Development of design method for support system of cavern using cable bolt

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Rock bolts or cable bolts have been used as a primary support member of underground openings in the last two decades. However, a clear explanation for the support effect of those bolts has not been made sufficiently. In order to clarify the support effect of those bolts, the failure mechanism in a pull-out test of them has been discussed. Then a main support effect was explained by bond strength of rock bolts and cable bolts, and it is necessary to visualize wider area globally and to discuss the failure mechanism of bolt-grout interface, grout and rock mass. After the clarification, the design method for support system of cavern using rock bolts or cable bolts should be discussed.In this research, patterns of the failure in a pull-out test of rock bolt and cable bolt firstly were visualized by X-ray CT scanner to supply the basic data for the detail discussion on the bond failure of rock bolt and cable bolt. In the pull-out tests, a comparison was made between two types of rock bolts and cable bolts. From the results, it was shown that the microscopic failure mechanism is evaluated as the different failure mode. Secondly, the Shear Resistance Model(SRM) was suggested from analyses of the pull-out test in detail. Then the constitutive model of a cable bolt was constructed, based on the SRM. It was clarified that the behavior of cable bolt during the pull-out test can be simulated precisely using the constitutive model. Furthermore, the Characteristics Curve of Cable bolt(CCC) was calculated by the SRM, then a support design of cavern using cable bolts was performed, using the CCC. As a result, the suggested model was convenience for designing embedment length of cable bolt around a cavern.