Stably Control Technology And Weakening Instability Mechanism Of Post-peak Anchorage Bearing Structure In Soft-rock Roadway

Bolt was acted on the rock mass in and outside anchorage range for high stress and soft rock roadway. Supporting and reinforcing function were provided by bolt for the fractured rock mass in anchorage range under the bolt’s pretention and anchorage effect. And anchorage bearing structure with self stabilizing ability was formed by bolt and fractured rock mass. The load outside the anchor range was beared and the deformation of deep rock mass was controlled by the bearing structure. Therefore, the anchorage bearing structure which had been formed by bolt and fractured rock mass was key facter which could control deformation of high stress and soft rock roadway by bolting with wire mesh. Site survey, laboratory test, theoretical analysis, numerical simulation, field monitoring and field test were applied to study the strength and stability of post-peak anchorage bearing structure.Firstly, aim at post-peak anchorage body which was the basic composition unit of post-peak anchorage bearing structure, similar simulation triaxial loading test with large scale was carried out. The similarity ratio of bulk density, geometric and stress were 1.53, 3.5 and 5.34. The method of pre loading and unloading complete test block was applied for making post-peak fractured rock mass. Whereafter, loading and failure characteristics of post-peak anchorage body were studied after installing bolts and loading. There were increasing stage, stable stage and decline stage in loading process of post-peak anchorage body under the situation of triaxial loading. Meanwhile, there were several peak values in the stable stage.Secondly, it was the basic assumed condition that post-peak anchorage body had met mohr-coulomb criterion. And using the data of stress and deformation by laboratory test, the strength decay model of post-peak anchorage body was modelled by selecting equivalent cohesion and plastic shear strain as strength parameter and plastic parameter. On this basis, the capacity decay model of post-peak anchorage bearing structure was modelled under limit equilibrium condition. With dilation and expansion deformation of the rock mass in bearing structure, there was positive correlation between bearing structure capacity for deep rock mass with equivalent cohesion of post-peak anchorage body. In other words, there were increasing stage, stable stage and decline stage in loading process of post-peak anchorage bearing structure. The weakening mechanism of bearing structure was revealed.Thirdly, the strength decay model of post-peak anchorage body and deformation parameter was embedded numerical simulation model, and instability characteristics and process were analysed. With weakening of rock mass in and outside anchorage range, the stability of bearing structure decreased duing to that dilation deformation of rock mass in bearing structure and its outer boundary displacement had been incearsing. And stability of sidewall centre and springing line significantly decreased causing stability of arch bearing structure being decreased. Finally, overall instability of postpeak anchorage bearing structure was occurred.Based on the above study, the compensation principle of post-peak anchorage bearing structure was proposed. The position which was easy to weaken strength and lose stability by strength and shape of bearing structure was confirmed. And then, reasonable compensation time and measurement were implemented for compensation of structure strength and stability so as to decrease or restrict the dilation deformation of rock mass in and outside bearing structure. The capacity of post-peak anchorage bearing structure was fully exerted to reduce inhomogeneous deformation ratio of bearing structure. Meanwhile, the compensation mechanism which contained compensation measurement, compensation time and compensation position was proposed.Based on compensation principle and mechanism of post-peak anchorage bearing structure, the stably control technology which included basic supporting scheme, grouting reinforcement scheme and structure compensation scheme was proposed and successfully applied in field test.