Construction method for large-angle bank slope concrete diaphragm wall of earth and rockfill dam

Abstract

A construction method for a large-angle inclined bank slope concrete diaphragm wall of an earth and rockfill dam comprises the following steps that a total concrete diaphragm wall construction scheme is determined according to a lower reservoir dam structure and dam foundation geological conditions; dividing the bank slope diaphragm wall into a plurality of groove sections according to the bank slope design gradient; a dam foundation is excavated to form a construction platform, a guide wall is made on the construction platform, and mechanical equipment is in place; pilot holes are drilled, the geological conditions of the dam foundation are re-surveyed, and the bottom line of the concrete diaphragm wall is determined; and diaphragm wall construction of the corresponding groove sections is conducted, a wall section is formed after concrete is poured into one groove hole, and a plurality of wall sections are connected into a whole wall till diaphragm wall construction is completed. According to the construction method for the large-angle inclined bank slope concrete diaphragm wall of the earth and rockfill dam, the problems that the construction space on a large-angle slope is limited, and the working face is long are solved; meanwhile, the concrete loss and the construction safety risk are reduced, and the working efficiency is improved.

Description

Technical Field

[0001] The present invention relates to the field of impervious wall construction, in particular to a construction method for a concrete impervious wall on a large-angle bank slope of an earth-rock dam. Background Art

[0002] At present, all industries in our country are in a stage of rapid and stable development, and water conservancy and hydropower projects are also constantly changing and developing. The construction of water conservancy projects is mainly for the economic benefits of people and the quality of the ecological environment in which they live. Water conservancy and hydropower projects have high standards exceeding the standard requirements in terms of safe operation and ecological environmental protection. Various problems will be encountered during the construction of water conservancy and hydropower projects. However, the leakage problem is a frequent and common phenomenon in many current water conservancy and hydropower projects in our country, and it is also the most serious problem, which greatly affects the normal operation of water conservancy projects. If any leakage problem occurs during the construction or later use of a water conservancy and hydropower project, it will cause the water conservancy and hydropower project to be unable to be put into production and use normally, and will also waste a large amount of fresh water resources. In serious cases, it will also affect the property and life safety of the residents around the water conservancy project.

[0003] At present, the concrete impervious wall has become the main impervious measure for the overburden foundation and earth-rock dam (cofferdam) projects. The application of the impervious wall construction technology for water conservancy and hydropower projects can fully solve the leakage problem during construction and improve the stability and safety of the dam body itself.

[0004] For the large-angle inclined bank slope of the earth-rock dam, the excavation of the dam foundation of the earth-rock dam forms an angle of 26-33° with the horizontal. The following problems need to be overcome during construction: 1). Complex terrain and difficult construction platform erection. The terrain of the large-angle inclined bank slope has large undulations and irregular topography, which poses great challenges to the erection of the construction platform. It is necessary to level the bank slope to ensure that the construction equipment can operate stably. However, the construction operation on the inclined bank slope is difficult and risky, and the cost will also increase accordingly. Due to the inclination of the bank slope, it is difficult to guarantee the stability of the construction platform. During the construction process, the vibration of the equipment and the stacking of materials may cause the platform to displace and settle, thereby affecting the construction accuracy and quality of the impervious wall.

[0005] 2). Difficult concrete pouring. When pouring concrete on an inclined bank slope, due to the influence of gravity, the concrete is prone to flow downward, making it difficult to ensure its uniform distribution in the groove. This may cause excessive accumulation of concrete at the lower part of the groove section while insufficient pouring at the upper part, affecting the overall quality and performance of the impervious wall. The large-angle inclined bank slope may cause difficulties in the installation and fixation of the concrete pouring conduit. If the conduit is not installed vertically or stably, problems such as conduit blockage and concrete segregation are likely to occur during the pouring process, seriously affecting the pouring effect. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a construction method for a concrete cut-off wall on a large-angle bank slope of an earth-rock dam. By combining the dam foundation excavation and setting construction platforms step by step from top to bottom for the construction of the cut-off wall on the bank slope, the problems of limited construction space and long working face on the large-angle slope are solved. Different groove lengths are divided according to different inclination angles, reducing concrete loss and construction safety risks, and improving work efficiency.

