Foundation settlement calculation method

Abstract

The invention relates to a method for calculating foundation settlement, which comprises the following steps of: partitioning a base plane of a building or a structure and the like into blocks, giving an additional pressure coefficient of each block area, and obtaining a geological section of a settlement part to be calculated and physical and mechanical parameters of soil; the method comprises the following steps: dividing foundation soil into a plurality of thin layers, calculating self-weight stress and additional vertical stress of each thin layer, determining an initial small strain modulus under a corresponding stress level, and determining initial rigidity of a spring for simulating a transverse constraint effect of a soil body; the initial deformation modulus and the spring stiffness are reduced according to the shear strain in the small strain stage, the tangent modulus and the vertical strain of each thin layer are calculated according to the shear stress level in the large strain stage, and then the compression amount of each thin layer is calculated and accumulated to obtain a foundation settlement value. According to the method, by considering the horizontal elastic-plastic constraint of the surrounding soil body on the soil body of the to-be-calculated settlement part, the problems that the lateral confinement compression modulus adopted by an existing method does not conform to the actual stress condition of the foundation, and settlement of saturated soil under the undrained condition cannot be calculated are solved.

Description

Technical Field

[0001] The present application relates to the technical field of foundation engineering, and in particular to a method for calculating foundation settlement. Background Art

[0002] In the related art, the settlement calculation of foundation has always adopted the layered summation method, that is, the vertical additional stress caused by the average pressure of the foundation at different depths below the center of the base is calculated using the Boussinesq solution (assuming that the foundation is a linear elastic homogeneous semi-infinite body), and then the compression is calculated by the vertical additional stress in each layer and the lateral limit compression modulus. The compression of each soil layer within the affected depth is accumulated to give the settlement of the foundation. However, the use of the lateral limit compression modulus does not conform to the actual situation of the force and deformation of the foundation, so the error in the calculated settlement is very large, and the settlement of the saturated foundation under undrained conditions cannot be calculated at all. Related improvement schemes include: for hard soil, the deformation modulus that is reduced with the increase of load calculated by inverse calculation of the on-site load plate test is used, and for soft soil, three normal stress components are used, and the calculation is decomposed into two parts according to Hooke's law, namely, the lateral limit compression and the compression settlement corresponding to the difference between the actual horizontal stress and the lateral limit stress. However, it is not convenient to conduct expensive load plate tests in general projects, and the calculation method using three normal stresses will result in low accuracy in settlement calculation due to the large difference between the actual horizontal stress of the foundation and the Boussinesq solution. Summary of the invention

[0003] The present application provides a method for calculating foundation settlement to solve the problem that the existing method in the industry adopts the lateral confinement compression modulus, which does not conform to the actual stress and deformation of the foundation and cannot calculate the short-term settlement of saturated clay soil at all.

[0004] The first aspect of the present application provides a method for calculating foundation settlement, comprising the following steps: dividing a base plane into a plurality of rectangular blocks, determining an additional pressure coefficient of each of the plurality of rectangular blocks, and determining a base additional pressure distribution according to the additional pressure coefficient; obtaining a geological profile of a location where settlement is to be calculated and physical and mechanical parameters of each layer of soil; dividing the foundation soil into a plurality of thin layers, and calculating the self-weight stress and additional vertical stress at the middle depth of thin layers of different depths based on the physical and mechanical parameters of each layer of soil and the base additional pressure distribution, and determining an initial small strain modulus at a corresponding stress level through the self-weight stress and the additional vertical stress, and determining an initial stiffness of a spring reflecting the lateral constraint of the soil according to the initial small strain modulus; reducing an initial deformation modulus and an initial stiffness of the spring according to the shear strain in a small strain stage, and calculating a tangent modulus according to the shear stress level when entering a large strain stage, so as to calculate the vertical strain of each thin layer according to the tangent modulus; obtaining a compression amount according to the vertical strain of each thin layer, and accumulating the compression amount to obtain a settlement value of a building foundation.

[0005] Optionally, in one embodiment of the present application, the foundation soil is divided into multiple thin layers, and based on the physical and mechanical parameters of each layer of soil and the additional pressure distribution of the base, the self-weight stress and the additional vertical stress at the middle depth of the thin layers of different depths are calculated, and the initial small strain modulus at the corresponding stress level is determined by the self-weight stress and the additional vertical stress, and the initial stiffness of the spring reflecting the lateral constraint of the soil is determined according to the initial small strain modulus, including: dividing the foundation soil into the multiple thin layers, and calculating the self-weight stress and the additional vertical stress at the middle depth of the thin layers of different depths according to the physical and mechanical parameters of each layer of soil and the additional pressure distribution of the base; calculating the additional horizontal stress based on the ratio of the deformation modulus of the soil corresponding to the small strain modulus to the spring stiffness, and using the self-weight stress and the additional stress to calculate the initial small strain modulus at the corresponding stress level, and determining the initial stiffness of the spring reflecting the lateral constraint of the soil according to the small strain shear modulus.

