Abstract: To solve the problem of slurry being difficult to diffuse during grouting construction in silty fine sand stratum, a case study is conducted on the grouting project of the mining excavation section of the connecting line between Zijingshan and Dongda Street stations of Zhengzhou metro line 2, and the composite grouting scheme of sodium metaaluminate modified sodium silicate slurry and ultrafine cement single slurry is tested and applied. The practical results show the following: (1) The diffusion radius of sodium metaaluminate modified sodium silicate slurry is more than 1 m, the injectability is good, and the total amount of grouting reaches 92% of the design. (2) The sodium aluminatemodified sodium silicate slurry is injected first. Then, it solidifies and forms a chemical slurry vein. Furthermore, the ultrafine cement slurry is injected into adjacent holes to split and diffuse along the chemical slurry vein to form a composite slurry vein, to fully improve the strength of the surrounding rocks in the reinforcement area. In the whole process of grouting and excavation, the cumulative deformation of surrounding buildings (structures) and strata is less than 4 mm. Recently, several grouting construction cases in silty fine sand stratum are summarized and analyzed. After comparison with phosphoric and sulfuric acids modified sodium silicate slurry, it is pointed out that sodium metaaluminate modified sodium silicate slurry has the advantages of good safety, short setting time, and large diffusion radius. The sodium metaaluminate modified sodium silicate slurry can be obtained from various sources at a greatly reduced cost, thereby reaching good economic and applicable benefits.

Key words: metro tunnel, silty fine sand formation, grouting reinforcement, scheme optimization, modified sodium silicate, sodium metaaluminate