Design and construction method for improving stress state of hanging type concrete diaphragm wall of concrete faced rockfill dam on deep and thick covering layer

Abstract

The invention discloses a design and construction method for improving the stress state of a hanging type concrete diaphragm wall of a concrete faced rockfill dam on a deep and thick covering layer, and belongs to the technical field of water conservancy and hydropower. The construction sequence is as follows: firstly, constructing a first-stage dam body; secondly, gradually constructing a first-stage concrete anti-seepage wall and a second-stage dam body which are positioned at a river valley section from the river valley to two banks; and thirdly, gradually constructing a second-stage concrete anti-seepage wall of which the bottom can be embedded into bedrocks of the two banks from a bank slope to the river valley. And 4, constructing a third-stage concrete diaphragm wall between the first-stage diaphragm wall and the second-stage diaphragm wall, and finally constructing a panel, a connecting plate, a toe board and a panel peripheral seam. The construction scheme that the impervious wall is closed after the dam body is completed is innovatively provided, the problem of high stress caused by bending deformation of the dam body filled in the later period under the action of dead weight due to the fact that a simply supported beam stress mode is formed by premature construction and embedding into a bedrock section is solved, the stress state of the concrete impervious wall is improved, and the concrete impervious wall is protected. And the risk of damage cracking is reduced, and the safety margin of the concrete faced rockfill dam anti-seepage system under the complex geological condition is effectively improved.

Description

Technical Field

[0001] The 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 concrete cut-off wall of a concrete face rockfill dam on a deep overburden layer. Background Art

[0003] In the field of earth-rock dam engineering construction, the anti-seepage system is the "lifeline" to ensure the safe and stable operation of the dam, and the concrete cut-off wall is the core component of the dam anti-seepage system. When building an earth-rock dam on a deep overburden foundation, a suspended concrete cut-off wall is generally used as the anti-seepage structure of the dam foundation, forming a stress form similar to that of a simply supported beam. However, there is a large difference in stiffness between the deep overburden foundation and the concrete cut-off wall. During the dam construction and reservoir impoundment process, the concrete cut-off wall is subjected to the actions of gravity, peripheral soil friction force and reservoir water pressure, resulting in excessive compressive stress at the junction of the bottom of the concrete cut-off wall and the dam foundation on both banks, which may cause damage to the concrete cut-off wall, and then affect the anti-seepage function and endanger the safety of the dam body.

[0004] Therefore, how to solve the damage of the anti-seepage system caused by excessive stress of the concrete cut-off wall of the earth-rock dam on the deep overburden layer and improve the stress state of the concrete cut-off wall is of great importance. Summary of the Invention

[0005] Aiming at the problems existing in the prior art, the invention provides a design and construction method for improving the stress state of a suspended concrete cut-off wall of a concrete face rockfill dam on a deep overburden layer, and innovatively proposes a construction plan to seal the cut-off wall after the completion of the dam body, which solves the problem that the traditional design and construction plan leads to the premature construction of the concrete cut-off wall embedded in the bedrock section to form a stress mode of a simply supported beam, resulting in high stress problems caused by the bending deformation of the later filled dam body under its own weight, and reduces the risk of damage and cracking of the concrete cut-off wall.

[0006] In order to achieve the above purpose, the invention adopts the following technical solutions:

[0007] A design and construction method for improving the stress state of a suspended impervious wall in a concrete face rockfill dam on a deep overburden layer. In the design and construction method, the concrete impervious wall is constructed in three phases. The first-phase concrete impervious wall 1 is located in the river valley section, the second-phase concrete impervious wall 2 is located on both banks, and the third-phase concrete impervious wall 3 is located between the first-phase concrete impervious wall 1 and the second-phase concrete impervious wall 2. The construction sequence includes the following: First, construct the first-phase dam body. Second, gradually construct the first-phase concrete impervious wall located in the river valley section and the second-phase dam body from the river valley towards both banks. Third, gradually construct the second-phase concrete impervious wall that can be embedded in the bedrock on both banks along the slope towards the river valley. Fourth, construct the third-phase concrete impervious wall between the first-phase and second-phase impervious walls. Finally, construct the concrete face, connecting plate, toe slab, and the peripheral joint of the concrete face. The construction plan of closing the impervious wall after the completion of the dam body is adopted in the present invention, which avoids the stress mode of a simply supported beam formed by the premature construction and embedding of the concrete impervious wall into the bedrock section, can significantly reduce the stress amplitude of the tensile and compressive stresses of the concrete impervious wall, improve the stress state of the concrete impervious wall, and enhance the reliability and durability of the impervious system. Specifically, it includes the following steps:

[0008] First step, the first-phase dam body 9 is filled layer by layer on the overburden layer by the vibration rolling method until it reaches the height of h1.

