A simplified design method and system for drainage blind ditch grid water head distribution

Abstract

The present invention provides a simplified design method and system for the water head distribution of a drainage blind ditch grid. The method first preliminarily designs the drainage blind ditch unit size, then determines the basic calculation parameters and calculates the drainage volume, and finally calculates the water head distribution within each unit. The beneficial effect of the present invention is that the current design and calculation process of drainage blind ditches basically uses finite element software to simulate and calculate their precipitation effects. This method is not simple and fast enough when making a preliminary rough estimate of the blind ditch's pressure reduction effect. The present invention proposes a simplified design method for drainage blind ditch networks, which greatly improves the efficiency of the preliminary design stage, shortens the calculation time, reduces the investment in labor costs, and provides a quick and reasonable reference for drainage blind ditch network design.

Description

Technical Field

[0001] The invention belongs to the technical field of civil engineering dewatering, and in particular relates to a simplified design method and system for grid water head distribution of drainage blind ditch. Background Art

[0002] As the area and depth of underground building structures become larger and larger, the anti-floating problem of underground structures becomes more and more prominent. In the construction or use of some large-scale underground projects, cases such as structural floating and bottom plate cracking caused by anti-floating problems have occurred frequently. [1-3] Conventional anti-floating measures, such as driving pullout piles and increasing heap loads, are too passive and may still fail in the event of a sudden increase in groundwater levels. Drainage blind ditches, combined with water-stop curtains, have played a significant role in some projects as a means of actively lowering the basement floor water level.

[0003] At present, there have been some reports on the research of analytical solutions of horizontal guide rail structures at home and abroad. [5,6] et al. established a dual-porosity model for the flow of leachate from a municipal solid waste landfill to a horizontal well. Through Laplace integral transformation and variable separation, they obtained an analytical solution for the leachate level drop under horizontal well drainage conditions. [7] Using the dual-porosity model, a three-dimensional semi-analytical solution for a finite-diameter horizontal well in a fractured shallow aquifer (i.e., underground aquifer and leaky confined aquifer) is derived. [8] et al. proposed an analytical solution for the hydraulic head distribution in an unconfined aquifer pumped from a single horizontal well parallel to the flow direction. On this basis, combined with Darcy's law, an expression for the river depletion rate was derived. [9,10] A correction to the flow equation for a horizontal well of finite length is proposed. This correction extends the confined flow equation so that the hydraulic head around the well can be estimated under unconfined conditions.

[11] After deriving the Laplace domain solution for the pressure drop caused by a point source in a uniform anisotropic unconfined aquifer, the point source solution was extended to the case of horizontal and inclined wells by applying the superposition principle and the numerical inverse Laplace transform method.

[12] et al. established a mathematical model and analytical solution for drainage of seepage ditches on both sides of the roadbed, and compared it with the simulation calculation results of Modflow software to verify the rationality of its analytical solution.

[13] Combining the characteristics of hydraulics and hydrodynamics in seepage calculation, the flow rate of single drainage blind ditch and double drainage blind ditch as well as the approximate calculation method of the highest water level in the site after setting the blind ditch are summarized.

[14] et al. established a seepage model for horizontal blind ditch drainage in landfills, obtained an analytical solution for the groundwater level infiltration line with blind ditch drainage, and provided a design method for the spacing of horizontal blind ditches.

[0004] However, the analytical solutions for horizontal seepage calculation given by the above scholars are only for one-dimensional flow, that is, one section is taken for calculation. There is insufficient research on the analytical solutions for calculating the head at any point in the drainage blind ditch network that crisscrosses on the plane.

[0005] At the same time, the current analysis and calculation methods used for drainage blind ditch networks are mainly numerical simulation methods such as finite element modeling. Zhao Jian and Shen Zhenzhong

[15] It is proposed to use drainage substructure to simulate the drainage body in numerical calculation, which improves the efficiency of computer seepage calculation of drainage structures such as drainage ditches in terms of the number of units and nodes.

[16] The influence of five drainage ditch layout types on the change and stability of the seepage field under the tailings dam was studied by using relevant finite element software.

[17] The substructure method was used in the finite element method to analyze the effect of vertical and horizontal drainage blind ditches on the seepage field during the tailings pond filling process. These numerical simulation methods are relatively complex and require a long time.

[0006] [1] Zeng Guoji, Wang Xianneng, Hu Daiwen. Analysis on the current status of application of anti-floating technical measures [J]. Underground Space, 2004, 01): 105-109+142.

[0007] [2] Gao Xianmin, Kong Hong. Application of water discharge and anti-floating technology in Shenzhen Metro Project [C] / / China Civil Engineering Society, Tunnel and Underground Engineering Branch of China Civil Engineering Society, Proceedings of the 15th Annual Conference of China Civil Engineering Society and the 17th Annual Conference of Tunnel and Underground Engineering Branch [C], Kunming, Yunnan, China: China Railway Southwest Research Institute Co., Ltd., 2012: 550-552.

[0008] [3] Xu Chunguo. Identification and reinforcement treatment of basement floating cracking accidents [J]. Building Structure, 2002, 11): 26-28.

