Method for predicting loess high fill humidifying settlement induced by drainage blind ditch failure

Abstract

The invention provides a method for predicting loess high fill humidifying settlement induced by drainage blind ditch failure, and relates to the field of loess high fill, related data of compacted loess is collected, and a damage function of loess with increase of water content under different compaction degrees under a humidifying condition is obtained according to the related data of the compacted loess; establishing a simulation method for the influence of the drainage blind ditch failure on the loess high fill humidification according to the damage function, analyzing change rules of a displacement field, a stress field and a moisture field, defining evaluation parameters of the loess high fill humidification effect induced by the blind ditch failure, and constructing a prediction model according to the evaluation parameters and the change rules; and utilizing the obtained prediction model to analyze the humidifying and settling conditions of the loess high fill. According to the prediction method for the loess high-fill humidifying settlement induced by the drainage blind ditch failure, the influence of underground water lifting induced by the blind ditch failure in the loess high-fill engineering foundation on the stability of the fill and the deformation of the foundation is accurately predicted, and a scientific basis is provided for engineering design and construction.

Description

Technical Field

[0001] The invention relates to the field of loess high fill, and in particular to a method for predicting wetting and settlement of loess high fill induced by failure of drainage blind ditch. Background Art

[0002] Drainage blind ditch is a common drainage measure in loess high fill projects. Its main function is to reduce the humidity and deformation of the fill soil by draining groundwater, lowering the groundwater level, and reducing the collapsibility of loess. However, if the drainage blind ditch measure fails, it will affect the humidification, deformation and settlement of the loess high fill.

[0003] When the blind drainage ditch fails, it may cause the following problems: (1) Rising groundwater level: The failure of the blind drainage ditch may cause the groundwater level to rise, which will increase the moisture content of the fill soil. Loess is sensitive to moisture. When the moisture content increases, its water absorption and collapsibility will also increase, causing the fill soil to collapse. Under the influence of gravity, the surface settlement will further increase, bringing instability and safety hazards to the project. (2) Reduced shear strength: The shear strength of loess will decrease under high humidity conditions. The failed blind drainage ditch will cause the moisture content of the fill soil to increase, and the shear strength of the loess will decrease accordingly, thereby increasing the risk of shear failure of the fill soil.

[0004] Therefore, the failure of drainage blind ditch measures will have a negative impact on the wetting, deformation and settlement of loess high fill. The rise of groundwater level caused by the failure of drainage blind ditch will increase the moisture of fill soil, causing the fill foundation to have wetting and deformation problems. In order to ensure the safety and stability of the project, effective measures need to be taken to repair or improve the drainage system, restore the drainage function in time, and control the moisture and deformation of the fill soil. Summary of the invention

[0005] The purpose of the present invention is to provide a method for predicting wetting settlement of loess high fill induced by drainage blind ditch failure, so as to more accurately predict the influence of groundwater uplift induced by blind ditch failure on the stability of the fill and foundation deformation in the foundation of loess high fill engineering, and provide a scientific basis for engineering design and construction.

[0006] To achieve the above object, the present invention provides a method for predicting wetting settlement of loess high fill induced by blind drainage ditch failure, comprising the following steps:

[0007] Collect relevant data of compacted loess, and obtain the damage function of loess with different compaction degrees and increasing water content under moistening conditions according to the relevant data of compacted loess;

[0008] A simulation method for the effect of blind drainage ditch failure on loess high fill wetting is established based on the damage function. The changing laws of displacement field, stress field and moisture field under the initial state, seepage state and stable state are analyzed, and a prediction model is obtained based on the changing laws.

[0009] The obtained prediction model is used to analyze the wetting settlement of loess high fill, including the average water level rise, wetting deformation and wetting deformation ratio.

[0010] Preferably, the relevant data of compacted loess include cohesion c, internal friction angle, and Compression modulus E s And the data of soil specific gravity γ.

[0011] Preferably, the damage function of compacted loess with different compaction degrees under humidification conditions with increasing moisture content is obtained based on the relevant data of compacted loess:

[0012]

[0013] Where c is the cohesion, is the internal friction angle, E s is the compression modulus, γ is the density of the soil, θ w is the volume moisture content, m1, m2, m3, m4, n1, n2, n3, n4 are constants related to the degree of compaction.

[0014] Preferably, a simulation method for the effect of blind drainage ditch failure on loess high fill wetting is established based on the damage function, comprising the following steps:

[0015] Analysis of initial displacement field and initial moisture field;

[0016] The study was set as a steady-state study; the calculation model was divided into equivalent units using Comsol, and the initial moisture field w0, initial stress field σ0 and initial displacement field S0 in the fill were obtained by setting initial conditions;

[0017] Analysis of displacement field under the influence of blind drainage ditch failure infiltration;

[0018] Set the total time of blind drainage ditch leakage and the output time step; set the pressure head boundary condition; set the dependent variable to study the initial state and the last solution of the steady-state analysis to the initial value of the seepage state study for analysis; calculate the moisture field w1, stress field σ1 and displacement field S1 of the high fill foundation after humidification in the soil under different compaction degrees and different blind ditch failure rates through the Comsol seepage module;

[0019] Analysis of displacement field after seepage stabilization in drainage blind ditch

[0020] Set the total time and output time step of the settlement stabilization process. The dependent variable is set to use the last solution of the transient analysis of the seepage state study as the initial value of the steady state study for analysis. At this time, the seepage stage is completed, and the last solution of the seepage stage study is used as the initial value of the steady state study to simulate the surface settlement stabilization process of loess high fill after the drainage blind ditch fails.

