A deep foundation pit horizontal sealing bottom thickness and precipitation height combined optimization method

Abstract

The present invention belongs to the technical field of foundation pit water-proof control, and specifically discloses a method for jointly optimizing the horizontal bottom seal thickness and the dewatering height of a deep foundation pit. In the construction of the joint optimization model of the horizontal bottom seal thickness and the dewatering height, the relationship between the horizontal bottom seal thickness and the dewatering height caused by instability damage and seepage damage is considered, and the total surface settlement caused by dewatering outside the pit and foundation pit excavation construction is introduced into the total settlement of the foundation pit dewatering construction. The pit bottom safety constraint considering the horizontal bottom seal thickness, the surrounding environment settlement constraint considering the total surface settlement, and the precipitation constraint considering the precipitation amount are used as constraint conditions, and the objective function is solved to achieve the joint optimization of the horizontal bottom seal thickness and the precipitation amount. The horizontal bottom seal optimized by this method has good seepage-proof performance and better economy, and the precipitation height effectively meets the environmental protection requirements.

Description

Technical Field

[0001] The present invention belongs to the technical field of foundation pit water isolation control, and in particular relates to a method for jointly optimizing the horizontal bottom sealing thickness and dewatering height of a deep foundation pit. Background Art

[0002] When excavating foundation pits in deep, water-rich soft soil, the presence of dense and thick groundwater creates difficulties in excavation and support. To ensure safe excavation in deep, water-rich strata, pit dewatering is the most widely used method. However, deep pit dewatering can sometimes have a significant impact on the surrounding environment. To minimize this impact, vertical water curtains are often used to control water flow.

[0003] However, for deep, water-rich strata, using only precipitation and vertical waterproof curtains will lead to problems such as excessive precipitation, making precipitation difficult, and excessive surface settlement. Therefore, in order to avoid excessive groundwater extraction and reduce the impact of precipitation on the surrounding environment, the engineering project often uses a combination of horizontal bottom sealing and precipitation design and construction at the bottom of the foundation pit. The existing technology lacks an effective combined design method, resulting in excessive precipitation height affecting the surrounding environment or the horizontal bottom sealing being unable to effectively isolate water. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the defect in the prior art that it is difficult to effectively combine the design of horizontal bottom sealing and dewatering for foundation pit construction in deep water-rich strata, resulting in poor water-isolating efficiency, thereby providing a method for jointly optimizing the thickness of the horizontal bottom sealing and dewatering height of deep foundation pits.

[0005] The present invention discloses a method for jointly optimizing the thickness of the horizontal bottom seal of a deep foundation pit and the height of a water drop, comprising the following steps:

[0006] Based on the distance between the groundwater level and the bottom of the foundation pit and the excavation width of the foundation pit, calculate the relationship between the thickness of the horizontal bottom seal and the distance from the bottom of the foundation pit. Based on the relationship between the thickness of the horizontal bottom seal and the distance from the bottom of the foundation pit, calculate the relationship between the thickness of the horizontal bottom seal and the height of the water level.

[0007] Based on the allowable unit seepage volume of the horizontal bottom seal and the excavation width of the foundation pit, calculate the relationship between the thickness of the horizontal bottom seal considering seepage damage and the distance from the horizontal bottom seal to the bottom of the foundation pit; based on the relationship between the thickness of the horizontal bottom seal considering seepage damage and the distance from the horizontal bottom seal to the bottom of the foundation pit, calculate the relationship between the thickness of the horizontal bottom seal considering seepage damage and the precipitation height;

[0008] The total surface settlement caused by dewatering outside the pit is calculated based on the effective stress increment of the soil. The effective stress increment of the soil includes the effective stress change in the dewatering area after dewatering outside the pit and the additional stress caused by seepage in the saturated area. The total surface settlement caused by dewatering outside the pit and the surface settlement caused by foundation pit excavation construction are recorded as the total settlement of foundation pit dewatering construction.

[0009] Establish a joint optimization model for horizontal bottom seal thickness and dewatering height, including the relationship between horizontal bottom seal thickness and dewatering height considering instability damage, the relationship between horizontal bottom seal thickness and dewatering height considering seepage damage, and the total settlement of foundation pit dewatering construction;

[0010] Establishing constraints, including pit bottom safety constraints, surrounding environmental settlement constraints, and precipitation constraints; the pit bottom safety constraints require that the horizontal bottom thickness be greater than or equal to the horizontal bottom thickness considering instability damage and the horizontal bottom thickness considering seepage damage; the surrounding environmental settlement constraints require that the total settlement of the foundation pit dewatering construction be less than or equal to the preset environmental allowable settlement; and the precipitation constraint requires that the precipitation be less than or equal to the preset environmental allowable precipitation;

[0011] An objective function is established based on the joint optimization model of the horizontal bottom cover thickness and precipitation height, and the objective function satisfies the constraints to minimize the horizontal bottom cover thickness; and a final horizontal bottom cover thickness and final precipitation are obtained by calculation and solution based on the objective function.

