Easily-liquefied roadbed liquefaction impedance correction method considering embankment loading influence

Abstract

The invention discloses a liquefiable roadbed liquefaction impedance correction method considering embankment loading influence, which comprises the following steps: acquiring basic conditions of a site, and calculating to obtain a vertical normal stress sigma0; determining liquefaction cycle impedance values DRR corresponding to different earthquake magnitudes under the working condition of the horizontal site; the influence of the vertical normal stress on the circulating liquefaction circulating impedance value is corrected; the influence of the initial shear stress on the circulating liquefaction circulating impedance value is corrected; calculating to obtain a vertical normal stress coefficient beta and a shear stress coefficient alpha; the influence of embankment loading on the stratum is comprehensively considered, and the liquefaction cycle impedance value DRR * of the liquefiable stratum is obtained. By considering the embankment loading effect, the cyclic liquefaction resistance value can be quantitatively corrected by adopting the vertical normal stress coefficient and the shear stress coefficient, scientific selection of a foundation treatment scheme in an embankment project is facilitated, the project safety and reliability are improved, and the construction period is shortened. And a theoretical basis and data support can be provided for roadbed treatment of a liquefiable stratum under an embankment surcharge loading working condition.

Description

Technical Field

[0001] The invention relates to a method for correcting liquefaction impedance of a silt roadbed, in particular to a method for correcting liquefaction impedance of an easily liquefied roadbed taking into account the influence of embankment loading, and belongs to the technical field of roadbed treatment. Background Art

[0002] Soil liquefaction is a term used in earthquake engineering, which refers to the process in which solid soil becomes liquid or viscous fluid under the action of external forces. Soil liquefaction mainly occurs in shallow, saturated loose fine sand, silty sand or clay with poor bottom drainage. Usually, under repeated external force shocks (such as earthquakes), the loose soil is compressed, the internal voids are reduced, and the water pressure in the voids increases. When the water pressure increases to a level that exceeds the external pressure in the soil, and the water cannot be discharged from the ground, soil liquefaction will occur, which will cause the entire site to lose its bearing capacity and deform significantly.

[0003] Embankment refers to a fill roadbed with the top surface higher than the original ground. It is a common form of road cross section in road construction for transportation engineering. Embankments are usually line structures with a certain density built with soil or stone on natural ground. They can effectively fill and stabilize the roadbed and increase the stability of the roadbed. Under the action of the embankment, the increase in the effective stress of the soil within a certain depth range below the road surface will make the soil particle structure more tightly arranged and improve the soil's anti-liquefaction performance, but it will also cause the soil within a certain range near the toe of the slope to be subjected to shear stress, thereby reducing the anti-liquefaction performance of this part of the soil. At present, the study on the anti-liquefaction characteristics of silt due to changes in vertical normal stress and shear stress is in the qualitative analysis stage, and there is a lack of unified understanding of the correction of roadbed liquefaction impedance caused by changes in the vertical normal stress and initial shear stress of the site caused by the liquefiable roadbed loading. Summary of the invention

[0004] In view of the problems existing in the above-mentioned prior art, the present invention provides a liquefaction impedance correction method for easily liquefied roadbed taking into account the influence of embankment loading, which can quantitatively describe the liquefaction cycle impedance value of the site and provide a theoretical basis and data support for the roadbed treatment of easily liquefied strata under embankment loading conditions.

[0005] To achieve the above purpose, the liquefaction impedance correction method of the liquefiable roadbed considering the influence of embankment loading specifically includes the following steps:

[0006] Step 1: Investigate the liquefiable strata conditions of the existing horizontal sites of the embankment loading liquefaction site, obtain the basic site conditions, calculate the vertical normal stress σ0, and obtain in-situ soil samples through the low-disturbance method;

[0007] Step 2: Conduct indoor dynamic single shear test on the undisturbed soil samples. During the test, the vertical load and density are kept consistent with the in-situ conditions of the site. Use a variety of shear stress amplitudes to obtain the relationship between the shear stress ratio and the number of liquefaction vibrations, and determine the liquefaction cycle impedance DRR corresponding to different earthquake magnitudes under horizontal site conditions.

