Gravity foundations. Interesting and necessary information about building materials and technologies Construction of embankments by dumping soil into water
Overlapping methods and areas of their application
Blocking the river bed during the construction of a river hydroelectric complex is one of the difficult stages of work in the overall scheme of skipping construction costs. The essence of the damming process is to switch water flows in the river to a drainage tract prepared in advance at stage I (various holes, tunnels, channels) by gradually or instantly blocking the riverbed with various types of materials (sand and gravel mixture, rock mass, sorting stone, special concrete elements (cubes) , tetranuclei, etc.), (Fig. 2.13).
The channel is blocked in the following ways (Fig. 2.14): by frontal filling of a stone banquet in flowing water(frontal method); pioneer pouring a stone banquet into flowing water (pioneer method); alluvium of sand and gravel soil by means of hydromechanization (alluvial method); instantaneous collapse of earthen or rock masses into the channel (directed explosion method); other special methods (dropping large concrete masses or overturning them, flooding floating structures, driving sheet piling rows, immersing wicker or straw mattresses, etc.).
The most common methods of blocking a river bed are the frontal and pioneer methods of pouring a stone banquet into the water. The difficulty of overlapping when using these methods depends mainly on two factors: the maximum flow velocity in the hole V max and the maximum specific flow power
Thus, the maximum speeds with frontal overlap are significantly lower than with pioneer overlap (with the same final differences DZKOH). Therefore, it has an advantage for use in blocking rivers that have easily eroded soils in their beds. But its use is complicated by the need to build a bridge across the hole for filling the banquet. When using the pioneer method of covering, on the contrary, the hydraulic conditions in the riverbed become more difficult, but the organization and execution of work is simplified, and no bridge is required.
The choice of overlapping method should, in principle, be made on the basis of a technical and economic comparison of options.
The greatest influence on the choice of slab method is exerted by the natural geological and hydrological conditions in the slab area. From hydrological
The timing of channel closures coincides with low-water periods and is usually set at the end of the shipping period in the autumn-winter months.
Channel closure calculations
The justification for blocking the channel must be accompanied by a number of relevant calculations.
In general, hydraulic and other calculations to justify blocking the channel include: determining the permissible preliminary restriction of the river bed before opening the dams; determination of the final drop at the Akon banquet; control over changes in the hydraulic characteristics of the flow (flow rate Q, differences AZ, speeds in the hole, total and specific flow powers N and N°) in the hole and on structures during the closure process; determining the size of the stone required to close the hole at different stages; determination of the volume of stones of various sizes.
All these calculations are performed using the laws of hydraulics and computer programs.
Organization of work to block the channel
The blocking of the channel can be divided into the following stages: preparatory, preliminary restriction of the channel, blocking the hole and the final stage.
At the preparatory stage, work is carried out on the organization of warehouses for materials, on the construction of roads (and, if necessary, bridges) from warehouses to the overlap area, on the preparation of transport and loading equipment, on the installation of lighting for the overlap area, on the organization of a hydrological service and other work that ensures the successful and timely closure of the channel. These works are completed in 1-2 months. before closing the hole in parallel with the main work on the construction of structures in the foundation pit of the 1st stage.
Preliminary restriction of the channel provides for the narrowing of the blocked channel to those acceptable under the conditions of 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 pioneering the filling of a stone banquet from the banks (from one or two) or the alluvium of sandy gravel soil.
To improve the conditions for overlapping with easily eroded soils in the channel, provision is made for preliminary fastening of the bottom with low-erosibility soil (usually rock mass or stone) by dumping this soil from watercraft. Fastening is carried out across the entire width of the hole 5-10 m upstream and 50-100 m downstream from the axis of the bank, depending on the foundation soils and the conditions of their erosion when the channel is constrained.
To avoid subsequent erosion, the thickness of the fastening must be at least 3 diameters of the poured stone. 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 carried out.
Closing the channel breach is the most critical moment in the entire stage of closure and begins with dismantling the lintels of the 1st stage, flooding the pit and switching part of the flow from the riverbed to the spillway structures. In this case, special attention should be paid to the thorough disassembly of the jumpers to the design dimensions. If the jumpers are insufficiently dismantled, the total difference during the overlap can significantly exceed the main design difference on the structure, which complicates the overlap.
After the opening of the dams, part of the flow is transferred to the spillway structures, the flow, drops and velocities in the riverbed fall, which makes it possible to begin blocking the hole with the same material that was used in the banquet during preliminary constriction (usually rock mass). Since the speed in the hole after the start of filling gradually increases as the hole narrows and the drop increases, material of different sizes should, in principle, be used for filling at different stages of the overlap. However, in practice, two types of materials are most often used. On initial stage rock mass is used, and at the final stage - large stone (oversized) and various concrete elements (cubes, tetrahedrons, reinforced concrete hedgehogs and etc.). The higher the difference in overlap and the specific power of the flows, the larger, in principle, the poured elements should be.
When rivers with slightly eroded and non-eroded channels are blocked, the differences reach significant values. Thus, during the pioneering blocking of the Angara at the site of the Ust-Ilimsk hydroelectric power station, the maximum drop reached 3.82 m with a flow rate of 2970 m3A and a specific flow power of 900 kW. To block the hole at the last stage, bundles of oversized items with a total weight of up to 25 tons were used. When blocking the river. Chirchik (Charvak hydroelectric power station), the drop reached 4.2 m, and the rivers Vilyuy (Vilyuy hydroelectric power station) and Naryn (Toktogul hydroelectric power station), respectively, 5 and 7.32 m. At the Charvak hydroelectric power station, large stones up to 1 m were used, oversized and concrete masses up to 10 tons, at the Vilyuiskaya HPP - large block stone weighing up to 25 t, and at the Toktogul HPP - concrete tetrahedrons weighing 10 t and stone blocks weighing up to 25 t.
To reduce differences and speeds in the hole with the pioneering method, it is possible to use two-banquet overlap schemes, dispersing the total difference into two banquets.
With the frontal method additional element organizing the closure of the hole is the need to arrange transport communications to be able to dump material simultaneously across the entire width of the hole. Usually, floating bridges are installed for these purposes (Fig. 2.18). Sometimes cable cars, cable cranes and stationary bridges are 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 stone. For end unloading of dump trucks with a carrying capacity of 5-15 tons, it is 18-20 m, for side unloading - 10-12 m. Filling should be carried out evenly across the entire width of the hole to avoid uneven erosion of the riverbed, therefore, backfilling from bridges requires continuous organization of measurements of the backfilled layers and clear regulation of the movement of vehicles to dumping sites based on the results of measurements. The intensity of backfilling when blocking large rivers reaches 1000-1300 m/h (Volzhskaya named after the XXII Congress of the CPSU, Saratov, Krasnoyarsk hydroelectric power stations), and the number of vehicle trips is up to 360 per hour (Saratov hydroelectric power station).
Just as with the pioneer method, at the initial stage rock mass is used for backfilling, and at the final stage oversized concrete elements are used. Thus, on the floors of riverbeds during the construction of the Kama and Votkinsk hydroelectric power stations with drops of 1.4 and 1 m, respectively, concrete cubes weighing up to 5 tons were used, at the Volzhsk hydroelectric power station with drops of up to 2 m, concrete tetrahedrons weighing up to 10 tons were used, and at the Gorky hydroelectric station 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 directly blocking the hole, the banquet is filled to the design profile of the required structure. The ceiling banquet is usually included in the lower drainage banquet of the dam with the corresponding filters and is located in its place.
If there is a pit of the 2nd stage, the ceiling banquet, as a rule, is part of the future transverse roof lintel and is located in its place. In this case, immediately after the closure, this lintel is erected to the marks corresponding to the water level during the slab, and later (toward the flood) to the marks corresponding to the omission of the estimated construction flow. At the same time, a lower transverse lintel is being erected.
Since overlap is usually carried out late autumn, it is very important at this stage to quickly and timely organize the pit of the 2nd stage and, before the onset of cold weather, carry out its pumping and excavation of loose soil. Otherwise, the development of saturated sandy-gravel soils after they have frozen will significantly complicate and increase the cost of excavation excavation in winter conditions.
