Abstract:
Soil and the interface between soil and construction materials at elevated temperature occurs in many geotechnical situations. Ground-source heat pumps (GSHPs) installed into the foundations or subsurface walls of a structure are being used increasingly for energy efficiency. During the operation of heat pumps, the soil around the energy foundations encounters heating and cooling cycles which may result in expansion and contraction of soil and foundation materials. The change of temperature can cause a change in interface shear strength, possibility for plastic thermal deformations in soil and increased axial settlement of the foundation. Historically, most laboratory interface testing between soil and different construction materials has been performed at room temperature. An extensive research study was undertaken in an effort to investigate the temperature effects on interface shear behaviour between (a) sand and concrete (b) sand and steel (c) clay and concrete and (d) clay and steel. For this purpose direct shear box testing apparatus was used with some modifications to simulate the field conditions at elevated temperatures and evaluate shear displacement failure mechanisms at these higher temperatures. The physical laboratory testing program consisted of multiple series of interface shear tests between material combinations (as above) under a range of normal stress levels from 50 to 150 kPa and at a range of test temperatures from 20 to 50°C. The established factors which can affect the interface shear strength like surface roughness, relative density and particle shape and size are kept constant to study the effect of temperature variation on interface shear strength. The results from these tests were compared to evaluate the impact of elevated temperature on shear strength parameters. These results provided insightful information about the influence of temperature variation and highlighted the importance of the research. Analysis of results indicated variation in shear strength parameters with temperature and normal stress. Finally, future recommendations are provided for achieving the overall goal of the research.