[0009] [4]RPBeaven,SECox,W.Powrie.Operation and performance of horizontal wells for leachate control in a waste landfill[J].Journal ofGeotechnical and Geoenvironmental Engineering,2007,133(8):1040-1047.

[0010] [5]J.Hu,H.Ke,Y.M.Chen,X.B.Xu,H.Xu.Analytical analysis of the leachateflow to a horizontal well in dual-porosity media[J].Computers andGeotechnics,2021,134(104105.

[0011] [6]J.Hu,H.Ke,L.T.Zhan,Z.Y.Chen,J.W.Lan,W.Powrie,Y.M.Chen.Installationand performance of horizontal wells for dewatering at municipal solid wastelandfills in China[J].Waste Management,2020,103(159-168.

[0012] [7]E.Park,H.Zhan.Hydraulics of horizontal wells in fractured shallowaquifer systems[J].Journal of Hydrology,2003,281(1):147-158.

[0013] [8]C.S.Huang,Y.L.Chen,H.D.Yeh.A general analytical solution for flowto a single horizontal well by Fourier and Laplace transforms[J].Advances inWater Resources,2011,34(5):640-648.

[0014] [9]M.W.Kawecki.Transient Flow to a Horizontal Water Well[J].Groundwater,2000,38(6):842-850.

[0015]

[10] M.W.Kawecki,H.N.Al-Subaikhy.Unconfined linear flow to ahorizontal well[J].Ground Water,2005,43(4):606-610.

[0016]

[11] H.Zhan,VAZlotnik.Groundwater flow to a horizontal or slantedwell in an unconfined aquifer[J].Water Resources Research,2002,38(7):13-1-13-11.

[0017]

[12] Wei Yunjie, Xu Mo, Lu Shuqiang, Yang Yanna, Ren Jiaguo. Simulation study on internal drainage effect of western highway subgrade [J]. Chinese Journal of Geological Hazard and Control, 2003, 01): 34-38.

[0018]

[13] Zhou Hua, Wang Shaoli, Qu Xingye, Yang Jifu. Research and discussion on the calculation method of seepage flow in plain area[J]. Journal of Hydraulic Engineering, 2007, 08): 991-997.

[0019]

[14] Ye Jian, Lan Jiwu, Chen Yunmin, Ke Han, Wang Kehong. Seepage model and spacing design of horizontal drainage blind ditches in landfills[J]. Chinese Journal of Geotechnical Engineering, 2016, 38(10): 1923-1929.

[0020]

[15] Zhao Jian, Shen Zhenzhong. Improvement of seepage calculation method for complex drainage system of tailings dam [J]. Journal of Hohai University, 1997, 02): 112-115.

[0021]

[16] Han Yabing, Cui Xuan. Simulation analysis of the influence of drainage blind ditch layout on the seepage stability of a tailings dam [J]. Modern Mining, 2019, 35(09): 68-71.

[0022]

[17] Lu Ruili, Sun Dongpo, Wei Wei. Influence of drainage system on seepage field during tailings pond filling period[J]. Journal of Basic Science and Engineering, 2013, 21(03): 532-543. Summary of the Invention

[0023] The purpose of the present invention is to solve the technical defect that the design of drainage blind ditch network can only rely on simulation calculation through finite element software and lacks simplicity and speed, and proposes a simple calculation method for reasonably calculating the head distribution of drainage blind ditch network, simplifies the preliminary design of drainage blind ditch network, greatly improves the efficiency of the preliminary design stage, shortens the calculation time, reduces the investment of labor costs, and provides a quick and reasonable reference for the design of drainage blind ditch network.

[0024] To achieve the purpose of the present invention, the present invention provides a simplified design method for the water head distribution of a drainage blind ditch grid, wherein a hydrophobic layer is provided at the bottom of the blind ditch and the bottom plate, and the permeability coefficient of the hydrophobic layer is greater than that of the underlying soil layer. The method comprises the following steps:

[0025] Determine basic parameters;

[0026] The drainage blind ditch network includes multiple blind ditch rectangular units. The size and layout of the drainage blind ditch rectangular units are preliminarily designed.

[0027] Calculate the total decompression drainage volume of the blind ditch network according to the calculation method of the drainage decompression specification. The total drainage volume Q of the blind ditch includes the flow bypassing the water-stop curtain and the flow penetrating through the curtain to the other side.

[0028] According to the formation conditions, the infiltration distribution is determined, and the unit flow distribution coefficient η is calculated;

[0029] Calculate the unit infiltration of each blind ditch rectangular unit based on the unit flow distribution coefficient and the reduced pressure drainage volume;

[0030] Based on the above steps, the water head size at each location of the blind drainage ditch network is obtained;

[0031] By adjusting the size of the rectangular unit of the drainage blind ditch and the unit flow distribution coefficient η, the result can meet the preset verification conditions and the bottom plate head distribution can be obtained.

