Soft soil settlement prediction method considering nonlinear permeability

Abstract

The invention discloses a soft soil settlement prediction method considering nonlinear permeability, which comprises the following steps of: firstly, collecting a soil sample of a target soft soil area to be predicted, performing a large-scale consolidation-permeability test, and measuring data of a permeability coefficient k and a void ratio e of a soil body when settlement is stable under the action of different consolidation stresses # imgabs0 #; fitting a relation model between the permeability coefficient k and the void ratio e and a relation model between the permeability coefficient k and the consolidation stress # imgabs1 #; according to the obtained relation model between the permeability coefficient k and the void ratio e and the obtained relation model between the permeability coefficient k and the consolidation stress # imgabs2, a soil consolidation control model influenced by the load effect under a solid-phase coordinate system is constructed, and a difference equation of the soil consolidation control model is determined; finally, for a target soft soil area to be predicted, the obtained difference equation is adopted, and according to the load condition, the soil consolidation settlement amount is solved and calculated.

Description

Technical Field

[0001] The invention belongs to the technical field of soft soil settlement calculation, and in particular relates to a soft soil settlement prediction method considering nonlinear permeability. Background Art

[0002] Soft soils usually exhibit high compressibility and low permeability, which makes their settlement behavior a key issue in engineering design and construction. Traditional soft soil settlement prediction methods are usually based on the linear permeability assumption. However, this assumption is often not accurate enough in actual engineering, especially when the nonlinear characteristics of the soil are significant. Its permeability changes with the stress state and porosity of the soil, which significantly affects the settlement of the soil. At present, there are several methods for calculating soft soil settlement: standard method, nonlinear consolidation settlement analytical solution and numerical simulation method. Among them, the standard method is simple to calculate and is widely used in engineering, but it cannot consider the nonlinear permeability characteristics of soft soil, and the calculated settlement has certain errors; while the nonlinear consolidation settlement analytical solution or numerical simulation method can consider the nonlinear permeability characteristics of soft soil, but it has the following disadvantages: ① The permeability coefficient is obtained by traditional indoor permeability test or consolidation-permeability combined instrument. Since the soil sample is only 2 cm thick, it is impossible to consider the influence of size effect on permeability coefficient, especially the main consolidation settlement of deep soft soil is often accompanied by creep, and the 2 cm thick soil sample is difficult to reproduce the size effect and complexity in actual engineering; ② In actual engineering, soft soil settlement is usually affected by multi-level loading, and traditional settlement prediction methods often assume a single loading condition, which makes it difficult to accurately calculate the settlement behavior under multi-level loading. Therefore, it is urgent to develop a new method to accurately and efficiently predict soft soil settlement. Summary of the invention

[0003] The purpose of the present invention is to solve the deficiencies of the prior art and provide a soft soil settlement prediction method taking nonlinear permeability into consideration.

[0004] The present invention is achieved through the following technical solutions: A method for predicting soft soil settlement considering nonlinear permeability includes the following steps: Step 1: Collect soil samples from the target soft soil area to be predicted, conduct large-scale consolidation-permeability tests, and measure different consolidation stresses. Under the action of k And the porosity ratio e data; Step 2: Fit the permeability coefficient based on the test data obtained in step 1 k and porosity ratio e The relationship model between k and consolidation stress The relationship model between Step 3: Based on the permeability coefficient obtained in step 2k and porosity ratio e The relationship model between the conductivity and permeability k and consolidation stress The relationship model between them is constructed to build the soil consolidation control model under the influence of load in the solid phase coordinate system; Step 4: Determine the differential equation of the soil consolidation control model under the influence of load in the solid phase coordinate system obtained in step 3; Step 5: For the target soft soil area to be predicted, use the differential equation obtained in step 4 and solve and calculate the soil consolidation settlement according to the load conditions.

[0005] In the above technical solution, the permeability coefficient k and porosity ratio e The relationship model between them is: ; In the formula, k —Permeability coefficient, unit: m / s; e —porosity ratio; A, B, C are fitting parameters.

[0006] In the above technical solution, the permeability coefficient k and consolidation stress The relationship model between them is: ; In the formula, —consolidation stress, unit: kPa; —Yield stress, unit: kPa; D, E, F, G and H are fitting parameters.

[0007] In the above technical solution, the height of the soil sample in the large-scale consolidation-permeability test is not less than 20 cm; the stability standard for each level of load is that the deformation per hour is less than 0.02 mm.