[0006] Optionally, in one embodiment of the present application, the initial deformation modulus and the initial stiffness of the spring are reduced according to the shear strain size in the small strain stage, and the tangent modulus is calculated according to the shear stress level when entering the large strain stage, so as to calculate the vertical strain of each thin layer according to the tangent modulus, including: constructing a calculation model of an additional horizontal spring, and determining a vertical strain calculation strategy corresponding to the calculation model of the additional horizontal spring; determining the boundary stress between the small strain stage and the large strain stage, and judging the current strain stage according to the boundary stress and the additional vertical stress; when in the small strain stage, based on the vertical strain calculation strategy and the reduction curve of the small strain stiffness with shear strain, the soil modulus and the initial stiffness of the spring are synchronously reduced to obtain the vertical strain corresponding to the reduced modulus; when the vertical strain enters the large strain stage, based on the Duncan-Zhang model and the vertical strain calculation strategy, the initial deformation modulus is reduced according to the shear stress level, and the vertical strain of each thin layer is calculated and accumulated step by step.

[0007] Optionally, in one embodiment of the present application, the mathematical expression of the vertical strain calculation strategy corresponding to the calculation model of the additional horizontal spring is:

[0008]

[0009] Among them, ε z is the vertical strain corresponding to the large strain stage, σ z is the vertical additional stress, E is the deformation modulus, G is the shear modulus, ν is the Poisson's ratio, and α is the spring stiffness correction coefficient.

[0010] Optionally, in one embodiment of the present application, the calculation formula for the vertical strain corresponding to the small strain stage is:

[0011]

[0012] Among them, ε z is the vertical strain corresponding to the small strain stage, σ z is the vertical additional stress, E0 is the initial deformation modulus, A is the elastic horizontal stress coefficient, and ν is the Poisson's ratio.

[0013] Optionally, in one embodiment of the present application, the calculation formula for the vertical strain corresponding to the large strain stage is:

[0014]

[0015]

[0016] Among them, ε z is the vertical strain corresponding to the large strain stage, Δε z is the vertical strain increment, Δσ z is the vertical additional stress increment, E t is the tangent deformation modulus, G t is the tangent shear modulus, ν is the Poisson's ratio, and α is the spring stiffness correction factor.

[0017] The embodiment of the present application can obtain vertical additional stress more accurately and reflect the actual situation of base pressure by dividing the base plane into zones and calculating the additional pressure coefficient of each block area in combination with elastic-plastic finite element. The soil layer parameters are obtained according to professional geological survey reports, the non-isotropy of the soil is considered, and the compression is calculated with a reasonable functional relationship. The stress calculation is carried out comprehensively and scientifically from the modulus determination to the tangent modulus and vertical strain calculation. The final cumulative compression is used to obtain the settlement value. Compared with the traditional method, the accuracy of the calculation is significantly improved, and a highly reliable basis is provided for the design and construction of building foundations, which effectively guarantees the stability and safety of the project. By considering the horizontal elastic-plastic constraints of the surrounding soil on the soil at the location to be calculated for settlement, the present application overcomes the problem that the current method in the industry uses the side limit compression modulus which does not conform to the actual stress condition of the foundation soil and cannot calculate the settlement of saturated soil under undrained conditions.

[0018] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become apparent from the description below, or will be learned through the practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The above and / or additional aspects and advantages of the present application will become apparent and easily understood from the following description of the embodiments in conjunction with the accompanying drawings, in which:

[0020] Figure 1 is a schematic diagram of a foundation settlement calculation model according to an embodiment of the present application;

[0021] Figure 2 A flow chart of a method for calculating foundation settlement provided according to an embodiment of the present application;

[0022] Figure 3 A schematic diagram of load-settlement curve comparison in a specific embodiment of the present application;

[0023] Figure 4 It is a schematic diagram of load-settlement curve comparison in another specific embodiment of the present application. DETAILED DESCRIPTION

[0024] The embodiments of the present application are described in detail below, and examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present application, but should not be understood as limiting the present application.

[0025] The following describes the calculation method of foundation settlement of the embodiment of the present application with reference to the accompanying drawings. With respect to the related technologies mentioned in the above background technology, since the common method in the industry is to use the lateral compression modulus for calculation, this is equivalent to fixing the soil around with a steel hoop, and then applying a vertical load to exert downward pressure on the soil. The soil is fixed with a steel hoop, and there can be no horizontal (lateral) movement when under pressure. This calculation model is not correct enough, and it cannot calculate the settlement of saturated soil under undrained conditions. The calculation model of the present application is as follows Figure 1 As shown in the figure, it is equivalent to adding a horizontal spring around the soil. When the soil is compressed and produces horizontal displacement, the spring allows the soil to have a certain displacement, but at the same time the spring is compressed due to the displacement of the soil to the surroundings, the force of the spring to restrict the displacement of the soil increases, and the displacement of the soil is limited. Therefore, the soil can have a certain displacement to the surroundings, but it is not an unrestricted displacement, which correctly reflects the actual situation when the soil is compressed and deformed.

