Design and construction method for improving stress state of suspended concrete cutoff wall of face rockfill dam on deep overburden

Abstract

The application relates to a design and construction method for improving the stress state of a suspended concrete cutoff wall of a face slab rockfill dam on a deep overburden layer, belonging to the technical field of water conservancy and hydropower. The construction sequence is as follows: first, a first-stage dam body is constructed; second, a first-stage concrete cutoff wall located in a valley section and a second-stage dam body are gradually constructed along the valley to the two banks; third, a second-stage concrete cutoff wall with a bottom embedded in the bedrock of the two banks is gradually constructed along the bank slope to the valley; fourth, a third-stage concrete cutoff wall in the middle of the first-stage and second-stage cutoff walls is constructed; and finally, a face slab, a connecting plate, a toe plate and a peripheral joint with the face slab are constructed. The application innovatively proposes a construction scheme of sealing the cutoff wall after the completion of the dam body, solves the problem of the stress mode of a simply supported beam formed by the early construction of the embedded bedrock section, causes the bending deformation of the dam body filled in the later period under the action of the dead weight and the high stress problem, improves the stress state of the concrete cutoff wall, reduces the risk of damage and cracking, and effectively improves the safety margin of the cutoff system of the face slab rockfill dam under the complex geological conditions.

Description

Technical Field

[0001] This invention belongs to the field of water conservancy and hydropower technology, and relates to a design and construction method for improving the stress state of a suspended concrete cutoff wall in a rockfill dam with a thick overburden layer. Background Technology

[0002] In the field of earth-rock dam construction, the seepage prevention system is the "lifeline" ensuring the safe and stable operation of the dam, and the concrete cutoff wall is the core component of the dam's seepage prevention system. When constructing an earth-rock dam on a foundation with a deep overburden layer, a suspended concrete cutoff wall is generally used as the dam foundation seepage prevention structure, forming a stress form similar to a simply supported beam. However, the significant difference in stiffness between the deep overburden foundation and the concrete cutoff wall means that during dam construction and reservoir impoundment, the concrete cutoff wall is subjected to gravity, friction from the surrounding soil, and reservoir water pressure. This causes excessive compressive stress at the junction of the bottom of the concrete cutoff wall and the dam foundation on both banks, which may lead to damage and failure of the concrete cutoff wall, thereby affecting its seepage prevention function and endangering the safety of the dam.

[0003] Therefore, it is crucial to address the problem of excessive stress in the concrete cutoff wall of an earth-rock dam on a deep overburden layer, which can lead to damage to the seepage control system and to improve the stress state of the concrete cutoff wall. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention provides a design and construction method for improving the stress state of suspended concrete cutoff walls in rockfill dams with thick overburden layers. It innovatively proposes a construction scheme of sealing the cutoff wall after the dam body is completed, which solves the problem of high stress caused by the concrete cutoff wall being prematurely embedded in the bedrock section and forming a simply supported beam stress mode in traditional design and construction schemes. This results in the dam body bending and deforming under its own weight in the later filling stage, thus reducing the risk of damage and cracking of the concrete cutoff wall.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A design and construction method for improving the stress state of a suspended cutoff wall in a rockfill dam with a thick overburden layer is disclosed. In this method, the concrete cutoff wall is constructed in three phases: Phase I concrete cutoff wall 1 is located in the valley section; Phase II concrete cutoff wall 2 is located on both banks; and Phase III concrete cutoff wall 3 is located between Phase I and Phase II concrete cutoff walls 1 and 2. The construction sequence includes: first, constructing the Phase I dam body; second, gradually constructing the Phase I concrete cutoff wall and Phase II dam body located in the valley section along the valley towards both banks; third, gradually constructing the Phase II concrete cutoff wall, whose bottom can be embedded in the bedrock on both banks, along the bank slope towards the valley; fourth, constructing the Phase III concrete cutoff wall between the Phase I and Phase II cutoff walls; and finally, constructing the face panel, connecting plates, toe plates, and the seams around the face panel. This invention employs a construction scheme where the anti-seepage wall is sealed after the dam body is completed. This avoids the premature embedding of the concrete anti-seepage wall into the bedrock section, resulting in a simply supported beam stress mode. This significantly reduces the tensile and compressive stress amplitude of the concrete anti-seepage wall, improves its stress state, and enhances the reliability and durability of the anti-seepage system. Specifically, it includes the following steps:

[0007] The first step involves filling the first phase dam body 9 layer by layer on the overburden using the vibratory compaction method, until it reaches a height of h1.

