Design and construction method for improving stress state of earth and rockfill dam suspension type diaphragm wall on deep and thick covering layer

Abstract

The invention belongs to the technical field of water conservancy and hydropower, and provides a design and construction method for improving the stress state of an earth and rockfill dam suspension type diaphragm wall on a deep and thick covering layer. The design and construction method comprises the following construction sequences: firstly, constructing a river valley middle diaphragm wall, secondly, constructing a river valley middle first-stage dam body, thirdly, constructing two-bank second-stage concrete diaphragm walls, fourthly, constructing two-bank second-stage dam bodies, and finally, constructing a third-stage dam body. The axial length of the first-stage anti-seepage wall dam needs to be smaller than the width of river valley bedrock at the corresponding position, and it is avoided that the two ends of the anti-seepage wall are embedded into bedrock on the two banks to form simply supported beams. Compared with a traditional construction sequence that the anti-seepage wall is poured firstly and then the dam body is filled, the alternative construction scheme of the anti-seepage wall and the dam body and the specific construction sequence are innovatively provided, vertical bending deformation of the anti-seepage wall caused by first-stage dam body filling in the middle of the river valley can be avoided, the stress of the anti-seepage wall is effectively reduced, the anti-cracking performance of the anti-seepage wall is improved, and the service life of the anti-seepage wall is prolonged. And the reliability and the safety of the earth and rockfill dam diaphragm wall on the deep covering layer are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of water conservancy and hydropower, and relates to a design and construction method for improving the stress state of a suspended cut-off wall of an earth-rock dam on a deep overburden layer. Background Art

[0002] Deep overburden layers are widely distributed in rivers in China, especially in the southwestern region, such as the Dadu River, the Jinsha River, etc., and the depth of the overburden layer can reach several hundred meters. More than 80% of China's water energy resources are concentrated in the western region. Building earth-rock dam projects on deep overburden foundations has become an unavoidable problem that requires key research. Earth-rock dams, with their unique advantages, are the preferred dam type on deep overburden foundations. The physical and mechanical characteristics of deep overburden layers have a greater impact on water conservancy projects. Concrete cut-off walls are the main anti-seepage structures for the foundations of earth-rock dams under deep overburden foundation conditions and are the key line of defense to ensure the stable and long-term safe operation of dams. Therefore, improving the stress state of the cut-off wall and increasing its safety margin have important guiding significance for the construction of earth-rock dam projects on deep overburden layers in China.

[0003] In the core wall dam project on the overburden foundation, the cut-off wall and the dam body are constructed alternately in stages, avoiding the vertical bending deformation of the cut-off wall caused by the filling of the dam body in the middle of part of the river valley. Due to the obvious difference in the material moduli of the overburden foundation soil and the cut-off wall concrete, under the action of the self-weight of the dam body and the water pressure of the reservoir, it is easy for the cut-off wall to bear excessive stress at the junction of the two banks of the dam foundation and cause damage. Therefore, how to solve the problem of seepage failure caused by the excessive stress of the cut-off wall of the traditional core wall dam on the overburden layer and the resulting concrete structure damage is crucial. Summary of the Invention

[0004] Aiming at the problem of the limited stress-bearing capacity of the concrete cut-off wall, the present invention provides a design and construction method for improving the stress state of a suspended cut-off wall of an earth-rock dam on a deep overburden layer, and innovatively proposes a scheme for the alternate construction of the cut-off wall and the dam body and the specific construction sequence, which can ultimately reduce the stress amplitude of the cut-off wall, improve the stress state of the cut-off wall, and enhance the crack resistance of the cut-off wall.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A design and construction method for improving the stress state of a suspended cut-off wall of an earth-rock dam on a deep overburden layer. The design and construction method includes the following construction sequence: First, construct the cut-off wall in the middle of the river valley. Second, construct the first-stage dam body in the middle of the river valley. Third, construct the second-stage concrete cut-off walls on both banks. Fourth, construct the second-stage dam bodies on both banks. Finally, construct the third-stage dam body. Specifically: ① The first-stage cut-off wall in the middle area of the river valley. ② The first-stage dam body within the dam axial range corresponding to the first-stage cut-off wall. ③ The second-stage cut-off walls on both banks. ④ The second-stage dam bodies within the dam axial range corresponding to the second-stage cut-off walls. ⑤ The third-stage dam body on top of the first-stage and second-stage dam bodies. The present invention adopts an alternating construction method of concrete cut-off walls and dam bodies, delaying the time when a stress mode similar to that of a simply supported beam is formed vertically after the completion of the suspended cut-off wall, avoiding the bending deformation of the concrete cut-off wall similar to that of a simply supported beam caused by the self-weight of the first-stage dam body, effectively reducing the tensile and compressive stresses of the cut-off wall, improving the stress state of the cut-off wall, and enhancing the safety of the cut-off wall. Specifically, it includes the following steps:

