Frost Heave Characteristics Of Screw Pile-Soil System In Seasonally Frozen Soil Region

Compared with traditional cast-in-place piles and straight piles,screw pile foundation has significant advantages such as high degree of construction mechanization,low engineering cost and short construction period.The screw pile foundation has a wide range of application prospects in engineering construction,and has been put into use in many types of engineering practices in China,such as photovoltaic support foundations,transmission line tower foundations,and slope support structures.With the deepening of the "The Belt and Road Initiative" construction and the development of the western region,a large number of projects have been carried out in seasonally frozen soil areas.However,there are relatively few studies on the bearing characteristics of screw piles in frozen soil regions.Therefore,it is of great practical significance to study the interaction characteristics between screw piles and soil in seasonally frozen soil areas.This thesis takes the screw pile foundation as the research object,and studies the frost heave mechanism of the screw pile-frozen soil interaction in the seasonal frozen soil area by combining theoretical analysis and model test.The details are as follows:(1)Based on the frost heave characteristics of the frozen soil area,the influencing factors of the screw pile-frozen soil frost heave characteristics in the seasonal frozen soil area were analyzed.According to the bearing capacity of the screw pile foundation and the bearing capacity of the horizontal load,the mechanical characteristics of the screw pile foundation and the design methods of the pile diameter,pitch,blade thickness,blade width,and number of blades are determined.The numerical model of frozen soil-screw pile was constructed by ABAQUS finite element software,and the reliability of the model was verified by temperature distribution and force change.At the same time,the influence of various structural parameters of the screw pile on the pile-soil interaction and the frost heave characteristics are also studied.The results show that the pile diameter and the number of blades have a greater influence on the frost heave effect of the screw pile-frozen soil,followed by the blade inclination angle,and the blade thickness has the least effect on the frost heave effect.(2)Considering the screw pile-soil interaction under actual working conditions,the influence of external loads(lateral load,longitudinal load)on the frost heave effect of screw pile-soil was studied.Under the external load,the lateral load has a more prominent effect on the frost heave effect than the longitudinal load.Within a certain range,as the lateral load increases,the frost heave effect increases gradually.However,to a certain extent,the effect of longitudinal load on the pile-soil frost heave effect is negligible.In addition,the effect of screw pile-soil frost heave under different soils was also studied,and the degree of influence of different soils on the frost heave effect was analyzed.(3)In order to reduce the damage to piles and buildings caused by frost heaving in frozen soil area,a scheme of temperature-controlled telescopic steel pipe screw pile device was studied and designed.It includes a temperature control system,a hydraulic system,a fastening device,a solar energy system and other structures.When the device is running,the sensor system can be used to sense the change of the external temperature,and the height of the pile body can be adjusted by itself through the hydraulic system.In this way,it can ensure that the structure does not rise and fall significantly due to frost heave,achieve the purpose of protecting the superstructure,and effectively eliminate the damage caused by frost heave to the pile body and the building.