An example of the blocking of large rivers in the last period is the blocking of the river. Yangtze at the construction of the Three Gorges hydroelectric complex in China. The closure of the river was carried out in November 1997. And it took place under conditions that were unknown to the practice of world hydraulic construction.
One of the significant features of the overlap at the site of the waterworks is the great depth of the river; the maximum depth reached 60 m, which complicated the work. The closure project provided for simultaneous constriction of the riverbed from both banks of the river using dump trucks with a carrying capacity of 44 - 77 tons. The width of the cofferdam (banquet) at the top was 30 m, which made it possible for three dump trucks to operate simultaneously in parallel. As a result, a rock dumping rate of 194,000 cubic meters per day, or 17,100 cubic meters per hour, was achieved. 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 when blocked was 11,600 cubic meters per second, the maximum drop was 0.66 m, maximum speed current 4.22 m/s. The discharge during closure 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 cubic meters per second, with a check for a flow rate of 0.01%. The total length of the dam's spillway sections is 483 m. The dam has 23 bottom spillways with a cross-section of 79 m and 22 surface spillways with a span width of 8 m.
SNiP 3.07.01-85
BUILDING REGULATIONS
HYDRAULIC STRUCTURES
Date of introduction 1986-01-01
DEVELOPED by the Institute "Hydroproekt" named after. S.Ya. Zhuk of the USSR Ministry of Energy (candidate of technical sciences I.S. Moiseev - topic leader, Y.K. Yankovsky, V.M. Braude, I.A. Ivanov, Yu.A. Orlov) together with the Hydrospecial Project of the USSR Ministry of Energy (candidate. technical sciences A.E. Azarkovich, V.V. Kotulsky).
INTRODUCED by the USSR Ministry of Energy.
PREPARED FOR APPROVAL BY Glavtekhnormirovanie Gosstroy USSR (M.M. Borisova).
APPROVED by Decree of the USSR State Committee for Construction Affairs dated April 8, 1985 No. 47.
With the entry into force of SNiP 3.07.01-85 “River hydraulic structures”, Section no longer applies. 1 regarding river hydraulic structures and section. 2 SNiP III-45-76 “Structures of hydraulic engineering transport, energy and reclamation systems.”
These rules and regulations apply to the construction of new, reconstruction and expansion of existing river hydraulic structures: dams of concrete, reinforced concrete and from soil materials, hydroelectric power stations, pumping stations, retaining walls, shipping locks, fish passages and fish protection structures, - as well as structures for protection against floods, mudflows and gully formation.
1. GENERAL PROVISIONS
1.1. When performing work on the construction of river hydraulic structures, in addition to the requirements of these rules, the requirements of the relevant SNiP Part 3 must be met.
1.2. The construction of river hydraulic structures should be carried out with the involvement of specialized contract construction and installation organizations that have the necessary special construction and installation equipment and accessories.
1.3. When reconstructing or expanding existing river hydraulic structures, construction work must be carried out using methods that ensure the safety of existing structures and underground communications located in the construction zone and not subject to demolition.
1.4. The procedure for carrying out work on navigable rivers must ensure the safe passage of ships and floating equipment with the necessary intensity during the construction period. Navigable areas of the water area in places of construction and installation work must be equipped with navigation fence signs.
1.5. When constructing river hydraulic structures, protection of unfinished and temporary structures or parts thereof must be ensured from damage during floods, ice movements, storms and squalls, wave action, pile-ups and impacts of ships, floating equipment and objects floating on the water.
Schemes for passing river (ice) flows through unfinished permanent, as well as through temporary river hydraulic structures, should be developed in the construction organization project (COP) and specified in the work execution project (WPP).
2. CONSTRUCTION OF MEMORKS
FROM GROUND MATERIALS, DRY
2.1. When constructing embankments from soil materials dry, in addition to the rules of this section, the requirements of SNiP III-8-76 must be met.
2.2. The construction of the embankment, preparation of the foundation and interfaces with the banks must be carried out in accordance with the technical specifications of the design organization, including requirements for geotechnical control.
Immediately before laying the first layer of cohesive soil, the surface of the compacted base, as well as the surface of the compacted, previously laid layer, is loosened to a depth of at least 3 cm or wetted before laying the next one. The amount of water to wet the surface is determined experimentally.
2.3. To create reliable contact between the dam core or screen and the rocky base, it is necessary to thoroughly clean the base surface and prevent the accumulation of lumps and large fractions of soil poured on the contact.
2.4. For dams constructed from soil of heterogeneous composition containing coarse-grained material in the form of inclusions, the PPR establishes the permissible size of these fractions, which should not exceed half the thickness of the backfilled soil layer in a compacted state. Fractions larger than permitted must be removed. Debris material in the body of the embankment should be distributed evenly, without forming clusters in the form of nests and chains.
2.5. The thickness of the compacted layers, established by the PPR, should be clarified based on the results of experimental rolling under production conditions.
2.6. When constructing dams and dams, soil laying should begin from lower places. During backfilling, the soil is leveled in layers of a given thickness with a slope of 0.01 towards the downstream to ensure the drainage of atmospheric precipitation. When filling drainage soils, the laid layers must be horizontal.
2.7. The working area of the structure being constructed or part of it (top wedge, core, transition zone, screen, etc.) must be divided into horizontal maps, on which soil intake, leveling and compaction of the laid soil layer are sequentially carried out in accordance with the PPR.
The dimensions of the maps when filling waterproof elements of dams are assigned depending on the intensity of soil filling and the outside air temperature. Individual cards should be mated to each other along a slope no steeper than 1:2.
2.8. When constructing dams and dikes consisting of several zones filled in layers from different soils, it is necessary to take measures to prevent soil from getting from one zone to another.
2.9. The dam can be constructed regardless of the time of laying the dam body. If there is a screen, the slope must be erected to the screen device or its part adjacent to the slope.
2.10. In dams with a soil screen, thrust prisms must be erected ahead of time so that the laying of soil into the screen is not interrupted until its construction is completed.
2.11. Screens made of clay or loam must be laid in horizontal layers and compacted to the required density. The loading of the erected part of the screen should be carried out with a lag from the filling of the screen by no more than 2 m in height.
2.12. The construction of dams from lumpy, non-waterlogged clays must be carried out according to the technical conditions of the design organization.
2.13. When constructing dams with a central core that has steep slopes (up to 10:1), the soil of the transition zones should be laid while maintaining the angle of natural repose of the soil of the transition zones and successively shifting the layers one relative to the other (herringbone laying).
2.14. Laying of material in transition zones (filters) should be done in layers up to 1 m thick (in a loose state) with compaction using soil compaction machines to the density required by the project.
2.15. When constructing dams with soil screens and cores, the laying of transition zones, in order to avoid clogging of the filter material by the soils of waterproof devices, must be carried out ahead of schedule, the value of which is established in each specific case by the PPR.
2.16. When constructing rockfill dams, the thickness of the rockfill layers poured using the pioneer method is determined in the PIC, taking into account the filtration strength of the core and transition zones.
Filling of rock fill into rock-and-earth dams using the layer-by-layer rolling method should be carried out in layers up to 3 m, unless otherwise justified in the design. The accepted layer thickness must correspond technical capabilities compaction machines and mechanisms.
2.17. When pouring stone into flowing water, the size and order of pouring must be established by the POS.
2.18. Technical conditions for the construction of embankments in winter period years must contain additional requirements for the procurement, storage, transportation, laying and compaction of soil.
2.19. Filling of soil into the anti-filtration elements of dams (ponur, core, screen, tooth) is allowed to be done at air temperatures down to minus 20°C, provided that the soil on the dam is not allowed to freeze until it is compacted. Frozen lumps are allowed no more than 15% of the volume of dumped soil.
Before laying soil on a frozen layer, the surface of this layer must be heated or treated with solutions of chloride salts. The thawing depth should be at least 3 cm.
2.20. To ensure the design density of the soil, the slopes of hydraulic embankments that are subject to rigid fastening should be filled with a widening of 20-40 cm normal to the slope (depending on the means used to compact the soil). Uncompacted soil from slopes must be removed and placed into the structure during its construction.
