Study of Gas Jets in Structured Loess Compaction Using a Numerical and Experimental Approach

Abstract

In this work, the effect of gas jets used in the deep vertical vibratory compaction technique are studied. Gas jets play a vital role in treating structured loess foundations by the pneumatic-vibratory probe compaction method. Utilizing the geotechnical particle finite-element method numerically, we estimate the limit gas injection pressure and delineate the injection-induced damage and plastic zones. The behavior of structured soil is described using an elastoplastic constitutive model considering its structure evolution. The analysis of structured loess under gas injection is based on the cavity expansion approach. Experimentally, we performed a scale model test of gas injection to investigate the mechanism of the gas jets on the surrounding soil and compared relevant results with numerical results. Numerical results show that the limit gas injection pressure for structured loess beyond a depth of 8.0 m ranges from 1,409.7 to 1,467.2 kPa, increasing with the increase of overburden depth while the current cavity expansion radius decreases. The radius of the plastic zone induced by cavity expansion is 2.0 to 3.0 times the current cavity radius within this depth range; for the damage zone, however, it ranges from 0.1 to 0.4 times. The horizontal pressure recorded during the model test is observed to be lower compared with the numerical simulation results. This discrepancy can be attributed to factors such as the neglect of gas leakage within the soil and the utilization of a uniform parameter. The gas jets expand soil in cyclic shear form. It goes through a process from destruction of soil structure to compression in the horizontal direction; then, its pressure gradually drops to zero in the expansion direction of the dominant channel in soil.