Design and construction method of clay joint between asphalt concrete panel on deep overburden layer and diaphragm wall

Abstract

The present application belongs to the technical field of earth and rockfill dam construction, and particularly discloses a design and construction method of clay joint between asphalt concrete face slab and cutoff wall on deep overburden layer. The steps are as follows: 1) constructing the concrete face slab dam body and the concrete cutoff wall main body; 2) setting trapezoidal support on the downstream side of the cutoff wall top area and connecting with the asphalt concrete face slab; 3) wrapping high plastic soil and clay on the cutoff wall top and extending horizontally to the face slab. The present application has the beneficial effects that: the high plastic soil and clay can well adapt to the uneven settlement caused by the modulus difference between the overburden layer and the concrete cutoff wall; the support structure on the downstream side of the cutoff wall further reduces the gradient of the settlement difference between the cutoff wall and the overburden layer; the double-layer cutoff design of the asphalt concrete face slab and the clay avoids the penetration damage of the clay and reduces the leakage in the area near the joint of the face slab and the cutoff wall.

Description

Technical Field

[0001] This invention belongs to the field of earth-rock dam construction technology, and relates to the design and construction method of a clay joint between an asphalt concrete panel and a seepage-proof wall on a thick overburden layer. Background Technology

[0002] With the continuous advancement of hydropower development, the dam site conditions for water conservancy projects in my country are becoming increasingly complex, making dam construction on overburden foundations "unavoidable." Currently, my country has several completed and planned high earth-rock dam projects, including Shiziping, Huangjinping, Xiabandi, Luding, Pangduo, Yele, and Altash, all with overburden depths reaching or exceeding 100 meters. The seepage prevention system is the most crucial component of the dam, making it particularly important to research design and construction technologies to further improve the safety of seepage prevention systems in earth-rock dams with deep overburden.

[0003] In concrete-faced rockfill dams built on overburden foundations, the cutoff wall is positioned upstream of the dam body, avoiding direct impact from the dam's weight and minimizing the risk of damage. However, traditional concrete-faced rockfill dams have a complex seepage control system, consisting of a concrete face, toe slab, connecting slab, cutoff wall, and water-stop joints between them. Due to the significant difference in modulus between the overburden foundation soil and the concrete cutoff wall, excessive shear deformation at the water-stop joints between the connecting slab and the cutoff wall can easily occur under reservoir water pressure, leading to damage. Therefore, addressing the problem of excessive deformation of the water-stop joints in traditional overburden-faced rockfill dams, which causes dam leakage and subsequent seepage failure, is crucial. Summary of the Invention

[0004] To address the problem of excessive deformation and damage to the waterstop joints in traditional concrete-faced rockfill dams with overburden layers due to the large difference in modulus between the overburden foundation soil and the anti-seepage wall concrete, this invention provides a design and construction method for a clay joint between the asphalt concrete face and the anti-seepage wall in a deep overburden layer. This method eliminates the design of the connecting plate and the waterstop joint, and adopts a double-layer anti-seepage design of clay and asphalt concrete, which effectively improves the safety of the anti-seepage body.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A design and construction method for a clay joint between an asphalt concrete panel and a cutoff wall on a deep overburden layer is disclosed. This method involves wrapping the concrete cutoff wall with highly plastic soil and clay, and reserving an extra-high (to accommodate the cutoff wall's insertion depth) horizontal cutoff design between the cutoff wall and the panel. This eliminates the need for a connecting plate and its water-stop joint structure with the cutoff wall. Simultaneously, a supporting structure is installed on the downstream side of the cutoff wall to further reduce the gradient of settlement between the cutoff wall and the overburden layer. This double-layer cutoff design of asphalt concrete panel and clay avoids clay seepage damage and reduces leakage in the area near the joint between the panel and the cutoff wall. The method includes the following steps:

[0007] 1) A trapezoidal support structure is installed on the downstream side of the top of the cutoff wall 4, and it is constructed using the cast-in-place method. The trapezoidal support structure refers to a trapezoidal protrusion designed on the downstream side of the cutoff wall.

