Research On The Equivalent Elastic Properties Of Rockmass Reinforced By Rockbolts Based On The Composite Theory Of Layered Material

Since support technique of shotcrete and rockbolts was adopted in underground excavations, it has changed support concept from passive support into active or overall support. This technique is to make full use of bearing capacity of surrounding rock and accepted generally in geotechnical engineering. Nevertheless, design theory for rockbolt support is not-well-thought. Its engineering design is carried out usually in terms of empirical or semi-empirical methods such as engineering analogy, and may also make use of information obtained by in-situ measurement for design feedback or construction guidance. At present, studies in rockbolt support are particularly concentrated on stress and deformation distribution of the rock mass in the vicinity of a single rockbolt. Although there is a difference in the studied scale, the studying methods and thought of composite material mechanics for fiber reinforcement can be used for reference in studying support system of rockmass and rockbolts. If the overall elastic properties of support composite material(SCM) can be analyzed by this kind of supporting theory of SCM, convenient and valid parameter for stability calculation of reinforced rock mass can be available and theoretical support can be also provided for the choice of new material and design parameter of anchoring in the design of underground structures. It is possible to make support system more economical, reasonable and effective.In this work, support system of rockmass and rockbots is considered to consist of three types of different constituent material which are rockmass, rockbolts and cement mortar. In order to study the reinforcement mechanism and overall elastic properties of this support composite material, an equivalent homogeneous elastic model of orthorhombic layers is established by making use of conditions of force equilibrium deformation compatibility and equal stored strain energies. Expressions for equivalent properties of SCM are given in terms of elastic properties of constituent materials, spatial and geometrical arrangements of rockbolts. On the basis of above analysis, the effects of the variation of rockbolt diameter and the mechanical behavior of rockmass to the mechanical properties of SCM are discussed.The diameter of the rockbolt also has an effect on the mechanical properties.The larger is the diameter, the larger is the increasing of the moduli of the rock mass, but variation of the equivalent elastic constants are little.When the mechanical behavior of rockmass varies, analysis shows that the more inferior are the elastic moduli of rockmass, the more obvious is the anchoring reinforcement effect. Studies indicate that improvement of mechanical properties of rockbolts to the inferior rockmass is better than that of rockbolts to the superior rockmass.