[0007] First step, establish a construction site centered on the central axis of the concrete cut-off wall. Through a grab bucket or a hydraulic milling machine, excavate the overburden layer 6 into a trench along the axis of the concrete cut-off wall, and use slurry to support the wall. Then, pour ordinary concrete by the direct-pumping method through a vertical conduit to complete the construction of the first-stage concrete cut-off wall 1 in the middle of the river valley. The dam axial length b1 of the first-stage concrete cut-off wall 1 should be less than the river valley width b to avoid the formation of a simply supported beam effect due to the two ends of the first-stage concrete cut-off wall 1 being embedded in the bedrock.

[0008] Second step, adopt the layered rolling construction method to fill the first-stage dam body 3 within the dam axial length range corresponding to the first-stage concrete cut-off wall 1. The two ends of the first-stage dam body 3 in the dam axial direction need to be slope-treated. The slope is recommended to be the steepest slope i allowed for the construction of a rockfill dam to connect slopes, and the height h0 is recommended to be the maximum height difference allowed for the construction of a rockfill dam to connect slopes.

[0009] Third step, use the same construction method as the first step to pour the second-stage concrete cut-off walls 2 on both banks.

[0010] Fourth step, adopt the layered rolling construction method to fill the second-stage dam body 4 within the dam axial length range corresponding to the second-stage concrete cut-off wall 2. The height is h0, which is the same as that of the first-stage dam body. The connecting slope between the first-stage dam body 3 and the second-stage dam body 4 is treated by the slope-cutting method.

[0011] Fifth step, adopt the layered rolling construction method to fill the third-stage dam body 5 on top of the first-stage and second-stage dam bodies within the entire dam axial range. The height is h1 until the completion of the dam construction.

[0012] Furthermore, the dam axial length of the first-stage cut-off wall 1 should be less than the river valley width at the corresponding position.

[0013] Furthermore, the axial length of the first-stage dam body 3 should not be greater than that of the first-stage cutoff wall 1.

[0014] Furthermore, the design and construction method is applicable to both core rock-fill dams and concrete face rock-fill dams.

[0015] The beneficial effects of the present invention are as follows:

[0016] The design and construction method for the stress state of the cutoff wall of the core wall dam on deep overburden proposed by the present invention delays the time for the formation of a stress mode similar to that of a simply supported beam in the vertical direction after the completion of the suspended cutoff wall through the staged and alternating construction of the cutoff wall and the dam body, avoids the bending deformation of the concrete cutoff wall similar to that of a simply supported beam caused by the self-weight of the first-stage dam body, effectively improves the stress state of the suspended concrete cutoff wall, and enhances the safety of the cutoff wall. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram of the design scheme of the cutoff wall and the dam body of the core wall dam on deep overburden according to the present invention;

[0018] Reference numerals in the figure: 1 First-stage concrete cutoff wall; 2 Second-stage concrete cutoff wall; 3 First-stage dam body in the middle of the river valley; 4 Second-stage dam bodies on both banks of the river valley; 5 Third-stage dam body; 6 Overburden; b Length of the bottom of the cutoff wall; b1 Length of the top of the first-stage cutoff wall; b2 Length of the bottom of the first-stage dam body; h0 Heights of the first-stage and second-stage dam bodies; h1 Height of the third-stage dam body; i Slope at the joint of the first-stage and second-stage dam bodies.

[0019] Figure 2 It is the compressive stress nephogram of the traditional scheme of the cutoff wall of the core wall dam on deep overburden in the case of the present invention, with the unit of MPa.

[0020] Figure 3 It is the compressive stress nephogram of the optimized scheme of the cutoff wall of the core wall dam on deep overburden in the case of the present invention, with the unit of MPa.

[0021] Figure 4 It is the tensile stress nephogram of the traditional scheme of the cutoff wall of the core wall dam on deep overburden in the case of the present invention, with the unit of MPa.

