超 前 锚 杆

松散地层结构松散，稳定性差，若有地下水时则更甚。在施工中极易发生坍塌，在这类地层中施工时，除减少对围岩的扰动外，还应加强临时支护，临时支护可采用超前锚杆。
1． 施工方法
超前锚杆又分为悬吊式超前锚杆及格栅拱支撑超前锚杆。
1.1悬吊式超前锚杆
采用这种方法是在baopo前，将超前锚杆打入掘进前方稳定岩层内，末端支承在拱部围岩内专为超前锚杆提供支点的径向悬吊锚杆，或支承在作为支护的结构锚杆上，使其起到支护掘进进尺范围内拱部上方，有效地约束围岩在baopo后的一定时间内不发生松弛坍塌，为大断面开挖与喷锚支护创造了条件。施工中，因超前锚杆与悬吊锚杆的外露端往往不易直接相交，故以φ22的横向短钢筋焊在邻近的悬吊锚杆上，再焊在超前锚杆的末端上。
1.2格栅拱支撑超前锚杆
如图所示：超前锚杆的末端支撑在格栅拱架上。
Chaoqianmaogan

Loose loose formation, stability is poor, if it is even worse when groundwater. Easily occur in the construction collapsed in the construction of these strata, in addition to reducing the disturbance of surrounding rock, it should also strengthen the temporary support, temporary support can be used ahead of Bolt.
1. Construction Method
Lead anchor is divided into grid suspended ahead of arch support bolt and bolt ahead.
1.1 suspended ahead of Bolt
This approach is in the blast, before driving into the front will advance stability and rock bolts, the end of the supporting rock within the arch to provide the fulcrum for advanced radial suspension bolt anchor, or as a support for supporting structural bolt on to play a range of support driving rate above the arch, the effective constraint rock blasting within a certain period of time after the collapse relaxation does not occur for the large section excavation and shotcrete support created the conditions. Construction, due to advanced suspension bolt anchor and often difficult to directly intersect the exposed side, so as to φ22 short horizontal sealing the adjacent bolt on suspension, and then welding the end of the bolt in advance.
1.2 grid ahead of arch support bolt
Shown: the end of support ahead of bolts on the steel grid.