Experimental Research On The Shear Characteristics Of Pile-soil Interface In Permafrost Region

Pile foundation is widely applied in permafrost region of our country, such as theconstruction of infrastructure projects in Qinghai Tibet Plateau, the northeast, Xinjiang andother parts. The pile foundation is also largely applied in the construction of Qinghai Tibetrailway. There are problems of frost heaving damage and capacity degradation with pilefoundation while used, and they may result in project failure. Property of the interfacebetween pile and soil has an important effect on the safety and long-term stability of pilefoundation in permafrost region. The site excavation test in the field shows that the surfaceof the pile body is attached to the ice, and the ice film makes the interface between pile andsoil special and the bearing capacity of pile foundation complex. At the same time, theformation of ice film on the interface is associated with many factors, such as the methodwith the forming of pile and the pile-hole, the properties of pile material, types andproperties of frozen soil around the pile, foundation temperature field of pile body and themelting and freezing process of the soil around the pile.The nature of the permafrost is rather complex,and studies on the pile foundation inpermafrost are not so perfect as the general soil pile,which lacks systemic research on thefreezing stress of the interface between pile and soil. The problem of interface between pileand soil is the key factor to the bearing capacity of the pile foundation, and the relatedresearch is always the key technical problems of pile foundation in the field. Study on themechanical properties of interface between pile and soil in the permafrost area is a keyproblem in the pile foundation theory,and the scientific solution has important significanceon the deeply understanding to the working condition, bearing performance degradationand even failure of pile foundation in permafrost area.According to the background, this paper studies the mechanical properties of frozensoil, the main formation process and influence factors of freezing stress of pile-soilinterface (including temperature, moisture content, loading time and particle composition),and determines to take the pile material, temperature and water content into account in thetest research of shear properties of interface between pile and soil in permafrost area.This paper mainly adopts the method of model test to study the shear characteristics ofpile-soil interface in the permafrost area,with the aid of low temperature box, freezing coldbath system, thawing test box XT5405,5704LT low temperature and constant temperaturebox and strain controlled direct shear apparatus,in the low-temperature laboratory of Schoolof Civil Engineering,LanZhou JiaoTong University. Aluminum block-powder soil interface,concrete block-powder soil interface, organic glass block-powder soil interface andwood-powder soil interface are selected, with three different water content of soil (20%, 23%,26%), four types of test temperature (18℃,-1℃,-3℃,-5℃),four normal stressapplied(100kpa,200kpa,300kpa,400kpa), rotation factor method adopted to designthe test scheme.192groups of the indoor direct shear test are accomplished.According to the data measured by the model test, the shear stress and sheardisplacement curves of the different temperature, different water content and different pilematerial of pile-soil interface are drawed, the Cohesive force and Angle of internal frictionof the different pile material of pile-soil interface are calculated, the attenuation changerule of the interface strength parameters are studied. This thesis also compares the testresults of different working conditions and obtains some constructive conclusions, whichcan enrich and encomplete the theoretical research of pile foundation in permafrost region,and play a guiding role in the pile foundation construction in permafrost areas.