Calculation method for predicting horizontal deformation of foundation pit

Abstract

The invention discloses a calculation method for predicting horizontal deformation of a foundation pit, which comprises the following steps of: establishing a geometric model of the foundation pit, and meshing; different excavation working conditions and supporting structure construction are simulated in the grid model; the supporting structure is a cast-in-place pile used as a soil retaining structure after a foundation pit is excavated. The different excavation working conditions comprise excavation of foundation pit soil bodies at different depths; calculating through the soil constitutive model to obtain a horizontal displacement change curve of the supporting structure under different excavation working conditions; and under the condition of following the Nelder function basic formula, fitting the horizontal displacement change curve of the supporting structure and the field actual detection result through a Nelder-Mead simplex algorithm, and performing optimization regression to obtain a foundation pit horizontal deformation empirical model. By the adoption of the scheme, the foundation pit horizontal deformation empirical model is obtained through fitting, the foundation pit horizontal deformation values at different excavation depths can be obtained, and reference is provided for foundation pit supporting design under the same engineering condition.

Description

Technical Field

[0001] The invention relates to the technical field of foundation pit deformation measurement, and in particular to a calculation method for predicting horizontal deformation of a foundation pit. Background Art

[0002] In the prior art, the commonly used simplified calculation methods for foundation pit deformation are the limit equilibrium method and the foundation reaction method.

[0003] The limit equilibrium method was proposed in the early stage of foundation pit design. The calculation method is relatively simplified and is only applicable to relatively conventional support structures with no obvious spatial effects, relatively uniform strata, and relatively simple surrounding environments. However, this method does not consider wall deformation and lateral support deformation, and only calculates wall inclination through known soil pressure. The calculation results cannot meet the requirements.

[0004] When the elastic foundation beam method is used to analyze the deformation of foundation pit retaining structures, the m method has a clear calculation mode, the results are more in line with reality, and it is widely used. However, since there are many factors affecting the horizontal resistance coefficient m of the soil, the value range of the m value usually has a large deviation, and the accurate calculation of the m value cannot be guaranteed, resulting in the calculated value of the horizontal deformation is not accurate enough. Summary of the invention

[0005] The present invention aims to solve the problems in the prior art that the calculation results of the horizontal deformation of the foundation pit are not accurate enough and the calculation process is relatively complicated. The purpose is to provide a calculation method for predicting the horizontal deformation of the foundation pit. By adopting this scheme, the horizontal deformation values ​​of the foundation pit at different excavation depths can be obtained by fitting the empirical model of the horizontal deformation of the foundation pit, which provides a reference for the foundation pit support design under the same engineering conditions.

[0006] The present invention is achieved through the following technical solutions:

[0007] A calculation method for predicting horizontal deformation of a foundation pit comprises the following steps:

[0008] Establish the geometric model of the foundation pit and mesh it;

[0009] Simulating different excavation conditions and support structure construction in the grid model; the different excavation conditions include excavating foundation pit soil at different depths;

[0010] The horizontal displacement curve of the supporting structure at different excavation depths is obtained by finite element model calculation;

[0011] Under the condition of following the basic formula of Nelder function, the horizontal displacement change curve of the supporting structure and the actual on-site detection results are fitted by Nelder-Mead simplex algorithm, and the regression is optimized to obtain the empirical model of horizontal deformation of the foundation pit.

[0012] In a further solution, the empirical model of horizontal deformation of the foundation pit is:

[0013]

[0014] Where, v (mm) - represents the horizontal deformation value at the calculation depth (mm); z i (m)——represents the calculated depth of the support structure (m); a (mm)——displacement of the top of the support structure; v b (mm) – displacement of the bottom of the supporting structure.

[0015] A further solution is that when there is no measured value for the displacement of the top of the supporting structure, 1 / 5 of the displacement of the bottom of the foundation pit is taken.

[0016] A further solution is that when there is no measured value for the displacement of the bottom of the supporting structure, a value of 10 mm is taken according to the specification.

[0017] In a further solution, the supporting structure is cast-in-place piles used as retaining structure after the foundation pit is excavated.

[0018] A further solution is to establish the geometric model of the foundation pit and perform meshing. The specific steps include:

[0019] Establish a three-dimensional geometric model of the foundation pit and its associated supporting structures through finite element software;

[0020] Based on the stratum models at different depths of the foundation pit, the geometric model of the foundation pit is meshed to obtain a solid mesh model of the foundation pit divided by various strata.

[0021] A further solution is to simultaneously consider the coupling effect analysis of the effective stress under the groundwater seepage condition when simulating the relationship between the support structure and different excavation conditions in the gridded model.

