A method and system for calculating rebound deformation of a foundation pit in a thick sand and gravel stratum excavation unloading

Abstract

The application relates to a thick sand and soil layer excavation unloading foundation pit rebound deformation calculation method and system, and relates to the technical field of urban underground engineering design and construction. The method comprises the following steps: constructing an unloading modulus change curve, wherein the unloading modulus change curve comprises a corresponding relationship between unloading rates and unloading modulus under different initial unloading stresses; fitting the corresponding relationship between the unloading modulus and the initial unloading stress when completely unloading according to the unloading modulus change curve; fitting the corresponding relationship between the unloading modulus, the initial unloading stress and the unloading ratio under a certain excavation state according to the unloading modulus change curve; and calculating the rebound deformation according to the corresponding relationship between the unloading modulus and the initial unloading stress when completely unloading, the corresponding relationship between the unloading modulus, the initial unloading stress and the unloading ratio under the certain excavation state, the corresponding relationship between the rebound deformation and the unloading modulus and the unloading rate. The application has the effect of accurately calculating the rebound deformation.

Description

Technical Field

[0001] This application relates to the technical field of urban underground engineering design and construction, and in particular to a method and system for calculating the rebound deformation of foundation pits during excavation and unloading in thick sandy soil strata. Background Technology

[0002] Top-down construction, also known as cut-and-cover construction, involves using the underground structure of the main project as the foundation pit support structure during excavation, and adopting a top-down design and construction method for the underground structure. Accurately calculating the rebound deformation of the soil and structure at the bottom of the pit due to excavation unloading is crucial for mitigating potential safety hazards during construction.

[0003] In related technologies, the layered summation method, residual stress method, and numerical analysis method are commonly used to predict the rebound deformation of foundation pits in soft soil strata. However, during calculations, the Brookfield and Minkowski solutions used to predict the additional stress in the soil are theoretical values, often resulting in calculated results that are greater than measured values, thus significantly underestimating the rebound deformation. In other words, the accuracy of the prediction methods in these technologies is limited. Furthermore, the rebound deformation of thick sandy soil strata under rapid excavation and unloading is also significant. However, the characteristics of thick sandy soil strata make it difficult for researchers to sample and study them, resulting in a lack of prediction methods for the rebound deformation of foundation pits in thick sandy soil strata under excavation and unloading. Summary of the Invention

[0004] In order to accurately calculate the rebound deformation of the foundation pit after excavation and unloading in thick sandy soil strata, this application proposes a method and system for calculating the rebound deformation of the foundation pit after excavation and unloading in thick sandy soil strata.

[0005] In a first aspect of this application, a method for calculating the rebound deformation of a foundation pit during excavation and unloading in thick sandy soil strata is provided, the method comprising:

[0006] Construct an unloading modulus variation curve, which includes the correspondence between unloading rate and unloading modulus under different initial unloading stresses;

[0007] The correspondence between the unloading modulus at complete unloading and the initial unloading stress is obtained by fitting the unloading modulus change curve.

[0008] The relationship between the unloading modulus under a certain excavation state and the initial unloading stress and unloading ratio is obtained by fitting the unloading modulus change curve.

[0009] The rebound deformation is calculated based on the correspondence between the unloading modulus and the initial unloading stress at complete unloading, the correspondence between the unloading modulus and the initial unloading stress and unloading ratio under a certain excavation state, the correspondence between the rebound deformation and the unloading modulus, and the unloading rate.

[0010] By adopting the above technical solution, an unloading modulus variation curve is constructed using the measured values ​​of initial unloading stress, unloading rate, and unloading modulus. Then, based on the fitting of the unloading modulus variation curve, the correspondence between the unloading modulus and initial unloading stress at complete unloading, as well as the correspondence between the unloading modulus and initial unloading stress and unloading ratio under a certain excavation state, are obtained. Finally, the rebound deformation is calculated based on the relationships between the above parameters and the unloading rate. Since the rebound deformation calculation uses measured values ​​and considers the influence of the unloading rate on the rebound deformation, the calculated rebound deformation is closer to the measured value than the theoretical value, i.e., more accurate.