[0012] Furthermore, the calculation method considering the relationship between the horizontal bottom cover thickness and the precipitation height for instability damage includes:

[0013] Based on the distance between the groundwater level and the bottom of the foundation pit and the excavation width of the foundation pit, calculate the relationship between the thickness of the horizontal bottom seal and the distance from the bottom of the foundation pit considering instability:

[0014] ;

[0015] in, h s Indicates the distance from the horizontal bottom cover to the bottom of the foundation pit. h g Indicates the thickness of the horizontal back cover. h w Indicates the distance between the groundwater level and the bottom of the foundation pit excavation; B Indicates the excavation width of the foundation pit; x Indicates the sudden surge safety factor of the foundation pit; c s Indicates the saturated density of the soil above the horizontal bottom cover, c g Indicates the weight of the horizontal back cover. c w Indicates the weight of water; g is the preset empirical coefficient; q u Indicates the uniaxial compressive strength of the horizontal bottom cover;

[0016] Based on the relationship between the thickness of the horizontal bottom seal and the distance from the bottom of the foundation pit considering instability damage, and the calculation formula of the groundwater level after and before precipitation considering the change of groundwater level caused by precipitation outside the pit, the relationship between the thickness of the horizontal bottom seal and the precipitation height considering instability damage is calculated:

[0017] ;

[0018] in, h eu Indicates the water level outside the pit before precipitation, Δ h u Indicates the depth of precipitation outside the pit.

[0019] Furthermore, the calculation method considering the relationship between the horizontal bottom seal thickness and the precipitation height for seepage damage includes:

[0020] Based on the allowable unit seepage volume of the horizontal bottom seal and the excavation width of the foundation pit, calculate the relationship between the thickness of the horizontal bottom seal and the distance from the bottom of the foundation pit considering seepage damage:

[0021] ;

[0022] in,[ q ] represents the permissible unit water seepage of the horizontal bottom cover; k u represents the equivalent permeability coefficient of the soil outside the foundation pit, k i and M i Indicates the i Soil permeability coefficient; c g ´ Indicates the floating weight of the horizontal bottom cover, c s ´ Indicates the floating density of the original soil layer;

[0023] Based on the relationship between the thickness of the horizontal bottom seal and the distance from the bottom of the foundation pit considering seepage damage, the calculation formula for the groundwater level after and before precipitation due to groundwater level changes caused by precipitation outside the pit, and the calculation formula for the floating density of the horizontal bottom seal and the original soil layer, the relationship between the thickness of the horizontal bottom seal and the precipitation height considering seepage damage is calculated:

[0024] ;

[0025] in, heu Indicates the water level outside the pit before precipitation, Δ h u Indicates the depth of precipitation outside the pit.

[0026] Furthermore, the calculation method considering the relationship between the horizontal bottom seal thickness and the precipitation height for seepage damage includes:

[0027] Based on the dewatering depth outside the pit, the thickness of the horizontal bottom seal, and the distance between the top of the horizontal bottom seal and the bottom of the foundation pit, a calculation formula for the groundwater level after dewatering and the groundwater level before dewatering is established, which takes into account the changes in the groundwater level caused by dewatering outside the pit:

[0028] ;

[0029] ;

[0030] in, h eu Indicates the water level outside the pit before precipitation; h u Indicates the water level outside the pit after precipitation; Δ h u Indicates the depth of precipitation outside the pit; h g Indicates the horizontal bottom cover thickness, h s Indicates the distance between the top of the horizontal bottom seal and the bottom of the foundation pit; h w Indicates the distance between the water level outside the pit and the bottom of the foundation pit after precipitation.

[0031] Furthermore, the calculation method considering the relationship between the horizontal bottom seal thickness and the precipitation height for seepage damage includes:

[0032] Based on the saturated density of the soil above the horizontal bottom cover, the density of the horizontal bottom cover and the density of water, the calculation formula for the floating density of the horizontal bottom cover and the original soil layer is established:

[0033] ;

[0034] in, c s Indicates the saturated density of the soil above the horizontal bottom cover, c g Indicates the weight of the horizontal back cover. c w Indicates the weight of water.

