Experimental study on shear behavior of geotextile encased lime energy column - soil interface in degraded permafrost environment

The differential settlement of warm permafrost foundations significantly impacts the safe operation of highway and railway embankments. The use of geotextile encased lime energy columns (GELECs) has been proven to be effective in pre-thawing shallow layers of warm permafrost as a novel method to reduce the post-construction settlement of embankments. Understanding the interaction between the GELECs and the soil is crucial in illustrating the load transfer mechanism. This study conducted a series of large-scale direct shear tests on GELEC-soil in degraded permafrost environments using an improved temperature-controlled direct shear test apparatus with assembled large shear boxes. The effects of different shear rates, water contents, and types of geotextiles on the mechanical behavior of the interface were analyzed. The strength development of the interface under various curing times was studied in detail. The experimental results indicate that the interface strength increases significantly during the initial stage of curing while the rate of strength increase diminishes over time. The improvement in peak shear strength is primarily attributed to the increase in interfacial cohesion, and the increasing trend of the cohesion follows an exponential decay function. And the microscopic strengthening mechanism of the interface was analyzed through SEM tests. Finally, a nonlinear elastic model incorporating a parameter to represent the variation of cohesion was developed to describe the shear stress-strain relationship at the GELEC-soil interface under different curing times.