High-pressure jet grouting construction method for concrete dam diaphragm wall

Abstract

The invention discloses a high-pressure jet grouting construction method for a concrete dam diaphragm wall, and belongs to the technical field of concrete dams. Comprising the following steps: S1, determining an anti-seepage wall method; s2, determining the position of an anti-seepage wall; s3, an anti-seepage wall optimizing procedure is carried out; and S4, connection treatment of the anti-seepage wall is conducted. Whether the diaphragm wall method is feasible or not is determined through a series of operations; when the seepage gradient does not meet the requirement, the seepage gradient is reduced by prolonging the seepage path; the position of the diaphragm wall is optimized, and the diaphragm wall is moved to the upstream side of the dam body; the dam body and the diaphragm wall are constructed at the same time and do not interfere with each other, and the construction progress is accelerated; the anti-seepage wall abutment cap is poured firstly, then the high-pressure-spraying anti-seepage wall is constructed, the platform excavation time and the secondary backfilling time are saved, the construction cost is saved, and the construction period is shortened.

Description

Technical Field

[0001] The invention relates to the technical field of concrete dams, and in particular to a high-pressure rotary spraying construction method for a concrete dam anti-seepage wall. Background Art

[0002] In the case of complex geological conditions, the riverbed at the dam foundation is a covering layer structure, and is mainly alluvial and diluvial materials, with an overall boulder, sand, gravel layer, and a covering layer within 5m of drift (block) sand, gravel, and boulders throughout the surface, with a content of more than 25%, and the rest is gravel and sand. This layer has poor grading, loose soil, partial overhead, and strong permeability; the riverbed below 5m is mainly composed of pebbles, gravel, and sand, with partial boulder, and the dam foundation layer has strong to medium permeability conditions: the construction of the dam foundation anti-seepage wall requires the use of concrete ground-anchored wall technology; however, the construction of the concrete ground-anchored wall takes a long time.

[0003] In some dam anti-seepage wall structures, high-pressure rotary grouting and curtain grouting are also used for anti-seepage, but only when the construction period and geological environment allow. In the above geological environment, there are currently no construction cases using high-pressure rotary grouting, and there is no corresponding technical disclosure. Summary of the invention

[0004] The purpose of the present invention is to provide a high-pressure rotary spraying construction method for a concrete dam anti-seepage wall, which is applied to a construction environment where the geological conditions of the dam body are complex, the basic geological conditions are a deep covering layer containing boulders, boulders, pebbles, gravel, and the dam base layer is of strong to medium permeability; on the basis of ensuring the construction quality, the construction efficiency is improved and the construction timeliness is guaranteed.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions: A high-pressure rotary spraying construction method for a concrete dam anti-seepage wall comprises the following steps: S1. Determine the method of anti-seepage wall; S2. Determine the location of the cut-off wall; S3. Optimize the anti-seepage wall process; S4. Connection treatment of anti-seepage wall.

[0006] In some embodiments, it is applied to the construction environment where the geological conditions of the dam are complex, the basic geological conditions are a deep overburden layer containing boulders, boulders, pebbles, gravel, and the dam base layer is of strong to medium permeability.

[0007] In some embodiments, in step S1: Through high-pressure rotary grouting experiments and quality inspections under similar geological conditions in the project area, it is determined whether it is feasible to use high-pressure rotary grouting walls as dam foundation anti-seepage walls.

[0008] In some embodiments, in step S1, it further includes: determining anti-seepage wall parameters; Specifically, it includes: leakage calculation, infiltration slope calculation, and comprehensive analysis and determination; Among them, if the infiltration gradient is greater than the specification requirements, and is still greater than the specification requirements after increasing the depth of the anti-seepage wall, the infiltration gradient can be reduced by extending the seepage path.

[0009] In some embodiments, in step S2: The dam body and the cut-off wall are designed to be constructed simultaneously without interfering with each other; the axis of the cut-off wall is moved to the upstream side of the dam body; The anti-seepage wall and the dam body are connected with cap concrete, and a PVC waterstop is installed at the connection between the cap and the dam body.

[0010] In some embodiments, in step S3: First, cast the anti-seepage wall cap, and then construct the high-pressure rotary spray anti-seepage wall.

[0011] In some embodiments, in step S3: When jet jet drilling, the following pipe method is used; the bottom elevation of the hole is at least 30cm lower than the design elevation; After the hole depth meets the requirements of the design drawings, put in the brittle PVC pipe wall that can be broken by the jet jet pressure, and pull out the follower pipe.

[0012] In some embodiments, in step S3, it further includes: special situation control; (1) Treatment of gushing water; In order to prevent the gushing water from washing away the fine particles in the hole and forming stratum cavities, the outer side of the PVC wall protection pipe is backfilled with gravel and coarse sand while pulling out the heel pipe, and the hole is sealed with mortar; (2) Treatment of permeable layer; When the rotary spraying reaches the strong permeable layer, reduce the lifting speed, increase the density and amount of slurry, and add 1%~3% water glass to the cement slurry; (3) No slurry return or leakage treatment; When there are large gaps in the formation causing no slurry return or serious slurry leakage, the main measures are: stop lifting the rotary jet pipe, reduce the rotation speed, reduce the water pressure, increase the slurry density or slurry feed volume; or, add water glass to the slurry and perform rotary jetting in situ; When the amount of slurry returning from the orifice is small, reduce the rotation and lifting speed, reduce the water pressure, and increase the density of the slurry; or, add water glass to the slurry to shorten the consolidation time and allow the slurry to solidify within a certain soil layer. When the slurry return is normal, start lifting and rotary spraying. (4) Handling of boulders and rocks; When rotary spraying reaches the boulder, block or pebble layer, increase the rotation speed 50cm up and down and slow down the lifting speed to fully wrap the boulder, block or pebble with cement slurry to make the pile body continuous and complete.