When securing slopes by sowing grass, rock riprap, pouring gravel, etc. embankments must be filled without widening the design profile.
2.21. Loose soil from the mating surface of the slope of the previously erected part of the structure must be cut to form a slope 1:4 and placed in the newly backfilled area. The surface of the slope, located normal to the axis of the structure, should have a broken outline in plan.
2.22. Control samples to determine the characteristics of the laid soil in the embankment of hydraulic structures should be taken according to Table. 1.
Control samples should be taken evenly throughout the entire structure in plan and height, as well as in places where reduced soil density can be expected.
2.23. When monitoring the quality of the dam's side prisms, made from throwing stone in tiers, the density and granulometric composition of the stone should be determined, for which pits are dug in each tier at the rate of one pit per 30 thousand cubic meters of laid stone.
2.24. Soil samples from the backfills of the foundation sinuses of hydraulic structures must be taken in accordance with clause 2.22, as well as at a distance of 0.2 m from the foundations.
Table 1
|
Soil selection method |
Soil characteristics |
Volume of laid soil for control sample |
|
|
Clayey and sandy without large inclusions |
Cutting ring, radioisotope |
Density and humidity |
100-200 cubic meters |
|
20-50 thousand cubic meters |
|||
|
Gravel-pebble and fine-grained (with the inclusion of large fractions) |
Test pits (holes) |
Density and humidity |
200-400 cubic meters |
|
Grading |
1-2 thousand cubic meters |
||
|
Other characteristics (for buildings of classes I and II) |
20-50 thousand cubic meters |
3. CONSTRUCTION OF EMBARKS BY THE METHOD OF PILLING SOILS INTO WATER
3.1. The method of dumping soil into water is used for the construction of dams, dikes, anti-filtration elements, pressure structures in the form of screens, cores, depressions and backfilling at the interface between earthen structures and concrete ones. For the construction of an embankment by dumping soil into water and preparing the foundation and interfaces with the banks for it, the design organization must develop technical specifications, including requirements for organizing geotechnical supervision.
3.2. Filling of soil into water should be done using the pioneer method, both in artificial, formed by embankment, and in natural reservoirs. Filling soil into natural reservoirs without installing dams is allowed only in the absence of current speeds capable of eroding and carrying away small fractions of soil.
3.3. Soil filling should be done in separate dumps (ponds), the dimensions of which are determined by the work plan. The axes of the maps of the laid layer, located perpendicular to the axis of the structures, should be shifted relative to the axes of the previously laid layer by an amount equal to the width of the base of the embankment dams. Permission to create ponds for filling the next layer is issued by the construction laboratory and technical supervision of the customer.
3.4. When pouring embankments into natural reservoirs and ponds with a depth from the water's edge to 4 m, the preliminary thickness of the layer should be assigned based on the physical and mechanical properties of the soil and the availability of a supply of dry soil above the water horizon to ensure the passage of vehicles according to Table. 2.
table 2
|
Backfill layer thickness, m |
Carrying capacity of vehicles, t |
Layer of dry soil, cm, above the horizon water in the pond when filling |
||
|
sands and sandy loams |
loams |
|||
The thickness of the fill layer is adjusted during the construction of embankments.
At depths of natural reservoirs from the water's edge of more than 4 m, the possibility of filling soils should be determined experimentally under production conditions.
3.5. The embankment dams within the structure being constructed should be made from soil placed into the structure. Longitudinal embankment dams can serve as transition layers or filters with screens on internal slope from waterproof soils or artificial materials.
The height of the embankment dams must be equal to the thickness of the backfill layer.
3.6. When dumping soil, the water horizon in the pond must be constant. Excess water is drained into an adjacent map through pipes or trays or pumped to an overlying map by pumps.
Filling should be carried out continuously until the pond is completely filled with soil.
In case of a forced break in work for more than 8 hours, the water from the pond must be removed.
3.7. Compaction of the dumped soil is achieved under the influence of its own mass and under the dynamic influence of vehicles and moving mechanisms. During the dumping process, it is necessary to ensure uniform traffic movement over the entire area of the dumped map.
3.8. When transporting soil using scrapers, dumping soil directly into the water is not allowed. In this case, dumping the soil into the water should be carried out by bulldozers.
3.9. When the average daily air temperature is down to minus 5°C, work on dumping soil into water is carried out according to summer technology without special events.
When the outside air temperature is from minus 5°C to minus 20°C, soil filling should be done according to winter technology, taking additional measures to maintain positive soil temperatures. Water must be supplied to the pond at a temperature above 50°C (with an appropriate feasibility study).
3.10. The sizes of maps when working using winter technology should be determined based on the conditions of preventing interruption in work; soil filling on the map must be completed during one continuous cycle.
Before filling the cards with water, the surface of the previously laid layer must be cleared of snow and the upper crust of frozen soil must be thawed to a depth of at least 3 cm.
3.11. When dumping soil into water, you should control:
fulfillment of project requirements and technical conditions for the construction of structures by dumping soil into water;
compliance with the design thickness of the filling layer;
uniform compaction of the surface layer of soil by moving vehicles and mechanisms;
compliance with the design depth of water in the pond;
temperature of the surface of the base of the fill map and the water in the pond.
3.12. To determine the characteristics of soils, one sample should be taken for every 500 sq.m of the area of the backfilled layer (underwater) with a thickness of more than 1 m - from a depth of at least 1 m, with a layer thickness of 1 m - from a depth of 0.5 m (from the water horizon to pond).
4. STRENGTHENING THE SLOPE OF EARTH STRUCTURES AND
SHORE PROTECTION WORKS
4.1. During the construction of canals and the construction of embankments of river hydraulic structures, strengthening of slopes and banks should, as a rule, be carried out dry.
4.2. The slopes and banks to be strengthened must be pre-planned in the above-water part, and trawled, cleaned and, if necessary, leveled in the underwater part.
The layout of earthen slopes and banks in the above-water part is carried out in accordance with the requirements of SNiP III-8-76. Underwater slopes are planned by cutting or adding non-cohesive soils.
4.3. Deviation of slope edge marks for rigid fastening from the design is allowed ±5 cm.
Deviation of the surface of the surface slope from project line after cutting uncompacted soil and leveling, ±10 cm is allowed. Leveling accuracy is determined using templates and sighting along pegs installed every 20 m along the slope, or instrumentally.
4.4. Treatment of a slope prepared for rigid dry fastening with pesticides should be carried out after the planning provided for by the project.
Treatment of slopes with continuous herbicides must be carried out no earlier than 10 days before laying the fasteners, preventing the herbicides from being washed away by rainfall.
4.5. Compaction of the base for rigid fastening to the required density should be carried out after leveling and etching with pesticides.
4.6. At subzero air temperatures, the installation of the filter or preparation for rigid fastening of the slope should be done from unfrozen, non-cohesive soils, and the following conditions must be observed:
a) frozen lumps measuring 5 cm or more should be crushed or removed; in the layers, the presence of evenly distributed lumps less than 5 cm in size is allowed, not more than 10% of the total volume;
b) each layer should be laid immediately to its entire thickness;
c) before laying layers, snow and ice must be removed from the base;
d) during snowfall and blizzards, work on installing a return filter must be stopped. Before resuming work, it is necessary to remove snow and frozen clods of soil from the slope.
4.7. The installation of stops that protect the slope clothing from sliding should be carried out before strengthening it.
4.8. Laying of crushed stone and crushed stone on steep slopes should be carried out by pavers and graders. It is allowed to carry out grading with a bulldozer on slopes no steeper than indicated in its passport.
4.9. The use of stone paving to strengthen slopes and banks is permitted subject to an appropriate feasibility study. Stone fastenings of the shores under water are arranged in the form of a stone cast with a natural slope from 1:1.25 to 1:1.5.
4.10. The planning of the rock fill to give the slope the required profile should be done after its settlement.
4.11. The installation of monolithic concrete and reinforced concrete facing of slopes with a steeper 1:1 slope is carried out through a strip (in two stages) using formwork installed on concrete beacons.
4.12. Fastening device made of monolithic concrete and reinforced concrete on earthen slopes with a slope of 1:2.5 and more flat should be carried out in accordance with the requirements of clause 7.11.