[0021] The Comsol seepage module is used to calculate the moisture field w2, stress field σ2 and displacement field S2 in the soil of the high fill foundation after the drainage blind ditch fails and the leakage stabilizes. The difference between S2 and S0 is the foundation humidification deformation caused by the failure of the drainage blind ditch, as shown in the following formula.

[0022] ΔS = S2 - S1;

[0023] Where △S is the surface wetting deformation during seepage.

[0024] Preferably, three parameters used to describe the wetting effect of loess high fill induced by blind ditch failure: wetting deformation ratio ζ, blind ditch failure rate β and average water level rise height △h include

[0025] Wet deformation ratio ζ: The ratio of the wetting deformation caused by the rise of groundwater level due to the failure of drainage blind ditch to the average water level rise is defined as the wetting deformation ratio ζ caused by water level rise.

[0026]

[0027] Where △S is the surface humidification deformation during seepage, △h max is the height of the highest water level rise, l is the model groundwater level depth, and l0 is the initial groundwater level depth;

[0028] Blind ditch failure rate β: The failure degree of drainage blind ditch is defined as the drainage blind ditch failure rate β, the expression is

[0029]

[0030] Where Q is the infiltration of water from the blind ditch into the fill, Q 总 is the total amount of water infiltrating from the blind ditch into the fill when the blind ditch fails completely;

[0031] Average water level rise △h: Average water level rise △h refers to the average increase in water level at a measuring point within a certain period of time, which is used to describe the change of water in high fill soil. The expression is

[0032]

[0033] Where b is the fill volume width.

[0034] Preferably, the empirical prediction model of average water level rise height △h, wetting deformation △S and wetting deformation ratio ζ under different compaction degrees and blind ditch failure rates is

[0035] Δh=(-74.002β+16.449)λ+87.985β-19.616;

[0036] ΔS=(1433.7β-1.7995)λ-1991.5β+583.09;

[0037] ξ=(0.0083ln(β)-0.0521)ln(λ)+0.0023e 0.1386β ;

[0038] Where λ represents the compaction degree of different fill bodies.

[0039] Therefore, the present invention adopts the above-mentioned blind drainage ditch failure-induced loess high fill wetting settlement prediction method, and the technical effects are as follows:

[0040] (1) The law of the maximum water level change increment under the same compaction degree and different blind ditch failure rates: Under the same compaction degree, the maximum water level rises rapidly in the early stage with the increase of the blind ditch failure rate β, and the growth rate gradually slows down in the later stage and finally tends to be stable. When the compaction degree λ of the fill body decreases from 0.98 to 0.88 and the blind ditch failure rate β increases from 25.42% to 100%, the maximum water level rises in the foundation △h max Increased from 7.91m to 23.13m;

[0041] (2) The law of average water level change increment under the same compaction degree and different blind ditch failure rates: Under the same compaction degree, the average water level rise height increases rapidly in the early stage with the increase of blind ditch failure rate β, and the growth rate gradually slows down in the later stage and finally tends to be stable. When the fill compaction degree λ decreases from 0.98 to 0.88 and the blind ditch failure rate β increases from 25.42% to 100%, the average water level rise height △h in the foundation increases from 3.89m to 21.69m.

[0042] (3) The wetting deformation ratio ζ decreases with the increase of fill compaction λ and blind ditch failure rate β. As the blind ditch failure rate β increases, the wetting deformation ratio ζ gradually decreases and does not change much. This phenomenon may be due to the combined effect of factors such as the increase in soil saturation, the gradual equilibrium of soil settlement, and the gradual weakening of the impact of rising water levels on the soil.

[0043] (4) By comparing the results of deep water immersion tests with those of actual projects, it was found that the wetting deformation ratio ζ of the actual deep water immersion test results was 1.2%, while the wetting deformation ratio of the numerical simulation test results ranged from 0.4% to 1.1%. The obtained wetting deformation ratio law curve was close to the measured value. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 It is a finite element and mesh numerical model;

[0045] Figure 2 It is the failure leakage model of drainage blind ditch;

[0046] Figure 3 This is a schematic diagram of the failure process of blind drainage ditch blockage;

[0047] Figure 4 The curve of average water level rise height change under different compaction degrees and blind ditch failure rates; Figure 4 (a) is the average water level rise height variation curve under different compaction degrees; Figure 4 (b) is the average water level rise height variation curve under different blind ditch failure rates;

[0048] Figure 5 It is the relationship curve between blind ditch failure rate and average water level rise fitting parameter;

[0049] Figure 6 It is the change curve of moisture deformation under different compaction degree and blind ditch failure rate; Figure 6 (a) is the moisture deformation change curve under different compaction degrees; Figure 6 (b) is the humidification deformation change curve under different blind ditch failure rates;

[0050] Figure 7 It is the relationship curve between blind ditch failure rate and humidification deformation fitting parameters;

[0051] Figure 8 The curves of wetting deformation ratio change under different compaction degrees and blind ditch failure rates are shown; Figure 8 (a) is the change curve of moistening deformation ratio under different compaction degrees; Figure 8 (b) is the change curve of humidification deformation ratio under different blind ditch failure rates;

[0052] Fig. 9 This is the relationship curve between blind ditch failure rate and humidification deformation ratio fitting parameters. DETAILED DESCRIPTION

[0053] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0054] 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.

