Study On Deformation Law Of Deep Loess

In the development and construction of the loess region in the central and western regions,the loess subsidence deformation has always been one of the concerned problems of the rock and soil boundary.The building foundation will inevitably encounter the deep loess subsidence deformation subsidence,which seriously threatens the safety and stability of the superstructure of the building.Therefore,it is particularly important to accurately evaluate the type of loess site subsidence and to study the foundation subsidence deformation law of deep loess under the action of additional stress.In the current study,the subsidence deformation of loess piles is studied,and the soil around the pile foundation is subject by the changing negative friction resistance.The load change of pile foundation and the subsidence deformation of pile foundation are studied.However,the negative friction resistance is constantly changing in the process of water immersion change,so it is difficult to accurately describe the deformation law of pile foundation under the static load.In view of this problem,the immersion test of the deformation rule of the foundation under external static stress is simulated by FLAC3D.The following results have been obtained.(1)Through the field soil subsidence test,measured the subsidence coefficient with the pressure curve:in the test pressure range,ancient soil subsidence coefficient is less than 0.015,shows that the ancient soil does not have the subsidence characteristics,and the second layer Q3 loess,Q2 loess and the eighth ancient soil subsidence coefficient deformation curve,indicating the corresponding formation subsidence is poor.Calculating the subsidence amount and self-weight subsidence,it is known that the site belongs to the self-weight subsidence site,and the subsidence grade is grade(medium).(2)Under the condition of day and night,the loess flooding range of sand well bottom about 10m,under the action of the additional stress sand well bottom subsidence loess subsidence deformation only a peak deposition deformation,then smaller,the greater the pressure of the well bottom,the greater the maximum subsidence of the proportion of the total subsidence.Loess collapsible deformation under dead weight stress appeared three peaks,and the peak continuously decreases with the immersion time.Under the action of additional external force,the subsidence deformation of loess is faster than that under self-gravity,the time needed to complete the subsidence deformation is short,and the subsidence deformation is released centrally.(3)The maximum settlement value of the shallow punctuation point is 6.11mm,and the subsidence value of 5m and 15m shows the subsidence value of 5 m 5 m sand well is 5.08mm,7.88mm,and the site is determined to belong to a non-dead weight collapsible site.This is inconsistent with the judgment results of indoor test.When the calculation of indoor test is large,because the influence of "ancient soil layer structure" on subsidence deformation is not considered.It is embodied in the indoor compression test on the samples of different depths according to the saturation weight stress of the upper soil,and due to the structure of the ancient soil layer,the actual stress of the lower soil is less than the saturation weight stress of the upper soil.The action of ancient soil stratum structure makes the continuous distribution of collapsible loess layer in space,which suppresses the development of subsidence deformation,and thus leads to the large indoor test value.(4)Through numerical modeling,the relationship between the subsidence deformation under the dead weight and additional stress,the soil capacity weight and modulus is analyzed.The smaller the value of the reduction coefficient,the greater the subsidence deformation.When the reduction coefficient ξ3=0.1,the numerical simulation result is closer to the field measured value.Because the ancient soil strata are not reduced by modulus,the subsidence deformation is discontinuous in the longitudinal range.It is concluded that the deformation of ancient soil is obviously constrained.