Experimental study on new grouting material of acidic sodium silicate and its properties of grouted-sand

Slurry selection and ratio optimization are the key points and difficulties in the construction of subway tunnels in poorly graded medium sand strata. In this paper, a kind of acidic grouting material was prepared by using sodium silicate and phosphoric acid. The properties of the acidic grouting material including gel time and viscosity were studied. Orthogonal test was carried out to optimize the ratio of sodium silicate to phosphoric acid for poorly graded sand stratum. At the same time, X-ray diffraction (XRD) and scanning electron microscope (SEM) were used to analyze the sand consolidation process of the slurry. The results show that the gel time and funnel viscosity of the phosphoric acid-sodium silicate slurry are related to the Baume degree of sodium silicate and the volume ratio of sodium silicate to phosphoric acid. The compressive strength of the grouted sand is related to four factors, i.e., water content of the sand, and Baume degree, pH value and curing time of the slurry, the in-fluence degree of which is in the following order: D (curing time) > A (water content) > B (Baume degree of sodium silicate) > C (pH value of the slurry). The final slurry selected for grouting reinforcement of the weakly alkaline medium sand strata was prepared by 30 degrees Be & PRIME; sodium silicate with 14 % phosphoric acid at a volume ratio of 0.5. It has a gel time of 51.48 min, a funnel viscosity of 16.43 s and a pH value of 3.47. The increased amount of silica gel in the sample is the main reason for the increased strength of the grouted sand. The amount of silica gel generated increases with the increase of the curing time of the sample.