[0055] Embodiment 1

[0056] A method for predicting wetting settlement of loess high fill induced by drainage blind ditch failure comprises the following steps:

[0057] Step 1: Collect relevant data of compacted loess, and obtain damage functions of compacted loess with different compaction degrees and increasing water content under humidification conditions according to the relevant data of compacted loess;

[0058] The model parameters of soil displacement field under different compaction degrees are shown in Table 1.

[0059] Table 1 Displacement field model parameters

[0060] Compactness λ 0.88 0.9 0.93 0.95 0.98 Poisson's ratio 0.36 0.35 0.34 0.33 0.32 <![CDATA[Density ρ, g / cm 3 > 1650 1690 1750 1790 1840

[0061] The relevant parameters of the moisture field model and the VG water retention model parameters under different compaction degrees are shown in Table 2.

[0062] Table 2 Water field model and water holding model parameters

[0063]

[0064] The cohesion c and internal friction angle under different fill compaction degrees and moisture contents were obtained through the consolidation compression test and shear strength test results of Q3 compacted loess under different compaction degrees and moisture contents. Compression modulus E S0.1-0.2 Taking the test results of compaction degree λ=0.93 as an example, the cohesion c and internal friction angle of Q3 compacted loess are obtained by fitting the least squares curve. Compression modulus E S , soil specific gravity γ and other parameters with the volume water content θ w The changing rule of is shown in formula (1).

[0065]

[0066] Where c is the cohesion, is the internal friction angle, E s is the compression modulus, γ is the density of the soil, θ w is the volume water content.

[0067] By summarizing and summarizing, we can get the cohesion c and internal friction angle of Q3 compacted loess. Compression modulus E S Parameters such as compaction degree and volumetric water content θ w The changing rules are shown in Table 3.

[0068] Table 3 Variation of mechanical strength parameters of reshaped Q3 loess

[0069]

[0070]

[0071] According to the relevant data of compacted loess, the damage function of compacted loess with different compaction degrees under humidification conditions with increasing moisture content is obtained.

[0072]

[0073] Where c is the cohesion, is the internal friction angle, E s is the compression modulus, γ is the density of the soil, θ w is the volume moisture content, m1, m2, m3, m4, n1, n2, n3, n4 are constants.

[0074] Step 2: Establish a simulation method for the effect of blind drainage ditch failure on loess high fill wetting based on the damage function, analyze the changing laws of displacement field, stress field and moisture field under the initial state, seepage state and stable state, and obtain a prediction model based on the changing laws;

[0075] According to the research needs, a geometric model of a 110m loess high fill foundation under the condition of drainage blind ditch failure was established. In order to improve the calculation efficiency and accuracy, the high fill soil grid within the leakage and humidification range of the drainage blind ditch was densified, and the high fill soil grid outside the leakage and humidification range of the drainage blind ditch was sparse. The height of the established model was set to 110m, the drainage blind ditch type was a full gravel blind ditch, the upper bottom width of the drainage blind ditch was 0.41m, the lower bottom width was 0.33m, the height was 0.2m, the soil was set to fill, the groundwater level was 105m, and the height of the drainage blind ditch from the high fill bottom was 5m. The specific numerical model is as follows: Figure 1 shown.

[0076] (1) Initial state study: analysis of initial displacement field and initial moisture field;

[0077] Set the study as a steady-state study; disable the pressure head boundary condition in the Richards equation (dl) module. Use Comsol to divide the calculation model into equivalent units, and set the initial conditions to obtain the initial moisture field w0, initial stress field σ0, and initial displacement field S0 in the fill.

[0078] (2) Seepage state research: displacement field analysis under the influence of drainage blind ditch failure infiltration;

[0079] Set the total time of blind drainage ditch leakage and the output time step; enable the pressure head boundary condition; set the dependent variable to the initial state to study the last solution of the steady-state analysis as the initial value of the seepage state study for analysis. The Comsol seepage module is used to calculate the moisture field w1, initial stress field σ1 and initial displacement field S1 of the high fill foundation after humidification under different compaction degrees and different blind ditch failure rates.

[0080] (3) Stable state study: Analysis of displacement field after the seepage in the drainage blind ditch stabilizes.

[0081] Set the total time and output time step of the settlement stabilization process, disable the pressure head boundary condition; set the dependent variable to analyze the last solution of the transient analysis of the seepage state study as the initial value of the steady state study. At this time, the seepage stage is completed, and the last solution of the seepage stage study is used as the initial value of the steady state study, which can simulate the surface settlement stabilization process of loess high fill after the drainage blind ditch fails.

[0082] The Comsol seepage module is used to calculate the moisture field w2, initial stress field σ2 and initial displacement field S2 in the soil of the high fill foundation after the blind drainage ditch fails and the leakage stabilizes. The difference between S2 and S0 is the foundation humidification deformation caused by the failure of the blind drainage ditch, as shown in the following formula:

[0083] ΔS=S2-S1 (3);

[0084] Where △S is the surface wetting deformation during seepage.

[0085] The above simulation method is used to simulate

[0086] In the process of unsaturated loess wetting deformation analysis, the change of water environment conditions will cause the change of moisture field in the soil, resulting in the weakening of the mechanical strength parameters of the wetting soil. Therefore, in order to simulate the wetting process through numerical analysis software, the parameters of the soil after wetting must be changed in real time and accordingly. Only in this way can the real soil wetting process be simulated. Therefore, in the specific analysis later, the interpolation function of soil parameters and effective saturation / volume moisture content is first set. In the subsequent seepage calculation, the mechanical and stiffness parameters of the soil will change with the change of effective saturation / volume moisture content of the soil under the influence of seepage. According to the changed seepage field, new mechanical and stiffness parameters are given to the soil, which can simulate the wetting deformation process of the soil under the influence of moisture field changes.

