Experimental Study On Deformation And Fracture Of Ice-Rich Frozen Soils In Thermal Gradient Environment

The engineering and environmental problems derived from the ice-rich frozen soils increased gradually in permafrost region in China.The deformation mechanism and the frost heave are the major issues to be addressed.The frost heave is the response of the water migration-induced segregated ice under the applied thermal gradient.The frost heave force thus initiates under the restriction from the engineering structures.The frost heave force leads to the deformation of frozen soils and the locally distributed fracture.The fracture weakened the mechanical properties and altered the deformation mechanism of frozen soils.Further,the fracture in soils can enhance the seepage,and thus contributing to the water migration in thawing and refreezing process.The icerich frozen soil samples with thermal gradient were the investigated objective in present study,and the deformation process as well as the fracture evolution were investigated systematically using the digital processing technology(DPT)and CT comprehensively.The DPT was added in previous test system under thermal gradient.A novel speckle technique was developed for fine-grained frozen soils,and thus overcoming the difficultly in automatic tracking of the target spot.In addition,the end friction was decreased effectively by adding a special device between the sample ends and freezing plates.The surface deformation and fracture characteristics of ice-frozen soil samples with thermal gradient were observed by DIP.The deformation process can be divided into two stages.The critical point was corresponding to the failure stage.After the critical point,the deformation of the frozen soil samples were mainly undertaken by the deformation of the zone with significant deformation level(ZSD).The increasing trends of ZSD height and fracture height approached identical.However,the height of ZSD was slightly smaller than that of the fracture.The internal fracture of ice-rich frozen soil samples with thermal gradient was observed using CT.The deformation of frozen soil samples was mainly undertaken by the evolution of fracture and the deformation of the zone with little deformation(ZLD).The CT-based fracture height approached identical with DPT-based ZSD height.The relationship between fracture height and damage gradient satisfied a linear equation.The fracture height increased as damage gradient increased.The increase in the ice-particle size and water content enhanced the increasing rate of the observed fracture height.