

Thus, the maximum speeds with frontal overlap are much lower than with pioneer overlap (with the same final differences DZKOH). Therefore, it has the advantage of being used for blocking rivers with easily eroded soils in their channels. But its use is complicated by the need to build a bridge across the hole to fill the banquet. When using the pioneer method of overlapping, on the contrary, the hydraulic conditions in the channel become more difficult, but the organization and production of work are simplified, and a bridge is not required.

The choice of the method of overlapping, in principle, should be carried out on the basis of a technical and economic comparison of options.

The greatest influence on the choice of the method of overlap is exerted by the natural geological and hydrological conditions in the alignment of the overlap. From hydrological

The timing of the blocking of the channel is timed to coincide with low water periods and is usually set at the end of the shipping period in the autumn-winter months.

Channel overlap calculations

Justification of the channel blocking option should be accompanied by a number of relevant calculations.

In general, hydraulic and other calculations to justify the blocking of the channel include: determination of the permissible preliminary restriction of the river channel before the opening of the barriers; determination of the final drop at the Akon banquet; control over changes in the hydraulic characteristics of the flow (flow rate Q, differentials AZ, velocities in the hole, total and specific flow rates N and N°) in the hole and on the structures during the closing process; determination of the size of the stone required to close the hole at different stages; determination of the volume of stone of various sizes.

All these calculations are performed using the laws of hydraulics and computer programs.

Organization of work on blocking the channel

The blocking of the channel can be divided into the following stages: preparatory, preliminary constraint of the channel, closing the gap and final.

At the preparatory stage, work is carried out to organize warehouses for materials, to build roads (and, if necessary, bridges) from warehouses to the alignment of the overlap, to prepare transport and loading facilities, to arrange lighting for the overlap area, to organize a hydrological service and other work that ensures successful and timely blocking of the channel. These works are completed in 1-2 months. before closing the gap in parallel with the main work on the construction of structures in the pit of the 1st stage.

Preliminary restriction of the channel provides for the narrowing of the blocked channel to allowable conditions for navigation and erosion of the channel while maintaining the design opening. This restriction of the channel with all methods of blocking is carried out by the pioneer filling of a stone banquet from the banks (from one or two) or by alluvium of sandy-gravel soil.

To improve the conditions for overlapping with easily eroded soils in the channel, preliminary fixing of the bottom with low-erosive soil (usually rock mass or stone) is provided by dumping this soil from floating craft. Fastening is carried out along the entire width of the hole 5-10 m upstream and 50-100 m downstream from the axis of the banquet, depending on the base soils and the conditions of their erosion when the channel is constrained.

To avoid subsequent erosion, the thickness of the fastening should be at least 3 diameters of the stone being poured. In parallel with these works, at this stage, the preparation of the entire drainage tract in the pit of the 1st stage and the compression of the jumpers are being carried out.

The overlapping of the channel opening is the most crucial moment in the entire stage of overlapping and begins with the dismantling of the lintels of the 1st stage, flooding the pit and switching part of the flow from the channel to spillways. In this case, special attention should be paid here to the thoroughness of disassembling the jumpers to the design dimensions. With insufficient disassembly of the jumpers, the total difference during overlapping can significantly exceed the main design difference at the structure, which complicates the overlap.

After the opening of the bridges, part of the flow is switched to spillways, the flow, drops and velocities in the channel fall, which makes it possible to start closing the gap with the same material that was used in the banquet during the preliminary constraint (usually rock mass). Since the speed in the gap after the start of backfilling gradually increases as the gap narrows and the difference increases, material of different sizes should in principle be used for backfilling at different stages of overlap. However, in practice, two types of materials are most often used. At the initial stage, the rock mass is used, and at the final stage, a large stone (oversized) and various concrete elements (cubes, tetrahedrons, reinforced concrete hedgehogs and etc.). The higher the difference in overlapping and the specific power of the flows, the larger the dumped elements should be in principle.

When rivers with weakly eroded and non-eroded channels are blocked, the differences reach significant values. Thus, during the pioneering closure of the Angara in the alignment of the Ust-Ilimskaya HPP, the maximum drop reached 3.82 m at a flow rate of 2970 m3A and a specific flow power of 900 kW. At the last stage, bundles of oversized pieces with a total mass of up to 25 tons were used to block the gap at the last stage. Chirchik (Charvak HPP) the difference reached 4.2 m, and the rivers Vilyui (Vilyui HPP) and Naryn (Toktogul HPP), respectively, 5 and 7.32 m. 10 tons, at the Vilyui HPP - large-block stone weighing up to 25 tons, and at the Toktogul HPP - concrete tetrahedra weighing 10 tons and stone blocks up to 25 tons.