[0026] Specifically, Figure 2 A schematic flow chart of a method for calculating foundation settlement provided in an embodiment of the present application.

[0027] like Figure 2 As shown, the calculation method of foundation settlement includes the following steps:

[0028] In step S201, the base plane is divided into a plurality of rectangular blocks, and the additional pressure coefficient of each of the plurality of rectangular blocks is determined, and the base additional pressure distribution is determined according to the additional pressure coefficient.

[0029] It is understood that the location to be calculated for settlement refers to a specific location or area within the foundation of a building or structure that is predetermined and requires settlement calculation and analysis. This may be selected based on factors such as the structural layout of the building, key locations (such as but not limited to different locations such as the corners and middle of the building, or areas that are more sensitive to settlement), so as to specifically evaluate the settlement amount and settlement characteristics of the location under the action of the building load.

[0030] In the actual implementation process, the building base is divided into multiple rectangular blocks. Based on the multiple rectangular blocks, the additional pressure coefficient of each rectangular block is given according to the preset elastic-plastic finite element calculation to calculate the vertical additional stress of the settlement location to be calculated.

[0031] Specifically, the building base is divided into multiple rectangular blocks. For these divided rectangular blocks, the additional pressure coefficients are determined in two ways. First, if there are measured data, the corresponding analysis and extraction can be directly performed based on the measured data to accurately determine the additional pressure coefficients of each block; second, in the absence of measured data, rough elastic-plastic finite element calculation methods are used to simulate the stress-deformation characteristics of complex foundation soils, and the additional pressure coefficients of each block are obtained through a series of calculation processes and model analysis.

[0032] The embodiment of the present application can refine the base pressure by dividing the building base into multiple rectangular blocks. The additional pressure coefficient can be determined based on measured data or elastic-plastic finite element calculations. The former is true and accurate data, and the latter can simulate complex soil characteristics to make up for the shortcomings of actual measurements. The corner point method is subsequently used to calculate the vertical additional stress with the additional pressure coefficient, providing key and reliable basic data for foundation settlement calculations, effectively improving the accuracy and adaptability of foundation settlement calculations, and can better respond to the needs of building foundation settlement calculations under different working conditions, ensuring the stability and safety of construction projects.

[0033] In step S202, the geological profile of the location where settlement is to be calculated and the physical and mechanical parameters of each layer of soil are obtained.

[0034] It is understood that the physical and mechanical parameters of each layer of soil include but are not limited to the thickness of each layer of soil, the shear strength index c, (or undrained strength c u ), severity γ, lateral pressure coefficient K0, Poisson's ratio ν (ν=K0 / (1+K0) when the foundation is drained, and 0.5 when the foundation is undrained), unloading modulus E ur , initial small strain shear modulus G0 and threshold shear strain γ 0.7 wait.

[0035] In the actual implementation process, a geological survey report of the building foundation is obtained. The geological survey report is a comprehensive document about the detailed information of the foundation soil obtained by a professional geological survey team through a series of survey methods (such as but not limited to drilling, in-situ testing, etc.). Based on the geological survey report, the geological profile information of the calculated part can be extracted, that is, the distribution, thickness and mutual relationship of different soil layers in the vertical direction can be understood, and the physical and mechanical parameters of each layer of soil can be obtained.

[0036] For example, if the geological survey report gives the wave velocity of each layer of soil, the initial small strain shear modulus G0 of each layer of soil can be calculated based on the specific theoretical formula in soil mechanics, because there is an intrinsic connection between the wave velocity and the shear modulus of the soil, and this connection can be used to achieve conversion calculation. If the geological survey report does not give the wave velocity, since the compression modulus is a common parameter in the geological survey report, the empirical formula can be used to estimate the G0 value based on the compression modulus in the geological survey report. Although it is an estimate, it can also provide a relatively reasonable initial value of the small strain shear modulus when there is a lack of wave velocity data. In addition, for another parameter of small strain stiffness, γ 0.7 , because it is usually difficult to measure directly, based on a large amount of previous engineering practice experience and research results on different types of soil, corresponding empirical values ​​are given according to factors such as soil type. These parameters obtained through geological survey reports and further processed will serve as important basic data for a series of subsequent calculation processes such as calculating foundation settlement and analyzing the stress-strain relationship of foundation soil.