[0007] To solve the above technical problems, the technical solution adopted by the present invention is as follows: A construction method for a concrete cut-off wall on a large-angle inclined bank slope of an earth-rock dam, comprising the following steps: Step 1: Determine the overall construction plan for the concrete cut-off wall according to the structure of the lower reservoir dam and the geological conditions of the dam foundation; Step 2: Divide the cut-off wall on the bank slope into several groove sections according to the designed slope of the bank slope; Step 3: Excavate the dam foundation to form a construction platform, construct a guide wall on the construction platform, and position the mechanical equipment; Step 4: Drill a pilot hole, re-survey the geological conditions of the dam foundation, and determine the bottom line of the concrete cut-off wall; Step 5: Use a grab bucket or an impact drill to make holes. During the drilling and grabbing process, use slurry to support the wall, and detect the performance of the slurry; Step 6: After the depth of the groove hole reaches the depth of the pilot hole, promptly take samples of the bedrock at the bottom of the groove hole to judge whether it enters the strongly weathered bedrock by 1 m and reaches the bottom line of the concrete cut-off wall; Step 7: Use the "air-lift method" to replace the slurry in the groove hole, and clean the foundation parts of adjacent groove sections; Step 8: Check items such as the verticality, thickness, slurry density, slurry viscosity, and bottom sediment of the groove hole; Step 9: Set up a connector pipe; Step 10: Install the pouring conduit; Step 11: Pour concrete. During the pouring process, always ensure that the outlet of the conduit is buried in the concrete surface by not less than 1 m, and check the height difference between the conduit and the concrete surface in the groove hole every half hour; Step 12: Pull out the connector pipe; Step 13: Repeat steps 3 - 12 to carry out the dam foundation excavation and the construction of the cut-off wall for the next groove hole until the construction of the cut-off wall is completed; Step 14: Conduct quality inspection.

[0008] In step 1, the overall construction plan for the concrete cut-off wall is as follows: The cut-off wall is built in sections. After pouring concrete in one groove hole, it forms one wall section, and many wall sections are connected into a complete wall; both ends of the wall are connected to the anti-seepage facilities of the dam body or both banks, and the bottom of the wall is embedded in the bedrock or a relatively impermeable stratum to a certain depth.

[0009] In Step 2, the lengths of the trench segments are divided in combination with the designed slope of the bank slope. When the slope of the cut-off wall is 26°-33°, after the cut-off wall is segmented, the width of each trench segment is between 6 m and 8 m, and each trench segment is numbered.

[0010] In Step 2, when the total length of the lower reservoir axis is 350 m, there are 56 trench segments in total. Among them, the lengths of the 1#-31# trench segments are 6 m, the lengths of the 32#-53# trench segments are 6.5 m, and the lengths of the 54#-56# trench segments are 7 m.

[0011] In Step 3, 1-3 trench segments are constructed on each construction platform, and the construction is carried out from top to bottom and from high to low on both the left and right banks, and the construction on both the left and right banks is carried out simultaneously. For the 1# trench segment on the left bank, the first construction platform is used; for the 2#-3# trench segments, the second construction platform is used; for the 4#-6# trench segments, the third construction platform is used; for the 7#-9# trench segments, the fourth construction platform is used; for the 10#-11# trench segments, the fifth construction platform is used; for the 12#-14# trench segments, the sixth construction platform is used; for the 15#-17# trench segments, the seventh construction platform is used; for the 18#-20# trench segments, the eighth construction platform is used; for the 21#-23# trench segments, the ninth construction platform is used; for the 24#-40# cut-off wall, the original riverbed is leveled to serve as the construction platform; for the 53#-56# trench segments on the right bank, the tenth construction platform is used; for the 51#-52# trench segments, the eleventh construction platform is used; for the 49#-50# trench segments, the twelfth construction platform is used; for the 47#-48# trench segments, the thirteenth construction platform is used; for the 45#-46# trench segments, the fourteenth construction platform is used; for the 43#-44# trench segments, the fifteenth construction platform is used; for the 41#-42# trench segments, the sixteenth construction platform is used.

