Research On The Bearing Mechanism Of Expended Anchor Cable And Its Simulation Method In Numerical Analysis Of Deep Foundation Pit

In the foundation pit engineering with weak stratum and without other supporting means,due to the poor physical and mechanical properties of the strata,the traditional anchor cable cannot often provide sufficient uplift bearing capacity.To ensure the safety of construction and structure,the application of extended anchor cable will be an excellent and optional construction scheme.However,the research and application of the expanded anchor cable started relatively late,and its bearing mechanism is complex.At present,the understanding of its bearing mechanism and ultimate bearing capacity is not deep enough.Most engineering design still relies on existing engineering experience,and often there is a huge difference between the expected ultimate bearing capacity and the measured value,which brings uncertain factors to engineering safety and even induces related safety accidents.At the same time,the current simulation method for foundation pit engineering cannot easily consider the end resistance of the extended anchor cable,which also brings great adverse effects on the deformation and stability evaluation of the foundation pit.In this context,this paper adopts the method of combining numerical simulation,theoretical analysis,and field monitoring data analysis to systematically study the bearing mechanism of extended anchor cable and its simulation method in a deep foundation pit.The main work and research results of this paper are as follows:(1)Application of numerical simulation method,the bearing capacity and the response law of surrounding strata of the expanded anchor cable with an inclined arrangement under different drawing forces are studied,and then the relationship between the side resistance,earth pressure before the expanded end and bearing ratio of the expanded anchor cable and the drawing force is proved.(2)Based on the upper bound theorem of limit analysis,two failure modes of the mechanism of the extended anchor cable in the free plastic flow stage generated by the ultimate drawing are constructed.The external force power and internal energy dissipation rate of the damaged soil area under the corresponding failure mode are analyzed.Based on the virtual power principle,the upper bound solution of the ultimate uplift bearing capacity of the extended anchor cable under the corresponding failure mode is derived.On this basis,the correctness of the upper bound solution is verified and the better failure mode is determined by comparing the theoretical solutions of side resistance,earth pressure before the expanded end,and ultimate uplift force with the corresponding numerical solutions.(3)Based on the upper bound solution of the ultimate uplift force of the expanded anchor cable,the effects of the diameter of the hole,the length of the anchorage section,the length of the free section,the inclination angle of the rod and the buried depth on the end resistance,lateral resistance and ultimate uplift bearing capacity of the expanded anchor cable are studied.It is found that the diameter of the hole,the length of the anchorage section,the length of the free section,and the buried depth have important effects on the ultimate uplift bearing capacity of the expanded anchor cable.(4)In view of the defect that the cable element in FLAC3 D finite difference software cannot consider the end resistance of the extended anchor cable,a numerical iteration method that can consider both the side resistance and the earth pressure of the expanded cable is proposed.Then,the correctness of the proposed method is verified by comparing the numerical simulation results of this method with the numerical simulation results without considering the earth pressure before the expanded end and the field measured data.