[0022] A further solution is that after obtaining the empirical model of the horizontal deformation of the foundation pit, it is necessary to compare and analyze the calculated horizontal deformation of the support structure at different depths with the measured data to determine the error value and verify its effectiveness.

[0023] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0024] The present invention provides a calculation method for predicting the horizontal deformation of a foundation pit. By adopting this scheme, the horizontal deformation values ​​of the foundation pit at different excavation depths can be obtained by fitting the empirical model of the horizontal deformation of the foundation pit, which provides a reference for the foundation pit support design under the same engineering conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and should not be regarded as limiting the scope. For those of ordinary skill in the art, other relevant drawings can be obtained based on these drawings without creative work. In the drawings:

[0026] Figure 1 A three-dimensional finite element model diagram of foundation pit support established in Example 2 provided by the present invention;

[0027] Figure 2 It is a line diagram of the horizontal displacement distribution of the cast-in-place piles in the first layer excavation condition in Example 2 provided by the present invention;

[0028] Figure 3 It is a line diagram of the horizontal displacement distribution of the cast-in-place piles in the second layer excavation condition in Example 2 provided by the present invention;

[0029] Figure 4 A comparison chart of the inventive formula in Example 2 provided by the present invention and the field measured horizontal displacement data;

[0030] Figure 5 This is a comparison chart between the inventive formula in Example 3 provided by the present invention and the field measured horizontal displacement data. DETAILED DESCRIPTION

[0031] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments and drawings. The exemplary embodiments of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention.

[0032] Embodiment 1:

[0033] This embodiment 1 provides a calculation method for predicting horizontal deformation of a foundation pit, comprising the following steps:

[0034] A three-dimensional geometric model of the foundation pit and its auxiliary support structures is established through finite element software; based on the stratum model at different depths of the foundation pit, the geometric model of the foundation pit is meshed to obtain a solid mesh model of the foundation pit divided by various strata.

[0035] Different excavation conditions and support structure construction are simulated in the grid model; the support structure is a cast-in-place pile used as a retaining structure after foundation pit excavation; the different excavation conditions include excavating foundation pit soil at different depths; when simulating different excavation conditions and support structure construction in the grid model, the coupled influence analysis on the effective stress under the groundwater seepage condition needs to be considered simultaneously.

[0036] The horizontal displacement curve of the supporting structure at different excavation depths is obtained by finite element model calculation;

[0037] Under the condition of following the basic formula of Nelder function, the horizontal displacement change curve of the support structure and the actual on-site detection results are fitted by Nelder-Mead simplex algorithm, and the empirical model of horizontal deformation of foundation pit is obtained by optimizing regression. The empirical model of horizontal deformation of foundation pit is:

[0038]

[0039] Where, v (mm) - represents the horizontal deformation value at the calculation depth (mm); z i (m)——represents the calculated depth of the support structure (m); a (mm)——displacement of the top of the support structure. When there is no measured value for the displacement of the top of the support structure, take 1 / 5 of the displacement of the bottom of the foundation pit; v b (mm)——Displacement of the bottom of the supporting structure. When there is no measured value for the displacement of the bottom of the supporting structure, the value of 10mm shall be taken according to the specification.

[0040] After obtaining the empirical model of horizontal deformation of the foundation pit, it is also necessary to compare and analyze the calculated horizontal deformation of the support structure at different depths with the measured data to determine the error value and verify its effectiveness.

[0041] The simple calculation method for horizontal deformation of foundation pit obtained above provides a reference for foundation pit support design under the same engineering conditions, and improves the empirical calculation method for horizontal deformation of soft soil foundation pit in the Pearl River Delta in existing design specifications.

[0042] Embodiment 2:

[0043] This embodiment 2 provides a specific implementation case of a project, such as Figure 1-Figure 4 As shown, the foundation pit depth of this project is about 8 to 10m. In order to ensure the safety of surrounding buildings and foundation pits, the foundation pit is supported by cast-in-place piles. In order to prevent a large amount of water seepage during foundation pit excavation, anti-seepage treatment is carried out around the foundation pit. D500 cement mixing piles @350 are arranged in a row around the foundation pit 1m away from the foundation pit support cast-in-place piles. The cast-in-place piles use DN800 rotary bored cast-in-place piles to enter the strong weathering layer 3m. The edges of the cast-in-place piles are close to the boundary line of the plant structure. The center spacing of the piles is 1.4m. A C30 concrete crown beam of 0.8m (width) × 0.6m (height) is set on the top of the pile. An I-beam waist beam is set at an interval of 3m under the top of the pile, with a total of two rows of waist beams. The foundation pit crown beam layer is equipped with an I-beam support beam, which is located in the middle of the span and the corner of the foundation pit. One layer is set at a vertical elevation interval of 3m, with a total of 3 layers. The finite element software three-dimensional model is as follows Figure 1 shown.

