Self–sensing, anti–liquefaction, and long–term settlement characteristics of calcareous sand seeped by high-concentration colloidal silica

Abstract

Low–concentration of colloidal silica (usually from 5 to 20 wt%) for liquefaction mitigation has been widely studied. But fewer literatures have focused on higher concentration of colloidal silica for cementing sand. For calcareous sand seeped by 40 wt% colloidal silica, cyclic loadings were performed to explore its anti–liquefaction, long–term settlement and self–sensing characteristics. Cyclic triaxial apparatus were to perform anti–liquefaction and long–term settlement tests, and use self-built setup to perform self-sensing tests. The new findings are as follows: (1) for anti–liquefaction, specimens seeped by 40 wt% colloidal silica can’t achieve liquefaction, i.e., the excess pore pressure ratios cyclically fluctuates between 1 and negative, which is not discovered by lower concentration of colloidal silica in the previous literatures; (2) for long–term settlement, cumulative strain is small after 20,000 cycles, and the cumulative strain is less than 1 % even the cyclic stress ratio (CSR) is greater than 1.1, indicating that the colloidal–silica–cemented sand has good resistance to deformation; (3) self–sensing characteristics have been discovered, i.e., a stress change of 90 kPa can lead to 59.37 % change in electrical resistivity, compared to Portland–cement-treated sand without change of resistivity under the same stress change. When Portland–cemented materials are added with conductive fillers in the previous literatures, they can exhibit self-sensing characteristics, but the stress sensitivity is still two orders lower than colloidal–silica–cemented sand. For colloidal–silica–cemented sand, based on the fact that the dry silica gel is non–conductive and only the salt solution in the micro porous media is conductive, the self–sensing feature can be attributed to the stress–induced deformation of micro conductive–salt–solution–filled channels (i.e., the deformation of conductive network). The above research indicates that colloidal–silica–seeped sand has a potential for self–sensing subgrades in the marine environments.