Experimental Study On Vertical Compressive Bearing Capacity And Seismic Performance Of Drilling With Large Diameter PHC Pipe Cased Pile

Pile foundation is the most common basic form of high-rise buildings in China.There are various types of piles in China,such as drilling(punting)bored piles,artificial excavated piles and prestressed concrete piles,but they all have their own advantages and disadvantages.The Drilling Followed Pipe Pile Construction Method developed by Guang Zhou Institute of Building Science has realized simultaneous drilling,pile-dumping and dumping,while avoiding the pollution caused by the mud wall and the difficulty in ensuring the quality of drilled piles And other issues.In order to further verify the reliability of the engineering method used in practical projects,this paper tests and numerically analyzes the vertical compressive bearing capacity of the test pile,and in accordance with the corresponding scaling,launched a follow-up drill pipe pile model shaking table test study,the specific research content and the main conclusions are as follows:1?This article describes in detail the process of construction while drilling and pipe piles,and according to "Technical code for testing of building foundation piles" JGJ106-2014,carries out a vertical compressive static load test on two test piles while drilling and follow-up tests.The ultimate bearing capacity of the 1# and 2# test piles reached 20571 kN and 15100 kN,respectively,and the ultimate bearing capacity of the bored cast-in-place piles or driven piles(hammered piles or static pressure piles)with the same diameter and the same geological conditions(Experience value about 12000kN)1.25~1.7 times.2?Based on the theory of cohesion force model,the cohesive element is used to simulate the contact surface of the pile-grouting soil,and an ABAQUS numerical model of the two-dimensional pile-grouting body-soil is established to reflect the large-diameter follow-up drill pipe.The pile's vertical compressive bearing capacity and its potential failure mechanism summarizes three common failure modes when the pile-grouting system-soil system is subjected to vertical load,and the grouting quality of the process drilling hole is obtained.The trade-off relationship between the stiffness and stability of the borehole wall(deterioration of soil modulus at the pile side)is very important.Combining with numerical analysis,several suggestions are made for the construction process of the following drilling and pipe pile.3?Based on the predecessor's development soil box,the research group developed a circular stacking shear box and designed and implemented a shaking table test for the model while drilling and pipe piles.In the empty-box state,the natural vibration frequency is measured as 4.25 Hz.Using the free vibration attenuation method,the damping ratio in the empty state of the model earth box is measured as 4.32%.The result shows the natural vibration frequency of the circular laminated shear box.The damping ratio is far away from the natural frequency and damping ratio of the model soil in the box.The results of the later boundary effect test also show that the boundary effect of the circular stacked shear box developed by the research group is small and may be to a certain extent.The reflection effect or scattering effect of seismic waves on the boundary of the model box side wall is reduced or even eliminated,thereby realizing a more realistic simulation of the free shearing motion of the soil in the soil box under the action of the earthquake.4?The shaking table test considers the comparison between the squeezing model pile and the grouting model pile,the different constraint forms of the pile top,the different top load(25kg,50 kg,100kg)at the top of pile,the seismic wave excitation of different magnitudes,and other forms of input.Three types of typical seismic waves: El-Centro wave,Tianjin wave and Kobe wave.Acceleration response of the pile-side soil,pile strain amplitude response,and pile body under different working conditions were obtained for the compaction and grouting piles.The response law of the amplitude of the bending moments is compared with the law of the pile foundations formed by the two simulations of different construction methods.The experimental results show that,under the same working conditions,the accelerating magnification factor of the soil around the excavating pile is always greater than the accelerating magnification factor of the soil around the grouting pile;regardless of the constraint type(articulated or fixed)adopted at the top of pile,The acceleration coefficient of the soil on the pile side decreases first and then increases from bottom to top,similar to the distribution law of “k”;the maximum bending moment of the soil pile in the same working condition is always greater than the maximum value of the pile.The ratios of the maximum bending moment amplitudes of the squeezing piles of the El-Centro wave,Tianjin wave,and Kobe wave along with 0.2g,0.4g and 0.6g peak acceleration strengths are respectively 1.3~2.52 times,1.1~1.63 times,1.53~2.63 times,it is clear that the grouting pile is beneficial in the seismic design of the pile foundation.