[0032] As a further solution of the present invention: the basic parameters include:

[0033] Groundwater level for site anti-floating defense h d , anti-floating design control water level h;

[0034] Geometric parameters: permeability coefficient K of the hydrophobic layer at the bottom of the area, permeability coefficient k of the weak permeable layer, permeability coefficient k of the water-stop curtain s , the thickness of the weak permeable layer on the non-excavation side T1, the thickness of the weak permeable layer on the excavation side T1', the thickness of the soil layer below the bottom of the cut-off wall T2, and the distance l between the anti-floating design control water level and the bottom of the wall.

[0035] As a further solution of the present invention, the size and arrangement of drainage blind ditch units are as follows:

[0036] The preliminary design of drainage blind ditch is half the length of the rectangular unit a and half the width of the rectangular unit b. The design principles are as follows:

[0037] The design principle of blind ditch unit size is different according to different stratum conditions. If the stratum below the bottom plate is a weak permeable layer sandwiched between a strong permeable layer (i.e. composite stratum conditions, see Figure 2), the bottom plate infiltration will be evenly distributed, and the blind ditches can be evenly spaced or unevenly spaced; if the lower stratum has no strong permeable layer (i.e. single stratum condition, see Figure 3 ), most of the infiltration is concentrated in the range of 1 to 1.5 times the thickness of the aquifer at the bottom of the pit from the curtain, and the spacing of the blind ditches should be reduced within this range and increased in the middle of the bottom plate.

[0038] As a further solution of the present invention: when determining the unit flow distribution coefficient η, the method for determining the unit flow distribution coefficient needs to be determined according to the formation conditions, which can be divided into composite formation conditions and single formation conditions:

[0039] 1) Under composite stratum conditions, when there is a highly permeable layer at the bottom of the base plate, the infiltration rate is considered to be uniformly distributed throughout the base plate, and η is taken as 1; S is taken as the sum of all unit areas, that is, the total area of ​​the base plate.

[0040] 2) Under single stratum conditions, the bottom plate infiltration is basically distributed within a range of 1.5 times the thickness of the aquifer at the bottom of the pit. The specific calculation formula is as follows:

[0041]

[0042] Where M is the thickness of the aquifer, s is the depth of the curtain embedment, and K' is the fill mold The first kind of complete elliptic integral, F = (φ, λ) is the first kind of incomplete elliptic integral, C is the integration constant, P is the ratio of the infiltration volume within the range x from the water-stop curtain to the total flow in the case of non-uniform infiltration, x is the distance from the water-stop curtain, q x is the flow rate per unit width from the water-stop curtain to the positive direction of x, q is the total flow rate per unit width, i is an imaginary number, and φ is λ is

[0043] As a further solution of the present invention, the calculation formula of the unit infiltration rate of the blind ditch is:

[0044]

[0045] Where p is the unit infiltration of the blind ditch, η is the flow distribution coefficient, and S is the sum of the partial unit areas.

[0046] The following example illustrates how to determine η and S: Let P(0.1,0.1) represent the calculated value of P when x / M = 0.1 and s / M = 0.1 in Table 1. Assuming a foundation pit with s / M = 0.3, then for all cells within the range x < 0.5 M, η = P(0.5,0.3) = 0.577, S is the sum of the areas of these cells, and p is obtained using the above formula. For cells within the range 0.5 M ≤ x < M, η = P(1,0.3) - P(0.5,0.3) = 0.236, S is the sum of the areas of these cells, and p is obtained using the above formula. The infiltration rates of the remaining cells can be calculated in the same way.

[0047] As a further solution of the present invention, the bottom plate head distribution calculation formula is:

[0048]

[0049] Where h(x, y) is the water head size at the position (x, y) of the blind ditch unit, a is half the length of the drainage blind ditch rectangular unit, b is half the width of the drainage blind ditch rectangular unit, K is the permeability coefficient of the hydrophobic layer at the bottom of the area, and D is the thickness of the hydrophobic layer. Figure 1 .

[0050] As a further solution of the present invention, the calculation results are verified to see whether they meet the following requirements:

[0051] h max κ≤h d (4)

[0052] where h max is the maximum water head of the bottom plate, κ is the safety factor greater than or equal to 1, h d Protect the site from the water table.

[0053] If the above formula is not satisfied, adjust the parameters a, b, and η so that the calculation result meets the requirements.

[0054] The present invention also provides a simplified design system for blind drainage ditch grid water head distribution for implementing the aforementioned simplified design method, the system comprising:

[0055] Preliminary design module, used to preliminarily design the size and layout of drainage blind ditch rectangular units;

[0056] The module for determining the total decompression drainage volume is used to calculate the total decompression drainage volume of the drainage blind ditch network according to the calculation method of the drainage decompression related specifications. The total drainage volume Q of the blind ditch includes the flow bypassing the water-stop curtain and the flow penetrating through the curtain to the other side.

[0057] The unit flow distribution coefficient determination module is used to determine the infiltration distribution according to the formation conditions, thereby calculating the unit flow distribution coefficient η;

[0058] The unit infiltration volume determination module calculates the unit infiltration volume of each blind ditch rectangular unit based on the unit flow distribution coefficient and the reduced pressure drainage volume;

[0059] The water head determination module is used to obtain the water head size at each location of the drainage blind ditch network;

[0060] Adjust the verification module to make the results meet the preset verification conditions by adjusting the size of the drainage blind ditch rectangular unit and the unit flow distribution coefficient η.

