Determination method of Burgers model parameters for coarse-grained soil and model construction method considering wetting effect

Abstract

The present invention relates to a method for determining the parameters of the Burgers model for coarse-grained soil and a method for constructing a model considering the wetting effect. First, the creep deformation data of the soil body under different wetting degrees are obtained through direct shear creep tests on coarse-grained soil. Then, the test data can be used to simply determine the constitutive parameters required for the Burgers model, and the formula for the soil body parameters under different wetting degrees is established, enabling the parameters to be directly used for numerical simulation. For actual engineering, a numerical model is established, and the Burgers model considering the wetting effect with known constitutive parameters is obtained using the above construction method, which can obtain reasonable constitutive and external conditions for predicting long-term deformation. In the test device, the direct shear box is set in the form of an external direct shear box, an internal direct shear box, a cross-shaped support, and a water storage bag, replacing the traditional direct shear box composed of two equal-sized shear boxes in the upper and lower parts, and long-term shear tests under two working conditions of soaking and dry-wet cycling can be realized, that is, long-term loading under the working conditions of long-term soaking and dry-wet cycling is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of geotechnical engineering, and particularly relates to a method for determining the parameters of the Burgers model applicable to coarse-grained soil and a method for constructing a model considering the wetting effect. Background Art

[0002] The rock-fill dam composed of coarse-grained soil is the main dam type of dams in China at present. However, during the actual operation of the rock-fill dam, obvious deformation will occur to its dam body, and this kind of deformation usually lasts for a long time. An important reason for the long-term deformation of the dam body is its main building material - coarse-grained soil. At present, the long-term deformation prediction of coarse-grained soil is carried out through numerical simulation by constructing a constitutive model. However, most models basically only consider the influence of load factors on the long-term deformation prediction of soil, and do not consider the wetting effect. According to the existing observation data, it shows that the deformation rate of the dam body before and after rainfall is significantly higher than that during the non-rainfall period. How to consider the influence of the wetting effect on the long-term deformation of coarse-grained soil is a blank in the current research field.

[0003] The FLAC3D program provides a non-linear deformation model - the Burgers model for simulating the long-term deformation of materials. However, the constitutive parameters required by it generally cannot be directly determined by experiments, and there are often great human factors and uncertainties in the determination of constitutive parameters. In order to consider the wetting effect, a new method for constructing the Burgers model is provided to realize the objective and convenient use of the model. Summary of the Invention

[0004] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a method for determining the parameters of the Burgers model applicable to coarse-grained soil and a method for constructing a model considering the wetting effect. The Burgers model considering the wetting effect obtained by this construction method is applicable to the long-term deformation prediction of coarse-grained soil with different wetting degrees.

[0005] The purpose of the present invention is realized by the following technical solutions:

[0006] In the first aspect, the present invention provides a method for determining the parameters of the Burgers model for coarse-grained soil. The determination method includes the following contents:

[0007] Express the stress-strain equation of the Burgers model as Equation (2)

[0008] ε = A + Bt + C(1 - e -Dt ) (2),

[0009] where t is time; ε is the shear strain of the soil; A, B, C, and D are parameters respectively, τ is the shear stress applied to the material; me For the elastic modulus of the Maxwell body and m in the Burgers model η For the viscous modulus of the Maxwell body and k in the Burgers model e For the elastic modulus of the Kelvin body and k in the Burgers model η For the viscous modulus of the Kelvin body in the Burgers model;

[0010] Adopt direct shear creep test and parameter fitting methods according to different parameter characteristics to determine the values of parameters A, B, C, and D;

[0011] The determination process of parameter A is as follows: Set the target shear stress value. The shear strain value of the coarse-grained soil during the period from the start of the direct shear creep test to the first time the shear stress reaches the set target shear stress value is parameter A. Then, according to And the set target shear stress value to determine the constitutive parameter m e ;

[0012] The determination process of parameters B and C is as follows:

[0013] Conduct a direct shear creep test to obtain the shear strain-time curve of the object to be measured. When t→∞, Equation (2) is: ε = A + Bt + C. At this time, the shear strain-time curve is approximately a straight line. Draw the asymptote of its curve to obtain the slope and intercept values of the asymptote. The asymptote intersects the strain axis at the point (0, A + C); After determining the value of parameter A, according to the point (0, A + C), obtain parameter C, and then according to Determine the constitutive parameter k e ; The expression of the asymptote can be calculated by taking any two points on the gently deformed section at the end of the soil shear strain-time curve;