In order to reduce the drops and velocities in the gap with the pioneering method, it is possible to use two-banquet overlap schemes, dispersing the total drop into two banquets.

With the frontal additional element organization of overlapping of the breach is the need to arrange transport communications for the possibility of dumping the material simultaneously across the entire width of the breach. Usually floating bridges are arranged for these purposes (Fig. 2.18). Ropeways, cable cranes and fixed bridges are sometimes used. Dumping of materials from bridges is carried out using dump trucks with end or side unloading, for which they must be specially prepared. The width of the bridges should ensure free maneuvering of vehicles when unloading the stone. At end unloading of dump trucks with a carrying capacity of 5-15 tons, it is 18-20 m, with side unloading - 10-12 m. clear regulation of the movement of vehicles to the places of dumping based on the results of measurements. The intensity of backfilling when large rivers are blocked reaches 1000-1300 m/h (Volzhskaya named after the XXII Congress of the CPSU, Saratovskaya, Krasnoyarskaya hydroelectric power stations), and the number of car trips is up to 360 per hour (Saratovskaya hydroelectric power station).

As with the pioneer method, at the initial stage, rock mass is used for backfilling, and at the final stage, oversized and concrete elements are used. So, on the ceilings of the channels during the construction of the Kamskaya and Votkinskaya HPPs with drops, respectively, of 1.4 and 1 m, concrete cubes weighing up to 5 tons were used, the Volga HPPs with drops up to 2 m - concrete tetrahedra weighing up to 10 tons, and the Gorkovskaya HPP with a drop 0.9 m-concrete cubes weighing up to 5 tons and reinforced concrete hedgehogs weighing 0.6 tons.

At the final stage, after the direct closure of the opening, the banquet is filled up to the design profile of the required design. The overlap banquet is usually included in the downstream drainage dam of the dam with appropriate filters and is located in its place.

If there is a foundation pit of the 2nd stage, the floor banquet, as a rule, is part of the future transverse overhead lintel and is located in its place. In this case, immediately after the overlap, this jumper is erected to the marks corresponding to the water level during the overlap, and later (to the flood) to the marks corresponding to the omission of the estimated construction flow. In parallel, a lower transverse lintel is being erected.

Since the overlap is usually carried out in late autumn, it is very important at this stage to quickly and timely organize a pit of the 2nd stage and, before the onset of cold weather, pump it out and excavate loose soils. Otherwise, the development of saturated sandy-gravelly soils after their freezing will significantly complicate and increase the cost of excavation in winter conditions.

An example of the overlap of large rivers in the last period is the overlap of the river. Yangtze at the construction of the Three Gorges hydroelectric complex in China. The blocking of the river was carried out in November 1997. And it took place under conditions that the practice of world hydraulic construction did not know.

One of the essential features of the overlap in the alignment of the hydroelectric complex is the great depth of the river; the maximum depth reached 60 m, which complicated the work. The overlap project provided for the simultaneous restriction of the channel from both banks of the river using dump trucks with a carrying capacity of 44 - 77 tons. The width of the cofferdam (banquet) on top was 30 m, which made it possible to simultaneously work of three dump trucks in parallel. As a result, the rock dumping rate was 194,000 m3/day, or 17,100 m3/h. In total, 208,000 cubic meters of rock were poured into the hole. The width of the hole is 40 m, the depth is 60 m.

The actual flow of the river during the closure was 11,600 m3/s, the maximum drop was 0.66 m, and the maximum flow velocity was 4.22 m/s. The discharge of discharges during the blocking was carried out through 23 bottom spillways with a cross section of 79 m in the spillway sections of the dam. In general, the dam is designed to allow a flow rate of 0.1% during operation equal to 116,000 m3/s with a test for a flow rate of 0.01%. The total length of the spillway sections of the dam is 483 m. The dam has 23 bottom spillways with a cross section of 79 m and 22 surface spillways with a span of 8 m.

The erection of structures by the method of backfilling soil into water into artificial ponds should be carried out by separate maps, the dimensions and volumes of which are determined by the productivity of the equipment and the established intensity of backfilling. The boundaries of the maps of the laid layer, fixed by dike dams, must be shifted relative to the boundaries of the previously laid layer by a distance set by the thickness of the layers being dumped. It should be at least two times the width of the embankment dams.

