Abstract:

A favorable yielding performance of yielding bolt in soft rock tunnel with high ground stress and the stability of surrounding rock when release its deformation energy should be guaranteed As a result, an analytical design method for yielding pipe length of yielding bolt is proposed Based on the neutral point theory of bolt, the yielding effect of yielding bolt is taken into consideration in analysis of the interaction between surrounding rock and the bolt; the relative tensile deformation caused by yielding deformation along the tunnel radius is supposed to be coincide with the hyperbolic curve rule is assumed; and the calculation formula of internal forces of full length yielding bolt is deduced by establishing the equilibrium equation of axial tension on the two sides of bolt neutral point The axial force distribution of yielding bolt and its performance with the variation of yielding pipe length are obtained by application to Wanxichong Tunnel on KunmingYiliang Highway, and it is described as follow: the maximum axial force of the bolt decreases with the increase of yielding pipe length, while the distribution pattern of the axial force changes little Based on the abovementioned results, the design criteria for yielding pipe length is drawn as follows: (1) The lower limit of yielding pipe length is determined by the ultimate tensile force of yielding bolt to ensure that the bolt is not damaged due to pulloff (2) The upper limit of yielding pipe length is determined by adhesive frictional resistance acting on bolt at the wall of tunnel to guarantee the bolt neutral point theory established

Key words: tunnel, yielding bolt, yielding pipe length, neutral point theory, analytical design method