[0008] The second step involves completing the construction of the first-phase concrete cutoff wall 1 and the main structure construction of the second-phase dam body 10. Specifically:

[0009] The second phase dam body 10 is constructed using the same method as the first phase dam body 9, continuing to fill layer by layer until it reaches the top of the dam, thus completing the main construction of the second phase dam body 10. The filling height of the second phase dam body 10 is h2.

[0010] The construction of the first-phase cutoff wall 1 and the second-phase dam 10 was carried out simultaneously. A construction site was established centered on the central axis of the location of the concrete cutoff wall 1, and the first-phase cutoff wall 1 was constructed from the middle of the valley towards both banks. The overburden layer 4 was excavated into a trench using a grab bucket or hydraulic milling machine, and slurry was used for wall protection. Ordinary concrete was poured using a vertical tremie pipe method, proceeding simultaneously from the middle of the valley towards both banks, completing the construction of the concrete cutoff wall 1.

[0011] The third step involves using the same construction method as the second step to pour a second-stage concrete cutoff wall 2 at the bottom of the first-stage dam body 9, which can be embedded in the bedrock on both banks. The axial length of the second-stage concrete cutoff wall 2 on the left bank is l. 21 The axial length of the dam located on the right bank is l 22 .

[0012] The fourth step involves pouring the third-stage seepage barrier 3, located between the first-stage concrete cutoff wall 1 and the second-stage concrete cutoff wall 2, using the same construction method as the second step. The axial length of the third-stage concrete cutoff wall 3 on the left bank is l. 31The axial length of the dam located on the right bank is l 32 .

[0013] The fifth step is to install the connecting plate 5, toe plate 6, and concrete panel 7, and complete the construction of the perimeter joint 8 of the panel before water storage; the connecting plate 5 and toe plate 6 are constructed by cast-in-place method, and the perimeter joint 8 is located between the downstream side of toe plate 6 and concrete panel 7.

[0014] Furthermore, the axial length l1 of the first-phase concrete cutoff wall 1 should be less than the valley width l0 at the corresponding location to avoid the first-phase concrete cutoff wall 1 from contacting the two ends of the first-phase concrete cutoff wall with the banks of the valley and forming a simply supported beam stress form.

[0015] Furthermore, the thickness and depth of the first-stage concrete cutoff wall 1, the second-stage concrete cutoff wall 2, and the third-stage concrete cutoff wall 3 can be the same or different.

[0016] Furthermore, the sum of the axial lengths of the first-stage concrete cutoff wall 1 and the third-stage concrete cutoff wall 3 is equal to the valley width l0.

[0017] Furthermore, the first-stage concrete cutoff wall 1 is constructed from the middle of the valley towards both banks, while the second-stage concrete cutoff wall 2 is constructed from the bank slope towards the valley.

[0018] Furthermore, the design and construction methods described are applicable to panel rockfill dams.

[0019] The beneficial effects of this invention are as follows:

[0020] This invention addresses the problem of premature embedment of the cutoff wall into the bedrock during dam construction, which causes the concrete cutoff wall to bend under the dam's own weight, resulting in a bending deformation similar to a simply supported beam. This significantly reduces the stress amplitude of the suspended concrete cutoff wall structure, improves its stress state, and lowers the risk of damage and cracking. Consequently, it effectively enhances the safety margin of the cutoff wall system and provides an important reference for the foundation cutoff structure of rockfill dams with thick overburden foundations. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the maximum cross-sectional area of ​​the seepage barrier wall along the river in the design scheme of the concrete seepage barrier wall and dam body of the rockfill dam with a thick overburden layer according to the present invention.