[0012] In Step 3, each construction platform includes a concrete guide wall. A drilling rig platform is arranged on the downstream side of the concrete guide wall, and a slag flushing platform, a slurry discharge trench, and a heavy load platform are arranged on the other side of the concrete guide wall; among them, the drilling rig platform is paved with sleepers and steel rails, the slag flushing platform and the slurry discharge trench are hardened with concrete, and the heavy load platform is hardened with stone slag.

[0013] The concrete guide wall adopts an inverted "L" cross-section and is all cast-in-place concrete with a concrete strength of C20; single-row deformed steel bars are arranged in the concrete guide wall, and the adjacent deformed steel bars are spaced 20 cm apart, and the thickness of the steel bar protection layer is not less than 5 cm.

[0014] In Step 11, the pouring elevation of the cut-off wall for each trench segment is controlled by exceeding the designed wall top elevation by 0.5 m. Due to the stepped construction on the left and right bank slopes, the actual over-pouring height for each trench segment is between 0.5 m and 3 m.

[0015] During the dam foundation excavation, the over-poured part is chiseled to the designed wall top elevation in two layers; the first layer is broken to the dividing line with a small-sized breaker; the second layer is chiseled and trimmed by manual pneumatic pick, and the chiseled surface meets the design requirements.

[0016] The present invention provides a construction method for a concrete cut-off wall on a large-angle bank slope of an earth-rock dam, having the following technical effects: 1). With the research on the concrete cut-off wall of the dam foundation bank slope of the Yunxiao Pumped Storage Power Station, a construction technology for the inclined bank slope cut-off wall has been explored. It is proposed that "according to the designed slope of the bank slope, the bank slope cut-off wall is divided into several groove sections (construction platforms)", which not only solves the problem of the operation platform for construction equipment, but also divides different groove section lengths according to different inclination angles, reducing concrete loss and construction safety risks, and improving work efficiency.

[0017] 2). When constructing the cut-off wall on a large-angle bank slope, by dividing the groove sections, the overall slope is transformed into multiple relatively low and gentle steps, reducing the height and slope of each step slope, thereby reducing the possibility of instability caused by factors such as self-weight and external forces during slope construction and improving the construction safety factor.

[0018] 3). Through the division of groove sections, when constructing on the construction platform, the stability of the construction equipment is better, and it is easier to control the verticality during the process of forming the groove of the cut-off wall. Compared with directly constructing on a large-angle inclined bank slope, step construction can provide a more stable working surface for the construction equipment, reducing the verticality deviation of the wall caused by equipment shaking or inclination, thereby improving the construction quality of the cut-off wall.

[0019] 4). Combining with the designed slope of the bank slope, through reasonable division of groove sections, the lateral pressure inside the groove is reduced, which can effectively reduce the risk of collapse of the groove wall due to excessive lateral pressure, and is conducive to ensuring the stability of the groove wall.

[0020] 5). Through the division of groove sections and the division (planning) of the construction platform, the construction task of the bank slope cut-off wall can be decomposed into multiple relatively independent step construction tasks, which is convenient for the construction unit to reasonably arrange the construction sequence and construction progress according to the actual situation, improving the flexibility and efficiency of construction organization.

[0021] 5). Since the bank slope is constructed in a step-by-step manner, the cut-off wall concrete needs to be overpoured by 0.5 - 3 m. By combining with the designed slope for groove section division in step 2, the amount of concrete chiseling can be reduced subsequently, reducing the construction cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The present invention will be further described below in conjunction with the drawings and embodiments: Figure 1 It is the construction groove section division diagram of the present invention.

