Study On Analysis Method Of Stabilizing Piles Used To Reinforce Expansive Soil Slope In Chengdu Area

Expansive soil slope is a kind of problematic soil slopes in engineering practice,especially in the southwest area in China.The problem of stability of expansive soil slope has always been a focus in practice.The dissertation focuses on the expansive soil slope strengthened by single row stabilizing piles in Chengdu and other related areas.Based on the previous experimental results,stability analysis method and of expansive soil slopes and the corresponding calculation method of the piled slopes with considering expansive pressure is further studied via limit equilibrium theory and three-dimensional numerical simulation method.The main results are as follows:(1)For expansive soil in Chengdu,according to the polyline distribution model of expansive pressure varied with depth,the expansive pressure is introduced into four classical limit equilibrium methods for slope stability analysis.The related formulas of the factor of safety for the expansive soil slope are derived.The search method for the most dangerous circular slip surface is also given.Analysis results of practical examples show that the factors of safety decrease with the increase of expansive pressure,and the expansive slopes are liable to slide in their shallow zones as the expansive pressure increases.The factors of safety obtained using the simplified Bishop method,Morgenstern-Price method,and Spencer method are fairly close,but they are higher than those computed by the Fellenius method.(2)Based on the four limit equilibrium methods of slope stability,a calculation method for single row of stabilizing piles used to reinforce expansive soil slopes is proposed with fully considering expansive pressure on potential slide mass and the piles,as well as the friction of local soil between adjacent piles on them.The formulas for calculating internal forces of the stabilizing piles at the slip surface of the expansive soil slope under a design factor of safety is derived.Additionally,the upper and lower solutions to the shear force considering the frictional effect are given.Analysis results of practical examples show that the shear force increases linearly with the expansive pressure.Compared with the results obtained using simplified Bishop method,Morgenstern-Price method and Spencer method,the shear force by Fellenius method is about 20% higher.According to comprehensive comparison and analysis,Morgenstern-Price method and Spencer method are recommended as preferentially applicable approaches in engineering design.(3)By using numerical simulation method of the FLAC3 D,characteristics of expansive pressure varying with depth are reproduced,which is basically consistent with the distribution model assumed in the theoretical analysis.On this basis,the factor of safety of the slope and design internal forces of stabilizing pile can be reasonably computed via the numerical simulation method.The results are in good agreement with those obtained by the limit equilibrium method.Particularly,the shear force of the pile by the FLAC3 D is closer to those obtained using Morgenstern-Price method and Spencer method.So,the rationality of the proposed analysis method for stabilizing piles used to reinforce expansive soil slopes is further demonstrated.The analysis method of single row stabilizing piles for reinforcing expansive soil slopes presented in this dissertation can provide theoretical guidance and reference for the practical engineering design.