Study On The Shear Characteristics Of Energy Pile-soil Interface Under Saturated Powdery Clay Stratum

Energy pile is a green construction technology in line with the concept of low carbon economic development,with the advantages of energy saving,environmental protection,high efficiency and safety.Powdered clay strata are soils containing a high proportion of powder and clay particles.Powdered clay strata are mainly found in northeast,north,northwest and southwest regions of China.The soil interface of energy pile is the key part of energy pile,which directly affects the thermal and mechanical properties of energy pile.Therefore,it is of great significance to study the thermal coupling mechanism and deformation characteristics of the energy pile-soil interface in the widely distributed pulverized clay strata,in order to optimize the design and construction of energy piles and improve the efficiency and safety of energy piles.In this thesis,a direct shear test of concrete slab-saturated powdered clay interface under different normal loads was carried out using the fine stone concrete slab interface as the pile interface and the saturated powdered clay interface as the soil interface,and the effects of different interface temperatures and different interface temperature cycling patterns on the frictional properties of the energy pile-soil interface were investigated.At the same time,the FRIC subroutine was developed based on the temperature-controlled direct shear test research,and the simulation software was used to simulate the load-bearing characteristics of energy pile monopiles.The main work and research results are as follows:(1)In order to study the characteristics of the temperature effect at the pile-soil interface,indoor tests were used and the straight shear instrument was modified.A temperature control module was added and a variable temperature straight shear was developed to suit the needs of the test.This modification enables a more accurate study of the properties of the pile-soil interface at different temperatures,leading to more reliable test results.(2)To investigate the changes in temperature and moisture content of the upper and lower surfaces of soil samples under loading conditions.The shear test of the contact interface at different temperatures was carried out by setting the number of temperature cycles of the contact surface of the saturated powdered clay and concrete slab to obtain the shear force-shear displacement curve and the friction angle and cohesion of the interface in the direct shear test.The shear force-shear displacement curve and the friction angle and cohesion of the interface were obtained by setting the temperature difference between the contact surface of the saturated powdered clay and the concrete slab for the direct shear test.(3)A Goodman unit hyperbolic model was used and substituted into the experimentally obtained parameters related to the shear at the contact surface of the powdered clay-concrete slab structure,and a secondary development of the FRIC subroutine was carried out to define an appropriate friction model.A comparison with the results of the direct shear test of the saturated powdered clay-concrete slab structure under indoor temperature utility shows that the calculated results of the numerical tests are in general agreement with the direct shear test results and the laws reflected are in good agreement.The ABAQUS finite element software was used to simulate the direct shear test of the contact interface between saturated powdery clay and concrete to investigate the distribution of shear stress and strain at the pile-soil contact surface under different contact surface temperatures and normal loading conditions.(4)For the energy pile project in typical powdered clay ground,ABAQUS software was used to analyse the bearing capacity of energy pile monopile,and to investigate the bearing characteristics and analyse the bearing capacity of energy pile under different contact surface temperature conditions with graded loading.