[0008] 2) The part of the top of the seepage barrier 4 that is higher than the cover layer 5 is wrapped with high plastic soil and clay in sequence, and extends horizontally to the asphalt concrete panel 6. It is constructed by vibratory compaction.

[0009] The specific implementation process includes the following steps:

[0010] 1) The dam body is constructed by layering rockfill 1, transition material 3, and cushion material 2, using vibratory compaction, until the top of the dam. Specifically: the surface of the rockfill 1 is filled with a layer of transition material 3, which extends horizontally upstream to the downstream of the anti-seepage wall 4; the entire upper surface of the transition material 3 is filled with cushion material 2.

[0011] 2) At the top elevation EL1 of the overburden 5, establish a construction site with the central axis of the concrete cutoff wall 2 as the center. Using a grab bucket or hydraulic milling machine, excavate the overburden 5 into a trench with a width of d1 along the axis of the concrete cutoff wall 4, and use mud slurry for wall protection. Then, pour ordinary concrete using the vertical tremie method to complete the main construction of the cutoff wall 4. The main body of the concrete cutoff wall 4 is also a first-stage cutoff wall with a width of d1.

[0012] 3) The top h2 meters of the cutoff wall 4 constitute the second-stage cutoff wall. A trapezoidal support structure is installed on the downstream side of the bottom of the second-stage cutoff wall. This trapezoidal support structure is integrated with the cutoff wall 4 and is made of the same material. The transition material 3 extends horizontally to the trapezoidal support structure. The trapezoidal support structure is vertically arranged on the downstream side of the cutoff wall 4, with a vertical height of h1, a horizontal width of d3, and a narrow end height of h3. The top of the second-stage cutoff wall is designed as a trapezoid with a top width of d2. A formwork is installed, and the second-stage cutoff wall is constructed using the cast-in-place method. Where d2 is less than d1.

[0013] 4) Pour asphalt concrete panel 6 on the surface of the subbase material 2. The asphalt concrete panel 6 is connected to the downstream side of the second-phase anti-seepage wall and the trapezoidal support structure. That is, the asphalt concrete panel 6 is in contact with the downstream side of the anti-seepage wall 4 and the top surface of the trapezoidal support structure. The asphalt concrete panel 6 is constructed by vibratory compaction.

[0014] 5) A filter layer 7 with a height of h4 and a width of d4 is set on the upstream side of the anti-seepage wall 4, and is constructed by vibration compaction.

[0015] 6) Centered on the central axis of the concrete cutoff wall 2, a high-plasticity soil zone 8 with a width of d5 and a height of h5 is set in the area where the cutoff wall 2 is higher than the overburden layer 5 (the top surface of the high-plasticity soil zone 8 is located above the top surface of the second-phase cutoff wall), extending horizontally downstream to the asphalt concrete panel 6. The extension zone has a height of h6, meaning that the bottom surface of the upstream high-plasticity soil zone 8 contacts the filter layer 7, and the bottom surface of the downstream high-plasticity soil zone 8 contacts the asphalt concrete panel 6. A clay zone 9 with a height of h7 is set outside the high-plasticity soil 8, extending horizontally downstream to the asphalt concrete panel 6 and horizontally upstream to the filter layer 7. The upstream end is protected by the filter layer 7, and construction is carried out using vibratory compaction. The upper surface of the clay zone 9 is located above the high-plasticity soil zone 8.

[0016] Furthermore, the thickness of the high-plasticity soil zone 8 must meet the requirements for seepage failure and seepage flow.