4.13. When strengthening a slope with monolithic reinforced concrete slabs, the following requirements must be monitored:
a) deviations from the slab thickness established by the project are allowed within the range from + 8 to - 5 mm;
b) there should be no cracks in the slabs;
c) there should be no gaps between the joint filling material and the vertical edges of the slabs.
4.14. Precast reinforced concrete slabs should be laid on a reinforced slope from the base to the crest of the structure. The size of the protrusions between adjacent slabs should not exceed 10 mm.
4.15. When laying prefabricated reinforced concrete slabs in winter, the planned surface of the return filter must first be cleared of snow and ice. The fastening plates must evenly adhere to the surface of the filter.
4.16. Monolithic asphalt concrete pavement is made using grippers using asphalt pavers on a dry, non-frozen base at an air temperature of at least 5°C. With a coating thickness of up to 10 cm, the asphalt concrete mixture can be laid in one layer, and if the design provides for reinforcement of the coating, the reinforcement cage is laid on the slope before laying the mixture and during the laying process it is moved to the middle of the laid asphalt layer concrete mixture until it compacts. When the pavement thickness is more than 10 cm, the asphalt concrete mixture is laid in layers with individual layers being rolled to the design density. If the design provides for reinforcement of the coating, then the frames are laid between the layers of the coating.
Deviations from the thickness established by the project asphalt concrete pavement should not exceed 10%. Laying the asphalt concrete mixture into the gripper should be carried out at a mixture temperature of 140 to 120°C. Laying a mixture with a temperature below 100°C is prohibited.
4.17. The asphalt concrete mixture should be compacted using a smooth roller or vibratory roller. Rolling should be carried out until the roller stops leaving marks on the surface of the coating, and the density of asphalt concrete reaches the design value.
4.18. The compliance of the physical and mechanical properties of asphalt concrete and the thickness of its layer with the requirements of the project is checked by a construction laboratory, for which cores or cuttings of cooled asphalt concrete must be taken at the rate of one core or one cutting per 450 sq.m of pavement. Taking cores or cuttings in the area of the edge and fluctuations in water levels is prohibited. Holes from cores and cuttings should be immediately sealed with cast asphalt mortar.
4.19. Fastening of underwater slopes with a laying of 1:2.5 or more flat from reinforced concrete and asphalt concrete slabs should be done using floating cranes across the slope from the bottom up in the direction against the flow of the river.
5. DRILLING AND BLASTING WORKS
5.1. The rules of this section apply to drilling and blasting operations when developing cut-ins, pits, and clearing rock foundations and slopes for the construction of river hydraulic structures.
When carrying out drilling and blasting operations, the requirements of SNiP III-8-76, the Uniform Safety Rules for Blasting Operations and the Uniform Safety Rules for the Development of Mineral Deposits must be observed. open method, approved by the USSR Gosgortekhnadzor, as well as the requirements of this section.
Drilling and blasting operations in deep canyons must be carried out in accordance with the Safety Instructions for Open-pit Mining at Hydraulic Construction Sites in Deep Canyons and Mountainous Areas, approved by the USSR Ministry of Energy and agreed upon with the USSR State Mining and Technical Supervision Authority.
5.2. When carrying out drilling and blasting operations, special requirements for the safety of rock foundations and slopes of constructed structures must be taken into account, depending on their membership in a particular group:
Group I - structures in the base and slopes of which an increase in natural cracks and the formation of additional cracks are allowed (outlet canals of hydroelectric power stations, spillway canals, clearing of the channel in the downstream, areas of open distribution devices, approach channels of shipping locks in the downstream);
Group II - structures, the foundations and slopes of which require protective measures against the increase in fracturing during blasting operations (pits for concrete spillway and blind dams, supply channels to dam hydroelectric power plants, trenches for the teeth of earthen and fill dams, pits for dam hydroelectric power station buildings, approach channels in the upper pool , pits of shipping locks).
The assignment of structures to groups I and II must be made in the PIC.
5.3. Drilling and blasting operations at Group I facilities are carried out without special protective measures.
5.4. For objects of group II, technical conditions for conducting drilling and blasting operations must be drawn up, which indicate the development method, the permissible amount of over- and under-extraction of soil, restrictions on seismic safety of protected objects, the need for seismic control of explosions, blasting conditions near freshly laid concrete and other technological factors that ensure high-quality and safe work performance.
5.5. The development of rocks at objects of group II should be carried out using ledges, leaving protective layer between the bottom of the blast holes of the lower bench and the design contour of the pit in order to protect the base and interface it with the slopes from cracking during an explosion.
5.6. In areas located directly above the protective layer, soil loosening should be done with borehole charges. In this case, re-drilling wells into the protective layer is not allowed, and the size of the well grid is reduced to 70% of the grid size used in development without a protective layer.
5.7. The thickness of the protective layer is determined by calculation in the PIC using the formula
|
Power of the protective layer; |
|||||||||||
|
The thickness of the zone of disturbance of the soil massif by explosion; |
|||||||||||
|
Permissible amount of soil lifting along the base. |
|||||||||||
The thickness of the disturbance zone h is within the range of up to 15 diameters of borehole charges, exploded on a ledge directly above the protective layer, and must be clarified by calculations in the drilling and blasting project, depending on the properties of the rock mass.
5.8. The permissible values of oversupply and undersupply of soil should be specified in the technical specifications for drilling and blasting operations, depending on the design features of the structures.
5.9. Loosening the soil of the protective layer is carried out by exploding charges on the overlying ledge. The protective layer is developed using rock-clearing machines (excavators equipped with a backhoe, bulldozers with rippers) after removing the soil from the overlying ledge.
When planning the foundation for prefabricated reinforced concrete structures, it is allowed to loosen the protective layer with explosive charges according to Table. 3.
Table 3
|
Estimated power of the soil mass disturbance zone in charge diameters |
|||
|
Permissible maximum diameter of charges, mm |
In this case, re-drilling wells and boreholes beyond the protective layer is not allowed.
5.10. When carrying out blasting operations near the slopes of pits at objects of group II, it is necessary to use contour blasting. For Group I objects, the feasibility of contour blasting should be established in the PIC and specified in the drilling and blasting project.
5.11. The parameters of contour blasting (the distance between the charges, their mass and design) are determined by calculations in the drilling and blasting project and are specified based on the results of experimental explosions. The use of bottom charges at the bases of Group II structures during contour blasting is not allowed.
The order of detonation of contour charges and loosening charges is established by the drilling and blasting project.
5.12. Under unfavorable geological conditions, to ensure the safety of the rock surface behind the contour plane and to protect the slopes from weathering during prolonged exposure to atmospheric phenomena during contour blasting, a protective layer is left by placing a plane of contour charges in front of the design contour of the slope.
5.13. Cleaning and processing of slopes after contour blasting should be carried out without the use of explosions.
5.14. The development of a protective layer after contour blasting to prepare the surface for laying concrete should be carried out in small areas without the use of explosions. The size of the prepared areas for concrete is established by the production design concrete works.
5.15. If it is necessary to carry out blasting operations near freshly laid (up to 15 days old) concrete, as well as protected above-ground and underground structures and equipment, permissible blasting parameters (bench height, diameter and mass of charges, deceleration pattern and intervals) are established by calculation in the drilling and blasting project.
The values of permissible vibration speeds for protected objects and equipment must be established in the technical specifications for drilling and blasting operations. Permissible vibration speeds for process equipment must be agreed with the manufacturers.
The need for constant or periodic seismic monitoring during explosions is established by the technical conditions for drilling and blasting operations.
5.16. Underwater loosening of rocky soils is carried out in accordance with the requirements of section. 3 SNiP III-45-76.
6. UNDERGROUND CHAMBER MININGS
6.1. When carrying out work on underground chambers of river hydraulic structures (turbine rooms of hydroelectric power plants, pumped storage and nuclear power plants, turbine water pipelines, gates, transformers, equalization tanks, pumping stations, underground pools, installation chambers), the requirements of SNiP III-44-77, SNiP III- 15-76 and this section.