[0009] Second step, complete the construction of the first-phase concrete impervious wall 1 and the main construction of the second-phase dam body 10. Specifically:

[0010] The second-phase dam body 10 is continuously filled layer by layer on the first-phase dam body 9 by the same construction method as the first step until it reaches the dam crest, and the main project construction of the second-phase dam body 10 is completed. The filling height of the second-phase dam body 10 is h2.

[0011] The construction of the first-phase impervious wall 1 is carried out simultaneously with that of the second-phase dam body 10. A construction site is established with the central axis of the position where the concrete impervious wall 1 is located as the center, and the first-phase impervious wall 1 is constructed from the middle of the river valley towards both banks. The overburden layer 4 is excavated into a groove by a grab or a hydraulic milling machine, and mud slurry is used for wall protection. Ordinary concrete is poured by the direct-lift pipe method, and it is carried out simultaneously from the middle of the river valley towards both banks to complete the construction of the concrete impervious wall 1.

[0012] Third step, the second-phase concrete impervious wall 2 that can be embedded in the bedrock on both banks is poured at the bottom of the first-phase dam body 9 by the same construction method as the second step, where the axial length of the second-phase concrete impervious wall 2 on the left bank part is l 21 , and the axial length of the second-phase concrete impervious wall 2 on the right bank part is l 22 .

[0013] Fourth step, the third-phase impervious wall 3 located between the first-phase concrete impervious wall 1 and the second-phase concrete impervious wall 2 is poured by the same construction method as the second step, where the axial length of the third-phase concrete impervious wall 3 on the left bank part is l 31, the axial length of the dam on the right bank part is l 32 .

[0014] Fifthly, install the connecting plate 5, toe slab 6, and concrete face slab 7, and complete the construction of the peripheral joint 8 of the face slab before impounding water; the connecting plate 5 and toe slab 6 are constructed by the in-situ casting method, and the peripheral joint 8 is located between the downstream side of the toe slab 6 and the concrete face slab 7.

[0015] Furthermore, the axial length l1 of the first-stage concrete cut-off wall 1 needs to be less than the valley width l0 at the corresponding position to avoid the first-stage concrete cut-off wall 1 contacting both banks of the valley at both ends and forming a simply supported beam stress form.

[0016] Furthermore, the thickness and depth of the first-stage concrete cut-off wall 1, the second-stage concrete cut-off wall 2, and the third-stage concrete cut-off wall 3 can be the same or different.

[0017] Furthermore, the sum of the axial lengths of the first-stage concrete cut-off wall 1 and the third-stage concrete cut-off wall 3 is equal to the valley width l0.

[0018] Furthermore, the first-stage concrete cut-off wall 1 is constructed from the middle of the valley towards both banks, and the second-stage concrete cut-off wall 2 is constructed from the slope towards the valley direction.

[0019] Furthermore, the design and construction method are applicable to the concrete face rockfill dam.

[0020] The beneficial effects of the present invention are as follows:

[0021] Through the construction plan of closing the cut-off wall after the completion of the dam body, the present invention solves the problem of the similar simply supported beam bending deformation effect of the concrete cut-off wall caused by the self-weight load of the dam body when the cut-off wall is constructed and embedded in the bedrock too early, significantly reduces the stress amplitude of the suspended concrete cut-off wall structure, improves the stress state of the concrete cut-off wall, reduces the risk of damage and cracking, and thus effectively improves the safety margin of the anti-seepage system structure, providing an important reference for the dam foundation anti-seepage structure of the concrete face rockfill dam on the deep overburden foundation. Description of the Drawings

[0022] Figure 1 It is a schematic diagram of the anti-seepage wall area of the maximum longitudinal section of the concrete anti-seepage wall and dam body design scheme of the concrete face rockfill dam on the deep overburden of the present invention;

[0023] Figure 2 It is a schematic diagram of the transverse direction of the anti-seepage wall and dam body design scheme of the concrete face rockfill dam on the deep overburden of the present invention;