[0011] In one possible implementation: the correspondence between the unloading modulus at complete unloading and the initial unloading stress is as follows:

[0012]

[0013] in, The unloading modulus at which the load is completely unloaded. The initial unloading stress, All are constants.

[0014] In one possible implementation: the correspondence between the unloading modulus under a certain excavation state and the initial unloading stress and unloading ratio is as follows:

[0015]

[0016] in, Let be the unloading modulus under a certain excavation condition. For unloading ratio, All are constants.

[0017] In one possible implementation: the unloading ratio is:

[0018]

[0019] in, To relieve stress, For the maximum preload, The additional stress coefficient is based on the Minkowski solution. This refers to the excavation height.

[0020] In one possible implementation: the correspondence between the unloading modulus under a certain excavation state and the initial unloading stress and unloading ratio is as follows:

[0021]

[0022] in, The average unit weight of the soil layer.

[0023] In one possible implementation: the calculation of rebound deformation based on the correspondence between the unloading modulus and the initial unloading stress at complete unloading, the correspondence between the unloading modulus and the initial unloading stress and the unloading ratio under a certain excavation state, the correspondence between rebound deformation and unloading modulus, and the unloading rate includes:

[0024] The rebound deformation reference value is determined based on the correspondence between the unloading modulus and the initial unloading stress when fully unloaded, the correspondence between the unloading modulus and the initial unloading stress and unloading ratio under a certain excavation state, and the correspondence between the rebound deformation and the unloading modulus.

[0025] By combining experimental samples, the relationship between the unloading rate and the unloading modulus was obtained through fitting, and the excavation rate influencing factor was obtained.

[0026] The rebound deformation is calculated based on the excavation rate influence factor and the rebound deformation reference value.

[0027] In one possible implementation: determining the rebound deformation reference value based on the correspondence between the unloading modulus and the initial unloading stress at complete unloading, the correspondence between the unloading modulus and the initial unloading stress and the unloading ratio under a certain excavation state, and the correspondence between rebound deformation and unloading modulus includes:

[0028] Substituting the correspondence between the unloading modulus and the initial unloading stress at complete unloading, and the correspondence between the unloading modulus and the initial unloading stress and unloading ratio under a certain excavation state into the correspondence between the rebound deformation and the unloading modulus, the reference value of the rebound deformation is obtained.

[0029] In one possible implementation: the correspondence between the springback deformation and the unloading modulus is as follows:

[0030]

[0031] in, This is the springback deformation value. To influence the depth of the rebound, This is the unloading stress.

[0032] In one possible implementation: the calculation of rebound deformation based on the excavation rate influence factor and the rebound deformation reference value includes:

[0033] The springback deformation is calculated using the following formula;

[0034]

[0035] in, The final calculated springback deformation, This is a factor affecting the excavation rate.

[0036] In a second aspect of this application, a system for calculating the rebound deformation of a foundation pit during excavation and unloading in thick sandy soil strata is provided. The system includes:

[0037] A construction module is used to construct an unloading modulus variation curve, which includes the correspondence between unloading rate and unloading modulus under different initial unloading stresses;

[0038] The first fitting module is used to fit the unloading modulus change curve to obtain the correspondence between the unloading modulus and the initial unloading stress when fully unloaded;

[0039] The second fitting module is used to fit the unloading modulus variation curve to obtain the correspondence between the unloading modulus under a certain excavation state and the initial unloading stress and unloading ratio; and

[0040] The calculation module is used to calculate the rebound deformation based on the correspondence between the unloading modulus and the initial unloading stress at the time of complete unloading, the correspondence between the unloading modulus and the initial unloading stress and the unloading ratio under a certain excavation state, the correspondence between the rebound deformation and the unloading modulus, and the unloading rate.

