混凝土喷射机说明2.docVIP

中国矿业大学2007届本科生毕业设计 第  PAGE 75页 Where , is the length of bolted end ; is the length of outer part.  Bolt spacing a can be derived by the criteria that no slip occurs along bedding planes. Besides the above-mentioned conditions, the safety of the combined beam must be checked to prevent it from longitudinal instability. When all the conditions are satisfied, roof bolt parameters can ready be determined. As for sidewall bolts, their length and spacing can be derived by soil bracing theory in soil mechanics. It should be noticed when roof is composed of weak and loose strata, some bracing measures must be taken to protect the integrity of the fragile roof. Bolting of the gateway and its assessment Support assessment by discrete element method We consider two case in order to compare , first case: only the roof is bolted; second case: both roof and sidewall are bolted. Having been bolted in the first case, the roof has a obvious higher stiffness and strength, in the initial stage, only slight deflection occurs. However, with the sidewall coal failing and caving, the free span of the roof increases, the roof gradually enters unstable stage, subsiding and bedding separating as shown in Fig.5. Compared with the unsupported gateway, the gateway with roof bolted can keep stability for much longer time even it destabilizes finally. In the second case, the sidewall coal deformation and failure are strictly controlled by the sidewall bolts, the sidewalls are stable. Roof deflects only a small amount. Displacement can be hardly seen in the block diagram(Fig.6). The overall surrounding strata are in stable conditions. Even influenced by mining activity the gateway only fails locally, the roof is, however rather stable. It is, thus important to adopt a comprehensive bolt support pattern including the sidewalls. Bolting scheme and its implementation Based on the inclined combined beam theory, gateway loosed zone measuremen