[0024] In the figure: 1 First-phase concrete cut-off wall in the middle of the river valley; 2 Second-phase concrete cut-off walls on both banks of the river valley; 3 Third-phase concrete cut-off wall at the junction of the dam foundation and both banks; 4 Overburden layer; 5 Connecting plate; 6 Toe slab; 7 Face slab; 8 Peripheral joint of the face slab; 9 First-phase dam body; 10 Second-phase dam body; l0 Valley width corresponding to the bottom of the cut-off wall; l1 Axial length of the first-phase concrete cut-off wall 1 along the dam axis; l 21 Axial length of the second-phase concrete cut-off wall 2 on the left bank along the dam axis; l 22 Axial length of the second-phase concrete cut-off wall 2 on the right bank along the dam axis; l 31 Axial length of the third-phase concrete cut-off wall 3 on the left bank along the dam axis; l 32 Axial length of the third-phase concrete cut-off wall 3 on the right bank along the dam axis; h1 Height of the first-phase dam body; h2 Height of the second-phase dam body.

[0025] Figure 3 It is the compressive stress nephogram of the traditional scheme of the cut-off wall of the concrete face rockfill dam on the deep overburden layer in the comparative example, with the unit of MPa.

[0026] Figure 4 It is the compressive stress nephogram of the optimized scheme of the cut-off wall of the concrete face rockfill dam on the deep overburden layer in the embodiment, with the unit of MPa.

[0027] Figure 5 It is the tensile stress nephogram of the traditional scheme of the cut-off wall of the concrete face rockfill dam on the deep overburden layer in the comparative example, with the unit of MPa.

[0028] Figure 6 It is the tensile stress nephogram of the optimized scheme of the cut-off wall of the concrete face rockfill dam on the deep overburden layer in the embodiment, with the unit of MPa.

[0029] Having an implementation mode

[0030] The present invention will be further described below in conjunction with specific implementation cases.

[0031] Embodiment (engineering case):

[0032] In this embodiment, an asphalt concrete face rockfill dam on a certain deep overburden layer is taken as an engineering case. The elevation of the foundation surface is 2550 m, the elevation of the dam crest is 2700 m, the maximum dam height is 150.0 m, and the width of the dam crest is 12.0 m. The upstream slope of the dam body is 1:1.7, and the downstream slope is 1:1.8. The riverbed overburden layer is deep, with a maximum depth of about 460 m. A suspended concrete cut-off wall (the first-stage concrete cut-off wall 1, the second-stage concrete cut-off wall 2, and the third-stage concrete cut-off wall 3) is used for the anti-seepage of the dam foundation, with a depth of 170 m and a thickness of 1.3 m. The axial length l1 of the first-stage concrete cut-off wall 1 in the dam axis direction is taken as 1420 m, the axial length l2 of the second-stage concrete cut-off wall 2 in the dam axis direction is taken as 450 m, and the axial length l3 of the third-stage concrete cut-off wall 3 in the dam axis direction is taken as 155 m. The valley width l0 at this part is 1575 m, the height h1 of the first-stage dam body is 50 m, and the height h2 of the second-stage dam body is 100 m. Specifically as follows:

[0033] First step, the first-stage dam body 9 is filled layer by layer through the layer-by-layer rolling construction method, with a height h1 = 50 m.

[0034] Second step, the construction of the first-stage concrete cut-off wall 1 and the second-stage dam body 10 is carried out simultaneously. Specifically:

[0035] The foundation is cleaned. At the elevation of the foundation surface of 2550 m, a construction site is established with the central axis of the concrete cut-off wall as the center. Through hydraulic milling construction, the overburden layer 4 is excavated into a groove along the axis of the cut-off wall. The excavation depth is 170 m and the thickness is 1.3 m. Mud is used for wall protection. Then, the first-stage concrete cut-off wall 1 is constructed from the center of the valley at its location to both banks. Ordinary concrete is poured by the direct lift conduit method, and the construction is carried out simultaneously to both banks. The axial construction length l1 of the first-stage concrete cut-off wall 1 in the dam axis direction is 1420 m, the valley width l0 corresponding to the first-stage concrete cut-off wall 1 is 1575 m, and the first-stage concrete cut-off wall 1 does not embed into the valley banks on both sides. Finally, the construction of the first-stage concrete cut-off wall 1 and the dam is completed.

