Method for optimizing under-membrane cushion layer of partition dam of composite geomembrane impervious body

Abstract

The invention discloses a composite geomembrane impervious body partition dam membrane lower cushion layer optimization method, which comprises the following steps: S1, establishing a dam model, and dividing the dam model into different areas; s2, in the dam model, four layers of materials are laid on the bottom of the reservoir area and an upstream dam; a clay layer, a composite geomembrane layer, an under-membrane cushion layer and a broken stone hardcore layer are sequentially laid at the bottom of the reservoir area from top to bottom; the upstream dam sequentially comprises a concrete precast block, a geotechnical mat, a composite geomembrane layer and an under-membrane cushion layer from top to bottom; s3, setting the under-membrane cushion layer to be a clay cushion layer, a geotechnical mat cushion layer or a pervious concrete cushion layer, and simulating displacement and stress strain of the dam under different working conditions; and S4, according to the calculation result of S3, evaluating the influence of different under-membrane cushion layer materials on the stress state of the anti-seepage body, and optimizing the cushion layer design. According to the method, corresponding anti-seepage cushion layers can be designed according to geological conditions of different regions, stress and strain of the dam under different working conditions are simulated, and scientific basis and practical suggestions are provided for selection of the composite geomembrane anti-seepage body cushion layers in the karst region.

Description

Technical Field

[0001] The invention belongs to the technical field of water conservancy engineering anti-seepage simulation, and in particular relates to a method for optimizing a cushion layer under a composite geomembrane anti-seepage body partition dam membrane. Background Art

[0002] In dam engineering anti-seepage, composite geomembrane is often used as an anti-seepage material laid in the dam body and other areas that need anti-seepage to form a composite geomembrane anti-seepage body. In order to ensure the long-term stability and safety of the composite geomembrane anti-seepage body, it is very important to reasonably select the underlying material of the composite geomembrane.

[0003] The existing technology lays sand cushions and clay cushions under the geomembrane in the reservoir area, but the strength of the sand cushions and clay cushions is limited, the water permeability is poor, and the anti-collapse ability needs to be further improved. In addition, a rock cushion is often required under the geomembrane laid at the upstream dam foot and upstream slope area. Since the rock cushion is relatively rough, it is easy to damage the geomembrane.

[0004] Commonly used membrane cushions include clay cushions, permeable concrete cushions, geomats, etc. The research on membrane cushions in the existing technology is limited to seepage and stability calculations, but it can no longer meet the design requirements of composite geomembrane anti-seepage body partition dams. The membrane cushion of composite geomembrane anti-seepage body partition dams needs to have good permeability or support. Therefore, it is necessary to propose a more optimized optimization method for the membrane cushion of composite geomembrane anti-seepage body partition dams. Summary of the invention

[0005] The purpose of the present invention is to provide a method for optimizing the cushion layer under the composite geomembrane anti-seepage body partition dam membrane, so as to solve the technical problem that the cushion layer under the composite geomembrane anti-seepage body partition dam membrane is difficult to select in the prior art.

[0006] In order to solve the above technical problems, the present invention adopts the following solutions:

[0007] The optimization method of the cushion layer under the composite geomembrane anti-seepage body partition dam membrane includes the following steps:

[0008] Step S1, establishing a dam model and dividing it into different areas;

[0009] Step S2: In the dam model, four layers of materials are laid on the bottom of the reservoir area and the upstream dam; wherein the bottom of the reservoir area is laid with a clay layer, a composite geomembrane layer, a cushion layer under the membrane and a crushed stone cushion layer from top to bottom; the upstream dam is laid with prefabricated concrete blocks, geomats, composite geomembrane layers and a cushion layer under the membrane from top to bottom;

[0010] Step S3, setting the cushion layer under the membrane to clay, geomat or permeable concrete cushion layer, respectively, to simulate the horizontal displacement, settlement and stress of the dam under different working conditions;

[0011] Step S4: Based on the simulation results of step S3, the influence of different cushion materials under the membrane on the stress state of the anti-seepage body is evaluated to optimize the cushion design.

[0012] Further optimization, in step S1, Midas GTS NX is used to establish a constitutive model of the dam, and the constitutive model is a Mohr-Coulomb and elastic model.

