Study On The Impact Of Water Level Rapid Drawdown To Inland River Framework Wharf Pile Foundation

With the need of the reservoir water level to normal scheduling,and the effect of drought,flood discharge,water level plummeting has become an inevitable working conditions of the port construction and operation stages after the impoundment of the Three Gorges Project.This paper relied on the Twelfth Five-Year National Science and Technology Support Program "Research on the key technology of mountain river channelized river ports construction",and on the base of Chongqing Port Orchard Port Phase ? project examples,the practical hydrogeological conditions in the Three Gorges reservoir area,the existing basic theory and previous research results,to study the effects of Water level drop on the bearing behavior of inland river framework wharf by the way of model experiment combined with numerical simulation.The specific contents and results include:(1)To plan and design the model test according to the similarity theory,and then determine the model ratio scale and the model layout,the water level deceleration and loading schemes.To identify the mechanical parameters of the pile,the foundation of rock and soil particle size distribution,compaction index and shear strength parameters through a series of soil test such as uniaxial compression test,mechanical crushing and screening tests,compaction test,direct shear test,and triaxial test.(2)With the study of model pile foundation static load test before and after precipitation in sand or sand-shale mixture foundation,this paper analyzed the bearing behavior of pile foundation in the different foundation soil.Meanwhile,with the comparison of subgrade bearing capacity for the two foundation-above,the distribution rules before and after precipitation of pile axial force,bending moments and lateral friction,the pile-soil load transfer mechanism and the load sharing ratio on pile side and pile tip were studied.(3)In the process of water level plummeting,through the observation of model pile foundation in sand or sand-shale mixture foundation under the conditions of permanent load,this paper analyzed the force characteristics of pile foundation and the differential settlement of pile-soil.In addition,foundation-internal saturation line and the settlement variation law of pile soil and pile were specifically studied.The pile mechanical characteristic of different sections and lateral friction play mechanism in the process of water level plummeting were explored as well.And then,load sharing ratio,the position and quantity trends of neutral point are obtained eventually.(4)Based on PLAXIS 3D Foundation numerical simulation of model tests,by the finite element analysis of the second phase of the orchard Wharf Bank,this paper studied the pier slope safety factor,slope trend potential slide area,the vertical and lateral maximum displacement of the pile foundation,the variation law of transverse and vertical maximum displacement and their position under the condition of different water level and the water level drop speed.(5)Through the analysis of the model test and numerical simulation results,in result:When the wharf slope is gentler,the bank slope is unstably or the destruction is unconsidered,in some ways,the bearing capacity of pile foundation would have enhanced after the precipitation;the most dangerous stage of wharf pile foundation appeared in the process of water level plummeting,and at this moment,the adverse factors that pile suffered mainly were the additional load caused by negative skin friction and the pile-soil system failure collapse caused by the instability and destruction of the slope.