[0041] In summary, this application includes at least one of the following beneficial technical effects:

[0042] This application uses measured values ​​of initial unloading stress, unloading rate, and unloading modulus to construct an unloading modulus variation curve. Then, based on the unloading modulus variation curve, it obtains the correspondence between the unloading modulus and initial unloading stress at complete unloading, as well as the correspondence between the unloading modulus and initial unloading stress and unloading ratio under a certain excavation state. Finally, it calculates the rebound deformation based on the relationships between the above parameters and the unloading rate. Since the rebound deformation calculation uses measured values ​​and considers the influence of the unloading rate on the rebound deformation, the calculated rebound deformation is closer to the measured value than the theoretical value, i.e., more accurate. Attached Figure Description

[0043] Figure 1 This is a flowchart illustrating a method for calculating the rebound deformation of a foundation pit during excavation and unloading in a thick sandy soil stratum, according to one embodiment of this application.

[0044] Figure 2 This is a schematic diagram of the relationship between unloading modulus and unloading time when the unloading ratio is 1 in one embodiment of this application.

[0045] Figure 3This is a schematic diagram of the unloading modulus distribution under the standard test conditions for sandy soil in one embodiment of this application, after 24 hours of unloading stabilization.

[0046] Figure 4 This is a schematic diagram of the unloading modulus distribution during rapid unloading of sand and soil in one embodiment of this application, showing the unloading stabilization time of 1 hour.

[0047] Figure 5 This is a schematic diagram of a foundation pit rebound deformation calculation system for excavation and unloading of thick sandy soil strata, according to one embodiment of this application.

[0048] In the diagram, 21 is the building module; 22 is the first fitting module; 23 is the second fitting module; 24 is the calculation module; 301 is the CPU; 302 is the ROM; 303 is the RAM; 304 is the bus; 305 is the I / O interface; 306 is the input section; 307 is the output section; 308 is the storage section; 309 is the communication section; 310 is the driver; and 311 is the removable medium. Detailed Implementation

[0049] The present application will be further described in detail below with reference to the accompanying drawings.

[0050] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

[0051] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0052] Furthermore, the term "and / or" in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Additionally, the character " / " in this article, unless otherwise specified, generally indicates that the preceding and following related objects have an "or" relationship.

[0053] This application provides a method for calculating the rebound deformation of a foundation pit under the unloading action of excavation in thick sandy soil strata, which can accurately calculate the rebound deformation of the foundation pit under the unloading action of excavation in thick sandy soil strata.

[0054] The embodiments of this application will now be described in further detail with reference to the accompanying drawings.

[0055] The main process of the method for calculating the rebound deformation of a foundation pit during excavation and unloading in thick sandy soil strata provided in this application embodiment is described as follows.

[0056] like Figure 1 As shown:

[0057] Step S100: Construct the unloading modulus change curve.

[0058] The unloading modulus variation curve includes the relationship between unloading rate and unloading modulus under different initial unloading stresses. The initial unloading stress is the stress of the excavated soil from before construction to the point of complete unloading. The initial unloading stress varies depending on the size of the required foundation pit. Unloading modulus values ​​at different unloading rates under different initial unloading stresses are collected to construct the unloading modulus variation curve, which is then used as a reference. Figure 2 .

[0059] It is understandable that the initial unloading stress, unloading rate and unloading modulus mentioned above are all measured values, which can be obtained by conducting sand unloading and rebound experiments in the laboratory.

[0060] Step S200: Based on the unloading modulus change curve, obtain the correspondence between the unloading modulus at complete unloading and the initial unloading stress.

[0061] Complete unloading refers to an unloading ratio of 1. The unloading ratio describes the progress of unloading during foundation pit excavation and is defined as the ratio of unloading stress to the maximum preload or initial overburden load. The maximum preload is the maximum preload pressure borne by the soil during foundation pit excavation and unloading, and is also the initial overburden load.

