STRESS AND ACTION MECHANISM OF ROCK BOLT IN LOESS TUNNEL
CHEN Jianxun1，QIAO Xiong1，2，WANG Mengshu3
(1. School of Highway，Chang?an University，Xi?an，Shaanxi 710064，China；2. School of Civil Engineering，Lanzhou University of Technology，Lanzhou，Gansu 730050，China；3. School of Civil Engineering and Architecture，Beijing Jiaotong University，Beijing 100044，China)
Abstract：In order to study the action effect and mechanism of rock bolt in loess tunnel，the stresses of 48 rock bolts in 3 loess tunnels in Wubao—Zizhou Expressway in Shaanxi Province are measured by in-situ tests and statistically analyzed. It is shown that under the condition of steel arch support，the arch systematic rock bolts in loess tunnel are compressed and the stress is very small；the feet-lock bolts in arch foot are mainly subjected to tension and the stresses of feet-lock rock bolts are larger than those of arch systematic rock bolts. The mechanical state of arch systematic rock bolts in loess tunnel is analyzed from the deformation of soil and anchoring effect of rock bolt and soil. It is revealed as follows：(1) After tunnel excavation，the arch of shallow loess tunnel settles entirely；and there is no anchoring section in systematic rock bolts. (2) After tunnel excavation，there is a large part of plastic area in deep loess tunnel；and there is no anchoring section in systematic rock bolts. (3) The anchoring effect of rock bolt and soil by cement mortar and anchor agent is not very well；so the anchoring force of rock bolt in loess tunnel is small. (4) Rock bolt is anchored in the first lining and inserted into the soil，which can constrain the soil inside. After the construction of the first lining，the arch systematic rock bolts are subjected to downward frictional resistance from soil，corresponding to negative friction in pile；so the arch systematic rock bolts in loess tunnel are compressed. From the above analysis，it is shown that under the condition of steel arch support，the support effect of systematic rock bolts in loess tunnel is not obvious，which can be ignored. Engineering practice shows that ignoring systematic bolts under the condition of steel arch support can reduce construction procedure，making construction safe and improving the safety of support structure；it also can reduce the engineering cost and shorten the construction period. It will achieve obvious economic and social benefits.
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2011, Vol. 30 
