Design of cable bolts using numerical modelling.

摘要

Cable bolt supports are widely used as ground support in underground hard rock and coal mines. During the last two decades, the cable bolt technology has improved significantly and new types of cable bolts, new grouts and new installation methods and pumps have been introduced and successfully developed. The design of cable bolts is currently attempted by empirical methods based on rockmass characterization. However, until such methods do not take into account all the important parameters affecting the mechanical behaviour of cable bolts namely, the type of cable geometry, grout quality, stiffness of the host medium, the amount of confining pressure and the presence of end anchorage and pretension.; This thesis deals with the numerical modelling of cable bolts considering all of the above mentioned factors. To evaluate the shear bond stiffness of cable bolts, which simulate the interface between the cable bolt and the rockmass, a new empirical model is developed. A database with data of pull-out tests is constructed. Empirical relations were derived between the shear bond stiffness and the variation of confining pressure, the modulus of elasticity of host medium and the water:cement ratio. The relations were derived for three types of cables (standard cable, nutcase cable and garford bulb cable). A new numerical model using the finite element method is developed for the numerical simulation of cable bolts. Together with the empirical model for shear bond stiffness, the numerical model computes the load distribution along the cable bolt and thus can simulate fully grouted, partially grouted, end anchored and tensioned cable bolts. The model is implemented in an existing finite element code (e-z tools). Parametric analyses are performed on the new model, and proved useful in the demonstration of the role of each design parameter.; A new design methodology is proposed to evaluate the load distribution along the cable bolt. Two case studies are presented: a stope hanging-wall support by cable bolt in a hardrock mine and a tailgate secondary supports in a coal mine. A comparison with measurements in the field shows good agreement with computed forces.