[0087] The Richards equation seepage module of Comsol software can analyze the unsaturated seepage in loess high fill foundation caused by water infiltration. By setting the Richards and solid mechanics physical field interface, the fluid-solid coupling analysis and calculation of unsaturated loess can be realized. The idea of ​​​​wetting deformation analysis in this paper is to calculate the initial displacement field S0 in the initial state and the displacement S2 after the water infiltration is stabilized. The difference between the two displacements is the wetting deformation of unsaturated loess caused by wetting.

[0088] The specific module selection and calculation interface settings in Comsol software are:

[0089] (1) Setting of seepage field: After the blind ditch fails, seepage occurs in the fill soil in the high fill valley, forming a saturated-unsaturated seepage zone. Therefore, the Richards equation that can simulate the seepage of unsaturated soil is selected in the software. 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, a water retention model based on the VG function is set; the relevant soil parameters that affect the seepage of the unsaturated soil and the relevant boundary conditions of the model are input.

[0090] (2) Stress field setting: Select the solid mechanics interface in the software, first set the soil model to the ideal elastic-plastic model and input the relevant basic soil parameters, then replace the soil cohesion, internal friction angle, and Young's modulus with the interpolation function E=f1(S e ), c=f2(S e ), And set the relevant model boundary conditions. Finally, the change of displacement field is obtained through fluid-solid coupling analysis.

[0091] (3) Setting of fluid-solid coupling correlation analysis: By consulting relevant data, the fitting functions of soil mechanical strength parameters and volumetric water content are summarized and summarized, and the relationship between soil parameters and water content under different compaction degrees is obtained. w ), c=f2(θ w ), According to formula (4), E, ​​c, Regarding the interpolation function of the effective saturation Se, we get E=int1(S e ), c = int2(S e ), That is, “E=f1(S e ), c=f2(S e ),

[0092]

[0093] S e is the effective saturation; θ is the volumetric water content / %; θ r is the residual volume moisture content / %; θ s It is the saturated volume moisture content (%).

[0094] By bringing the above interpolation function into the elastoplastic constitutive model, the change of the displacement field in the foundation caused by wetting can be obtained through calculation, thereby obtaining the wetting deformation of the loess high fill foundation. The soil is set as an isotropic material, and the size of the Biot-Willis coefficient represents the interaction between soil stress and moisture in the soil, as shown in formula (5), which is a calculation formula built into the software.

[0095] σ=Dε v -α B pI (5);

[0096] Where σ is soil stress, D is stiffness matrix; ε v is the volume strain; p is the pore water pressure / Pa; I is the unit matrix, α B Represents the Biot-Willis coefficient.

[0097] Specific drainage blind ditch model and calculation results diagram, such as Figure 2 shown.

[0098] When the drainage blind ditch is blocked and the geotextile fails, the water in the drainage blind ditch cannot be effectively discharged, causing the water in the drainage blind ditch to infiltrate into the surrounding soil, thereby causing the groundwater level to rise. This change in the moisture field will cause the rearrangement and compaction of soil particles in the humidification area, leading to surface subsidence.

[0099] Gravel blind drainage ditch is a common surface drainage system used to collect and discharge surface runoff to prevent hydrological disasters and soil erosion. However, these drainage systems may suffer from sediment accumulation, silt erosion, debris blockage and other reasons, causing the blind drainage ditch to fail. The above factors accumulate over time, causing the blind drainage ditch to become increasingly blocked. As the degree of blockage increases, the drainage efficiency of the blind drainage ditch gradually decreases, and it may eventually fail completely. The general process analysis diagram of the blockage failure of the full gravel blind drainage ditch is shown in the figure below. Figure 3 shown.

[0100] Three parameters are used to describe the wetting effect of loess high fill induced by blind ditch failure: wetting deformation ratio ζ, blind ditch failure rate β and average water level rise height △h, including

[0101] Wet deformation ratio ζ: The ratio of the wetting deformation caused by the rise of groundwater level due to the failure of drainage blind ditch to the average water level rise is defined as the wetting deformation ratio ζ caused by water level rise.

[0102]

[0103] Where △S is the surface humidification deformation during seepage, △h maxis the height of the highest water level rise, l is the model groundwater level depth, and l0 is the initial groundwater level depth;

[0104] Blind ditch failure rate β: The failure degree of drainage blind ditch is defined as the drainage blind ditch failure rate β, the expression is

[0105]

[0106] Where Q is the infiltration of water from the blind ditch into the fill, Q 总 is the total amount of water infiltrating from the blind ditch into the fill when the blind ditch fails completely;

[0107] Average water level rise △h: Average water level rise △h refers to the average increase in water level at a measuring point within a certain period of time, which is used to describe the change of water in high fill soil. The expression is

[0108]

[0109] Where b is the fill volume width.

[0110] A typical unsaturated loess high fill project is taken as the numerical analysis object. The fill height is 110.0m and the groundwater level is set at 105m underground. The humidification deformation of the unsaturated loess high fill caused by the failure and leakage of the drainage blind ditch is numerically analyzed to obtain its changing law.

