Prediction method for rainfall infiltration induced loess high fill humidifying settlement

Abstract

The invention belongs to the technical field of geological research, and particularly discloses a rainfall infiltration induced loess high fill humidifying settlement prediction method which comprises the following steps: S1, acquiring mechanical property parameters of a soil body under different compaction degrees, and fitting the mechanical property parameters under different compaction degrees and different moisture contents to obtain a fitting function; s2, on the basis of an unsaturated loess fluid-solid coupling analysis principle, transforming the fitting function to obtain a soil body humidification interpolation function under different compaction degrees and different water contents; s3, through Comsol finite element software, the interpolation function is embedded into the soil elastic-plastic constitutive model, and the weakening process of soil strength parameters along with soil humidifying deformation is simulated. By the adoption of the method for predicting the rainfall infiltration induced loess high-fill humidifying settlement, the problem that a loess high-fill foundation cannot be subjected to systematic humidifying settlement prediction aiming at rainfall is solved, and safety guarantee is provided for high-fill foundation engineering.

Description

Technical Field

[0001] The invention relates to the technical field of geological research technology, and in particular to a method for predicting rainfall infiltration-induced wetting and sedimentation of loess high fill. Background Art

[0002] High fill construction projects in Northwest my country and other places have shown a sustained and vigorous development momentum, and the demand for land resources is increasing day by day. High fill foundation engineering has become a commonly used engineering method in various engineering practices. However, the loess high fill foundations in these areas are mostly soft and collapsible loess, with loose soil structure and strong collapsibility. This special geological feature makes it very easy for high fill foundations to suffer from disasters such as wetting, deformation and settlement when facing changes in hydrological factors such as rainfall, drainage pipe leakage and drainage blind ditch failure. In addition, the wetting, deformation and settlement laws of high fill foundations are also affected by a combination of factors such as foundation material characteristics, water infiltration, fill structure, foundation reinforcement and treatment.

[0003] There are many water environment change conditions that cause loess high fill foundation to produce wetting deformation. Surface rainfall infiltration is an important factor affecting the wetting deformation of loess high fill foundation, because it directly affects the degree of moisture and stability of the foundation. First of all, the high fill foundation engineering in the loess area has the special properties of collapsible loess. When rainfall occurs, surface moisture will gradually penetrate into the soil through infiltration, resulting in an increase in soil moisture content. For loess high fill foundation, this surface rainfall infiltration process will cause the soil moisture content to increase, resulting in the soil matrix suction and strength parameters to decrease with the soil moisture content, further causing the soil to humidify and deform, and ultimately causing slope instability or uneven settlement of upper buildings.

[0004] In the prior art, due to the differences in the compaction degree and soil properties of the fill body under different rainfall intensities and different rainfall conditions, the water infiltration law and the wetting deformation law in the compacted loess of the high fill site can be obtained through in-situ monitoring or numerical analysis. However, there is a lack of a systematic method for predicting wetting and sedimentation for rainfall to prevent or avoid the occurrence of the above-mentioned disasters. Summary of the invention

[0005] The purpose of the present invention is to provide a method for predicting wetting and settlement of loess high fill induced by rainfall infiltration, which solves the problem that loess high fill foundation cannot perform systematic wetting and settlement prediction for rainfall, and provides safety guarantee for high fill foundation engineering.

[0006] To achieve the above object, the present invention provides a method for predicting rainfall infiltration-induced loess high fill wetting settlement, comprising the following steps:

[0007] S1. Obtain the mechanical characteristic parameters of the soil under different compaction degrees, and respectively fit the mechanical characteristic parameters under different compaction degrees and different water contents to obtain a fitting function;

[0008] S2. Based on the principle of fluid-solid coupling analysis of unsaturated loess, the fitting function is transformed to obtain the soil wetting interpolation function under different compaction degrees and different water contents;

[0009] S3. Through Comsol finite element software, the interpolation function is embedded into the elastic-plastic constitutive model of soil to simulate the weakening process of soil strength parameters as the soil deforms due to wetting.

[0010] Preferably, S1 is specifically:

[0011] The indoor humidification test results of soils under different compaction degrees λ and different moisture contents were used to obtain the variation law of mechanical characteristic parameters. The indoor humidification test included soil moisture characteristic curve test, shear strength degradation test and elastic modulus softening test. The mechanical characteristic parameters included cohesion c, internal friction angle The values ​​of elastic modulus E, soil weight γ, and compaction degree λ range from 0.80 to 0.99;

[0012] At the same compaction degree λ, the least squares curve is fitted to obtain the cohesion c and internal friction angle Fitting functions of elastic modulus E and soil weight γ as moisture content changes, respectively.

