Analyzing and studying factors for determining neutral point position of fully grouted rock bolt

The neutral point theory is the important theory in underground engineering reinforcement theory. At present, the formula to determine neutral point position has been existed some unreasonable place. The neutral point theory had been further consummated and improved on the foundation of pre-researchers. Base on the developed analytical model and the theory of frictional resistance is zero at the neutral point, the factors have been detailed analyzed for affecting the neutral point position; and the correlations have been gained which affecting neutral point position. Through analyzing, it is revealed that the hydrostatic primary stress, bolt length, bolt spacing having no influence to neutral point position, and the radius of tunnel, Young's moduli of rock and bolt, the bolt diameter having remarkable influence to it. Among them, it is linear relation among the radius of tunnel, the bolt diameter with the neutral point position, but it is exponential function relations among the Young's modulus of rock and bolt with the neutral point position. The relationship of Young's modulus of rock mass and neutral point position presents exponential decreasing; the relationship of Young's modulus of bolt and neutral point position presents exponential increasing. Through the factors analyzed, it has obtained that the general functional between the neutral point position and the correlation parameter, for further to study the neutral point theory providing the certain reference significance.