A prediction method for the surface settlement curve behind diaphragm walls in deep foundation pits with rich water

Abstract

The present invention relates to the technical field of underground engineering, and specifically relates to a method for predicting the surface settlement curve behind a diaphragm wall in a deep foundation pit with rich water, comprising the following steps: determining the curve of the drawdown line outside the deep foundation pit after dewatering according to the thickness of the aquifer before dewatering and the thickness of the aquifer close to the diaphragm wall after the dewatering is stable; determining the effective stress increment in the drained area above the drawdown line outside the pit and the saturated area below the drawdown line outside the pit according to the drawdown line curve outside the pit, so as to determine the surface settlement curve of the foundation pit dewatering; obtaining the deformation curve of the diaphragm wall, and determining the surface settlement curve of the foundation pit excavation based on the relationship between the deformation curve of the diaphragm wall and the envelope area of the surface settlement curve of the foundation pit excavation; determining the surface settlement curve behind the diaphragm wall after dewatering and excavation according to the surface settlement curve of the foundation pit excavation and the surface settlement curve of the foundation pit dewatering. It can solve the problem that the surface settlement prediction method used in the existing excavation construction cannot well reflect the deformation characteristics of the soil outside the pit, resulting in inaccurate prediction.

Description

Technical Field

[0001] The present invention relates to the technical field of underground engineering, and particularly relates to a method for predicting the surface settlement curve behind a diaphragm wall in a deep foundation pit with rich water depth. Background Art

[0002] Foundation pit engineering is widely used in various engineering constructions, such as underground shopping malls, subway stations, building foundations, etc. During the construction of foundation pit dewatering and excavation, the groundwater level changes, the soil in the pit unloads, and the stress of the soil outside the pit redistributes, which will induce a series of deformations such as the offset of the retaining structure and the surface settlement behind the pit. This not only affects the stability of the foundation pit itself, but also affects the safety of the buildings and structures around the foundation pit.

[0003] Currently, a large number of deep foundation pit projects are constructed in cities, often facing problems such as large excavation depth, large excavation scale, small construction site, and many surrounding buildings and structures. The excavation of large-sized deep foundation pits is often accompanied by three-dimensional space deformation. The monitoring items commonly used to reflect the deformation characteristics of foundation pits mainly include the axial displacement of the retaining structure and the surface settlement. In the construction of ultra-deep foundation pits, diaphragm walls and internal supports are often used as retaining structures. During the pouring process of the diaphragm wall, the horizontal displacement gauges can be poured into the wall body, and the layout interval is generally 0.5 m. Therefore, the horizontal displacement gauges can better reflect the overall deformation of the wall body. However, due to the limitation of the construction site conditions for surface settlement, it is difficult to determine the settlement amount of the surrounding soil. For example, in the foundation pit of a subway station in the city, the excavation depth is large, the surrounding buildings are dense, and the construction site is limited. The range of surface settlement monitoring points that can be arranged in the factory area is much smaller than the surface settlement range caused by excavation. It is difficult to determine the maximum settlement point, and it is even more difficult to obtain the maximum settlement amount. In addition, there are often sundries piled up in the factory area and large vehicles staying, which also brings great difficulties to the monitoring and measurement of surface settlement during the excavation process, resulting in the on-site monitoring data not being able to accurately reflect the deformation space characteristics of the foundation pit project in a timely manner. The monitoring data cannot dynamically guide the design work, bringing great risks to the construction of the foundation pit project.

[0004] In addition, both dewatering and excavation will cause the soil outside the foundation pit to settle. The existing theoretical calculation formulas for surface settlement induced by dewatering all assume that the water level lines inside and outside the foundation pit are continuous, and the settlement amounts are calculated and superimposed for the overall height of the aquifer. The calculated values are too conservative. However, in fact, deep foundation pits often use retaining structures such as diaphragm walls with good water isolation effect and large buried depth, which basically cut off the hydraulic connection inside and outside the pit. The water level lines inside and outside the foundation pit are no longer continuous, and the change of the effective stress outside the pit will not affect the strata with large self-weight stress. Therefore, the current calculation formulas have certain limitations; at the same time, a large number of engineering measured data show that the front half of the groove-shaped settlement curve behind the wall caused by excavation is upward-opening, and the second half is downward-opening, while the existing methods for surface settlement induced by excavation construction cannot well reflect the deformation characteristics of the soil outside the pit. Summary of the Invention

[0005] In view of the defects existing in the prior art, the purpose of the present invention is to provide a prediction method for the surface settlement curve behind the diaphragm wall of a deep foundation pit in deep water, which can solve the problem that the method adopted for predicting the surface settlement induced by excavation construction in the prior art cannot well reflect the deformation characteristics of the soil outside the pit, resulting in inaccurate prediction.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] On the one hand, the present invention provides a prediction method for the surface settlement curve behind the diaphragm wall of a deep foundation pit in deep water, including the following steps:

[0008] Determine the drawdown curve outside the deep foundation pit after dewatering according to the thickness of the aquifer before dewatering behind the diaphragm wall and the thickness of the aquifer close to the diaphragm wall after the dewatering is stable.