[0061] Compared with the prior art, the present invention can at least achieve the following beneficial effects:

[0062] The present invention can greatly improve the efficiency of the preliminary design stage of the drainage blind ditch network, shorten the calculation time, reduce the investment of manpower cost, and provide a quick and reasonable reference for the design of the drainage blind ditch network. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] Figure 1 This is a simplified model diagram of the blind ditch unit;

[0064] Figure 2 This is a schematic diagram of the composite soil layer;

[0065] Figure 3 This is a schematic diagram of the uniform layout of the drainage blind ditch network;

[0066] Figure 4 This is a schematic diagram of a single soil layer;

[0067] Figure 5 This is a schematic diagram of the uneven layout of the drainage blind ditch network;

[0068] Figure 6 Schematic diagram for calculating the amount of drainage and decompression;

[0069] Figure 7 This is a schematic diagram of the calculation results of the simplified algorithm for Example 1;

[0070] Figure 8 This is a schematic diagram of the calculation results of the simplified algorithm for Example 2;

[0071] Figure 9 This is a schematic diagram of the calculation results of the simplified algorithm for Example 3;

[0072] Figure 10 This is a schematic diagram of the finite element method calculation results for Example 1;

[0073] Figure 11 This is a schematic diagram of the finite element method calculation results for Example 2;

[0074] Figure 12 This is a schematic diagram of the finite element method calculation results for Example 3;

[0075] Figure 13 This is a flow chart of the simplified design method for water head distribution in drainage blind ditch networks. DETAILED DESCRIPTION

[0076] To further clarify the objectives, technical solutions, and advantages of the present invention, the example analysis of the present invention is clearly and completely described in conjunction with the accompanying drawings. It is obvious that the described embodiments are only a portion of the embodiments of the present invention, not all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0077] In actual engineering, underground structures are often located in two typical stratum environments: composite soil layer and single soil layer. The simplified method provided by the present invention is used to perform blind ditch design calculations for the two typical soil layers.

[0078] Calculation example 1

[0079] Drainage blind ditch grid in composite soil layer

[0080] See Figure 2 The foundation pit is located in a soil layer with average permeability, and there is a 5m thick highly permeable layer 5m away from the bottom of the base plate and connected to the distant place (i.e. composite stratum conditions).

[0081] In this case, due to the existence of a highly permeable layer, the flow is basically evenly distributed over the entire bottom plate area, and is not only concentrated within a certain range at the edge of the foundation pit.

[0082] The ground surface is the inflow boundary, and a storm head is applied, with the head value equal to the ground surface elevation. The permeability coefficient k1 of the weak permeable layer is taken as 2×10 -5 cm / s, water-stop curtain permeability coefficient k s Take 1×10 -7 cm / s, and the permeability coefficient k2 of the highly permeable layer and the hydrophobic layer is taken as 2×10 -3 cm / s.

[0083] For a foundation pit with a length of 100m, a width of 50m and a depth of 5m, a 0.5m thick hydrophobic layer is laid under the foundation pit, and a 1m thick water-stop curtain is set around the foundation pit. The water-stop curtain cuts through the strong permeable layer at the bottom of the pit, and the blind ditch is evenly arranged. Figure 3 .

[0084] Calculation example 2

[0085] Drainage ditch grid in a single soil layer (non-uniform arrangement)

[0086] See Figure 4 , the foundation pit is in a single soil layer.

[0087] In this case, most of the drainage is discharged by a certain range of drainage blind ditch grids on the edge;

[0088] The ground surface is the inflow boundary, and a storm head is applied, with the head value equal to the ground surface elevation. The soil permeability coefficient k is taken as 2×10 -5 cm / s, water-stop curtain permeability coefficient k s Take 1×10 -7 cm / s, and the permeability coefficient K of the hydrophobic layer is taken as 2×10 -3 cm / s.

[0089] For a foundation pit with a length of 100m, a width of 50m and a depth of 5m, a 0.5m thick hydrophobic layer is laid under the foundation pit, and a 1m thick water-stop curtain is set around the foundation pit. The water-stop curtain is 5m below the bottom of the bottom plate. The blind ditch arrangement plan is shown in Figure 5 .

[0090] Calculation example 3

[0091] Drainage ditch grid in a single soil layer (evenly arranged)

[0092] See Figure 4 , the foundation pit is in a single soil layer.

[0093] To calculate the safety of this method, this example assumes that the bottom plate flow is basically evenly distributed throughout the entire bottom plate area;

[0094] The ground surface is the inflow boundary, and a storm head is applied, with the head value equal to the ground surface elevation. The soil permeability coefficient k is taken as 2×10 -5 cm / s, water-stop curtain permeability coefficient k s Take 1×10 -7 cm / s, and the permeability coefficient K of the hydrophobic layer is taken as 2×10 -3 cm / s.

