Experimental Study On Effect Of Particle Gradation And Shape And Thermal Characteristics On Soil Thermal Conductivity

As an important physical parameter,the thermal conductivity is of great significance for the design of many geotechnical structures,such as energy pile,granular insulation layers for pavements or landfills in cold regions,etc.The pile is often accompanied by a large impact load during pile sinking process,which sufficient to cause particle breakage and change in gradation and particle shape that alter the heat-transfer processes of energy pile.Therefore,only thermal conductivity of soil after crushing can be used to design energy pile.In addition,the tire shred – sand with excellent thermal insulation properties can also be applied to granular insulation layers for pavements or landfills in cold regions.However,the influence of tire shred on the thermal conductivity of mixed soils has not been fully studied.Based on above purpose,the main research contents and research results of this paper are as follows:(1)The influence of gradation and void ratio on the thermal conductivity of carbonate sand was studied.When the uniformity coefficient is less than 4.7,the thermal conductivity increase rapidly with the increase of uniformity coefficient.But the thermal conductivity increase gradually as the uniformity coefficient exceed 4.7.The percent difference in thermal conductivity will reach a maximum of 13.9% at the uniformity coefficient of 20,which indicates that it is important to investigate the influence of gradation on soil thermal conductivity.Finally,uniformity coefficient(fractal dimension)and void ratio were used to establish the thermal conductivity empirical model and it is found that the fractal dimension was used to describe the empirical model is more consistent with the measured values.(2)Rounded glass beads were mixed with angular glass beads at different mixing ratios(The ratio of quality of angular glass beads to the mass of mixtures is 0、25%、50%、75%、100%,respectively)to obtain different mixtures with different particle shape.Aspect ratio,sphericity and convexity were used to quantitatively describe the shapes of three different dimensions of the same particles and the particle shape of the mixtures were determined according to cumulative curves of above three parameters.The effects of different particle shapes and relative densities(30%、50%、60%、70%、80%)on the thermal conductivity of mixtures were investigated.It was found that the particle shape can only directly affect the void ratio,which indirectly affects the thermal conductivity of the soil.It was also found that there is a linear relationship between the thermal conductivity and void ratio.(3)The Fujian standard sand was mixed with different size of tire shred particles at a different mixing ratio(The ratio of volume of tire shred to volume of mixtures is 0、25%、50%、75%、100%,respectively).The effects of the size and content of tire shred particles on the matrix mode and thermal conductivity of mixtures were also investigate.When the content is the same,the matrix mode of mixture changes from the rubber matrix mode to the sand matrix mode as the tire shred size increase,which could result in increased thermal conductivity.When the size of tire shred is the same,the matrix mode of mixture changes from the sand matrix mode to the rubber matrix mode as the tire shred size increase,which could result in decreased thermal conductivity.Finally,two parameters(relative size ratio and volumetric mixing ratio)were used to establish the thermal conductivity empirical model.