[0009] Determine the effective stress increment in the drained area above the drawdown curve outside the pit and the effective stress increment in the saturated area below the drawdown curve outside the pit according to the drawdown curve outside the pit.

[0010] Determine the surface settlement curve of the foundation pit dewatering behind the diaphragm wall according to the effective stress increment in the drained area and the effective stress increment in the saturated area.

[0011] Obtain the deformation curve of the diaphragm wall, and determine the surface settlement curve of the foundation pit excavation behind the diaphragm wall based on the relationship between the deformation curve of the diaphragm wall and the envelope area between the surface settlement curves of the foundation pit excavation.

[0012] Determine the surface settlement curve behind the diaphragm wall of the dewatering excavation according to the surface settlement curve of the foundation pit excavation and the surface settlement curve of the foundation pit dewatering.

[0013] In some alternative solutions, the obtaining of the deformation curve of the diaphragm wall and determining the surface settlement curve of the foundation pit excavation behind the diaphragm wall based on the relationship between the deformation curve of the diaphragm wall and the envelope area between the surface settlement curves of the foundation pit excavation includes:

[0014] Obtain the deformation curve of the diaphragm wall and determine the envelope area of the deformation curve of the diaphragm wall.

[0015] According to the deformation shape of the diaphragm wall surface settlement caused by the foundation pit excavation, express the surface settlement curve of the foundation pit excavation by a piecewise parabola function, and express the envelope area function of the surface settlement curve of the foundation pit excavation by a piecewise parabola function.

[0016] Based on the relationship between the deformation curve of the diaphragm wall and the envelope area between the surface settlement curves of the foundation pit excavation, solve the envelope area function of the surface settlement curve of the foundation pit excavation to obtain the surface settlement curve of the foundation pit excavation behind the diaphragm wall.

[0017] In some alternative solutions, the deformation curve of the diaphragm wall is where y max is the maximum deformation of the diaphragm wall, z max is the maximum deformation position of the diaphragm wall, z is the vertical distance from the ground surface, and e is the base of the natural logarithm;

[0018] The envelope area of the deformation curve of the diaphragm wall is where H is the height of the diaphragm wall;

[0019] The piecewise parabolic function is z1 = a(x - x0) 2 + z0, 0 < x < x0; z2 = b(x - 2h) 2 , x0 < x < 2h; where z0 is the maximum ground settlement, x0 is the maximum ground settlement position, h is the excavation depth of the foundation pit, x is the horizontal distance from the diaphragm wall, and the first intermediate parameter The first intermediate parameter

[0020] The envelope area function of the ground settlement curve during foundation pit excavation is

[0021] The relationship between the envelope area between the deformation curve of the diaphragm wall and the ground settlement curve during foundation pit excavation is βW1 = W2, where β is an empirical coefficient;

[0022] The ground settlement curve after foundation pit excavation behind the diaphragm wall is:

[0023]

[0024]

[0025] In some alternative solutions, determining the ground settlement curve behind the diaphragm wall during dewatering excavation based on the ground settlement curve during foundation pit excavation and the ground settlement curve during foundation pit dewatering includes:

[0026] z(x1) = z1 + z(x), 0 < x < x0;

[0027] z(x2) = z2 + z(x), x0 < x < 2h;

[0028] where z(x) is the ground settlement curve during foundation pit dewatering behind the diaphragm wall.

[0029] In some alternative solutions, the deformation curve of the diaphragm wall is obtained by fitting field measurement data.

[0030] In some alternative solutions, determining the curve of the phreatic line outside the deep foundation pit after dewatering based on the thickness of the aquifer before dewatering behind the diaphragm wall and the thickness of the aquifer close to the diaphragm wall after dewatering stabilization includes:

[0031] According to the formula determine the curve of the phreatic line outside the deep foundation pit after dewatering, h 水 ;

[0032] wherein, H 水 is the thickness of the aquifer before dewatering, h w is the thickness of the aquifer close to the diaphragm wall after the dewatering is stable, x is the horizontal distance from the diaphragm wall, k is the permeability coefficient of the soil layer, and H a is the effective influence depth of dewatering in the foundation pit.

