Determination of disturbance depth due to excavation using multifunctional CPTU tests

The disturbance depth of excavations is an important parameter for their design. Most of the existing methods for determining the disturbed depth are laboratory tests, which cannot reflect the in-situ stress state of soils. The in-situ multifunctional piezocone penetration tests (CPTU) are carried out before and after the excavation of three projects in Nanjing, Wuxi and Changzhou. The influences of unloading induced by excavation on the cone resistance (q_t), sleeve resistance (f_s), friction ratio (R_f) and resistivity (ρ) are also analyzed. Further combining with the laboratory unloading resilience tests, the disturbance depth of excavation based on in-situ tests is proposed. The results show that the unloading effect may reduce the values of cone resistance and sleeve resistance for silt and silty sand foundations, and the corresponding influences on the amplitudes decrease with the increase of depth. However, the excavation has little effect on the friction ratio and resistivity. The disturbance depth of excavation can be determined by the depth beneath the excavation bottom where the cone resistance (q_t) is reduced by 20% as compared to that prior to excavation.