Strength Deterioration Law Of Loess Under Dry-wet Cycle And The Effect On The Safety Of Filling Slope

With the development of national economy and the gradual implementation of the western development strategy,the large-scale construction investment projects carried out in Western China have increased unprecedentedly in recent years.Loess is widely used as filling material in hill-cutting and ditch-filling projects in Western China,resulting in many compacted loess fill slopes.Natural factors such as rainfall,evaporation and groundwater level change will lead to strength deterioration of slope soil due to wetting-drying cycling effect,which will affect the safety of slope.Compared with undisturbed loess which has experienced enough wetting-drying cycles in sedimentary history,the effect of wetting-drying cycles on the strength degradation of compacted loess is much more significant.Previous studies mostly take the number of wetting-drying cycles as the only variable,and few studies take the path of wetting-drying cycles into account.However,no comprehensive model of wetting-drying cycles was established.Furthermore,there are no research that combine the macro-performance,micro-mechanism of strength deterioration of compacted loess under the influence of wetting-drying cycles and the safety reduction of filling slope caused by strength deterioration.Based on triaxial shear test,scanning electron microscopy（SEM）imaging test,theoretical deduction and geotechnical numerical method,the macro-strength deterioration,micro-structure change and subsequent macro-engineering problems of compacted loess before and after wetting-drying cycling are studied in this paper.（1）Through a large number of wetting-drying cyclic triaxial compression tests,the effects of dry density and wetting-drying cyclic path on the strength deterioration of compacted loess are comprehensively considered.Through fitting analysis,a compacted loess strength deterioration model（CLDM）considering the influence of dry density,wetting-drying cycle amplitude and lower bounds of drying–wetting cycles is proposed.Finally,the CLDM model is applied to the finite element method through the secondary development of ABAQUS finite element software based on Python,and the stability analysis of the wetting-drying cyclic compacted loess slope is carried out,which verifies the practicability and accuracy of the deteriorated model.（2）The pore morphology and arrangement characteristics of compacted loess with different wetting-drying cycles were extracted by image processing technology and the evolution law of pore structure of compacted loess with different dry-wet cycles was analyzed by means of electron microscopy imaging test.（3）With the help of Particle Flow Code 2D(PFC^2D)software and the introduction of bond rate parameter,the biaxial numerical samples with different dry densities are established.The contact model parameters of compacted loess under wetting-drying cyclic triaxial test were calibrated.Based on the analysis of the calibration results,the influence of wetting-drying cycle on the Meso-Structural parameters of compacted loess under different dry densities and different wetting-drying cyclic paths was obtained.Also,slope stability under the influence of dry-wet cycle was carried out with the help of DEM.（4）Based on the theory of random field,the 1-D local averaging of two-dimensional random field on curve is obtained,and the formula of local averaging standard deviation is obtained.On this basis,a simple and reliable reliability analysis method for homogeneous natural slope and fill slope is proposed.Through the statistical analysis of the shear strength parameters of the original slope or the index of the compaction degree of the fill slope,the standard deviation of the spatial characteristics of the index is obtained by the calculation formula of local averaging standard deviation,the limit state index is obtained by a small amount of deterministic finite element,and the reliability index is finally calculated by integral calculation.Comparative analysis shows that the result of the slope reliability analysis method based on 1-D local averaging of two-dimensional random field is reliable,and can greatly improve the efficiency of slope reliability analysis.Finally,combining with CLDM,the proposed method was applied in the reliability of a slope.