隧洞穿越高应力压密散体施工对策及其适应性分析

Measures and Adaptability of Constructing Tunnel Crossing Compacted Granite under High Geostress

滇中引水工程狮子山隧洞处于F_(Ⅲ-102)和F_(16)断裂构造夹持带,地应力高,其D_(1)^(1)钙质页岩、炭质页岩呈散体压密结构。地质分析表明,区域地质挤压构造残余高地应力是隧洞大变形的主要动力源,低抗载性劣化破碎结构是隧洞产生失稳变形主要内因。现场揭示隧洞破坏形式主要表现为开挖卸荷失稳坍塌、掌子面挤出、支护严重挤压变形。针对高地应力条件下散体压密结构的围岩特性和典型破坏特征,提出施工应遵循“预支护、快掘进、快支护、快闭合”的原则,并总结了适用于该地质条件的针对性施工对策:选用ST-20管棚钻机进行长15 m的Φ108 mm大管棚超前预支护施作与周边和掌子面围岩注浆加固;采取“及时强支护”并设置让压锚杆和长锁脚锚管抑制变形措施;施工期间加强围岩监控量测和围岩内部变形监测,实施动态控制,信息化施工。实践证明,隧洞穿越高地应力挤压破碎带时,采取对浅部围岩进行加固、主动支护与被动支护相结合的施工措施,能有效抑制围岩松动圈向深部发展与变形,有力保障隧洞安全顺利施工。

The Shizishan tunnel of the Central Yunnan Water Diversion Project runs through the fracture structure clamping belt between F_(Ⅲ-102) and F_(16) where the D_(1)^(1) calcareous shale and carbonaceous shale are loosely consolidated under high in-situ stress.Geological analysis shows that the residual high in-situ stress of geological compression structure is the major driving force of the large deformation of tunnel,and the low load-resistance and degraded broken structure is the main internal cause of the instability and deformation of tunnel.Site investigation reveals the damage of tunnel reflected as instability and collapse induced by excavation unloading,extrusion of working face,and severely deformed support.To tackle these problems,we propose a principle of“advance support,fast excavation,fast support,and fast closure”for tunnel construction.We summarize the construction measures applicable to the geological condition:1)advance support with 15mΦ108 mm large pipe shed by using ST-20 pipe shed drilling rig,and grouting reinforcement of surrounding rock of working face;timely strong support with pressure-relieving anchor rods and long-lock-foot anchor pipes to restrain deformation;dynamic control and informatized construction by strengthening deformation monitoring of surrounding rock.Practice has proved that,for tunnels passing through crushed zone of high geostress,construction measures such as reinforcing the shallow surrounding rock and combining active support and passive support can effectively restrain the deep development and deformation of surrounding rock’s loose circle,hence guaranteeing safe and smooth construction.