[0022] Figure 2 This is a transverse river-oriented schematic diagram of the design scheme of the seepage prevention wall and dam body of the rockfill dam with a thick overburden layer upper panel according to the present invention.

[0023] In the diagram: 1. Phase I concrete cutoff wall in the middle of the valley; 2. Phase II concrete cutoff walls on both banks of the valley; 3. Phase III concrete cutoff wall at the junction of the dam foundation and both banks; 4. Overburden layer; 5. Connecting plate; 6. Toe plate; 7. Panel; 8. Peripheral joint of the panel; 9. Phase I dam body; 10. Phase II dam body; l0. Valley width corresponding to the bottom of the cutoff wall; l1. Axial length of the Phase I concrete cutoff wall 1; l 21 The axial length of the second-phase concrete cutoff wall 2 on the left bank of the dam; l 22 The axial length of the second-phase concrete cutoff wall 2 on the right bank of the dam; l 31 The axial length of the third-phase concrete cutoff wall 3 on the left bank; l 32 The axial length of the third-phase concrete anti-seepage wall 3 on the right bank; h1 is the height of the first-phase dam; h2 is the height of the second-phase dam.

[0024] Figure 3 The image shows the compressive stress cloud diagram of the traditional scheme of the anti-seepage wall of the dam with a thick overburden layer in the comparative example, with the unit being MPa.

[0025] Figure 4 The image shows the compressive stress cloud diagram of the optimized scheme for the anti-seepage wall of the dam above the thick overburden layer in the embodiment, with units of MPa.

[0026] Figure 5 The tensile stress cloud diagram is shown in MPa for the traditional scheme of the anti-seepage wall of the dam with a thick overburden layer in the comparative example.

[0027] Figure 6 The figure shows the tensile stress cloud diagram of the optimized scheme for the anti-seepage wall of the dam above the thick overburden layer in the embodiment, with units of MPa.

[0028] Implementation methods

[0029] The present invention will be further described below with reference to specific implementation examples.

[0030] Example (Engineering Case):

[0031] In this embodiment, an asphalt concrete face dam on a thick overburden layer is used as an engineering case. The foundation elevation is 2550 m, the dam crest elevation is 2700 m, the maximum dam height is 150.0 m, and the dam crest width 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 thick, with a maximum depth of about 460 m. Suspended concrete cutoff walls (first-stage concrete cutoff wall 1, second-stage concrete cutoff wall 2, and third-stage concrete cutoff wall 3) are used for dam foundation seepage prevention, with a depth of 170 m and a thickness of 1.3 m. The axial length l1 of the first-phase concrete cutoff wall 1 is taken as 1420 m, the axial length l2 of the second-phase concrete cutoff wall 2 is taken as 450 m, and the axial length l3 of the third-phase concrete cutoff wall 3 is taken as 155 m. The valley width at this location is l0 = 1575 m. The height h1 of the first-phase dam is 50 m, and the height h2 of the second-phase dam is 100 m. Details are as follows:

[0032] The first step involved constructing the first phase of the dam body 9 layer by layer using a layered compaction method, with a height of h1=50 m.

[0033] The second step involves the simultaneous construction of the first-phase concrete cutoff wall 1 and the second-phase dam body 10. Specifically:

[0034] Foundation clearing was carried out, and a construction site was established at an elevation of 2550 m, centered on the central axis of the concrete cutoff wall. Using hydraulic milling, the overburden layer 4 was excavated into a trench along the cutoff wall axis to a depth of 170 m and a thickness of 1.3 m. Mud slurry was used to stabilize the wall. Then, the first-phase concrete cutoff wall 1 was constructed from the valley center towards both banks, using a vertical tremie pipe method to pour ordinary concrete simultaneously. The axial construction length of the first-phase concrete cutoff wall 1 is l1 = 1420 m, and the valley width at the corresponding location is l0 = 1575 m. The first-phase concrete cutoff wall 1 is not embedded into either bank of the valley. Finally, the construction of the first-phase concrete cutoff wall 1 and the dam was completed.