[0014] Determine parameter B according to the value of the asymptote slope, and then according to Determine the constitutive parameter m η , where τ is the shear stress suffered by the material when t→∞;

[0015] Fitting of parameter D:

[0016] After determining the values of parameters A, B, and C, use Origin software, input Equation (2), and input the values of A, B, and C. Let Origin software automatically calculate parameter D according to the soil shear strain-time curve determined by the direct shear creep test, and according to Obtain the constitutive parameter k therefrom η .

[0017] In the second aspect, the present invention provides a method for constructing a model considering the wetting effect. The model is the Burgers model of coarse-grained soil, which is a rheological model. The construction method includes the following contents:

[0018] 1) Conduct direct shear creep tests on soil under different normal stresses σ and different shear stresses τ under the natural water content state to obtain the soil shear strain-time curves under different stresses in the natural water content state; according to the soil shear strain-time curves under different stresses in the natural water content state, use the above-mentioned method for determining the parameters of the Burgers model to determine the corresponding values of parameters A, B, C, and D and the constitutive parameter values respectively, and then obtain the functional relationship between the four constitutive parameters and the stress in the natural water content state, that is, the constitutive parameter expression in the natural water content state;

[0019] 2) Conduct direct shear creep tests on soil under the same normal stress and shear stress as in the natural water content state under the soaking and dry-wet cycling states respectively to obtain the soil shear strain-time curves under different stresses in the soaking and dry-wet cycling states; determine the corresponding values of parameters A, B, C, and D and the constitutive parameter values respectively according to the soil strain-time curves under different stresses in the soaking and dry-wet cycling states, and then obtain the functional relationship between the four constitutive parameters and the stress in the soaking and dry-wet cycling states;

[0020] 3) Compare the constitutive parameters in the soaking and dry-wet cycling states with the corresponding constitutive parameters in the natural water content state respectively, and determine the soaking wetting coefficients and dry-wet cycling wetting coefficients of the four constitutive parameters in the soaking and dry-wet cycling states respectively;

[0021] 4) Based on the constitutive parameter expression in the natural water content state, introduce the above-mentioned soaking wetting coefficient and dry-wet cycling wetting coefficient into the constitutive parameter expression in the natural water content state to convert it into the constitutive parameter expressions under soaking and dry-wet cycling;

[0022] 5) After determining the stress state and wetting condition, substitute them into the corresponding expressions in step 4) to obtain the constitutive parameters of the Burgers model considering the wetting effect, and then establish the Burgers model considering the wetting effect with known constitutive parameters.

[0023] Obtain the soaking wetting coefficients and dry-wet cycling wetting coefficients of coarse grains of different types of materials, establish the corresponding relationship between the types of material coarse grains and the wetting coefficients, and when the material type and wetting condition are known, the corresponding wetting coefficients can be directly determined, and then the corresponding Burgers model considering the wetting effect can be determined.

[0024] Directly apply the Burgers model considering the wetting effect to numerical simulation for long-term deformation prediction under different wetting conditions.

[0025] The constitutive parameter expression in the natural water content state is:

[0026] m e = 120*σ - 2500;

[0027] m η = τ / (1 * 10 -5 );

[0028] k e = 60 * τ + 100;

[0029] k η = 290 * τ + 500;

[0030] Wherein, σ is the normal stress and τ is the shear stress;

[0031] The soaking and humidifying coefficient is: the soaking and humidifying coefficient a of k of the modified Kelvin body e 、the soaking and humidifying coefficient a of k of the modified Kelvin body ke 、the soaking and humidifying coefficient a of k of the modified Kelvin body η 、the soaking and humidifying coefficient a of m of the modified Maxwell body kη 、the soaking and humidifying coefficient a of m of the modified Maxwell body e 、the soaking and humidifying coefficient a of m of the modified Maxwell body me ,

[0032] The wetting and drying cycle humidifying coefficient is: the wetting and drying cycle humidifying coefficient b of k of the modified Kelvin body e 、the wetting and drying cycle humidifying coefficient b of k of the modified Kelvin body ke 、the wetting and drying cycle humidifying coefficient b of k of the modified Kelvin body η 、the wetting and drying cycle humidifying coefficient b of m of the modified Maxwell body kη 、the wetting and drying cycle humidifying coefficient b of m of the modified Maxwell body e 、the wetting and drying cycle humidifying coefficient b of m of the modified Maxwell body me ,

[0033] a ke = 0.73 b ke = 0.55

[0034] a kη = 0.75 b kη = 0.93

[0035] a me = 0.79 b me = 0.74

[0036] m η The expression remains unchanged under different humidifying states.