[0017] The beneficial effects of this invention are as follows:

[0018] Compared with existing technologies, the beneficial effects of this invention are that it proposes a design and construction method for a clay joint between an asphalt concrete panel and a cutoff wall on a deep overburden layer, eliminating the need for the water-stop joint structure of traditional panel dams. This is mainly reflected in the fact that highly plastic soil and clay can effectively adapt to the uneven settlement caused by the difference in modulus between the overburden layer and the concrete cutoff wall; the downstream support structure of the cutoff wall further reduces the gradient of settlement between the cutoff wall and the overburden layer; and the double-layer cutoff design of the asphalt concrete panel and clay avoids clay seepage damage and reduces leakage in the area near the joint between the panel and the cutoff wall. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the design scheme for the asphalt concrete panel dam seepage prevention system on the overburden layer according to the present invention;

[0020] Numbers in the diagram: 1-Dam body rockfill; 2-Subbase material; 3-Transition material; 4-Isolation wall; 5-Cover layer; 6-Asphalt concrete panel; 7-Filter layer; 8-High plastic soil; 9-Clay; EL1-Cover layer top elevation; d1-Isolation wall width; h1-Downstream support structure height of the isolation wall; d2-Isolation wall top width; h2-Isolation wall top zone height; d3-Support structure width; h3-Support structure end height; d4-Filter layer width; h4-Filter layer thickness; d5-High plastic soil width; h5-High plastic soil thickness; h6-High plastic soil extension zone height; h7-Clay thickness. Detailed Implementation

[0021] The present invention will be further described below with reference to specific implementation examples.

[0022] The following are some engineering examples:

[0023] Taking an asphalt concrete-faced dam with an overburden layer as an engineering case study, the top elevation of the overburden layer is 2950m, the dam crest elevation is 3030m, the dam height is 80m, and the dam crest width is 10m. The upstream slope of the dam body is 1:1.6, and the downstream slope is 1:1.8. The thickness of the concrete face varies from the dam crest to the dam base by 0.4 + 0.0035h, where h is the height from the dam crest in meters. A reinforced concrete toe slab, 4.0m wide and 1.2m high, is installed at the bottom of the face. A suspended cutoff wall is used for seepage prevention at the dam foundation, with a depth of 150m and a thickness of 1.2m. The axis of the cutoff wall is 12m from the toe slab. The cutoff wall is connected to the toe slab and the face using asphalt concrete and clay as a horizontal seepage barrier. The specific operation process is described below:

[0024] 1) The dam rockfill material 1, cushion material 2 and transition material 3 are filled layer by layer and constructed by vibratory compaction until the top of the dam is reached.

[0025] 2) At the top elevation EL1 of the overburden, establish a construction site with the central axis of the concrete cutoff wall 2 as the center. Using a grab bucket or hydraulic milling machine, excavate the overburden 5 into a trench with a width of 1.2m along the axis of the concrete cutoff wall 4, and use mud slurry to protect the wall. Then, pour ordinary concrete using the vertical tremie method to complete the main construction of the cutoff wall 4.

[0026] 3) The top 5m of the cutoff wall 4 forms the second-stage cutoff wall. A trapezoidal support structure is installed on the downstream side of the bottom of the second-stage cutoff wall. This trapezoidal support structure is integrated with the cutoff wall 4 and is made of the same material. The vertical height of the trapezoidal support structure is 2m, the horizontal width is 1m, and the height of the narrow end is 0.5m. The top of the second-stage cutoff wall is designed as a trapezoid with a top width of 0.4m. A formwork is installed, and the second-stage cutoff wall is constructed using the cast-in-place method.

[0027] 4) The asphalt concrete panel is connected to the top of the downstream support structure of the anti-seepage wall, and the asphalt concrete panel is constructed by vibratory compaction.

[0028] 6) A 2m high and 20m wide reverse filter layer 7 is installed on the upstream side of the seepage barrier wall, constructed using the vibratory compaction method.

[0029] 7) Centered on the central axis of the concrete cutoff wall 2, a high plastic soil zone 8 with a width of 4m and a height of 5m is set up and extends downstream to the asphalt concrete panel. The extension zone has a height of 1.2m. A clay zone 9 with a height of 10m is set up outside the high plastic soil and extends downstream to the concrete panel. It extends horizontally upstream to the filter layer and is protected by the filter layer at the end. Vibration compaction method is used for construction.

[0030] The above-described embodiments are merely illustrative of the implementation methods of the present invention, but should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the protection scope of the present invention.