[0095] For a foundation pit with a length of 100m, a width of 50m and a depth of 5m, a 0.5m thick hydrophobic layer is laid under the foundation pit, and a 1m thick water-stop curtain is set around the foundation pit. The water-stop curtain is 5m below the bottom of the bottom plate. The blind ditch arrangement plan is shown in Figure 3 .

[0096] See also Figures 2 to 9 The present invention provides a simplified design method for water head distribution of a drainage blind ditch network, comprising the following steps:

[0097] Step 1: Determine the basic parameters.

[0098] In this step, the basic parameters to be determined include the groundwater level h of the site anti-floating defense d , anti-floating design controls water level h and geometric parameters.

[0099] The geometric parameters include: the permeability coefficient K of the hydrophobic layer at the bottom of the area, the permeability coefficient k of the weak permeable layer, and the permeability coefficient k of the water-stop curtain. s, the thickness of the weak permeable layer on the non-excavation side T1, the thickness of the weak permeable layer on the excavation side T1', the thickness of the soil layer below the bottom of the cut-off wall T2, and the distance l between the anti-floating design control water level and the bottom of the wall.

[0100] Step 2: The drainage blind ditch network includes multiple blind ditch rectangular units, and the size and layout of the drainage blind ditch rectangular units are preliminarily designed.

[0101] Different forms of drainage blind ditch network design are carried out according to different stratum conditions. The design principles of blind ditch unit size are different for different stratum conditions. If the stratum below the bottom plate is a weak permeable layer sandwiched between a strong permeable layer (i.e. composite stratum conditions, see Figure 2 ), the bottom plate infiltration will be evenly distributed, and the blind ditch rectangular units can be evenly arranged at equal intervals (of course, in other embodiments, they can also be arranged at different intervals); if the lower stratum has no strong permeable layer (i.e., single stratum conditions, see Figure 4 ), most of the infiltration is concentrated in the range of 1 to 1.5 times the thickness of the aquifer at the bottom of the pit from the water-stop curtain. The spacing of the rectangular units of the blind ditch should be reduced in this range and increased in the middle of the bottom plate.

[0102] In this step, half the length a of the rectangular unit of the drainage blind ditch and half the width b of the rectangular unit of the drainage blind ditch are preliminarily designed.

[0103] The specific layout of Example 1 is shown in Figure 3 , the blind ditch units are evenly spaced; the specific arrangement of Example 2 is shown in Figure 5 , the blind ditch units are arranged non-uniformly; the specific arrangement of Example 3 is shown in Figure 3 , the blind ditch units are evenly arranged at equal intervals.

[0104] Step 3: Calculate the reduced pressure drainage volume of the drainage blind ditch network.

[0105] In this step, according to the relevant standards for drainage decompression (South China University of Technology, Guangzhou Academy of Building Research Co., Ltd. T / CECS942-2021 Technical Specification for Decompression and Anti-floating of Underground Structure Water Supply and Drainage [S]. Beijing: China Architecture & Building Press, 2021), the decompression drainage volume is calculated as follows:

[0106]

[0107] in

[0108]

[0109]

[0110]

[0111]

[0112] Where Q is the total drainage volume of the entire blind ditch to reduce water pressure according to the anti-floating precipitation requirement. The total drainage volume Q of the blind ditch is composed of the flow bypassing the water-stop curtain and the flow penetrating through the water-stop curtain to the other side; d is the thickness of the cut-off wall; ζ a ,ζ b ,ζ c ,ζ w All are empirical coefficients; L is the perimeter of the basement, see Figure 6 .

[0113] Step 4: Determine the flow distribution coefficient of the blind ditch rectangular unit.

[0114] In some embodiments of the present invention, the infiltration distribution is determined according to the formation conditions, thereby calculating the unit flow distribution coefficient.

[0115] In the above example 1, under composite strata conditions, when a highly permeable layer exists in the soil at the bottom of the base plate, the infiltration volume is assumed to be evenly distributed throughout the base plate, and the unit flow distribution coefficient η is taken as 1. S is taken as the sum of all unit areas, that is, the total base plate area.

[0116] In the above example 2, under the condition of a single stratum, 85%-95% of the bottom plate infiltration is distributed within a range of 1.5 times the thickness of the aquifer at the bottom of the pit. The specific calculation formula is as follows:

[0117]

[0118] Where M is the thickness of the aquifer, s is the depth of the curtain embedment, and K' is the fill mold The first kind of complete elliptic integral, F = (φ, λ) is the first kind of incomplete elliptic integral, C is the integration constant, P is the ratio of the infiltration volume within the range x from the water-stop curtain to the total flow in the case of non-uniform infiltration, x is the distance from the water-stop curtain, q x is the flow rate per unit width from the water-stop curtain to the positive direction of x, q is the total flow rate per unit width, i is an imaginary number, and φ is λ is

[0119] It can be seen that when the formation parameters are determined, P is only related to the ratio of x to the aquifer thickness M and the ratio of the water-stop curtain embedding depth s to the aquifer thickness M.