[0035] Furthermore, the calculation method of the total settlement of the foundation pit dewatering construction includes:

[0036] Calculate the surface settlement caused by foundation pit excavation construction, and record the total surface settlement caused by dewatering outside the pit and the surface settlement caused by foundation pit excavation construction as the total settlement of foundation pit dewatering construction;

[0037] Calculate the total surface settlement caused by dewatering outside the pit based on the soil effective stress increment, which includes the effective stress change in the dewatering area after dewatering outside the pit and the additional stress caused by seepage in the saturated area;

[0038] Calculate the stress change of soil in the drainage area due to self-weight after dewatering outside the pit, including the total stress of soil in the drainage area , pore water pressure and effective stress change :

[0039] ;

[0040] ;

[0041] ;

[0042] in, h 0 means the depth of groundwater level. y Indicates the depth of the unit body in the drainage area, c 0 represents the natural density of soil above the groundwater level. c 1 represents the weight of the soil after pumping water, c sat Indicates the saturated density of soil.

[0043] Furthermore, the calculation method of the total settlement of the foundation pit dewatering construction includes:

[0044] Based on the dewatering funnel curve of the foundation pit, the additional stress caused by seepage in the saturated zone after dewatering outside the pit is calculated:

[0045] ;

[0046] Where D represents the permeability of the unit soil, y represents the depth of the unit soil below the drainage area, and H(x) represents the coordinate depth of the precipitation funnel curve corresponding to the unit soil below the drainage area.

[0047] Establish the precipitation funnel curve of the foundation pit:

[0048] ;

[0049] in, H ( 0 ) represents the height of the foundation pit groundwater level from the impermeable layer before dewatering outside the pit. H ( t ) indicates precipitation time tThe height of the groundwater level in the foundation pit from the impermeable layer, F (λ) represents the groundwater influence coefficient.

[0050] Furthermore, the safety constraints at the pit bottom are:

[0051] ;

[0052] in,[ h g ] l Indicates the designed horizontal back cover thickness, max[ h g ] represents the maximum value of the horizontal bottom thickness considering instability damage and the horizontal bottom thickness considering penetration damage;

[0053] The surrounding environment settlement constraints are:

[0054] ;

[0055] in,[ W x ] l represents the total settlement of the designed foundation pit dewatering construction, [ W ax ] indicates the preset allowable settlement of the environment;

[0056] The precipitation constraints are:

[0057] ;

[0058] in,[ Q ] l represents the designed precipitation, [ Q ax ] indicates the preset environment's allowable precipitation.

[0059] Furthermore, the objective function is expressed as:

[0060] ;

[0061] in, I represents the solution region, h g It represents the horizontal bottom thickness considering instability damage, h g ´ represents the horizontal bottom cover thickness considering penetration damage, and δ(h) represents the Kronecker δ function.

[0062] Furthermore, the objective function of the joint optimization model of the horizontal bottom cover thickness and the precipitation height is established and solved by the trial and error iterative method.

[0063] Beneficial effect: The present invention discloses a joint optimization method for the horizontal bottom seal thickness and the dewatering height of a deep foundation pit. In the construction of the joint optimization model of the horizontal bottom seal thickness and the dewatering height, the relationship between the horizontal bottom seal thickness and the dewatering height due to instability damage and seepage damage is considered, and the total surface settlement caused by dewatering outside the pit and the foundation pit excavation construction is introduced into the total settlement of the foundation pit dewatering construction. The pit bottom safety constraint considering the horizontal bottom seal thickness, the surrounding environment settlement constraint considering the total surface settlement, and the precipitation constraint considering the precipitation amount are used as constraint conditions, and the objective function is solved to achieve the joint optimization of the horizontal bottom seal thickness and the precipitation amount. The horizontal bottom seal optimized by this method has good seepage-proof performance and good economy, and the precipitation height effectively meets the environmental protection requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0065] Figure 1 Schematic diagram of the method flow of the present invention;

[0066] Figure 2 This is a schematic diagram of the horizontal bottom sealing structure of the foundation pit of the present invention;

[0067] Figure 3 This is a schematic diagram of the foundation pit dewatering funnel curve of the present invention;

[0068] Figure 4 Schematic diagram of the model solving method of the present invention. DETAILED DESCRIPTION

[0069] To make the above-mentioned objects, features, and advantages of the present application more clearly understood, the specific embodiments of the present application are described in detail below with reference to the accompanying drawings. The following description sets forth many specific details to facilitate a full understanding of the present application. However, the present application can be implemented in many other ways than those described herein, and those skilled in the art can make similar improvements without violating the scope of the present application. Therefore, the present application is not limited to the specific embodiments disclosed below.

[0070] In the description of the present application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0071] In this embodiment, the foundation pit is a long, completely symmetrical foundation pit, and the influence of the three-dimensional structure is ignored. The foundation pit problem is regarded as a two-dimensional plane strain problem. At the same time, the friction between the horizontal reinforcement body and the adjacent retaining structure is not considered, and it is assumed that the horizontal bottom rotary grouting reinforcement body obeys the Tresca yield criterion; and it is believed that the horizontal water-stop curtain reinforcement body and the ground-connected wall can form a good anti-seepage sealing system, and the influence of precipitation in the foundation pit on the external stratum deformation of the foundation pit can be ignored. Therefore, the external stratum deformation of the foundation pit is divided into two parts: the influence of precipitation outside the pit and the influence of foundation pit excavation.

