Partitioned variable permeability coefficient suspended anti-seepage wall structure and construction method thereof

Abstract

The present invention relates to a partitioned variable permeability coefficient suspended anti-seepage wall structure and a construction method thereof. The purpose of the present invention is to provide a partitioned variable permeability coefficient suspended anti-seepage wall structure and a construction method thereof, so as to reduce the hydraulic gradient at the end of the anti-seepage wall under the premise of meeting the overall anti-seepage function requirements, avoid the situation of seepage damage inside the soil body, and ensure the long-term safe operation of the anti-seepage wall. The technical solution of the present invention is: a partitioned variable permeability coefficient suspended anti-seepage wall structure, characterized in that: the anti-seepage wall is arranged in a deep and permeable foundation, and the anti-seepage wall is divided into a hydraulic gradient relief section, an overlap section and an anti-seepage control section from bottom to top; the permeability coefficient of the hydraulic gradient relief section is controlled at about 1 / 10 of the natural permeability coefficient of the foundation. The present invention is suitable for water retaining projects with a deep permeable soil layer of the foundation and a suspended anti-seepage wall for anti-seepage.

Description

Technical Field

[0001] The invention relates to a zoned variable permeability coefficient suspended anti-seepage wall structure and a construction method thereof, which is suitable for water retaining projects with thick permeable soil layers at the foundation and anti-seepage using suspended anti-seepage walls. Background Art

[0002] When the dam foundation is a permeable soil layer, in order to improve the anti-seepage effect, an anti-seepage wall is generally used for the dam foundation. However, when the foundation cover layer is thick, due to the limitation of construction capacity and the comprehensive consideration of functional benefits, a suspended anti-seepage wall is often used. When a suspended anti-seepage wall is used, the hydraulic gradient concentration phenomenon will appear at the end of the anti-seepage wall, causing the loss of fine particles in the end soil during operation, and the hydraulic gradient will be further concentrated. In severe cases, it will cause cavities in the soil within a certain range at the end of the anti-seepage wall, and the anti-seepage wall will break due to loss of support, resulting in anti-seepage failure. The direct reason for the concentration of hydraulic gradient at the end of the anti-seepage wall is that the anti-seepage effect of the anti-seepage wall is significant, and the permeability coefficient is much lower than that of the dam foundation soil, which leads to changes in the seepage field, and the seepage bypasses to the bottom of the anti-seepage wall, forming a local head concentration. Studies have shown that under the same basic conditions, the better the anti-permeability of the anti-seepage wall and the deeper the depth of the anti-seepage wall, the greater the hydraulic gradient at the end of the anti-seepage wall. Summary of the invention

[0003] The technical problem to be solved by the present invention is: in response to the above-mentioned problems, a partitioned variable permeability coefficient suspended anti-seepage wall structure and a construction method thereof are provided to reduce the hydraulic gradient at the end of the anti-seepage wall while meeting the overall anti-seepage function requirements, avoid seepage damage inside the soil, and ensure the long-term safe operation of the anti-seepage wall.

[0004] The technical solution adopted by the present invention is: a zoned variable permeability coefficient suspended anti-seepage wall structure, characterized in that: the anti-seepage wall is arranged in a deep and permeable foundation, and the anti-seepage wall is divided into a hydraulic gradient relief section, an overlap section and an anti-seepage control section from bottom to top; the permeability coefficient of the hydraulic gradient relief section is controlled at 1 / 20 to 1 / 10 of the natural permeability coefficient of the foundation.

[0005] From the perspective of reducing the hydraulic gradient concentration at the end of the cut-off wall, the closer the permeability coefficient of the cut-off wall is to the natural seepage coefficient of the foundation, the better. However, the actual permeability coefficient of the cut-off wall is much lower than that of the natural foundation, so a hydraulic gradient relief section with a large permeability coefficient must be set up. After calculation, when it is controlled at one-tenth of the natural foundation, the hydraulic gradient is acceptable. If it is one percent, there is almost no relief effect. If it is 1 / 8, it is closer to the permeability coefficient of the natural foundation, and the relief effect is better, but the closer to the permeability coefficient of the natural foundation, the higher the semi-permeability requirements of the cut-off wall and the greater the technical difficulty. Therefore, for this structure, the goal is to seek a minimum permeability coefficient requirement that can effectively alleviate the hydraulic gradient concentration.

[0006] The hydraulic gradient relief section is cast by using semi-permeable concrete, and the semi-permeable concrete uses permeable ceramsite as part of the aggregate.

[0007] The semi-permeable concrete is mixed with slag or fly ash.

[0008] The semi-permeable concrete is prepared by wetting the permeable ceramsite as aggregate in advance before mixing. The wet ceramsite should be in a "moist but not wet" state, that is, there is no water film on the surface of the ceramsite.

