Study On Active Earth Pressure Of Finite Width Soil Based On Unified Strength Theory

As a classic research project in geotechnical engineering,earth pressure is widely involved in underground engineering,municipal,road,water conservancy.Especially for the retaining structure that resists the deformation of the rock and soil,the accuracy of the earth pressure calculation is one of the main factors for the rationality and safety of its design.At present,the process of urban construction and urbanization is accelerating.Excavation of foundation pits near adjacent buildings and construction of embankments near rock faces are common.When supporting the foundation pit or embankment in this type of project,the backfill is in a finite width state.It is not appropriate to use classical earth pressure theory based on semi-finite space.In addition,the backfill is actually in a three-dimensional stress state and is affected by many factors.However,the intermediate principal stress is not considered by classic MohrCoulomb theory.Therefore,this paper is based on the characteristics of finite soil in practical engineering.Through theoretical derivation and numerical simulation,the distribution form and action mechanism of earth pressure with finite width under complex conditions are systematically analyzed.Based on the unified strength theory,the active earth pressure using the planar and curved slip surface assumption,and non-limit state were discussed deeply.The main research contents and conclusions are as follows:(1)For the earth pressure of the classic trapezoidal soil wedge,that is,the assumption of the planar slip surface.The effects of intermediate principal stress,wall-soil adhesion,lateral pressure of adjacent buildings,height of tension cracks,and uniform surcharge were comprehensively considered.Firstly,the formula of finite soil earth pressure was derived based on the sliding wedge theory.Considering the process of soil changing from semi-infinite to finite state,the change of inclination angle of slip surface was discussed.Secondly,considering the soil arching effects,the calculation formulas of active earth pressure,resultant force and its action point were deduced based on the thin-layer element method.The earth pressure distribution form was discussed,and it was verified by numerical simulation and previous results.The results show that compared with the previous test,the two methods in this paper are reasonable,and the active earth pressure decreases with the intermediate principal stress increases.When the depth is shallow and the soil width is small,the sliding wedge method should be used,while when the depth and soil width are large,the thin-layer element method is more consistent.(2)For the earth pressure problem of finite cohesive soil under earthquake.This paper adopted the assumption of curved slip surface,and considered the influence of soil arching effects.The pseudostatic method and the thin-layer element method were combined,the seismic active lateral pressure coefficient and the analytical solution of active earth pressure were deduced.At the same time,the numerical simulation was also carried out and compared with the previous theoretical results.The sensitivity of the main parameters was also discussed through numerical examples.The results showed that the assumed slip surface is similar to the numerical solution.The earth pressure distribution form is in good agreement with the previous theoretical results,and the theoretical results are close to the numerical solutions.The method in this paper is feasible,but the classical M-O theory is linear and its calculation result is too large.(3)Considering that for some projects with strict control for displacement of retaining structure.The soil behind the retaining structure under small displacement often does not reach the active limit state.According to the displacement characteristics of translation movement mode,considering the influence of intermediate principal stress and soil arching effects,a calculation method of non-limit earth pressure of semi-infinite and finite soil was proposed.The influence of displacement of retaining structure on lateral earth pressure coefficient,earth pressure distribution and resultant force were discussed.The results showed that the shear strength parameters of non-limit soil considering intermediate principal stress accord with the test law.The earth pressure coefficient decreases with the increase of displacement.For the special working condition that the displacement of the retaining structure is far less than its limit displacement,the solution in this paper is much smaller than the static earth pressure in the static state.But it is larger than Rankine’s solution in the initial displacement stage.When reaching the active limit state,it is smaller than Rankine’s solution.It should be paid attention to the internal force calculation of retaining structure.