[0033] In some alternative solutions, determining the effective stress increment in the drained zone above the phreatic line curve outside the foundation pit and the effective stress increment in the saturated zone below the phreatic line curve outside the foundation pit according to the phreatic line curve outside the foundation pit includes:

[0034] According to the formula determine the effective stress increment Δσ1 in the drained zone above the phreatic line curve outside the foundation pit;

[0035] According to the formula Δσ2 = γ 水 (H 水 -h 水 ), determine the effective stress increment Δσ2 in the saturated zone below the phreatic line curve outside the foundation pit;

[0036] wherein, γ 水 is the unit weight of water.

[0037] In some alternative solutions, determining the surface settlement curve of the foundation pit dewatering behind the diaphragm wall according to the effective stress increment in the drained zone and the effective stress increment in the saturated zone includes:

[0038] Determine the surface settlement caused by the effective stress increment in the drained zone according to the effective stress increment in the drained zone;

[0039] Determine the surface settlement caused by the effective stress increment in the saturated zone according to the effective stress increment in the saturated zone;

[0040] Determine the surface settlement curve of the foundation pit dewatering behind the diaphragm wall according to the surface settlement caused by the effective stress increment in the drained zone and the surface settlement caused by the effective stress increment in the saturated zone.

[0041] In some alternative solutions, according to the formula determine the surface settlement S1 caused by the effective stress increment in the drained zone;

[0042] According to the formula determine the surface settlement S2 caused by the effective stress increment in the saturated zone;

[0043] According to the formula z(x) = S1 + S2, determine the surface settlement curve z(x) of the foundation pit dewatering behind the diaphragm wall;

[0044] Among them, ψ w is the empirical coefficient for settlement calculation, and E si is the compression modulus of the i-th soil layer, and Δh i is the thickness of the i-th soil layer.

[0045] In some alternative solutions, when determining the ground settlement S2 caused by the increment of effective stress in the dewatering area according to the formula if △σ2 ≤ αγ 土 h′, then the superposition calculation of the ground settlement S2 caused by the increment of effective stress in the saturated area is terminated. Among them, α is the influence coefficient of soil self-weight, and γ 土 is the unit weight of the soil, and h′ is the thickness from the i-th soil layer to the ground surface.

[0046] Compared with the prior art, the advantages of the present invention are as follows: This solution takes into account the influence of the diaphragm wall for water isolation, corrects the curve of the phreatic line outside the pit after dewatering, divides the soil layer after dewatering into a dewatering area above the phreatic line curve outside the pit and a saturated area below the phreatic line curve outside the pit, determines the increment of effective stress in the dewatering area above the phreatic line curve outside the pit and the increment of effective stress in the saturated area below the phreatic line curve outside the pit respectively, and calculates the ground settlement curve of the foundation pit dewatering behind the diaphragm wall according to the increment of effective stress in the dewatering area above the phreatic line curve outside the pit and the increment of effective stress in the saturated area below the phreatic line curve outside the pit; obtains the deformation curve of the diaphragm wall, and determines the ground settlement curve of the foundation pit excavation behind the diaphragm wall based on the relationship between the deformation curve of the diaphragm wall and the envelope area of the ground settlement curve of the foundation pit excavation; obtains the ground settlement curve after dewatering and excavation of the diaphragm wall according to the ground settlement curve of the foundation pit excavation and the ground settlement curve of the foundation pit dewatering. And a piecewise parabola is used to express the ground settlement curve, which can make the calculation more accurate. This method can, during the excavation process, according to the on-site monitoring data situation, timely predict the position of the maximum ground settlement point and the maximum settlement amount behind the diaphragm wall, avoiding the problems that due to site limitations, it is difficult to arrange the monitoring point positions or the monitoring is difficult, and the monitoring information cannot be accurately and timely fed back. It can more accurately predict the ground settlement and the deformation of the supporting structure, providing technical support for reasonable construction design. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained according to these drawings.

[0048] Figure 1 is a schematic flow chart of the method for predicting the ground settlement curve behind the diaphragm wall of a deep foundation pit with rich water in the embodiment of the present invention;

[0049] Figure 2 Schematic diagram of the water level line behind the diaphragm wall under the action of deep foundation pit dewatering in the embodiment of the present invention;

[0050] Figure 3 Schematic diagram of the change of effective stress in the drained area and saturated area under the action of dewatering in the embodiment of the present invention;

[0051] Figure 4 Schematic diagram of the deformation of the diaphragm wall and ground surface settlement under the action of excavation in the embodiment of the present invention;

[0052] Figure 5 Schematic diagram of the envelope area of the horizontal displacement of the diaphragm wall in the embodiment of the present invention;

[0053] Figure 6 Schematic diagram of the envelope area of the ground surface settlement curve under the action of excavation in the embodiment of the present invention;

[0054] Figure 7 Schematic diagram of the water level line behind the wall after dewatering in the embodiment of the present invention;

