Experimental Research On Micro-characteristics Of Soil Around Energy Pile Under Cyclic Temperature Field

Energy pile technology is a research field that has emerged in China in recent years.This is a technology that came into being under the policy of the country vigorously promoting new energy.The energy pile avoids some shortcomings of the traditional ground source heat pump,and replaces the ground source heat pump with its own advantages.Although the energy pile has some engineering applications,such as the Bolang Wal-Mart Commercial Plaza project in Ningbo,the Yanzhou People ’s Hospital project in Yanzhou,Shandong Province,and the Expo Axis project at the Shanghai World Expo,the exploration of the energy pile is far from over.At present,most of the research on energy piles is based on the heat transfer mechanism and macro mechanical behavior of energy piles.There is little research on the influence of energy piles on the surrounding soil.The soil around the pile supports full loads of the superstructure.And energy piles are different from ordinary piles.The cold and heat cycles of energy piles may cause disturbance to the soil around the pile,causing the soil structure around the pile to be destroyed,and thus losing the bearing capacity,so the study of the soil around the energy pile cannot be ignored.In order to further illustrate the influence of energy piles on the soil around the pile,this thesis combines the project of the Science and Technology Office of Jilin Province,takes the soil around the pile as the research object,and takes the micro structure as the research direction.On the basis of the indoor model test of the energy pile,it analyzes the micro structure and makes the following preliminary conclusions:(1)Establishment of the indoor test model of energy pileThrough the temperature monitoring of the soil around the pile in the model test,the temperature gradient curve of the soil around the pile is obtained.When hot water is passed,the temperature at the entrance of the pile top is the highest and the temperature at the bottom of the pile is the lowest;With continuous growth,the temperature of the soil near the middle of the pile changes most obviously.When cold water is passed through,the temperature of the middle soil drops the fastest,indicating that the soil in the middle is affected by the temperature most.(2)Analysis of pore distribution characteristics using nuclear magnetic resonance technologyUsing nuclear magnetic resonance technology,the pore distribution characteristics of the soil before and after the operation of the energy pile were analyzed,and the variation curve of the transverse relaxation time(T2 spectrum)before and after the operation of the energy pile was obtained,which is increasing.Through the calibration curve,the porosity content of the soil samples to be measured was tested,and the variation law of the porosity at each observation point was obtained.The lateral distribution of porosity at each point showed an increasing trend,and the porosity at the first observation point of the upper soil layer is the smallest,the porosity of the observation point of the lower soil layer farthest from the pile body is the largest,indicating that the soil sample here is least affected by the operation process of the energy pile.(3)Quantitative analysis based on scanning electron microscope picturesQuantitative analysis of soil particles and pores in the micro structure of the soil by scanning electron microscopy was carried out on the soil around the pile before and after the operation of the energy pile.The energy piles were measured by the microscopic parameters selected by IPP software such as average diameter,average area,average circularity,average fractal dimension,the abundance and directionality,which revealed the influence of the energy pile operation process on the soil around the pile.(4)Establishment of BP neural network modelThe basic principle and calculation process of BP neural network are briefly introduced,and the microscopic pictures obtained by scanning electron microscope and the microscopic data obtained by IPP analysis software are predicted,which reflects the interrelationship of various microscopic parameters to a certain extent,and also indirectly reflects changes in porosity.