[0008] Step 3, carry out indoor dynamic single shear test on the undisturbed soil samples, use a variety of vertical normal stresses and a variety of shear stress ratios to obtain the relationship between vertical normal stress and liquefaction vibration times, and correct the influence of vertical normal stress on the cyclic liquefaction cycle impedance value by the following formula:

[0009] DRR1=DRR·(1+β) k

[0010] Where: DRR1 is the cyclic liquefaction impedance considering the influence of vertical normal stress; β is the vertical normal stress coefficient; k is the normal stress correlation coefficient;

[0011] Step 4: Conduct indoor dynamic single shear tests on the undisturbed soil samples, using a variety of initial shear stresses and a variety of shear stress ratios to obtain the relationship between the shear stress ratio and the number of liquefaction vibrations. The influence of the initial shear stress on the cyclic liquefaction impedance value is corrected by the following formula:

[0012] DRR2=e m·α+ln(DDR)

[0013] Where: DRR2 is the cyclic liquefaction impedance considering the influence of shear stress; α is the shear stress coefficient; m is the shear stress correlation coefficient;

[0014] Step 5, according to the embankment load design conditions, calculate the additional vertical normal stress Δσ and additional shear stress Δτ of the load at different positions of the liquefiable stratum through numerical simulation or analytical methods, and then calculate the vertical normal stress coefficient β and shear stress coefficient α according to the following formula:

[0015] β=Δσ / σ0

[0016] α=Δτ / σ0

[0017] Where: β is the vertical normal stress coefficient; α is the shear stress coefficient; Δσ is the additional vertical normal stress of the pile load; Δτ is the additional shear stress of the pile load;

[0018] Step 6, comprehensively considering the influence of embankment load on the stratum, the liquefaction cycle resistance value DRR* of the liquefiable stratum corrected by the vertical normal stress and shear stress is obtained by the following formula:

[0019] DRR * =DRR1+DRR2-DRR

[0020] Where: DRR1 is the cyclic liquefaction impedance considering the influence of vertical normal stress; DRR2 is the cyclic liquefaction impedance considering the influence of shear stress; DRR is the liquefaction cyclic impedance value corresponding to different earthquake magnitudes.

[0021] Furthermore, in Step 1, the basic site conditions include the site soil stratification, the depth of the liquefiable stratum, and the weight of each soil layer above the liquefiable stratum.

[0022] Furthermore, in Step 1, the calculation formula of the vertical normal stress σ0 is as follows:

[0023] σ0=γd

[0024] Where: d is the depth of the liquefiable stratum; γ is the effective weight of the soil layer above the depth d.

[0025] Furthermore, in Step 5, the additional vertical normal stress Δσ and the additional shear stress Δτ of the pile load at different positions of the liquefiable formation are calculated by numerical simulation or analytical method.

[0026] Compared with the existing technology, the liquefaction impedance correction method for liquefiable roadbed considering the influence of embankment loading can quantitatively correct the cyclic liquefaction impedance value by using the vertical normal stress coefficient and the shear stress coefficient by considering the embankment loading effect. It can provide a more accurate soil liquefaction assessment tool, which is helpful for the scientific selection of foundation treatment schemes in embankment projects, improves the safety and reliability of the project, and can provide a theoretical basis and data support for the roadbed treatment of liquefiable strata under embankment loading conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of the change of vertical normal stress and shear stress of the original stratum caused by the embankment loading in an embodiment of the present invention;

[0028] Figure 2 Schematic diagram of cyclic liquefaction impedance strength of liquefiable formation according to an embodiment of the present invention;

[0029] Figure 3 Schematic diagram of the effect of vertical normal stress on soil liquefaction impedance according to an embodiment of the present invention;

[0030] Figure 4 Schematic diagram of the effect of shear stress on soil liquefaction impedance according to an embodiment of the present invention;

[0031] Figure 5 It is a comparison diagram of the circulation liquefaction impedance before and after correction at three representative points A, B, and C of the embodiment of the present invention. DETAILED DESCRIPTION

[0032] This liquefaction impedance correction method for liquefiable roadbed considering the influence of embankment loading first surveys the liquefiable strata in the existing horizontal site, conducts tests on the liquefiable strata to obtain the liquefaction cycle impedance value under the original working conditions; then, according to the embankment loading design conditions, the additional vertical normal stress and shear stress of the loading at different positions of the liquefiable strata are calculated; finally, the liquefaction cycle impedance value is corrected by the correction formula considering the vertical normal stress and shear stress, so as to realize the correction of the liquefaction cycle impedance value of the liquefiable area of ​​the strata under different embankment working conditions.

