Study on Deep-hole Pre-grouting for Shallow Tunnelling in Gravel Stratum

Gravel stratum is a kind of one with loose structure, poor arching capacity and strong permeability; meanwhile it is eementingless and low in self-stability. At present, construction technique and method of shallow tunnelling in this stratum are not so perfect, such as conduit pore-forming process, grouting material selection, grout proportion, grouting pressure and grouting capacity parameter, which are less of experience for reference during construction. Based on the engineering background of the Shallow tunnelling test section in Beijing Metro Line 9, deep-hole pre-grouting experiment was done under the condition of gravel stratum. This paper compares and analyses the laws and different characteristics of pore-forming effect, drilling efficiency, grouting pressure,grouting capacity, grout proportion and grouting reinforcement effect among five pore-forming methods as well as two grouting methods, which are progressive style and retrograde style, and proposes a deep-hole pre-grouting method which is suitable for gravel stratum. The research conclusions will provide useful reference for following construction of the Beijing Metro Line 9 and deep-hole pre-grouting in similar strata.