[0072] Reference Figure 1 and Figure 2 and Figure 3 As shown, the present invention discloses a method for jointly optimizing the thickness of the horizontal bottom cover of a deep foundation pit and the dewatering height, comprising the following steps:

[0073] Step S1: Based on the distance between the groundwater level and the bottom surface of the foundation pit excavation and the excavation width of the foundation pit, the relationship between the thickness of the horizontal bottom cover considering instability damage and the distance between the horizontal bottom cover and the bottom of the foundation pit is calculated; based on the relationship between the thickness of the horizontal bottom cover considering instability damage and the distance between the horizontal bottom cover and the bottom of the foundation pit, the relationship between the thickness of the horizontal bottom cover considering instability damage and the dewatering height is calculated;

[0074] Step S2: Based on the allowable unit seepage rate of the horizontal bottom seal and the excavation width of the foundation pit, the relationship between the thickness of the horizontal bottom seal considering seepage damage and the distance between the horizontal bottom seal and the bottom of the foundation pit is calculated; based on the relationship between the thickness of the horizontal bottom seal considering seepage damage and the distance between the horizontal bottom seal and the bottom of the foundation pit, the relationship between the thickness of the horizontal bottom seal considering seepage damage and the precipitation height is calculated;

[0075] Step S3: Calculate the total surface settlement caused by dewatering outside the pit based on the soil effective stress increment, where the soil effective stress increment includes the effective stress change in the dewatering area after dewatering outside the pit and the additional stress caused by seepage in the saturated area; record the total surface settlement caused by dewatering outside the pit and the surface settlement caused by foundation pit excavation as the total settlement of foundation pit dewatering construction;

[0076] Step S4: establishing a joint optimization model of horizontal bottom seal thickness and dewatering height, including the relationship between horizontal bottom seal thickness and dewatering height considering instability damage, the relationship between horizontal bottom seal thickness and dewatering height considering seepage damage, and the total settlement of foundation pit dewatering construction;

[0077] Step S5: Establishing constraint conditions, including pit bottom safety constraints, surrounding environment settlement constraints, and precipitation constraints; the pit bottom safety constraints require that the horizontal bottom thickness is greater than or equal to the horizontal bottom thickness considering instability damage and the horizontal bottom thickness considering seepage damage; the surrounding environment settlement constraints require that the total settlement of the foundation pit dewatering construction is less than or equal to the preset environmental allowable settlement; and the precipitation constraint requires that the precipitation is less than or equal to the preset environmental allowable precipitation;

[0078] Step S6: establishing an objective function based on the joint optimization model of the horizontal bottom cover thickness and precipitation height, wherein the objective function satisfies the constraint conditions and minimizes the horizontal bottom cover thickness; and calculating and solving based on the objective function to obtain the final horizontal bottom cover thickness and the final precipitation.

[0079] Specifically, in step S1, the calculation method considering the relationship between the horizontal bottom cover thickness and the precipitation height in terms of instability damage includes:

[0080] Based on the distance between the groundwater level and the bottom of the foundation pit and the excavation width of the foundation pit, calculate the relationship between the thickness of the horizontal bottom seal and the distance from the bottom of the foundation pit considering instability:

[0081] ;

[0082] in, h s Indicates the distance from the horizontal bottom cover to the bottom of the foundation pit. h g Indicates the thickness of the horizontal back cover. h w Indicates the distance between the groundwater level and the bottom of the foundation pit excavation; B Indicates the excavation width of the foundation pit; x Indicates the sudden surge safety factor of the foundation pit; c s Indicates the saturated density of the soil above the horizontal bottom cover, c g Indicates the weight of the horizontal back cover. c w Indicates the weight of water; g is the preset empirical coefficient; q u Indicates the uniaxial compressive strength of the horizontal bottom cover;

[0083] Based on the relationship between the thickness of the horizontal bottom seal and the distance from the bottom of the foundation pit considering instability damage, and the calculation formula of the groundwater level after and before precipitation considering the change of groundwater level caused by precipitation outside the pit, the relationship between the thickness of the horizontal bottom seal and the precipitation height considering instability damage is calculated:

[0084] ;

[0085] in, h eu Indicates the water level outside the pit before precipitation, Δ h u Indicates the depth of precipitation outside the pit.

