Study on the CPTu inversion methods for strength and consolidation parameters of gassy soil with different gas contents

Abstract

Gassy clay deposits are widely distributed in marine sediments. Clarifying the influence patterns of the trapped gas phase on the mechanical properties of gassy clay is of significant importance. Establishing an in-situ strength parameter and consolidation coefficient inversion method based on CPTu is crucial for gassy clay characterization. In this study, gassy clay was prepared using the zeolite method. The variations of strength and consolidation parameters of gassy clay concerning gas content were obtained based on laboratory triaxial and one-dimensional tests. It was observed that the trapped gas phase enhances the undrained shear strength and hinders drainage. Specifically, gassy clay with a gas content of 3.5 % exhibited an 18 % increase in undrained shear strength compared to saturated clay and a 50 % reduction in consolidation coefficient. In addition, laboratory calibration chamber tests were conducted to investigate the cone penetration test (CPTu) in gassy clay with varying gas contents and penetration rates. The drainage effect during the CPTu penetration process in gassy clay was discussed. The reasons behind the variations in static cone penetration parameters under undrained conditions for normally consolidated gassy clay were analyzed by combining the results of triaxial tests and one-dimensional consolidation experiments. A proposed formula for the cone factor Nkt was also provided under undrained penetration conditions. The accuracy of conventional methods for estimating the consolidation coefficient of gassy clay was verified, the basic properties of the gassy clay used in the indoor experiment are similar to those of the seabed gassy silt at the project site, and the environmental conditions are similar to those at locations with low initial pore pressure, such as mudflat or shallow sea bed, thereby offering a reference for in-situ testing of strength parameters and consolidation coefficients in gassy clay seabed.