[0013] Preferably, S2 is specifically:

[0014] The volume of water in the pores of unsaturated soil as a percentage of the total pore volume is the effective saturation S of the soil. e , the effective saturation S e As a variable characterizing the humidification deformation process, then:

[0015]

[0016] In the formula, S e is the effective saturation, ρ d is the dry density of the soil / g / cm 2 , S r ' is the residual saturation / %, d s is the relative density of the soil, ω is the water content of the soil;

[0017] By the effective saturation S e The fitting function in is transformed to obtain the soil wetting interpolation function under different compaction degrees:

[0018] E=f1(S e );

[0019] c=f2(Se );

[0020]

[0021] Preferably, in S2, the rainfall conditions are divided into heavy rain, heavy rain, moderate rain and light rain according to the rainfall amount, and the rainfall amount is defined as G, which is expressed as follows:

[0022] G = q·t;

[0023] Where q is the rainfall intensity / m / d, and t is the rainfall duration / d.

[0024] Preferably, S3 comprises the following steps:

[0025] S31. Analysis of initial displacement field and initial moisture field:

[0026] Set the study as a steady-state study; disable the sedimentation boundary conditions in the fluid flow module, first divide the foundation into equivalent units through the fluid flow module simulation, and obtain the initial moisture field w0, initial stress field σ0 and initial displacement field S0 inside the soil by setting the initial conditions;

[0027] S32. Analysis of displacement field under the influence of rainfall infiltration:

[0028] Set the total rainfall time and output time step, enable the precipitation boundary condition, set the dependent variable to the last solution of S31 as the initial value for analysis, at this time the initial displacement field is cleared, and the subsequent deformation is caused by the wetting of the foundation caused by rainfall. The fluid flow module is used to simulate the moisture field w1, stress field σ1 and displacement field S1 of the foundation after wetting in the soil under different rainfall conditions;

[0029] S33. Analysis of displacement field after rainfall stabilization:

[0030] Set the total time of the settlement stabilization process and the output time step, disable the sedimentation boundary conditions, set the dependent variable to the last solution of S32 as the initial value for analysis, and simulate the settlement stabilization process after rainfall. The depth reached by the infiltration line is the maximum rainfall infiltration depth h max The moisture field w2, stress field σ2 and displacement field S2 after stable rainfall in the foundation are calculated through the fluid flow module.

[0031] Preferably, in S3, the humidification deformation ratio ζ is defined as the humidification deformation amount ΔS and the maximum rainfall infiltration depth h max The ratio of is expressed as follows:

[0032]

[0033] Where ΔS is the difference between the displacement field S2 after rainfall stabilization and the initial displacement field S0.

[0034] Preferably, in S3, Comsol finite element software has a built-in calculation module, and the calculation module includes:

[0035] Basic module, used to set global parameters, interpolation functions, geometric dimensions, and boundary conditions;

[0036] Fluid flow module, used to select Richards equation and VG water retention model for simulating unsaturated soil seepage in the software, set fluid material parameters and porous matrix material parameters in unsaturated porous media, input relevant soil parameters and sedimentation boundary conditions affecting unsaturated soil seepage, the fluid material parameters are the density of the fluid, and the porous matrix material parameters are the porosity and hydraulic conductivity of the soil;

[0037] The solid mechanics module is used to select the solid mechanics interface in the software to perform fluid-solid interaction analysis.

[0038] Preferably, in S3, the displacement field calculation formula of the soil under different compaction degrees λ is an extended form of the Richards equation, which is expressed as follows:

[0039]

[0040] Where ρ is the density of the soil / g / cm 3 , S e is the effective saturation, S is the displacement field, C m Specific water capacity / kg / m 3 , g is gravity / N, ▽p is pressure difference / kPa, k s is the saturated permeability coefficient / %, k r is the residual permeability coefficient / %, D is the elevation / m, is the gradient operator, which represents the spatial gradient.

[0041] Preferably, in S3, the moisture field under different compaction degrees is obtained by the VG water retention model, and the calculation formula is as follows:

[0042]

[0043] In the formula, θ ω is the volume moisture content / %,θ s is the saturated volume moisture content / %,θ r is the residual volume moisture content / %, α is the soil air intake value parameter, ψ is the matrix suction / kPa, m and n are the soil moisture characteristic curve parameters, H p Indicates soil water potential.