The thickness of the layers when filling the soil into the water is established by the project or technical conditions, depending on the nature of the soil, the intensity of its filling, the carrying capacity of transport vehicles, the type and size of the structure.

When assigning the height of the backfill layer depending on the granulometric composition of the soil, it is recommended to use the graph (Fig. 3), built according to table 13.

Rice. 3. Curves of granulometric compositions of soils used in the construction of various types of structures

Curves I-II limit the area of ​​soils recommended for laying in ponura, screens and cores with layers of no more than 2 m; curves II-III limit the area of ​​soils recommended for laying in screens, cores and homogeneous dams with layers of 2-4 m;

1 - earthen dam Niva HPP-1; 2 - earthen dam of Knyazhegubskaya HPP; 3 - Upper Tuloma dam; 4 - Vilyuyskaya dam; 5 - the core of the dam of the Irkutsk hydroelectric power station; 6 - downcast and screen of the Iriklinskaya dam; 7 - the core of the dam of the Serebryanskaya HPP-1; 8 - Khantai dam;

9 - declining dam of the Volgograd hydroelectric power station; 10 - earthen dam Khishrau HPP; 11 - bridge of the Nurek dam; 12 - earthen dam Bolgar-Chay; 13 - jumper screen and experimental site of the Cheboksary dam; 14 - the screen of the dam of the Perepadnaya hydroelectric power station.
The approximate values ​​of the height of the backfill layer are as follows: when erecting structures from sandy-gravel soils, the height of the backfill layer should be taken from 4 to 10 m, for sands and sandy loams - up to 4 m. When building structures from loam, the height of the backfill layer should not exceed 2 m, for clay - no more than 1 m.

The suitability of a particular type of soil for its filling into water is determined by the project. Backfilling of soil into water must be carried out in compliance with special technical conditions (see "Guidelines for the construction of soil structures by the method of filling soil into water", P 22-74 / VNIIG, 1975).

5.15. A representative of the soil laboratory (field control post) should be present at the place where the soil was dumped into the maps. He monitors the quality of the brought soil, the uniformity of soil dumping along the front of the constructed map and the correct movement Vehicle on the laid ground.

5.16. Preparation of the base of the structure, installation of benchmarks, mapping, backfilling of the embankment dam, filling the ponds with water, etc. preparatory work are checked by a commission with the participation of representatives of design and construction organizations and geotechnical control services and, as far as they are ready, are accepted according to the acceptance certificate.

5.17. When dumping into the water, it is necessary to ensure uniform laying of the soil along the front of the constructed map, while achieving a constant water saturation of the laid soil. It is necessary to set such an intensity of backfilling soils into water, which eliminates the possibility of their waterlogging, free soaking and swelling, provides the specified soil moisture and a sufficiently high density after the completion of the process of soil compaction in the structure.

Backfilling should be carried out continuously until the map is completely filled with soil. In the event of a forced break with a stoppage of work for 4 hours or more, the water from the pond must be removed.

By the end of backfilling, a certain amount of liquefied soil is formed in each pit, therefore, before the completion of filling the pit, the level of the pond must be sharply reduced by unloading the soil from the last 15-20 dump trucks into liquefied soil.

Particular attention should be paid to: compliance with the design thickness of the backfill layer, uniform initial soil compaction by moving vehicles, maintaining the specified water depth in the pond and water saturation of the laid soil.

5.18. For the construction of structures by the method of filling soils into water, soils of any degree of clodiness are suitable, from homogeneous in a powdery state to large clods that are difficult to mechanically crush. In the mechanized development of dense clays slowly soaking in water, it is necessary to control the presence of at least 20-30% of soil with a clod size of no more than 10 cm, which will soak in water and serve as material for monolithic larger clods.

The initial water saturation of the soil during backfilling is controlled by determining the degree of moisture, which should not be more than 0.75-0.85. To determine it, the density of the soil, humidity and density of dry soil are established from the samples taken.

5.19. The degree of moisture is determined by samples of the soil laid in each layer. Samples should be taken along the entire height of the laid layer and at least three samples along the depth of the pit.

5.20. Degree of humidity S r soil is determined by calculation by the formula:

S r = (W ·  d ·  s) / [( s -  d)  W ], (11)

where W- humidity;  d- density of dry soil (density in a dry state);  s- density of particles of the dumped soil.

