在地铁盾构法施工中，最难通过的应属“上软下硬”地层，其表现为刀具损伤快且无法常压及压气换刀。针对深圳市填海区施工的特殊性在实践中采用旋喷桩将盾构切口环及刀盘前方进行加固及仓内砂浆回填的方法，彻底解决了“上软下硬”地质条件下的换刀难题，保障了换刀人员的安全，同时实现了低成本及短时间恢复掘进。

For the shield construction of the subway tunnel, the “upper soft and lower hard” stratum layer is the most difficult to drill through. It is characterized by the fact that the drill bit is easily subject to damage and drill bit replacement cannot be carried out under atmospheric pressure or being pressurized. According to the particularity of the construction in Tianhai District, Shenzhen City, we adopt the method of stabilizing the cutting ring of the shield machine and the front part of the cutter head by rotary shotcreting pile and of mortar backfilling in the bin , which has completely solved the difficulty in drill bit replacement under “upper soft and lower hard” geological conditions, ensuring the safety of the person for drill bit replacement and making reboring with low cost and within short time.