[0055] Figure 8 Schematic diagram of the ground surface settlement curve under the action of dewatering in the embodiment of the present invention;

[0056] Figure 9 Measured data and fitting function curve of the horizontal deformation of the diaphragm wall under the action of excavation in the embodiment of the present invention;

[0057] Figure 10 Piecewise parabolic curve of the ground surface settlement trough behind the wall under the action of excavation in the embodiment of the present invention

[0058] Figure 11 Schematic diagram of the superposition of the ground surface settlement curves behind the wall under the action of dewatering and excavation in the embodiment of the present invention. Detailed implementation manners

[0059] To make the objectives, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Apparently, the described embodiments are some but not all of the embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative efforts shall fall within the scope of protection of the present application.

[0060] The following further elaborates on the embodiments of the present invention with reference to the accompanying drawings.

[0061] As Figure 1 shown, the present invention provides a method for predicting the ground surface settlement curve behind the diaphragm wall of a deep foundation pit with rich water, including the following steps:

[0062] S1: Determine the curve of the phreatic line outside the deep foundation pit after dewatering based on the thickness of the aquifer before dewatering behind the diaphragm wall and the thickness of the aquifer close to the diaphragm wall after the dewatering is stable.

[0063] The existing standard algorithms are applicable to the calculation of surface settlement for shallow excavation depths, where the dewatering wells are arranged outside the foundation pit or the retaining structure, i.e., the diaphragm wall's water-blocking effect, is not considered. They are not applicable to deep foundation pits with deep excavation depths and dewatering wells arranged inside the pit. Compared with the case without a retaining structure, when dewatering inside the pit with a retaining structure, the hydraulic connection between the inside and outside of the foundation pit is cut off by the diaphragm wall or the dewatering curtain. The dewatering curves inside and outside the pit are no longer continuous, and the water level outside the pit no longer freely flows under unconstrained conditions. Therefore, the actual groundwater level will be higher than the Dupuit curve. With the development of foundation pit engineering, the depth of the foundation pit gradually increases, and the demand for groundwater protection and the stability of the retaining structure gradually improves. In most projects, the method of arranging dewatering wells inside the pit is used, and the Dupuit dewatering curve is no longer suitable as the dewatering curve for calculating the surface settlement of foundation pit engineering. Therefore, using a fitting equation to replace the Dupuit dewatering curve in the formula for calculating the surface settlement outside the pit can reduce the calculation error and make the results more in line with the actual situation.

[0064] In this solution, behind the diaphragm wall refers to the other side of the diaphragm wall relative to the excavation of the foundation pit. The curve of the phreatic line outside the pit is the liquid surface curve of the groundwater on the other side of the diaphragm wall relative to the excavation of the deep foundation pit after dewatering inside the pit.

[0065] In this solution, the experimental research on the mechanism of water level change caused by dewatering of a typical unconfined aquifer subway station foundation pit by Yang Qingyuan et al. is adopted, and the proposed equation of the dewatering curve outside the pit is used as the curve of the phreatic line after dewatering of the deep foundation pit. Specifically:

[0066] According to the formula Determine the curve of the phreatic line outside the deep foundation pit after dewatering, h 水 ; where, H 水 is the thickness of the aquifer before dewatering, h w is the thickness of the aquifer close to the diaphragm wall after the dewatering is stable, obtained from on-site tests or numerical simulations, x is the horizontal distance from the diaphragm wall, k is the permeability coefficient of the soil layer, H a is the effective influence depth of dewatering inside the foundation pit, generally 0.5 - 1 m larger than the depth of the foundation pit.

[0067] S2: Based on the curve of the phreatic line outside the pit, determine the increment of the effective stress in the drained area above the curve of the phreatic line outside the pit and the increment of the effective stress in the saturated area below the curve of the phreatic line outside the pit.

[0068] As Figure 2 and Figure 3 shown, H 水 is the thickness of the aquifer; h 水It is the distance between the water level line after precipitation and the bottom of the aquifer; S0 is the dry soil area; S1 area is the dewatered area caused by precipitation; S2 area is the saturated area. The reason for the change in the effective stress in the soil mass is that the soil in the S1 area is gradually dewatered due to precipitation, and the change in the effective stress in different areas is different.

[0069] Before and after the precipitation work, the soil in the S0 area is above the groundwater level surface, so the effective stress in the S0 area is not affected by precipitation.

[0070] Due to precipitation, the originally horizontal water level line will gradually form a precipitation funnel curve, and the precipitation curve divides the soil mass into two parts: the dewatered area and the saturated area. Precipitation causes an increase in the effective stress in the soil mass.