[0033] The present invention will be further described below by taking a road including an embankment as an example and combining with the accompanying drawings.

[0034] The liquefaction impedance correction method for the liquefiable roadbed considering the influence of embankment loading specifically includes the following steps:

[0035] Step 1, investigate the liquefiable strata conditions of the existing horizontal site of the embankment loading liquefiable site, obtain the basic conditions of the site, including the site soil stratification, the depth of the liquefiable stratum, the weight of each layer of soil above the liquefiable stratum and other parameters, calculate the vertical normal stress σ0; and obtain in-situ soil samples through the low-disturbance method.

[0036] The calculation formula of vertical normal stress σ0 is as follows:

[0037] σ0=γd

[0038] In the formula: d is the depth of the liquefiable stratum; γ is the natural density of the soil layer above the depth d (i.e., effective density); the density below the groundwater level is the saturated density; and multi-layer soil should be calculated layer by layer.

[0039] Example A road section including an embankment Figure 1 As shown in the figure, the liquefiable strata conditions of the existing horizontal strata of the surveyed embankment loading site are easy to liquefy. The strata from the ground to the bottom include strata ①, strata ②, strata ③, ... strata i, among which: the liquefiable stratum is stratum ③, the depth center value of stratum ③ is 7.5m from the ground, and the effective gravity of stratum ③ is γ3=9kN / m 3 ; The groundwater level of the site is -2m; the thickness of layer ① is 2m, and the effective gravity of layer ① is γ1=16kN / m 3 ; The thickness of layer ② is 3m, and the effective gravity of layer ② is γ2 = 10kN / m 3 The initial vertical normal stress value of the liquefiable stratum ③ is calculated as follows:

[0040] σ0=16×2+10×3+2.5×9=84.5kPa

[0041] The initial shear stress value τ0 = 0 kPa. The in-situ soil sample was obtained by the low disturbance method.

[0042] Step 2: Conduct indoor dynamic single shear test on the undisturbed soil samples. During the test, the vertical load and density are kept consistent with the in-situ conditions of the site. A variety of shear stress amplitudes are used, and the relationship between the shear stress ratio and the number of liquefaction vibrations is obtained by experimental fitting to determine the liquefaction cycle impedance value DRR corresponding to different earthquake magnitudes under horizontal site conditions.

[0043] Embodiment Indoor dynamic single shear test was carried out on the undisturbed soil sample. The initial vertical normal stress value was calculated as 84.5 kPa by Step 1. Three shear stress amplitudes (0.25, 0.31, 0.43) were used to obtain the relationship between shear stress ratio and liquefaction vibration frequency, as shown in FIG. Figure 2 As shown, taking an earthquake of magnitude 8 as an example, the liquefaction cycle impedance value DRR corresponding to the magnitude (12) is determined to be 0.31.

[0044] Step 3, carry out indoor dynamic single shear test on the undisturbed soil samples, use a variety of vertical normal stresses and a variety of shear stress ratios, and obtain the relationship between vertical normal stress and liquefaction vibration times through test fitting. The influence of vertical normal stress on the cyclic liquefaction cycle impedance value is corrected by the following formula:

[0045] DRR1=DRR·(1+β) k

[0046] Where DRR1 is the cyclic liquefaction resistance considering the influence of vertical normal stress; β is the vertical normal stress coefficient; k is the normal stress correlation coefficient, which is obtained by fitting the test data.

[0047] Embodiment Indoor dynamic single shear test was carried out on the undisturbed soil samples, and three vertical normal stresses (50 kPa, 84.5 kPa, 120 kPa) and three shear stress ratios (0.25, 0.30, 0.35) were used to obtain the relationship between the shear stress ratio and the liquefaction vibration frequency, and the liquefaction cycle impedance values ​​corresponding to the three vertical normal stresses at an earthquake magnitude of 8 were determined respectively, so as to obtain the relationship between the vertical normal stress coefficient and the liquefaction cycle impedance value as shown in FIG. Figure 3 As shown, k = 0.31 is obtained by fitting the experimental data.