[0022] Figure 5 It is the tensile stress nephogram of the optimized scheme of the cutoff wall of the core wall dam on deep overburden in the case of the present invention, with the unit of MPa.

[0023] There are implementation modes

[0024] The present invention will be further described below in conjunction with specific implementation cases.

[0025] The engineering case is as follows:

[0026] A certain river - blocking dam adopts an earth - core rock - fill dam. The elevation of the foundation surface is 1900m, the elevation of the dam crest is 2050m, the maximum dam height is 150.0m, the width of the dam crest is 14.0m, and the length of the dam crest is 907m. The upstream slope of the dam body is 1:1.6, and the downstream slope is 1:1.8. The river - bed overburden is deep, with a maximum thickness of about 480m. A suspended concrete cut - off wall (the first - stage concrete cut - off wall 1 and the second - stage concrete cut - off wall 2) is used for dam - foundation seepage prevention, with a depth of 140m and a thickness of 1.4m. The first - stage concrete cut - off wall 1 and the second - stage concrete cut - off wall 2 are both connected to the core wall to form a complete seepage - prevention system. The axial length b1 of the first - stage concrete cut - off wall 1 along the dam axis is taken as 1440m, the valley width b at this part is 1450m, the height h0 of the first - stage dam body 3 and the second - stage dam body 4 is 35m, the height h1 of the third - stage dam body 5 is 115m, and the axial slope i of the first - stage dam body 3 along the dam axis is 1:2.4. Specifically as follows:

[0027] First step, carry out foundation cleaning. At the elevation of the foundation surface of 1900m, a construction site is established with the axis of the cut - off wall as the center. Through hydraulic milling construction, the overburden layer 6 is excavated into a groove along the axis of the cut - off wall, with an excavation depth of 140m and a thickness of 1.4m. Mud is used for wall - face protection, and then ordinary concrete is poured by the direct - lift pipe method. The axial construction length b1 = 1440m, and the construction of the first - stage concrete cut - off wall 1 is completed. The width of the valley bedrock at the corresponding position of the first - stage concrete cut - off wall 1 is b = 1450m, and the first - stage concrete cut - off wall 1 is not embedded in the bedrock;

[0028] Second step, further, adopt the layered rolling construction method to fill the first - stage dam body 3 within the axial range corresponding to the first - stage concrete cut - off wall 1. The axial length b2 = 1440m, the height h0 = 35m, and the slopes at both axial ends are i = 1:2.4;

[0029] Third step, adopt the same construction method as the first step to pour the second - stage concrete cut - off wall 2 on both sides of the valley to complete the construction of the entire cut - off wall;

[0030] Fourth step, adopt the layered rolling construction method to fill the second - stage dam body 4 within the axial range corresponding to the second - stage cut - off wall 2, with a height h0 = 35m. The slope - connecting part between the first - stage dam body 3 and the second - stage dam body 4 is treated by the slope - cutting method;

[0031] Fifth step, adopt the layered rolling construction method to fill the third - stage dam body 5 above the first - stage and second - stage dam bodies within the entire axial range, with a height h1 = 115m to complete the construction of the dam.

[0032] Effect analysis of the embodiment and comparative example of the present invention:

[0033] The project is designed using the present invention and compared with the traditional design and construction plan of first pouring the concrete cut-off wall and then filling the dam body. When the dam stores water to the normal storage level, the stress distribution of the concrete cut-off wall calculated by numerical simulation is shown in Figure 2 ~~ Figure 4 , and the maximum value is shown in Table 1. As can be seen from Figure 2 , the traditional design and construction plan results in the early formation of a simply supported beam effect for the cut-off wall, and the maximum compressive stress appears at the position where the bottom of the cut-off wall intersects with the bedrock on both banks, which is 100 MPa. As can be seen from Figure 3 , the present invention avoids the early embedding of the cut-off wall at both ends into the bedrock and the formation of a simply supported beam effect. The maximum compressive stress no longer appears at the position where the bottom of the cut-off wall intersects with both banks, and the maximum compressive stress is reduced to 50 MPa. As can be seen from Figure 4 , due to the support effect of the cut-off wall at the bottom of both banks in the traditional design and construction plan, a relatively large tensile stress appears at the top of the cut-off wall, and the maximum value is 30 MPa. As can be seen from Figure 5 , the present invention avoids the early formation of the support effect of the bedrock, and the maximum tensile stress of the cut-off wall is reduced to 11 MPa. In summary, as can be seen from Table 1, compared with the traditional plan, the design and construction plan proposed by the present invention can reduce the maximum compressive stress and tensile stress of the concrete cut-off wall by 50% and 63% respectively. The present invention effectively reduces the stress of the suspended concrete cut-off wall of the earth-rock dam on the deep overburden layer and improves the safety of the project.