[0071] In the dewatered area S1, during the precipitation work, the precipitation process is dynamic, and the precipitation curve changes and finally stabilizes. When calculating the water level change in the dewatered area, the distance from the midpoint of the soil layer to the water level surface is taken, that is

[0072] In the saturated area S2, the soil mass is always in a saturated state, and the height of the precipitation curve y = H 水 -h 水 That is, the water level change.

[0073] Specifically, step S2 includes:

[0074] According to the formula Determine the increment of effective stress △σ1 in the dewatered area above the infiltration line curve outside the pit; according to the formula △σ2 = γ 水 (H 水 -h 水 ), determine the increment of effective stress △σ2 in the saturated area below the infiltration line curve outside the pit; where γ 水 is the unit weight of water.

[0075] S3: According to the increment of effective stress in the dewatered area and the increment of effective stress in the saturated area, determine the ground settlement curve of the foundation pit precipitation behind the diaphragm wall.

[0076] The ground settlement curve of the foundation pit precipitation is the curve formed by the ground settlement behind the diaphragm wall caused by the foundation pit precipitation.

[0077] This calculation method assumes that only the main consolidation phenomenon of the soil skeleton is considered; both the "Code for Building Foundation Pit Support" and the "Code for Construction Safety Technology of Deep Building Foundation Pits" mention the calculation method of ground settlement caused by precipitation. Currently, they are the main basis for calculating ground settlement caused by precipitation in China, and both are based on the layer-wise summation method to estimate ground settlement.

[0078]

[0079] Where: S is the ground settlement caused by precipitation; ψ w is the empirical coefficient for settlement calculation, which should be determined according to the engineering experience of the region. In the absence of experience, it should be determined according to the engineering experience of the region; for soft soil strata, it is advisable to take 1 - 1.2; Δσ′ zi is the increment of effective stress at the midpoint of the i-th soil layer under the action of precipitation; E si is the compression modulus of the i-th soil layer; Δh i is the thickness of the i-th soil layer.

[0080] Step S3 specifically includes:

[0081] Determine the ground settlement caused by the increment of effective stress in the dewatering area according to the increment of effective stress in the dewatering area.

[0082] Specifically: According to the formula Determine the ground settlement S1 caused by the increment of effective stress in the dewatering area.

[0083] Determine the ground settlement caused by the increment of effective stress in the saturated area according to the increment of effective stress in the saturated area.

[0084] Specifically, according to the formula Determine the ground settlement S2 caused by the increment of effective stress in the saturated area.

[0085] Determine the ground settlement curve of the foundation pit dewatering behind the diaphragm wall according to the ground settlement caused by the increment of effective stress in the dewatering area and the ground settlement caused by the increment of effective stress in the saturated area.

[0086] According to the formula z(x) = S1 + S2, determine the ground settlement curve of the foundation pit dewatering behind the diaphragm wall; where, ψ w is the empirical coefficient for settlement calculation, E si is the compression modulus of the i-th soil layer, Δh i is the thickness of the i-th soil layer.

[0087] In some alternative embodiments, the weighted permeability coefficient and unit weight of the soil layer behind the diaphragm wall are calculated, and it is simplified into a single soil layer, then the ground settlement situation caused by precipitation can be calculated, and the ground settlement curve trough formula can be obtained:

[0088]

[0089] In addition, in the conventional algorithm, the settlement superposition calculation of the diving stratum is carried out according to the change of effective stress. However, according to a large number of engineering practices, the surface settlement data calculated by this method often deviate greatly from the measured values, and the calculation of this method is on the conservative side. This is because after reaching a certain depth, the self-weight stress of the soil mass is much greater than the change of effective stress caused by the dewatering effect. At this time, the settlement of the upper soil layer will not cause substantial deformation to the lower soil layer and can be ignored. In the present invention, according to the soil mechanics settlement calculation method, the depth at which 0.2 times the self-weight stress is equal to the change of effective stress is denoted as the settlement calculation depth:

[0090] γ 水 (H 水 -h 水 )=0.2γ 土 h′

[0091] In the formula: h′ is the depth of the soil layer where 0.2 times the self-weight stress is equal to the change of effective stress, that is, the settlement calculation depth

[0092] Therefore, in some selected embodiments, when determining the surface settlement S2 caused by the increment of effective stress in the dewatering area according to the formula if △σ2 ≤ αγ 土 h′, then the superposition calculation of the surface settlement S2 caused by the increment of effective stress in the saturated area is terminated, where α is the coefficient of influence of soil self-weight, γ 土 is the unit weight of the soil, and h′ is the thickness from the i-th soil layer to the ground surface. In this example, the value of α is 0.2.

[0093] S4: Obtain the deformation curve of the diaphragm wall, and determine the surface settlement curve after the foundation pit excavation based on the relationship between the deformation curve of the diaphragm wall and the envelope area of the surface settlement curve during the foundation pit excavation.