[0048] Step 4: Conduct indoor dynamic single shear tests on the undisturbed soil samples, using a variety of initial shear stresses and a variety of shear stress ratios. The relationship between the shear stress ratio and the number of liquefaction vibrations is obtained by experimental fitting. The influence of the initial shear stress on the cyclic liquefaction impedance value is corrected by the following formula:

[0049] DRR2=e m·α+ln(DDR)

[0050] Where DRR2 is the cyclic liquefaction impedance considering the influence of shear stress; α is the shear stress coefficient; m is the shear stress correlation coefficient, which is obtained by fitting the experimental data.

[0051] In the embodiment, an indoor dynamic single shear test was carried out on the undisturbed soil samples, and three shear stress coefficients (0.1, 0.2, 0.3), three shear stress ratios (0.2, 0.25, 0.30), and a constant vertical normal stress (84.5 kPa) were used to obtain the relationship between the shear stress ratio and the number of liquefaction vibrations, and the liquefaction cycle impedance values ​​corresponding to the three shear stress coefficients at an earthquake magnitude of 8 were determined respectively, so as to obtain the relationship between the shear stress coefficient and the liquefaction cycle impedance value as shown in FIG. Figure 4 As shown, m = -1.51 was obtained by fitting the experimental data.

[0052] Step 5, according to the embankment load design conditions, calculate the additional vertical normal stress Δσ and additional shear stress Δτ of the load at different positions of the liquefiable stratum through numerical simulation or analytical methods, and then calculate the vertical normal stress coefficient β and shear stress coefficient α according to the following formula:

[0053] β=Δσ / σ0

[0054] α=Δτ / σ0

[0055] Where: β is the vertical normal stress coefficient; α is the shear stress coefficient; Δσ is the additional vertical normal stress of the pile load; Δτ is the additional shear stress of the pile load.

[0056] Example: The designed embankment height is 10m, the slope is 1:2, and the weight of the piled material is 16kN / m 3 , the additional vertical stress Δσ and additional shear stress Δτ of the pile load at the typical position of the liquefiable stratum ③ are calculated by numerical simulation method; Figure 1 As shown in the figure, Δσ at point A below the center of the embankment A =160kPa, Δτ A = 0 kPa, Δσ at point B below the embankment slope B =80kPa, Δτ B =30kPa, Δσ at point C outside the slope foot C =0kPa, Δτ C =30kPa, then the vertical normal stress coefficient β is obtained respectively A =Δσ A / σ0=1.89、β B =Δσ B / σ0=0.95、β C =Δσ C / σ0=0, and the shear stress coefficient α is obtained respectively A =Δτ A / σ0=0、α B =Δτ B / σ0=0.36、α C =Δτ C / σ0=0.36.

[0057] Step 6, comprehensively considering the influence of embankment load on the stratum, the liquefaction cycle resistance value DRR* of the liquefiable stratum corrected by the vertical normal stress and shear stress is obtained by the following formula:

[0058] DRR * =DRR1+DRR2-DRR

[0059] Where: DRR1 is the cyclic liquefaction impedance considering the influence of vertical normal stress; DRR2 is the cyclic liquefaction impedance considering the influence of shear stress; DRR is the liquefaction cyclic impedance value corresponding to different earthquake magnitudes.

[0060] The corrected circulating liquefaction impedance values ​​of the three locations A, B, and C in the easily liquefied formation ③ are DRR and DRR, respectively. * (A) = 0.43, DRR * (B) = 0.25, DRR * (C) = 0.18.

[0061] The comparison diagram of the circulating liquefaction impedance before and after correction at three representative points A, B, and C of the easily liquefied formation ③ in the embodiment is as follows Figure 5 As shown. Figure 5 It can be seen that the increase in vertical normal stress caused by embankment loading increases the cyclic liquefaction impedance at point A by 38.71%, while the cyclic liquefaction impedance at points B and C decreases by 19.35% and 41.94% respectively due to the increase in shear stress.