[0086] In step S1, the calculation method for the relationship between the horizontal bottom cover thickness and the precipitation height considering the penetration damage includes:

[0087] Based on the allowable unit seepage volume of the horizontal bottom seal and the excavation width of the foundation pit, calculate the relationship between the thickness of the horizontal bottom seal and the distance from the bottom of the foundation pit considering seepage damage:

[0088] ;

[0089] in,[ q ] represents the permissible unit water seepage of the horizontal bottom cover; k u represents the equivalent permeability coefficient of the soil outside the foundation pit, k i and M i Indicates the i Soil permeability coefficient; c g ´ Indicates the floating weight of the horizontal bottom cover, c s ´ Indicates the floating density of the original soil layer;

[0090] In this embodiment, k u Expressed as ,in k i and M i For the i Soil permeability coefficient.

[0091] Based on the relationship between the thickness of the horizontal bottom seal and the distance from the bottom of the foundation pit considering seepage damage, the calculation formula for the groundwater level after and before precipitation due to groundwater level changes caused by precipitation outside the pit, and the calculation formula for the floating density of the horizontal bottom seal and the original soil layer, the relationship between the thickness of the horizontal bottom seal and the precipitation height considering seepage damage is calculated:

[0092] ;

[0093] in, h eu Indicates the water level outside the pit before precipitation, Δ h u Indicates the depth of precipitation outside the pit.

[0094] Among them, based on the dewatering depth outside the pit, the thickness of the horizontal bottom seal, and the distance between the top of the horizontal bottom seal and the bottom of the foundation pit, the calculation formula for the groundwater level after dewatering and the groundwater level before dewatering is established, which takes into account the changes in the groundwater level caused by dewatering outside the pit:

[0095] ;

[0096] ;

[0097] in, h eu Indicates the water level outside the pit before precipitation; h u Indicates the water level outside the pit after precipitation; Δ h u Indicates the depth of precipitation outside the pit; h g Indicates the horizontal bottom cover thickness, h s Indicates the distance between the top of the horizontal bottom seal and the bottom of the foundation pit; h w Indicates the distance between the water level outside the pit and the bottom of the foundation pit after precipitation.

[0098] Based on the saturated density of the soil above the horizontal bottom cover, the density of the horizontal bottom cover and the density of water, the calculation formula for the floating density of the horizontal bottom cover and the original soil layer is established:

[0099] ;

[0100] in, c s Indicates the saturated density of the soil above the horizontal bottom cover, c g Indicates the weight of the horizontal back cover. c w Indicates the weight of water.

[0101] In this embodiment, the method for calculating the total settlement of the foundation pit dewatering construction includes:

[0102] Calculate the surface settlement caused by foundation pit excavation construction, and record the total surface settlement caused by dewatering outside the pit and the surface settlement caused by foundation pit excavation construction as the total settlement of foundation pit dewatering construction;

[0103] Calculate the total surface settlement caused by dewatering outside the pit based on the soil effective stress increment, which includes the effective stress change in the dewatering area after dewatering outside the pit and the additional stress caused by seepage in the saturated area;

[0104] Calculate the stress change of soil in the drainage area due to self-weight after dewatering outside the pit, including the total stress of soil in the drainage area , pore water pressure and effective stress change :

[0105] ;

[0106] ;

[0107] ;

[0108] in, h 0 means the depth of groundwater level. y Indicates the depth of the unit body in the drainage area, c 0 represents the natural density of soil above the groundwater level. c 1 represents the weight of the soil after pumping water, c sat Indicates the saturated density of soil.

[0109] The calculation method of the total settlement of the foundation pit dewatering construction includes:

[0110] Based on the dewatering funnel curve of the foundation pit, the additional stress caused by seepage in the saturated zone after dewatering outside the pit is calculated:

[0111] ;

[0112] Where D represents the permeability of the unit soil, y represents the depth of the unit soil below the drainage area, and H(x) represents the coordinate depth of the precipitation funnel curve corresponding to the unit soil below the drainage area.

[0113] The vertical permeability D of unit soil is expressed as:

[0114] ;

[0115] in, c w Indicates the weight of water. i Indicates hydraulic slope;

[0116] And there are , ; H(x) represents the coordinate depth of the precipitation funnel curve corresponding to the unit soil below the drainage area.

[0117] Reference Figure 3As shown in the figure, after the foundation pit adopts and maintains internal and external precipitation measures, a stable precipitation funnel is formed within a certain range with the center line of the foundation pit as the symmetry axis, and the precipitation funnel curve of the foundation pit is established:

[0118] ;

[0119] in, H ( 0 ) represents the height of the foundation pit groundwater level from the impermeable layer before dewatering outside the pit. H ( t ) indicates precipitation time t The height of the groundwater level in the foundation pit from the impermeable layer, F (λ) represents the groundwater influence coefficient;

[0120] F (λ) is expressed as, when 0<λ<2:

[0121] ;

[0122] When λ≥2:

[0123] ;

[0124] in, , x Indicates the horizontal distance from the bottom of the foundation pit ( m ), m Indicates the water content of the soil, which can be determined through experiments. t Indicates precipitation time ( d ), K represents the permeability coefficient ( m / d ), H m represents the average thickness of the aquifer below the precipitation funnel curve, .in, , n is the porosity, K is the permeability coefficient ( cm / s ),in f ( K )=0.067 (3.063+lgK) .