[0111] 1. Distribution law of water field inside fill body under different blind drainage ditch failure conditions

[0112] (1) Variation of the maximum water level under different compaction degrees and different blind ditch failure rates

[0113] After the deep drainage blind ditch of loess high fill foundation failed and leaked, the highest water level in the high fill foundation increased rapidly in the early stage, and the water level rise rate gradually slowed down in the later stage, and finally stabilized. When the soil compaction degree is 0.88, after 100 years of seepage, when the blind ditch failure rate β is 100%, the maximum height of the highest water level in the high fill foundation is 23.13m; when the soil compaction degree is 0.98, after 100 years of seepage, when the blind ditch failure rate β is 25.42%, the minimum height of the highest water level in the high fill foundation is 7.91m; it can be seen that with the increase of external water pressure and the increase of moisture content of surrounding soil, the water pressure inside and outside the drainage blind ditch gradually balances and finally reaches a stable state. The greater the blind ditch failure rate β, the greater the water pressure in the drainage blind ditch, the faster the maximum water level rises, and the higher the maximum water level that can be achieved; the greater the compaction of the soil, the more difficult it is for the water leaking from the drainage blind ditch due to failure to infiltrate into the surrounding soil, the slower the maximum water level rises, and the lower the maximum water level that can be achieved. The smaller the compaction and blind ditch failure rate β, the shorter the time it takes for the maximum water level to reach a stable state.

[0114] (2) Variation of average water level rise under different compaction degrees and different blind ditch failure rates

[0115] After the deep drainage blind ditch of loess high fill foundation fails and leaks, the average water level in the high fill foundation increases rapidly in the early stage, and the water level rise rate slows down gradually in the later stage, and finally tends to be stable. When the soil compaction degree is 0.88, after 100 years of seepage, when the blind ditch failure rate β=100%, the average water level rise height in the high fill foundation is 21.69m at most; when the soil compaction degree is 0.98, after 100 years of seepage, when the blind ditch failure rate β=25.42%, the average water level rise height in the high fill foundation is 3.89m at most. The larger the blind ditch failure rate β, the greater the water pressure in the drainage blind ditch, the faster the average water level rises, and the higher the average water level that can be achieved; the greater the soil compaction degree, the more difficult it is for the water leaked from the drainage blind ditch to infiltrate into the surrounding soil, the slower the average water level rises, and the lower the highest water level that can be achieved. The smaller the compaction degree and blind ditch failure rate β, the shorter the time it takes for the average water level to reach a stable state.

[0116] 2. Distribution law of displacement field inside fill body under different blind drainage ditch failure conditions

[0117] With the increase of compaction degree, the wetting deformation of fill foundation gradually decreases, and with the increase of blind ditch failure rate, the wetting deformation of fill foundation gradually increases; due to the influence of the overlying soil weight of drainage blind ditch, the closer to the surface, the greater the foundation deformation.

[0118] After 100 years of seepage, at the same compaction degree, the greater the blind ditch failure rate β, the greater the surface humidification deformation △S; at the same blind ditch failure rate, the greater the fill compaction degree, the smaller the △S, when the compaction degree is 0.88, the blind ditch failure rate β is 100%, the maximum △S is -204.93mm; when the compaction degree is 0.98, the blind ditch failure rate β is 25.42%, the minimum △S is -15.73mm. At the same fill compaction degree, the greater the blind ditch failure rate β, the greater the water pressure in the drainage blind ditch and the difference between the internal and external water pressures of the surrounding soil, the faster the water in the drainage blind ditch can be discharged into the surrounding soil, and the greater the humidification deformation caused by the water level rise; at the same blind ditch failure rate β, the greater the fill compaction degree, the denser the fill, the smaller the pores between the soil, the more difficult it is for the water in the drainage blind ditch to infiltrate into the surrounding fill, and the smaller the humidification deformation caused by the water level rise.

[0119] After 100 years of seepage, under the same fill compaction condition, the greater the blind ditch failure rate β, the smaller the wetting deformation ratio ζ; under the same blind ditch failure rate condition, the greater the fill compaction, the smaller the wetting deformation ratio ζ. When the compaction degree is 0.88 and the blind ditch failure rate β is 19.64%, ζ is the maximum of 1.1%; when the compaction degree is 0.98 and the blind ditch failure rate β is 100%, ζ is the minimum of 0.4%.

[0120] As the blind ditch failure rate increases, the wetting deformation ratio ζ will gradually decrease and change little. This phenomenon may be due to the combined effect of factors such as the increase in soil saturation, the gradual equilibrium of soil settlement, and the gradual weakening of the impact of rising water levels on the soil. The specific manifestations are:

[0121] (1) The saturation of the soil gradually increases: When the drainage blind ditch is blocked and the geotextile fails, water infiltration will gradually saturate the soil around the drainage blind ditch. The saturated soil will gradually become denser, so that the moisture reduction deformation ratio ζ becomes smaller and gradually stabilizes;

[0122] (2) Soil settlement gradually tends to equilibrium: In the initial stage, the blockage of drainage blind ditches will cause the surface settlement to be faster. However, as time goes by, the moisture in the soil will gradually reach equilibrium and the surface settlement rate will gradually decrease.

[0123] (3) The impact of rising water levels on soil gradually weakens: In the initial stage, rising water levels may have a greater impact on soil compaction, resulting in a faster surface subsidence rate. As time goes by, the impact of rising water levels on soil may gradually weaken, resulting in a slower surface subsidence rate.

[0124] Empirical model of wetting deformation caused by blind drainage ditch failure

[0125] (1) The simplified empirical models of the average water level rise △h and the different blind ditch failure rates β and different fill compaction degrees λ are shown in Tables 4 and 5.