[0037] In a third aspect, the present invention provides a test device for use in the construction method. The test device is mainly used for direct shear creep tests of materials with different degrees of wetting, including natural water content, immersion, and wet-dry cycles. The test device includes an external direct shear box, an internal direct shear box, a cross-shaped support, a water pump, and a water storage bag. The internal direct shear box is nested inside the external direct shear box, and their shear planes are at the same height. A cross-shaped support 3 is provided at the lower part of the internal direct shear box, and the external direct shear box is located inside the water storage bag. The external direct shear box includes an external direct shear upper box 5 and an external direct shear lower box 4, and the periphery of the external direct shear upper box 5 and the external direct shear lower box 4 is closed. The internal direct shear box includes an internal direct shear upper box 1 and an internal direct shear lower box 2.

[0038] The external direct shear upper box 5 is placed on the external direct shear lower box 4. Both the external direct shear upper box and the external direct shear lower box are located inside the water storage bag. The cross-shaped support 3 is installed inside the external direct shear lower box 4. The internal direct shear lower box 2 is located on the cross-shaped support, and the internal direct shear upper box 1 is placed on the internal direct shear lower box 2. The internal direct shear lower box 2 is connected and fixed to the external direct shear lower box through an extension support. The internal direct shear upper box 1 is connected and fixed to the external direct shear upper box 5 through an extension support.

[0039] A number of through holes are evenly opened on at least one side wall of the internal direct shear lower box and the internal direct shear upper box, and a number of through holes are opened at the bottom of the internal direct shear lower box.

[0040] A water pump is placed inside the cross-shaped support. There is a gap between the external direct shear box and the internal direct shear box, and the gap can accommodate a water pipe. The water pipe is connected to the water pump for drainage.

[0041] In the present invention, the stress refers to the normal stress and the shear stress.

[0042] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0043] First, the present invention obtains the creep deformation data of the soil body under different degrees of wetting through direct shear creep tests of coarse-grained soil. Then, the test data can be used to simply determine the constitutive parameters required for the Burgers model, establish the soil body parameter formula under different degrees of wetting, and make the parameters directly applicable to numerical simulation. For an actual project, a numerical model is established, and the Burgers model considering the wetting effect with known constitutive parameters is obtained by using the above construction method, which can obtain reasonable constitutive and external conditions for predicting long-term deformation.

[0044] In the construction method of the present invention, for each constitutive parameter value of the Burgers model, a relationship is established with the stress received by the material, and the value of each constitutive parameter can be generally deduced from the stress received by the material. The wetting coefficient is introduced, and based on the constitutive parameter expression in the natural water content state, it is transformed into the constitutive parameter expression under immersion and wet-dry cycles, so as to achieve the purpose of directly obtaining the constitutive parameters of the model from the stress state and wetting conditions.

[0045] In the test device of the present invention, the direct shear box is set in the assembled form of an external direct shear box, an internal direct shear box, a cross-shaped support, and a water storage bag, replacing the traditional direct shear box composed of two equal-sized shear boxes, the upper and the lower. It can realize the long-term shear test under two working conditions of soaking and wet-dry cycling, that is, the long-term loading under the working conditions of long-term soaking and wet-dry cycling is realized. Description of the Drawings

[0046] Figure 1 It is a schematic structural diagram of the test device used in the construction method of the present invention;

[0047] Figure 2 It is a structural diagram of the assembly of the upper and lower boxes of the internal direct shear box of the present invention;

[0048] Figure 3(a) is a physical diagram of the opening condition of the upper internal direct shear box;

[0049] Figure 3(b) is a physical diagram of the opening condition of the lower internal direct shear box;

