Study Of Peeling Disease Treatment On The Roof Of Sandstone Grottoes By Micro-anchor Bolt Technique

The Chinese grotto art has an important place in Chinese and world culture. The art of grottoes of china is one of the very rich in content and form, which has great artistic, historical and scientific value。According to the incomplete statistics, there are more than 600 existing grottoes which throughout the country, in which sandstone account for 80%. Most of the grottoes have been suffered a certain extent damage even collapse due to natural forces and human activities during more than 2000 years long history. Falling of the dangerous rock mass and the flake peeling are one of the main roof diseases of grottoes.After years of study and practice, traditional rock anchor(anchor rope)techniques have been successfully applied to reinforce the dangerous rock mass on the roof of the grottoes, the design theory and practice tend to be mature. Yet, for the flake peeling disease on the roof of grottoes, which has the characters of shallow in depth, extensive in area, small in bulk, rich in culture information, the traditional anchor technique with the characteristics of large borehole and deep anchorage is obviously not suitable. Therefore,this paper is going to develop the micro-anchor bolt technique for curing the flake peeling disease on the roof of sandstone grottoes and study the related parameters through the indoor model experiment.This paper has produced the indoor simulated rock which has similar composition and strength with the scene cave through indoor mixture experiments, the compressive strength is 13.56 MPa and the density of 2.13 g/cm3.By adding different amounts of fly ash which has been surface modified by coupling agent KH-560 to determine the appropriate ratio, and the mechanical performance indexes has improved greatly. By testing the operable time, the initial time and the curing time in different temperatures found that the temperature significantly affected the mixed slurry curing reaction, thus we shall take reasonable measures in grouting work. We have found the following conclusions through a series of pull tests: In the short length of bolt(anchor length is less250mm) and the same anchorage conditions, the steel bolt anchoring effect is greater than the wood anchor and the ultimate pullout force increases with the growth of the lengthand the diameter of the anchor bolt; the suitable drilling aperture should be bolt diameter+4mm;Change the wooden bolt surface morphology effectively improve the bonding effect between the anchor bolt-grouting body and the interface and enhance the anchoring effect.