[0062] In actual foundation pit engineering, the unloading ratio corresponding to point i at a depth of h meters below the pit bottom is:

[0063]

[0064] in, The stress diffusion coefficient is... The vertical self-weight stress caused by the excavation. The vertical self-weight stress at point i is considered before excavation. .0, for simplicity, is temporarily set to 0. Furthermore, assuming the actual foundation pit soil is uniform, the unloading ratio can be understood as the ratio of the excavation depth to the burial depth of the consideration point. That is:

[0065]

[0066] in, This refers to the depth of the foundation pit.

[0067] Therefore, when considering the location of point i at the bottom of the foundation pit, The unloading ratio is 1.

[0068] Furthermore, based on the unloading modulus variation curve, it can be analyzed that there is a linear relationship between the unloading modulus and the initial unloading stress at complete unloading. Since the data in the unloading modulus variation curve are all measured values, the corresponding relationship between the unloading modulus and the initial unloading stress at complete unloading can be obtained through fitting:

[0069]

[0070] in, The unloading modulus at which the load is completely unloaded. The initial unloading stress, All are constants.

[0071] Step S300: Based on the unloading modulus change curve, obtain the correspondence between the unloading modulus under a certain excavation state and the initial unloading stress and unloading ratio.

[0072] It is understandable that the unloading modulus of the soil at the bottom of the pit under a certain excavation state is related not only to the initial unloading stress but also to the unloading ratio. Different initial unloading stresses and different unloading ratios result in different unloading moduli. Further analysis of the unloading modulus variation curve reveals the following relationship between the unloading modulus under a certain excavation state and the initial unloading stress and unloading ratio:

[0073]

[0074] in, Let be the unloading modulus under a certain excavation condition. For unloading ratio, All are constants.

[0075] Based on the above definition of unloading ratio, the unloading ratio can be further evolved to obtain:

[0076]

[0077] in, To relieve stress, For the maximum preload, The additional stress coefficient is based on the Minkowski solution. This refers to the excavation height.

[0078] When using the layered summation method to predict the rebound deformation of foundation pits, it is usually necessary to consider the additional soil stress. This additional soil stress can be calculated using either the Brinell solution or the Minkowski solution, with the Brinell solution being the more fundamental one. Compared to the Brinell solution, the Minkowski solution considers the effect of the load acting inside a semi-infinite elastic body, offering a more realistic advantage. Therefore, an additional stress coefficient based on the Minkowski solution is introduced into the above formula for calculating the unloading ratio.

[0079] Based on this, by substituting the correspondence between the unloading modulus and the initial unloading stress at complete unloading, as well as the unloading ratio, into the formula, the correspondence between the unloading modulus and the initial unloading stress and unloading ratio under a certain excavation state can be transformed, thus obtaining:

[0080]

[0081] in, The average unit weight of the soil layer.

[0082] Step S400: Calculate the rebound deformation based on the correspondence between the unloading modulus and the initial unloading stress when fully unloaded, the correspondence between the unloading modulus and the initial unloading stress and unloading ratio under a certain excavation state, the correspondence between the rebound deformation and the unloading modulus, and the unloading rate.

[0083] Optionally, step S400 includes the following steps: (steps S410 to S430)

[0084] Step S410: Determine the reference value of rebound deformation based on the correspondence between the unloading modulus and the initial unloading stress when fully unloaded, the correspondence between the unloading modulus and the initial unloading stress and the unloading ratio under a certain excavation state, and the correspondence between rebound deformation and unloading modulus.

[0085] Specifically, the relationship between unloading modulus and initial unloading stress when fully unloaded, the relationship between unloading modulus and initial unloading stress under a certain excavation state, and the relationship between unloading ratio are substituted into the relationship between rebound deformation and unloading modulus to obtain the reference value of rebound deformation.

[0086] It can be understood that the relationship between rebound deformation and unloading modulus is that the product of unloading modulus and rebound deformation equals unloading stress. Therefore, rebound deformation is the ratio of unloading stress to unloading modulus. Furthermore, since the rebound stress in the soil layer at the bottom of the foundation pit is not constant during excavation, the formula used to calculate the reference value of rebound deformation is:

[0087]

[0088] in, This is the springback deformation value. To influence the depth of the rebound, This is the unloading stress.

