A practical method for calculating additional settlement of foundation considering the "pot lid effect"

Abstract

The present invention discloses a practical method for calculating additional foundation settlement considering the "pot lid effect", which relates to the field of geotechnical engineering technology. The method comprises: calculating the increase in soil moisture content and suction variation at different depths caused by the "pot lid effect"; constructing unsaturated soil model parameters through indoor triaxial tests; and calculating foundation settlement based on the layered summation algorithm with the unsaturated soil UH constitutive model as the core. The present invention calculates the suction variation of soil at different depths and combines the soil parameters determined by indoor tests, takes the unsaturated soil UH constitutive model as the core, and establishes a calculation method for additional foundation settlement that correctly reflects the influence of the "pot lid effect" based on the layered summation algorithm, realizing for the first time the practical calculation of additional foundation settlement caused by the "pot lid effect".

Description

Technical Field

[0001] The invention relates to the technical field of geotechnical engineering, and in particular to a practical method for calculating additional foundation settlement taking into account a "pot cover effect". Background Art

[0002] The "pot lid effect" is a phenomenon in which water in the deep soil migrates from the warm area to the cold area in the form of water vapor under the drive of the temperature gradient, condenses in the cold area under the closed cover layer, and causes the moisture content of the shallow soil to increase. In geotechnical engineering analysis, the increase in moisture content caused by water vapor migration exists in large quantities in practice and has a significant impact on foundation settlement. Accurate settlement calculation is the key to engineering prediction and early warning.

[0003] The layered summation algorithm is a very important and widely used method for studying the settlement and deformation characteristics of foundations. The principle of this method is simple and it can reflect the settlement and deformation characteristics of soil under complex stress conditions. However, when using the layered summation algorithm to calculate foundation settlement, the wetting deformation of unsaturated soil caused by the "lid effect" is often ignored. In addition, the constitutive model used in calculating soil deformation cannot reasonably reflect the dilatancy, softening and wetting characteristics of unsaturated soil. These limitations lead to large deviations in the settlement calculation results of unsaturated foundation soils, which restricts the prediction accuracy of actual projects.

[0004] Under the influence of the "pot lid effect", the water content gradient and temperature gradient in the unsaturated foundation soil can cause the migration of gaseous water and the increase of water content in the unsaturated foundation soil, resulting in elastic-plastic deformation caused by reduced suction. The wetting deformation caused by the "pot lid effect" is often ignored in conventional foundation settlement calculations, thus underestimating the actual settlement of the soil.

[0005] In addition, the wetting deformation caused by the "pot lid effect" requires a constitutive model that can accurately describe the stress-strain relationship of unsaturated soil. However, the existing unsaturated soil model has the following problems:

[0006] (1) The existing constitutive model for unsaturated soil is established under the framework of the classic Cambridge model. When describing the stress-strain characteristics of overconsolidated soil, the wetting deformation of the soil is often underestimated due to the large elastic region.

[0007] (2) The existing constitutive model for unsaturated soil considers the deformation caused by stress and the deformation caused by suction separately, without considering the mutual coupling between the two, thus underestimating the total deformation of the soil;

[0008] (3) The difference in deformation caused by different saturation and overconsolidation of soil at different depths in the foundation cannot be considered. Traditional unsaturated soil constitutive models usually consider the effects of the current stress state, suction and overconsolidation separately, without considering the mutual coupling between the three, thus underestimating the total deformation of the soil.

[0009] In summary, it is difficult for existing technical means to accurately and conveniently calculate the additional settlement of the foundation affected by the "pot lid effect", which leads to a large deviation between the calculated results of the settlement of the foundation soil and the actual situation.

[0010] Therefore, it is necessary to provide a practical method for calculating additional settlement of foundation taking into account the “pot lid effect” to solve the above problems. Summary of the invention

[0011] The purpose of the present invention is to provide a practical method for calculating additional settlement of foundation considering the "pot cover effect", to determine the suction change based on the partial differential equation of water vapor migration and to determine the soil parameters based on indoor triaxial tests, and to establish a practical method for additional settlement of foundation affected by the "pot cover effect" by adopting a calculation method based on the unsaturated soil UH model.

[0012] To achieve the above object, the present invention provides a practical method for calculating additional settlement of foundation considering the "pot cover effect", comprising the following steps:

[0013] S1: Calculate the increase in soil moisture content and suction change at different depths caused by the “pot cover effect”;

[0014] S2: Conduct triaxial isotropic compression and triaxial shear tests on unsaturated soil under different suctions to construct model parameters of unsaturated soil under different suctions;

[0015] S3: Based on the UH constitutive model of unsaturated soil, the foundation settlement is calculated by the layered summation algorithm.