[0044] Preferably, in S3, the soil model built into the Comsol finite element software is an ideal elastic-plastic model and relevant soil parameters are input, and then the elastic modulus, cohesion, and internal friction angle of the soil are replaced by interpolation functions E=f1(S e ), c=f2(S e ), And set the sedimentation boundary conditions, and obtain the change of displacement field through fluid-solid coupling analysis;

[0045] The soil model is set as an isotropic material. The Comsol finite element software has a built-in Biot-Willis coefficient, which is used to represent the interaction between the soil and the water in the soil. The Biot-Willis coefficient formula is as follows:

[0046] σ=Aε v -α B pI;

[0047] In the formula, σ is the soil stress, A is the stiffness matrix, and ε v is the volume strain, α B is the Biot-Willis coefficient, P is the pore water pressure / Pa, and I is the unit matrix.

[0048] Therefore, the present invention adopts the above-mentioned rainfall infiltration-induced loess high fill wetting settlement prediction method, and the beneficial effects are as follows:

[0049] (1) Based on indoor humidification tests (soil moisture characteristic curve test, shear strength degradation test, elastic modulus softening test) of unsaturated compacted loess, the present invention obtains a fitting function that changes with moisture content under different compaction degrees.

[0050] (2) Based on the principle of fluid-solid coupling analysis of unsaturated loess, the present invention proposes a simulation method for the effect of rainfall infiltration on the moistening of high fill foundation (moisture field and displacement field).

[0051] (3) The present invention proposes the concept of wetting deformation ratio ζ (wetting deformation of high fill foundation and maximum rainfall infiltration depth), and based on numerical analysis, obtains the wetting deformation ratio ζ, wetting deformation △S and maximum rainfall infiltration depth h of soil under different rainfall conditions and different compaction degrees. max The variation law of △S and h caused by rainfall was proposed. max The empirical prediction model with rainfall G and different compaction degrees λ solves the problem that loess high fill foundation cannot make systematic wetting and settlement prediction according to rainfall, and provides safety guarantee for high fill foundation engineering.

[0052] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 1 is a diagram showing the change of rainfall infiltration in high fill under different rainfall conditions in an embodiment of a method for predicting wetting and sedimentation of loess high fill induced by rainfall infiltration of the present invention, wherein (a) is a rainstorm condition, (b) is a heavy rain condition, (c) is a moderate rain condition, and (d) is a light rain condition;

[0054] Figure 2 It is a wetting deformation ratio curve diagram of an embodiment of a method for predicting wetting and settlement of loess high fill induced by rainfall infiltration of the present invention, wherein (a) is a wetting deformation ratio curve of different compaction degrees, and (b) is a wetting deformation ratio curve of different rainfall conditions;

[0055] Figure 3 It is a model building framework diagram of an embodiment of a method for predicting loess high fill humidification settlement induced by rainfall infiltration of the present invention;

[0056] Figure 4 It is a numerical realization framework diagram of an embodiment of a method for predicting wetting and settlement of loess high fill induced by rainfall infiltration of the present invention. DETAILED DESCRIPTION

[0057] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0058] 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.

[0059] Embodiment 1

[0060] A method for predicting rainfall infiltration-induced loess high fill wetting and settlement, comprising the following steps:

[0061] S1. Obtain the mechanical characteristic parameters of the soil under different compaction degrees, and fit the mechanical characteristic parameters under different compaction degrees and different water contents to obtain a fitting function.

[0062] In this embodiment, based on the hydrological data of the high-fill airport and the new district engineering area in Yan'an for many years, the mechanical property parameters of the remolded loess at compaction degrees λ=0.88, λ=0.90, λ=0.93, λ=0.95 and λ=0.98 were statistically analyzed respectively.

[0063] At the same compaction degree λ, the least squares curve is fitted to obtain the cohesion c and internal friction angle The elastic modulus E and soil weight γ change with the moisture content θ w Taking the test results of compaction degree λ = 0.93 as an example, the cohesion c and internal friction angle of compacted loess are obtained. Parameters such as elastic modulus E and soil weight γ change with the water content θ wThe changing fitting function is as follows:

[0064]

[0065] By summarizing and summarizing, we can get the cohesion c and internal friction angle of loess. Parameters such as elastic modulus E vary with compaction degree and water content θ w The specific fitting function is shown in Table 1.

[0066] Table 1 Mechanical strength parameter fitting function

[0067]

[0068]

[0069] S2. Based on the principle of fluid-solid coupling analysis of unsaturated loess, the fitting function is transformed to obtain the soil wetting interpolation function under different compaction degrees and different water contents.

