Abstract: As cementing materials, cement and chemical grouts have often been used for soil improvement. However, high energy consumption, high-pollution discharge and high cost restrict their applications. A new soil improvement method, called bio-grouting reinforcement technology, has recently emerged, which is based on microbial induced calcite precipitation by injecting bacteria solution and nutrient into loose sand for the purpose of binding soil particles together and improving its physico-mechanical properties. Laboratory and field experimental studies of bio-grouting treated soils are systematically summarized. The engineering characteristics of bio-treated soils, non-destructive geophysical process monitoring method, and factors influencing the improvement effect are also discussed. The research results show that the bio-grouting process has many advantages such as small disturbance, low grouting pressure, less environmental harm, and remarkable treatment effect on improving the engineering properties of the soil (e.g. strength, stiffness, liquefaction resistance), which make it a broad engineering application prospect in soil improvement. However, the durability of bio-treated soils and economy of bio-grouting still need discussing and investigating further.

Key words: soil improvement, microbial induced calcite precipitation(MICP), bio-cementation, bio-grouting, sandy soil