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.