[0009] A construction method of the partitioned variable permeability coefficient suspended anti-seepage wall structure is characterized by:

[0010] According to the permeability characteristics of deep permeable foundation and the requirements of anti-seepage function, the seepage field analysis is carried out to determine the design parameters of the anti-seepage control section and hydraulic gradient relief section, including the thickness of the anti-seepage wall, the depth of each section, and the anti-seepage performance of each section;

[0011] According to the concrete performance requirements, carry out mix ratio tests and underwater pouring performance tests to determine the concrete mix ratio, ceramsite content, ceramsite pre-wetting process, and underwater pouring performance reliability;

[0012] Conduct overlapping strip simulation casting test and analyze the overlapping strip distribution width;

[0013] Review the impact of the overlap band on the anti-seepage effect based on the test results, and revise the depth of the anti-seepage control section based on the anti-seepage function requirements;

[0014] According to the design results of the anti-seepage wall structure and considering the process requirements, calculate the amount of concrete and make construction preparations;

[0015] The anti-seepage wall is constructed according to the construction procedure of the slotted concrete underground continuous wall and the parameters determined by the underwater casting process test.

[0016] The beneficial effects of the present invention are as follows: the present invention utilizes the high water permeability of permeable ceramsite as aggregate to produce semi-permeable concrete with underwater casting performance. The semi-permeable concrete is used as an extension section of the anti-seepage bottom, and the hydraulic gradient at the end of the anti-seepage wall is significantly reduced under the premise of ensuring the anti-seepage function, eliminating the problem of seepage damage caused by the concentration of hydraulic gradient at the end of the suspended anti-seepage wall, and improving the operational reliability of the anti-seepage wall. The simulation calculation results show that by adopting the anti-seepage wall structure of the present invention, the hydraulic gradient at the end can be reduced by more than 50%, and the increase in leakage is controlled within 10%. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a structural schematic diagram of an embodiment.

[0018] In the figure: 1. Deep and permeable foundation; 2-1. Hydraulic gradient relief section; 2-2. Overlap section; 2-3. Anti-seepage control section; 2-4. Top concrete; 2-5. Double-layer steel mesh; 2-6. Concrete; 3. Cast concrete guide wall; 4. Steel mesh; 5. Waterstop. DETAILED DESCRIPTION

[0019] This embodiment is a zoned variable permeability coefficient suspended anti-seepage wall structure, which includes a deep and permeable foundation 1 and a suspended anti-seepage wall 2 built inside the foundation.

[0020] In this embodiment, the anti-seepage wall 2 is divided into three sections according to the function, permeability coefficient and process requirements. The end 5 to 10 m is the hydraulic gradient relief section 2-1, and the permeability coefficient is controlled at about 1 / 10 of the natural permeability coefficient of the foundation; most of the anti-seepage wall above the hydraulic gradient relief section is the anti-seepage control section 2-3, and the permeability coefficient is controlled according to the anti-seepage function and the performance of the underwater cast anti-seepage concrete itself, and the permeability coefficient is generally much less than 10 -6 cm / s; due to the casting process, there is an overlap section 2-2 between the hydraulic gradient relief section and the upper anti-seepage control section (the length is determined by the process and is as short as possible while ensuring the casting quality).

[0021] In this example, the hydraulic gradient relief section 2-1 at the end of the anti-seepage wall uses a special mix of semi-permeable concrete with underwater pouring performance. Semi-permeable concrete uses permeable ceramsite with different particle diameters to replace part of the coarse aggregate of the same grade, and adjusts the proportion of cementitious materials, appropriately adds slag or fly ash, and appropriately adjusts the fineness modulus of sand and admixtures, so as to achieve the unity of high permeability and underwater pouring function.

[0022] The permeable ceramsite used in the semi-permeable concrete in this embodiment has the characteristics of high porosity and easy floating, which are not conducive to underwater pouring. Before mixing the concrete, the ceramsite needs to be wetted in advance and the mixing time is appropriately increased. Before mixing the concrete, the wet ceramsite should be in a "moist but not wet" state, that is, there is no water film on the surface of the particles that affects the bonding of the aggregate and the cement slurry.

[0023] In this embodiment, the overlap section is a mixture of the semi-permeable concrete poured above the conduit opening at the beginning of the pouring of the upper anti-seepage control section 2-3 concrete and the anti-seepage control section concrete that falls later. The distribution range of the mixture needs to be determined based on the analysis of the underwater pouring simulation test, and the process parameters are adjusted through the underwater simulation pouring test to reduce the distribution range and improve the stability of the distribution range.

[0024] The process characteristics of the overlap section 2-2 in this example can be summarized as: dense conduit, semi-buried depth, and frequent pipe lifting. "Dense conduit" means that the spacing of the conduits in this process is smaller than that of the conventional underwater casting of the cut-off wall, so as to improve the performance stability of the casting structure, especially the overlap section 2-2; "semi-buried depth" means that the depth of the conduit buried under the concrete surface in the overlap section 2-2 is shallower than that of the conventional underwater casting of the cut-off wall, so as to accelerate the fusion of the concrete; "frequent pipe lifting" means that the conduit is slowly lifted during the casting process of the overlap section 2-2, so that the buried depth between the pipe mouth and the concrete surface is always stable.