[0125] In this example, the settlement caused by precipitation outside the pit is calculated using the layered summation method:

[0126] ;

[0127] in, w j is the total surface settlement caused by precipitation outside the pit, w iFor the i Soil settlement of the layer, Δ s i For the i The effective stress increment of the soil layer, E i For the i Compression modulus of soil layer, h i For the i Height of soil layer.

[0128] If there is no deformation of the soil above the groundwater level caused by precipitation outside the pit, the settlement of the drainage area above the precipitation funnel curve after precipitation outside the pit is:

[0129] ;

[0130] The settlement of the saturated zone below the precipitation funnel curve outside the pit is:

[0131] ;

[0132] The total surface settlement induced by precipitation outside the pit is:

[0133] .

[0134] Since the measured surface settlement data was obtained by on-site monitoring after dewatering was carried out outside the pit and a stable dewatering funnel was formed and the foundation pit excavation began, it is believed that the surface settlement was caused only by the foundation pit excavation construction:

[0135] ;

[0136] ;

[0137] in, w k Indicates the surrounding surface settlement caused by foundation pit excavation; w km Indicates the maximum value of surface settlement; x Indicates the distance from the foundation pit boundary; H j Indicates the excavation depth of the foundation pit;

[0138] Therefore, the distance from the foundation pit boundary induced by foundation pit excavation and precipitation outside the pit The total surface settlement calculation expression at is:

[0139] .

[0140] In this embodiment, the pit bottom safety constraint condition is:

[0141] ;

[0142] in,[ h g ] l Indicates the designed horizontal back cover thickness, max[ h g ] represents the maximum value of the horizontal bottom thickness considering instability damage and the horizontal bottom thickness considering penetration damage;

[0143] The surrounding environment settlement constraints are:

[0144] ;

[0145] in,[ W x ] l represents the total settlement of the designed foundation pit dewatering construction, [ W ax ] indicates the preset allowable settlement of the environment;

[0146] The precipitation constraints are:

[0147] ;

[0148] in,[ Q ] l represents the designed precipitation, [ Q ax ] indicates the preset environment's allowable precipitation.

[0149] The objective function is expressed as:

[0150] ;

[0151] in, I represents the solution region, h g It represents the horizontal bottom thickness considering instability damage, h g ´ represents the horizontal bottom cover thickness considering penetration damage, and δ(h) represents the Kronecker δ function, which is specifically expressed as:

[0152] .

[0153] Reference Figure 4 As shown, the objective function of the joint optimization model of horizontal bottom seal thickness and dewatering height is established and solved by trial and error iterative method. In this embodiment, the actual engineering geological parameter data are used to gradually approach the thickness values ​​of the two horizontal bottom seal reinforcement bodies under the two failure modes, and finally the optimal solution is sought. The entanglement method disclosed in this embodiment can effectively speed up the calculation efficiency and improve the calculation accuracy when there are many joint design parameters for foundation pit dewatering and horizontal water-stop curtain. As a preferred embodiment of this embodiment, the iteration value spacing δ=0.5m is taken.

[0154] The present invention discloses a method for jointly optimizing the horizontal bottom seal thickness and dewatering height of a deep foundation pit. In constructing a joint optimization model for the horizontal bottom seal thickness and dewatering height, the relationship between the horizontal bottom seal thickness and dewatering height due to instability damage and seepage damage is considered. Furthermore, the total surface settlement caused by dewatering outside the pit and excavation is introduced into the total settlement of the foundation pit dewatering construction. The method uses the pit bottom safety constraint considering the horizontal bottom seal thickness, the surrounding environment settlement constraint considering the total surface settlement, and the precipitation constraint considering the precipitation amount as constraints. The objective function is solved to achieve joint optimization of the horizontal bottom seal thickness and precipitation amount. The horizontal bottom seal optimized by this method has good seepage-proof performance and is relatively economical, while the precipitation height effectively meets environmental protection requirements.

[0155] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0156] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that a person of ordinary skill in the art may make various modifications and improvements without departing from the spirit of the present application, and these modifications and improvements fall within the scope of protection of the present application. Therefore, the scope of protection of the present patent application shall be determined by the appended claims.