[0035] The second phase of dam body 10 will continue to be constructed layer by layer on the first phase of dam body 9 using the same construction method as the first phase, until it is filled to the top of the dam, thus completing the main construction of the second phase of dam body 10. The filling height of the second phase of dam body 10 is h2=100m.

[0036] The third step involves pouring the second-phase concrete cutoff wall 2, located on both banks of the river valley, using the same construction method as the second step. The axial construction length of the second-phase concrete cutoff wall 2 on both banks is l. 21 With l 22 The sum is 450 m, completing the second phase of concrete anti-seepage wall construction.

[0037] The fourth step involves pouring the third-stage concrete cutoff wall 3, located at the junction of the dam foundation and both banks, using the same construction method as the second step. The axial construction length of the third-stage concrete cutoff wall 3 on both banks is l. 31 With l 32 The sum of these is 155 m, completing the entire anti-seepage wall construction.

[0038] Fifth step: Install connecting plate 5 and toe plate 6 sequentially on the downstream side of the concrete anti-seepage wall towards the dam body, and pour concrete panel 7 along the upstream dam slope. The bottom of concrete panel 7 contacts toe plate 6. Connecting plate 5 and toe plate 6 are constructed using the cast-in-place method, while panel 5 is poured using the slipform construction method.

[0039] Step 6: Complete the construction of the surrounding joint 8 before water is stored.

[0040] Comparative Example

[0041] The structural parameters of the comparative example and the embodiment are exactly the same. The traditional construction scheme and the construction scheme of this invention have significant adjustments in the construction sequence of the cutoff wall. In the traditional construction scheme, the first-stage dam body is filled to h1=50 m before constructing the cutoff wall. After the overall cutoff wall project is completed, the second-stage dam body is filled until it reaches the dam crest. During the second-stage dam body filling process in the traditional scheme, the concrete cutoff wall prematurely forms a stress mode similar to a simply supported beam, resulting in greater stress on the concrete cutoff wall.

[0042] Analysis of the effects of the embodiments and comparative examples of the present invention:

[0043] This invention was used to design the panel dam project, and numerical analysis was conducted. When the dam is filled to the normal water level, the stress distribution of the concrete cutoff wall calculated by numerical simulation in the comparative and embodiment examples is shown below. Figure 3 ~~ Figure 6 The maximum values ​​are shown in Table 1. The analysis is as follows:

[0044] Depend on Figure 3 It is known that traditional structures lead to premature construction of the concrete cutoff wall, embedding it into the bedrock section and forming a simply supported beam stress mode. The maximum compressive stress occurs at the junction of the concrete cutoff wall's bottom foundation and the two banks, reaching 29.2 MPa. Figure 4 It can be seen that the construction scheme of finally sealing the concrete cutoff wall in this invention effectively delays the completion time of the concrete cutoff wall closure, avoiding the premature formation of a stress form similar to a simply supported beam during the dam construction and filling process. The maximum compressive stress no longer appears at the intersection of the bottom of the cutoff wall and the two banks (the location of the maximum stress in this invention is as follows). Figure 4 As shown, at the bottom of the seepage barrier in the middle of the valley), and the maximum compressive stress is reduced to 16 MPa.

[0045] Depend on Figure 5It is known that, due to the supporting effect of the river valley banks and bottom, the anti-seepage wall constructed using traditional methods experiences significant tensile stress at its top, with a maximum tensile stress value of 14 MPa. From Figure 6 It can be seen that, by adopting the construction scheme of finally sealing the anti-seepage wall, the present invention can delay the time for the anti-seepage wall to be supported by the banks and bedrock during the dam filling process, and reduce the maximum tensile stress of the anti-seepage wall to 6.4 MPa.

[0046] In summary, as shown in Table 1, compared with traditional methods, the design and construction method proposed in this invention can reduce the maximum compressive stress of the concrete cutoff wall by 45% and the maximum tensile stress by 54%. This invention effectively improves the stress state of the suspended concrete cutoff wall of the earth-rock dam on a deep overburden layer, thereby enhancing the safety of the cutoff wall.