[0016] Preferably, the specific steps in step S1 are as follows:

[0017] S11: Based on the partial differential equation of water vapor migration in unsaturated soil and the difference form, the numerical solution of the water content change is obtained. The temperature gradient and water content gradient are considered in the partial differential equation of water vapor migration;

[0018] S12: The change in saturation is calculated based on the change in moisture content, and the suction value before and after the change in saturation is obtained through the soil-water characteristic equation:

[0019] ;

[0020] In the formula, Indicates the change in saturation. represents the derivative of the soil-water characteristic curve equation with respect to the suction variable, represents the derivative of the soil-water characteristic curve equation with respect to the void ratio variable, represents the change in void ratio, Indicates the change in suction force;

[0021] Preferably, in step S2, the following steps are specifically included:

[0022] S21: According to the initial stress state corresponding to the indoor triaxial specimen, the constitutive integral calculation of the unsaturated soil UH constitutive model along the isotropic compression strain path and the triaxial compression path is carried out to obtain the unit stress-strain curve of the model;

[0023] S22: Based on the indoor isotropic compression and triaxial shear test data, the parameters of the UH constitutive model are adjusted, and the calculated unit stress-strain curve is fitted with the test data to obtain the suction parameters, compression coefficient, rebound coefficient and triaxial critical state stress ratio of overconsolidated or normally consolidated soil under different suctions.

[0024] Preferably, step S3 specifically includes the following steps:

[0025] S31: Suction force before and after the moisture content changes calculated in step S12 s and the suction parameter obtained in step S22 a , substitute into the following formula to get the suction value before and after the moisture content changes p s :

[0026] ;

[0027] S32: Divide the foundation soil into several soil layers, and reduce the thickness of the soil layers in areas with large changes in moisture content. ; For the divided soil layers, the unsaturated soil UH model is used to calculate the wetting elastic-plastic deformation caused by the change of matrix suction :

[0028] ;

[0029] In the formula, p s1 and p s2 is the suction value before and after the moisture content changes, p i is the current stress state of the soil layer, , and M are the isotropic compression, isotropic rebound and critical state stress ratio parameters calibrated based on triaxial tests;

[0030] S33: According to the hierarchical summation algorithm, n The deformations calculated for each layer of soil are added together, and the total settlement of the foundation is obtained by the following formula :

[0031] .

[0032] Therefore, the present invention adopts the above-mentioned practical method for calculating additional foundation settlement taking into account the "pot cover effect", which has the following beneficial effects:

[0033] (1) The present invention uses the partial differential equation of vapor water migration to calculate the increase in moisture content in the foundation soil, taking into account the elastic-plastic deformation caused by unsaturated wetting.

[0034] (2) Compared with the single calculation of the traditional unsaturated soil constitutive model, the present invention adopts the unsaturated soil UH model which can accurately calculate the stress-strain relationship of unsaturated soil, fully considers the coupling effect of the current stress state, suction and overconsolidation, and obtains accurate foundation settlement value accordingly.

[0035] (3) The foundation settlement calculation formula of the present invention only requires simple basic geotechnical engineering mechanical tests to obtain soil parameters, so the operation is less difficult, the cost is low, and the repeatability is high.

[0036] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a principle diagram of a practical method for calculating additional settlement of foundation taking into account the "pot cover effect" of the present invention;

[0038] Figure 2 The present invention is a flow chart of an embodiment of a practical method for calculating additional settlement of a foundation taking into account the "pot cover effect". DETAILED DESCRIPTION

[0039] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0040] Unless otherwise defined, technical or scientific terms used in the present invention shall have the common meanings understood by one having ordinary skills in the field to which the present invention belongs.

[0041] The words "include" or "comprises" and the like used in the present invention mean that the elements before the word include the elements listed after the word, and do not exclude the possibility of also including other elements. The orientation or position relationship indicated by the terms "inside", "outside", "upper", "lower", etc. is based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it cannot be understood as a limitation of the present invention. When the absolute position of the described object changes, the relative position relationship may also change accordingly. In the present invention, unless otherwise clearly specified and limited, the terms "attachment" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral body; it can be directly connected, or indirectly connected through an intermediate medium, and it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0042] Example

[0043] like Figure 1-Figure 2 As shown, the present invention provides a practical method for calculating additional settlement of foundation considering the "pot cover effect". According to the layered summation algorithm, with the unsaturated soil UH model as the core, the moisture content increase caused by water vapor migration is calculated and the soil parameters are obtained through indoor triaxial tests, so as to realize the correct calculation of additional settlement of foundation affected by the "pot cover effect". Specifically, the following steps are included:

[0044] S1: Calculate the increase in water content and suction change of soil at different depths caused by the "pot cover effect"; the specific steps in step S1 are as follows:

[0045] S11: Based on the partial differential equation of water vapor migration in unsaturated soil and the difference form, the numerical solution of the water content change is obtained. The temperature gradient and water content gradient are considered in the partial differential equation of water vapor migration;

[0046] S12: The change in saturation is calculated based on the change in moisture content, and the suction value before and after the change in saturation is obtained through the soil-water characteristic equation:

[0047] ;