[0025] In this embodiment, the anti-seepage wall 2 adopts an underground continuous wall structure. In order to construct the anti-seepage wall 2, a concrete guide wall 3 is first cast on the foundation surface as a construction platform for the anti-seepage wall 2, and the anti-guide wall 3 is removed after the anti-seepage wall 2 is cast to the surface. A double-layer steel mesh 2-5 is set inside the anti-seepage wall 2. The concrete 2-6 within a certain range on the top of the anti-seepage wall 2 is in contact with the wall-fixing mud and needs to be chiseled out, and the top concrete 2-4 is cast on the top. The thickness of the top concrete 2-4 is appropriately increased and wraps the top of the anti-seepage control section 2-3. When pouring the top concrete 2-4, according to the requirements for the connection between the anti-seepage wall and the upper anti-seepage structure, the water stop 5 is pre-buried, and a reinforcing steel mesh 4 is set in the upper and lower directions of the water stop.

[0026] The specific implementation steps of the zoned variable permeability coefficient suspended anti-seepage wall structure in this embodiment are as follows:

[0027] 1. According to the permeability characteristics and anti-seepage function requirements of the deep permeable foundation 1, the influence of the overlap section 3-2 is not considered first, and the seepage field analysis is carried out to determine the design parameters of the anti-seepage control section 2-3 and the hydraulic gradient relief section 2-1, mainly the thickness of the anti-seepage wall 2, the depth of each section, and the anti-seepage performance of each section;

[0028] 2. Carry out mix ratio test and underwater pouring performance test according to concrete performance requirements, focusing on determining the mix ratio of concrete, the content of ceramsite, the pre-wetting process of ceramsite, and the reliability of underwater pouring performance;

[0029] 3. Carry out simulated pouring test of overlap band 2-2, analyze the distribution width of overlap band 2-2, and reduce the width and distribution stability of overlap band 2-2 by adjusting process measures;

[0030] 4. Review the effect of the overlapping strip 2-2 on the anti-seepage effect according to the results of the process test, and modify the depth of the anti-seepage control section 2-3 according to the anti-seepage function requirements;

[0031] 5. According to the design results of the anti-seepage wall 2 structure and considering the process requirements, calculate the amount of concrete and prepare for construction;

[0032] 6. The anti-seepage wall 2 is constructed according to the construction procedure of the slotted concrete underground continuous wall and the parameters determined by the underwater pouring process test. The main processes include the construction of the guide wall 3 - drilling holes to form slots - mud wall consolidation - the steel mesh 2-5 and the guide tube below - pouring the anti-seepage wall concrete to the top.

[0033] 7. Remove the guide wall 3 and the wall 2-6 at the top of the anti-seepage wall in contact with the mud and water, install the water stop 5, and set up the steel mesh 4 on the upper and lower sides, and set up the mold to pour the top concrete 2-4.

Claims

1. A partitioned variable permeability coefficient suspended anti-seepage wall structure, characterized in that: The anti-seepage wall is set in a deep and permeable foundation. The anti-seepage wall is divided into a hydraulic gradient relief section, an overlap section and an anti-seepage control section from bottom to top. The permeability coefficient of the hydraulic gradient relief section is controlled to be 1 / 20 to 1 / 10 of the natural permeability coefficient of the foundation. The hydraulic gradient relief section is cast by semi-permeable concrete, and the semi-permeable concrete uses permeable ceramsite as part of the aggregate; The permeability coefficient of the anti-seepage control section is less than 10 -6 cm / s.

2. The partitioned variable permeability coefficient suspended anti-seepage wall structure according to claim 1 is characterized in that: The semi-permeable concrete is mixed with slag or fly ash.

3. The partitioned variable permeability coefficient suspended anti-seepage wall structure according to claim 1 is characterized in that: The semi-permeable concrete is wetted in advance for the permeable ceramsite used as aggregate before mixing. The wet ceramsite should be in a "moist but not wet" state, that is, there is no water film on the surface of the ceramsite.

4. A construction method of a partitioned variable permeability coefficient suspended anti-seepage wall structure according to any one of claims 1 to 3, characterized in that: According to the permeability characteristics of deep permeable foundation and the requirements of anti-seepage function, the seepage field analysis is carried out to determine the design parameters of the anti-seepage control section and hydraulic gradient relief section, including the thickness of the anti-seepage wall, the depth of each section, and the anti-seepage performance of each section; According to the concrete performance requirements, carry out mix ratio tests and underwater pouring performance tests to determine the concrete mix ratio, ceramsite content, ceramsite pre-wetting process, and underwater pouring performance reliability; Conduct simulated casting test of overlap section and analyze the distribution width of overlap section; Review the impact of the overlap band on the anti-seepage effect based on the test results, and modify the depth of the anti-seepage control section based on the anti-seepage function requirements; According to the design results of the anti-seepage wall structure and considering the process requirements, calculate the amount of concrete and make construction preparations; The anti-seepage wall is constructed according to the construction procedure of the slotted concrete underground continuous wall and the parameters determined by the underwater casting process test.

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