[0050] Figure 4 It is the soil creep curve of strain-time obtained from the test of the present invention;

[0051] Figure 5 It is a schematic structural diagram of the Burgers model;

[0052] Figure 6 It is a curve diagram for determining parameters B and C;

[0053] Figure 7(a) is a comparison result diagram of the experimental curve and the numerical simulation curve under the natural water content condition;

[0054] Figure 7(b) is a comparison result diagram of the experimental curve and the numerical simulation curve under the long-term soaking condition;

[0055] Figure 7(c) is a comparison result diagram of the experimental curve and the numerical simulation curve under the wet-dry cycling condition;

[0056] In the figure, 1 is the upper internal direct shear box; 2 is the lower internal direct shear box; 3 is the cross-shaped support; 4 is the lower external direct shear box; 5 is the upper external direct shear box. Detailed Embodiments

[0057] The present invention will be further explained below in conjunction with the embodiments and the drawings, but this is not used as a limitation to the protection scope of the present application.

[0058] The test device described in the present invention is mainly used for the direct shear creep test of materials with different humidification degrees (natural water content, soaking, wet-dry cycling). The structure of the test device is shown in Figure 1, including an external direct shear box, an internal direct shear box, a cross-shaped support, and a water storage bag. The internal direct shear box is nested inside the external direct shear box, and their shear planes are at the same height. A cross-shaped support 3 is provided at the lower part of the internal direct shear box, and the external direct shear box is located inside the water storage bag; the external direct shear box includes an external direct shear upper box 5 and an external direct shear lower box 4, and the periphery of the external direct shear upper box 5 and the external direct shear lower box 4 is closed; the internal direct shear box includes an internal direct shear upper box 1 and an internal direct shear lower box 2,

[0059] The external direct shear upper box 5 is placed on the external direct shear lower box 4. Both the external direct shear upper box and the external direct shear lower box are located inside the water storage bag (not shown in the figure). The cross-shaped support 3 is installed inside the external direct shear lower box 4. The internal direct shear lower box 2 is located on the cross-shaped support, and the internal direct shear upper box 1 is placed on the internal direct shear lower box 2. The internal direct shear lower box 2 is fixedly connected to the external direct shear lower box through the support outside its box body; the internal direct shear upper box 1 is fixedly connected to the external direct shear upper box 5 through the support outside its box body.

[0060] Extension brackets are provided on one side of the internal direct shear lower box 2 and the internal direct shear upper box 1. The internal direct shear lower box 2 and the internal direct shear upper box 1 are respectively fixedly connected to the external direct shear lower box 4 and the external direct shear upper box 5 through the corresponding extension brackets, capable of transmitting force.

[0061] Direct shear test: The upper box is fixed, and the lower box moves horizontally to shear the soil. During the test, the test instrument loads the external direct shear box. Extension brackets outside the box body are designed for the internal direct shear box, so that the force condition of the large box (external direct shear box) is transmitted to the small box (internal direct shear box), ensuring that the force conditions of the external direct shear box and the internal direct shear box are the same.

[0062] The reason for only connecting one side of the small box and the large box: During the test, the moving direction of the external direct shear lower box is into the picture. In order to let the external direct shear lower box drive the internal lower box to move, only one-side connection needs to be established for the internal direct shear lower box. The same applies to the upper box. The external direct shear upper box is fixed, and the one-side connection between the external direct shear upper box and the internal direct shear upper box through the extension bracket can ensure that the internal direct shear upper box is also fixed. Since the internal direct shear upper box will be driven by the internal direct shear lower box to move in the direction into the picture, it is preferred that the extension bracket is set on the opposite surface where the shear box moves.

[0063] The height of the cross-shaped support is set so that the shear planes of the external direct shear box and the internal direct shear box are at the same horizontal level.

[0064] The whole test device is installed on a direct shear creep test bench.

[0065] On one side wall of the inner direct shear upper box 1 and the inner direct shear lower box 2, an extension bracket is provided. On the opposite side wall, through holes are evenly opened. The bottom of the inner direct shear lower box 2 is also provided with a number of evenly distributed through holes. In this embodiment, only one side wall is opened with holes, and holes can also be opened on other side walls of the inner direct shear upper box and the inner direct shear lower box.

