Study On The Behavior Of Interface Friction Characteristics Of Energy Pile-Soil In Soft Soil Foundation

In China,the energy consumption on building heating and cooling exceeds 10% of the total.Since fossil fuels have been a major energy supply,environmental problems are mounting.Shallow geothermal energy has been listed as one renewable energy,which edges out fossil fuels in building heating and cooling.With frictional energy piles being its ideal form in use,the practice of those piles enjoys huge potential.In recent field test,it turns out that temperature changes at the pile-soil interface affect its bearing capacity.In a nutshell,an acknowledgement of how temperature factors frictional properties on the pile-soil interface contributes to its promotion and practice.This paper took fine-aggregate concrete as the pile interface,and the kaolin for the soil,so as to carry out the direct shear test under different normal stresses,as well as to further study its frictional property in different temperatures and temperature cycles at diverse interfaces(including the frequency,temperature difference and pattern of the cycle).Adhering to the direct shear test,a series of numerical simulations have deepened the finding via analyzing how the inlet temperature and temperature cycle under different conditions change the bearing capacity of each energy pile.Here come the profound findings and outcomes:(1)This paper delivered a systematic insight on features and deficiencies of the existing device for direct shear tests.Besides,it also developed a direct shear tester with a constant shear area and controlled temperature to cope with temperature changes.(2)The paper studied the effect of temperature on the frictional property of pile-soil interface through the temperature-controlled direct shear test.The test showed that the shear strength and temperature revealed a positive correlation when the interface temperature changed.For instance,if the temperature reached 10,20,30,40,and 50 Celsius,friction angles followed up as 12.93°,13.97°,14.42°,15.22°,and 16.07° respectively.In addition,the cohesion of the interface also related to the temperature,which decreased once the temperature fluctuated.(3)The paper also adopted the temperature-controlled direct shear test,in order to clarify the interaction between the temperature cycle(including the frequency,temperature difference and pattern of the cycle)and its friction property.The test highlighted that the shear strength decreased with an increase of temperature cycles.After 1 to 3 rounds of temperature cycles,the friction angle decreased by 2.27 %,4.68 % and 5.46 % respectively,with a reduction of cohesion as 11.61%,16.12% and 18.31% in turns.The shear strength of the pile-soil interface decreased with the increase of temperature difference after rounds of temperature cycle within different ranges.After keeping the temperature difference at 5,10,20 Celsius,the friction angle decreased by 1.49 %,2.27 % and 4.11 %,and the cohesion reduced by 4.10 %,11.61 % and 31.14 % subsequently.Apart from that,under different cycle path,the cohesion fell as the temperature stress path grew.(4)In this paper,Comsol was applied to get a full picture of temperature field distribution of the energy pile in work.When the temperature of pile-soil interface approached stability,the formula concerning temperature and depth were accordingly worked out through a piecewise linear function.Afterwards,the data and formula were imported into Abaqus,which calculated the load-settlement curves of how the energy piles in soft soil locations reacted to a change of temperature cycles under differentiate inlet temperatures and interface.In terms of the result,as the inlet temperature lowered by 20 and 10 Celsius,or rose by 10,20,30 Celsius,its ultimate bearing capacity dropped by 5.85%,and 1.33%,or added up by 2.02%,3.86 %,and 5.26 %.After its temperature undergoing 1-3 rounds of cycles,the ultimate bearing capacity was cut by 1.45 %,2.74 % and 3.28%.So to see,this capacity decreased along with the increase of temperature cycles.After going through temperature cycle at 5,10 and 20 Celsius,the ultimate capacity of the pile-soil interface was reduced by 0.75 %,1.45% and 2.48% respectively.Those figures prove that the expansion of temperature differences in cycling results into a decline of the ultimate bearing capacity of piles.