Penetration grouting diffusion and strengthening mechanism of sand layer with crucial grout

Abstract

Ordinary Portland Cement (OPC), micro-fine Portland cement (MPC), micro-fine sulfur-alumina cement (MSAC) and effective micro-fine cementitious grout (EMCG) were adopted. A visual simulation test device for fixed pressure permeation grouting for sandy soil was designed, and osmotic spreading and strengthening tests were conducted. The time-dependent variation rules of spreading distance and slurry amount were analyzed, and the influence of grout type, sand gradation, and grouting pressure on the reinforcement result were studied. The strengthening mechanism of EMCG at different spreading distances was analyzed emphatically, the microscopic strengthening modes of grout-rock interface with different grouts were obtained, and the essential reinforcement differences of various grouts were revealed. Based on the Kozeny-Carman model, the generalized percolation coefficient was deduced. The results showed that grout types and particle mass fraction were key factors to determine injectability of fine sand, the effect of grouting pressure was not significant, and the injectability of EMCG was the most satisfied. At the water-binder ratio (W/B) of 1.0, the 3 d strength of EMCG reached 13.3 MPa, and it was 1.25, 1.37 and 2.46 times as those of OPC, MPC and MSAC, respectively. The 7 d strength of EMCG exceeded 70 % of its 28 d strength, the diffusion distance of EMCG exceeded 2 m for S2 sand (0.3–0.6 mm), and its 28 d strength of reinforced sand reached 2.18 MPa as the W/B of EMCG was 2.5. The dense C–S–H gels generated at the EMCG slurry-rock interface can effectively improve cementation strength of sand and grout.