[0036] The second-stage dam body 10 is continuously filled layer by layer on the first-stage dam body 9 using the same construction method as in the first step until it is filled to the dam crest, and the main project construction of the second-stage dam body 10 is completed. The filling height of the second-stage dam body 10 is h2 = 100 m.

[0037] Third step, the second-stage concrete cut-off walls 2 located on both sides of the valley are poured using the same construction method as in the second step. The sum of the axial construction lengths l 21 and l 22 on the left and right banks of the second-stage concrete cut-off wall 2 is 450 m, and the construction of the second-stage concrete cut-off wall 2 is completed.

[0038] In the fourth step, the third-phase concrete cutoff wall 3 located at the junction of the dam foundation and both banks is poured using the same construction method as in the second step. The axial construction length l of the third-phase concrete cutoff walls 3 on both the left and right banks 31 and l 32 add up to 155 m, completing the construction of the entire cutoff wall.

[0039] In the fifth step, connecting plates 5 and toe slabs 6 are sequentially installed on the downstream side of the concrete cutoff wall towards the dam body. The concrete face slab 7 is poured along the upstream dam slope direction. The bottom of the concrete face slab 7 contacts the toe slab 6. The connecting plates 5 and toe slabs 6 are constructed by the in-situ casting method, and the face slab 5 is poured using the slip form construction method.

[0040] In the sixth step, the construction of the peripheral joint 8 is completed before impoundment.

[0041] Comparative example

[0042] The structural parameters of the comparative example are exactly the same as those of the embodiment. There are obvious adjustments in the construction sequence of the cutoff wall between the traditional construction plan and the construction plan of the present invention. In the traditional construction plan, the first-phase dam body is filled to h1 = 50 m before constructing the cutoff wall. After the completion of the overall project of the cutoff wall, the second-phase dam body is filled until the dam crest is reached. During the filling process of the second-phase dam body in the traditional plan, the concrete cutoff wall prematurely forms a stress mode similar to that of a simply supported beam, causing the concrete cutoff wall to bear a relatively large stress.

[0043] Effect analysis of the embodiment and comparative example of the present invention:

[0044] The present invention is used to design the face rockfill dam project, and numerical analysis is carried out. When the dam is impounded to the normal impoundment level, the stress distribution of the concrete cutoff wall in the numerical simulation calculation of the comparative example and the embodiment is shown in Figure 3 ~~ Figure 6 , and the maximum value is shown in Table 1. The analysis is as follows:

[0045] As can be seen from Figure 3 , the traditional structure will cause the concrete cutoff wall to be prematurely constructed and embedded in the bedrock section, forming a stress mode of a simply supported beam. The maximum compressive stress appears at the position where the bottom of the concrete cutoff wall meets the dam foundation and both banks, which is 29.2 MPa. As can be seen from Figure 4 , the present invention adopts the construction plan of finally closing the concrete cutoff wall, effectively delaying the closing and completion time of the concrete cutoff wall, avoiding the premature formation of a stress form similar to that of a simply supported beam in the concrete cutoff wall during the dam body construction and filling process. The maximum compressive stress no longer appears at the position where the bottom of the cutoff wall intersects with both banks (the maximum stress position of the present invention is as shown in Figure 4 ), at the bottom of the cutoff wall in the middle of the river valley), and the maximum compressive stress is reduced to 16 MPa.

[0046] As can be seen from Figure 5It can be seen that due to the supporting effects of the river valley banks and bottom on the cutoff wall in the traditional design and construction plan, large tensile stresses occur at the top of the cutoff wall, and the maximum tensile stress value is 14 MPa. From Figure 6 It can be seen that in the present invention, due to the construction plan of finally closing the cutoff wall, the time for the banks and bedrock to form a supporting effect on the cutoff wall during the dam filling process can be delayed, and the maximum tensile stress of the cutoff wall is reduced to 6.4 MPa.

[0047] In summary, as can be seen from Table 1, compared with the traditional plan, the design and construction method proposed in the present invention can reduce the maximum compressive stress of the concrete cutoff wall by 45% and the maximum tensile stress by 54%. The present invention effectively improves the stress state of the suspended concrete cutoff wall of the earth-rock dam on the deep overburden layer and improves the safety of the cutoff wall.

[0048] Table 1 Maximum values of tensile and compressive stresses of the cutoff wall during the full storage period (unit: MPa)

[0049]

[0050] The above-described embodiments are only the implementation manners of the present invention and should not be construed as limiting the scope of the present invention patent. It should be noted that for those skilled in the art, any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention should be included within the protection scope of the present invention.