[0070] The rainfall conditions are divided into heavy rain, heavy rain, moderate rain and light rain according to the rainfall amount. The rainfall amount is defined as G, and its expression is as follows:

[0071] G = q·t;

[0072] Where q is the rainfall intensity, m / d, and t is the rainfall duration.

[0073] In this embodiment, according to the hydrological data of the high-fill airport and the new district engineering area in Yan'an for many years, the range of rainfall is 330 mm to 871.2 mm, and the average rainfall is 562.1 mm. Statistics can be used to obtain rainfall parameters under four rainfall conditions: heavy rain (SR), heavy rain (HR), moderate rain (MR), and light rain (LR), as shown in Table 2.

[0074] Table 2 Parameters of different rainfall intensities

[0075] Rainfall Type Duration of rainfall, d Rainfall intensity, m / d Total rainfall, m SR 0.4 1.44 0.576 HR 2.0 0.72 1.44 MR 5.0 0.36 1.8 LR 15.0 0.072 1.08

[0076] The saturation degree is used to indicate the water content in the soil, which has an important influence on the mechanical properties of unsaturated loess. Through indoor test analysis of the mechanical properties of unsaturated undisturbed soil and remolded soil, a calculation method for the measured saturation degree is proposed, which can be used to calculate the volume water content S r Or effective saturation S e As the characterization variable of the humidification process of loess high fill foundation humidification deformation, the formula is obtained: S e =S r .

[0077] According to the conversion of the three indicators of soil, the expression of effective saturation is obtained:

[0078]

[0079] According to the calculation formula of effective saturation:

[0080]

[0081] The volumetric moisture content expression is:

[0082]

[0083] Combining the above formulas, we can get formula (1):

[0084]

[0085] Where: S e is the effective saturation; ρ d is the dry density of soil / g / cm 2 ; S r ' is the residual saturation / %; θ is the volumetric water content / %; θ r is the residual volume moisture content / %; θ s is the saturated volume moisture content / %; d s is the relative density of the soil.

[0086] Transforming the above formula (1) we can get the interpolation function of soil with different compaction degrees:

[0087] E=f1(S e );

[0088] c=f2(S e );

[0089]

[0090] S3, such as Figure 3 and Figure 4 As shown in the figure, the interpolation function is embedded into the elastic-plastic constitutive model of soil through Comsol finite element software to simulate the weakening process of soil strength parameters with soil wetting and deformation.

[0091] Comsol finite element software has built-in calculation modules, which include basic module, fluid flow module and solid mechanics module. The basic module is used to set global parameters, interpolation functions, geometric dimensions and boundary conditions. The (Richards equation) fluid flow module of Comsol finite element software analyzes the unsaturated seepage in the foundation caused by rainfall. The fluid-solid coupling analysis and calculation of unsaturated loess is realized by setting the Richards and solid mechanics physical field interface. By calculating the initial displacement field S0 in the initial state and the displacement field S2 after rainfall stabilization, the difference between the two displacement fields is the wetting deformation of unsaturated loess caused by rainfall.

[0092] The specific module selection and calculation interface settings in Comsol software are:

[0093] (1) Setting of seepage field: After rainfall seeps into the soil at the top of the foundation, a saturated-unsaturated seepage zone is formed. Therefore, the Richards equation that can simulate the seepage of unsaturated soil is selected. At the same time, the fluid material parameters and porous matrix material parameters in the unsaturated porous medium are set. The fluid material parameters are the density of the fluid, and the porous matrix material parameters are the porosity and hydraulic conductivity (permeability) of the soil. At the same time, the VG water retention model is set; the relevant soil parameters and sedimentation boundary conditions that affect the seepage of unsaturated soil are input.

[0094] (2) Stress field setting: Select the solid mechanics interface, first set the soil model to the ideal elastic-plastic constitutive model and input the relevant soil parameters, then replace the elastic modulus, cohesion, and internal friction angle of the soil with the interpolation values ​​E = f1(S e ), c=f2(S e ), And set the sedimentation boundary conditions. Finally, the change of displacement field is obtained through fluid-solid coupling analysis.

[0095] (3) Setting of fluid-solid coupling correlation analysis: Establish E, c, About effective saturation S e The interpolation function is brought into the ideal elastic-plastic model. The change in the displacement field in the foundation caused by humidification can be obtained by calculation, thereby obtaining the humidification deformation of the foundation. The soil is set as an isotropic material, and the size of the Biot-Willis coefficient represents the interaction between the soil and the water in the soil, as shown in the following formula (this formula is a built-in calculation formula in the software):

[0096] σ=Aε v -α B pI;

[0097] Where, σ is soil stress; A is stiffness matrix; ε v is the volume strain; α B is the Biot-Willis coefficient; P is the pore water pressure / Pa; I is the unit matrix.

