Abstract: To observe and analyze the impact of trapped cavities on the flow dynamics of soft clay during cyclic T-bar penetration, we prepared transparent clay using Laponite RD, sodium pyrophosphate, and deionized water, and constructed a cyclic T-bar penetration testing apparatus comprising loading equipment, a CCD camera, a laser, and a control system. By using this test apparatus, we conducted cyclic T-bar penetration test on the transparent clay to investigate the influence of trapped cavities on the flow characteristics of soil. The findings reveal that trapped cavities impeded soil flow around the probe during initial T-bar penetration, preventing it from attaining a full-flow state. As the T-bar was initially extracted, the trapped cavities disengaged from the probe and remained suspended above it, gradually diminishing its effect on soil flow. By the time the T-bar was extracted to a depth twice the probe diameter, the soil flow was unaffected by the trapped cavity and achieved a full-flow state. Throughout the 2^nd to the 10^th cycle penetrations, trapped cavities remained stably suspended in the soil, without impeding soil flow. When the penetration depth was equivalent to one time the probe diameter, the soil reached full-flow state. In conclusion, trapped cavities exert no significant impact on the outcomes of cyclic T-bar penetration test. Hence, it is rational to test the remolded shear strength of soft clay using cyclic T-bar penetration during the initial penetration through trapped cavities.

Key words: transparent clay, T-bar, cyclic penetration test, trapped cavity, flow characteristics