[0120] By varying the values ​​of s and x and calculating the value of P, reference values ​​for the x-direction infiltration ratio are obtained, as shown in Table 1 (i.e., the unit flow distribution coefficient η). After multiple trial calculations, the flow distribution coefficient η for the rectangular blind ditch units located around the foundation pit (units A, B, and C) was set to 0.85, and the flow distribution coefficient η for the rectangular blind ditch unit located in the center of the foundation pit (unit D) was set to 0.15. This still ensures that the infiltration is evenly distributed within each unit. Specifically, when calculating the blind ditch unit infiltration for units ABC, the unit flow distribution coefficient η is set to 0.85, and S is the sum of the areas of units ABC. When calculating the blind ditch unit infiltration for unit D, the unit flow distribution coefficient η is set to 0.15, and S is the sum of the areas of unit D.

[0121] In the above example 3: This example assumes that the infiltration volume is evenly distributed throughout the entire base plate, so the unit flow distribution coefficient η is taken as 1; S is taken as the sum of all unit areas, that is, the total base plate area.

[0122] Table 1 Reference value table of infiltration volume in the x direction

[0123]

[0124] Step 5: Calculate the unit infiltration rate of the blind ditch.

[0125] In some embodiments of the present invention, the unit infiltration rate of each rectangular unit of the blind ditch is calculated based on the unit flow distribution coefficient and the reduced pressure drainage volume.

[0126] In some embodiments of the present invention, the formula for calculating the unit infiltration rate of the blind ditch is:

[0127]

[0128] Where p is the unit infiltration of the blind ditch, η is the unit flow distribution coefficient, and S is the sum of the partial unit areas.

[0129] The following example illustrates how to determine η and S: Let P(0.1,0.1) represent the calculated value of P when x / M = 0.1 and s / M = 0.1 in Table 1. Assuming a foundation pit with s / M = 0.3, then for all cells within the range x < 0.5 M, η = P(0.5,0.3) = 0.577, S is the sum of the areas of these cells, and p is obtained using the above formula. For cells within the range 0.5 M ≤ x < M, η = P(1,0.3) - P(0.5,0.3) = 0.236, S is the sum of the areas of these cells, and p is obtained using the above formula. The infiltration rates of the remaining cells can be calculated in the same way.

[0130] Step 6: Calculate the bottom plate head distribution.

[0131] Using the calculation results of the above steps and the derived calculation formula, the water head size at each location of the drainage blind ditch network is calculated.

[0132] The calculation formula for the bottom plate head distribution is:

[0133]

[0134] Where h(x, y) is the water head size at the position (x, y) of the blind ditch unit, a is half the length of the drainage blind ditch rectangular unit, b is half the width of the drainage blind ditch rectangular unit, K is the permeability coefficient of the hydrophobic layer at the bottom of the area, and D is the thickness of the hydrophobic layer. Figure 1 . m is a positive integer.

[0135] In some embodiments of the present invention, the simplified calculation formula converges very quickly, and the results are basically stable starting from m=2. In actual calculations, it is recommended to take m=3.

[0136] Step 7: Verification and parameter adjustment.

[0137] In some embodiments of the present invention, it is necessary to verify whether the calculation results meet the following requirements:

[0138] h max κ≤h d (4)

[0139] where h max is the maximum water head of the bottom plate, κ is the safety factor greater than or equal to 1, h d Protect the site from the water table.

[0140] If the above formula is not satisfied, adjust the parameters a, b, and η so that the calculation results meet the requirements.

[0141] In the actual calculation of the simplified algorithm, the geometric parameters are all given and have limited room for adjustment. Parameters a and b represent the plane layout of the blind ditch, η represents the distribution of infiltration, and the calculated head distribution and the unit maximum head value h max The influence is great, so the appropriate results are mainly obtained by adjusting a, b, and η.

[0142] In the finite element simulation, the geometric parameters are the same as above, and the outlet elevation h0 is generally slightly lower than the control water level h d .

[0143] The calculation results of the above example obtained by the method of the present invention are shown in Figures 7-8 :

[0144] The calculation results of Example 1 are shown in Figure 7 ;

[0145] The results of Example 2 are shown in Figure 8 ;

[0146] The calculation results of Example 3 are shown in Figure 9 .

[0147] The finite element calculation results obtained by the finite element method in the above example are shown in Figures 10-12 :

[0148] The calculation results of Example 1 are shown in Figure 10 ;

[0149] The results of Example 2 are shown in Figure 11 ;

[0150] The calculation results of Example 3 are shown in Figure 12 .

[0151] Analysis of the results of each case:

[0152] 1) Example 1: The total drainage volume Q = 23.79 m obtained by the simplified method provided by the present invention 3 The total displacement Q obtained by finite element modeling is 24.45m 3 , the relative error is 2.69%, which shows that the simplified flow calculation provided by the present invention has a high accuracy. On the whole, the head distributions calculated by the two methods are very similar, and the nine unit head distributions are basically the same, which is consistent with the assumption that the infiltration volume is evenly distributed on the entire bottom plate. The effective reduction value of the unit bottom plate head of the simplified method provided by the present invention is 4.817m, and the average effective reduction value of the nine unit bottom plate heads of the finite element method is 4.859m. In this case, the relative error between the two is also very small, only 0.87%. At the same time, the maximum head of the bottom plate calculated by the simplified method of the present invention is too high, and the result is on the safe side in terms of the estimation angle of the pressure reduction effect.