[0062] This method for correcting the liquefaction impedance of liquefiable roadbed considering the influence of embankment loading can quantitatively correct the cyclic liquefaction impedance value by using the vertical normal stress coefficient and the shear stress coefficient by considering the embankment loading effect. It can provide a more accurate soil liquefaction assessment tool, which is helpful for the scientific selection of foundation treatment schemes in embankment projects, improves the safety and reliability of the project, and can provide a theoretical basis and data support for the roadbed treatment of liquefiable strata under embankment loading conditions.

Claims

1. A method for correcting liquefaction impedance of liquefiable roadbed considering the influence of embankment loading, characterized in that: The specific steps include: Step 1: Investigate the liquefiable strata conditions of the existing horizontal sites of the embankment loading liquefaction site, obtain the basic site conditions, calculate the vertical normal stress σ0, and obtain in-situ soil samples through the low-disturbance method; Step 2: Conduct indoor dynamic single shear test on the undisturbed soil samples. During the test, the vertical load and density are kept consistent with the in-situ conditions of the site. A variety of shear stress amplitudes are used to obtain the relationship between the shear stress ratio and the number of liquefaction vibrations through test fitting, and determine the liquefaction cycle impedance DRR corresponding to different earthquake magnitudes under horizontal site conditions. Step 3, carry out indoor dynamic single shear test on the undisturbed soil samples, use a variety of vertical normal stresses and a variety of shear stress ratios, and obtain the relationship between vertical normal stress and liquefaction vibration times through test fitting. The influence of vertical normal stress on the cyclic liquefaction cycle impedance value is corrected by the following formula: DRR1=DRR·(1+β) k Where: DRR1 is the cyclic liquefaction impedance considering the influence of vertical normal stress; β is the vertical normal stress coefficient; k is the normal stress correlation coefficient; Step 4: Conduct indoor dynamic single shear tests on the undisturbed soil samples, using a variety of initial shear stresses and a variety of shear stress ratios. The relationship between the shear stress ratio and the number of liquefaction vibrations is obtained by experimental fitting. The influence of the initial shear stress on the cyclic liquefaction impedance value is corrected by the following formula: DRR2=e m·α+ln(DDR) Where: DRR2 is the cyclic liquefaction impedance considering the influence of shear stress; α is the shear stress coefficient; m is the shear stress correlation coefficient; Step 5, according to the design conditions of the embankment load, calculate the additional vertical normal stress Δσ and additional shear stress Δτ of the load at different positions of the liquefiable stratum, and then calculate the vertical normal stress coefficient β and shear stress coefficient α according to the following formula: β=Δσ / σ0 α=Δτ / σ0 Where: β is the vertical normal stress coefficient; α is the shear stress coefficient; Δσ is the additional vertical normal stress of the pile load; Δτ is the additional shear stress of the pile load; Step 6, comprehensively considering the influence of embankment load on the stratum, the liquefaction cycle resistance value DRR* of the liquefiable stratum corrected by the vertical normal stress and shear stress is obtained by the following formula: DRR * =DRR1+DRR2-DRR Where: DRR1 is the cyclic liquefaction impedance considering the influence of vertical normal stress; DRR2 is the cyclic liquefaction impedance considering the influence of shear stress; DRR is the liquefaction cyclic impedance value corresponding to different earthquake magnitudes.

2. The method for correcting liquefaction impedance of liquefiable roadbed considering the influence of embankment loading according to claim 1 is characterized in that: In Step 1, the basic site conditions include the site soil stratification, the depth of the liquefiable stratum, and the weight of the soil layers above the liquefiable stratum.

3. The method for correcting liquefaction impedance of liquefiable roadbed considering the influence of embankment loading according to claim 2 is characterized in that: In Step 1, the calculation formula of vertical normal stress σ0 is as follows: σ0=γd Where: d is the depth of the liquefiable stratum; γ is the effective weight of the soil layer above the depth d.

4. The method for correcting liquefaction impedance of liquefiable roadbed considering the influence of embankment loading according to claim 1 is characterized in that: In Step 5, the additional vertical normal stress Δσ and the additional shear stress Δτ of the pile load at different positions in the liquefiable formation are calculated by numerical simulation or analytical methods.

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