[0126] Table 4 Fitting formula for average water level elevation of reshaped loess under different blind ditch failure rates

[0127] Compactness λ Fitting formula Fitting accuracy 0.88 Δh=10.6081ln(β)+2.9282 0.9533 0.9 Δh=10.3471ln(β)+2.9615 0.9562 0.93 Δh=9.5277ln(β)+3.1368 0.9605 0.95 Δh=9.105ln(β)+3.2414 0.9755 0.98 Δh=7.0094ln(β)+3.1862 0.9704

[0128] Table 5 Fitting formula for average water level elevation of remolded loess at different compaction degrees

[0129]

[0130] From the data in Tables 4 and 5 above, we can get the variation law of average water level rise height under different fill compaction degree and blind ditch failure rate, see Figure 4 .

[0131] Table 5 shows the relationship between the average water level rise △h and the compaction degree λ of different fill bodies.

[0132] Δh=a1·λ+b1 (9);

[0133] Where a1 and b1 are the fitting curve parameters related to the average water level rise height.

[0134] In order to more accurately reflect the change in moisture field caused by the rise in water level after the blind drainage ditch fails and obtain its average water level rise height, the parameters a1 and b1 in formula (9) can be used to establish a functional relationship with the blind ditch failure rate β, as shown in Table 6. Figure 5 shown.

[0135] Table 6 Fitting formula of blind ditch failure rate - + and average water level rise height fitting parameters

[0136] parameter Fitting formula Fitting accuracy <![CDATA[a1]]> <![CDATA[a1=-74.002β+16.449]]> 0.9625 <![CDATA[b1]]> <![CDATA[b1=87.985β-19.616]]> 0.8008

[0137] (2) The simplified empirical models of wetting deformation △S, different blind ditch failure rates β and different fill compaction degrees λ are shown in Tables 7 and 8.

[0138] Table 7 Fitting formulas for wetting deformation and blind ditch failure rate under different compaction degrees

[0139] Compactness λ Fitting formula Fitting accuracy 0.88 ΔS=-95.021ln(β)-36.712 0.9541 0.9 ΔS=-76.65ln(β)-30.521 0.9561 0.93 ΔS=-59.68ln(β)-24.412 0.9589 0.95 ΔS=-42.99ln(β)-18.861 0.9635 0.98 ΔS=-26.221ln(β)-13.526 0.9725

[0140] Table 8 Fitting formula of wetting deformation and compaction degree under different blind ditch failure rates

[0141] Blind channel failure rate, % Fitting formula Fitting accuracy 21.63 ΔS=324.43λ-332.81 0.9934 42.77 ΔS=591.8λ-607.91 0.9921 61.95 ΔS=886.95λ-906.33 0.9937 82.29 ΔS=1168.9λ-1192.1 0.9936 100 ΔS=1444λ-1470.7 0.9932

[0142] From the data in Tables 7 and 8 above, we can get the changing rules of moisture deformation under different fill compaction degrees and blind ditch failure rates, see Figure 6 .

[0143] It can be seen from Table 8 that the relationship between the average water level rise △h and the compaction degree λ of different fill bodies conforms to the characteristics of formula (10).

[0144] ΔS=a2·λ+b2 (10);

[0145] Where a2 and b2 are the fitting curve parameters related to humidification deformation.

[0146] In order to more accurately reflect the displacement field changes caused by the water level rise after the blind drainage ditch fails and obtain its humidification deformation, the parameters a2 and b2 of formula (10) can be used to establish a functional relationship with the blind ditch failure rate β, as shown in Table 9. Figure 7 shown.

[0147] Table 9 Fitting formula for blind ditch failure rate and humidification deformation fitting parameters

[0148] parameter Fitting formula Fitting accuracy <![CDATA[a2]]> <![CDATA[a2=1433.7β-1.7995]]> 0.9989 <![CDATA[b2]]> <![CDATA[b2=-1991.5β+583.09]]> 0.5843

[0149] (3) The simplified empirical models of the wetting deformation ratio ζ and the failure rates of different blind gullies β and different fill compaction degrees λ are shown in Tables 10 and 11.

[0150] Table 10 Fitting formula of wetting deformation ratio and blind ditch failure rate under different compaction degrees

[0151] Compactness λ Fitting formula Fitting accuracy 0.88 ξ=-0.0011ln(β)+0.0112 0.9541 0.9 ξ=-0.0011ln(β)+0.0093 0.9561 0.93 ξ=-0.0011ln(β)+0.0073 0.9589 0.95 ξ=-0.0011ln(β)+0.0057 0.9635 0.98 <![CDATA[ξ=0.0041e -0.017β ]]> 0.5312

[0152] Table 11 Fitting formula of wetting deformation ratio and fill compaction degree under different blind ditch failure rates

[0153]

[0154] From the data in Tables 10 and 11 above, the variation law of the wetting deformation ratio under different fill compaction degrees and blind ditch failure rates is obtained. Figure 8 .

[0155] The relationship between the wetting deformation ratio ζ and the compaction degree λ of different fill bodies:

[0156] ξ=a3ln(λ)+b3 (11);

[0157] Where a3 and b3 are the fitting curve parameters related to the humidification deformation ratio.

[0158] In order to more accurately reflect the change of humidification deformation ratio caused by water level rise after the blind drainage ditch fails, a simplified empirical model of humidification deformation ratio can be obtained. The parameters a3 and b3 of formula (11) can be used to establish a functional relationship with the blind ditch failure rate β, as shown in Table 12. Fig. 9 shown.