[0023] Figure 2 It is Figure 1 the partial schematic diagram (at the left bank).

[0024] Figure 3 It is Figure 1 the partial schematic diagram (at the right bank).

[0025] Figure 4 This is a sectional view of a certain construction platform in the present invention.

[0026] In the figure: the first construction platform 1, the second construction platform 2, the third construction platform 3, the fourth construction platform 4, the fifth construction platform 5, the sixth construction platform 6, the seventh construction platform 7, the eighth construction platform 8, the ninth construction platform 9, the tenth construction platform 10, the eleventh construction platform 11, the twelfth construction platform 12, the thirteenth construction platform 13, the fourteenth construction platform 14, the fifteenth construction platform 15, the sixteenth construction platform 16, the connecting line 17 between the bank slope and the right reservoir peripheral cutoff wall, the connecting line 18 between the bank slope and the left reservoir peripheral cutoff wall, the groundwater level line 19, the bottom line 20 of the cutoff wall, the bottom line 21 of the core wall excavation, the original ground line 22, the top 23 of the cast-in-place concrete wall of the cutoff wall, the concrete structure 24 of the spillway, the drill rig platform 25, the concrete guide wall 26, the slag washing platform 27, the slurry discharge ditch 28, the heavy load platform 29, the water pipe 30, the slurry pipe 31. Specific implementation manners The construction method of the concrete cutoff wall for the large-angle inclined bank slope of the earth-rock dam includes the following steps: Step 1: Determine the overall construction plan of the concrete cutoff wall according to the structure of the lower reservoir dam and the geological conditions of the dam foundation.

[0027] Step 2: Divide the cutoff wall into several groove sections according to the designed slope of the dam foundation.

[0028] Step 3: Excavate the bank slope and build the construction platform to form the cutoff wall bank slope construction platform. Among them, the first construction platform 1 is at the 1# groove section on the left bank, the second construction platform 2 is at the 2 - 3# groove sections, the third construction platform 3 is at the 4 - 6# groove sections, the fourth construction platform 4 is at the 7 - 9# groove sections, the fifth construction platform 5 is at the 10 - 11# groove sections, the sixth construction platform 6 is at the 12 - 14# groove sections, the seventh construction platform 7 is at the 15 - 17# groove sections, the eighth construction platform 8 is at the 18 - 20# groove sections; the ninth construction platform 9 is at the 21 - 23# groove sections, and the original riverbed is leveled to be the construction platform for the 24 - 40# cutoff wall; the tenth construction platform 10 is at the 53 - 56# groove sections on the right bank, the eleventh construction platform 11 is at the 51 - 52# groove sections, the twelfth construction platform 12 is at the 49 - 50# groove sections, the thirteenth construction platform 13 is at the 47 - 48# groove sections, the fourteenth construction platform 14 is at the 45 - 46# groove sections, the fifteenth construction platform 15 is at the 43 - 44# groove sections, and the sixteenth construction platform 16 is at the 41 - 42# groove sections.

[0029] Step 4: Position the drill rig, drill the pilot hole, re - survey the geological conditions of the dam foundation, and determine the bottom line 20 of the concrete cutoff wall.

[0030] Step 5: Use a grab bucket or impact drill to create holes along the designed axis. During the drilling and grabbing process, use slurry to support the wall and test the performance of the slurry.

[0031] Step 6: After the groove hole depth reaches the pilot hole depth, promptly sample the bedrock at the bottom of the groove hole to determine whether it has entered the strongly weathered bedrock by 1 m.

[0032] Step 7: Use the "air-lift method" to replace the slurry in the groove hole and clean the joint parts of adjacent groove sections.

[0033] Step 8: Check items such as the verticality, thickness, slurry density, slurry viscosity, and bottom sediment of the groove hole.

[0034] Step 9: Install the joint pipe and the guide pipe.

[0035] Step 10: Pour concrete.

[0036] Step 11: Withdraw the joint pipe and the guide pipe.