[0094] The surface settlement curve during the foundation pit excavation is the curve formed by the surface settlement behind the diaphragm wall caused by the foundation pit excavation.

[0095] In some optional embodiments, step S4 includes:

[0096] S41: Obtain the deformation curve of the diaphragm wall and determine the envelope area of the deformation curve of the diaphragm wall.

[0097] In this solution, it is assumed that, as Figure 4 : The surface settlement range affected by the excavation is twice the excavation depth, including a main influence area of one times the excavation depth and a secondary influence area of one times the excavation depth. The connection line between the main influence area and the retaining structure is parallel to the connection line between the point of maximum surface settlement and the point of maximum deformation of the retaining structure. It can be seen that the position of maximum surface settlement occurs behind the wall position; where h is the excavation depth; H is the depth of the diaphragm wall; z max is the buried depth of the position of maximum deformation of the retaining structure.

[0098] During the construction of the foundation pit, the displacement gauge data of a certain measuring point section inside the diaphragm wall is extracted (generally, 1 monitoring point is arranged every 0.5 m), and the horizontal deformation curve of the diaphragm wall and the maximum deformation position z can be obtained completely. max And the maximum deformation amount y max .

[0099] As Figure 5 shown, the deformation curve of the diaphragm wall is obtained by fitting the on-site measured data. According to the on-site measured data, it can be found that the deformation curve of the diaphragm wall shows a bell-shaped curve with low sides and high in the middle. The normal distribution function with a similar curve shape is used to fit the measured data, and the fitting function is:

[0100] The deformation curve of the diaphragm wall described above is where y max is the maximum deformation amount of the diaphragm wall, z max is the maximum deformation position of the diaphragm wall, z is the vertical distance from the ground surface, and e is the base of the natural logarithm.

[0101] The corresponding envelope area of the deformation curve of the diaphragm wall obtained according to the deformation curve of the diaphragm wall is where H is the height of the diaphragm wall.

[0102] S42: According to the deformation shape of the ground surface settlement of the diaphragm wall caused by the foundation pit excavation, the segmented parabola function is used to express the ground surface settlement curve of the foundation pit excavation, and the envelope area function of the ground surface settlement curve of the foundation pit excavation is expressed by the segmented parabola function.

[0103] As Figure 6 shown, according to the research of a large number of scholars on the ground surface settlement caused by the foundation pit excavation and the fitting of a large number of on-site monitoring data of engineering, the conclusion is: the settlement curve of the groove behind the wall caused by the excavation action, and the front half of the groove opens upward and the rear half opens downward. Therefore, the present invention uses a segmented parabola to represent.

[0104] The segmented parabola function is: the first segment: z1 = a(x - x0) 2 + z0, 0 < x < x0; the second segment: z2 = b(x - 2h) 2 , x0 < x < 2h; where z0 is the maximum ground surface settlement amount, x0 is the maximum position of the ground surface settlement, and h is the foundation pit excavation depth.

[0105] Assume that the settlement values at 2h behind the wall and close to the diaphragm wall of the ground surface settlement trough are 0, that is, z1 passes through the point (0,0) and z2 passes through the point (2h,0). Substituting z1 and z2 into the above formulas, we can get:

[0106]

[0107] Integrate the surface settlement curve of foundation pit excavation to obtain the envelope area function of the surface settlement curve of foundation pit excavation as

[0108] S43: Based on the relationship between the envelope area of the diaphragm wall deformation curve and the surface settlement curve of foundation pit excavation, solve the envelope area function of the surface settlement curve of foundation pit excavation to obtain the surface settlement curve of foundation pit excavation behind the diaphragm wall.

[0109] According to engineering experience, the relationship between the envelope area of the surface settlement curve of foundation pit excavation and the envelope area of the diaphragm wall deformation curve is determined as: βW1 = W2, where β is an empirical coefficient, generally 0.5 - 0.8.

[0110] After expansion, we get:

[0111] According to the above formula, we can solve: Substitute a and b back to obtain the formula for the surface settlement trough caused by excavation:

[0112] The first paragraph:

[0113] The second paragraph:

[0114] S5: According to the surface settlement curve of foundation pit excavation and the surface settlement curve of foundation pit dewatering, determine the surface settlement curve behind the diaphragm wall after dewatering and excavation.

[0115] Add the surface settlement curve of foundation pit excavation and the surface settlement curve of foundation pit dewatering to obtain the surface settlement curve behind the diaphragm wall after dewatering and excavation:

[0116] z(x1) = z1 + z(x), 0 < x < x0;

[0117] z(x2) = z2 + z(x), x0 < x < 2h.