[0037] The embodiment of the present application can obtain the geological profile and physical and mechanical parameters of each layer of soil at the site where the settlement is to be calculated by obtaining a geological survey report of the building foundation. The geological survey report is based on professional survey methods and the data source is reliable. It can accurately determine the geological profile and rich parameters, such as calculating the initial value of the small strain shear modulus based on the wave velocity or compression modulus, etc., to provide key basic data for subsequent calculations, so that calculations such as foundation settlement and soil stress-strain relationship are more scientific and accurate. The existing information in the geological survey report can be fully utilized. Even if some data is missing, it can be reasonably estimated with the help of empirical formulas or empirical values, which enhances the adaptability and flexibility of the solution, effectively improves the quality and reliability of calculations and analysis related to building foundations, and ensures the stable development of construction projects.

[0038] In step S203, the foundation soil is divided into multiple thin layers, and the self-weight stress and additional vertical stress at the middle depth of thin layers of different depths are calculated based on the physical and mechanical parameters of each layer of soil and the distribution of additional pressure on the base. The initial small strain modulus under the corresponding stress level is determined by the self-weight stress and the additional vertical stress, and the initial stiffness of the spring reflecting the lateral constraint of the soil is determined according to the initial small strain modulus.

[0039] It is understandable that the foundation soil is divided into multiple thin layers. This is a commonly used method in soil mechanics calculations. Each thin layer can be regarded as a relatively independent unit with relatively uniform physical and mechanical properties. The division of thin layers can be determined according to the actual distribution of soil layers and the requirements of calculation accuracy. For example, it can be divided according to a certain thickness interval, or according to the boundaries of different soil layers.

[0040] Optionally, in an embodiment of the present application, the foundation soil is divided into multiple thin layers, and the self-weight stress and additional vertical stress at the middle depth of the thin layers of different depths are calculated based on the physical and mechanical parameters of each layer of soil and the distribution of additional pressure on the base, and the initial small strain modulus at the corresponding stress level is determined by the self-weight stress and the additional vertical stress, and the initial stiffness of the spring reflecting the lateral constraint of the soil is determined according to the initial small strain modulus, including: dividing the foundation soil into multiple thin layers, and calculating the self-weight stress and additional vertical stress at the middle depth of the thin layers of different depths according to the physical and mechanical parameters of each layer of soil and the distribution of additional pressure on the base; calculating the additional horizontal stress based on the ratio of the deformation modulus of the soil corresponding to the small strain modulus to the spring stiffness, and using the self-weight stress and the additional stress to calculate the initial small strain modulus at the corresponding stress level, and determining the initial stiffness of the spring reflecting the lateral constraint of the soil through the small strain shear modulus.

[0041] In the actual implementation process, when dividing thin layers, specific thickness requirements must be followed, that is, the thickness of each layer Δz is set to no more than one-fifth of the half-width b of the foundation, which helps to more accurately capture the stress changes of the foundation soil at different depths in subsequent calculations. Further calculations are carried out based on the physical parameters of each layer of soil and the vertical additional stress of the foundation. For the calculation of the self-weight stress at the middle depth of thin layers at different depths, it is necessary to comprehensively consider the physical parameters such as the weight of each layer of soil. Starting from the surface, the thickness Δz of each layer of soil is gradually accumulated and calculated to accurately obtain the self-weight stress at the middle depth of each thin layer. This self-weight stress is the stress generated by the weight of the foundation soil alone in its natural state, and is the basis for the subsequent analysis of the stress state of the foundation soil.

[0042] At the same time, the additional vertical stress at the middle depth of the thin layer at different depths is calculated. The additional vertical stress is the additional vertical stress generated by the foundation of the building transferring the upper load to the foundation soil. The calculation process needs to be based on the distribution law of the additional vertical stress of the foundation, combined with the physical parameters of each layer of the foundation soil and the divided thin layer structure. Taking into account the complex factors such as the shape, size, and load distribution of the foundation, professional calculation methods such as the corner point method are used to determine the specific values ​​of the additional vertical stress of the foundation at the middle depth of the thin layer at different depths, thereby obtaining the additional vertical stress.

[0043] After calculating the self-weight stress, it is necessary to consider that the modulus is related to the compressive stress level, that is, the compressive hardness of the soil, and determine the initial small strain modulus under the corresponding stress level (under drainage conditions, the compressive hardening effect of additional stress on the soil must also be considered):

[0044]

[0045] Where E0 is the initial deformation modulus, G0 is the initial shear modulus, ν is the Poisson's ratio, is the reference stress p ref = initial shear modulus at 100 kPa level, the power exponent m is empirically taken as 0.5~1.0, σ z0 and σ x0 are the vertical and horizontal self-weight stresses, respectively.

