An Investigation On The Thermal And Thermo-consolidation Behaviour Of Ningbo Soft Soil

Geothermal energy pile is a new type of pile that can withstand both building load and heat exchange.This paper mainly studies the thermal properties and thermo-consolidation behaviour of soft soil in Ningbo area,and provides theoretical basis for the application of geothermal energy pile in Ningbo area.Three typical areas in Ningbo were selected as the sites for soil survey and sampling.The transient plane heat source method was applied to test the soil thermal properties.The main factors affecting the soil thermal properties were considered from two aspects: macroscopic factors and microscopic factors.By using several common heat transfer models,the calculation error of the thermal conductivity of Ningbo soft soil is compared and analyzed.The thermo-consolidation process is a self-developed one dimensional consolidation instrument for water bath temperature control,which is saturated with one dimensional consolidation under different temperature gradients.Through the above research and analysis,the main conclusions are as follows:(1)It is found that the thermal conductivity of the original soil of Ningbo soft soil is greatly influenced by different soil layers,and the thermal conductivity of the same soil layer increases slightly with the increase of the depth of the soil.From the test results of the remolded soil samples,the thermal conductivity increases linearly with the dry density when the soil moisture content is certain,and the thermal conductivity increases with the dry density at different water content.The thermal conductivity of soil increases with the increase of saturation,and the rate of increase increases with the increase of saturation.(2)The heat storage coefficient increases with the increase of dry density in the water content,and the moisture content reaches a certain value.The heat storage coefficient begins to decrease with the increase of dry density,and the variation of different soil heat storage coefficient varies with the dry density,but the thermal diffusion coefficient has no significant relationship with the soil density and water content.(3)The thermal conductivity is influenced by the content of soil quartz to some extent,but it does not necessarily increase with the increase of quartz content.Other minerals should be considered synthetically.In the microstructure and structural factors that affect the thermal conductivity of soil,the biggest influence is particlegradation.The porosity,particle morphology and contact form between particles and particles will also affect the thermal conductivity.(4)In the empirical model,the Campbell model is proposed to estimate the thermal conductivity of Ningbo silty clay.In the semi theoretical model,the error of the thermal conductivity estimation of the Johansen model is small.(5)The soil moisture content is more sensitive to temperature;temperature makes the compression coefficient becomes smaller;influence of e-p curve is also influenced by temperature,temperature variation ratio in the soil pore water content decreased;and the higher the temperature,the settlement consolidation process in the smaller.