[0034] Table 1

[0035]

[0036] The above-described embodiments only represent the implementation modes of the present invention, but should not be construed as limiting the scope of the present invention patent. It should be noted that for those skilled in the art, without departing from the concept of the present invention, several deformations and improvements can still be made, and these all belong to the protection scope of the present invention.

Claims

1. A design and construction method for improving the stress state of a suspended cut-off wall of an earth-rock dam on a deep overburden layer, characterized in that, The described design and construction method includes the following construction sequence: First, construct the cut-off wall in the middle of the river valley, defined as the first-phase cut-off wall; Second, construct the first-phase dam body in the middle of the river valley; Third, construct the second-phase cut-off walls on both banks; Fourth, construct the second-phase dam bodies on both banks; Finally, construct the third-phase dam body on top of the first-phase and second-phase dam bodies.

2. The design and construction method for improving the stress state of the suspended cut-off wall of the earth-rock dam on deep overburden according to claim 1, characterized in that Both the first-phase cut-off wall and the second-phase cut-off wall are concrete cut-off walls.

3. A design and construction method for improving the stress state of a suspended cut-off wall of an earth-rock dam on a deep overburden layer according to claim 1, characterized in that, In the second item, the first-phase dam body in the middle of the river valley is constructed within the dam axial range corresponding to the first-phase cut-off wall.

4. A design and construction method for improving the stress state of a suspended cut-off wall of an earth-rock dam on a deep overburden layer according to claim 1, characterized in that, In the fourth item, the second-phase dam bodies on both banks are constructed within the dam axial range corresponding to the second-phase cut-off walls.

5. A design and construction method for improving the stress state of a suspended cut-off wall of an earth-rock dam on a deep overburden layer according to any one of claims 1-4, characterized in that, Specifically, it includes the following steps: The first step is to establish a construction site centered on the central axis of the concrete cut-off wall, excavate the overburden layer into a groove along the axis of the concrete cut-off wall, use slurry to support the wall, and then pour ordinary concrete through the direct-pouring conduit method to complete the construction of the first-phase concrete cut-off wall in the middle of the river valley; The second step is to use the layered compaction construction method to fill the first-phase dam body within the dam axial length corresponding to the first-phase concrete cut-off wall. The two ends of the first-phase dam body in the dam axial direction need to be slope-treated. The third step is to use the same construction method as the first step to pour the second-phase concrete cut-off walls on both banks; The fourth step is to use the layered compaction construction method to fill the second-phase dam body within the dam axial length corresponding to the second-phase concrete cut-off wall. The slope connection between the first-phase dam body and the second-phase dam body is treated by the slope-cutting method. The fifth step is to use the layered compaction construction method to fill the third-phase dam body on top of the first-phase and second-phase dam bodies within the entire dam axial range until the dam construction is completed.

6. A design and construction method for improving the stress state of a suspended cut-off wall in an earth-rock dam on a deep overburden layer according to claim 5, characterized in that, In the first step, the dam axial length of the first-phase concrete cut-off wall needs to be less than the river valley width at the corresponding position.

7. A design and construction method for improving the stress state of a suspended cut-off wall in an earth-rock dam on a deep overburden layer according to claim 5, characterized in that, In the second step, the slope of the slope treatment is the steepest slope allowed for the slope connection in the construction of the rockfill dam, and the height is the maximum height difference allowed for the slope connection in the construction of the rockfill dam.

8. A design and construction method for improving the stress state of a suspended cut-off wall of an earth-rock dam on a deep overburden layer according to claim 5, characterized in that, In the second step, the dam axial length of the first-phase dam body needs to be no greater than the dam axial length of the first-phase concrete cut-off wall.

9. A design and construction method for improving the stress state of a suspended cut-off wall of an earth-rock dam on a deep overburden layer according to claim 5, characterized in that, In the fourth step, the height of the second-phase dam body is the same as that of the first-phase dam body.

10. A design and construction method for improving the stress state of a suspended cut-off wall of an earth-rock dam on a deep overburden layer according to claim 1, characterized in that, The described design and construction method is applicable to both core-wall rockfill dams and concrete-face rockfill dams.

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