[0037] Step 12: Transfer the construction equipment.

[0038] Step 13: Excavate the foundation of the dam's bank slope to form the next construction platform, and repeat the above Steps 4 to 11.

[0039] The cut-off wall of the bank slope section is constructed from high to low. The left bank constructs Platform 1 first, and the right bank constructs Platform 10 first. The left and right banks can be constructed simultaneously or separately.

[0040] Step 14: Conduct quality inspection on the cut-off wall 28 days after its construction. The inspection items include core sample inspection and water injection test.

[0041] Example 1 Take the concrete cut-off wall construction of the lower reservoir of Fujian Yunxiao Pumped Storage Power Station as an example. The lower reservoir dam uses a clay core rockfill dam with a dam height of 138.0 m. A wave wall is set upstream of the dam crest, and the wave wall height is 0.6 m. The maximum dam height is 68.0 m, the dam crest length is 350.0 m, and the dam crest width is 8.0 m. The dam foundation seepage prevention adopts an anti-seepage structure form of an underground cut-off wall connected with curtain grouting. The cut-off wall is arranged along the dam axis with a length of 350.0 m, a slot width of 0.8 m, a depth of 3 - 35 m, and a horizontal included angle of 26° - 33° for the cut-off walls of the inclined sections on the left and right banks.

[0042] As Figure 1As shown in the figure, the overall concrete anti-seepage wall construction plan is determined according to the structure of the lower reservoir dam and the geological conditions of the dam foundation. The anti-seepage wall is constructed in sections. After pouring concrete in a slot hole, it constitutes a wall section, and many wall sections are connected to form a whole wall. The two ends of the wall are connected to the anti-seepage facilities of the dam body or both banks, and the bottom is embedded in the bedrock or relatively impermeable strata to a certain depth, which can cut off or reduce the seepage water flow in the foundation. The specific construction process is as follows: (1) Ensure the convenience of impact drilling and grab construction and reduce the number of joints. On the basis of ensuring the safety of the hole wall, try to increase the length of the slot section, which is conducive to reducing the slot section joints, ensuring the construction quality and speeding up the construction progress. According to the engineering geological conditions, the grab bucket body opening distance, the requirements for the layout of the casting conduit and other factors, the slot length: the first and second phase slot length is 6.0~7.0m, with a total of 56 slot sections.

[0043] (2) The construction platform includes a drilling platform 25, a slag flushing platform 27, a slurry discharge ditch 28, and a heavy load platform 29.

[0044] (3) A drilling platform 25 is arranged on the downstream side of the concrete guide wall 26, and a ballast dumping platform and a trenching machine platform are arranged on the other side. The drilling platform 25 after construction is 5.5 to 7.0 meters wide. Sleepers and rails are evenly installed on the platform. The ballast dumping platform and the slurry discharge ditch 28 use a plain concrete structure of grade C10 with a thickness of 10 cm. During pouring, a flat vibrator is used to vibrate and compact it. The hydraulic grab construction platform is backfilled with gravel and compacted to ensure that the construction road is unobstructed.

[0045] (4) To meet the construction requirements of the impact drill, the concrete guide wall 26 is constructed with reinforced concrete structure. The concrete guide wall 26 adopts an inverted "L" shaped section, with a depth of 1.0, a wall thickness of 0.3m, a top width of 0.6m, and is entirely cast-in-place concrete with a concrete strength of C20. A single row of 12mm diameter threaded steel bars is arranged in the concrete guide wall 26, with a spacing of 20cm, and the thickness of the steel bar protective layer is not less than 5cm, so as to enhance the shear resistance of the wall and improve the integrity of the guide wall. The net spacing of the constructed guide wall is 0.9m.

[0046] (5) Before the construction of the anti-seepage wall, geological re-survey is required, and a pilot hole is arranged every 20m along the axis of the concrete anti-seepage wall. The geological data is reviewed based on the pilot hole data, and the bottom line of the anti-seepage wall is finally determined.