5.21. If the density of the dry soil is 85% or more of the design density of the dry soil, then the initial compaction for the slopes should be considered satisfactory. For dams with a height of up to 25 m from homogeneous soil or with screens and cores, the initial soil compaction should be at least 90% of the design density of dry soil, and for high dams, the initial soil density must be determined empirically, and the requirements for the initial soil density must be increased .

5.22. In case of unsatisfactory indicators of the density of dry soil of the constructed map, additional compaction of the soil by loaded dump trucks should be carried out. In such cases, for subsequent maps, the thickness of the fill layer must be reduced so that the initial compaction meets the established requirements. A change in the thickness of the backfill layer should be made in agreement with the representative of the design organization.

5.23. In order to take soil samples, pits or wells are passed in the body of the embankment. One of the indirect indicators of high-quality soil filling is the stability of the vertical walls and the solidity of the soil throughout the entire depth of the pit.

The assessment of the quality of laying the soil in the structure is carried out on the basis of laboratory tests of samples taken in pits with cutting rings or in boreholes with a sampler.

When erecting structures from soils with impurities of pebbles and boulders, sampling is carried out using the "hole" method.

When erecting structures by dumping soil into water, it should be borne in mind that the final density of the soil in the body of the structure is reached over time as a result of the effect of the structure's own weight and the physicochemical processes occurring in soils poured into water. Therefore, quality control of work should be carried out not only in the process of filling the soil, but also 15 and 30 days after the construction of the map.

5.24. Soil samples taken 15 and 30 days after filling are tested in a soil laboratory - moisture content, soil density, dry soil density, porosity coefficient and degree of moisture are determined.

At the same time, the density of dry soil, equal on average to the design density of dry soil specified in clause 5.21, should be recognized as sufficient for a satisfactory assessment of the quality of work.

5.25. For a satisfactory assessment of the quality of construction of a structure, quantitative indicators should be on average not less than 95% of the corresponding indicators established by the project.

Upon receipt of indicators that constantly meet the requirements of this paragraph, sampling and their research after 15 and 30 days may be terminated.

If after 30 days the density specified in clause 5.21 is not achieved, the decision on further research and the possibility of changing the technical conditions regarding the appointment of a control value for the density of dry soil must be made by the design organization and the customer.

The sealing of the pits should be carried out in layers of 30-40 cm moistened with soil with compaction to the design density.

All identified deficiencies, recommendations for their elimination, agreed changes in the technology of work, records of acceptance of finished maps and other instructions from the geotechnical control service should be entered in the field control log.
Alluvial structures
5.26. The geotechnical service controls the alluvium technology in terms of:

a) the correct laying of distribution slurry lines and the supply of slurry to the alluvium map in accordance with the project;

b) pulp distribution over the surface of the alluvium map;

c) embankment devices in accordance with the project and interface of adjacent sections of maps;

d) compliance with the intensity of alluvium adopted in the project (the rate of build-up of the alluvial soil in height per day) and the thickness of the layer of alluvial soil;

e) preventing the formation of scours in the reclaimed soil or stagnant zones where fines can be deposited within the side zones;

f) the state of the slopes of the structure and their formation according to the project;

g) compliance with the operating regime of spillways and clarification of waste water, as well as preventing the discharge of waste water with increased turbidity compared to the project into water bodies;

h) compliance with the width of the pond adopted in the project and technical conditions at various levels of alluvium;

i) fulfillment of the requirements of the project and SNiP 3.01.04-87 for the alluvium of structures during the performance of work.

Observations of the alluvial structure are carried out by the geotechnical service until the end of its construction. If the structure is not put into operation immediately after that, the geotechnical department of construction or the central geotechnical laboratory takes over the supervision until the acceptance of the structure into operation. Further observations are carried out by the personnel operating the hydroelectric complex.

5.27. During the device of the embankment, its height, dimensions are checked cross section and its placement in the plan in accordance with the location specified by the project. Before the beginning of the alluvium of the structure, the excess of the lowest mark of the embankment crest above the top of the water intake openings of the discharge structures and the compliance of this value with the one adopted in the project or established by calculations must be checked.

When arranging the embankment using a bulldozer inside the pit, it is necessary to pay attention to preventing the creation of depressions on the surface of the pit near the embankment, where, as a result of stagnant phenomena, small fractions can be deposited, and there may also be alluvial rollers (combs) between the penetrations of bulldozers, which prevent the correct distribution of the pulp along alluvium surface and lead to a decrease in the density of the alluvial soil.