[0118] The surface settlement curve behind the diaphragm wall after dewatering and excavation is represented by the piecewise functions z(x1) and z(x2), which is a curve formed by the settlement caused by dewatering and excavation together; z(x) is the surface settlement curve of foundation pit dewatering behind the diaphragm wall.

[0119] In a specific embodiment given below, the basic parameters of a deep foundation pit in a water-rich area are shown in the table:

[0120]

[0121] Using the above method, the data of each step are obtained as follows: the water level line behind the diaphragm wall after dewatering, as Figure 7 shown; the surface settlement curve under the action of dewatering, as Figure 8Shown are the measured data of the horizontal deformation of the diaphragm wall under excavation and the fitting function curve, as Figure 9 shown; the segmented parabolic curve of the ground surface settlement trough behind the wall under excavation, as Figure 10 shown; the superimposed curve of the ground surface settlement curve behind the wall under the action of dewatering and excavation, as Figure 11 shown.

[0122] In summary, this scheme takes into account the influence of the water isolation of the diaphragm wall, corrects the curve of the phreatic line outside the pit after dewatering, divides the soil layer after dewatering into the drained area above the phreatic line curve outside the pit and the saturated area below the phreatic line curve outside the pit, determines the increment of effective stress in the drained area above the phreatic line curve outside the pit and the increment of effective stress in the saturated area below the phreatic line curve outside the pit respectively, and calculates the ground surface settlement curve of the foundation pit dewatering behind the diaphragm wall according to the increment of effective stress in the drained area above the phreatic line curve outside the pit and the increment of effective stress in the saturated area below the phreatic line curve outside the pit; obtains the deformation curve of the diaphragm wall, and determines the ground surface settlement curve of the foundation pit excavation behind the diaphragm wall based on the relationship between the deformation curve of the diaphragm wall and the envelope area of the ground surface settlement curve of the foundation pit excavation; obtains the ground surface settlement curve behind the diaphragm wall of the dewatering and excavation according to the ground surface settlement curve of the foundation pit excavation and the ground surface settlement curve of the foundation pit dewatering. And the ground surface settlement curve is expressed by a segmented parabola, which can make the calculation more accurate. This method can, during the excavation process, timely predict the position of the maximum ground surface settlement point and the maximum settlement amount behind the diaphragm wall according to the on-site monitoring data, avoiding the problems that it is difficult to arrange the monitoring points or difficult to monitor due to site restrictions, and unable to accurately and timely feedback the monitoring information, and can more accurately predict the ground surface settlement and the deformation of the support structure, providing technical support for reasonable construction design.

[0123] It should be noted that in this application, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or also includes elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "comprising a..." does not exclude the existence of additional identical elements in the process, method, article or device comprising the element.

[0124] The above are only specific embodiments of the present application, enabling those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown herein, but rather to the broadest scope consistent with the principles and novel features claimed herein.

Claims

1. A prediction method for the surface settlement curve behind the diaphragm wall of a deep foundation pit in deep water, characterized in that, Including the following steps: Determine the drawdown curve outside the deep foundation pit after dewatering according to the thickness of the aquifer before dewatering behind the diaphragm wall and the thickness of the aquifer close to the diaphragm wall after the dewatering is stable; Determine the effective stress increment in the drained zone above the drawdown curve outside the pit and the effective stress increment in the saturated zone below the drawdown curve outside the pit according to the drawdown curve outside the pit; Determine the surface settlement curve of the foundation pit dewatering behind the diaphragm wall according to the effective stress increment in the drained zone and the effective stress increment in the saturated zone; Obtain the deformation curve of the diaphragm wall, and determine the surface settlement curve of the foundation pit excavation behind the diaphragm wall based on the relationship between the deformation curve of the diaphragm wall and the envelope area of the surface settlement curve of the foundation pit excavation, including: Obtain the deformation curve of the diaphragm wall and determine the envelope area of the deformation curve of the diaphragm wall; According to the deformation shape of the diaphragm wall surface settlement caused by the foundation pit excavation, express the surface settlement curve of the foundation pit excavation with a piecewise parabolic function, and express the envelope area function of the surface settlement curve of the foundation pit excavation with a piecewise parabolic function; Based on the relationship between the envelope area between the deformation curve of the diaphragm wall and the surface settlement curve of the foundation pit excavation, solve the envelope area function of the surface settlement curve of the foundation pit excavation to obtain the surface settlement curve of the foundation pit excavation behind the diaphragm wall; The deformation curve of the diaphragm wall is where y max is the maximum deformation of the diaphragm wall, z max is the maximum deformation position of the diaphragm wall, z is the vertical distance from the ground surface, and e is the base of the natural logarithm; The envelope area of the diaphragm wall deformation curve is where H is the height of the diaphragm wall; The piecewise parabolic function is z1 = a(x - x0) 2 + z0, 0 < x < x0; z2 = b(x - 2h) 2 , x0 < x < 2h; where z0 is the maximum ground settlement, x0 is the position of the maximum ground settlement, h is the excavation depth of the foundation pit, x is the horizontal distance from the diaphragm wall, the first intermediate parameter The first intermediate parameter The envelope area function of the surface settlement curve during foundation pit excavation is The relationship between the envelope area between the deformation curve of the diaphragm wall and the surface settlement curve of the foundation pit excavation is βW1 = W2, where β is an empirical coefficient; The surface settlement curve of the foundation pit excavation behind the diaphragm wall is: Determine the surface settlement curve behind the diaphragm wall after dewatering and excavation according to the surface settlement curve of the foundation pit excavation and the surface settlement curve of the foundation pit dewatering.