[0159] Table 12 Fitting formula for blind ditch failure rate and humidification deformation ratio fitting parameters

[0160] parameter Fitting formula Fitting accuracy <![CDATA[a3]]> <![CDATA[a3=0.0083ln(β)-0.0521]]> 0.6239 <![CDATA[b3]]> <![CDATA[b3=0.0023e 0.1386β ]]> 0.4962

[0161] pass Figures 4 to 9 The fitting parameter relationship curve can be used to obtain the prediction model of average water level rise height △h, wetting deformation △S and wetting deformation ratio ζ under different compaction degrees and blind ditch failure rates.

[0162] Δh=(-74.002β+16.449)λ+87.985β-19.616 (12);

[0163] ΔS=(1433.7β-1.7995)λ-1991.5β+583.09 (13);

[0164] ξ=(0.0083ln(β)-0.0521)ln(λ)+0.0023e 0.1386β (14);

[0165] Where β represents the failure rate of blind ditch, and λ represents the compaction degree of different fill bodies.

[0166] Step 3: Use the obtained prediction model to analyze the wetting and settlement of loess high fill, including the average water level rise, wetting deformation and wetting deformation ratio.

[0167] The above method is used for prediction and compared with the actual measured cases.

[0168] The topography and landforms in the planning area of ​​Yan'an New District are characterized by interlaced gullies, alternating ridges and hills, and undulating ups and downs. Generally speaking, it is high in the southeast and low in the northwest. The elevation of the gullies and hills is between 974 and 1294 meters. According to the distribution and direction of ridges and slopes, Yan'an New District can be divided into four basins: Huanghaowa Basin, Liushudian Basin, Yehuzigou Basin and Wangchagou Basin. The specific landforms are composed of tops, ditches, ridges and slopes, with an overall slope of about 2-3%. The original terrain of the proposed construction site is undulating, and the scope includes three independent main ditch basins, namely Huanghaowa Basin, Yehuzigou Basin and Liushudian Hougou.

[0169] In a drainage blind ditch scheme in a certain place, the drainage blind ditch adopts a structure combining crushed stone and culvert, and geotextile is laid on the outside. According to the cross-sectional flow of the valley in each basin, the diameter of the culvert set in the main blind ditch is 500-800mm. At the same time, the setting of crushed stone on the upper part of the culvert can effectively reduce the pressure of the soil overlying the culvert and protect the culvert from being squeezed and damaged by the upper soil; wire mesh gabions are placed on both sides of the culvert, and the crushed stone is placed in the gabions on both sides of the culvert. At the same time, a 40cm thick geogrid reinforced crushed stone cushion is laid on the top of the gabion, which can form a soil arch effect, thereby reducing the soil pressure on the top of the pipe. The culvert in the drainage blind ditch is a plastic pipe. As a flexible pipe, it can reduce the squeezing of the crushed stone on the top of the pipe, play a buffering role, and protect the culvert.

[0170] The established model adopts the same cross-sectional dimensions as the drainage blind ditch arranged in the above-mentioned actual project, and the type of drainage blind ditch is selected as a full-gravel blind ditch. On this basis, the model is established and numerical analysis is carried out.

[0171] Based on the Yan'an New District project, a deep immersion test was conducted to study the impact of deep groundwater rise on foundation wetting and deformation. The rising process of groundwater level was simulated by continuous water injection.

[0172] The soil samples used in the deep immersion test came from the loose loess of the Middle and Late Pleistocene excavated from the Yan'an New District project. The compacted soil was obtained through the method of loose spreading-humidification-rolling-testing. The moisture content of each layer of the fill soil was continuously monitored by using a TDR moisture meter buried in advance.

[0173] The deep immersion test was conducted in the soil of the high fill site that had been filled for 12 months and the settlement of each layer of soil had basically stabilized. The deep immersion lasted for 30 days and the groundwater level rose by 10 meters. Through monitoring, the wetting deformation of the fill soil reached 58mm and the wetting deformation ratio ζ was 1.2%. Since the soil filling time in the actual project was early and the compaction time during the construction process was long, the compaction degree of the compacted soil was large and the wetting deformation coefficient was very low, so the wetting deformation at the bottom of the fill was not large.

[0174] The model established in this paper has a fill depth of 110m, a fill width of 40m, a depth l from the top of the fill to the groundwater level of 105m, and a seepage time of 100 years. The compacted loess parameters used in the experiment are: relative density of soil particles d s =2.70, initial porosity e0 is 0.47-0.64, natural dry density ρ d 1.65-1.84g / cm 3 The natural moisture content w of the soil sample is 9.5% to 12.8%, and the hydraulic conductivity K s 8.1×10 -10 -7.29×10 -9 m / s.

[0175] When the compaction degree is 0.88 and the blind ditch failure rate β is 19.64%, the maximum wetting deformation ratio ζ is 1.1%; when the compaction degree is 0.98 and the blind ditch failure rate β is 100%, the minimum wetting deformation ratio ζ is 0.4%. Since the dry density of the test soil in the actual project is less than the dry density of the compacted soil used in the simulation in this paper, the actual deep immersion test has a larger wetting deformation caused by the rise of the groundwater level, and the wetting deformation ratio is also larger. By comparing with the test results of the deep immersion test of the actual project mentioned above, it is found that the simulated wetting deformation ratio law curve is close to the measured value. The comparison of the parameters and results of the measured and simulated values ​​is shown in Table 13.