6.2. Depending on the requirements for the safety of rocks surrounding the workings, drilling and blasting operations should be carried out when excavating chambers:
in the base, walls and roof of which a slight increase in natural cracks and the formation of artificial cracks is allowed - with borehole and blasthole charges;
in the base, walls and roof of which an increase in natural cracks and the formation of artificial cracks is not allowed, - borehole and blasthole charges by contour blasting along the roof and walls and leaving a protective layer of rock soil (rock)* along the base, the size and method of development of which are determined by the PPR.
* Classification of rocky soils (rocks) is determined according to GOST 25100-82.
The amount of overruns beyond the design contour when excavating chamber openings should not exceed, mm, for a group of rocky soil:
IV, V ......... 100
VI,VII ........ 150
VIII-ХI ....... 200
A shortage of rock that causes a decrease in the thickness of supporting structures is not permitted.
6.3. The excavation of chambers left completely or partially without lining must be carried out by contour blasting to ensure the preservation of the natural state of the surrounding rocky soils.
6.4. As construction approaches to chamber workings, workings of permanent structures should be used: outlet, supply and transport tunnels, tire and cargo, installation and ventilation shafts. With an appropriate feasibility study, the construction of additional approaches is allowed.
6.5. The construction of chambers over 10 m high, in which the design provides for permanent lining, must be carried out in the following order: excavation of the under-arch part of the excavation and installation of arch support, followed by the development of the main rock mass (core) of the chamber and the construction of wall lining.
6.6. The excavation of the under-arch part of chamber workings with a span of up to 20 m in strong, medium-cracked rocky soils should, as a rule, be carried out to the full cross-section, followed by the construction of a permanent arch lining.
Drilling of the under-arched part of chamber workings with a span of over 20 m in strong, medium-fractured rocky soils and, regardless of the span in rocky soils of medium strength, should be carried out, as a rule, using the bench method, ahead of the central part of the section, or with the excavation of an advanced working along the entire length of the chamber. The need and possibility of developing the under-arched part of chamber excavations in strong, medium-fractured rocky soils for a full cross-section with a span of over 20 m must be justified in the PPR.
The excavation of the under-arch part in low-strength soils, regardless of the span of the chamber excavation, should be carried out, as a rule, using the supported arch method. The feasibility of excavation with preliminary consolidation of a mass of weakly resistant rocks should be justified by technical and economic calculations. Methods for preliminary consolidation of the massif (cementation, chemical consolidation, installation of prestressed and conventional anchors from auxiliary excavations) are established by the PIC depending on the engineering and geological conditions.
6.7. The development of the core of chamber workings, in which the design provides for permanent lining, should be carried out from top to bottom with ledges in height, m:
in strong, medium-cracked rocky soils - up to 10;
in rocky soils of medium strength - up to 5;
in low-strength soils - up to 3.
At the same time, in weakly stable rocks, the development of ledges should be carried out by leaving pillars of rock (to support the overlying sections of the arch or walls) and then developing them and concreting the walls in a checkerboard pattern or driving sections of trenches along the walls to the height of the ledge being developed and concreting the walls first.
When developing chamber excavations, systematic and careful monitoring of the stability of the walls should be carried out. If there is a danger of the walls moving into the chamber, the nature of the possible movements over time should be identified and, if necessary, measures should be taken to strengthen the support of the walls by installing spacer beams or anchors.
The height of the ledges, the dimensions of rock pillars and chamber sections, measures to reduce the influence of wall deformation on the stressed state of structures, the material of spacer beams, and the length of anchors are assigned by the PPR depending on the specific engineering and geological conditions of construction.
6.8. The development of chamber openings in permafrost rocks should be carried out in accordance with the requirements of paragraphs. 6.5-6.7, exercising day-to-day control of change temperature regime workings, rock stability and thawing aura. The temperature regime during the construction of chambers in permafrost rocks and measures to maintain it are established by the PIC.
6.9. The type of temporary fastening of chamber workings during their development is determined in the PPR, while:
in strong, medium-cracked rocky soils, temporary fastening, as a rule, is not carried out, but in order to avoid possible detachments and fallouts of rocky soil in individual cracked areas of the arch and walls (cracked areas are determined during the removal of rocky soil after blasting), a metal mesh should be installed over the anchors;
in rocky soils of medium strength, fastening should be done with anchors and shot concrete;
in low-strength soils, the vault and walls should be secured with anchors with metal mesh and shot concrete; the time before the construction of a permanent lining of the chamber should be minimal and justified by the PPR.
The use of arched support as temporary fastening is allowed in exceptional cases for fastening individual workings (phases of work) with a proper feasibility study.
6.10. The installation of temporary support when developing chamber openings in permafrost rocky soils should be carried out after the development of the face. The type of temporary support is determined by the PIC. The development of chamber openings in permafrost rocky soils without temporary support is allowed only in soils whose stability does not decrease during thawing.
6.11. In projects for the production of concrete works for the construction of permanent linings of chamber excavations, measures must be taken to ensure dense filling of the vault locking part with concrete mixture, as well as the solidity of the joints of the walls with the heels of the vaults.
7. CONCRETE WORK IN THE CONSTRUCTION OF MONOLITHIC
AND PREFABRICATED MONOLITHIC STRUCTURES
7.1. During the production and quality control of formwork, reinforcement and concrete work, as well as work on the preparation and transportation of concrete mixture, installation of prefabricated reinforced concrete structures, the requirements of SNiP III-15-76, SNiP III-16-80 and this section must be met.
7.2. For the preparation, transportation, laying, maintenance and quality control of concrete during the construction of river hydraulic structures, technical conditions must be drawn up, approved in the prescribed manner.
7.3. In the process of preparing, transporting and laying the concrete mixture in order to ensure the required characteristics of concrete for river hydraulic structures, along with fulfilling the requirements of the relevant sections of SNiP III-15-76, it is necessary:
ensuring, as a rule, no more than two overloads during transportation and supply of concrete mixture to concreting blocks;
the use of powerful vibrators or vibrator packages to compact the concrete mixture during laying;
the use of machines specially equipped with mechanical brushes for removing cement film from horizontal surfaces of blocks of concrete lightly reinforced structures.
7.4. Road and rail bulk transportation of concrete mixture for concreting river hydraulic structures, as a rule, should be carried out in specially equipped concrete dump trucks. The capacity of vehicles for transporting concrete mixture must correspond to the capacity of the buckets used to supply the concrete mixture to the concreting blocks.
The concrete mixture should be transported over a distance of more than 15 km in concrete mixer trucks. Transportation of concrete mixture over a distance of more than 15 km in concrete dump trucks is permitted provided that additives - retarders - are used in the concrete mixture.
7.5. The bases and surfaces of construction joints prepared for laying the concrete mixture, along with the instructions of SNiP III-15-76, must meet the following requirements:
the base must be cleared of debris, dirt, snow, ice;
The surfaces of concrete bases of horizontal and inclined construction joints must, in addition, be cleaned of cement film. Removal of the cement film should be carried out, as a rule, by mechanization;
the surfaces of horizontal and inclined construction joints in reinforced concrete structures and vertical construction joints in concrete and reinforced concrete structures should be cleared of cement film if there are appropriate requirements in the project.
7.6. In order to prevent the formation of cracks from temperature influences During the process of concrete hardening, the construction of a structure should be carried out, as a rule, evenly along the entire front with breaks in laying blocks of adjacent heights ranging from 3 to 10 days. In case of increasing breaks, the following steps must be taken: Additional requirements project to the temperature regime of block hardening.
7.7. The period of overlapping of individual layers or grips during the concreting of blocks should not exceed 3 hours, depending on the type and properties of cement, as well as the temperature conditions of concrete laying. If additives - set retarders - are used in the concrete mixture, the overcoating period can be increased. In each specific case, the period of overlapping must be clarified by the construction laboratory.
7.8. Depending on the possible intensity of concreting, the size of the blocks in plan and the permissible timing of overlapping layers or grips, laying the concrete mixture into blocks can be carried out using:
layer-by-layer technology, when concreting is carried out in several layers over the entire area of the block;
step technology with the number of steps no more than three - when compacting the concrete mixture with manual deep vibrators and no more than two - when using means of intra-block mechanization of work;
Toktogul (single-layer) technology, which involves concreting blocks up to 1.5 m high at once in one layer.
