Research On Bolt Load Transfer Mechanism Under Bed Separation Effect And Its Support Design

With the continual expansion in the production scale of coal mine and the wide use of large mechanical equipment, roadway section has been increased to meet the requirements of production and transportation. Coal mine roadway roof is mostly layered by the sedimentary rock. Large cross-section produces large surrounding rock deformation, and bed separation occurs easily, thus initiated problem of roadway support has to be solved. Surrounding rock was regarded as continuous homogeneous medium in the traditional supporting design, and the negative impact of the bed separation was not considered. Following the research of current anchoring theory and the status and existing problems of the mechanical mechanism of anchorage interface, the complexity of rock mass that is anchorage supported was considered in this paper, especially the effect of bed separation caused by underground excavation. The research has been done in the following aspects.The bed separation was classified based on its generation mechanism. Following the characteristic analysis of roof separation layer, the location and value of the bed separation were judged by theoretical and test method. Combined with the geological conditions of roadway of the N1205 working face in Ning tiaota Coal Mine, the location and value of the bed separation can be judged comprehensively, which provides a basis for anchorage support.Load transfer mechanism of bolt affected by bed separation was analyzed. Through the shear slide model, the elastic-plastic load transfer model was obtained under the different conditions of vertical and inclined bolt in single separation layer and multiple separation layers. Formulas of bolt stress distribution and load variation in the development of bed separation were gained. The bolt mechanical characteristics were obtained under the conditions of different bed separation values, location and angle.Laboratory model test was designed in order to observe the bolt stress distribution form in the crack propagation of rock mass and the relationship between bolt load and the amount of crack opening. Comparing with the theoretical analysis, the correctness and applicability of the theoretical model were verified. 2D discrete element simulation analysis was carried out on the bolt element under heterogeneous condition. The parameter influence law of the bed separation value and position were summarized, which was consistent with the theory.The effect of bolt loading caused by bed separation was considered in fully grouted bolt and end anchoring-grouting bolt, and the mechanics models were established respectively. According to the theoretical calculation and numerical simulation results, the stress distribution of bolt in the rock mass which has bed separation was achieved. Through the solving of systematic bolt load, the safety of the existing bolt support design can be evaluated, which also can provide the basis for supporting design.Achievements all above were applied in roadway supporting design of the N1205 working face in Ning tiaota Coal Mine. Compared with the traditional design method, the analysis revealed bolt load has exceeded the bearing capacity design value, so it is neccessary to adjust the design parameter of the support in order to ensure the safety of the design and construction. Through the solving of systematic bolt load, the diameter, interval and anchorage length of bolts were redesigned, then the reasonable pre-tension load was discussed. Field monitoring results showed that the supporting design considered the effect of bed separation was more safe and reasonable.