[0044] After determining the scope of the geometric model and each stratum model, the rectangular entity with the same scope as the geometric model is imported into Midas / GTS NX. Using the grid segmentation function provided by the software, the complete foundation pit entity is segmented with each stratum model, thereby establishing a grid model that conforms to the actual situation.

[0045] In the above simulation model, the groundwater of this project is mostly shallow groundwater, and the water content of the bottom pressure water is small. The drainage work in the pit and the surrounding area during the construction period has basically no impact on the project. Therefore, the research process considers the impact of reducing groundwater on the surrounding soil, retaining structure and surrounding environment before excavation of the foundation pit. It is assumed that under the same working conditions, during the deformation process, the retaining structure maintains contact with the soil without separation or cracking. The research process of this scheme does not consider the effects of soil drainage consolidation and parameter attenuation.

[0046] The above-mentioned divided model has a total of 116703 grids and 60064 nodes. Among them, the grid size of the foundation pit area is 0.5m, the grid size of the outermost side of the model is 2m, and there is a natural transition in the middle.

[0047] Among them, the process table of foundation pit excavation construction stage is shown in the following table:

[0048]

[0049] The constitutive models of other retaining structures such as cast-in-place piles, beams, slabs, and columns all adopt elastic models; the retaining structure parameters and constitutive relationships analyzed in this analysis are shown in the following table:

[0050]

[0051] The excavation process of the foundation pit reflecting different strata and different excavation conditions is shown in the following table:

[0052]

[0053]

[0054] The soil constitutive model input into the finite element software of this project uses the MCC model (Modified-Cambridge Clay) and MMC (Modified-Mohr-Coulomb) model commonly used in soft soil areas for comparison; according to the horizontal displacement curve of the cast-in-place pile extracted by post-processing of the finite element calculation of this project, such as Figure 2 and Figure 3 As shown, it can be found that with the increase of excavation depth, the deformation behind the cast-in-place pile increases rapidly, reaches the maximum value after a certain distance below the bottom of the pit, and then gradually decreases, showing a special nonlinear distribution.

[0055] After obtaining the horizontal displacement curve of the above-mentioned bored piles, based on a large number of similar projects in the region and the monitoring data of this project, a horizontal comparison was made between the calculation results of the three-dimensional finite element numerical simulation using different constitutive parameters (modified-Mohrkull constitutive and modified-Cambridge constitutive). Starting from the correlation principle of the horizontal displacement law curve of the bored piles and combining the principles of mathematical statistics, a method for approximate Nelder function to fit the deformation curve of the foundation pit retaining structure was proposed.

[0056] And use the Nelder-Mead simplex algorithm to find the optimal value. The steps are as follows:

[0057] Step-1 Initialization: Initialize n+1 points;

[0058] x 1 ,.....,x n+1 , the actual calculated parameters and field monitoring points are input as the vertices of the simplex;

[0059] Step-2 Sorting: Calculate the fitness function values ​​of n+1 vertices and sort them:

[0060] f(x 1 )≤f(x 2 )≤...≤f(x n+1 );

[0061] Step-3 Centroid: Calculate the average of the first n points:

[0062] Step-4 Reflection: The reflection point consists of the centroid and the worst solution: where p is the reflection coefficient.

[0063] If f(x r ) is better than f(x n ) but worse than f(x 1 ), such as f(x 1 )≤f(x r )≤f(x n ), then x n+1 =x r ;x e =x 0 +ρ(x 0 -x n+1 ).

[0064] Step-5 Expansion: If f(x r )>f(x 1 ), then combined with the centroid x 0 and reflection point x r Further expand the exploration area. In other words, if f(x r )>f(x 1), it means that the best way to find the global optimal solution is to search in the reflection direction. At this time, calculate the expansion point (x e ), where p is the reflection coefficient. If f(x e ) <f(x r ), then x n+1 =x e , otherwise x n+1 =x r .

[0065] x e =x 0 +γ(x 0 -x n+1 );

[0066] Step-6 Contraction: If f(x n )≤f(x r )≤f(x n+1 ), calculate the external contraction point:

[0067] x c =x 0 +a(x r -x 0 );

[0068] If f(x c ) <f(x r ),x n+1 =x c ; If f(x r )>f(x n+1 ), calculate the inner contraction point: x cc =x 0 +a(x n+1 -x 0 ); if f(x cc ) <f(x n+1 ),x n+1 =x cc .