[0013] In some embodiments, in step S4: An additional row of piles is added at the location where the high-pressure rotary jetting anti-seepage wall connects with the original concrete ground-connected wall anti-seepage wall, that is, three rows of rotary jetting piles are set up to make the rotary jetting piles closely combined with the original anti-seepage wall.

[0014] In some embodiments, in step S1: The anti-seepage wall is composed of two rows of high-pressure jet-jet piles; The pile depth is 20~25m, the spacing between piles is 60cm, and the pile diameter is 75cm.

[0015] Compared with the prior art, the present invention provides a high-pressure rotary spraying construction method for a concrete dam anti-seepage wall, which has the following beneficial effects.

[0016] 1. The present invention determines whether the anti-seepage wall method is feasible by comparing and analyzing the dam body anti-seepage technology, supplementing geological exploration, and conducting high-pressure rotary jet pile experiments; when the seepage gradient does not meet the requirements, the seepage gradient is reduced by extending the seepage path.

[0017] 2. The present invention optimizes the position of the anti-seepage wall, moves it to the upstream side of the dam body, connects it to the dam body with a cap concrete, and installs a water stop strip; after the dam body is constructed to a certain height, the construction of the anti-seepage wall begins; the dam body and the anti-seepage wall are constructed simultaneously without interfering with each other, thus speeding up the construction progress; at the same time, the original dam section is retained and used as a dam access road after backfilling with concrete.

[0018] 3. The present invention optimizes the construction process, first casts the anti-seepage wall cap, and then constructs the high-pressure spraying anti-seepage wall; saves the platform excavation and secondary backfilling time, saves construction costs and construction period, and at the same time optimizes the process of chiseling out the pile head, further saving construction costs and construction period.

[0019] 4. The present invention records the thickness of different strata, the depth of boulders or boulders and the approximate particle size during jet grouting drilling to provide a reference for adjusting jet grouting parameters during jet grouting construction; designs corresponding treatment methods for special situations to ensure the construction effect; adds a row of piles at the junction of the high-pressure jetting anti-seepage wall and the original anti-seepage wall to closely combine the jet grouting piles with the original concrete anti-seepage wall.

[0020] Other advantages, objectives and features of the present invention will be described in part in the following description; and in part, will be apparent to those skilled in the art based on an examination of the following; or, may be taught from the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Design layout for the dam's anti-seepage wall.

[0022] Figure 2 This is the design rendering of the dam section restoration.

[0023] Figure 3 Design the section for the newly built 1# dam section.

[0024] Figure 4 This is a schematic diagram of the design layout of high-pressure rotary spraying.

[0025] In the figure: 1. The axis of the concrete ground-connected wall and anti-seepage wall of the original dam section 2#; 2. Original 1# dam section; 3. Build a new 1# dam crest axis; 4. Design of high-pressure jet grouting anti-seepage wall and pile layout for the new 1# dam section; 5. Public road on the right bank; 6. Build a new 1# dam section; 8. 2# dam section; 9. Concrete backfill section downstream of 1# dam section; 10. Backfill concrete in the flushing area at the bottom of the original 1# dam section; 11. Build a new high-pressure jet grouting anti-seepage wall on the top of 1# dam; 12. Cap concrete; 13. The original dam body ground-connected wall and anti-seepage wall; 14. Water-stopping structure between the concrete cap on the top of the high-pressure jet-jet pile and the concrete of the dam structure; 15. Schematic diagram of dam section. DETAILED DESCRIPTION

[0026] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0027] A high-pressure rotary spraying construction method for a concrete dam anti-seepage wall is applied to a construction environment where the geological conditions of the dam body are complex, the basic geological conditions are a deep overburden layer containing boulders, boulders, sand pebbles, and gravel, and the dam base layer is highly to moderately permeable.

[0028] The design and construction of the concrete gravity dam foundation anti-seepage wall of a hydropower station is a concrete ground-connected wall system; due to earthquakes and floods, the dam shoulders, anti-seepage walls, and gravity dams were severely damaged, and the project lost its power generation function. Combined with the necessary time schedule for the project to be repaired, the left bank gates and sedimentation basins must be repaired within one dry season, and the right bank dam section and all structures must be rebuilt within the second dry season. In order to ensure that the project node targets within a single dry season are achieved on schedule, power generation is resumed as soon as possible, and good contract performance is achieved, it is not feasible to continue to construct the concrete ground-connected wall of the dam anti-seepage wall according to the original design.

[0029] The technical solution provided in this application is adopted to adjust the construction method and position of the dam's anti-seepage wall; through rapid repair measures, it is ensured that the repair of the damaged dam is completed on schedule; at the same time, the anti-seepage capacity of the dam foundation and the bonding strength of the dam foundation and the dam body are guaranteed.

[0030] like Figure 1 As shown; 1 is the axis of the concrete ground-connected wall and anti-seepage wall of the original dam section 2#; 2 is the original 1# dam section, with a dam crest elevation of 1430m. It was demolished according to the initial requirements and rebuilt in situ, and retained after optimization; and used as the access road to the dam; 3 is the newly built 1# dam top axis, where 1# dam section intersects 2# dam section at 35°; the dam section elevation is divided into three steps from 1430m to connect with the right bank road 5, and the top elevation is 1445.6m; 4 is the design and pile arrangement of the high-pressure jet grouting anti-seepage wall of the new 1# dam section; the pile depth is 20m, the spacing between rows is 60m, and it is designed in two rows; one row of piles is added on the upstream side of the intersection with the 2# dam section, that is, three rows of jet grouting piles are set; the anti-seepage wall is arranged in steps along the slope, and the pile position extends 1m outside the road; 5 is the public road on the right bank.