[0066] The purpose of setting through holes on the inner direct shear lower box and the inner direct shear upper box is to facilitate the transformation of the specimen from wet to dry in the wet-dry cycling condition and drain the water.

[0067] The functions of the cross-shaped bracket are as follows: 1) To make the bottom surface of the inner direct shear lower box higher than the bottom surface of the outer direct shear lower box, which is convenient for the water in the inner direct shear lower box to drain into the outer direct shear lower box. Mainly for the wet-dry cycle, to enable the material to transform from the soaked state to the dry state, and the dry state refers to the natural moisture content state. A water pump is placed inside the cross-shaped bracket. There is a gap between the outer direct shear box and the inner direct shear box, and the gap can accommodate a water pipe. Connect the water pipe to the water pump to carry out the drainage work. 2) To make the shear surfaces of the outer direct shear box and the inner direct shear box at the same horizontal level.

[0068] The present invention is applicable to coarse-grained soil masses, that is, as stipulated in the existing geotechnical test method standards: the mass percentage of particles with a particle size in the range of 0.1 mm - 60 mm is greater than 50% in the soil-rock mixture, and the soaked state is the completely immersed state.

[0069] The process of the method for constructing the burgers model considering the wetting effect in the present invention is as follows:

[0070] 1) First, conduct direct shear creep tests on coarse-grained soil masses with different degrees of wetting through the test device to obtain their shear strain-time curves (i.e., soil creep curves). The soil creep curves obtained from the tests are as Figure 4 shown.

[0071] 2) The burgers model is composed of a Maxwell body and a Kelvin body in series, as Figure 5 shown. For the burgers model, four constitutive parameters are required, m e (Maxwell body elastic modulus), m η (Maxwell body viscosity modulus), k e (Kelvin body elastic modulus), k η (Kelvin body viscosity modulus).

[0072] As is well known, the stress-strain equation of the burgers model is Equation (1):

[0073]

[0074] where t is time; ε is the shear strain of the soil mass; τ is the shear stress applied to the material;

[0075] Let Then equation (1) is transformed into:

[0076] ε = A + Bt + C(1 - e -Dt ) (2)

[0077] Determination of parameter A:

[0078] From equation (2), when t = 0, ε = A. A is the strain generated in the soil mass at the moment when the shear stress is applied. However, in the actual test process, when t = 0, the shear force is 0, and the shear strain of the soil mass should also be 0.

[0079] After setting the loading data of the direct shear apparatus for coarse-grained soil and starting the test, the loading of the shear stress does not reach the target shear stress value set in the test instantaneously, but will increase slowly and gradually reach the set target shear stress value. To unify the test standards, it is stipulated that: the shear strain within the time period from the start of the test to the moment when the shear stress first reaches the set target shear stress value is A, and m is determined based on this e , and the shear stress remains unchanged in subsequent experiments.

[0080] Determination of parameters B and C:

[0081] Conduct a direct shear creep test to obtain the shear strain-time curve of the soil mass of the object to be measured. When t → ∞, equation (2) becomes: ε = A + Bt + C. At this time, the shear strain-time curve of the soil mass is approximately a straight line. Draw the asymptote of the shear strain-time curve of the soil mass to obtain the slope and intercept values of the asymptote. The asymptote intersects the strain axis at the point (0, A + C); after determining the value of parameter A, parameter C is obtained based on the point (0, A + C), and then according to the constitutive parameter k is determined e ;

[0082] During the test process, the normal stress and shear stress remain unchanged and are fixed. Parameter B is determined according to the value of the asymptote slope, and then according to the constitutive parameter m is determined η .

[0083] Fitting of parameter D:

[0084] Based on the direct shear creep test, the values of parameters A, B, and C are determined, and only parameter D is not determined. Since it is difficult to directly measure parameter D, a fitting method is used to determine it. After determining the values of parameters A, B, and C, use the oringin software, input formula (2), and input the values of A, B, and C. Let the oringin software automatically calculate parameter D according to the shear strain-time curve of the soil mass determined by the direct shear creep test, and according to In this way, the constitutive parameter k is obtained. η .

