Upper-Bound Limit Analysis Of Active Earth Pressure For Retaining Walls Considering Crack And Seepage Effect

Retaining wall plays a significant role in supporting embankment fills and resisting soil deformation.Considering the complexity of natural geological conditions,such as earthquake,rainfall,seepage,etc,it is a classic topic to establish earth pressure calculation model and effective failure mechanism.Although commonly neglected in the evaluation of active earth pressure,cracks exert a significant influence on integrity and strength of earthen structures.In this thesis,the modified pseudo-dynamic method is utilized to describe wave characteristics of earthquakes based on the constitutive model of viscoelastic soils,which are combined with the crack effect to calculate the synthetic earth pressure.Furthermore,within the framework of plasticity theory,the influence of steady seepage and pore pressure on the stability of unsaturated soils is explored by means of upper bound method.The main contents are as follows:(1)To overcome traditional pseudo-dynamic method,the modified pseudo-dynamic method is employed to describe the space-time characteristics of seismic wave propagation.Meanwhile,a vertical crack is introduced into the rotational failure mechanism,where two crack forms are included.One is pre-existing crack,the other is developing crack.Considering varying characteristics of seismic acceleration,a layer-wise summation method is used herein to calculate the work rate induced by seismic forces.Later,the explicit equation of active thrust can be derived,and the sensitivity analysis of seismic dynamic parameters,such as wave velocity,period and damping on the soil stability is investigated.(2)On this basis,the fracture form is extended to three-dimensional space,which modifies the cone curve mechanism to characterize soil failure.Since soil is frequently unsaturated in nature,a suction stress-based effective stress principle is introduced.Therefore,the most unfavorable crack depth and earth pressure expression under one-dimensional steady seepage condition can be derived.Comparison results with the extant literature show good agreements,which verifies the accuracy of the proposed arithmetic,and the response of hypothetic soil types on particular geotechnical and hydraulic parameters is also investigated.(3)Rainfall leads to the rise of groundwater,and as a result,the backfill is usually in a partially saturated situation,where matric suction exists above the groundwater level and accordingly,the influence of pore-water pressure below the groundwater should be considered.Several empirical formulas are adopted to fit the shear strength of unsaturated soils.Moreover,previous studies purely concentrated on pore-water pressure for simplification.Therefore,this thesis discusses the influence of varying groundwater on synthetic earth pressure and critical failure surface under partially saturated condition,and explores their respective applicability of shear strength formulas in cooperation with soilwater characteristic curves.(4)The numerical model can be achieved to simulate the appropriate soilwall system based on the accurate geological and hydrological parameters,which Luohu shanty reconstruction project in Shenzhen provides.Comparing the critical earth pressure from the theoretical calculation and those from FLAC3 D software,the accuracy of the proposed method can be verified.