Abstract:

With shortages of energy and increasing awareness of environmental protection, the limited resources of shallow underground space have been rapidly developed and utilized. It is very important to master the variation of thermal physical parameters of rock and soil for using limited underground thermal energy efficiently and reasonably. Based on the thermal physical properties test of rock and soil in the geological prospecting projects of Beijing plain shallow geothermal energy resources, this paper analyses statistically the factors affecting the thermal conductivity of the silty clay and fine sand. The statistical results show that the average thermal conductivity of silty clay is 174 W/(m·K), and the average thermal conductivity of fine sand is 155 W/(m·K) and that the variation trend of these thermal conductivity rates is clear with the variation of the natural water content, natural density and porosity, with increasing water content the thermal conductivity decreases. The variation trends are listed as following:  the thermal conductivity increases with increasing density; the thermal conductivity reduces with increasing porosity; the best thermal conductivity is of about 20% water content in silty clay and 15% in fine sand; because the differences of samples in geological structural position, sedimentary environment, sedimentary history, material composition of rock and soil and composition microstructure affect the combination of the heat transfer, the thermal conductivity and water content in different areas, even  in the same areas, have different fitting equations but the same variation trend.

Key words: silty clay, fine sand, thermal physical property, rate of natural water content, Beijing area