[0013] Further optimization, in the step S1, in the established dam model, a reservoir drainage blind ditch and a foot retaining wall are provided between the reservoir area and the upstream dam foot; a wave-breaking wall is constructed on the side of the dam top close to the upstream slope, and a dam top road surface is constructed on the dam top on the backwater side of the wave-breaking wall; the upstream dam includes an upstream dam foot and an upstream slope, and a plurality of anti-skid grooves are provided in the area between the upstream slope and the dam top, and a sand and gravel mixed filter layer is laid under the anti-skid groove.

[0014] Further optimization, in step S3, the sequence of dam body construction and filling is divided into 8 levels, and the stress and deformation of the dam are simulated by applying load step by step.

[0015] Further optimization, in step S3, the horizontal displacement, settlement and stress of the dam corresponding to different cushion layers under the membrane during the completion period and the water storage period are calculated respectively.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] The present invention establishes a dam model in which the sub-membrane cushion layers at the bottom of the reservoir area and the upstream dam are respectively set as clay, geomat or permeable concrete cushion layers, and simulates stress and strain under different working conditions, evaluates the influence of different sub-membrane cushion materials on the stress state of the impermeable body, and optimizes the cushion design. The method can design corresponding impermeable cushion layers according to the geological conditions of different regions, conducts simulation research from aspects such as permeability and supporting force, and provides scientific basis and practical suggestions for the accurate selection of composite geomembrane impermeable body cushion layers in karst areas. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The 2D finite element calculation model of the cross section of the dam is established;

[0019] Figure 2 It is the standard cross-section of the dam model;

[0020] Figure 3 It is the simulation diagram of dam displacement contour corresponding to different cushion layers under the membrane at the completion period;

[0021] Figure 4 It is the simulation diagram of dam stress contour corresponding to different cushion layers under the membrane at the completion period;

[0022] Figure 5 It is the contour map of dam displacement corresponding to different cushion layers under the membrane during the water storage period;

[0023] Figure 6 It is a simulation diagram of dam stress contours corresponding to different cushion layers under the membrane during the water storage period;

[0024] In the figure: 1. Reservoir area; 11. Reservoir drainage blind ditch; 12. Foot retaining wall; 2. Upstream dam foot; 3. Upstream slope; 31. Sand and gravel mixed filter layer; 32. Anti-skid groove; 4. Dam top; 41. Wave-breaking wall; 44. Dam top road surface; 5. Downstream slope; 51. Drainage prism; 52. Drainage ditch; 6. Downstream dam foot. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0026] The optimization method of the cushion layer under the composite geomembrane anti-seepage body partition dam membrane includes the following steps:

[0027] Step S1: Establish a dam model and divide it into different areas.

[0028] In this embodiment, the geomembrane anti-seepage partition dam of Mingbaihai Reservoir in Mengzi City is taken as the calculation and analysis object, the constitutive model is established by Midas GTS NX, and the maximum typical cross-section is selected to establish a 2D finite element calculation model, as shown in the figure. Figure 1 shown.

[0029] The total designed storage capacity of the Mengzi Baibaihai Project is 3.0525 million m 3 The dam top elevation is 2058.00m, the maximum dam height is 25.20m, the dam length is 255.72m, the dam top width is 5.0m, the upstream dam slope ratio is 1:2.75, the downstream slope ratio is 1:2.0, and the dam foundation is placed on weakly weathered rock.

[0030] In the established dam model, the dam body is divided into upstream dam, dam crest 4, downstream slope 5 and downstream dam foot 6 areas, such as Figure 2 As shown. Among them, a reservoir drainage blind ditch 11 and a foot retaining wall 12 are provided between the reservoir area 1 and the upstream dam foot 2; a wave-breaking wall 41 is built on the side of the dam top 4 close to the upstream slope 3, and a dam top road surface 44 is built on the dam top on the backwater side of the wave-breaking wall 41; the upstream dam includes the upstream dam foot 2 and the upstream slope 3, and the area between the upstream slope 3 and the dam top 4 is provided with a plurality of anti-skid grooves 32, and a sand and gravel mixed filter layer 31 is laid under the anti-skid grooves 32, and a drainage prism 51 and a drainage ditch 52 are built on the downstream dam foot 6.

[0031] Step S2: In the dam model, four layers of materials are laid on the bottom of the reservoir area and the upstream dam; wherein, the bottom of the reservoir area is laid with a clay layer, a composite geomembrane layer, a cushion layer under the membrane and a crushed stone cushion layer from top to bottom; the upstream dam is laid with precast concrete blocks, geomats, composite geomembrane layers and a cushion layer under the membrane from top to bottom.