[0046] The embodiment of the present application can divide the foundation soil into multiple thin layers, determine the division method according to the actual soil layer and accuracy requirements, and control the thickness of each layer to not exceed one-fifth of the half-width of the foundation, which can accurately capture the stress changes at different depths. The calculation of self-weight stress is obtained by accumulating parameters such as the weight of each layer of soil, laying the foundation for analyzing the stress state of the foundation soil; when calculating the additional vertical stress, it combines multiple factors of the foundation and the soil layer, uses professional methods such as the corner point method, and fully considers the complex conditions such as the foundation shape, size, and load distribution, making the calculation results more accurate and reliable, effectively improving the accuracy and scientificity of foundation stress analysis in soil mechanics calculations, and providing strong support for subsequent work such as building foundation design and settlement estimation.

[0047] In step S204, the initial deformation modulus and the initial stiffness of the spring are reduced according to the shear strain in the small strain stage, and the tangent modulus is calculated according to the shear stress level when entering the large strain stage, so as to calculate the vertical strain of each thin layer according to the tangent modulus.

[0048] Optionally, in one embodiment of the present application, in the small strain stage, the initial deformation modulus and the initial stiffness of the spring are reduced according to the size of the shear strain, and when entering the large strain stage, the tangent modulus is calculated according to the shear stress level to calculate the vertical strain of each thin layer according to the tangent modulus, including: constructing a calculation model of an additional horizontal spring, and determining a vertical strain calculation strategy corresponding to the calculation model of the additional horizontal spring; determining the boundary stress between the small strain stage and the large strain stage, and judging the current strain stage according to the boundary stress and the additional vertical stress; when in the small strain stage, based on the vertical strain calculation strategy and the reduction curve of the small strain stiffness with shear strain, the soil modulus and the initial stiffness of the spring are synchronously reduced to obtain the vertical strain corresponding to the reduced modulus; when the vertical strain enters the large strain stage, based on the Duncan-Zhang model and the vertical strain calculation strategy, the initial deformation modulus is reduced according to the shear stress level, and the vertical strain of each thin layer is calculated and accumulated step by step.

[0049] This application considers the limitations of the layered summation method and adds the spring of the viscoelastic boundary in the finite element analysis of foundation vibration to the side of the soil column, so that the distributed spring plays a moderate constraint role. Figure 1 The calculation model shown in Figure 2 is shown in Figure 2. The spring stiffness in this model should be 2G / Δr (Δr is the distance between the spring action point and the settlement calculation site, which is a small value; G is the shear modulus) according to the spring stiffness in the viscoelastic transmission boundary. However, through research, it is found that the spring stiffness of 2αG / Δr is more accurate for the calculation of actual foundation settlement. The spring stiffness correction coefficient α is a function of the depth z, and the formula is as follows:

[0050]

[0051] According to the calculation results of the previous steps, the ratio of the physical and mechanical parameters of each layer of soil corresponding to the small strain modulus to the spring stiffness is further introduced to calculate the additional horizontal stress. The additional horizontal stress is calculated by a specific calculation method, that is, the ratio of the deformation modulus E of the soil corresponding to the small strain modulus to the spring stiffness 2αG. In this process, it is necessary to accurately determine the values ​​of the deformation modulus E and the spring stiffness 2αG of the soil. The deformation modulus E is intrinsically related to other physical and mechanical parameters of the soil, and the spring stiffness 2αG needs to be determined based on the above model settings and foundation soil characteristics, such as the initial shear modulus G0 corresponds to the initial stiffness of the spring.

[0052] It can be understood that the reduction calculation is a calculation method based on the small strain modulus and shear stress level. Since the mechanical properties of soil will change under different stress conditions, when considering the influence of shear stress, the small strain modulus needs to be reduced. The reduction process is to adjust the value of the small strain modulus according to a certain theoretical or empirical formula, combined with the size of the shear stress level, to more accurately reflect the deformation capacity of the soil under actual complex stress conditions (including shear stress). When the strain of the soil exceeds the small strain range and enters the larger strain stage, the deformation characteristics of the soil change significantly, such as obvious plastic deformation. At this stage, the stress-strain relationship of the soil is no longer a simple linear relationship. In the large strain stage, the slope of the tangent at a certain point on the stress-strain curve is called the tangent modulus. It is used to describe the instantaneous deformation characteristics of the soil under a certain stress-strain state in the large strain stage, and can more accurately reflect the stiffness changes of the soil in the complex deformation process.

[0053] Specifically, the soil modulus and spring stiffness are reduced by using the reduction curve of small strain stiffness with shear strain. This reduction curve is obtained through a large number of experimental studies and theoretical analysis, and it can more accurately reflect the change law of soil modulus and spring stiffness under different shear stress levels. By substituting the actual shear stress level into the reduction curve, the corresponding reduction coefficient can be obtained, and then the soil modulus and spring stiffness can be reasonably reduced to obtain the vertical strain corresponding to the reduced modulus. The vertical strain reflects the deformation degree of the soil in the vertical direction after considering the influence of shear stress and modulus reduction, and is the key basis for the subsequent calculation of compression.