[0031] like Figure 2 As shown; 6 is the newly built 1# dam section; 2 is the original 1# dam section. The area between the newly built 1# dam section and the original 1# dam section is backfilled and compacted to be used as the access road to the dam. 8 is the 2# dam section, and the dam crest elevation is the same as the original 1# dam section; 9 is the downstream concrete backfill section of the 1# dam section; it protects the newly built dam section and the right side slope, backfills the top with slag to 30cm below the original dam crest, and pours concrete pavement to maintain the same elevation as the original 1# dam section, and is used as the dam crest road; 10 is the backfill concrete of the bottom flushing area of ​​the original 1# dam section to ensure the stability of the original 1# dam section.

[0032] like Figure 3 As shown; 11 is the newly built 1# dam top high-pressure rotary grouting anti-seepage wall, with a depth of 20m, which is excavated at the dam foundation section to the bottom elevation of the original 1# dam section bottom in-situ connecting wall; 12 is the platform cap concrete, the bottom concrete thickness is 2.7m, and the thickness of other areas is 2m; 13 is the anti-seepage wall of the original dam body; 14 is a water stop structure between the concrete cap on the top of the high-pressure jet grouting pile and the concrete of the dam structure, with two layers arranged in total; 15 is a schematic diagram of the dam section, which is one of the cross sections when the anti-seepage wall is adjusted and optimized to the outside of the dam structure.

[0033] The high-pressure rotary spraying construction method for the concrete dam anti-seepage wall comprises the following steps: S1. Determine the method of anti-seepage wall; S2. Determine the location of the cut-off wall; S3. Optimize the anti-seepage wall process; S4. Connection treatment of anti-seepage wall.

[0034] In step S1, the cut-off wall method is determined.

[0035] Specifically, through high-pressure rotary jet grouting experiments and quality inspections under similar geological conditions in the project area, it is determined whether it is feasible to use high-pressure rotary jet grouting walls as dam foundation anti-seepage walls.

[0036] For example, it was determined in the aforementioned project that when the anti-seepage depth of the dam foundation is 20m, it is feasible to use a high-pressure rotary jet wall as the anti-seepage wall of the dam foundation; accordingly, the anti-seepage wall is composed of two rows of high-pressure rotary jet piles, with a pile depth of 20~25m, a row spacing of 60cm between piles, and a pile diameter of 75cm; among which the preferred pile depth is 20m.

[0037] In step S1, it also includes: determining the parameters of the anti-seepage wall.

[0038] Specifically, it includes: leakage calculation, infiltration gradient calculation, and comprehensive analysis and determination.

[0039] in: For leakage calculation, take two cut-off wall depths (such as 20m and 25m) respectively and compare the calculation results; the dam foundation leakage should be less than the requirements of the design report; When calculating the seepage gradient, take the above two cut-off wall depths and calculate the seepage gradient of the cut-off wall, the stratum below the cut-off wall and the stratum downstream of the cut-off wall respectively; Comprehensive analysis determined that: if the permeability gradient of the stratum below the cut-off wall and the stratum downstream of the cut-off wall are both greater than the specification requirements, and are still greater than the specification requirements after increasing the depth of the cut-off wall, then based on the relationship between the permeability gradient and the seepage path, the permeability gradient should be reduced by extending the seepage path.

[0040] Preferably, the leakage should be less than 0.2m 3 / s, the penetration gradient should be less than 0.2.

[0041] In step S1, it also includes: The original dam section is retained, and a new dam section is set up to intersect with the original dam section; the space between the dam sections is densely backfilled and used as the access road to the dam.

[0042] In step S2, the position of the cut-off wall is determined.

[0043] In the aforementioned project, the original dam's anti-seepage wall was located at the lower part of the dam body. The construction of the anti-seepage wall must be completed first during the construction of the concrete dam. The construction progress of the anti-seepage wall directly affects the construction of the gravity dam and related projects. In addition, the anti-seepage wall is an underground concealed engineering construction. The geological conditions of the dam base are relatively complex. Various factors that arise during construction are uncontrollable and the progress cannot be guaranteed.

[0044] The dam body and the cut-off wall are designed to be constructed simultaneously without interfering with each other, thus speeding up the construction progress.

[0045] Specifically, through analysis of progress, quality, construction organization, etc., the axis of the anti-seepage wall was moved to the upstream side of the dam body; the anti-seepage wall and the dam body were connected with cap concrete, and two PVC waterstops were installed at the connection between the cap and the dam body; the anti-seepage wall was constructed after the dam body was constructed to a certain height.

[0046] The thickness of the concrete at the bottom of the cap is 2.5-3.0 m, and the thickness of other areas is 1.8-2.2 m; preferably, the thickness of the concrete at the bottom of the cap is 2.7 m, and the thickness of other areas is 2.0 m.

[0047] In step S3, the anti-seepage wall process is optimized.

[0048] Specifically, the anti-seepage wall cap is poured first, and then the high-pressure rotary spray anti-seepage wall is constructed.

[0049] In the aforementioned project, due to the constraints of the construction site, the anti-seepage wall on the right bank slope was constructed in stages according to the elevation of the horse trail; the construction sequence was: filling of the construction platform of this stage → high-pressure spraying wall construction → qualified quality inspection → excavation of the construction platform → chiseling of the pile heads → pouring of the platform cap → backfilling of this stage → high-pressure spraying wall construction of the next stage.

[0050] During each stage of cap concrete construction, the construction platform must be excavated and backfilled, and repeated backfilling and excavation are all within a linear construction period. After the process is optimized, the anti-seepage wall cap is poured first, and then the high-pressure spraying anti-seepage wall is constructed. This saves time for excavating the construction platform and secondary backfilling and compacting, saves construction costs, shortens the construction period, and optimizes the pile head removal process.

