Active Earth Pressure Calculation Under Non-limit State And Alarm Value Setting Of Deep Foundation Pit

The classical earth pressure theories has been widely used in engineering practice because of its clear mechanics concept and simple calculation process.However,in engineering practice,the soil often fails to reach the limit state,the classical Rankine theory and Coulomb theory can not meet the needs of practical engineering.Therefore,it is of great significance to study the earth pressure under non-limit state.Firstly,the finite element software ABAQUS was used to simulate the foundation pit excavation process.The displacement variation law and the earth pressure variation law on the supporting structure under different working conditions were obtained.It was confirmed that there was a non-limit state between the static state and the active state.The non-limit state change with the change of the displacement.The simulation results also show that the displacement of the supporting structure shows a form with small on both sides,big in the middle,and a maximum displacement appearing in the middle and lower part of the foundation pit.Then,the two kinds of theoretical calculation methods for earth pressure under non-limit state are improved respectively,by analyzing the earth pressure-displacement experience curve,a combined calculation model of active earth pressure under non-limit state was proposed and by verified reciprocal theorem of work.On the basis of the grey prediction model and the improved method of the pile lateral displacement,non-limit displacement in time dimension and space dimension were obtained and the time-space coupling calculation equation of non-limit displacement was offered.On the basis of some assumptions,the model of retaining wall in the non-limit state of cohesive soil was constructed,and the thin layer was taken for force analysis,and the relationship between active earth pressure and soil parameters under non-limit state was established.Combined the relationship between the soil parameters under non-limit state and the displacement ratio,the equation between non-limit state active earth pressure and the displacement ratio was constructed,and the angle between the imaginary failure surface and the horizontal plane under non-limit state was offered,at the same time,the theoretical calculation formula of crack depth under non-limit state was deduced,and the cracks law of cohesive soil under non-limit state at different factors was analyzed.Finally,in view of the shortcomings of the traditional alarm value setting mode,a new alarm value setting mode is proposed,which strengthens the monitoring during the foundation pit construction and is beneficial to guide the foundation pit construction.