Abstract:

In order to solve the technical problem of loose circle test in fractured soft stratum, a loose circle test technique for fractured soft rock tunnel with fulllength bonded glass fiber anchor as carrier is proposed. The test technology is based on the variation trend of the microstrain of the anchor, which can analyze the range of the surrounding rock loose circle according to the neutral point theory of the anchor. The measurement technology has been tested in the large deformation section of carbonaceous slate in Xingzishan Tunnel on DaliLincang Railway. The applicable results show that the fulllength bonded glass fiber anchor can effectively coordinate the deformation with the fractured soft surrounding rock in loose zone; the strain of the anchor is sensitive in different area of the surrounding rock and it can characterize the range of loose circle significantly. At the same time, the technical test accuracy can be compensated by the density of the strain gauge attached along the length of the bolt. The technology effectively compensates for the problem that the traditional loosecircle geophysical testing technology has high requirements on rock mass, which has good operability and applicability in the fractured soft surrounding rock stratum.

Key words: soft rock tunnel, loose circle of surrounding rock, glass fiber anchor, microstrain test