[0008] In the above technical solution, step 3 includes the following steps: Step 3.1: Establish the consolidation control equation of large deformation soil in the flow coordinate system: ; In the formula, — flow coordinates, , z is the solid phase coordinate, t For time; —Effective stress, unit: kPa; —Specific gravity of water, unit: kN / m 3 ; — specific gravity of soil; Step 3.2: According to the flow coordinates Solid phase coordinatesz The relationship between the consolidation control equation of large deformation soil in the solid coordinate system is obtained; ; Step 3.3: Establish the void ratio based on the effective stress principle and soil force balance condition e The relationship equation changes with depth: ; Step 3.4: According to the porosity ratio of step 3.3 e The relationship equation changes with depth, and the permeability coefficient is obtained k The relationship equation with consolidation change: ; Step 3.5: Substitute the permeability coefficient obtained in step 2 k and porosity ratio e The relationship model between the conductivity and permeability k and consolidation stress The relationship model between the porosity ratio obtained in step 3.3 e The relationship equation with depth and the permeability coefficient obtained in step 3.4 k Substitute the equation of the relationship between consolidation and deformation into the large deformation soil consolidation control equation in the solid phase coordinate system in step 3.2 to obtain the soil consolidation control equation in the solid phase coordinate system: ; When the soil is subjected to load during consolidation q is a uniformly distributed load that varies with time. According to the effective stress principle, the soil consolidation control equation in the solid phase coordinate system is transformed to obtain the soil consolidation control model under the influence of load in the solid phase coordinate system: ; In the formula, u It indicates pore pressure; ; ; .

[0009] In the above technical solution, step 4 includes the following steps: Step 4.1: Perform dimensionless processing on the soil consolidation control model under load in the solid phase coordinate system obtained in step 3: ; In the formula, ,in, u is the pore pressure, is the final value of the load, z is the soil depth, is the soil height, is the initial permeability coefficient, is the initial compression modulus; ; ; ; Step 4.2: Perform differential processing on the model after dimensionless processing in step 4.1 to obtain its differential equation: ; In the formula, is the spatial step length; is the time step; is a spatial node, , is the total number of spatial grids; For the time node.

[0010] In the above technical solution, in step 5, according to the solution conditions, the pursuit method is used to solve the differential equation to obtain the soil settlement The calculation formula is as follows: ; In the formula, m Represents the slope of the compression curve.

[0011] The advantages and beneficial effects of the present invention are: ① By adopting a large-scale consolidation-permeability test soil sample with a height of not less than 20 cm (the traditional method is only 2 cm), the boundary effect interference caused by small-size samples is significantly reduced, which can truly reflect the changing characteristics of the permeability coefficient of the deep soft soil layer during the consolidation process and the creep effect of the consolidation process; ② A dual-parameter dynamic correlation model of permeability coefficient-porosity ratio and permeability coefficient-stress is established simultaneously, breaking through the limitations of the traditional single permeability model; ③ The consolidation control equation constructed by the differential equation can dynamically couple the application process of multi-level loads, accurately reflecting the changes in the soil permeability path and drainage boundary conditions caused by graded loading in actual engineering, and solving the settlement prediction lag problem caused by the single loading assumption of the traditional method. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is a flow chart of the steps of the present invention.

[0013] Figure 2 yes e-k v Model fitting curve.

[0014] Figure 3 yes s - k v Model fitting curve.

[0015] Figure 4 It is the time history curve of calculated settlement and experimental settlement.

[0016] For ordinary technicians in this field, other relevant drawings can be obtained based on the above drawings without any creative work. DETAILED DESCRIPTION

[0017] In order to enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention is further described below in conjunction with specific embodiments.

[0018] A method for predicting soft soil settlement considering nonlinear permeability is shown in the Appendix. Figure 1 , including the following steps: Step 1: Collect soil samples from the target soft soil area to be predicted, conduct large-scale consolidation-permeability tests, and collect test data.

[0019] Measurement of different consolidation stresses through large-scale consolidation-permeability tests Under the action of k And the porosity ratio e data.

[0020] Step 2: Fit the permeability coefficient based on the test data obtained in step 1 k and porosity ratio e The relationship model between k - e model) and the permeability coefficient k and consolidation stress The relationship model between k - s Model).

[0021] k - e Model: (1); In the formula, k —Permeability coefficient, unit: m / s; e —porosity ratio; A, B, C are fitting parameters.

[0022] Model: (2); In the formula, s —consolidation stress, unit: kPa; s c —Yield stress, unit: kPa; D, E, F, G and H are fitting parameters.

[0023] It should be pointed out that the soil sample height of the large-scale consolidation-permeability test should be no less than 20 cm. k - e Model and k - s The model takes into account the influence of soil sample size on consolidation. The permeability coefficient varies during consolidation engineering, that is, the consolidation process is large strain consolidation. The stability standard for each load level is that the deformation per hour is less than 0.02mm.

