Strength assessment of frozen soils by instrumented dynamic cone penetrometer

As an interest in cold region resource development increases, infrastructure constructions on frozen soils have been actively conducted. Thus, the investigation of the frozen soils is fundamental and essential to ensure the stability of frozen ground. The goal of this study is to estimate the strength of the frozen soils by the instrumented dynamic cone penetrometer. The dynamic cone penetrometer is incorporated with strain gauges and accelerometer at the cone tip to figure out transferred energy through rods. During dynamic penetration phase, a rod guide is located on the frozen soils to prevent eccentricity of impact. Specimens are prepared with sand-silt mixture at the silt fraction of 30 % in weight. The relative density and the degree of saturation are of the soils is 60 % and 10 %, respectively. The specimens are located in the freezing chamber at sub-zero temperature to freeze under the specified vertical stresses for simulating frozen ground. The dynamic penetration tests are conducted after freezing phase. Experimental results show that as the vertical stress increases, the dynamic cone penetration index which represents the strength of the frozen soils decreases. The force signal increases and the velocity estimated by accelerometer decreases as the vertical stress during freezing and penetrating phases increases. This study suggests that instrumented dynamic cone penetration test may be suitable for the investigation of the strength of the frozen soils.