When concreting using step technology, steps must be made parallel to the longitudinal axis of the structures. The direction of concreting is from the downstream to the upstream. The width of the step must be at least: 2 m when compacting the concrete mixture with manual vibrators and 3 m when using mechanized means.
The height of the blocks when concreting using Toktogul technology should be from 0.5 to 1.5 m; concreting should be carried out under the protection of a tent; driving on previously laid concrete can be carried out after it reaches a strength of at least 5 MPa (50 kgf/sq.cm); all work must be performed mechanically; In terms of their technical capabilities, the means of intra-block mechanization must correspond to the accepted height of the blocks.
7.9. Compaction of concrete in blocks of lightly reinforced concrete structures (with reinforcement up to 15-20 kg per 1 cubic meter) should be carried out with the maximum use of single crane vibrators or packages of vibrators suspended on mechanisms for intra-block work (small-sized electric tractors, manipulators, etc. .), while the mobility of the concrete mixture, measured by the settlement of a normal cone, should not exceed 2 cm.
The distance between individual vibrators in a package should not exceed 1.5 times the radius of action of the vibrator. Vibrators in the package should, if possible, be installed with an inclination of up to 30° from the vertical, parallel to each other, in order to improve the development of the contact zone between the individual layers of the concrete mixture. The height of the laid concrete mixture layer should not exceed the length of the working part of the vibrators used.
7.10. For heavily reinforced reinforced concrete structures, where compaction of the concrete mixture is difficult, the use of concrete mixtures of increased plasticity, compacted with vibrators, is allowed, and in cases where the location of the reinforcement prevents the use of vibrators, it is allowed in agreement with design organization use of cast concrete mixtures with a normal cone draft of 22 to 24 cm without vibration compaction.
7.11. When concreting, fastenings for slopes of earthen structures (dams, dams) should be used mechanized methods supply and laying of concrete mixture (concrete-laying mechanisms and complexes) or bulldozer technology. When using bulldozer technology, the distribution of the concrete mixture along the slope during concreting is carried out by a bulldozer, and the compaction of the concrete mixture is carried out by a vibrating plate mounted on a tractor. The bulldozer must move the concrete mixture in the direction from the base of the slope to the ridge, moving along a layer of concrete mixture (without reaching reinforcement structures not covered with concrete mixture), the distance of movement of the mixture should not exceed 20-25 m. Bulldozer technology can be used with the thickness of the fastening no more than 20 cm. The speed of movement of a tractor with a mounted vibrating plate during the process of compacting the concrete mixture should not exceed 1 - 2 m/min. The mobility of the concrete mixture being laid when using bulldozer technology, measured by the settlement of a normal cone, should not exceed 2 cm. When compacting the concrete mixture with a vibrating plate mounted on a tractor, it is possible to use fine-grained (sand) concrete in the fastening structure.
7.12. To ensure the temperature regime of concrete hardening in massive concrete structures of the POS, the following measures must be taken:
regulation of the temperature of the concrete mixture during its preparation;
pipe and surface cooling of laid concrete; installing tents or greenhouses above the block and maintaining an artificial climate in them;
installation of warm formwork on the outer surfaces of the blocks;
insulation or covering of horizontal surfaces of blocks.
Regulation of the temperature regime of concrete in a massive structure must be regulated by technical conditions.
7.13. Cooling of concrete in massive concrete structures is carried out in two stages: the first stage - during the process of laying and hardening of concrete to reduce the temperature of exothermic heating in the block (duration 2-3 weeks); the second stage is cooling the concrete in the structure to the average long-term outside air temperature, which allows for grouting of the joints of the structure.
7.14. To regulate the temperature of concrete, surface or pipe cooling should be used at the first stage, using, as a rule, river or ground water at natural temperature.
Surface cooling of concrete should be used for blocks with a height of 0.5 to 1 m by irrigation, which provides a layer of water on the surface of the cooled concrete with a constant organized flow in one direction at a speed of 5-8 cm/s.
The cooling rate at the first stage when using both surface and pipe cooling should not exceed 1°C per day during the first 8-10 days. after laying the concrete mixture and 0.5°C per day in the subsequent period.
7.15. At the second stage, pipe cooling is usually used. The temperature of the water used for cooling at the second stage should be 2-3°C lower than the temperature of the concrete at which grouting of the joints of the structure is provided. If there are no natural sources of water with the specified temperature, an installation for artificial cooling of water should be provided.
The concrete cooling rate at the second stage should not exceed 0.4-0.5°C per day. Cooling of concrete should be carried out in tiers, usually at least 10 m high.
7.16. When selecting concrete compositions to reduce the temperature of exothermic heating in lightly reinforced structures with reinforcement saturation of up to 20 kg per 1 cubic meter, it is necessary to provide for the use of medium-thermal cements and the maximum reduction in their consumption. Reducing cement consumption should be achieved by using aggregates of a multi-fraction composition, low-flow concrete mixtures with a normal cone slump of up to 2 cm, the addition of fly ash, as well as the use of pozzolanic and slag Portland cement for the internal and underwater zones of the structure.
7.17. In winter, the temperature difference between the surface and the center (core) of the concrete mass should not exceed 25°C. Blocks concreted in winter must be kept in insulated formwork until the core of the block reaches a temperature exceeding the outside air temperature by no more than 25°C.
Stripping the side edges before concreting adjacent blocks should be done under the protection of a tent or greenhouse. The surface of blocks concreted in warm time year and did not have time to cool down before the onset of the cold period (minimum daily temperature 0°C, average daily temperature 5°C and below), must be insulated.
In dams with widened joints and buttress dams constructed in harsh climatic conditions, it is necessary to close the seams and sinuses in the winter and ensure their heating.
7.18. As the main type of formwork for concrete lightly reinforced structures (gravity, arched, arched-gravity, buttress dams), cantilever metal or wood-metal formwork should be used, for iron concrete structures hydraulic units - collapsible large-panel metal, wood-metal, plywood-metal or wooden formwork. When developing formwork, the requirements of GOST 23478-79 should be met.
Metal formwork structures must be factory-made.
The use of stationary and fine non-reversible formwork is allowed for formwork of edges with reinforcement outlets, concrete coating of embedded parts, cutting to the rock base, as well as for surfaces with a complex geometric shape, double curvature, in particular the structures of the flow part of a hydroelectric power station building.
For the surfaces of vertical and inclined construction joints, if it is possible to use working reinforcement structures as a load-bearing frame, mesh metal permanent formwork should be used.
For the surfaces of blocks that are to be kept in formwork for a long period (over 15 days), insulated formwork with an insulating board remaining on the concrete surface after stripping should be used.
7.19. Methods, timing, diagrams and technological sequence of work on the manufacture, transportation, installation and monolithization of prefabricated reinforced concrete elements of a hydraulic structure must be regulated by the PPR and special technical conditions.
7.20. Quality control of the concrete mixture must be carried out by a construction laboratory in accordance with GOST 10181.0-81 - GOST 10181.4-81. Control samples must be taken at least once per shift at the concrete plant and at least once a day at the placement site for each brand of concrete, as well as each time the quality of the starting materials changes.
7.21. Monitoring the strength of concrete of monolithic and prefabricated concrete and reinforced concrete structures must be carried out in accordance with GOST 18105.0-80 - GOST 18105.2-80 by a statistical method, which makes it possible to achieve constancy of the normative resistance of concrete accepted when calculating structures.
When manufacturing single structures of small volume, when it is not possible to obtain the number of results necessary to calculate statistical characteristics, as an exception, it is allowed to use a non-statistical method for monitoring the strength of concrete in compliance with GOST 18105.0-80, GOST 18105.2-80.
Simultaneously with strength control on the same samples, concrete density control should be carried out in accordance with GOST 12730.0-78 and GOST 12730.1-78.
Control of concrete water resistance should be carried out in accordance with GOST 12730.0-78 and GOST 12730.5-78, control of frost resistance - in accordance with GOST 10060-76.
The number of control samples for testing concrete for water resistance and frost resistance should be established according to the data in Table. 4.