[0047] (6) Drilling and grabbing method: Use an impact drill to drill the end hole, use a hydraulic slotting machine to grab the auxiliary hole with high efficiency, or use a grab bucket to grab the upper covering layer, and then use an impact drill to drill into the bedrock layer to complete the slotting, which will improve the construction progress and reduce waste slurry and waste residue.

[0048] (7) When constructing by the drill-grab method, clay slurry is used for shaft wall protection. The slurry should have good rheology, stability, inhibition, and good suspension and cuttings-carrying capabilities. The slurry should meet the requirements of the "Code for Construction of Concrete Cut-off Walls in Hydropower and Water Conservancy Projects" (DL / T 5199-2019).

[0049] (8) When identifying the bedrock, not only should the geological profile provided by the design and the drilling conditions of the pilot holes be referred to, and the rock samples taken during impact drilling be identified, but also the engineering geology should be studied, including the lithological characteristics of the overburden layer, and a comprehensive determination should be made on the rock-socketed depth of the cut-off wall.

[0050] (9) After the slot hole reaches the final depth, the work of cleaning the hole and replacing the slurry should be organized immediately. After the second-phase slot hole reaches the final depth, the joint hole also needs to be brushed. The "air-lift method" is used for hole cleaning and slurry replacement.

[0051] (10) The joint hole is brushed with a circular wire brush. The standard for the completion of brushing the joint hole wall is that the brush basically does not carry mud chips and the sediment thickness at the bottom of the hole no longer increases.

[0052] (11) Regarding the deviation of the connector pipe, preventive measures should be taken during its installation. The base should be leveled and leveled with a spirit level. The center of the connector pipe should coincide with the center of the joint hole. After the pipe is installed, the connector pipe should be lifted to a certain height and then allowed to freely fall to the lowest position to make the connector pipe vertical under its own weight. When the connector pipe deviates after the concrete is poured in the slot, the solution is to slightly lift it in advance and let it fall under its own weight and insert it into the concrete to reshape the hole shape to make the connector pipe as vertical or straight as possible.

[0053] (12) Before use, the conduits are inspected for straightness, pressure water test, roundness inspection, wear inspection, and welding inspection. The qualified conduits are marked with obvious qualified signs, and the unqualified conduits are not used. After each use, the conduits should be washed clean and stacked neatly.

[0054] (13) The pouring conduits are φ250 steel pipes connected by quick-threaded joints. Several short pipes with a length of 0.5 m are set at the upper part of each set of conduits and above the bottom section pipe. The conduit joints are equipped with hanging and lifting facilities.

[0055] (14) When pouring the concrete, the pressure-ball method should be used for pouring. An isolation rubber ball is lowered into each conduit to squeeze out the slurry in the conduit.

[0056] (15) During normal pouring, the minimum depth of the conduit buried in the concrete should not be less than 2 m, and the maximum depth should not be greater than 6 m. When the concrete surface is close to the hole opening or the designed wall top elevation, for the convenience of concrete flow, the conduit burial depth can be appropriately reduced, but it should not be less than 1 m.

[0057] (16) During the pouring process, the depth of the concrete surface in the trench should be measured every half an hour, and the depth of the concrete surface in the conduit should be measured every two hours. The number of measurements should be appropriately increased at the beginning and end of the pouring process. The pouring records should be filled in and the pouring index chart should be drawn. The pouring volume should be checked and the disassembly of the conduit should be guided.

[0058] (17) Before normal pipe pulling construction, that is, at the beginning of concrete pouring, about 3 hours after pouring, the joint pipe should be slightly moved. The interval between the movable joint pipe should not exceed half an hour. Each time, it should be lifted a short distance, and then the joint pipe should be freely dropped under its own weight to be inserted into the concrete. The purpose is to prevent the joint pipe from tilting in the slot and reshape the hole shape. The time for micro-movement should not be too early or too frequent, otherwise it will be detrimental to the coagulation of concrete and the stability of the hole wall.

