Experimental Study On Thermal Physical Properties Of Surrounding Soils Of Lanzhou Subway

Lanzhou subway began to be constructed from March 2014,which is of importance to the improvement of urban transportation situation and air pollution control.This thesis focus on the study of thermal physical parameters and geothermal field of the surrounding soil of Lanzhou subway for the design of ventilation and air conditioning system.Hot Disk thermal constants was conducted to measure the thermal physics parameter of different surrounding soils at Lanzhou subway,including the natural soils at different stratum depth,the same stratum after drying to different water content,and the same soil remolded to different dry density and water content.Test results show that the thermal conductivity of the soil mass increase with the stratum depth increase.The thermal conductivity and thermal diffusion coefficient of the middle sand layer soil at the depth of 13 m are larger than the corresponding of loess and silty soil.The thermal specific coefficient of middle sand layer soil is smaller than soil of other layers.The heat conductivity coefficient of natural soil increases linearly with the increase of water content.The thermal diffusion coefficient of natural soil increases firstly then decreases with the increase of water content,and exhibits maximum value with a water content between 5% and 10%.While the corresponding thermal diffusion coefficient decreases firstly then increases with the increase of water content,and exhibits minimum value with a water content between 2.5% and 5%.The types of soil of surrounding soils of Lanzhou subway include of sandy silt,loess,silty soil and organic.At the same dry density,the thermal conductivity of sandy silty soil changes with the change of water content,followed by loess and muddy soil,the change of organic matter soil is the smallest.The volume specific heat exhibits a different tendency with water content to soil condition.For example,undisturbed soils reach a minimum value between 2.5% and 5% of water content,while the remolded loess and sandy silty increase with increasing water content,and the muddy soils have a low value in the range of 0-5 %,and then increase with the increase of water content.The thermal diffusivity of loess and muddy soil have a maximum value at a specific water content which related to the type and structure of soil.