Table 4
|
Total volume of concrete in the structure, thousand cubic meters |
Volume of concrete mixture, cubic meters, from which is taken one sample each for testing |
|||
|
waterproof |
frost resistance |
|||
|
in massive concrete structures |
in reinforced concrete structures |
in massive concrete structures |
in reinforced concrete structures |
|
8. INSTALLATION WORK
8.1. When installing process equipment for river hydraulic structures, the requirements of SNiP 3.05.05-85, SNiP III-18-75 and this section must be met.
8.2. Before the start of installation work, the bases of installation organizations provided for in the PIC, as well as installation sites for the operational period, must be prepared for the reception of equipment.
8.3. Installation of operational cranes should be carried out, as a rule, on permanent crane tracks. In the case of installation of production cranes on temporary crane tracks, the latter should not exceed the settlement established by the Rules for the Design and Safe Operation of Load-Lifting Cranes, approved by the USSR State Mining and Technical Supervision.
8.4. With a no-fault method of installing embedded parts of mechanical and hydraulic power equipment, the base for installing the embedded parts must be made in accordance with the PPR or installation instructions of the equipment supplier.
8.5. During installation work, it is necessary to prevent clogging of the grooves or the gates and grilles installed in them.
8.6. The assembly of individual components and the installation of working mechanisms of hydraulic turbines and hydraulic generators must be carried out in an area protected from precipitation and protected from possible ingress of construction debris.
8.7. Installation of the control system, laying and soldering of the stator windings, soldering of the interpolar connections of the generator rotor, installation of the cooling system for the conductive parts of the generator, thrust bearing and bearings, as well as start-up, adjustment and testing of the mounted hydraulic unit must be carried out at a positive temperature of at least 5°C.
9. CEMENTATION OF SOILS
9.1. When carrying out cementation work, the requirements of SNiP 3.02.01-83 and this section must be met.
9.2. When combining cementation and general construction works calendar schedule construction must provide a front for cementation work, taking into account compliance with the requirements technological process cementation provided for by these standards and the work project.
9.3. Cementing work in the zone of influence of backwater, as a rule, should be carried out before filling the reservoir. If it is necessary to carry out grouting work under conditions of partial or full pressure on PPR structures, changes in the work conditions caused by an increase in pressure must be taken into account.
9.4. Cementation work at the base of the hydraulic structure must be completed before drainage is installed.
9.5. Cementing work, as a rule, must be carried out under loading (the thickness of the overlying soil, an artificial embankment, the body of a concrete structure, a special concrete slab). Cementing work should begin after completing work that ensures the design thickness of the load and its impermeability to cement mortar. When carrying out cementation work under a load of freshly laid concrete, work is allowed to begin 10 days after the completion of laying the concrete mixture.
9.6. After completing the cementation of all zones and carrying out the total cementation of the well, if it was provided for by the project, the wellbore must be plugged with solution.
9.7. When performing grouting work at an average daily outside temperature below 5°C, the following requirements must be met:
cemented soils within the zone of distribution of cement mortar must have a temperature of at least 2°C;
the temperature of the solution injected into the well should not be lower than 5°C;
measurements of the temperature of the injected solution, outside air and in the room should be recorded in the work log.
9.8. When ground cementation is used for anti-filtration purposes, control of the work performed should be carried out by drilling, hydraulic testing and cementation of control wells determined by the project.
9.9. The volume of monitoring wells should, as a rule, be 5-10% of the volume of working wells.
9.10. Cementation work in the area of the anti-filtration curtain should be considered sufficient if the specific water absorption in the control wells, in terms of its average value and permissible deviations from the average value, corresponds to the requirements of the project or the achievable values of specific water absorption for the soils of the tested area.
9.11. The method of monitoring completed work on strengthening cementation should be established by the project and consist of hydraulic testing and cementation of control wells or determination of the deformation properties of soils using geophysical methods. It is allowed to use these methods simultaneously.
10. PASSAGE OF RIVER FLOW DURING THE CONSTRUCTION PERIOD
AND CONSTRUCTION OF JUMPERS
10.1. The scheme for passing river flows during the construction period must be decided in the PIC, taking into account the layout of the main structures, the order and sequence of their construction, as well as taking into account topographic, geological and hydrological conditions and in compliance with the requirements of shipping and timber rafting.
10.2. The construction of dams should be carried out during the inter-flood period, timing the work on their construction to coincide with the minimum flow of the river.
When erecting jumpers in winter time from the ice, sufficient load-bearing capacity of the ice cover for vehicle traffic must be ensured. Before starting work on the construction of lintels, the lane should be completely cleared of ice.
10.3. When preparing the base of all types of lintels above the water's edge, the requirements of SNiP 3.02.01-83 must be met.
The foundation in the river bed for lintels made of soil materials is subject to inspection and, as a rule, does not require preparation. If there are stone screes and boulders at the base, the latter must be removed.
The base in the riverbed for row and cellular lintels is prepared by removing individual large stones and boulders and, if necessary, leveled by backfilling with crushed stone or gravel-sand materials.
10.4. Lintels made of soil materials should be erected, as a rule, from the soils of useful excavations (pits, channels, etc.). Jumpers included in the main structures must be made of materials and according to technical specifications in accordance with the requirements of the design of these structures.
10.5. Rib lintels should be constructed, as a rule, from double-edged timber. When the height of the rows is up to 6 m, it is allowed to use timber of any species; for a height of more than 6 m, only coniferous timber should be used. Connections in ryazhe jumpers should be made on metal dowels.
10.6. The racks are assembled on shore on stocks according to specified dimensions. The finished ridges are launched into the water, towed to the installation site and anchored at the dam site, after which they are loaded with stone or soil and installed on the bottom.
In winter, it is allowed to assemble ridges on ice with sufficient bearing capacity ice.
If the foundation is rocky, detailed measurements of the bottom must be taken, based on which lower crowns the rows are cut according to the configuration of the bottom.
10.7. Before installing a lintel of a cellular structure made of metal sheet piles, to determine the driving conditions, a test driving of the sheet pile should be performed to the designed depth and then pulled out. The cylindrical cells of the lintel must be filled to the full height, and the segment cells must be filled evenly, without allowing the level in adjacent cells to exceed 2 m.
10.8. Before pumping the pit, the lintels must be inspected by the customer, designer, and contractor, and a report must be drawn up on the readiness of the lintels to withstand pressure.
10.9. The condition of the jumpers must be constantly monitored. For timely repair and restoration of damaged parts of lintels during the period of pumping out the pit and floods, an emergency supply of materials should be prepared in the required quantity.
10.10. The decrease in water level when pumping the pit should not exceed 0.5 m per day. If soil removal is detected, it is necessary to carry out strengthening work at the removal site.
11. BLOCKING OF RIVER BEDS
11.1. The scheme for blocking the river bed must be decided in the PIC, taking into account hydrological and geological conditions, the drop in the banquet, the flow rate and speed of water flow, the capacity of the drainage tract, the size of the material for blocking, transport conditions, carrying capacity of transport and loading equipment.
11.2. The procedure for work and timing of channel blocking on navigable and timber-rafting rivers must be agreed upon with river fleet and timber-rafting organizations. In addition, if there are regulating reservoirs in the upper reaches, the procedure for damming work should also be agreed upon with the operation service of these reservoirs.
11.3. The closure of the river bed should be timed to coincide with flood periods from minimal costs water in the river, and on navigable and timber-rafting rivers - at the end of navigation or the non-navigable period.
11.4. The parameters of the channel damming (difference at the banquet, flow speed in the channel, size and volume of material for damming) at the project stage should be calculated on the maximum water flow in the river in the month of damming with a probability of exceeding 20%.
If there is a regulating reservoir dam on the river above the damming site, the calculated water flow rate during damming should be taken as the special reduced discharge flow agreed with the reservoir operation service.
Immediately before blocking the channel, the blocking parameters should be clarified taking into account the actual water flows in the river, taken on the basis of a short-term forecast for the period of blocking.