2. The prediction method for the surface settlement curve behind the diaphragm wall of a deep foundation pit in deep water according to claim 1, characterized in that, The determining the surface settlement curve behind the diaphragm wall after dewatering and excavation according to the surface settlement curve of the foundation pit excavation and the surface settlement curve of the foundation pit dewatering includes: z(x1) = z1 + z(x), 0 < x < x0; z(x2) = z2 + z(x), x0 < x < 2h; where z(x) is the surface settlement curve of the foundation pit dewatering behind the diaphragm wall.

3. The prediction method for the surface settlement curve behind the diaphragm wall of a deep foundation pit in deep water according to claim 1, characterized in that, The deformation curve of the diaphragm wall is obtained by fitting the on-site measured data.

4. The prediction method for the surface settlement curve behind the diaphragm wall of a deep foundation pit in deep water according to claim 1, characterized in that, The determining the drawdown curve outside the deep foundation pit after dewatering according to the thickness of the aquifer before dewatering behind the diaphragm wall and the thickness of the aquifer close to the diaphragm wall after the dewatering is stable includes: According to the formula determine the curve h of the phreatic line outside the deep foundation pit after dewatering 水 ; Among them, H 水 is the thickness of the aquifer before precipitation, h w is the thickness of the aquifer adjacent to the diaphragm wall after precipitation stabilization, x is the horizontal distance from the diaphragm wall, k is the permeability coefficient of the soil layer, H a is the effective influence depth of precipitation in the foundation pit.

5. The prediction method for the surface settlement curve behind the diaphragm wall of a deep foundation pit in deep water according to claim 1, characterized in that, The determining the effective stress increment in the drained zone above the drawdown curve outside the pit and the effective stress increment in the saturated zone below the drawdown curve outside the pit according to the drawdown curve outside the pit includes: According to the formula determine the effective stress increment Δσ1 in the dewatering area above the phreatic line curve outside the pit; According to the formula △σ2 = γ 水 (H 水 - h 水 ), determine the effective stress increment △σ2 in the saturated zone below the phreatic line curve outside the pit; where γ 水 is the unit weight of water.

6. The prediction method for the surface settlement curve behind the diaphragm wall of a deep foundation pit in deep water according to claim 5, characterized in that, The determining the surface settlement curve of the foundation pit dewatering behind the diaphragm wall according to the effective stress increment in the drained zone and the effective stress increment in the saturated zone includes: Determine the surface settlement caused by the effective stress increment in the drained zone according to the effective stress increment in the drained zone; Determine the surface settlement caused by the effective stress increment in the saturated zone according to the effective stress increment in the saturated zone; Determine the surface settlement curve of the foundation pit dewatering behind the diaphragm wall according to the surface settlement caused by the effective stress increment in the drained zone and the surface settlement caused by the effective stress increment in the saturated zone.

7. The method for predicting the surface settlement curve behind the diaphragm wall of a deep foundation pit with rich water depth according to claim 6, wherein: According to the formula determine the ground settlement S1 caused by the effective stress increment in the dewatering area; According to the formula determine the surface settlement S2 caused by the effective stress increment in the saturated zone; Determine the surface settlement curve z(x) of the foundation pit dewatering behind the diaphragm wall according to the formula z(x) = S1 + S2; Among them, ψ w is the empirical coefficient for settlement calculation, E si is the compression modulus of the i-th soil layer, and Δh i is the thickness of the i-th soil layer.

8. The method for predicting the surface settlement curve behind the diaphragm wall of a deep foundation pit with rich water depth according to claim 7, wherein: When determining the ground settlement S2 caused by the effective stress increment in the dewatering area according to the formula if △σ2 ≤ αγ 土 h′, the superposition calculation of the ground settlement S2 caused by the effective stress increment in the saturated area is terminated. Among them, α is the coefficient of influence of soil self-weight, γ 土 is the unit weight of the soil, and h′ is the thickness from the i-th soil layer to the ground surface.

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