Experimental Study On Vertical Bearing Characteristics Of Screw Cast-in-place Pile

Screw cast-in-place pile is a new type of variable section pile whose body part is straight pole pile and bottom is screw pile.Screw cast-in-place pile has the characteristics of small construction pollution,good pile quality,fast construction speed,strong construction penetration and so on.It has been widely used in engineering and has higher bearing capacity and smaller settlement compared with ordinary straight pile.Based on the research status of screw pile,this paper summarizes and analyzes the calculation method of vertical ultimate bearing capacity of screw pile.Through model test and finite element simulation method,and explores the screw pile rods of pile soil failure pattern and the vertical bearing mechanism,and combined with the static load test of single pile and pile axial force test,further verify the vertical bearing mechanism of screw pile,and presents a suitable for the engineering application of screw pile bearing capacity calculation formula.The main research contents and results of this paper are as follows:(1)Through the laboratory model test,the q-s curve of screw pile and straight pile,the displacement cloud diagram of pile circumference,the axial force curve of pile body and the sharing rule of pile lateral resistance and end resistance were analyzed with the help of self-made test device and Photoinfor image processing software.The test results show that the failure surface of the screw pile is continuous arch in the limit state,while the failure surface of the straight pile can be regarded as plane approximately.The lateral resistance of the screw pile is mainly the shear force between the soil and the lateral soil,while the lateral resistance of the straight pile is mainly the friction force between the pile and the soil.Under the same conditions,the ultimate bearing capacity and lateral resistance of screw pile are improved greatly compared with that of straight pile.(2)Through two groups of 6 field engineering tests,prefabricated strain gauge was used in pile body to obtain the strain of pile section at different depths,and the sharing rules of q-s curve,axial force curve of pile body,lateral resistance curve of pile and lateral resistance and end resistance of pile were analyzed.The test results show that under the same conditions,the ultimate bearing capacity of screw pile is higher than that of normal straight pile,and the increase range is 15%?30%.The limit lateral resistance of screw pile is 1.2?1.5 times of that of straight rod under the same condition.(3)Combining with practical engineering tests,the interaction between pile and soil was analyzed by Abaqus finite element software,and the q-s curves of screw pile and straight pile and the displacement fields of two pile types under different loading conditions were obtained.The test results verified the continuous arch failure surface theory of soil around screw pile in the model test.The influences of pitch and soil shear strength on the ultimate bearing capacity of screw pile are studied by finite element simulation.