Soft soil is mainly composed by fine-grained soil. It generally has features of loose soil, high moisture content, big void ratio, high compressibility and low intensity. There are 2 questions should be solved during self drilling rock anchor anchoring in soft soil: one is how to control the influence of bottom layer’s creep for loss of self drilling rock anchor’s prestress; another one is how to meet bearing capacity of self drilling rock anchor which is needed in engineering. To sum up, it can be concluded into following points:
1. Determining use boundary reasonably.
Silty clay, whose plastic index is less than 17, can be used as permanent self drilling rock anchor’s anchoring; silty clay more than 17 can be used as temporary self drilling rock anchor’s anchoring.
Natural moisture content is greater than liquid limit. Sludge, whose natural void ratio is greater or equal to 1.5, cannot be used as self drilling rock anchor’s anchoring before through reinforcement treatment.
Sludge, whose natural void ratio is smaller than 1.5 or greater than 1.5, can be used as temporary self drilling rock anchor’s anchoring, but relative measures should be adopted to enhance self drilling rock anchor’s bearing capacity.
2. Adopting repeated high-pressure grouting to improve bonding frictional resistance between soil and grouting body.
Repeated high-pressure grouting is that exerting secondary or multiple high-pressure split grouting when cement paste intensity in anchorage section of self drilling rock anchor reaches to certain strength. It can enhance surrounding soil’s shearing force and grouting body’s bonding frictional intensity, especially for multiple high-pressure grouting, because of its unique structures (self drilling rock bar combines drilling and grouting together). Then, it can enhance bonding frictional resistance between soil and grouting body, bearing capacity of self drilling rock anchor in soft soil.