Model Test Of Zhanjiang Group Structural Clay Pile Foundation Based On Thixotropic Effect

In recent years,the amount of infrastructure in the Beibu Gulf coastal areas has been increasing,and the scale will be larger.Pile foundation engineering,as one of the commonly used foundation forms of infrastructure in the coastal areas of beibu gulf,has been developed rapidly.The Zhanjiang Group Structural Clay is widely distributed in the area along the Beibu Gulf.Due to its special mechanical and engineering characteristics,the bearing behavior of pile foundation in the Zhanjiang Group Structural Clay is extremely complicated.Therefore,higher requirements are put forward for the design and construction of pile foundation in the structural clay layer of Zhanjiang Group in the coastal areas of Beibu Gulf.Due to the strong thixotropy of the Zhanjiang Group Structural Clay,the pile-soil interaction mechanism in the structural clay stratum of zhanjiang Group is complex and the pile foundation is evidently time effect.Therefore,it is of great significance to study the time effect of pile foundation in the structural clay layer of Zhanjiang group for further understanding the mechanical and engineering characteristics of the Zhanjiang Group Structural Clay,which for reasonably guiding the design and construction of pile foundation engineering.This paper is based on the practice of a pile foundation project in zhanjiang.The self-made transparent model box device is used to studied the bearing behavior of model pile foundation in Zhanjiang Group Structural Clay at different resting ages.The static load model tests of 9 groups of model piles with different pile length and different pile diameter are carried out in different rest ages,the pile body strain and settlement are measured,and the cross-plate shear test is performed on the soil around the model pile.Based on the above results,the quantitative relationship between the thixotropy of Zhanjiang group structural clay and the time effect of pile foundation is explored.The conclusion is as follows:(1)The Zhanjiang group structural clay has strong thixotropy,which the ratios of shear strength and thixotropy strength of the soil around model piles with different pile lengths and diameters showed an increasing trend with increasing dwell time.In the case of the same pile length,the smaller the pile diameter,the greater the increase of thixotropy strength ratio of the soil around the model pile.In the case of the same pile diameter,with the increase of pile length,there is no significant rule for the growth rate and amplitude of thixotropy strength ratio.The influence of pile length on the soil around the pile is not as great as the influence of pile diameter on the soil around the pile.(2)With the increase of the stagnation age,the ultimate bearing capacity of each model pile has been restored to different extents.Moreover,the recovery rate of vertical ultimate bearing capacity of single pile is fast in the early stage and slow in the later stage.(3)The frictional resistance of model piles along the pile body is approximately "R" distributed along the stagnation age.As the pile top load increases,the downward transfer of the pile top load is gradually realized.With the increase of rest time,the ultimate side friction of pile increases greatly.(4)The recovery of the soil strength around the pile is positively related to the increase of the ultimate bearing capacity of the model pile.The stronger the thixotropy of the soil,the more obvious the time effect of the pile foundation.