[0024] Step 3: Based on the permeability coefficient obtained in step 2 k and porosity ratio e The relationship model between the conductivity and permeability k and consolidation stress s The relationship model between them is established, and the soil consolidation control model affected by load in the solid phase coordinate system is constructed.

[0025] Step 3.1: Establish the consolidation control equation of large deformation soil in the flow coordinate system.

[0026] The governing equation for consolidation of large deformation soil in the flow coordinate system is shown in equation (3): (3); In the formula, — flow coordinates, , z is the solid phase coordinate, t For time; —Effective stress, unit: kPa; —Specific gravity of water, unit: kN / m 3 ; — specific gravity of soil; Step 3.2: According to the flow coordinates Solid phase coordinates z The relationship between and is used to obtain the governing equation for consolidation of soil with large deformation in the solid coordinate system.

[0027] Flow coordinates Solid phase coordinates z The relationship is as follows: (4); Substituting equation (4) into equation (3), we can obtain the consolidation control equation of large deformation soil in the solid phase coordinate system: (5); Step 3.3: Establish the void ratio based on the effective stress principle and soil force balance condition e The relationship equation varies with depth.

[0028] From the effective stress principle and the soil force balance condition, we can know that: (6); According to the above formula (6), the porosity ratio can be obtained e The relationship equation changes with depth: (7); Step 3.4: According to the porosity ratio of step 3.3 e The relationship equation changes with depth, and the permeability coefficient is obtained k The relationship equation changes with soil consolidation: (8); Step 3.5: Substitute the permeability coefficient obtained in step 2 k and porosity ratio e The relationship model between k - e model) and permeability coefficient k and consolidation stress s The relationship model between k - s Model), the porosity ratio obtained in step 3.3 e The relationship equation with depth and the permeability coefficient obtained in step 3.4 k Substitute the equation of the relationship with soil consolidation into the large deformation soil consolidation control equation in the solid phase coordinate system in step 3.2 to obtain the soil consolidation control equation in the solid phase coordinate system. That is, substitute equations (1), (2), (7) and (8) into equation (5) to obtain the soil consolidation control equation in the solid phase coordinate system, as shown in equation (9): (9); When the soil is subjected to load during consolidation q is the uniformly distributed load that varies with time According to the effective stress principle, the equation (9) is transformed to obtain the soil consolidation control model under the influence of load in the solid phase coordinate system: (10); In the formula, u It indicates pore pressure; (11); (12); (13); Step 4: Determine the differential equation of the soil consolidation control model under load in the solid phase coordinate system obtained in step 3.

[0029] Step 4.1: The soil consolidation control model under load in the solid phase coordinate system obtained in step 3 (i.e., Equation 10) is dimensionlessly processed: (14); In the formula, ,in, u is the pore pressure, is the final value of the load, z is the soil depth, is the soil height, is the initial permeability coefficient, is the initial compression modulus; (15); (16); (17); Step 4.2: Perform differential processing on the model after dimensionless processing in step 4.1 to obtain its differential equation: (18); In the formula, is the spatial step length; is the time step; is a spatial node, , is the total number of spatial grids; For the time node.

[0030] Step 5: For the target soft soil area to be predicted, use the differential equation obtained in step 4 and solve and calculate the soil consolidation settlement according to the load conditions.

[0031] Set the solution conditions as follows: Initial conditions: ; Boundary conditions: .

[0032] According to the solution conditions, the pursuit method is used to solve the differential equation to obtain the soil settlement The calculation formula is as follows: ; In the formula, m represents the slope of the compression curve, m Obtained from the compression curve.

[0033] Verification example: Prepare remolded soil sample with a density of 1.56 kg / cm 3 The water content is 68.3%, the initial porosity is 1.812, the specific gravity is 2.71, the sample size is 20cm×Φ25cm, and a large-scale consolidation permeability test is carried out. The load levels are 6kPa, 21kpa, 36kPa, 67kPa, 83kpa, 98kPa, 128kPa and 160kPa. The stability standard of each load level is a deformation of less than 0.02mm per hour.

[0034] According to the test results: k - e Model fitting curve Figure 2 , k - s Model fitting curve Figure 3 ; k - e Model: ; k - s Model: .

[0035] Will k - e Model and k - s Substituting the model parameters into equation (10), we get: ; Where: ; ; ; According to formulas (15), (16) and (17), we can obtain: ; ; ; Finally, the differential equation was solved and the soil consolidation settlement in 2487 hours was calculated to be 75.71 mm, while the soil settlement obtained from the test was 73.63 mm, with a calculation error of 1.4%. The calculated settlement and test settlement time history curves are shown in Figure 4 .