[0098] The displacement field of soil under different compaction degrees λ is an extended form of the Richards equation, and the calculation formula is as follows:

[0099]

[0100] Where ρ is the density of the soil / g / cm 3 , S e is the effective saturation, S is the displacement field, Cm Specific water capacity / kg / m 3 , g is gravity / N, ▽p is pressure difference / kPa, k s is the saturated permeability coefficient / %, k r is the residual permeability coefficient / %, D is the elevation / m, is the gradient operator, which represents the spatial gradient.

[0101] The moisture field under different compaction degrees is obtained by the VG water retention model, and the calculation formula is as follows:

[0102]

[0103] In the formula, θ ω is the volume moisture content / %,θ s is the saturated volume moisture content / %,θ r is the residual volume moisture content / %, α is the soil air intake value parameter, ψ is the matrix suction / kPa, m and n are the soil moisture characteristic curve parameters, H p represents soil water potential, H P <0 means the soil is in an unsaturated state, H p =0 means the soil is saturated.

[0104] The humidification deformation ratio ζ is defined as the humidification deformation △S and the maximum rainfall infiltration depth h max The ratio of is expressed as follows:

[0105]

[0106] Where △S is the difference between the displacement field S2 after rainfall stabilization and the initial displacement field S0.

[0107] The specific steps are as follows:

[0108] S31. Analysis of initial displacement field and initial moisture field:

[0109] Set the study as a steady-state study; disable the sedimentation boundary condition in the Richards equation module, first simulate the equivalent unit division of the fill body through the Comsol seepage module, and obtain the initial moisture field w0, initial stress field σ0 and initial displacement field S0 inside the soil by setting the initial conditions;

[0110] S32. Analysis of displacement field under the influence of rainfall infiltration:

[0111] Set the total rainfall time and output time step, enable the precipitation boundary condition, set the dependent variable to the last solution of S31 as the initial value for analysis, at this time the displacement of the model is reset to zero, and the subsequent deformation is caused by the wetting of the foundation caused by rainfall. The Comsol seepage module is used to simulate the moisture field w1, stress field σ1 and displacement field S1 of the foundation after wetting in the soil under different rainfall conditions;

[0112] S33. Analysis of displacement field after rainfall stabilization:

[0113] Set the total time of the settlement stabilization process and the output time step, disable the sedimentation boundary conditions, set the dependent variable to the last solution of S32 as the initial value for analysis, and simulate the settlement stabilization process after rainfall. The depth reached by the infiltration line is the maximum rainfall infiltration depth h max The moisture field w2, stress field σ2 and displacement field S2 in the foundation after stable rainfall are calculated through the Comsol seepage module.

[0114] Taking λ=0.93 as an example, after continuous rainfall for 0.4d, 2d, 5d, and 15d under heavy rain, heavy rain, moderate rain, and light rain conditions, respectively, the maximum rainfall infiltration depth is reached, and the distribution cloud diagram of the internal moisture field of the fill body under different compaction degrees and rainfall conditions at the initial stage, seepage stage, and stable stage is obtained, and then the rainfall infiltration law of high fill under different compaction degrees and rainfall conditions is obtained, such as Figure 1 As shown, it can be seen that the maximum rainfall infiltration depth increases linearly with the increase of rainfall. Under heavy rain conditions, when λ = 0.93, the saturated depth of the soil during the rainfall and the later rainwater infiltration process is 2m, and the wetting depth is 3.3m, and the maximum infiltration range is 5.3m below the surface. Under heavy rain conditions, when λ = 0.93, the saturated depth of the soil during the rainfall and the later rainwater infiltration process is 4.5m, and the wetting depth is 4.52m, and the maximum infiltration range is 9.02m below the surface. Under moderate rain conditions, when λ = 0.93, the saturated depth of the soil during the rainfall and the later rainwater infiltration process is 6.52m, and the wetting depth is 4.18m, and the maximum infiltration range is 10.7m below the surface. Under light rain conditions, when λ=0.93, the saturation depth of the soil during rainfall and the subsequent rainwater infiltration process is 3.7m, while the wetting depth is 3.8m, and the maximum infiltration impact range is 7.5m below the surface.

[0115] The wetting deformation ratio ζ is defined, and the wetting deformation ratio under different rainfall types and compaction degrees is obtained by calculation, as shown in Table 3.