When a bulldozer is building a dike from soil washed up behind the design slope contour from the outside of the structure, it is necessary to control the dimensions of the enumeration in relation to the design slope contour.

Note. All current geodetic works during the alluvium of structures and geotechnical control, they are carried out by the organization conducting the alluvium.
5.28. The correct distribution of the pulp on the alluvium map is fixed visually. During the construction of dams with a core, the pulp flows from the point of discharge from the slurry conduit to the edge of the pond should have a direction normal to the axis of the dam. Control over the position of distributing slurry lines can be carried out using rails that establish a straight pipe arrangement. In order to control the thickness of the alluvium layer according to the project during the pulp supply process, it is recommended to set up T-shaped stakes in 50-100 m along the alignment of the distribution slurry pipeline, the bar of which corresponds to the height of the layer to be applied.

5.29. The control over the intensity of alluvium, the thickness of the actually reclaimed soil layers and the slope of the alluvium of the side zones is carried out according to the readings of the rails. The intensity is determined by dividing the average thickness of the layer washed over a certain period by the duration of the period in days or hours.

The slope of the alluvial slope is set along the rails located on the same diameter, and is determined by the formula:

i = [( 1 -  2) / l r] 100, (12)

where i- slope, %;  1 - absolute or conditional mark of the ground surface along the first rail, m;  2 - the same, on the second rail, m; l r- distance between rails, m.

Operational control over the condition of the slopes and the embankment device is carried out visually by fixed special signs (milestones), which are installed every 50-100 m and increase as the alluvium flows.

A control check of the magnitude of the slope in the process of alluvium of the structure is carried out based on the results of monthly geodetic measurements.

5.30. When reclamation of structures with a nuclear zone, the size of the pond and its position on the map within the specified boundaries should be monitored every shift using rails set on each diameter, or by special milestones that fix the design outline of the pond at a given fill mark. Their installation is carried out periodically as alluvium, after 2-3 m in height. The state of the pond is recorded in the log of alluvial works. In the event that its size or position does not correspond to the specified ones, the personnel conducting the alluvium is immediately notified in order to take appropriate measures.

5.31. The size of the settling pond within the core zone of an inhomogeneous dam determines the granulometric composition of the soil deposited in the pond and forming the core of the dam. In some cases, for example, when supplying soil, the composition of which does not correspond to the design, the width of the pond can be changed on the spot. These changes are determined by the requirements for the formation of a core with a given granulometric composition of the soil and the conditions for the discharge of fine fractions, the deposition of which in the core is not allowed. The decision to change the width of the pond is made by the chief construction engineer in agreement with the organizations designing the dam and the work, on the proposal of the head of the geotechnical service.

5.32. When inundating heterogeneous dams with a core, a sketch of the boundaries of the pond should be periodically made with the designation of existing spillways for the removal of clarified water, since the outline of the nuclear zone is determined from these sketches. Simultaneously with the sketch, the mark of the water level in the pond should be fixed.

Note. Compliance with the location of the water edge accepted in the project on the transverse profile of the dam is one of the main requirements for the quality of the alluvium of the structure. Emergency, even short-term (less than 2 hours) rises in the level of the pond lead to flooding of the alluvium slope within the intermediate and lateral zones and the formation of layers of silt-clay fractions due to the sedimentation of these fractions from the water of the settling pond. Continuous interlayers of silty-clay fractions in the body of the lateral zone from non-cohesive soil can, during the operation of the dam, cause the formation of perched water and seepage of seepage water on the downstream slope.

5.34. Depth measurements in the pond during the influx of the dam with the core are carried out once or twice a month on the control diameters - on the axis of the dam and on quarters of the width of the pond. Measurements are made from a raft or boat using a basting with a metal disc at the end with a diameter of 15 cm.

5.35. Systematically, at least every two or three days, the condition of the spillway wells and their extension, as well as other spillway devices, should be checked, about which an appropriate entry is made in the quality control log of alluvial work.

5.36. During alluvium in winter conditions, the thickness of the frozen layer washed with fresh soil is subject to control. It is necessary to control the timely removal of ice from the surface of the alluvium map (in case of its formation), the condition of the embankment and discharge devices, the size and position of the pond, as well as monitoring the implementation of other requirements of the project for the production of works in winter conditions.

According to a special task of the design organization or the technical management of the construction, the geotechnical service, after the end of the winter period of work and the thawing of the surface layer of soil, drills pits in order to determine the state of the soil in the structure.

