Centrifuge modeling of slope failure induced by elevated gas pressure in wet municipal solid waste landfill

Abstract

Understanding triggering mechanisms of slope failure is of great importance to the stability analysis and safety warning of waste landfill. This paper presents a centrifuge model test on slope failure induced by elevated gas pressure in wet landfill. The formation process of liquid level and gas pressure in the landfill is simulated by means of liquid and gas injections under a centrifugal acceleration of 66.7 g. The injected liquid contains surfactants, which allow it to generate foam in the waste pores when mixed with the injected gas. The pore gas and liquid pressures under two-phase flow condition are monitored separately to clarify the instability process. It is found that the continuous gas injection makes the pore gas pressure increase to peak values of 83.0 kPa–100.8 kPa, which are higher than the peak liquid pressures of 61.3 kPa–75.6 kPa. The formation of high gas pressure zone is attributed to the low gas permeability, which is affected by high liquid saturation as well as foam generation. The slope failure occurs when the pore gas pressure increases to the peak value and the corresponding shear strength decreases to the critical value. Although the gas injection raises the liquid level, the factor of safety of landfill slope will be overestimated if only considering the effect of liquid pressure. According to the response curves of displacement to gas pressure rise, the critical ratios of gas pressure to earth pressure are determined to be 0.74–0.84, which fall within the range of the prototype landfill. The difference between foam and air on pore pressure distribution is also calculated and discussed.