Thermal and pore pressure gradient–dependent deformation and fracture behavior of saturated soils subjected to freeze–thaw

摘要

Fractures in soils subjected to freeze-thaw around underground facilities initiated from a connection of pores occupied by isolated ice and expansion of spaces occupied by layered ice in freezing, reserved in thawing, and varied due to a pore pressure. A digital image correlation (DIC) and X-ray CT-aided experiment was thus conducted to investigate the quantitative relationship between such behaviors and pore pressure in saturated soil specimen subjected to freezing to a stable thermal gradient and then thawing under uniform temperatures. The DIC-based data showed that an increase in heterogeneity level k(H) weakened the peak strength and enhanced the apparent brittleness of specimen. The maximum lateral strain and its occurrence height increased as k(H) increased with the height of lateral strain location zone reducing. The CT-based lateral strain approached the DIC- based data with an averaged deviation = 0.4%. It was found that pore localization zone existed within the lateral strain localization zone with the height of maximum pore ratio being approximately identical with that of the maximum lateral strain. The pre-existing fracture expanded and the isolated pores were connected gradually due to the strength attenuation near pore edge and the pore pressure; they together formed a fracture network. However, the influence of pore pressure to initiation of fracture was weakened as k(H) further increased. These observations were distinguished from the deformation and fracture behaviors occurring in frozen soil specimen and presented significances to better understand structure variation within soil layers subjected to artificial freezing.