Development of Temperature-Controlled Direct Shear Box

Abstract

Abstract An increase in the temperature of permafrost that is caused by global warming can lead to a significant decrease in shear strength. Seasonal freeze-thaw (F-T) cycles can also adversely affect the shear strength of soils. This can result in damages to infrastructure, negative impacts on the economy, and a decline in the quality of life. Thus, it is crucial to understand the shear strength of permafrost and seasonally frozen-thawed soils. Several studies have utilized various instruments to observe the behavior of soils under such conditions, including a temperature-controlled triaxial system to apply F-T cycles or a traditional direct shear apparatus placed within a temperature-controlled room. Since most commercial geotechnical labs do not have a temperature-controlled room or a temperature-controlled triaxial system, this article presents the design of a new cost-effective direct shear box that was developed to allow temperature-controlled testing in a traditional direct shear device. The modifications to the direct shear box comply with ASTM D3080/3080M, Standard Test Method for Direct Shear Test of Soils under Consolidated Drained Conditions. Like the standard direct shear box, it consists of two halves and a direct shear cap, but each of these components is hollow to allow for the circulation of glycol. The chiller is capable of imposing temperatures within the range of −40°C to +40°C on the sample being tested. It is also possible to freeze and thaw specimens at a desired normal stress while monitoring the associated heave and compression. The freezing mechanism applied to the soil sample affects the distribution of ice within the pore spaces, necessitating that samples be frozen from all sides if a uniform distribution of ice is necessary. Shear strength parameters from the newly designed temperature-controlled direct shear box matched well with those from the traditional shear box. In addition, the feasibility of temperature-controlled direct shear testing was evaluated at different temperatures, strain rates, and normal stresses.