[0048] In the formula, Indicates the change in saturation. represents the derivative of the soil-water characteristic curve equation with respect to the suction variable, represents the derivative of the soil-water characteristic curve equation with respect to the void ratio variable, represents the change in porosity ratio, Indicates the change in suction force;

[0049] S2: conducting triaxial isotropic compression and triaxial shear tests on unsaturated soil under different suctions, and constructing unsaturated soil model parameters under different suctions; in step S2, the following steps are specifically included:

[0050] S21: According to the initial stress state corresponding to the indoor triaxial specimen, the constitutive integral calculation of the unsaturated soil UH constitutive model along the isotropic compression strain path and the triaxial compression path is carried out to obtain the unit stress-strain curve of the model;

[0051] S22: Based on the indoor isotropic compression and triaxial shear test data, the UH constitutive model parameters are adjusted, and the calculated unit stress-strain curves are fitted with the test data to obtain the suction parameters of unsaturated soils at different depths. a , compression coefficient, rebound coefficient and triaxial critical state stress ratio M .

[0052] S3: Taking the unsaturated soil UH constitutive model as the core, the foundation settlement is calculated by the layered summation algorithm. In step S3, the following steps are specifically included:

[0053] S31: Suction force before and after the moisture content changes calculated in step S12 s and the suction parameter obtained in step S22 a , substitute into the following formula to get the suction value before and after the moisture content changes p s :

[0054] ;

[0055] S32: Divide the foundation soil into several soil layers, and reduce the thickness of the soil layers in areas with large changes in moisture content. ; For the divided soil layers, the unsaturated soil UH model is used to calculate the wetting elastic-plastic deformation caused by the change of matrix suction :

[0056] ;

[0057] In the formula, p s1 and p s2 is the suction value before and after the moisture content changes, p i is the current stress state of the soil layer, , and M are the isotropic compression, isotropic rebound and critical state stress ratio parameters calibrated based on triaxial tests;

[0058] S33: According to the hierarchical summation algorithm,n The deformations calculated for each layer of soil are added together, and the total settlement of the foundation is obtained by the following formula :

[0059] .

[0060] Therefore, the present invention adopts the above-mentioned practical method for calculating additional foundation settlement taking into account the "pot cover effect", based on the layered summation algorithm, with the unsaturated soil UH model as the core, obtains the increase in moisture content caused by water vapor migration by calculation and obtains soil parameters through indoor triaxial tests, thereby establishing a practical algorithm for additional foundation settlement that correctly reflects the influence of the "pot cover effect".

[0061] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A practical method for calculating additional settlement of foundation considering the "pot cover effect", characterized by: The following steps are involved: S1: Calculate the increase in soil moisture content and suction change at different depths caused by the "pot cover effect"; The specific steps in step S1 are as follows: S11: Numerical solution of the change of water content based on the partial differential equation of vapor water migration in unsaturated soil and the difference form; S12: The change in saturation is calculated based on the change in moisture content, and the suction value before and after the change in saturation is obtained through the soil-water characteristic equation: ； In the formula, Indicates the change in saturation. represents the derivative of the soil-water characteristic curve equation with respect to the suction variable, represents the derivative of the soil-water characteristic curve equation with respect to the void ratio variable, represents the change in porosity ratio, Indicates the change in suction force; S2: Conduct triaxial isotropic compression and triaxial shear tests on unsaturated soil under different suctions to construct model parameters of unsaturated soil under different suctions; In step S2, the following steps are specifically included: S21: According to the initial stress state corresponding to the indoor triaxial specimen, the constitutive integral calculation of the unsaturated soil UH constitutive model along the isotropic compression strain path and the triaxial compression path is carried out to obtain the unit stress-strain curve of the model; S22: Based on the indoor isotropic compression and triaxial shear test data, the parameters of the UH constitutive model are adjusted, and the calculated unit stress-strain curve is fitted with the test data to obtain the suction parameters, compression coefficient, rebound coefficient and triaxial critical state stress ratio of the over-consolidated or normally consolidated soil under different suctions; S3: Based on the UH constitutive model of unsaturated soil, foundation settlement calculation is performed through the layered summation algorithm; Step S3 specifically includes the following steps: S31: Suction force before and after the moisture content changes calculated in step S12 s and the suction parameter obtained in step S22 a , substitute into the following formula to get the suction value before and after the moisture content changes p s : ； S32: Divide the foundation soil into several soil layers, and reduce the thickness of the soil layers in areas with large changes in moisture content. ; For the divided soil layers, the unsaturated soil UH model is used to calculate the wetting elastic-plastic deformation caused by the change of matrix suction : ； In the formula, p s1 and p s2 is the suction value before and after the moisture content changes, p i is the current stress state of the soil layer, , and are the isotropic compression, isotropic rebound and critical state stress ratio parameters calibrated based on triaxial tests; S33: According to the hierarchical summation algorithm, n The deformations calculated for each layer of soil are added together, and the total settlement of the foundation is obtained by the following formula : 。

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