[0085] Under the natural water content condition, a direct shear creep test of soil is carried out under different shear stresses τ at normal stresses σ of 100 kPa, 200 kPa, 300 kPa, and 400 kPa. The soil shear strain-time curve is obtained, and the model parameters are determined according to the above parameter determination method. The relationship between the parameters and the stress can be expressed by the following formula:

[0086] m e , k e are the elastic moduli in Maxwell and Kelvin respectively (the following calculation unit is kPa)

[0087] m η , k η are the viscous moduli in Maxwell and Kelvin respectively (the following calculation unit is kPa·h)

[0088] For the convenience of description, the Burgers model parameters under different wetting conditions are distinguished by dry, wet, and cycle for the natural water content, immersion, and dry-wet cycle conditions respectively.

[0089] Under the natural water content:

[0090] m dry e = 120*σ - 2500

[0091] σ is the normal stress applied to the material

[0092] m dry η : It is stipulated that B = 1*10 -5 That is, m dry η = τ / (1*10 -5 )

[0093] τ is the shear stress applied to the material

[0094] k dry e = 60*τ + 100

[0095] τ is the shear stress applied to the material

[0096] k dry η = 290*τ + 500

[0097] τ is the shear stress applied to the material

[0098] According to the above process, under the same stress conditions but with the test conditions changed to immersion and dry-wet cycle conditions, the parameter expressions are obtained.

[0099] Soaking condition:

[0100] m wet e = 95*σ - 2500

[0101] σ is the normal stress suffered by the material

[0102] m wet η : It is specified that B = 1*10 -5 That is, m wet η = τ / (1*10 -5 )

[0103] τ is the shear stress suffered by the material

[0104] k wet e = 44*τ + 100

[0105] τ is the shear stress suffered by the material

[0106] k wet η = 222*τ + 500

[0107] τ is the shear stress suffered by the material

[0108] Wet-dry cycling condition:

[0109] m cyclet e = 88*σ - 2500

[0110] σ is the normal stress suffered by the material

[0111] m cycle η : It is specified that B = 1*10 -5 That is, m cycle η = τ / (1*10 -5 )

[0112] τ is the shear stress suffered by the material

[0113] k cycle e = 33*τ + 100

[0114] τ is the shear stress suffered by the material

[0115] k cycle η = 270*τ + 500

[0116] τ is the shear stress suffered by the material

[0117] Under the same stress state, the change in the humidification state will cause a change in the parameter value, but will not cause the trend of the parameter value to change with the applied stress, that is, only the slope of the parameter expression under the natural moisture content state changes.

[0118] Therefore, a humidification coefficient is introduced based on the expression under the natural moisture content state, so that the expression under the natural moisture content can be converted with the soaking state and the dry-wet cycling state.

[0119] Soaking introduces a soaking humidification coefficient: a ke (Correct k of the k body e )a kη (Correct k of the k body η )a me (Correct m of the M body e )

[0120] Dry-wet cycling introduces a dry-wet cycling humidification coefficient: b ke (Correct k of the k body e )b kη (Correct k of the k body η )b me (Correct m of the M body e )

[0121] a ke = 0.73 b ke = 0.55

[0122] a kη = 0.75 b kη = 0.93

[0123] a me = 0.79 b me = 0.74

[0124] That is:

[0125] k wet e = a ke *60*τ + 100

[0126] k cycle e = b ke *60*τ + 100

[0127] k wet η = a kη *290*τ + 500

[0128] k cycle η = b kη *290*τ + 500

[0129] m wet e = a me *120*σ - 2500

[0130] m cycle e = b me *120*σ - 2500

[0131] The overall situation is shown in Table 1;

[0132] Note: dry, wet, and cycle represent natural moisture content, immersion, and dry-wet cycling conditions respectively

[0133] Relationships between parameters in Table 1

[0134]

[0135] Note: dry, wet, and cycle represent natural moisture content, immersion, and dry-wet cycling conditions respectively

[0136] After establishing the relationship between the parameters of the Burgers model under different working conditions, that is, only by determining the stress and wetting state of the material can the parameter size be generally inferred. Since only fixed parameter values can be input in the existing numerical simulation software, when the external force conditions change, the parameters can only be adjusted manually. By writing the Fish language and inputting the relational expressions in Table 1 into the model, the constitutive parameters of the model can be adjusted with the change of the working conditions. Using the modified model to simulate the tests under the same working conditions, the comparison between the experimental curve and the numerical simulation curve is shown in Figure 7. Figure 7 is the shear strain-time curve of the soil body, and it is the comparison between the experimental curve and the numerical calculation curve:

