Pore pressure response during tube sampling in gold tailings

Abstract

Capturing the in-situ state of mine tailings is important in determining its behaviour under loading for evaluating the risk of failure of tailings dams. Obtaining a high-quality undisturbed sample through tube sampling is thus of great value to the responsible engineer. However, the sampling process itself disturbs the soil and changes its state. Since soil behaviour is driven by effective stress, one method to evaluate the disturbance induced during tube sampling is to monitor the soil’s positive and negative pore water pressure response during the process. A laboratory study was conducted where tailings samples were prepared at a controlled void ratio and subsequently saturated with water. Tube samplers of different diameters were driven into the material and extracted by means of an electric actuator during which internal sample pore pressures were monitored using tensiometers. The material experienced significant instantaneous contractive and dilative tendencies during insertion. Instantaneous negative responses during extraction of the tube samplers were also measured. It was found that the largest tube sampler (100mm diameter) performed best in the study.