[0051] In step S3, the following pipe method is adopted during the jet jet drilling; The elevation of the bottom of the hole is more than 30cm lower than the design elevation; after the hole depth meets the requirements of the design drawings, a brittle PVC pipe wall that can be broken by the jet jet pressure is put in, and the follower pipe is pulled out.

[0052] In addition, during the drilling process, the thickness of different strata, the depth of boulders or boulders, and the approximate particle size are recorded in detail to provide a reference for adjusting the jet grouting parameters during jet grouting construction.

[0053] In step S3, it also includes: special situation control.

[0054] (1) Treatment of gushing water; In order to prevent the gushing water from washing away the fine particles in the hole and forming stratum voids, gravel and coarse sand are backfilled to the outside of the PVC wall protection pipe while pulling out the heel pipe, and the hole mouth is sealed with mortar.

[0055] (2) Treatment of permeable layer; When the rotary spraying reaches the strong permeable layer, reduce the lifting speed, increase the density and amount of slurry, and add 1%~3% water glass to the cement slurry; Preferably, 2% water glass is added.

[0056] (3) No slurry return or leakage treatment; When there are large gaps in the formation causing no slurry return or serious slurry leakage, the main measures are: stop lifting the rotary jet pipe, reduce the rotation speed, reduce the water pressure, increase the slurry density or slurry feed volume; or, add water glass to the slurry and perform rotary jetting in situ; When the amount of slurry returning from the hole is small, reduce the rotation and lifting speed, reduce the water pressure, and increase the slurry density; or, add water glass to the slurry, shorten the consolidation time, and allow the slurry to solidify within a certain soil layer. When the slurry return is normal, start lifting and rotary spraying.

[0057] (4) Handling of boulders and rocks; When rotary spraying reaches the boulder, block or pebble layer, increase the rotation speed 50cm up and down and slow down the lifting speed to fully wrap the boulder, block or pebble with cement slurry to make the pile body continuous and complete.

[0058] In step S4, the anti-seepage wall is connected.

[0059] An additional row of piles is added at the location where the high-pressure rotary jetting anti-seepage wall connects with the original concrete ground-connected wall anti-seepage wall, that is, three rows of rotary jetting piles are set up to make the rotary jetting piles closely combined with the original anti-seepage wall.

[0060] At the same time, optionally, during the jet grouting construction process, measures such as increasing water pressure and rotation speed, reducing lifting speed, and increasing slurry concentration can be adopted to increase the diameter of the pile body to further tightly integrate the jet grouting pile with the original anti-seepage wall.

[0061] Also includes: Detection.

[0062] (1) Compressive strength and anti-seepage performance; 28 days after the construction of the high-pressure rotary jet anti-seepage wall is completed, core sampling and water pressure tests are carried out; samples are taken at different depths for compressive strength testing, and the inspection holes are inspected for anti-seepage using a hydrostatic head water pressure test. The water pressure test is carried out in full sections and in sections.

[0063] (2) Leakage detection; Arrange groundwater level observation holes and install piezometers, which are mainly used to monitor the rise and fall of groundwater levels during the operation of the power station, and are also used to monitor the leakage of the dam foundation and dam shoulders; continuous observations are carried out in the initial stage, before water storage, during the dam storage period, and after water storage.

[0064] The present application is described below in conjunction with specific engineering cases.

[0065] The Upper Bodiksi Hydropower Station is located on the Bodiksi River in the Sindhupalchok administrative district in north-central Nepal. The right bank of the dam site is the China-Nepal Highway, 110 kilometers from Kathmandu and 5 kilometers from the China-Nepal border (Zhangmu Port). The power station has an installed capacity of 2×22.5KW and was put into operation in January 2001. The 8.1-magnitude earthquake on April 25, 2015 caused the penstock to rupture and the powerhouse to be flooded. The barrier lake flood on July 5, 2016 destroyed the right shoulder of the dam, the adjacent China-Nepal Highway and the road to the dam. The right guide wall upstream of the spillway and the right wall of the sedimentation tank were destroyed, and the powerhouse was flooded again.

[0066] In 2018, the construction of the 1# gravity dam and anti-seepage wall, the right wall of the sedimentation tank, the upstream and downstream slope protection of the dam, the repair or replacement of other damaged buildings, metal structures and mechanical and electrical equipment in the head hub area, the replacement of some pressure steel pipes, the replacement of electrical equipment in the switch station, the repair or replacement of all equipment in the plant except the main engine, and the commissioning and trial operation were carried out. The contract requires the use of an underground concrete continuous wall consistent with the original design as the anti-seepage wall of the new 1# gravity dam, and extending 30m into the right bank slope, with a total length of about 100, of which about 70m is located on the slope.

[0067] According to the construction period and diversion and interception construction requirements, the construction technology of the ground-connected wall and the comprehensive analysis of the construction site are carried out. In the absence of full-section diversion and interception such as diversion holes, if a concrete underground continuous wall is used as the anti-seepage wall of the new No. 1 gravity dam, the construction will not be completed on schedule, which will directly affect the project schedule and power generation goals.

[0068] If high-pressure jet grouting wall is used as the anti-seepage structure of the new 1# gravity dam, the construction period will be shortened, the construction cost will be reduced, and the power generation target can be achieved on schedule or ahead of schedule. However, there are no construction cases using high-pressure jet grouting in this environment, and there is no corresponding technical disclosure. According to the previous geological exploration data of the dam base, the stratum contains large-sized boulders and boulders, and the feasibility and reliability of high-pressure jet grouting construction is worth studying.

[0069] First, determine the cut-off wall method.

[0070] Comparison and analysis of dam anti-seepage technologies and comparison of regional power stations.

