| Due to high construction efficiency and simple technology,steel sheet pile is widely used in foundation pit support.Aiming at the key technical problems encountered in the study of mechanical characteristics of steel sheet pile supporting system for small deep foundation pit,based on a practical project,the method of field monitoring,numerical simulation and theoretical derivation were used to carry out the research.Combined with the characteristics of engineering cases,the field monitoring work was carried out,and the time history curves of horizontal deformation and earth pressure were obtained.The horizontal displacement of steel sheet pile presents a nonlinear distribution law with time,which is large in the middle and small at both ends.The measured earth pressure of each soil layer shows the phenomenon of stress relaxation,and the rate of numerical reduction is first fast and then slow.PLAXIS was used to establish the three-dimensional calculation model of deep foundation pit engineering,and the numerical simulation of the construction process was carried out.The overall deformation characteristics of the steel sheet pile structure system and the internal force distribution law of the supporting structure were calculated.The spatial effect of stress and deformation of deep foundation pit supported by steel sheet pile is significant.The horizontal displacement of soil on the long side of foundation pit is larger than that on the short side.The surface of the long side of the foundation pit is subsidence,and the surface of the short side is uplift.The maximum horizontal displacement in the middle of the steel sheet pile on the long side of the foundation pit is much larger than that on the short side.Based on the mathematical idea of weighted combination,the calculation model of earth pressure in non-limit state was constructed,and a weighted combination calculation model of active and passive earth pressure was derived.With the help of the relationship between the coefficient of lateral earth pressure in non-limit state and the internal friction angle of fill and the wall-soil friction angle,the calculation method of weighted combination calculation model was obtained.Based on the reciprocal theorem of work,the calculation formula of relaxation stress exertion coefficient was deduced,and the calculation method of relaxation stress exertion coefficient of each soil layer was given.Based on the judgment coefficient of non-limit state of earth pressure and its judgment standard,a safety interval evaluation method of deep foundation pit composed of upper and lower limits of judgment coefficient was proposed,and the effective evaluation of the engineering case was carried out.The steel sheet pile in the elastic category was considered as a deflection thin plate,and the method of minimum complementary energy principle with mixed variables was used to solve the bending thin plate problem.This method is much better than Winkler thin plate theory method.Matlab was used to compile the calculation program to solve the deflection surface equation and draw the influence curve of the length width ratio of the steel sheet pile calculation model on the deformation characteristics of the steel sheet pile.It is found that the plate effect of steel sheet pile is significant.With the increase of the length-width ratio of the calculation model(the ratio of the side length of the foundation pit to the length of the steel sheet pile),the deflection value of the steel sheet pile increases.However,the increasing trend begins to weaken after the aspect ratio reaches a certain critical value,that is,the plate effect of steel sheet pile support is gradually disappearing. |
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