[0089] Furthermore, because the rebound stress of the soil layer at the bottom of the pit varies with spatial location during the excavation process, the unloading rate varies significantly at different spatial locations. Specifically, the effect of the excavation unloading rate weakens as the soil layer deepens. Therefore, it can be considered that the excavation unloading efficiency effect is mainly concentrated in the strong unloading area at the bottom of the pit.

[0090] To calculate rebound deformation more accurately, the effect of unloading rate on unloading modulus needs to be introduced. Specifically, the unloading modulus of soil in the strongly unloaded zone can be expressed as: k is the excavation rate influencing factor. 1. When the unloading rate increases, the unloading ratio in the strong unloading zone increases accordingly, the unloading modulus decreases accordingly, and the rebound deformation increases accordingly.

[0091] Step S420: Based on the experimental samples, fit the relationship between unloading rate and unloading modulus to obtain the excavation rate influencing factor.

[0092] Since the data in the unloading modulus variation curve are all measured values, the relationship between the unloading rate and the unloading modulus can be accurately obtained through fitting, thereby determining the excavation rate influencing factor.

[0093] Step S430: Calculate the rebound deformation based on the excavation rate influence factor and the rebound deformation reference value.

[0094] After introducing the excavation rate influence factor, the formula for calculating rebound deformation evolves into:

[0095]

[0096] in, This refers to the final calculated springback deformation; This is a factor affecting the excavation rate.

[0097] In a specific example, refer to Figure 3 and Figure 4The western throat area of ​​the foundation pit in Section 02 of the Beijing Municipal Sub-center Integrated Transportation Hub is approximately 360m long (east-west), 120-190m wide, and about 40m deep, classifying it as an ultra-large-scale deep foundation pit. According to on-site records, during the excavation of soil from the 13m elevation to the 3m elevation, the average elevation of the top of the reverse-constructed piles within the pit was +50mm to +60mm, with a local maximum reaching 103mm. If the unloading rate is not considered, and the unloading modulus of sand under standard test conditions is used in the formula (with a stabilization time of 24 hours per unloading stage), the rebound deformation is approximately 62mm. However, in actual engineering, the average deformation of the piles alone exceeds this value. Clearly, the above calculation result is significantly underestimated, and using this as a design basis would adversely affect subsequent construction. If the unloading rate is considered, the unloading modulus of sand at different depths at an unloading stabilization time h=1 is determined through experiments, and the relationship between the unloading modulus and the unloading ratio at this unloading rate is fitted.

[0098]

[0099] The calculated rebound deformation was 104 mm, which is basically consistent with the maximum deformation of the column obtained from actual monitoring. This shows that the calculation result considering the influence of unloading speed on unloading modulus is more in line with the actual situation. Due to the limited experimental sample, the direct fitting relationship is used here instead of the unloading rate influence factor.

[0100] On-site earthwork statistics show that the total earthwork excavation volume in July was 276,080 m³, with an average daily excavation volume of about 8,900 m³. Such a large volume of earthwork excavation in a short period of time resulted in a large unloading rate of the soil layer at the bottom of the pit, which inevitably led to a larger rebound deformation. In contrast, the average daily earthwork excavation volume in August was about 5,200 m³, and the maximum bulge of the column did not exceed 20 mm, further confirming the significant impact of the unloading rate on rebound deformation.

[0101] Figure 5 This application provides a calculation system for the rebound deformation of a foundation pit during excavation and unloading in thick sandy soil strata, according to one embodiment of the present application.

[0102] The method for calculating the rebound deformation of a foundation pit during excavation and unloading in thick sandy soil strata provided in this application embodiment can be well applied to the above-mentioned scenarios and can achieve the effect of accurately calculating the rebound deformation.