[0071] By collecting design data on anti-seepage walls of hydropower station buildings in Nepal and conducting comparative analysis on geological data, conducting supplementary geological exploration and high-pressure jetting tests, and leakage analysis and calculations, the feasibility of using high-pressure jet grouting to construct the anti-seepage wall of the dam was studied. Project Name Geological conditions Cut-off wall type Basic parameters of anti-seepage wall Upper Tamaxi Hydropower Station The riverbed surface 5m deep is mainly composed of gneiss and shale coarse sand, gravel and pebbles; below 5m it is mainly composed of silt, coarse sand, pebbles and cobbles; the strata on the left and right shoulders are mainly gneiss The anti-seepage wall of the dam and water inlet foundation is a combination of single-row high-pressure spray piles + steel sheet piles. The anti-seepage of the left shoulder of the upstream dam is a single-row high-pressure spray pile, both of which are suspended. The spacing between high-pressure grouting piles at the dam and water inlet is 0.6m, the pile length is 15m, and the steel sheet pile length is 7m; the spacing between high-pressure grouting piles at the left dam shoulder is 0.6m, the pile length is 19~26m, and the pile diameter is 0.75m Nasuwakali Hydropower Station The riverbed is mainly composed of fine sand and gravel layers, with a small amount of boulders mixed in some areas. The anti-seepage wall of the overflow dam foundation is a double row of high-pressure spray piles, and the anti-seepage wall at the end of the energy dissipation pool is a single row of high-pressure spray piles, both of which are suspended The spacing between high-pressure grouting piles at the overflow dam foundation is 0.8m, and the pile length is 15m. The spacing between high-pressure grouting piles at the end of the energy dissipation pool is 0.8m, the pile length is 11m, and the pile diameter is 1.0m. Middle Bo Dixie Hydropower Station The surface of the riverbed is generally composed of boulders, sand, pebbles and gravels. There are boulders and boulders all over the surface, and the rest is sand, pebbles and sand. The bedrock is below 15m from the riverbed surface. The anti-seepage wall of the dam and energy dissipation pool foundation is a single-row curtain grouting, and the anti-seepage wall of the downstream apron is an underground concrete continuous wall. Curtain grouting hole spacing is 3m, 3m into the rock; ground-connected wall width is 1m, 3m into the rock Upper Bodixie Hydroelectric Station The riverbed is composed of a layer of boulders, sand, pebbles and gravels. The thick surface layer is composed of boulders (blocks) of sand, pebbles and gravels. The surface is covered with boulders and boulders, and the rest is pebbles and sand. The lower part is mainly composed of pebbles, gravels and sand, with boulders in some parts. The original dam and spillway inlet foundation anti-seepage walls are suspended underground concrete continuous walls, and the bypass tunnel and sedimentation tank inlet foundation anti-seepage is single-row curtain grouting. The ground-connected wall is 0.8m wide and 20m deep

[0072] By collecting and comparing the geological data and anti-seepage wall data of four power stations in Nepal, the Upper Tamaxi Power Station and the Nasuwakali Power Station adopted high-pressure rotary jet grouting piles as the basic anti-seepage structure of the buildings; however, the geological conditions are better than those of the dam foundation of the Upper Bodixie Hydropower Station.

[0073] Further, supplement geological exploration.

[0074] In order to gain a deeper understanding of the geological conditions of the foundation of the new No. 1 gravity dam, two supplementary geological exploration holes were selected at both ends of the axis of the anti-seepage wall of the new No. 1 gravity dam to conduct supplementary surveys of the stratum geology of the dam base; the hole depths were 55m and 60m respectively.

[0075] Through the core analysis of the boreholes, the geological strata of the foundation of the new No. 1 gravity dam are mainly: the riverbed cover is mainly alluvial and diluvial materials, the overall boulder, sand, gravel layer, the riverbed cover is divided into two rock groups, the surface layer is 2.5m to 5.0m thick, it is drifting (block) sand, gravel, the surface boulder and boulders are scattered, the content is more than 25%, the rest is gravel and sand, this layer has poor grading, loose soil, partial overhead, and strong permeability; the riverbed below 5m is mainly composed of pebbles, gravel and sand, with boulders in some parts, and the gravel and sand layers are basically interlayered or tightly filled.

[0076] Combined with the permeability test and dynamic penetration test of Kathmandu National Laboratory, the dam base layer is strong to medium permeable, with a permeability of 10 -2 cm / s~10 -3 cm / s, and the allowable permeability gradient is i=0.1~0.2.

[0077] Conduct high-pressure jet grouting pile experiments.

[0078] In order to provide a reference for the high-pressure rotary jetting method in the design of the anti-seepage wall and the subsequent construction, two sets of parameters were selected on site for the high-pressure rotary jetting experiment; the high-pressure rotary jetting test piles were carried out on the right bank downstream of the dam to ensure that accurate and effective parameters were obtained under the same geological conditions as the dam anti-seepage wall.

[0079] The experimental piles were arranged in two rows perpendicular to the water flow, with a total of 13 piles, 9m long, and a wall length of 4.3m; the spacing between the piles was 60cm, the pile diameter was 75cm, and the wall width was about 1.05m. 28 days after the completion of the experimental piles, cores were taken from the bite of the two upstream and downstream piles and the middle of the pile body to conduct pile body compression and hole penetration water pressure tests, and a total of 5 core samples were taken; the maximum compressive strength of the core samples was 14.2Mpa, and the minimum was 7.3Mpa, both greater than the 6Mpa required by the contract; the water pressure test was carried out in sections, with a section length of 3m, and the maximum water permeability was 1.85Lu, less than the 2Lu required by the contract.