[0116] Table 3 Wetting deformation ratio of reshaped loess under different rainfall types

[0117]

[0118] The wetting deformation ratio curve under different compaction degrees and rainfall conditions is shown in the figure below. Figure 2 As shown in the figure, the wetting deformation ratio ζ decreases with the increase of compaction degree and increases with the increase of rainfall. The reason for this phenomenon is that the greater the compaction degree, the more difficult it is for rainwater to infiltrate into the foundation soil under the same rainfall infiltration condition, the smaller the wetting deformation produced by the fill body, and the smaller the wetting deformation ratio, which is in line with the actual situation.

[0119] The empirical model of humidification deformation caused by rainfall is as follows:

[0120] Maximum rainfall infiltration depth h max The simplified empirical models with different rainfall amounts G are shown in Table 4.

[0121] Table 4 Fitting formulas for maximum infiltration depth and rainfall under different compaction degrees

[0122] Compactness λ Fitting formula Fitting accuracy 0.88 <![CDATA[h max =8.0998ln(G)+1.375]]> 0.9856 0.9 <![CDATA[h max =7.1427ln(G)+0.9349]]> 0.9761 0.93 <![CDATA[h max =5.9489ln(G)+0.994]]> 0.9982 0.95 <h2 style=";text-align:left;direction:ltr"><![CDATA[h <h2 style=";text-align:left;direction:ltr"> max <h2 style=";text-align:left;direction:ltr"> =5.9762ln(G)+0.4778]]><h2 style=";text-align:left;direction:ltr"> 0.9817 0.98 <![CDATA[h max =5.8762ln(G)+0.2136]]> 0.9511

[0123] The simplified empirical model of wetting deformation △S and different rainfall G and different fill compaction degree λ is shown in Table 5.

[0124] Table 5 Fitting formula of moistening deformation and rainfall under different compaction degrees

[0125]

[0126] Embodiment 2

[0127] The Luliang area of ​​Shanxi Province is located at the junction of the North China Block and the North China Craton. The geological structure is complex and there may be structural geological problems such as faults and folds. The engineering geological conditions in the area are mainly affected by local geological structures, stratigraphic characteristics, topography and landforms. The strata are diverse and may include different types of strata such as coal seams, sandstones, and mudstones. At the same time, the terrain in the area is relatively undulating, and there may be hills, mountains and other landforms. The mechanical properties and hydrogeological conditions of different strata are different, which puts forward requirements for the foundation design and construction of airport projects. In summary, the engineering geological conditions of Luliang Airport in Shanxi Province are complex and diverse. It is necessary to fully consider the impact of geological conditions on the project in engineering design and construction, and take corresponding geological surveys, surveys and engineering measures to ensure the safety and stability of the airport project.

[0128] Aiming at the deformation and stability of the high fill foundation of the airport, the test section of Shanxi Luliang Airport was taken as the research object, and the deformation monitoring, internal deformation monitoring and internal stress monitoring of the high fill surface of the target project were carried out. In-situ monitoring was carried out by drilling holes deep into the foundation in the middle of the secondary horseway (0-22.0m is the fill body), 22.0-25.0m is the original foundation soil layer, and moisture sensors TDR are arranged every 2.0-3.0m to monitor the change process of the internal moisture of the foundation, and then obtain the measured values ​​of the loess wetting deformation parameters.

[0129] Taking the compacted loess with a compaction degree of 0.93 as an example, the following is obtained through seepage analysis:

[0130] (1) Under heavy rain conditions (rainfall intensity of 1.44 m / d), after 0.4 days of continuous rainfall, within 0 to 0.4 days: the volumetric moisture content of the soil within 2.0 m below the surface of the high fill is θ w Rapidly rising, the soil below 2.5mθ w Basically unchanged, 0.4 days after the rainfall stops, the soil moisture content remains basically unchanged, and its maximum infiltration impact range is h max The soil moisture content θ within 2.0 m below the ground surface is 2.5 m, and the foundation humidification deformation △S is -2.5 mm. Under heavy rain conditions (rainfall intensity is 0.72 m / d), after continuous rainfall for 1.3 days, the soil volume moisture content θ within 2.0 m below the ground surface is w Reaching the maximum value within 3.0d, h max The soil moisture content in the range of 3.8m below the ground surface is θ, which is 4.8m below the ground surface, and the foundation humidification deformation △S is -28.4mm; under moderate rain conditions (rainfall intensity is 0.36m / d), after continuous rainfall for 5.0d, the soil moisture content in the range of 3.8m below the ground surface is θ w Rapidly rising, its h max The soil moisture content in the high fill area within 2.5 m below the surface is θ, and the soil moisture deformation △S is -49.4 mm. Under the light rain condition (rainfall intensity is 0.072 m / d), after 15.0 days of continuous rainfall, the soil volume moisture content θ in the high fill area within 2.5 m below the surface is w The rise is obvious, its h max The soil humidification deformation △S is -9.4mm at 6.0m below the ground surface. Under the compaction degree of 0.93, the humidification deformation ratio ζ under different rainfall conditions varies from 1.0% to 3.5%.