[0054] In some cases, when the strain is found to enter the large strain stage during the calculation process, the tangent modulus of the soil at the corresponding stress level is calculated according to the Duncan-Zhang model. The Duncan-Zhang model is a widely used and mature constitutive model in the field of soil mechanics, which can effectively describe the complex stress-strain relationship of soil in the large strain stage. When applying this model, it is necessary to calculate based on the current stress state and the relevant physical and mechanical parameters of the soil to determine the tangent modulus of the soil at a specific stress level in the large strain stage. For the value of the spring stiffness, a cautious and reasonable approach is adopted, that is, the lower limit of the small strain modulus and the tangent deformation modulus of the soil are taken. The smaller value. This value selection strategy not only takes into account the matching of the spring stiffness and the soil deformation characteristics in the large strain stage, but also ensures the conservatism and reliability of the calculation results.

[0055] Optionally, in one embodiment of the present application, the mathematical expression of the vertical strain calculation strategy corresponding to the calculation model of the additional horizontal spring is:

[0056]

[0057] Among them, ε z is the vertical strain, σ z is the vertical additional stress, E is the deformation modulus, G is the shear modulus, ν is the Poisson's ratio, and α is the spring stiffness correction coefficient.

[0058] Specifically, in the small strain stage, the soil modulus and spring stiffness are reduced synchronously according to the reduction curve of small strain stiffness with shear strain. The tangent deformation modulus E t and tangent shear modulus G t The initial values ​​are E0 and G0 considering small strain stiffness, and the lower limits are E ur and G ur .

[0059] The boundary stress τ between the small strain stage and the large strain stage cut and σ z,cut The calculation is as follows:

[0060]

[0061] Where A is the elastic horizontal stress coefficient,

[0062] According to the additional stress σ z The size of the judgment, if σ z ≤σ z,cut It is only in the small strain stage. If σ z >σ z,cut It will enter a stage of great strain.

[0063] Optionally, in one embodiment of the present application, the calculation formula for the vertical strain corresponding to the small strain stage is:

[0064]

[0065] Among them, ε z is the vertical strain corresponding to the small strain stage, σ z is the vertical additional stress, E0 is the initial deformation modulus, A is the elastic horizontal stress coefficient, and ν is the Poisson's ratio.

[0066] In the embodiment of the present application, when only in the small strain stage, the vertical strain can be calculated by the following formula:

[0067]

[0068] Among them, ε z is the vertical strain corresponding to the small strain stage, σ z is the vertical additional stress, E0 is the initial deformation modulus, A is the elastic horizontal stress coefficient, α is the spring stiffness correction coefficient, and ν is the Poisson's ratio.

[0069] Optionally, in one embodiment of the present application, the calculation formula for the vertical strain corresponding to the large strain stage is:

[0070]

[0071]

[0072] Among them, ε z is the vertical strain corresponding to the large strain stage, Δε z is the vertical strain increment, Δσ z is the vertical additional stress increment, E t is the tangent deformation modulus, G t is the tangent shear modulus, ν is the Poisson's ratio, and α is the spring stiffness correction factor.

[0073] When entering the large strain stage, the tangent deformation modulus E t From E ur Start to reduce according to the following rules, Gt Keep G ur unchanged, but when G t Higher than E t When G t =E t . The vertical additional stress σ z Exceed σ z,cut The part is divided into n stress increments Δσ z , that is, Δσ z =(σ z -σ z,cut ) / n, for each Δσ z Adopt E t and G t Calculate the vertical strain increment Δε z ,Right now

[0074]

[0075] Among them, Δε z is the vertical strain increment, Δσ z is the vertical additional stress increment, E t is the tangent deformation modulus, G t is the tangent shear modulus, ν is the Poisson's ratio, and α is the spring stiffness correction factor.

[0076] Based on the Duncan-Zhang model (DC model), E t According to the shear stress level τ / τ f To make a reduction:

[0077]

[0078] Among them, the destruction ratio R f Take 0.9, τ f is the limiting shear stress, calculated according to the method described below, and the obtained τ / τ f If it exceeds 1, set it to 1.

[0079] In order to ensure the continuity of the tangent modulus in the two stages, E i Need to meet:

[0080]

[0081] Due to kinematic hardening, only the additional shear stress is considered, and the corresponding horizontal additional stress increment Δσ x Calculate as follows:

[0082]

[0083] The average compressive stress and additional shear stress at the jth load step (1≤j≤n) are:

[0084]

[0085]

[0086] When the foundation is not drained τ f =c u , when draining the foundation, first calculate the slope of the loading stress path when When the ultimate shear stress when When τ f is infinite, and can be taken as a large value in the calculation, so that τ / τ f Close to 0.