[0080] Among them, the minimum compressive strength and maximum water permeability are close to the allowable values ​​required by the contract, and both appear at the position where the two piles are engaged. Therefore, the experiment of high-pressure jet grouting piles is of reference value and can be used as the basis for the design of high-pressure jet grouting for anti-seepage walls.

[0081] Determine the parameters of the cut-off wall.

[0082] Dam foundation leakage calculation: The original anti-seepage wall depth is 20m. When calculating the dam foundation leakage, the anti-seepage wall depth is taken as 20m and 25m respectively, and the calculation results are compared. When the anti-seepage wall depth is 20m, the dam foundation leakage is 0.143m 3 / s; when the depth of the anti-seepage wall is 25m, the leakage of the dam foundation is 0.128m 3 / s; Both results are less than the 0.2m required in the original design report 3 / s.

[0083] Calculation of seepage slope: When calculating the seepage slope, the depth of the cut-off wall was taken as 20m and 25m, and the seepage slopes of the cut-off wall, the stratum below the cut-off wall, and the stratum downstream of the cut-off wall were calculated respectively; the seepage slopes of the stratum below the cut-off wall and the stratum downstream of the cut-off wall were both greater than the requirements of the specification, and only the seepage slope of the cut-off wall was less than the requirements of the specification. When the depth of the cut-off wall increased to 60m and extended into the underground rock formation, the seepage slopes of the stratum below the cut-off wall and the stratum downstream of the cut-off wall were still greater than the requirements of the specification, and the cut-off wall with a depth greater than 60m was unreasonable, and the construction conditions were not available on site.

[0084] Comprehensive analysis determined that: based on the relationship between the seepage gradient and the seepage path, the seepage gradient can be reduced by extending the seepage path; according to the length of the downstream apron and slope protection of the dam, when the depth of the anti-seepage wall is 20m, the seepage gradients at the downstream apron and the end of the slope of the dam are 0.149 and 0.116 respectively, both less than the design requirements.

[0085] Through comprehensive comparative analysis and research, combined with the results of the jet grouting experiment and the geological conditions analysis experiment, it was finally determined that it was feasible to use the high-pressure jet grouting method to construct the dam foundation anti-seepage wall under the unfavorable geological conditions of the Upper Bodixie Dam foundation; accordingly, the anti-seepage wall consists of two rows of high-pressure jet grouting piles, with a pile depth of 20m, a row spacing of 60cm, a pile diameter of 75cm, and a maximum wall width of 135cm (see Figure 4 ).

[0086] Optimization of the location of the cut-off wall.

[0087] The original design of the anti-seepage wall is located at the lower part of the gravity dam. During construction, the construction of the anti-seepage wall must be completed before the construction of the gravity dam can begin; the construction progress of the anti-seepage wall directly affects the construction of the gravity dam and related projects. In addition, the anti-seepage wall is an underground hidden project construction, the geological conditions of the dam base are relatively complex, and various factors that arise during construction are uncontrollable, and the progress cannot be guaranteed.

[0088] From the comparative analysis of construction progress and quality impact, it takes a long time to remove the concrete of the original 1# dam section. After design optimization, the original 1# dam section is retained, and a new 1# dam section is built, which intersects and connects with the 2# dam section at 35 degrees. The foundation flushing area of ​​the original 1# dam section is backfilled with concrete and used as the access road to the dam. The anti-seepage wall of the new dam section is connected with the original 2# dam section (see Figure 1 ).

[0089] The hollowed-out part at the bottom of the original 1# dam section was backfilled densely with plain concrete. The newly built 1# dam section is 10m higher than the original dam section and is set up in a stepped manner. The top of the dam is flush with the right bank road, and the top of the original dam section is used as the upper dam top road.

[0090] At the same time, the axis of the cut-off wall is moved to the upstream side of the dam body (see Figure 2 ), the anti-seepage wall and the dam body are connected with the platform cap concrete, and two PVC water stop strips are installed at the connection between the platform cap and the dam body; see Figure 3 , the anti-seepage wall was moved to the upstream of the dam body. After the dam body was constructed to a certain height, the construction of the anti-seepage wall began. The dam body and the anti-seepage wall were constructed at the same time without interfering with each other, which accelerated the construction progress.

[0091] High-pressure rotary spraying construction optimizes the construction process.

[0092] Due to the constraints of the construction site, the anti-seepage wall on the right bank slope was constructed in stages according to the different horse track elevations; the construction sequence was: filling of the construction platform of this stage → high-pressure spraying wall construction → qualified quality inspection → digging out the construction platform → chiseling out the pile heads → pouring the platform cap → backfilling of this stage → high-pressure spraying wall construction of the next stage.

[0093] In each stage of the cap concrete construction, the construction platform must be excavated and backfilled. Repeated backfilling and excavation took up the construction period. After discussion and research with the design and consulting engineers, the anti-seepage wall cap was poured first, and then the high-pressure spraying anti-seepage wall was constructed. This saves the time of excavating the construction platform and secondary backfilling and rolling, saves construction costs and construction period, and optimizes the process of chiseling the pile head.

[0094] Jet drilling: The drilling adopts the pipe-following method. The bottom elevation of the hole is more than 30cm lower than the design elevation. When the hole depth meets the requirements of the design drawings, a brittle PVC pipe wall that can be broken by the jet jet pressure is put in, and the pipe-following method is pulled out. During the drilling process, the thickness of different strata, the depth of boulders or boulders, and the approximate particle size are recorded in detail to provide a reference for adjusting the jet jet parameters during the jet jet construction.

[0095] Special situation control: Design corresponding handling methods for special situations.

[0096] (1) Treatment of gushing water; About 15 to 17 meters underground in the local area of ​​the EL1413.00 platform, there is a 1 to 1.5 meter thick highly permeable layer; after the completion of individual drilling, water gushed out and sand returned to the follower pipe; in order to prevent the gushing water from washing away the fine particles in the hole and forming stratum voids, gravel and coarse sand were backfilled to the outside of the PVC wall pipe while the follower pipe was pulled out, and the hole mouth was sealed with mortar.