[0137] It can be seen that using the method of the present invention to determine the parameters of the Burgers model considering the wetting effect and applying them to numerical simulation has a good degree of agreement with the test results, which proves the reliability of the determined parameters. By comparing the test and numerical results under the same working conditions with different wetting degrees (natural moisture content, immersion, dry-wet cycling), it can be seen that the degree of agreement is good, and the calculation method introducing the wetting coefficient is reliable.

[0138] Matters not described in the present invention are applicable to the prior art.

Claims

1. A method for constructing a model considering the wetting effect, characterized in that, the model is the Burgers model of coarse-grained soil, and the construction method includes the following: 1) Conduct direct shear creep tests on soil under different shear stresses τ at different normal stresses σ under the natural water content state to obtain the soil shear strain-time curves under different stresses in the natural water content state; According to the soil shear strain-time curves under different stresses in the natural water content state, use the above-mentioned method for determining the parameters of the Burgers model to determine the corresponding values of parameters A, B, C, and D and the constitutive parameter values respectively, and then obtain the functional relationship between the four constitutive parameters and the stress in the natural water content state, that is, the constitutive parameter expression in the natural water content state; The stress-strain equation of the Burgers model is expressed as Equation (2) ε = A + Bt + C(1 - e -Dt ) (2), where t is time; ε is the shear strain of the soil mass; A, B, C, and D are parameters respectively, τ is the shear stress applied to the material; m e is the elastic modulus of the Maxwell body in the Burgers model, m η is the viscous modulus of the Maxwell body in the Burgers model, k e is the elastic modulus of the Kelvin body in the Burgers model, k η is the viscous modulus of the Kelvin body in the Burgers model; 2) Conduct direct shear creep tests on soil under the same normal stress and shear stress as in the natural water content state under the soaking and dry-wet cycling states respectively to obtain the soil shear strain-time curves under different stresses in the soaking and dry-wet cycling states; Determine the corresponding values of parameters A, B, C, and D and the constitutive parameter values respectively according to the soil strain-time curves under different stresses in the soaking and dry-wet cycling states, and then obtain the functional relationship between the four constitutive parameters and the stress in the soaking and dry-wet cycling states; 3) Compare the constitutive parameters in the soaking and dry-wet cycling states with the corresponding constitutive parameters in the natural water content state respectively, and determine the soaking wetting coefficients and dry-wet cycling wetting coefficients of the four constitutive parameters in the soaking and dry-wet cycling states respectively; 4) Based on the constitutive parameter expression in the natural water content state, introduce the above-mentioned soaking wetting coefficient and dry-wet cycling wetting coefficient into the constitutive parameter expression in the natural water content state to convert it into the constitutive parameter expressions under soaking and dry-wet cycling; 5) After determining the stress state and wetting condition, substitute into the corresponding expressions in step 4) to obtain the constitutive parameters of the Burgers model considering the wetting effect, and then establish the Burgers model considering the wetting effect with known constitutive parameters.

2. The method for constructing a model considering the wetting effect according to claim 1, characterized in that, Adopt the direct shear creep test and parameter fitting method to determine the values of parameters A, B, C, and D according to different parameter characteristics; The determination process of parameter A is as follows: Set the target shear stress value. The shear strain value of the coarse-grained soil mass during the period from the start of the direct shear creep test to the first time the shear stress reaches the set target shear stress value is parameter A. Then, according to and the set target shear stress value, the constitutive parameter m is determined e ; The determination process of parameters B and C is: Perform a direct shear creep test to obtain the shear strain-time curve of the object to be measured. When t→∞, Equation (2) is: ε = A + Bt + C. At this time, the shear strain-time curve is approximately a straight line. Draw the asymptote of the curve to obtain the slope and intercept values of the asymptote. The asymptote intersects the strain axis at the point (0, A + C). After determining the value of parameter A, parameter C is obtained according to the point (0, A + C), and then according to Determine the constitutive parameter k e ; Determine the parameter B according to the value of the asymptote slope, and then according to determine the constitutive parameter m η , where τ is the shear stress suffered by the material when t → ∞; Parameter D fitting: After determining the values of parameters A, B, and C, use the Origin software to input formula (2) and enter the values of A, B, and C. Let the Origin software automatically calculate parameter D based on the soil shear strain-time curve determined by the direct shear creep test, and calculate the constitutive parameter k according to this to obtain the constitutive parameter k η .