[0153] 2) Example 2: The total drainage volume Q = 14.58 m obtained by the simplified method provided by the present invention 3 The total displacement Q obtained by finite element modeling is 15.635m 3 , with a relative error of 6.7%. The bottom plate head distribution trend obtained by the simplified method of the present invention is basically consistent with the finite element results. The blind ditches of the units around the foundation pit are densely distributed, and the head is lower. The blind ditch spacing of the central unit is larger, and the head is higher than that of the surrounding units. In the simplified method, the effective head reduction values ​​of unit A, unit B, unit C and unit D are 4.911m, 4.932m, 4.931m, and 4.959m respectively; in the finite element method, the effective head reduction values ​​of unit A, unit B, unit C and unit D are 4.925m, 4.968m, 4.966m, and 4.973m respectively; the relative errors of each unit are only 0.28%, 0.69%, 0.72%, and 0.28%. It can be seen that the effective head reduction value of the bottom plate obtained by the simplified method of the present invention is very close to the result of the finite element method, and the bottom plate head after decompression is slightly higher than that of the finite element method, and the calculation result is safe.

[0154] 3) Example 3: Results obtained using the method of this invention show that the hydraulic head distribution of each blind ditch unit after decompression is consistent. Finite element analysis shows that the unit at the center of the foundation pit experiences almost no water pressure after decompression, while the water pressure on the bottom plate of the peripheral units is significantly higher than that of the central unit. Furthermore, the maximum hydraulic head values ​​of the bottom plate obtained by the simplified method within the unit at all four locations are greater than those obtained by the finite element method. This shows that directly calculating the uniform infiltration rate under these soil conditions is safe for decompression design, but it is also overly conservative and detrimental to the economic efficiency of the design.

[0155] The present invention also provides a simplified design system for water head distribution in a blind drainage ditch grid, for implementing the aforementioned method, the system comprising:

[0156] Preliminary design module, used to preliminarily design the size and layout of drainage blind ditch rectangular units;

[0157] The module for determining the total decompression drainage volume is used to calculate the total decompression drainage volume of the drainage blind ditch network according to the calculation method of the drainage decompression related specifications. The total drainage volume Q of the blind ditch includes the flow bypassing the water-stop curtain and the flow penetrating through the curtain to the other side.

[0158] The unit flow distribution coefficient determination module is used to determine the infiltration distribution according to the formation conditions, thereby calculating the unit flow distribution coefficient η;

[0159] The unit infiltration volume determination module calculates the unit infiltration volume of each blind ditch rectangular unit based on the unit flow distribution coefficient and the reduced pressure drainage volume;

[0160] The water head determination module is used to obtain the water head size at each location of the drainage blind ditch network;

[0161] Adjust the verification module to make the results meet the preset verification conditions by adjusting the size of the drainage blind ditch rectangular unit and the unit flow distribution coefficient η.

[0162] The precondition for the application of this method is that a hydrophobic layer must be provided at the bottom of the blind ditch and the bottom plate, and the permeability coefficient of the hydrophobic layer must be much greater than that of the underlying soil layer. The presence of a hydrophobic layer can ensure uniform distribution of infiltration within the blind ditch unit, ensuring the accuracy of the simplified algorithm results.

[0163] Finally, it should be noted that the present invention is not limited to the details of the exemplary embodiments described above and that the invention may be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, those skilled in the art should regard the embodiments as illustrative and non-limiting. The scope of the present invention is defined by the appended claims, not the foregoing description, and all variations within the meaning and range of equivalents of the claims are intended to be encompassed therein. Any reference sign in a claim should not be construed as limiting the claim to which it relates.

[0164] In addition, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A simplified design method for drainage blind ditch grid water head distribution, characterized in that: A hydrophobic layer is provided at the bottom of the blind ditch and the bottom plate, and the permeability coefficient of the hydrophobic layer is much greater than that of the underlying soil layer. The method comprises the following steps: Determine basic parameters; The drainage blind ditch network includes multiple blind ditch rectangular units. The size and layout of the drainage blind ditch rectangular units are preliminarily designed. Calculate the total decompression drainage volume of the blind ditch network according to the calculation method of the drainage decompression specification. The total drainage volume Q of the blind ditch includes the flow bypassing the water-stop curtain and the flow penetrating through the curtain to the other side. According to the formation conditions, the infiltration distribution is determined, and the unit flow distribution coefficient η is calculated; Calculate the unit infiltration of each blind ditch rectangular unit based on the unit flow distribution coefficient and the reduced pressure drainage volume; Based on the above steps, the water head size at each location of the blind drainage ditch network is obtained; By adjusting the size of the rectangular unit of the drainage blind ditch and the unit flow distribution coefficient η, the result can meet the preset verification conditions and obtain the bottom plate head distribution; The calculation formula for the bottom plate head distribution is: Where h(x, y) is the water head size at the position (x, y) of the blind ditch unit, a is half the length of the drainage blind ditch rectangular unit, b is half the width of the drainage blind ditch rectangular unit, K is the permeability coefficient of the hydrophobic layer at the bottom of the area, and D is the thickness of the hydrophobic layer. is a positive integer, is the unit infiltration rate of the blind ditch.