[0103] like Figure 5 The foundation pit rebound deformation calculation system shown for excavation and unloading of thick sandy soil strata includes a construction module 21, a first fitting module 22, a second fitting module 23, and a calculation module 24, wherein:

[0104] Module 21 is used to construct the unloading modulus variation curve, which includes the correspondence between unloading rate and unloading modulus under different initial unloading stresses.

[0105] The first fitting module 22 is used to fit the unloading modulus change curve to obtain the correspondence between the unloading modulus and the initial unloading stress when fully unloaded.

[0106] The second fitting module 23 is used to fit the unloading modulus change curve to obtain the correspondence between the unloading modulus under a certain excavation state and the initial unloading stress and unloading ratio.

[0107] Calculation module 24 is used to calculate rebound deformation based on the correspondence between the unloading modulus and the initial unloading stress at the time of complete unloading, the correspondence between the unloading modulus and the initial unloading stress and the unloading ratio at a certain excavation state, the correspondence between rebound deformation and unloading modulus, and the unloading rate.

[0108] This embodiment is only one possible implementation method and does not limit other possible implementation methods.

[0109] The above description is merely a preferred embodiment of this application and an explanation of the technical principles employed. Those skilled in the art should understand that the scope of this application is not limited to technical solutions formed by specific combinations of the above-described technical features, but should also cover other technical solutions formed by arbitrary combinations of the above-described technical features or their equivalents without departing from the foregoing application concept. For example, technical solutions formed by substituting the above features with (but not limited to) technical features with similar functions claimed in this application.

Claims

1. A method for calculating the rebound deformation of a foundation pit during excavation and unloading in thick sandy soil strata, characterized in that, include: Construct an unloading modulus variation curve, which includes the correspondence between unloading rate and unloading modulus under different initial unloading stresses; The correspondence between the unloading modulus at complete unloading and the initial unloading stress is obtained by fitting the unloading modulus change curve. The relationship between the unloading modulus under a certain excavation state and the initial unloading stress and unloading ratio is obtained by fitting the unloading modulus change curve. The rebound deformation is calculated based on the correspondence between the unloading modulus and the initial unloading stress at the time of complete unloading, the correspondence between the unloading modulus and the initial unloading stress and the unloading ratio under a certain excavation state, the correspondence between the rebound deformation and the unloading modulus, and the unloading rate. The initial unloading stress, unloading rate and unloading modulus are all measured values, obtained by conducting sand unloading and rebound experiments in the laboratory. The calculation of rebound deformation based on the correspondence between the unloading modulus and the initial unloading stress at complete unloading, the correspondence between the unloading modulus and the initial unloading stress and the unloading ratio under a certain excavation state, the correspondence between rebound deformation and unloading modulus, and the unloading rate includes: The rebound deformation reference value is determined based on the correspondence between the unloading modulus and the initial unloading stress when fully unloaded, the correspondence between the unloading modulus and the initial unloading stress and unloading ratio under a certain excavation state, and the correspondence between the rebound deformation and the unloading modulus. By combining experimental samples, the relationship between the unloading rate and the unloading modulus was obtained through fitting, and the excavation rate influencing factor was obtained. Calculate the rebound deformation based on the excavation rate influence factor and the rebound deformation reference value; The step of determining the rebound deformation reference value based on the correspondence between the unloading modulus and the initial unloading stress at full unloading, the correspondence between the unloading modulus and the initial unloading stress and unloading ratio at a certain excavation state, and the correspondence between rebound deformation and unloading modulus includes: substituting the correspondence between the unloading modulus and the initial unloading stress at full unloading, and the correspondence between the unloading modulus and the initial unloading stress and unloading ratio at a certain excavation state, into the correspondence between rebound deformation and unloading modulus to obtain the rebound deformation reference value.

2. The method for calculating the rebound deformation of a foundation pit during excavation and unloading in thick sandy soil strata according to claim 1, characterized in that, The relationship between the unloading modulus at complete unloading and the initial unloading stress is as follows: ,in, The unloading modulus at which the load is completely unloaded. The initial unloading stress, Both are constants.