[0069] Step-7 Shrink: Shrink point:

[0070] x i =x 1 +σ(x i -x 1 );

[0071] Enter the Nelder-Mead algorithm code in Matlab to optimize the regression of the curve:

[0072] The calculation model is obtained:

[0073] The analysis model follows the basic formula of Nelder function:

[0074]

[0075] Based on the calculation model obtained in this scheme, the basic parameter error analysis of the Nelder function is shown in the following table:

[0076]

[0077] The numerical analysis results of the above indicators show that the Nelder function regression calculation method conforms to the basic algorithm rules of this deformation.

[0078] Through the comparative analysis of the deformation calculation results of each layer of excavation in this project and the measured data, such as Figure 4 As shown, the validity of the deformation expression of the Nelder function of the enclosure structure is verified.

[0079] Embodiment 3:

[0080] This Example 3 provides a specific implementation case of another project. The excavation depth of the regulating pool is 8m. The regulating pool is a two-span reinforced concrete wall structure, and a reinforced concrete frame structure with shear walls combined with mid-span columns is adopted. The retaining structure of the foundation pit excavation is excavated with 800mm cast-in-place piles combined with internal supports. The excavation depth of the foundation pit (h=10m) is set at 1.0m underground. At the same time, 2 Φ609 steel supports are set along the depth direction. Through on-site monitoring, the maximum horizontal displacement of the retaining structure is 21.432mm. The patented formula of the present invention is used for preliminary design to estimate the horizontal displacement of the retaining structure. Substituting it into the formula

[0081] The comparison curve of horizontal displacement of the foundation pit monitoring of this project can be obtained as follows Figure 5 shown.

[0082] Figure 5 The calculated and measured values ​​of the lateral deformation of the retaining structure are given in Figure 5 It can be seen that the fitting curve of the deformation of the enclosure structure by inputting the NELDER function into MATLAB is highly similar to the measured result curve, with good results. The maximum error is only -0.89mm at 15m. The curve shape and peak position are consistent with the measured data.

[0083] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A calculation method for predicting horizontal deformation of a foundation pit, characterized in that: The following steps are involved: Establish the geometric model of the foundation pit and mesh it; Simulating different excavation conditions and support structure construction in the grid model; the different excavation conditions include excavating foundation pit soil at different depths; The horizontal displacement curve of the supporting structure at different excavation depths is obtained by finite element model calculation; Under the condition of following the basic formula of Nelder function, the horizontal displacement change curve of the supporting structure and the actual on-site monitoring results are fitted by Nelder-Mead simplex algorithm, and the regression is optimized to obtain the empirical calculation model of horizontal deformation of foundation pit.

2. The calculation method for predicting horizontal deformation of a foundation pit according to claim 1 is characterized in that: The empirical model of horizontal deformation of foundation pit is: Where, v (mm) - represents the horizontal deformation value at the calculation depth (mm); z i (m)——represents the calculated depth of the support structure (m); a (mm)——displacement of the top of the support structure; v b (mm) – displacement of the bottom of the supporting structure.

3. The calculation method for predicting horizontal deformation of a foundation pit according to claim 2 is characterized in that: When there is no measured value for the displacement of the top of the supporting structure, take 1 / 5 of the displacement of the bottom of the foundation pit.

4. The calculation method for predicting horizontal deformation of a foundation pit according to claim 1 is characterized in that: When there is no measured value for the displacement of the bottom of the supporting structure, a value of 10 mm is taken according to the specification.

5. The calculation method for predicting horizontal deformation of a foundation pit according to claim 1 is characterized in that: The supporting structure is a cast-in-place pile used as a retaining structure after the foundation pit is excavated.

6. The calculation method for predicting horizontal deformation of a foundation pit according to claim 1 is characterized in that: The specific steps of establishing the geometric model of the foundation pit and meshing it include: Establish a three-dimensional geometric model of the foundation pit and its associated supporting structures through finite element software; Based on the stratum models at different depths of the foundation pit, the geometric model of the foundation pit is meshed to obtain a solid mesh model of the foundation pit divided by various strata.

7. The calculation method for predicting horizontal deformation of a foundation pit according to claim 1 is characterized in that: When simulating the relationship between the support structure and different excavation conditions in a gridded model, it is necessary to simultaneously consider the coupled influence analysis on the effective stress under the groundwater seepage condition.

8. The calculation method for predicting horizontal deformation of a foundation pit according to claim 1 is characterized in that: After obtaining the empirical model of horizontal deformation of the foundation pit, it is also necessary to compare and analyze the calculated horizontal deformation of the support structure at different depths with the measured data to determine the error value and verify its effectiveness.

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