[0131] Using the prediction method of Example 1, when the compaction degree is 0.93, the h of the simulated value (under heavy rain, heavy rain, moderate rain, and light rain conditions) is maxThe measured values ​​and simulated values ​​of loess moistening deformation parameters in the test section are compared, as shown in Table 6.

[0132] Table 6 Measured and simulated values ​​of humidification deformation

[0133]

[0134] Through Tables 4 and 5, the fill compaction degree and rainfall type of the actual project are brought into the simplified empirical model, and the comparison between the measured values ​​and the fitted predicted values ​​under different rainfall conditions and fill compaction degrees is obtained, as shown in Table 7.

[0135] Table 7 Measured values ​​and fitting prediction values ​​of humidification deformation

[0136]

[0137] It can be seen from Tables 5 and 7 that under heavy rain and torrential rain conditions, since the rainfall intensity far exceeds the infiltration intensity, most of the rainfall does not have time to infiltrate into the soil, but forms runoff on the surface, resulting in poor infiltration effect. The present invention does not consider the impact of surface runoff on rainfall infiltration, so the maximum rainfall infiltration impact depth h under heavy rain and torrential rain conditions is max , the humidification deformation △S and humidification deformation ratio ζ of high fill foundation are larger than the measured values, and the h max , △S and ζ are close to the measured values.

[0138] Therefore, the present invention adopts the above-mentioned rainfall infiltration induced loess high fill moistening settlement prediction method, which solves the problem that loess high fill foundation cannot perform systematic moistening settlement prediction for rainfall, and provides safety protection for high fill foundation engineering.

[0139] 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 method for predicting rainfall infiltration-induced loess high fill wetting and settlement, characterized in that: The following steps are involved: S1. Obtain the mechanical characteristic parameters of the soil under different compaction degrees, and respectively fit the mechanical characteristic parameters under different compaction degrees and different water contents to obtain a fitting function; S2. Based on the principle of fluid-solid coupling analysis of unsaturated loess, the fitting function is transformed to obtain the soil wetting interpolation function under different compaction degrees and different water contents; S3. Through Comsol finite element software, the interpolation function is embedded into the elastic-plastic constitutive model of soil to simulate the weakening process of soil strength parameters as the soil deforms due to wetting.

2. The method for predicting rainfall infiltration-induced loess high fill wetting settlement according to claim 1 is characterized in that: S1 is specifically: The indoor humidification test results of soils under different compaction degrees λ and different moisture contents were used to obtain the variation law of mechanical characteristic parameters. The indoor humidification test included soil moisture characteristic curve test, shear strength degradation test and elastic modulus softening test. The mechanical characteristic parameters included cohesion c, internal friction angle The values ​​of elastic modulus E, soil weight γ, and compaction degree λ range from 0.80 to 0.99; At the same compaction degree λ, the least squares curve is fitted to obtain the cohesion c and internal friction angle Fitting functions of elastic modulus E and soil weight γ as moisture content changes.

3. The method for predicting rainfall infiltration-induced loess high fill wetting settlement according to claim 1, characterized in that: S2 is specifically: The volume of water in the pores of unsaturated soil as a percentage of the total pore volume is the effective saturation S of the soil. e , the effective saturation S e As a variable characterizing the humidification deformation process, then: In the formula, S e is the effective saturation, ρ d is the dry density of the soil / g / cm 2 , S r ' is the residual saturation / %, d s is the relative density of the soil, ω is the water content of the soil; By the effective saturation S e The fitting function in is transformed to obtain the soil wetting interpolation function under different compaction degrees: E=f1(S e ); c=f2(S e ); 4. The method for predicting rainfall infiltration-induced loess high fill wetting settlement according to claim 3 is characterized in that: In S2, the rainfall conditions are divided into heavy rain, heavy rain, moderate rain and light rain according to the rainfall amount. The rainfall amount is defined as G, and its expression is as follows: G = q·t; Where q is the rainfall intensity / m / d, and t is the rainfall duration / d.

