A PPV-Strain-Based method for evaluating clay softening due to construction vibrations

ABSTRACT: Construction operations such as blasting, pile driving, and other heavy activities near sensitive clay deposits can disturb the soil structure. This disturbance may lead to both temporary and permanent deformations, causing a reduction in the soil’s shear strength. As a result, the stability of clay slopes and nearby structures can be compromised. In current practice, vibration monitoring is typically based on the Peak Particle Velocity (PPV) approach, which was originally developed for blasting in rock. This method has been extended to soils to help prevent damage from construction-induced vibrations. However, the PPV thresholds used today were mainly derived from tests on rock and do not accurately reflect the behaviour of soft clays. Applying the same PPV criteria to different soil types is not appropriate due to their varying properties. Clays have a specific critical shear strain (γt), below which negligible or no pore water pressure and strength degradation occur. This study introduces a new method that can better control vibration effects on clay deposits by establishing a correlation between the PPV measured at the ground surface and the maximum shear strain that develops within the soil profile at the same location. The correlation was validated using numerical simulations using FLAC2D and by a field setup in a natural soil deposit. The results show that the proposed equation can reliably estimate the maximum shear strain and is not affected by the characteristics of the vibration source when measured at locations sufficiently distant from the source.