[0032] Step S3, setting the cushion layer under the membrane to clay, geomat or permeable concrete cushion layer, respectively, to simulate the horizontal displacement, settlement and stress-strain of the dam under different working conditions.

[0033] In this embodiment, taking into account the nonlinear characteristics of the layered rolling filling and bedrock during dam construction, the load is applied step by step, and the filling and rising of each part of the dam body are carried out according to the actual filling process. The order of filling of the dam body construction is divided into 8 levels for simulation, and the filling is completed until the dam top elevation. The graded filling elevation of the dam body construction is shown in Table 1, the finite element calculation of the dam material parameters is shown in 2, and the simulation results are shown in Table 3. Among them, in Table 3, the Y displacement is negative when it is vertically downward, and positive when it is opposite. The x displacement is positive when it is horizontally pointing to the right, and negative when it is opposite; the positive value of stress is tensile stress, and the negative value is compressive stress.

[0034] Table 1 Dam construction graded filling elevation

[0035] Time Fill elevation Time Fill elevation 1 Drainage prism filling 5 The dam body is filled to 2048.60m 2 The dam body is filled to 2035.99m 6 The dam body is filled to 2053.60m 3 The dam body is filled to 2039.75m 7 The dam body is filled to 2058.00m 4 The dam body is filled to 2043.60m 8 The reservoir is filled to 2057.50m

[0036] Table 2 Finite element calculation parameters of dam materials

[0037]

[0038] Table 3 Simulation results of dam displacement and stress values ​​at different periods corresponding to different cushion layers under the membrane

[0039]

[0040] The simulation results are as follows Figure 3-6 As shown in Table 3 and Figure 3-6 Analyze the simulation results:

[0041] 1. Regarding the horizontal displacement of the dam: From the contour map of the maximum cross-section displacement in the downstream direction, it can be seen that: under the action of deadweight during the completion period, the dam body on the upstream side and the dam body on the downstream side of the dam axis displaced toward the reservoir basin (upstream) and downstream respectively. The horizontal displacement on the upstream side is slightly larger than that on the downstream side, and the zero displacement line basically coincides with the dam axis. During the completion period, the maximum displacement to the upstream side occurred at about 1 / 2 of the dam height upstream, and the maximum displacement to the downstream side occurred at about 1 / 3 of the dam height downstream. During the water storage period, due to the effect of water pressure, water storage causes the dam body to displace horizontally toward the downstream side, with the maximum value occurring near the dam crest elevation. The further downstream, the smaller the displacement.

[0042] 2. Regarding the settlement of the dam: The settlement displacement contour distribution diagram of the dam's largest section during the completion period and the water storage period (negative values ​​indicate settlement, positive values ​​indicate uplift, the same below). It can be seen from the figure that the maximum settlement displacement during the completion period occurred at about 1 / 2 of the dam height in the strongly weathered material at the dam axis, accounting for 0.55% of the maximum dam height, which is in line with the general settlement distribution law of core wall dams. During the water storage period, under the action of water load, the upstream side of the dam body settled again, and the maximum settlement occurred at a position above about 1 / 2 of the dam height on the upstream side of the dam body, which is in line with the settlement distribution law caused by water in general earth-rock dams.

[0043] 3. Stress analysis of the dam body during completion: From the stress distribution diagram after the dam is completed in layers, it can be seen that the major and minor principal stresses of the dam body are basically consistent with the horizontal and vertical stress distributions of the dam body after the layered filling is completed; this stress state shows that during the dam body filling process, the stress state of the dam body is mainly dominated by its own weight.

[0044] From the distribution diagram of the major principal stress (σ1), it can be seen that after the filling is completed, small tensile stress still appears on the surface of the dam body of the permeable concrete cushion layer and the geomat cushion layer. The extreme stress values ​​are 0.76kpa and 2.61kpa respectively, but they are less than the cohesion of the corresponding materials. Therefore, as long as the compaction quality is guaranteed during the dam body filling process, it is completely possible to ensure that the dam body will not be tensilely damaged after the filling is completed.

[0045] From the distribution diagram of the minor principal stress (σ3), it can be seen that after the filling is completed, the major principal stresses of the dam body are all compressive stresses. The maximum compressive stress near the foundation surface is about 0.9 MPa, which is much smaller than the bearing capacity of the rock mass at that location. Therefore, the rock mass near the foundation surface tends to be stable and there will be no lack of bearing capacity.

