Centrifuge Shaking Table Test Study On Seismic Performance Of Helical Piles

Seismic loading is one of the major causes of foundation damage,and during earthquakes,pile foundations may be subjected to higher vertical compression loads,which may lead to excessive settlement of pile foundations.Helical pile foundations demonstrated good seismic performance during the Christchurch,New Zealand earthquake and the Alaska,USA earthquake,proving that it can be a suitable foundation option for seismic zones.Therefore,it is important to study the seismic performance of helical piles and explore their feasibility as a form of structural foundation in earthquake-prone areas to ensure the seismic safety of cities and infrastructure in China.However,the research on the dynamic response regular and seismic performance of helical piles under seismic loading is in its initial stage,and most of the related studies are based on the experimental means of pile top loading,and the basic test data such as large shaking table and geotechnical centrifuge shaking table are very limited.This paper focuses on the seismic performance of helical pile foundations in dry sand sites as the research object,using centrifuge shaking table model tests to study the axial and lateral dynamic response of the helical pile-soil-structure system,the main work is as follows:(1)Centrifuge shaking table model test of helical pile-soil-structure system at dry sand site.The spacing of the helical blades,the mass of the superstructure,and the location of the sensor arrangement were designed by combining existing codes and available results,and the required parameters for the test were obtained through a series of tests,and then the centrifuge shaking table model test was conducted.Bending damage of the pile and significant soil settlement occurred at the end of the test.(2)Axial dynamic response of helical pile-soil-structure system at dry sand site.Based on the centrifuge shaking table test data,the pile axial force redistribution,pile settlement and soil settlement before and after the earthquake were studied,and the pile-soil axial dynamic response,inter-pile and free-field soil dynamic response of the helical pile foundation at the dry sand site under the earthquake load were analyzed in detail.The results showed that the increase in the number of helical blades did not improve the settlement resistance of helical pile foundation.The helical pile foundation reached the maximum static axial force at the intersection of soil layers,while the non-helical pile foundation reached the maximum static axial force at the loose sand layer.The fluctuation amplitude of dynamic axial force of doublespiral foundation under the same peak seismic wave was about twice the fluctuation amplitude of single-spiral pile foundation.(3)Lateral dynamic response of helical pile-soil-structure system at dry sand site.Based on the centrifuge shaking table test data,the dynamic bending moment variation,pile head acceleration,displacement time course and pile deflection along the depth variation of pile foundations under the action of El-Centro waves with different peak strengths were analyzed in detail.The results showed that the maximum bending moment of helical pile foundation appears near the top of the pile,and the maximum bending moment of helical pile foundation without helical pile appeared in the top soil.Under the same peak intensity seismic wave,the pile head displacement and pile deflection of helical pile foundation were smaller than that of helical pile foundation.