5. The method for predicting rainfall infiltration-induced loess high fill wetting settlement according to claim 1, characterized in that: S3 includes the following steps: S31. Analysis of initial displacement field and initial moisture field: Set the study as a steady-state study; disable the sedimentation boundary conditions in the fluid flow module, first divide the foundation into equivalent units through the fluid flow module simulation, and obtain the initial moisture field w0, initial stress field σ0 and initial displacement field S0 inside the soil by setting the initial conditions; S32. Analysis of displacement field under the influence of rainfall infiltration: Set the total rainfall time and output time step, enable the precipitation boundary condition, set the dependent variable to the last solution of S31 as the initial value for analysis, at this time the initial displacement field is cleared, and the subsequent deformation is caused by the wetting of the foundation caused by rainfall. The fluid flow module is used to simulate the moisture field w1, stress field σ1 and displacement field S1 of the foundation after wetting in the soil under different rainfall conditions; S33. Analysis of displacement field after rainfall stabilization: Set the total time of the settlement stabilization process and the output time step, disable the sedimentation boundary conditions, set the dependent variable to the last solution of S32 as the initial value for analysis, and simulate the settlement stabilization process after rainfall. The depth reached by the infiltration line is the maximum rainfall infiltration depth h max The moisture field w2, stress field σ2 and displacement field S2 after stable rainfall in the foundation are calculated through the fluid flow module.

6. A method for predicting rainfall infiltration-induced loess high fill wetting settlement according to claim 5, characterized in that In S3, the humidification deformation ratio ζ is defined as the humidification deformation △S and the maximum rainfall infiltration depth h max The ratio of is expressed as follows: Where ΔS is the difference between the displacement field S2 after rainfall stabilization and the initial displacement field S0.

7. A method for predicting rainfall infiltration-induced loess high fill wetting settlement according to claim 6, characterized in that: In S3, Comsol finite element software has built-in calculation modules, including: Basic module, used to set global parameters, interpolation functions, geometric dimensions, and boundary conditions; Fluid flow module, used to select Richards equation and VG water retention model for simulating unsaturated soil seepage in the software, set fluid material parameters and porous matrix material parameters in unsaturated porous media, input relevant soil parameters and sedimentation boundary conditions affecting unsaturated soil seepage, the fluid material parameters are the density of the fluid, and the porous matrix material parameters are the porosity and hydraulic conductivity of the soil; The solid mechanics module is used to select the solid mechanics interface in the software to perform fluid-solid interaction analysis.

8. A method for predicting rainfall infiltration-induced loess high fill wetting settlement according to claim 7, characterized in that: In S3, the displacement field calculation formula of soil under different compaction degrees λ is the extended form of Richards equation, which is expressed as follows: Where ρ is the density of the soil / g / cm 3 , S e is the effective saturation, S is the displacement field, C m Specific water capacity / kg / m 3 , g is gravity / N, ▽p is pressure difference / kPa, k s is the saturated permeability coefficient / %, k r is the residual permeability coefficient / %, D is the elevation / m, ▽ is the gradient operator, indicating the spatial gradient.

9. A method for predicting rainfall infiltration-induced loess high fill wetting settlement according to claim 8, characterized in that: In S3, the moisture field under different compaction degrees is obtained by the VG water retention model, and the calculation formula is as follows: In the formula, θ ω is the volume moisture content / %,θ s is the saturated volume moisture content / %,θ r is the residual volume moisture content / %, α is the soil air intake value parameter, ψ is the matrix suction / kPa, m and n are the soil moisture characteristic curve parameters, H p Indicates soil water potential.

10. A method for predicting rainfall infiltration-induced loess high fill wetting settlement according to claim 9, characterized in that: In S3, the soil model built into the Comsol finite element software is an ideal elastic-plastic model and the relevant soil parameters are input. Then, the elastic modulus, cohesion, and internal friction angle of the soil are replaced by the interpolation function E=f1(S e ), c=f2(S e ), And set the sedimentation boundary conditions, and obtain the change of displacement field through fluid-solid coupling analysis; The soil model is set as an isotropic material. Comsol finite element software has a built-in Biot-Willis coefficient, which is used to represent the interaction between soil stress and moisture in the soil. The Biot-Willis coefficient formula is as follows: σ=Aε v -a B pI; In the formula, σ is the soil stress, A is the stiffness matrix, and ε v is the volume strain, α B is the Biot-Willis coefficient, P is the pore water pressure / Pa, and I is the unit matrix.

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