[0059] (18) As the construction of the dam's anti-seepage wall concrete is underwater, in order to ensure the concrete quality and anti-seepage performance of the top of the anti-seepage wall and facilitate the subsequent cast-in-place concrete construction of the anti-seepage wall, the concrete pouring is controlled to exceed the designed wall top elevation by 0.5 meters. Due to the step-type construction of the left and right bank slopes, the actual over-casting height of each slot section varies from 0.5 to 3 meters. When the dam foundation is excavated, the over-casting part is chiseled out in two layers to the designed wall top elevation. The first layer is crushed to the dividing line with a small breaker; the second layer is chiseled out and trimmed with a manual pneumatic pick, and the chiseled surface should meet the design requirements.

[0060] (19) Excavate the construction platform in conjunction with the dam foundation to form the next construction platform. Repeat the above work until the anti-seepage wall of the slope section is completed.

[0061] (20) After the anti-seepage wall is completed for 28 days, the wall quality is checked by drilling and coring, with an inspection hole arranged every 150 meters along the axis. The uniaxial compressive strength of the concrete and the integrity and uniformity of the core sample are tested by drilling core samples. The permeability coefficient of the anti-seepage wall is tested by water injection test in the inspection hole. According to the "Regulations for Drilling and Water Injection Test of Hydropower Engineering" (NB / T35104-2017), the inspection hole is tested for water injection to check whether its permeability coefficient meets the design requirements.

Claims

1. Construction method of concrete cut-off wall for large-angle inclined bank slope of earth-rock dam, including the following steps: Step 1: Determine the overall construction plan of the concrete cut-off wall according to the structure of the lower reservoir dam and the geological conditions of the dam foundation; Step 2: Divide the cut-off wall of the bank slope into several groove sections according to the designed slope of the bank slope; Step 3: Excavate the dam foundation to form a construction platform, build a guide wall on the construction platform, and position the mechanical equipment; Step 4: Drill a pilot hole, re-survey the geological conditions of the dam foundation, and determine the bottom line of the concrete cut-off wall; Step 5: Use a grab bucket or impact drill to make holes. During the drilling and grabbing process, use slurry to support the wall, and detect the performance of the slurry; Step 6: After the depth of the groove hole reaches the depth of the pilot hole, promptly take samples of the bedrock at the bottom of the groove hole to judge whether it enters the strongly weathered bedrock by 1m and reaches the bottom line of the concrete cut-off wall; Step 7: Use the "air-lift method" to replace the slurry in the groove hole, and clean the foundation parts of adjacent groove sections; Step 8: Check items such as the verticality, thickness, slurry density, slurry viscosity, and sediment at the bottom of the hole of the groove hole; Step 9: Set down the connector pipe; Step 10: Install the pouring conduit; Step 11: Pour concrete. During the pouring process, always ensure that the outlet of the conduit is buried in the concrete surface by not less than 1m, and check the height difference between the conduit and the concrete surface in the groove hole every half hour; Step 12: Pull out the connector pipe; Step 13: Repeat steps 3 - 12 to carry out the dam foundation excavation and the construction of the cut-off wall for the next groove section until the construction of the cut-off wall is completed; Step 14: Quality inspection.

2. The construction method of the concrete cut-off wall for the large-angle inclined bank slope of the earth-rock dam according to claim 1, characterized in that: In step 1, the overall construction plan of the concrete cut-off wall is: the cut-off wall is built in sections. After pouring concrete in one groove hole, it forms one wall section, and many wall sections are connected into a whole wall; both ends of the wall are connected to the anti-seepage facilities of the dam body or both banks, and the bottom of the wall is embedded in the bedrock or a relatively impermeable stratum to a certain depth.

3. The construction method of the concrete cut-off wall for the large-angle inclined bank slope of the earth-rock dam according to claim 2, characterized in that: In step 2, the length of the groove section is divided in combination with the designed slope of the bank slope. When the slope of the cut-off wall is 26° - 33°, after the cut-off wall is segmented, the width of each groove section is between 6m and 8m, and each groove section is numbered.