[0087] The tangent deformation modulus E is calculated from the stress state after the jth load step is completed. t For the calculation of the (j+1)th load step, the compaction effect of additional stress on the soil must also be considered under drainage conditions.

[0088] Vertical strain ε z By comparing the small strain stage with the strain increment Δε calculated in each load step of this stage z Add up and you get:

[0089]

[0090] The embodiment of the present application adds a spring of viscoelastic boundary on the side of the soil column and optimizes its stiffness value. The additional horizontal stress is calculated by introducing the ratio of the deformation modulus of the soil corresponding to the small strain modulus and the spring stiffness, and then the small strain modulus under the corresponding stress level is calculated based on this. The characteristics of the soil modulus changing with the stress level are taken into account, which can more truly reflect the deformation characteristics of the foundation soil under the action of the building load, and effectively improve the accuracy and scientificity of the foundation settlement calculation. Based on the small strain modulus and the physical and mechanical parameters of each layer of soil, the calculation is accurately reduced according to the shear stress level, and the soil modulus and spring stiffness are reasonably adjusted with the help of professional reduction curves, fully considering the changes in the deformation capacity of the soil under complex forces. When entering the large strain stage, the Duncan-Zhang model is used to calculate the tangent modulus and reasonably determine the value of the spring stiffness, which can accurately describe the large strain characteristics and ensure the reliability of the results.

[0091] In step S205, the compression amount is obtained according to the vertical strain of each thin layer, and the compression amounts are accumulated to obtain the settlement value of the building foundation.

[0092] The compression is obtained by multiplying the vertical strain of each thin layer by its thickness, and the settlement s of the part is obtained by accumulating it, that is:

[0093]

[0094] The embodiment of the present application can ultimately calculate the compression amount in layers according to the derived formula and accumulate the settlement value. The entire process is scientific and rigorous, and comprehensively considers various factors and the characteristics of soil at different stages, effectively improving the accuracy and scientificity of foundation settlement calculations.

[0095] According to the calculation method of foundation settlement proposed in the embodiment of the present application, various factors can be comprehensively considered, vertical additional stress can be accurately calculated, detailed soil layer parameters can be obtained, and thin layers of foundation soil can be carefully divided to calculate related stresses, thereby accurately obtaining the additional stress level and the small strain modulus. The tangent modulus and vertical strain can be reasonably calculated based on the shear stress level, and the settlement value can be obtained by accumulating compression. The calculation process is comprehensive and scientific. Compared with traditional methods, it can more accurately calculate foundation settlement, effectively improve the accuracy and reliability of the calculation results, and provide a more reliable basis for the design and construction of building foundations.

[0096] The following describes in detail the execution logic and effect of a method for calculating foundation settlement of the present application through two specific embodiments and in combination with the accompanying drawings:

[0097] In a specific embodiment of the present application, a square foundation ballast test was conducted on a saturated clay site. The foundation side length was 2.4m, the burial depth was 0.8m, and the graded loading was to p = 89kPa. The compression layer below the base can be roughly divided into 3 layers, each with a thickness of 4m and a weight of γ = 16kN / m 3 , undrained strength from top to bottom c u are 18kPa, 23kPa and 30kPa respectively, and the shear wave velocity V s They are 90m / s, 110m / s and 130m / s respectively.

[0098] According to the instantaneous settlement of the foundation calculated in the embodiment of the present application, it belongs to the undrained condition, and ν = 0.5. s The initial small strain shear modulus G0 of the three layers of soil are calculated to be 13.2MPa, 19.8MPa and 27.6MPa respectively. ur =G0,γ 0.7 =2.0×10 -4 , according to Δz = 0.1m thickness uniform layering, the load step number n = 10 in the large strain stage. The calculated load-settlement curve is compared with the test results (minus consolidation settlement) Figure 3 As shown, it can be seen that the two are basically consistent, which proves the applicability of the embodiment of the present application.

[0099] In another specific embodiment of the present application, a square foundation ballast test is conducted on a sand foundation, the foundation side length is 3.0m, the burial depth is 0.8m. The sand layer is 10.7m thick, and the bedrock is below it. The internal friction angle of the shallow layer 5m is Heavy γ=15.5kN / m 3 , shear wave velocity Vs =240m / s. The groundwater depth is 4.9m. Each load level is 890kN (98.9kPa). The load is maintained until the settlement is basically stable. After applying the 5th and 9th load levels, an unloading-reloading cycle is performed.