[0176] Table 13 Comparison of measured and simulated parameters and results

[0177] parameter L / m <![CDATA[d s ]]> Β / % △h / m △S / mm Z / ％ Measured value 50 2.71 100 10 58 1.2 Analog value 105 2.70 19.64-100 3.9-21.7 15.73-204.93 0.4-1.1

[0178] Therefore, the present invention adopts the above-mentioned method for predicting wetting and settlement of loess high fill induced by drainage blind ditch failure to more accurately predict the influence of groundwater uplift induced by blind ditch failure in the foundation of loess high fill engineering on the stability of the fill body and foundation deformation, providing a scientific basis for engineering design and construction.

[0179] 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 wetting and settlement of loess high fill induced by blind drainage ditch failure, characterized in that: The following steps are involved: Collect relevant data of compacted loess, and obtain the damage function of loess with different compaction degrees and increasing water content under moistening conditions according to the relevant data of compacted loess; Based on the damage function, a simulation method for the effect of blind drainage ditch failure on loess high fill wetting is established, and the variation law of displacement field, stress field and moisture field under the initial state, seepage state and stable state is analyzed. The evaluation parameters of the loess high fill wetting effect induced by blind drainage ditch failure are further defined, and a prediction model is constructed based on the evaluation parameters and variation law. The obtained prediction model is used to analyze the wetting settlement of loess high fill, including the average water level rise, wetting deformation and wetting deformation ratio.

2. The method for predicting wetting settlement of loess high fill induced by blind drainage ditch failure according to claim 1 is characterized in that: The relevant data of compacted loess include cohesion c, internal friction angle, and Compression modulus E s And the data of soil specific gravity γ.

3. The method for predicting wetting settlement of loess high fill induced by blind drainage ditch failure according to claim 1 is characterized in that: According to the relevant data of compacted loess, the damage function of compacted loess with different compaction degrees under humidification conditions with increasing moisture content is obtained. Where c is the cohesion, is the internal friction angle, E s is the compression modulus, γ is the density of the soil, θ w is the volume moisture content, m1, m2, m3, m4, n1, n2, n3, n4 are constants related to the degree of compaction.

4. The method for predicting wetting settlement of loess high fill induced by blind drainage ditch failure according to claim 1 is characterized in that: The simulation method of the effect of blind drainage ditch failure on loess high fill wetting is established based on the damage function, including the following steps: Analysis of initial displacement field and initial moisture field; The study was set as a steady-state study; the calculation model was divided into equivalent units using Comsol, and the initial moisture field w0, initial stress field σ0 and initial displacement field S0 in the fill were obtained by setting initial conditions; Analysis of displacement field under the influence of blind drainage ditch failure infiltration; Set the total time of blind drainage ditch leakage and the output time step; set the pressure head boundary condition; set the dependent variable to study the initial state and the last solution of the steady-state analysis to the initial value of the seepage state study for analysis; calculate the moisture field w1, stress field σ1 and displacement field S1 of the high fill foundation after humidification in the soil under different compaction degrees and different blind ditch failure rates through the Comsol seepage module; Analysis of displacement field after seepage stabilization of drainage blind ditch; Set the total time and output time step of the settlement stabilization process. The dependent variable is set to use the last solution of the transient analysis of the seepage state study as the initial value of the steady state study for analysis. At this time, the seepage stage is completed, and the last solution of the seepage stage study is used as the initial value of the steady state study to simulate the surface settlement stabilization process of loess high fill after the drainage blind ditch fails. The Comsol seepage module is used to calculate the moisture field w2, stress field σ2 and displacement field S2 in the soil of the high fill foundation after the blind drainage ditch fails and the leakage is stabilized. The difference between S2 and S0 is the foundation humidification deformation caused by the failure of the blind drainage ditch. The specific formula is as follows: ΔS = S2 - S1; Where △S is the surface wetting deformation during seepage.

5. The method for predicting wetting settlement of loess high fill induced by blind drainage ditch failure according to claim 1 is characterized in that: Three evaluation parameters of the wetting effect of loess high fill induced by blind ditch failure include: Wet deformation ratio ζ: The ratio of the wetting deformation caused by the rise of groundwater level due to the failure of drainage blind ditch to the average water level rise is defined as the wetting deformation ratio ζ caused by water level rise, as follows: Where △S is the surface moisture deformation during seepage, △h max is the height of the highest water level rise, l is the model groundwater level depth, and l0 is the initial groundwater level depth; Blind ditch failure rate β: The failure degree of drainage blind ditch is defined as the drainage blind ditch failure rate β, which is expressed as: Where Q is the infiltration of water from the blind ditch into the fill, Q 总 is the total amount of water infiltrating from the blind ditch into the fill when the blind ditch fails completely; Average water level rise height △h: Average water level rise height △h refers to the average increase in water level at the measuring point within a certain period of time, which is used to describe the change of water in the high fill soil body. The expression is: Where b is the fill volume width.

6. The method for predicting wetting settlement of loess high fill induced by blind drainage ditch failure according to claim 1 is characterized in that: Empirical prediction model of average water level rise △h, wetting deformation △S and wetting deformation ratio ζ under different compaction degrees and blind ditch failure rates Δh=(-74.002β+16.449)λ+87.985β-19.616; ΔS=(1433.7β-1.7995)λ-1991.5β+583.09; ξ=(0.0083ln(β)-0.0521)ln(λ)+0.0023e 0.1386β ; Where λ represents the compaction degree of different fill bodies.

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