Research On The Behavior Of The Bearing Capacity Of The Pile Foundation In Liquefied Soil And Earthquake Subsidence Soft Soil

Rearch on the behavior of the bearing capacity of the pile foundation in liquefied soil and earthquake subsidence soft soil is one of the research focuses in current geotechnical engineering field. Special geologic structures consisting of sediment soft clay and gravel stratum widely exist in river basin of China, and they are characteristic of liquefied and seismic subsidence significantly. According to the characteristic of the bearing capacity of pile foundation, considering the bearing capacity’s change caused by soil liquefaction or seismic subsidence, buckling stability problem is studied. Researched mainly in the following several aspects:(1) The theory of bearing characteristic of the pile foundation in liquefied soil and earthquake subsidence soft soil is analyzed. In accordance with the standards, the bearing capacity of piles under different operation conditions is calculated. After comparative analysis, such conclusion can be reached: the soil strength will not completely lost after liquefaction or seismic subsidence, in fact, along with the liquefaction degree of side pile soil increasing, the diameter takes effect more obviously on the vertical bearing capacity of single pile, the smaller pile diameter is, the bearing capacity reduces more under same liquefaction environment.(2) Simplified the bound form of real piles as the pile bottom fixed,and pile top free, articulated or elastic block,suppose distribution of elastic resistance coefficient of pile side soil is:when the embedded depth of the pile is within the conversion point depth of pile side soil resistance coefficient (4.0/α), the elastic resistance coefficient showed parabola change (c method) or diagonal linear change (m method), and when the depth exceeds4.0/α, the elastic resistance coefficient is constant. Considering the effects of pile body weight and pile side friction, the energy method is used to solve the critical buckling load expression in all cases. By comparing various influence factors, it show that the calculation depth H (H=4.0/α) of the conversion point depth of pile side soil resistance coefficient is reasonable and accurate; when there is little restrain in the pile bottom, the effects of the pile side friction and pile body weight on the buckling critical load can not be ignored. When the pile diameter is greater than0.8meter, no matter how little pile top constraint is, this effect is beneficial to the pile buckling stability; while the pile diameter is less than0.8meter and the pile top is free, the two combined effects go against to the pile buckling stability.(3) As a result of defects in pile and nonuniformity in pile side soil, the actual buckling load of pile foundation is less than the critical buckling load. Based on the the energy method, perturbation method is proposed to analyze the post-buckling behavior of pile body. Through calculation and analysis, it shows that: the buckling critical load will increase with the ratio of pile-soil stiffness and the embedded depth of the pile increase, but the post-buckling behavior tends to be unstable.