3. The method for constructing a model considering the wetting effect according to claim 1, characterized in that, Obtain the soaking wetting coefficients and dry-wet cycling wetting coefficients of coarse grains of different types of materials, establish the corresponding relationship between the types of material coarse grains and the wetting coefficients, and when the material type and wetting condition are known, the corresponding wetting coefficients can be directly determined, and then the corresponding Burgers model considering the wetting effect can be determined.

4. The method for constructing a model considering the wetting effect according to claim 1, characterized in that, Directly apply the Burgers model considering the wetting effect to numerical simulation for long-term deformation prediction under different wetting conditions.

5. The method for constructing a model considering the wetting effect according to claim 1, characterized in that, The constitutive parameter expression under the natural water content state is as follows: m e = 120 * σ - 2500; m η = τ / (1 * 10 -5 ); k e = 60 * τ + 100; k η = 290 * τ + 500; where σ is the normal stress and τ is the shear stress; The soaking humidification coefficient is: k of the modified Kelvin body e The soaking humidification coefficient a ke of the modified Kelvin body k η The soaking humidification coefficient a kη of the modified Maxwell body m e The soaking humidification coefficient a me , The wetting coefficient of the dry-wet cycle is: k of the modified Kelvin body e The wetting coefficient b of the dry-wet cycle ke and k of the modified Kelvin body η The wetting coefficient bk of the dry-wet cycle η and m of the modified Maxwell body e The wetting coefficient b of the dry-wet cycle me , a ke = 0.73b ke = 0.55 a kη = 0.75b kη = 0.93 a me = 0.79b me = 0.74 m η The expression remains unchanged under different humidification states.

6. A test device for use in the construction method according to claim 1, characterized in that the test device is mainly used for direct shear creep tests of materials with different degrees of wetting, including natural water content, soaking, and dry-wet cycles. The test device includes an external direct shear box, an internal direct shear box, a cross-shaped support, a water pump, and a water storage bag. The internal direct shear box is nested inside the external direct shear box, and their shear planes are at the same height. A cross-shaped support is provided at the lower part of the internal direct shear box, and the external direct shear box is located inside the water storage bag; the external direct shear box includes an external direct shear upper box and an external direct shear lower box, and the periphery of the external direct shear upper box and the external direct shear lower box is closed; the internal direct shear box includes an internal direct shear upper box and an internal direct shear lower box, the external direct shear upper box is placed on the external direct shear lower box, both the external direct shear upper box and the external direct shear lower box are located inside the water storage bag, the cross-shaped support is installed inside the external direct shear lower box, the internal direct shear lower box is located on the cross-shaped support, and the internal direct shear upper box is placed on the internal direct shear lower box; the internal direct shear lower box is fixedly connected to the external direct shear lower box through an extension support; the internal direct shear upper box is fixedly connected to the external direct shear upper box through an extension support; a number of through holes are evenly opened on at least one side wall of the internal direct shear lower box and the internal direct shear upper box, and a number of through holes are opened at the bottom of the internal direct shear lower box; a water pump is placed inside the cross-shaped support. There is a gap between the external direct shear box and the internal direct shear box, and the gap can accommodate a water pipe. The water pipe is connected to the water pump for drainage.

7. The test device according to claim 6, characterized in that an extension support is provided on one side surface of the internal direct shear lower box and the internal direct shear upper box, and the internal direct shear lower box and the internal direct shear upper box are respectively fixedly connected to the external direct shear lower box and the external direct shear upper box through the corresponding extension supports; the height of the cross-shaped support is set so that the shear planes of the external direct shear box and the internal direct shear box are at the same horizontal level; the whole test device is installed on a direct shear creep test bench to conduct the test.

8. The test device according to claim 6, characterized in that an extension support is provided on one side wall of the internal direct shear upper box and the internal direct shear lower box, and a number of through holes are evenly opened on the other opposite side wall.

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