Claims

1. A method for jointly optimizing the thickness of the horizontal bottom cover of a deep foundation pit and the height of the water level reduction, characterized in that: The following steps are involved: Based on the distance between the groundwater level and the bottom of the foundation pit and the excavation width of the foundation pit, calculate the relationship between the thickness of the horizontal bottom seal and the distance from the bottom of the foundation pit. Based on the relationship between the thickness of the horizontal bottom seal and the distance from the bottom of the foundation pit, calculate the relationship between the thickness of the horizontal bottom seal and the height of the water level. Based on the allowable unit seepage volume of the horizontal bottom seal and the excavation width of the foundation pit, calculate the relationship between the thickness of the horizontal bottom seal considering seepage damage and the distance from the horizontal bottom seal to the bottom of the foundation pit; based on the relationship between the thickness of the horizontal bottom seal considering seepage damage and the distance from the horizontal bottom seal to the bottom of the foundation pit, calculate the relationship between the thickness of the horizontal bottom seal considering seepage damage and the precipitation height; The total surface settlement caused by dewatering outside the pit is calculated based on the effective stress increment of the soil. The effective stress increment of the soil includes the effective stress change in the dewatering area after dewatering outside the pit and the additional stress caused by seepage in the saturated area. The total surface settlement caused by dewatering outside the pit and the surface settlement caused by foundation pit excavation construction are recorded as the total settlement of foundation pit dewatering construction. Establish a joint optimization model for horizontal bottom seal thickness and dewatering height, including the relationship between horizontal bottom seal thickness and dewatering height considering instability damage, the relationship between horizontal bottom seal thickness and dewatering height considering seepage damage, and the total settlement of foundation pit dewatering construction; Establishing constraints, including pit bottom safety constraints, surrounding environmental settlement constraints, and precipitation constraints; the pit bottom safety constraints require that the horizontal bottom thickness be greater than or equal to the horizontal bottom thickness considering instability damage and the horizontal bottom thickness considering seepage damage; the surrounding environmental settlement constraints require that the total settlement of the foundation pit dewatering construction be less than or equal to the preset environmental allowable settlement; and the precipitation constraint requires that the precipitation be less than or equal to the preset environmental allowable precipitation; Establishing an objective function based on the joint optimization model of the horizontal bottom cover thickness and the precipitation height, wherein the objective function satisfies the constraint conditions and minimizes the horizontal bottom cover thickness; The objective function is calculated and solved to obtain the final horizontal bottom cover thickness and the final precipitation.

2. The method for jointly optimizing the horizontal bottom cover thickness and the dewatering height of a deep foundation pit according to claim 1, characterized in that: The calculation method for the relationship between the horizontal bottom cover thickness and the precipitation height considering instability damage includes: Based on the distance between the groundwater level and the bottom of the foundation pit and the excavation width of the foundation pit, calculate the relationship between the thickness of the horizontal bottom seal and the distance from the bottom of the foundation pit considering instability: ； in, h s Indicates the distance from the horizontal bottom cover to the bottom of the foundation pit. h g Indicates the thickness of the horizontal back cover. h w Indicates the distance between the groundwater level and the bottom of the foundation pit excavation; B Indicates the excavation width of the foundation pit; ξ Indicates the sudden surge safety factor of the foundation pit; γ s Indicates the saturated density of the soil above the horizontal bottom cover, γ g Indicates the weight of the horizontal back cover. γ w Indicates the weight of water; ζ is the preset empirical coefficient; q u Indicates the uniaxial compressive strength of the horizontal bottom cover; Based on the relationship between the thickness of the horizontal bottom seal and the distance from the bottom of the foundation pit considering instability damage, and the calculation formula of the groundwater level after and before precipitation considering the change of groundwater level caused by precipitation outside the pit, the relationship between the thickness of the horizontal bottom seal and the precipitation height considering instability damage is calculated: ； in, h eu Indicates the water level outside the pit before precipitation, Δ h u Indicates the depth of precipitation outside the pit.

3. The method for jointly optimizing the horizontal bottom cover thickness and the dewatering height of a deep foundation pit according to claim 1, characterized in that: The calculation methods for the relationship between the horizontal bottom cover thickness and the precipitation height considering the penetration damage include: Based on the allowable unit seepage volume of the horizontal bottom seal and the excavation width of the foundation pit, calculate the relationship between the thickness of the horizontal bottom seal and the distance from the bottom of the foundation pit considering seepage damage: ； in,[ q ] represents the permissible unit water seepage of the horizontal bottom cover; k u represents the equivalent permeability coefficient of the soil outside the foundation pit, k i and M i Indicates the i Soil permeability coefficient; γ g ´ Indicates the floating weight of the horizontal bottom cover, γ s ´ Indicates the floating density of the original soil layer; Based on the relationship between the thickness of the horizontal bottom seal and the distance from the bottom of the foundation pit considering seepage damage, the calculation formula for the groundwater level after and before precipitation due to groundwater level changes caused by precipitation outside the pit, and the calculation formula for the floating density of the horizontal bottom seal and the original soil layer, the relationship between the thickness of the horizontal bottom seal and the precipitation height considering seepage damage is calculated: ； in, h eu Indicates the water level outside the pit before precipitation, Δ h u Indicates the depth of precipitation outside the pit.

