Experimental Investigation of New Crack Initiation and Propagation in Fissured Clay under Tensile Stress

ABSTRACT Under tensile loading, the distribution, size, and arrangement of defects such as cracks and holes influence the transmission path of tensile stress, which directly affects the cracking angle and propagation trajectory of tension-induced fractures. To investigate the fracture behavior of newly formed tension cracks in clay specimens containing preexisting fissures and coexisting fissure-hole systems, a custom-designed dog-bone tensile testing apparatus was employed to conduct tensile experiments. Additionally, numerical simulations of fissured clay were performed using a damage model based on the traction-separation law, with results showing good agreement with experimental data. Key findings include the following: (1) New cracks initiate at the tip of preexisting fissures and propagate along a deflected angle following a serrated path. (2) Experimental results indicate that new cracks propagate into holes when the “L/D” ratio (fissure-to-hole distance divided by hole diameter) is ≤2, whereas numerical simulations yield a critical “L/D” ratio of 4/3. This discrepancy arises because hole formation in physical samples reduces compaction in the surrounding clay, which is an effect not replicated in the numerical model. (3) Holes with diameters ≤3 mm can partially inhibit crack propagation, whereas larger holes (>3 mm) accelerate fracture growth.