Claims

1. A design and construction method for improving the stress state of a suspended concrete cut-off wall in a concrete face rockfill dam on a deep overburden layer, characterized in that In the design and construction method, the concrete anti-seepage wall is constructed in three phases, the first phase concrete anti-seepage wall (1) is located in the river valley section, the second phase concrete anti-seepage wall (2) is located in the two bank sections, and the third phase concrete anti-seepage wall (3) is located between the first phase concrete anti-seepage wall (1) and the second phase concrete anti-seepage wall (2); The construction sequence includes the following: first, construct the first-phase dam body (9); second, gradually construct the first-phase concrete anti-seepage wall (1) and the second-phase dam body (10) located in the river valley section along the river valley toward both banks; third, gradually construct the second-phase concrete anti-seepage wall (2) whose bottom can be embedded in the bedrock on both banks along the bank slope toward the river valley; fourth, construct the third-phase concrete anti-seepage wall (3); and finally, construct other structures.

2. A design and construction method for improving the stress state of a suspended concrete cut-off wall in a concrete face rockfill dam on a deep overburden layer according to claim 1, characterized in that The following steps are involved: In the first step, the first-stage dam body (9) is filled layer by layer on the overburden layer by means of a vibration rolling method; The second step is to complete the construction of the first phase concrete anti-seepage wall (1) and the main body of the second phase dam (10). Specifically: The second-stage dam body (10) is constructed layer by layer on the first-stage dam body (9) using the same construction method as the first step, until the dam top is reached, thus completing the main construction of the second-stage dam body (10); The construction of the first-phase concrete anti-seepage wall (1) and the second-phase dam body (10) is carried out simultaneously, a construction site is established with the central axis of the location of the first-phase concrete anti-seepage wall (1) as the center, and the first-phase concrete anti-seepage wall (1) is constructed from the river valley to both banks; The third step is to use the same construction method as the second step to cast a second-stage concrete anti-seepage wall (2) that can be embedded in the bedrock on both sides at the bottom of the first-stage dam body (9); Step 4: Casting the third-phase concrete anti-seepage wall (3) between the first-phase concrete anti-seepage wall (1) and the second-phase concrete anti-seepage wall (2) using the same construction method as the second step; The fifth step is to install the connecting plate (5), the toe plate (6), the concrete panel (7), and complete the construction of the panel perimeter seam (8) before water storage.

3. A design and construction method for improving the stress state of a suspended concrete cut-off wall in a concrete face rockfill dam on a deep overburden layer according to claim 1, characterized in that, The axial length l1 of the first-stage concrete anti-seepage wall (1) is smaller than the width l0 of the river valley at the corresponding position.

4. A design and construction method for improving the stress state of a suspended concrete cut-off wall in a concrete face rockfill dam on a deep overburden layer according to claim 1, characterized in that, In the second step, during the construction of the first-phase concrete anti-seepage wall (1), the covering layer (4) is excavated into a groove by means of a grab bucket or hydraulic milling, and a mud wall is used for protection; ordinary concrete is poured by means of a vertical pipe method, from the middle of the river valley to both banks simultaneously, to complete the construction of the first-phase concrete anti-seepage wall (1).

5. A design and construction method for improving the stress state of a suspended concrete cut-off wall in a concrete face rockfill dam on a deep overburden layer, as described in claim 1, wherein The thickness and depth of the first-stage concrete anti-seepage wall (1), the second-stage concrete anti-seepage wall (2), and the third-stage concrete anti-seepage wall (3) may be the same or different.

6. The design and construction method for improving the stress state of the suspended concrete cut-off wall of the concrete face rockfill dam on the deep overburden layer according to claim 1, characterized in that, The sum of the axial lengths of the first-stage concrete anti-seepage wall (1) and the third-stage concrete anti-seepage wall (3) is equal to the river valley width l0.

7. A design and construction method for improving the stress state of the suspended concrete cut-off wall of a concrete face rockfill dam on a deep overburden layer according to claim 1, characterized in that The second-phase concrete anti-seepage wall (2) is constructed from the bank slope towards the river valley.

8. A design and construction method for improving the stress state of a suspended concrete cut-off wall in a concrete face rockfill dam on a deep overburden layer according to claim 1, characterized in that The design and construction method are applicable to concrete face rockfill dams.

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