3. The method for calculating the rebound deformation of a foundation pit during excavation and unloading in thick sandy soil strata according to claim 2, characterized in that, The correspondence between the unloading modulus under a certain excavation state and the initial unloading stress and unloading ratio is as follows: ,in, Let be the unloading modulus under a certain excavation condition. For unloading ratio, Both are constants.

4. The method for calculating the rebound deformation of a foundation pit during excavation and unloading in thick sandy soil strata according to claim 3, characterized in that, The unloading ratio is: ,in, To relieve stress, For the maximum preload, The additional stress coefficient is based on the Minkowski solution. This refers to the excavation height.

5. The method for calculating the rebound deformation of a foundation pit during excavation and unloading in thick sandy soil strata according to claim 4, characterized in that, The correspondence between the unloading modulus under a certain excavation state and the initial unloading stress and unloading ratio is as follows: ,in, The average unit weight of the soil layer.

6. The method for calculating the rebound deformation of a foundation pit during excavation and unloading in thick sandy soil strata according to claim 5, characterized in that, The relationship between the springback deformation and the unloading modulus is as follows: ,in, This is the springback deformation value. To influence the depth of the rebound, This is the unloading stress.

7. The method for calculating the rebound deformation of a foundation pit during excavation and unloading in thick sandy soil strata according to claim 6, characterized in that, The calculation of rebound deformation based on the excavation rate influence factor and the rebound deformation reference value includes: obtaining the rebound deformation according to the following calculation formula; ,in, The final calculated springback deformation, This is a factor affecting the excavation rate.

8. A calculation system for rebound deformation of foundation pits during excavation and unloading in thick sandy soil strata, characterized in that, include: The construction module (21) is used to construct the unloading modulus change curve, which includes the correspondence between unloading rate and unloading modulus under different initial unloading stresses. The first fitting module (22) is used to fit the unloading modulus change curve to obtain the correspondence between the unloading modulus and the initial unloading stress when fully unloaded; The second fitting module (23) is used to fit the unloading modulus change curve to obtain the correspondence between the unloading modulus under a certain excavation state and the initial unloading stress and unloading ratio; as well as, The calculation module (24) is used to calculate the rebound deformation based on the correspondence between the unloading modulus and the initial unloading stress when fully unloaded, the correspondence between the unloading modulus and the initial unloading stress and the unloading ratio under a certain excavation state, the correspondence between the rebound deformation and the unloading modulus, and the unloading rate. The initial unloading stress, unloading rate and unloading modulus are all measured values, obtained by conducting sand unloading and rebound experiments in the laboratory. The calculation of rebound deformation based on the correspondence between the unloading modulus and the initial unloading stress at complete unloading, the correspondence between the unloading modulus and the initial unloading stress and the unloading ratio under a certain excavation state, the correspondence between rebound deformation and unloading modulus, and the unloading rate includes: The rebound deformation reference value is determined based on the correspondence between the unloading modulus and the initial unloading stress when fully unloaded, the correspondence between the unloading modulus and the initial unloading stress and unloading ratio under a certain excavation state, and the correspondence between the rebound deformation and the unloading modulus. By combining experimental samples, the relationship between the unloading rate and the unloading modulus was obtained through fitting, and the excavation rate influencing factor was obtained. Calculate the rebound deformation based on the excavation rate influence factor and the rebound deformation reference value; The step of determining the rebound deformation reference value based on the correspondence between the unloading modulus and the initial unloading stress at full unloading, the correspondence between the unloading modulus and the initial unloading stress and unloading ratio at a certain excavation state, and the correspondence between rebound deformation and unloading modulus includes: substituting the correspondence between the unloading modulus and the initial unloading stress at full unloading, and the correspondence between the unloading modulus and the initial unloading stress and unloading ratio at a certain excavation state, into the correspondence between rebound deformation and unloading modulus to obtain the rebound deformation reference value.

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