[0036] The present invention is described above by way of example. It should be noted that, without departing from the core of the present invention, any simple deformation, modification or other equivalent replacement that can be made by those skilled in the art without inventive effort falls within the protection scope of the present invention.

Claims

1. A soft soil settlement prediction method considering nonlinear permeability, characterized in that: The following steps are involved: Step 1: Collect soil samples from the target soft soil area to be predicted, conduct large-scale consolidation-permeability tests, and measure different consolidation stresses. Under the action of k And the porosity ratio e data; Step 2: Fit the permeability coefficient based on the test data obtained in step 1 k and porosity ratio e The relationship model between k and consolidation stress The relationship model between Step 3: Based on the permeability coefficient obtained in step 2 k and porosity ratio e The relationship model between the conductivity and permeability k and consolidation stress The relationship model between them is constructed to build the soil consolidation control model under the influence of load in the solid phase coordinate system; Step 4: Determine the differential equation of the soil consolidation control model under the influence of load in the solid phase coordinate system obtained in step 3; Step 5: For the target soft soil area to be predicted, use the differential equation obtained in step 4 and solve and calculate the soil consolidation settlement according to the load conditions.

2. The method for predicting soft soil settlement considering nonlinear permeability according to claim 1 is characterized in that: Permeability coefficient k and porosity ratio e The relationship model between them is: ; In the formula, k —Permeability coefficient, unit: m / s; e —porosity ratio; A, B, C are fitting parameters.

3. The method for predicting soft soil settlement considering nonlinear permeability according to claim 2 is characterized in that: Permeability coefficient k and consolidation stress The relationship model between them is: ; In the formula, —consolidation stress, unit: kPa; —Yield stress, unit: kPa; D, E, F, G and H are fitting parameters.

4. The method for predicting soft soil settlement considering nonlinear permeability according to claim 1 is characterized in that: The height of soil samples for large-scale consolidation-permeability test shall not be less than 20cm; the stability standard for each level of load is that the deformation per hour is less than 0.02mm.

5. The method for predicting soft soil settlement considering nonlinear permeability according to claim 3 is characterized in that: Step 3 includes the following steps: Step 3.1: Establish the consolidation control equation of large deformation soil in the flow coordinate system: ; In the formula, — flow coordinates, , z is the solid phase coordinate, t For time; —Effective stress, unit: kPa; —Specific gravity of water, unit: kN / m 3 ; — specific gravity of soil; Step 3.2: According to the flow coordinates Solid phase coordinates z The relationship between the consolidation control equation of large deformation soil in the solid coordinate system is obtained; ; Step 3.3: Establish the void ratio based on the effective stress principle and soil force balance condition e The relationship equation changes with depth: ； Step 3.4: According to the porosity ratio of step 3.3 e The relationship equation changes with depth, and the permeability coefficient is obtained k The relationship equation with consolidation change: ； Step 3.5: Substitute the permeability coefficient obtained in step 2 k and porosity ratio e The relationship model between the conductivity and permeability k and consolidation stress The relationship model between the porosity ratio obtained in step 3.3 e The relationship equation with depth and the permeability coefficient obtained in step 3.4 k Substitute the equation of the relationship between consolidation and deformation into the large deformation soil consolidation control equation in the solid phase coordinate system in step 3.2 to obtain the soil consolidation control equation in the solid phase coordinate system: ； When the soil is subjected to load during consolidation q is a uniformly distributed load that varies with time. According to the effective stress principle, the soil consolidation control equation in the solid phase coordinate system is transformed to obtain the soil consolidation control model under the influence of load in the solid phase coordinate system: ； In the formula, u It indicates pore pressure; ； ； 。 6. The method for predicting soft soil settlement considering nonlinear permeability according to claim 5 is characterized in that: Step 4 includes the following steps: Step 4.1: Perform dimensionless processing on the soil consolidation control model under load in the solid phase coordinate system obtained in step 3: ； In the formula, ,in, u is the pore pressure, is the final value of the load, z is the soil depth, is the soil height, is the initial permeability coefficient, is the initial compression modulus; ； ； ； Step 4.2: Perform differential processing on the model after dimensionless processing in step 4.1 to obtain its differential equation: ； In the formula, is the spatial step length; is the time step; is a spatial node, , is the total number of spatial grids; For the time node.

7. The method for predicting soft soil settlement considering nonlinear permeability according to claim 6 is characterized in that: In step 5, according to the solution conditions, the pursuit method is used to solve the difference equation to obtain the soil settlement The calculation formula is as follows: ； In the formula, m Represents the slope of the compression curve.

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