[0097] (2) Treatment of permeable layer; During the jet grouting process, according to the drilling records, when the jet grouting reaches a highly permeable layer, the lifting speed is reduced, the density and amount of slurry are increased, and 2% water glass is added to the cement slurry.

[0098] The addition of water glass shortens the solidification time of cement slurry, makes the slurry solidify quickly, and prevents the slurry from being dispersed by groundwater.

[0099] (3) No slurry return or leakage treatment; When there are large voids in the stratum causing no slurry return or serious slurry leakage, the main measures are: stop lifting the rotary jet pipe, reduce the rotation speed, reduce the water pressure, increase the slurry density or slurry input; or, add water glass to the slurry and perform rotary jetting in situ.

[0100] When the amount of slurry returning from the hole is small, reduce the rotation and lifting speed, reduce the water pressure, and increase the slurry density; or, add water glass to the slurry, shorten the consolidation time, and allow the slurry to solidify within a certain soil layer. When the slurry return is normal, start lifting and rotary spraying.

[0101] (4) Handling of boulders and rocks; According to the drilling records, when the rotary spraying reaches the boulder, block or pebble layer, the rotation speed is increased 50 cm up and down and the lifting speed is slowed down to fully wrap the boulder, block or pebble with cement slurry, so as to make the pile body continuous and complete.

[0102] (5) Treatment of the joint with the original anti-seepage wall; At the part where the high-pressure jet grouting anti-seepage wall and the original concrete ground-connected wall anti-seepage wall are connected, one row of piles is added, that is, three rows of jet grouting piles are set, so that the jet grouting piles are closely combined with the original concrete anti-seepage wall; At the same time, optionally, during the jet grouting construction process, measures such as increasing water pressure and rotation speed, reducing lifting speed, and increasing slurry concentration can be adopted to increase the diameter of the pile body to further tightly integrate the jet grouting pile with the original concrete anti-seepage wall.

[0103] Application status.

[0104] A total of 1 set of equipment was invested in the construction of the high-pressure rotary jet anti-seepage wall of this project. Drilling began on March 6, 2019, and rotary jetting was completed on July 29, 2019. A total of 275 holes were constructed, with a total length of 5923.7m and a wall length of 78.08m. The construction was divided into four stages according to the platform elevation. The actual construction of the high-pressure rotary jet anti-seepage wall took 109 days, with an average of 3 piles per day, and an average of 2 piles per day in areas with particularly poor geological conditions.

[0105] 28 days after the construction of the high-pressure jet spraying anti-seepage wall was completed, a total of 9 piles were selected for coring and water pressure tests. From the appearance of the core sample, the pile body is continuous, the cement slurry condensate is dense, and the connection between the cement slurry condensate and the stone in the sample body is dense; 23 core samples taken from 9 piles at different depths were tested for compressive strength, and the minimum strength was 7.3Mpa, which was greater than the 6Mpa required by the contract and design. Each inspection hole was inspected for anti-seepage using a hydrostatic head water pressure test. The water pressure test was carried out in full section and in sections, and the maximum water permeability was 1.21Lu, which was less than the 2Lu required by the contract and design.

[0106] Four groundwater level observation holes were arranged downstream of the new No. 1 gravity dam, and two piezometers were installed, mainly to monitor the rise and fall of groundwater levels during the operation of the power station; at the same time, they were also used to monitor the leakage of the dam foundation and dam shoulders. Through continuous observations in the initial stage, before water storage, during the dam water storage period, and after water storage, the water level in the observation hole tended to stabilize with the rise of the water level in front of the dam, and the water level in the water level observation hole behind the dam rose by a maximum of 3.18m. The maximum water level elevation of each hole during the water storage period was less than the design requirements. The piezometer readings did not change during and after the dam water storage period, and there was no water discharge from the drainage holes installed on the downstream slope of the right bank and the drainage holes of the dam protection tank behind the dam. Hole No. Location Water level before impoundment (m) Maximum water level after impoundment (m) Design allowable maximum water level (m) OH-2 Dam 0+005.00 1423.406 1426.589 1430.40 OH-3 Dam 0+021.80 1419.507 1421.857 1424.70 0H-4 Dam 0+005.00 1416.390 1417.740 1423.30 OH-5 Dam 0+021.80 1416.278 1417.578 1421.40

[0107] Through core sampling compression test and water pressure test, water level observation hole and leakage detection behind the dam, all indicators are better than the design indicators and meet the contract requirements. The high-pressure rotary jet construction method of the dam anti-seepage wall has been successfully applied and is worthy of reference.

[0108] Application prospects.

[0109] Combined with the comparative analysis of the equipment and construction period invested in the construction of the underground concrete anti-seepage wall when the project was first built, the high-pressure rotary spraying method for the anti-seepage wall has the advantages of fast construction progress, no restrictions on the construction site, less equipment invested, and flexible movement of construction equipment. In addition, under complex geological conditions such as large-size gravel, pebbles, large boulders and highly permeable layers, it is feasible to use the high-pressure rotary spraying wall as the anti-seepage structure of the dam foundation. By strengthening the control of the construction process, its anti-seepage performance can fully meet the requirements of the design specifications. Through research and application in the construction of this project, the high-pressure rotary spraying method for the anti-seepage wall of the dam under complex geological conditions can also have certain promotion value.

