Scrutiny of freeze-thaw cycles effect on physical and dynamic fracture characteristics of cracked sandstone

Abstract

A series of freeze-thaw (FT) cycle experiments and drop-weight impact tests are performed to explore the dynamic fracture characteristics of fractured sandstone acted upon by FT cycles. To this end, an innovatively cracked sample, a tunnel with a single radial crack (TSRC), made from an intact sandstone rock is implemented. The experimental results reveal that for FT cycles 10, the dynamic elastic modulus and P/S wave velocities of sandstone exhibit the most drastically descending trend. In such a case, the decreasing percentage of the dynamic elastic modulus, P wave velocity, and S wave velocity reach 16.4%, 7.2%, and 8.3%, respectively. The percentage reduction of these three physical parameters is also tapered off as the number of FT cycles reaches 30 and 40. While the porosity of sandstone grows by 1%, the pore distribution substantially alters for the case of 10 cycles of FT. For the number of FT cycles greater than 30, the porosity of sandstone slightly increases. Further, the crack growth velocity generally grows with the number of FT cycles such that the highest crack growth velocity is detected for 40 cycles FT, and the corresponding velocity touches 427.6 m/s. The obtained results demonstrate that the dynamic fracture toughness lessens as the number of FT cycles increases, and the dynamic initiation toughness is less than the average dynamic propagation toughness in sandstone samples subjected to impact loads. The dynamic loading rate calculated from dynamic initiation toughness reduces with the number of FT cycles when the sandstone specimen experiences the same dynamic loading.