Claims

1. A construction method for a clay joint between an asphalt concrete panel and a seepage-proof wall on a deep overburden layer, characterized in that, The construction method involves wrapping a concrete cutoff wall with highly plastic soil and clay, and reserving a horizontal cutoff design between the cutoff wall and the panel for an extra-high cutoff wall. This eliminates the need for connecting plates and their water-stop joints with the cutoff wall. Simultaneously, a supporting structure is installed on the downstream side of the cutoff wall to further reduce the settlement gradient between the cutoff wall and the overburden layer. The double-layer cutoff design of asphalt concrete panel and clay avoids clay seepage damage while reducing leakage in the area near the joint between the panel and the cutoff wall. The method includes the following steps: 1) A trapezoidal support structure is set on the downstream side of the top of the seepage barrier (4), and the construction is carried out by cast-in-place method; the trapezoidal support structure refers to a trapezoidal protrusion designed on the downstream side of the seepage barrier; 2) The top part of the anti-seepage wall (4) that is higher than the cover layer (5) is wrapped with high plastic soil and clay and extends horizontally to the asphalt concrete panel (6), and is constructed by vibratory compaction. Specifically, the following steps are included: 1) The dam body rockfill (1), transition material (3) and cushion material (2) are filled layer by layer and constructed by vibratory compaction until the top of the dam; the surface of the dam body rockfill (1) is filled with a layer of transition material (3), and the layer of transition material (3) extends horizontally upstream to the downstream of the anti-seepage wall (4); the surface of the transition material (3) layer is filled with cushion material (2); 2) At the top elevation EL1 of the overburden (5), establish a construction site centered on the central axis of the concrete cutoff wall (4). Using a grab bucket or hydraulic milling machine, excavate the overburden (5) into a trench along the axis of the concrete cutoff wall (4). Use mud slurry for wall protection, and then pour ordinary concrete using a vertical tremie pipe method to complete the main construction of the cutoff wall (4). The main body of the concrete cutoff wall (4) is also a first-phase cutoff wall, with a width of [missing information]. d 1; 3) A secondary seepage barrier is designed at the top of the seepage barrier (4). A trapezoidal support structure is set on the downstream side of the bottom of the secondary seepage barrier. The trapezoidal support structure is integrated with the seepage barrier (4) and is made of the same material. The transition material (3) extends horizontally to the trapezoidal support structure. The top of the secondary seepage barrier is designed as a trapezoid with a top width of [missing information]. d 2. Set up formwork and complete the second-phase anti-seepage wall construction using the cast-in-place method; among which, d 2 less than d 1; 4) Pour asphalt concrete panel (6) on the surface of the cushion material (2). The asphalt concrete panel (6) is connected to the downstream side of the second phase anti-seepage wall and the trapezoidal support structure. The asphalt concrete panel (6) is constructed by vibratory compaction. 5) A reverse filter layer (7) is set on the upstream side of the seepage barrier (4) and constructed by vibration compaction method; 6) With the central axis of the concrete cutoff wall (4) as the center, a high plasticity soil zone (8) is set in the area where the cutoff wall (4) is higher than the cover layer (5), and extends horizontally downstream to the asphalt concrete panel (6). That is, the bottom surface of the upstream high plasticity soil zone (8) is in contact with the filter layer (7), and the bottom surface of the downstream high plasticity soil zone (8) is in contact with the asphalt concrete panel (6). A clay zone (9) is set outside the high plasticity soil zone (8), extending horizontally downstream to the asphalt concrete panel (6) and horizontally upstream to the filter layer (7). The upstream end is protected by the filter layer (7), and the construction is carried out by vibration rolling. The upper surface of the clay zone (9) is located above the high plasticity soil zone (8).

2. The construction method for the clay joint between the asphalt concrete panel and the anti-seepage wall on a deep overburden layer according to claim 1, characterized in that, The thickness of the high plasticity soil zone (8) must meet the requirements for seepage failure and seepage flow.

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