[0100] According to the embodiment of the present application, the settlement of the foundation is calculated under the drainage condition, and K0=1-sin32°=0.47, ν=K0 / (1+K0)=0.32. s The initial small strain shear modulus G0 = 91 MPa is calculated, which is the modulus within the shallow layer of 5 m, so the reference value of the self-weight stress calculation at a depth of 2.5 m is taken. Right now:

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[0103] For sandy soil, c = 0. γ 0.7 =3.1×10 -4 , according to Δz = 0.1m thickness uniform layering, the large strain stage load step number n = 20. The calculated load-settlement curve is compared with the test results. Figure 4 As shown, it can be seen that the two are quite close.

Claims

1. A method for calculating foundation settlement, characterized in that: The following steps are involved: Dividing the base plane into a plurality of rectangular blocks, determining an additional pressure coefficient of each of the plurality of rectangular blocks, and determining a base additional pressure distribution according to the additional pressure coefficient; Obtain the geological profile of the location where settlement is to be calculated and the physical and mechanical parameters of each layer of soil; Divide the foundation soil into multiple thin layers, calculate the self-weight stress and additional vertical stress at the middle depth of thin layers of different depths based on the physical and mechanical parameters of each layer of soil and the additional pressure distribution of the base, and determine the initial small strain modulus under the corresponding stress level through the self-weight stress and the additional vertical stress, and determine the initial stiffness of the spring reflecting the lateral constraint of the soil according to the initial small strain modulus; In the small strain stage, the initial deformation modulus and the initial stiffness of the spring are reduced according to the shear strain, and when entering the large strain stage, the tangent modulus is calculated according to the shear stress level, so as to calculate the vertical strain of each thin layer according to the tangent modulus; The compression amount is obtained according to the vertical strain of each thin layer, and the compression amount is accumulated to obtain the settlement value of the building foundation.

2. The method according to claim 1, characterized in that The method divides the foundation soil into a plurality of thin layers, calculates the self-weight stress and the additional vertical stress at the middle depth of the thin layers at different depths based on the physical and mechanical parameters of the soil layers and the additional pressure distribution of the base, determines the initial small strain modulus at the corresponding stress level through the self-weight stress and the additional vertical stress, and determines the initial stiffness of the spring reflecting the lateral constraint of the soil according to the initial small strain modulus, including: Dividing the foundation soil into the plurality of thin layers, and calculating the self-weight stress and the additional vertical stress at the middle depth of the thin layers of different depths according to the physical and mechanical parameters of each layer of soil and the distribution of additional pressure on the base; Based on the ratio of the deformation modulus of the soil corresponding to the small strain modulus to the spring stiffness, the additional horizontal stress is calculated, and the initial small strain modulus under the corresponding stress level is calculated using the self-weight stress and the additional stress, and the initial stiffness of the spring reflecting the lateral constraint of the soil is determined by the small strain shear modulus.

3. The method according to claim 1, characterized in that The initial deformation modulus and the initial stiffness of the spring are reduced according to the shear strain in the small strain stage, and the tangent modulus is calculated according to the shear stress level when entering the large strain stage, so as to calculate the vertical strain of each thin layer according to the tangent modulus, including: Constructing a calculation model of an additional horizontal spring, and determining a vertical strain calculation strategy corresponding to the calculation model of the additional horizontal spring; Determining the boundary stress between the small strain stage and the large strain stage, and judging the current strain stage according to the boundary stress and the additional vertical stress; When in the small strain stage, based on the vertical strain calculation strategy and the reduction curve of small strain stiffness with shear strain, the soil modulus and the initial stiffness of the spring are synchronously reduced to obtain the vertical strain corresponding to the reduced modulus; When the vertical strain enters the large strain stage, based on the Duncan-Zhang model and the vertical strain calculation strategy, the initial deformation modulus is reduced according to the shear stress level, and the vertical strain of each thin layer is calculated and accumulated step by step.

4. The method according to claim 3, characterized in that The mathematical expression of the vertical strain calculation strategy corresponding to the calculation model of the additional horizontal spring is: Among them, ε z is the vertical strain, σ z is the vertical additional stress, E is the deformation modulus, G is the shear modulus, ν is the Poisson's ratio, and α is the spring stiffness correction coefficient.

5. The method according to claim 3, characterized in that: The calculation formula of the vertical strain corresponding to the small strain stage is: Among them, ε z is the vertical strain corresponding to the small strain stage, σ z is the vertical additional stress, E0 is the initial deformation modulus, A is the elastic horizontal stress coefficient, and ν is the Poisson's ratio.

6. The method according to claim 3, characterized in that The calculation formula of the vertical strain corresponding to the large strain stage is: Among them, ε z is the vertical strain corresponding to the large strain stage, Δε z is the vertical strain increment, Δσ z is the vertical additional stress increment, E t is the tangent deformation modulus, G t is the tangent shear modulus, ν is the Poisson's ratio, and α is the spring stiffness correction factor.

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