11.5. Before starting work on blocking the river bed, the following preparatory work provided for by the PIC must be completed:
create warehouses for materials necessary for blocking the channel, placing them as close as possible to the place of blocking on non-flooded marks and organizing approaches to them;
prepare a drainage tract to transfer river flows to it;
before flooding the pit of the concrete structures to which the costs are transferred, carry out preliminary dismantling of the enclosing lintels to the minimum possible size according to the conditions for passing the costs before blocking the channel;
perform preliminary restriction of the river bed to the minimum size, taking into account navigation conditions.
12. PROTECTION OF THE NATURAL ENVIRONMENT
12.1. Before filling the reservoir begins, in accordance with the project, rare and endangered species of flora and fauna must be collected and removed from its area and created the necessary conditions for their development and reproduction, measures have been taken to scientific research, engineering protection or relocation of historical and cultural monuments.
12.2. Before the river bed is blocked, fish passage structures must be built, and before the reservoir begins to be filled, spawning and rearing farms and fish hatcheries must be built.
12.3. Quarries of soil materials for backfilling earthworks should, as a rule, be located in a flood zone.
12.4. When carrying out work, it is necessary to provide and strictly implement measures to ensure compliance with current legislation in the field of environmental protection.
The text of the document is verified according to:
official publication
Gosstroy USSR - M.: CITP, 1985
Read also:
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The type of dam is selected on the basis of a technical and economic comparison of layout options for the structure as a whole, taking into account the purpose of the dam, engineering-geological, climatic and other conditions.
Depending on the type of building material, dams are built from
· concrete and reinforced concrete,
· wood,
· soils.
Dams, being built from soils, are called ground. The widespread use of earth dams is explained by the following: advantages: the material for the construction of dams is local, the cost of extracting the material is minimal, it can be used in most geographic areas; the soil placed in the body of the dam does not lose its properties over time. Soil dams can be built to almost any height; all processes during their construction are highly mechanized.
Along with the advantages, earth dams have flaws: limited possibilities for releasing maximum flows through the dam crest; the presence of a filtration flow in the dam body, potentially creating conditions for filtration deformations; the possibility of large losses of water due to filtration if the body of the dam is made of soils with increased water permeability; the difficulty of laying the embankment at significant and prolonged subzero temperatures; uneven settlement along the transverse profile of the dam; restrictions on the use of certain types of soils for the dam body and foundations.
Based on the design of the body and anti-filtration devices, they are distinguished the following types earth dams:
from homogeneous and heterogeneous soil,
· with a screen made of ground and non-ground material,
with a core made of soil material,
· with a diaphragm made of non-priming material.
According to the anti-filtration measures at the base, dense structures are distinguished:
with a tooth, a lock, a diaphragm, with a tongue-and-groove wall, with a combination of a tongue-and-groove wall with a tooth, with an injection curtain (brought to a waterproof point or hanging), with a droop.
Soil dams are classified according to their height:
· low – with a pressure of up to 15 m;
medium height – with a pressure of 15–50 m,
· high – with a pressure of more than 50 m.
For the main part of the dam profile, all types of soils are used, with the exception of: those containing water-soluble inclusions of chloride or sulfate-chloride salts in an amount of more than 5% or sulfate salts of more than 2% of the mass; containing incompletely decomposed organic substances in an amorphous state in an amount of more than 8% of the mass.
The best soils for a homogeneous soil dam are considered loams and sandy loams. Sandy and sandy-gravel soils are quite suitable, however, due to their water permeability, it is necessary to provide anti-filtration devices. For the dam's anti-filtration elements, cohesive, plastic, low-permeability soils are used: clays, loams, as well as peat with a degree of decomposition of at least 50%.
Silty soils, as well as those that move easily when saturated with water, are unsuitable for laying in the dam body. An important quality of soil for a dam body is its easy compactability during rolling. The choice of soil for the dam body is justified by technical and economic calculations.
If there is a sufficient amount of relatively waterproof soil (loam, loess) in the construction area, a dam is built from homogeneous soil. The advantages of homogeneous dams are simplicity and speed of construction, the possibility of using complex mechanization, which significantly reduces the cost of work compared to other types of earth dams.
If there is an insufficient amount of low-permeable soil, the dam can be filled from existing ones on site sandy soils, sandy loam or other permeable materials. In this case, strong filtration of water through the body of the dam will occur. To prevent this phenomenon, anti-filtration devices are used in the form of a core, screen, or diaphragm. In our work, we provide a kernel device to prevent filtration processes.
The plastic core is made of clay or heavy loam and placed vertically under the crest of the dam, preferably closer to the upstream slope, in order to reduce the volume of water-saturated soil of the upstream prism facing the upstream, and to make the downstream part of the dam, i.e., located from the downstream side.
The same requirements apply to foundation soils as to dam body soils. Soils at the base of the dam body with an undecomposed root system and humified soils, as well as those with passages for digging animals, are usually removed.
According to the method of carrying out work, earth dams are divided into dams:
· with dry filling using the pioneer method and mechanical seal soil,
· with soil poured into water, alluvial,
· constructed using directed explosions.
The bulk method is considered the most accessible and cheapest. With this method, the soil delivered from the quarry is leveled into a layer 20–25 cm thick in a loose state. The soil is compacted with self-propelled or trailed rollers - smooth or spiked, sometimes with crawler tractors or self-propelled scrapers. Heavy-duty pneumatic trucks (weighing up to 26 tons) are also used, compacting soil layers up to 60 cm thick, and vibratory rollers, compacting soil layers up to 0.8–1.0 m. The degree of soil compaction is controlled in the laboratory and using density meters. To achieve the required degree of soil compaction, it is sometimes necessary to wet it with water, since the best soil compaction occurs when optimal humidity. The latter depends on the nature of the soil and the mass of the skating rink. For heavier rollers, the optimal humidity decreases, and for lighter ones, it increases. Soil moisture is determined experimentally in laboratory and field conditions. After compacting the layer, its surface is harrowed for better adhesion to the next layer.
If there is low-permeability soil (clay or loam) at the base of the dam with a thickness of at least 2 m, before laying the dam body, only the plant layer is removed to a depth of 30 cm from the surface.
When the low-permeable layer is located no deeper than 4 m, in addition to removing the plant layer, a lock is installed at the base of the dam. When the aquiclude lies at a depth of 4 to 6 m, a lock 2–3 m deep is built and a sheet pile row is driven into its bottom, cutting through the entire water-permeable layer and entering 1 m into the aquifer. The sheet pile row is constructed from beams or thick boards and top part enters the lock by 0.5 m.
The interface of the dam body with the banks should be done in the form inclined planes with short ledges for ease of work. Treatment of slopes with vertical ledges is not allowed, since due to sudden changes in the height of the embankment, dangerous transverse cracks are formed along the ledges. Their presence will contribute to increased filtration of water and destruction of the dam.
We are designing an earth dam made of sand, which will be erected by backfilling using the pioneer method. To reduce filtration, we will arrange a core and a lock.
The wet method of filling soil is relatively new. At first, this method was used only for filling loess soils; later it began to be used for filling clayey and ordinary sandy soils (sometimes with an admixture of coarse soils and stones).
The wet method has the following advantages over the dry method: a) there is no need to dry or moisten the quarry soil (to optimal humidity); b) the soaking of dense lumps of cohesive soil placed in the body of the dam is ensured; c) the duration of the construction season increases due to the possibility of carrying out work during precipitation, as well as during frosts; d) a high density of dumped soil is obtained (which is especially important when making clay impervious devices).
Work on dumping soil into water is carried out as follows. The dam is erected in horizontal layers up to 1.5...2.0 m thick for clay soils and up to 4.0 m for sandy soils. Each planned horizontal layer of soil is divided into maps (rectangular in plan), and dams are poured dry along the boundaries of the maps height equal to approximately the thickness of the layer. The map intended for backfilling with soil is pre-filled with water (using pumps). After this, work is carried out to fill the soil into the map according to the diagram in Fig. 2.93. As you can see, the map is filled with soil into the water using the pioneer method. The water displaced by the soil from the map's pond is drained into the adjacent map. The initial compaction of the soil is ensured by dump trucks during the process of dumping the delivered soil, as well as by bulldozers when leveling the surface of the dumped soil layer. No additional compaction is performed under these conditions.