[0110] In the present invention, the feasibility of the anti-seepage wall method is determined by comparing and analyzing the anti-seepage technology of the dam body, supplementing geological exploration, and conducting high-pressure rotary jet pile experiments; when the seepage slope does not meet the requirements, the seepage slope is reduced by extending the seepage path; the position of the anti-seepage wall is optimized, moved to the upstream side of the dam body, and connected to the dam body with a cap concrete and a water stop is installed; after the dam body is constructed to a certain height, the construction of the anti-seepage wall is started; the dam body and the anti-seepage wall are constructed at the same time without interfering with each other, which speeds up the construction progress; at the same time, the original dam section is retained and used as a dam access road after backfilling with concrete; the optimization In the construction process, the anti-seepage wall cap is poured first, and then the high-pressure jet anti-seepage wall is constructed; the platform excavation and secondary backfilling time are saved, the construction cost and construction period are saved, and the process of chiseling out the pile head is optimized, which further saves the construction cost and construction period; when jet jet drilling, the thickness of different strata, the depth of boulders or boulders and the approximate particle size are recorded to provide a reference for adjusting the jet jet parameters during jet jet construction; corresponding treatment methods are designed for special situations to ensure the construction effect; at the junction of the high-pressure jet anti-seepage wall and the original anti-seepage wall, a row of piles is added to make the jet jet piles closely combined with the original concrete anti-seepage wall.

[0111] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

[0112] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0113] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A high-pressure rotary spraying construction method for a concrete dam anti-seepage wall, characterized in that: The following steps are involved: S1. Determine the method of anti-seepage wall; S2. Determine the location of the cut-off wall; S3. Optimize the anti-seepage wall process; S4. Connection treatment of anti-seepage wall.

2. The high-pressure rotary spraying construction method for concrete dam anti-seepage wall according to claim 1 is characterized in that: It is used in construction environments where the geological conditions of the dam are complex, the basic geological conditions are deep overburden, containing boulders, boulders, pebbles, and gravel, and the dam base layer has strong to medium permeability.

3. The high pressure rotary grouting construction method for concrete dam anti-seepage wall according to claim 1, characterized in that: In step S1: Through high-pressure rotary grouting experiments and quality inspections under similar geological conditions in the project area, it is determined whether it is feasible to use high-pressure rotary grouting walls as dam foundation anti-seepage walls.

4. The high-pressure rotary spraying construction method for concrete dam anti-seepage wall according to claim 3 is characterized in that: In step S1, it also includes: determining the parameters of the anti-seepage wall; Specifically, it includes: leakage calculation, infiltration slope calculation, and comprehensive analysis and determination; Among them, if the infiltration gradient is greater than the specification requirements, and is still greater than the specification requirements after increasing the depth of the anti-seepage wall, the infiltration gradient can be reduced by extending the seepage path.

5. The high-pressure rotary grouting construction method for concrete dam anti-seepage wall according to claim 1 is characterized in that: In step S2: The dam body and the cut-off wall are designed to be constructed simultaneously without interfering with each other; the axis of the cut-off wall is moved to the upstream side of the dam body; The anti-seepage wall and the dam body are connected with cap concrete, and a PVC waterstop is installed at the connection between the cap and the dam body.

6. The high-pressure rotary spraying construction method for concrete dam anti-seepage wall according to claim 5 is characterized in that: In step S3: First, cast the anti-seepage wall cap, and then construct the high-pressure rotary spray anti-seepage wall.

7. The high-pressure rotary grouting construction method for concrete dam anti-seepage wall according to claim 1 is characterized in that: In step S3: When jet jet drilling, the following pipe method is used; the bottom elevation of the hole is at least 30cm lower than the design elevation; After the hole depth meets the requirements of the design drawings, put in the brittle PVC pipe wall that can be broken by the jet jet pressure, and pull out the follower pipe.

8. The high-pressure rotary grouting construction method for concrete dam anti-seepage wall according to claim 1, characterized in that: In step S3, it also includes: special situation control; (1) Treatment of gushing water; In order to prevent the gushing water from washing away the fine particles in the hole and forming stratum cavities, the outer side of the PVC wall protection pipe is backfilled with gravel and coarse sand while pulling out the heel pipe, and the hole is sealed with mortar; (2) Treatment of permeable layer; When the rotary spraying reaches the strong permeable layer, reduce the lifting speed, increase the density and amount of slurry, and add 1%~3% water glass to the cement slurry; (3) No slurry return or leakage treatment; When there are large gaps in the formation causing no slurry return or serious slurry leakage, the main measures are: stop lifting the rotary jet pipe, reduce the rotation speed, reduce the water pressure, increase the slurry density or slurry feed volume; or, add water glass to the slurry and perform rotary jetting in situ; When the amount of slurry returning from the orifice is small, reduce the rotation and lifting speed, reduce the water pressure, and increase the density of the slurry; or, add water glass to the slurry to shorten the consolidation time and allow the slurry to solidify within a certain soil layer. When the slurry return is normal, start lifting and rotary spraying. (4) Handling of boulders and rocks; When rotary spraying reaches the boulder, block or pebble layer, increase the rotation speed 50cm up and down and slow down the lifting speed to fully wrap the boulder, block or pebble with cement slurry to make the pile body continuous and complete.

9. The high-pressure rotary grouting construction method for concrete dam anti-seepage wall according to claim 1, characterized in that: In step S4: An additional row of piles is added at the location where the high-pressure rotary jetting anti-seepage wall is connected to the original concrete ground-connected wall anti-seepage wall, that is, three rows of rotary jetting piles are set up to make the rotary jetting piles closely combined with the original anti-seepage wall.

10. The high-pressure rotary spraying construction method for concrete dam anti-seepage wall according to any one of claims 1 to 4, characterized in that: In step S1: The anti-seepage wall is composed of two rows of high-pressure jet-jet piles; The pile depth is 20~25m, the spacing between piles is 60cm, and the pile diameter is 75cm.

Images