蘑菇山隧道超浅埋段暗挖法施工技术

Construction Technology of Undercutting Method for Serious Super Shallow-buried Section of Mogushan Tunnel

合福客运专线闽赣段蘑菇山隧道DK 454＋545~DK 454＋536段以埋深1．2 m的超浅埋方式穿越“V”字型山坳常年泉水出露自然沟,暗挖施工时如何避免出现冒顶、涌水等安全事故成为施工控制的关键。为此,现场首先通过改移自然沟、在拱顶回填10%水泥碎石改良土板结防渗及新建排水沟对地表进行排水处理；进而以管棚工作室为依托,实施40 m注浆长管棚及小导管补充注浆预支护加固措施；最后采用三台阶临时仰拱法开挖掘进。施工监测结果表明：拱顶下沉、围岩收敛、地表沉降最大值分别为6．5 mm、5．8 mm、7．2 mm及最大收敛速率分别为3．1 mm/d、2．8 mm/d、4．2 mm/d,均处于稳定状态,且初支及洞顶覆盖层未出现开裂、塌陷等现象,有效控制了洞周围岩变形及地表沉降。充分说明暗挖法施工技术所采取措施合理可行,方案安全可靠。

DK 454＋545~DK 454＋536 section of Mogushan tunnel in Min-Gan section of Hefei-Fuzhou passenger dedicated line passes V type mountain natural gully with spring exposed throughout the year with the super shallow bur-ied depth of 1. 2m, how to avoid roof fall, water burst and other safety accidents in the construction with undercutting method is the key of construction control. Therefore, firstly the drainage treatment is performed by removing the natural gully, backfilling 10% cement gravel improved soil, hardening and seepage controlling and building a new ditch ;and then, making use of pipe shed work room, the reinforcement measures of 40m grouting long pipe shed and small duct supplementary grouting pre-support are implemented;at last, excavation is done by using three-step temporary inverted arch method. The construction monitoring results show that the maximum and the maximum rate of convergence for vault sink, surrounding rock convergence and surface subsidence are respectively 6. 5 mm, 5. 8 mm, 7. 2 mm and 3. 1 mm/d, 2. 8 mm/d, 4. 2 mm/d,all of which are in a stable state without crack, collapse and other phenomena on primary support and top covering layer, the rock deformation and surface subsidence are controlled effectively. It shows that the measures for undercutting construction technology are feasible and rational, the scheme is safe and reliable.