4. The method for jointly optimizing the horizontal bottom cover thickness and the dewatering height of a deep foundation pit according to claim 3 is characterized in that: The calculation methods for the relationship between the horizontal bottom cover thickness and the precipitation height considering the penetration damage include: Based on the dewatering depth outside the pit, the thickness of the horizontal bottom seal, and the distance between the top of the horizontal bottom seal and the bottom of the foundation pit, a calculation formula for the groundwater level after dewatering and the groundwater level before dewatering is established, which takes into account the changes in the groundwater level caused by dewatering outside the pit: ； ； in, h eu Indicates the water level outside the pit before precipitation; h u Indicates the water level outside the pit after precipitation; Δ h u Indicates the depth of precipitation outside the pit; h g Indicates the horizontal bottom cover thickness, h s Indicates the distance between the top of the horizontal bottom seal and the bottom of the foundation pit; h w Indicates the distance between the water level outside the pit and the bottom of the foundation pit after precipitation.

5. The method for jointly optimizing the horizontal bottom cover thickness and the dewatering height of a deep foundation pit according to claim 4, characterized in that: The calculation methods for the relationship between the horizontal bottom cover thickness and the precipitation height considering the penetration damage include: Based on the saturated density of the soil above the horizontal bottom cover, the density of the horizontal bottom cover and the density of water, the calculation formula for the floating density of the horizontal bottom cover and the original soil layer is established: ； in, γ s Indicates the saturated density of the soil above the horizontal bottom cover, γ g Indicates the weight of the horizontal back cover. γ w Indicates the weight of water.

6. The method for jointly optimizing the thickness of the horizontal bottom cover of a deep foundation pit and the height of the water level reduction according to claim 1, characterized in that: The calculation method of the total settlement of the foundation pit dewatering construction includes: Calculate the surface settlement caused by foundation pit excavation construction, and record the total surface settlement caused by dewatering outside the pit and the surface settlement caused by foundation pit excavation construction as the total settlement of foundation pit dewatering construction; Calculate the total surface settlement caused by dewatering outside the pit based on the soil effective stress increment, which includes the effective stress change in the dewatering area after dewatering outside the pit and the additional stress caused by seepage in the saturated area; Calculate the stress change of soil in the drainage area due to self-weight after dewatering outside the pit, including the total stress of soil in the drainage area , pore water pressure and effective stress change : ； ； ； in, h 0 means the depth of groundwater level. y Indicates the depth of the unit body in the drainage area, γ 0 represents the natural density of soil above the groundwater level. γ 1 represents the weight of the soil after pumping water, γ sat Indicates the saturated density of soil.

7. The method for jointly optimizing the horizontal bottom cover thickness and the dewatering height of a deep foundation pit according to claim 6, characterized in that: The calculation method of the total settlement of the foundation pit dewatering construction includes: Based on the dewatering funnel curve of the foundation pit, the additional stress caused by seepage in the saturated zone after dewatering outside the pit is calculated: ； Where D represents the permeability of the unit soil, y represents the depth of the unit soil below the drainage area, and H(x) represents the coordinate depth of the precipitation funnel curve corresponding to the unit soil below the drainage area. Establish the precipitation funnel curve of the foundation pit: ； in, H ( 0 ) represents the height of the foundation pit groundwater level from the impermeable layer before dewatering outside the pit. H ( t ) indicates precipitation time t The height of the groundwater level in the foundation pit from the impermeable layer, F (λ) represents the groundwater influence coefficient.

8. The method for jointly optimizing the horizontal bottom cover thickness and the dewatering height of a deep foundation pit according to claim 1, characterized in that: The safety constraints at the pit bottom are: ； in,[ h g ] l Indicates the designed horizontal back cover thickness, max[ h g ] represents the maximum value of the horizontal bottom thickness considering instability damage and the horizontal bottom thickness considering penetration damage; The surrounding environment settlement constraints are: ； in,[ W x ] l represents the total settlement of the designed foundation pit dewatering construction, [ W ax ] indicates the preset allowable settlement of the environment; The precipitation constraints are: ； in,[ Q ] l represents the designed precipitation, [ Q ax ] indicates the preset environment's allowable precipitation.

9. The method for jointly optimizing the thickness of the horizontal bottom cover of a deep foundation pit and the height of the water level reduction according to claim 1, characterized in that: The objective function is expressed as: ； in, I represents the solution region, h g It represents the horizontal bottom thickness considering instability damage, h g ´ represents the horizontal bottom cover thickness considering penetration damage, and δ(h) represents the Kronecker δ function.

10. The method for jointly optimizing the horizontal bottom cover thickness and the dewatering height of a deep foundation pit according to claim 1, characterized in that: The objective function of the joint optimization model of horizontal bottom cover thickness and precipitation height is solved by trial and error iterative method.

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