Abstract:

During shield tunneling in the composite strata consisting waterrich sand and silty sandstone in Nanchang, difficulties such as water/muck gushing, muck blocking, poor muck plasticity, waterrich muck and highlypermeable muck may be faced. In the paper, the ground conditioning applied in the construction of ZhongZi running tunnel and BaBa running tunnel on Line 1 of Nanchang Metro is studied. Conclusions drawn are as follows: 1) Liquid highmolecular polymer may be taken as the common measure to control the water/muck gushing; Foam may be taken as the ground conditioning agent in silty sandstone geology and waterrich gravel sand strata; 2) In the composite ground consisting of sand gravel and silty sandstone, some bentonite or highmolecular polymer may be added so as to solve such problems as low fluidity of mucks, water/muck gushing and muck blocking; 3) Where the volume of the sand gravel is not more than 1/3 of the total volume of the mucks, foam and dispersing solution may be used for grounding conditioning; Where the volume of the sand gravel ranges from 1/3 to 2/3 of the total volume of the mucks, bentonite and foam solution may be used for grounding conditioning; Where the volume of the sand gravel is equal to or larger than 2/3 of the total volume of the mucks, bentonite solution (with the waterbentonite ratio being 8∶〖KG-*2/3〗1) and foam solution (with the foam concentration being 3%) may be used for grounding conditioning, and the consumption of bentonite shall be increased. 

Key words: Nanchang Metro, earth pressure balanced (EPB) shield, waterrich gravel sand, silty sandstone, composite ground, foam, highmolecular polymer, ground conditioning