The thermal conductivity is an important thermophysical parameter in geo-energy engineering design and research.Soils in engineering is usually in an unsaturated state.The thermal conductivity of unsaturated soils will affect the mechanical properties and the heat exchange efficiency of the underground structure

and further affect the working efficiency of the whole thermal structure.In order to provide reliable parameters for geo-energy design and research

the thermal conductivities of gravelly sand

silt and clay at different water contents and temperatures were measured by element tests to study the relationships of thermal conductivity with water content

matric suction and temperature of the three unsaturated soils.The results show that the thermal conductivities of the three unsaturated soils increase with the increase of water content and then tend to be stable.The increasing rate of thermal conductivity of gravelly sand is the largest

followed by silt and clay.With the same water content

the thermal conductivity of gravelly sand is the highest

followed by silt and clay.Matric suction affects the thermal conductivity of silt

and their relationship trend is similar to the soil-water characteristic curve.The thermal conductivities of the three soils increase linearly with temperature

but the increasing magnitude is only 10-3.Thus temperature influence can be ignored.