[0046] Step S4, evaluating the influence of different cushion materials under the membrane on the stress state of the anti-seepage body, and optimizing the cushion design.

[0047] In this example, based on the above simulation and analysis, the geomembrane anti-seepage body of Mengzi Baibaihai Reservoir is determined as follows: a 2m wide horseway is set at an elevation of 2044.00m, the upstream dam slope is protected by C25 precast concrete blocks with a thickness of 0.15m, and a geotechnical mat cushion layer with a thickness of 0.05m is set under the slope protection. The reservoir bottom elevation is 2030.00m. SNG / PET400-6 and GH2T2-6000 / 1.0 geomembranes are laid under the geotechnical mat cushion layer, and a 0.2m thick permeable concrete or a 3.0m horizontal width clay cushion layer is laid under the geomembrane.

[0048] A 0.7m thick clay protective layer is laid on the upper layer of the anti-seepage geomembrane at the bottom of the reservoir, and a 20cm thick C25 sandless concrete and a 50cm thick gravel cushion layer are laid on the lower layer.

[0049] In this example, the clay cushion under the geomembrane layer in the reservoir area was removed and replaced with a sandless concrete layer. The sandless concrete layer has better permeability and strength, which improves the dam's ability to resist collapse. In addition, the rock cushion on the upper part of the geomembrane layer in the upstream dam foot and upstream slope was removed and replaced with a geomat. The difficulty and workload of laying the geomat are much less than the rock cushion, and it has good adaptability to the geomembrane layer, reducing the risk of damaging the geomembrane layer during construction.

[0050] The above combined with the accompanying drawings are only specific implementation methods and processes of the present invention, but the protection scope of the present invention is not limited to this. Any technician familiar with the art should understand that this is only an example, and various changes and substitutions can be made to this implementation method without departing from the essential content of the present invention. The scope of the present invention is limited only by the attached claims. With the above ideal embodiment of the present invention as inspiration, through the above description, the relevant staff can make various changes and modifications without departing from the technical idea of ​​the present invention. The technical scope of this invention is not limited to the content in the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. A method for optimizing the cushion layer under the composite geomembrane anti-seepage partition dam membrane, characterized in that: The steps include: Step S1, establishing a dam model and dividing it into different areas; Step S2: In the dam model, four layers of materials are laid on the bottom of the reservoir area and the upstream dam; wherein the bottom of the reservoir area is laid with a clay layer, a composite geomembrane layer, a cushion layer under the membrane and a crushed stone cushion layer from top to bottom; the upstream dam is laid with prefabricated concrete blocks, geomats, composite geomembrane layers and a cushion layer under the membrane from top to bottom; Step S3, setting the cushion layer under the membrane to clay, geomat or permeable concrete cushion layer, respectively, to simulate the horizontal displacement, settlement and stress of the dam under different working conditions; Step S4: Based on the simulation results of step S3, the influence of different cushion materials under the membrane on the stress state of the anti-seepage body is evaluated to optimize the cushion design.

2. The optimization method for the cushion layer under the composite geomembrane anti-seepage body partition dam membrane according to claim 1 is characterized in that: In the step S1, Midas GTS NX is used to establish a constitutive model of the dam, and the constitutive model is a Mohr-Coulomb and elastic model.

3. The optimization method for the cushion layer under the composite geomembrane anti-seepage body partition dam membrane according to claim 2 is characterized in that: In the step S1, in the established dam model, a reservoir drainage blind ditch (11) and a foot retaining wall (12) are provided between the reservoir area (1) and the upstream dam foot (2); a wave-breaking wall (41) is constructed on the side of the dam top (4) close to the upstream slope (3), and a dam top road surface (44) is constructed on the dam top on the backwater side of the wave-breaking wall (41); the upstream dam includes an upstream dam foot (2) and an upstream slope (3), and a plurality of anti-skid grooves (32) are provided in the area between the upstream slope (3) and the dam top (4).

4. The optimization method for the cushion layer under the composite geomembrane anti-seepage body partition dam membrane according to claim 3 is characterized in that: In step S3, the order of the dam body construction and filling is set to 8 levels, and the stress and deformation simulation is performed according to the dam body filling and loading sequence.

5. The optimization method for the cushion layer under the composite geomembrane anti-seepage body partition dam membrane according to claim 4 is characterized in that: In step S3, the horizontal displacement, settlement and stress of the dam corresponding to different cushion layers under the membrane during the completion period and the water storage period are simulated and calculated respectively.

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