[0047] Table 1. Maximum tensile and compressive stresses of the cutoff wall during full storage period (unit: MPa)

[0048]

[0049] The above-described embodiments are merely implementation methods of the present invention and should not be construed as limiting the scope of the present invention. It should be noted that any modifications, equivalent substitutions, improvements, etc., made by those skilled in the art within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A construction method for improving the stress state of a suspended concrete cutoff wall in a rockfill dam with a thick overburden layer, characterized in that, In the construction method described above, the concrete cut-off wall is constructed in three phases: the first phase concrete cut-off wall (1) is located in the valley section, the second phase concrete cut-off wall (2) is located on both banks, and the third phase concrete cut-off wall (3) is located between the first phase concrete cut-off wall (1) and the second phase concrete cut-off wall (2). The construction sequence includes the following steps: first, construct the first-phase dam body (9); second, construct the first-phase concrete cutoff wall (1) and the second-phase dam body (10) along the river valley towards both banks; third, construct the second-phase concrete cutoff wall (2) with its bottom embedded in the bedrock on both banks along the river slope towards the river valley; fourth, construct the third-phase concrete cutoff wall (3); and finally, construct other structures. Includes the following steps: The first step is to fill the first phase of the dam body (9) layer by layer on the overburden layer using the vibratory compaction method; The second step involves completing the construction of the first-phase concrete cutoff wall (1) and the main structure of the second-phase dam (10). Specifically: The second phase dam body (10) is constructed using the same construction method as the first phase dam body (9) layer by layer until it reaches the top of the dam, thus completing the main construction of the second phase dam body (10). The construction of the first-phase concrete cutoff wall (1) and the second-phase dam (10) were carried out simultaneously. The construction site was established with the central axis of the location of the first-phase concrete cutoff wall (1) as the center, and the first-phase concrete cutoff wall (1) was constructed from the valley to both banks. The third step involves using the same construction method as the second step to pour a second-stage concrete anti-seepage wall (2) that can be embedded in the bedrock on both banks at the bottom of the first-stage dam body (9); The fourth step is to use the same construction method as the second step to pour the third-stage concrete cutoff wall (3) located between the first-stage concrete cutoff wall (1) and the second-stage concrete cutoff wall (2); The fifth step is to install the connecting plate (5), toe plate (6), and concrete panel (7), and complete the construction of the perimeter joints (8) of the panel before water storage.

2. The construction method for improving the stress state of a suspended concrete cutoff wall in a rockfill dam with a thick overburden layer according to claim 1, characterized in that, The axial length l1 of the first-phase concrete anti-seepage wall (1) is less than the valley width l0 at the corresponding location.

3. The construction method for improving the stress state of a suspended concrete cutoff wall in a rockfill dam with a thick 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 cover layer (4) is excavated into a trench by grab bucket or hydraulic milling and mud slurry is used for wall protection; ordinary concrete is poured by the straight-lift tremie pipe method, which is carried out simultaneously from the middle of the valley to both banks, to complete the construction of the first-phase concrete anti-seepage wall (1).

4. A construction method for improving the stress state of a suspended concrete cutoff wall in a rockfill dam with a thick overburden layer, as described in claim 1, characterized in that... The thickness and depth of the first-stage concrete cutoff wall (1), the second-stage concrete cutoff wall (2), and the third-stage concrete cutoff wall (3) can be the same or different.

5. A construction method for improving the stress state of a suspended concrete cutoff wall in a rockfill dam with a thick overburden layer, as described in claim 1, characterized in that... The sum of the axial lengths of the first-stage concrete cutoff wall (1) and the third-stage concrete cutoff wall (3) is equal to the valley width l0.

6. A construction method for improving the stress state of a suspended concrete cutoff wall in a rockfill dam with a thick overburden layer, as described in claim 1, characterized in that... The second-phase concrete anti-seepage wall (2) is constructed from the bank slope towards the valley.

7. A construction method for improving the stress state of a suspended concrete cutoff wall in a rockfill dam with a thick overburden layer, as described in claim 1, characterized in that, The construction method described herein is applicable to rockfill dams with concrete panels.

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