The Collapse Treatment of Self Drilling Anchor Bolt in Diversion Tunnel

During the construction of diversion tunnel in water conservancy projects, collapse is impossible to be avoided, so adopting self drilling anchor bolt to handle with is an efficient technical method.
It has the function of drilling holes and it combines drilling, grouting and anchoring together. Self drilling anchor bolt has been mainly used for excavation support or slope stabilization in IV or V cave surrounding rock and concretion in positions where is easy to collapse, such as gravel stratum. Take a middle-sized hydroelectric station for example, the collapse treatment of self drilling anchor bolt in diversion tunnel has been introduced as following:
1. Woven bag embankment.
To avoid stratum collapse and stability-lost, common woven bags filled with gravel and waste materials are put at footing or surface of collapse body. It has the function of stabilizing collapse body.
2. Spraying concrete on the surface of collapse body.
To avoid slurry leaking out, C20 concrete with 15cm should be sprayed outside woven bags.
3. Self drilling anchor bolt is installed on the apex of arch and grouting.
Adopting drilling machine to install self drilling anchor bolt with drill bit and reach to designed depth. When it needs to be lengthened, coupling is used to connect. Discharging drill machine and installing stop-grouting plug in self drilling anchor bolt. When the pressure of grouting is big, anchoring agent is used to block. Adopting common injection pump and connecting one end of self drilling anchor bolt with it rapidly. The pressure of grouting is generally controlled between 0.3Mpa and 0.5Mpa. Installing plate and nut, then removing grouting equipment and wait for solidification.
4. Settling self drilling anchor bolt and grouting fully in partition wall near collapse locations.
5. Subsequent construction.
Parts above collapse body are grouted; stratum is consolidates; excavating collapse body and diversion tunnel; the method of short-footage and strong-support is adopted to support project.
Adopting above methods can handle complex collapse sections successfully and self drilling anchor bolt plays good functions on anchoring and grouting in loose rock bodies. Self drilling anchor bolt can dill and bore at the same time, it is convenient and rapid. Also it can solve problem of anchor bolt that can’t insert into the bottom of hole. After drilling holes, it doesn’t need to drill grouting hole, which can reduce cost, simplify construction procedure and guarantee construction period.