2. A simplified design method for water head distribution in a blind drainage ditch grid according to claim 1, characterized in that: The basic parameters include the groundwater level h of the site anti-floating defense d , anti-floating design controls water level h and geometric parameters.

3. A simplified design method for water head distribution of blind drainage ditch grid according to claim 2, characterized in that: The geometric parameters include: the permeability coefficient K of the hydrophobic layer at the bottom of the area, the permeability coefficient k of the weak permeable layer, and the permeability coefficient k of the water-stop curtain. s , the thickness of the weak permeable layer on the non-excavation side T1, the thickness of the weak permeable layer on the excavation side T1 ’ , the thickness of the soil layer below the bottom of the cut-off wall T2, and the distance l between the anti-floating design control water level and the bottom of the wall.

4. A simplified design method for water head distribution in a blind drainage ditch grid according to claim 1, characterized in that: In the arrangement of the blind ditch rectangular units, if the stratum below the bottom plate is a weakly permeable layer sandwiched between a highly permeable layer, that is, a composite stratum condition, the bottom plate infiltration will be evenly distributed, and the blind ditch rectangular units will be evenly spaced, or unevenly spaced. If the lower stratum does not have a highly permeable layer, that is, a single stratum condition, most of the infiltration is concentrated in the range of 1 to 1.5 times the thickness of the pit bottom aquifer from the curtain, and the spacing of the blind ditch rectangular units in this range is smaller than the spacing at the corresponding position in the middle of the bottom plate.

5. A simplified design method for water head distribution in a blind drainage ditch grid according to claim 4, characterized in that: The unit flow distribution coefficient is determined according to the formation conditions. Under composite formation conditions, when there is a highly permeable layer in the soil at the bottom of the bottom plate, it is assumed that the infiltration volume is evenly distributed throughout the entire bottom plate. The unit flow distribution coefficient η is taken as 1, and S is taken as the sum of all unit areas, that is, the total area of ​​the bottom plate. Under single formation conditions, the bottom plate infiltration volume is basically distributed within a range of 1.5 times the thickness of the aquifer at the bottom of the pit. The unit flow distribution coefficient is determined by the P value. The specific calculation formula of the P value is: Where M is the thickness of the aquifer, s is the depth of the curtain embedment, and K' is the depth of the fill mold. The total elliptic integral of the first kind, is the first kind of incomplete elliptic integral, C is the integral constant, P is the ratio of the infiltration volume within the range x from the water-stop curtain to the total flow in the case of non-uniform infiltration, is the distance from the water-stop curtain, To stop the water curtain Single width flow in the positive direction, is the total single-width flow, is an imaginary number, for , for .

6. A simplified design method for water head distribution in a blind drainage ditch grid according to claim 1, characterized in that: The calculation formula for the total decompression drainage of the drainage blind ditch network is: Where Q is the total drainage volume of the entire blind ditch, d is the thickness of the cut-off wall, L is the perimeter of the basement, 、 、 、 are all empirical coefficients, k s is the permeability coefficient of the water-stop curtain, and k is the permeability coefficient of the weak permeable layer.

7. The simplified design method for water head distribution of blind drainage ditch grid according to claim 1 is characterized in that: The calculation formula for the unit infiltration of the blind ditch is: Where p is the unit infiltration of the blind ditch, η is the flow distribution coefficient, S is the sum of the partial unit areas, and Q is the total drainage volume of the entire blind ditch drainage pressure relief.

8. A simplified design method for water head distribution in a blind drainage ditch grid according to any one of claims 1 to 7, characterized in that: The preset verification conditions are: Where h max is the maximum water head of the bottom plate, is a safety factor greater than or equal to 1, h d Protect the site from the water table.

9. A simplified design system for drainage blind ditch grid water head distribution, characterized by: For implementing the simplified design method according to any one of claims 1 to 8, the system comprises: Preliminary design module, used to preliminarily design the size and layout of drainage blind ditch rectangular units; The module for determining the total decompression drainage volume is used to calculate the total decompression drainage volume of the drainage blind ditch network according to the calculation method of the drainage decompression related specifications. The total drainage volume Q of the blind ditch includes the flow bypassing the water-stop curtain and the flow penetrating through the curtain to the other side. The unit flow distribution coefficient determination module is used to determine the infiltration distribution according to the formation conditions, thereby calculating the unit flow distribution coefficient η; The unit infiltration volume determination module calculates the unit infiltration volume of each blind ditch rectangular unit based on the unit flow distribution coefficient and the reduced pressure drainage volume; The water head determination module is used to obtain the water head size at each location of the drainage blind ditch network; Adjust the verification module to make the results meet the preset verification conditions by adjusting the size of the drainage blind ditch rectangular unit and the unit flow distribution coefficient η.

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