5.37. During the construction of alluvial dams, systematic monitoring of the state of the slopes should be ensured in connection with the possibility of leakage of seepage water onto them. A filtration flow arises in the body of the building to be washed, which is formed due to the water loss of the washed soil, infiltration from the settling pond and from the slope of the alluvium, periodically covered with pulp flows. In the case of a high intensity of alluvium and with insufficient filtration capacity of the soil of the lateral zones, seepage of the filtration flow onto the slopes of the structure may occur, which can cause landslides and soil slumps.

5.38. Employees of the geotechnical service must daily inspect the slopes of the structure being washed and note all seepage water outlets. Dispersed and intermittent outflows of seepage water on the slopes of the dam usually do not harm the structure, however, intensive outflows in the form of keys can cause landslides or slumps, especially in fine-grained soils. Observations of seepage water outlet should be linked to control over the condition of the settling pond. The marks of the upper boundary of seepage water outlets are entered in the working journal-diary, they must be recorded simultaneously with the marks of the level of the pond and its dimensions.

In threatening cases, the head of the geotechnical service must demand that the organization producing the alluvium reduce the intensity of the alluvium and, in extreme cases, temporarily stop work in the area where seepage water seeps out.

5.39. The geotechnical service must monitor the condition of permanent drainage devices provided for by the construction project and built before alluvium or being built simultaneously with alluvial work. Clogging or washing out of these devices during the production of alluvium is not allowed. All violations of drainage devices must be immediately brought to the attention of the representative of the organization producing the alluvium of the structure and the chief construction engineer for the latter to take the necessary measures to restore these devices.

5.40. When signs appear that indicate abnormal settlements of the base or body of the structure (cracks, landslides on slopes, local soil subsidence, sharp increases in the settlement of control benchmarks, etc.), the geotechnical service must immediately notify the heads of the organization conducting the alluvium, and the chief construction engineer, to demand extraordinary geodetic measurements and involve the geological service in the survey of the structure in order to take measures to eliminate the detected deformations.

5.41. The geotechnical service should mark all gullies on the outer slopes of the dam, which occur when the rules for the production of work are violated, when, due to erosion of the embankment, the pulp flow breaks through to the outer slope. At the same time, the composition and volume of the soil with which the gullies are sealed are indicated and samples are taken for the density of this soil.

5.42. If the design of the dam provides for the installation of control and measuring equipment (benchmarks, piezometers, etc.), then the geotechnical service is obliged to monitor the installation and condition of this equipment. In some cases, the geotechnical service may be entrusted with monitoring the level of seepage water using piezometers.

5.43. The duties of the geotechnical service include periodically determining the magnitude of the slopes of the surface of the reclaimed soil above and below the water level in the settling pond; the frequency is set according to SNiP 3.02.01-87 (Table 13). The measurement of the slopes of the surface surface is carried out in accordance with the instructions of clause 5.29, and under water - by measuring the depth of the water in the pond along the alignment of the rails. The ground surface elevation is obtained as the difference between the pond water level and the water depth.

5.44. The geotechnical service should provide control over the thickness of the soil washed in per day (intensity of alluvium). When alluvium of structures from silty and clay soils or structures erected on an impervious foundation, the excess of the design daily intensity of alluvium must be agreed with the design organization. In special cases (when it is provided for by the project and the Specifications), the density and moisture content of alluvial layers of soil are controlled depending on the duration of breaks in alluvium.

The essence of the method lies in the fact that when pumping groundwater various methods(water-reducing wells, wellpoints, open drainage), the surface of the water in the soil acquires a funnel-shaped shape, while lowering to the place of pumping.

5.46. The task of construction dewatering is to create and maintain a depression funnel in aquifers during the construction period, where pits are laid, as well as to relieve excess pressure in the underlying aquifers separated from the base of the pit by an aquiclude.

5.47. The production of dewatering works can affect the change in the initial properties of the soil. Pumping out water in the ground leads to an increase in pressure from its own mass and to additional precipitation of the territory. This is especially true for soft soils, the precipitation of which can cause unacceptable deformations of structures built within the water pumping zone.

A change in soil properties can also be caused directly by drilling wells, especially if the dewatering must be carried out to a great depth in highly permeable soils, when a large number of wells are required, the drilling of which affects the properties of the surrounding soil.

5.48. Dangerous soil disturbances can also occur during open drainage. These include the removal of fine particles on the slopes, as well as swelling of the bottom of the pit due to hydrodynamic weighing.