4. The construction method of the concrete cut-off wall for the large-angle inclined bank slope of the earth-rock dam according to claim 3, characterized in that: In step 2, when the total length of the axis of the lower reservoir is 350m, there are a total of 56 groove sections. Among them, the lengths of groove sections 1# - 31# are 6m, the lengths of groove sections 32# - 53# are 6.5m, and the lengths of groove sections 54# - 56# are 7m.

5. The construction method of the concrete cut-off wall for a large-angle inclined bank slope of an earth-rock dam according to claim 4, characterized in that: In step 3, each construction platform constructs 1 - 3 groove sections, and the left and right banks are constructed from top to bottom from high to low, and the left and right banks are constructed simultaneously.

6. The construction method of the concrete cut-off wall for the large-angle inclined bank slope of the earth-rock dam according to claim 5, characterized in that: For the left bank, the 1# trench section utilizes the first construction platform (1), the 2 - 3# trench sections utilize the second construction platform (2), the 4 - 6# trench sections utilize the third construction platform (3), the 7 - 9# trench sections utilize the fourth construction platform (4), the 10 - 11# trench sections utilize the fifth construction platform (5), the 12 - 14# trench sections utilize the sixth construction platform (6), the 15 - 17# trench sections utilize the seventh construction platform (7), and the 18 - 20# trench sections utilize the eighth construction platform (8); for the 21 - 23# trench sections, the ninth construction platform (9) is utilized, and for the 24 - 40# cutoff wall, the original riverbed is leveled to serve as the construction platform; for the right bank, the 53 - 56# trench sections utilize the tenth construction platform (10), the 51 - 52# trench sections utilize the eleventh construction platform (11), the 49 - 50# trench sections utilize the twelfth construction platform (12), the 47 - 48# trench sections utilize the thirteenth construction platform (13), the 45 - 46# trench sections utilize the fourteenth construction platform (14), the 43 - 44# trench sections utilize the fifteenth construction platform (15), and the 41 - 42# trench sections utilize the sixteenth construction platform (16).

7. The construction method of the concrete cut-off wall for the large-angle inclined bank slope of the earth-rock dam according to claim 6, characterized in that: In step 3, each construction platform includes a concrete guide wall (26). A drilling rig platform (25) is arranged on the downstream side of the concrete guide wall (26), and on the other side of the concrete guide wall (26), a slag flushing platform (27), a slurry discharge trench (28), and a heavy load platform (29) are arranged; among them, the drilling rig platform (25) is paved with sleepers and steel rails, the slag flushing platform (27) and the slurry discharge trench (28) are hardened with concrete, and the heavy load platform (29) is hardened with stone slag.

8. The construction method of the concrete cut-off wall for the large-angle inclined bank slope of the earth-rock dam according to claim 7, characterized in that: The said concrete guide wall (26) adopts an inverted "L" - shaped cross - section and is entirely cast - in - place with concrete, and the concrete strength is C20; single - row deformed steel bars are configured in the concrete guide wall (26), with an interval of 20 cm between adjacent deformed steel bars, and the thickness of the steel bar protection layer is not less than 5 cm.

9. The construction method of the concrete cut-off wall for the large-angle inclined bank slope of the earth-rock dam according to claim 8, characterized in that: In step 11, the pouring elevation of the cutoff wall for each trench section is controlled by exceeding the designed wall top elevation by 0.5 meters. Due to the stepped construction on the left and right bank slopes, the actual over - pouring height for each trench section is between 0.5 - 3 meters.

10. The construction method of the concrete cut-off wall for a large-angle inclined bank slope of an earth-rock dam according to claim 9, characterized in that: During the excavation of the dam foundation, the over - poured part is chiseled to the designed wall top elevation in two layers; the first layer is broken to the dividing line with a small - sized breaker; the second layer is chiseled and trimmed by manual pneumatic picks, and the chiseled surface meets the design requirements.

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