| As an important means to maintain the stability of roadway,bolts/cables supporting has been widely used in the mine excavation.However,the conventional strength bolt cannot effectively prevent rockburst and slowly large deformation of rock mass around the roadway,which laid a hidden danger for the deep mining.Delightfully,the constant-resistance and large-deformation(CRLD)bolt with the stick-slip structure has been widely applied to support the surrounding rock mass,and has obtained excellent results for preventing the dynamic disasters and controlling the slowly large deformation and early warning the landslides.A large number of indoor and outdoor experiments investigate the characteristics of the CRLD bolt about the constant resistance,large deformation,negative poisson’s ratio structure and energy absorption.However,the theoretical analysis of the CRLD bolt is quite weak,only the statically constitutive relation is investigated.The dynamic theory of the CRLD bolt and the theory of the rock mass anchored with CRLD bolt are lacking,which makes no theoretical basis for all dynamic experiments and engineering applications.Therefore,the dynamic properties of the CRLD bolt and the mechanical behaviors of the rock mass anchored with CRLD bolt are further investigated,and some progress are achieved in the following aspects:1.The dynamic model is theoretically established for the single CRLD bolt and the theoretical results are experimentally verified with the SHTB impact tensile tests on the CRLD bolt samples.(1)The movement of the CRLD bolt under impact load is divided into three phases.In the stage of elastic deformation,the shank and the sleeve are relatively static,and the CRLD bolt only elastically deforms.During the stage of structural deformation,the CRLD bolt exports structural elongation with the relative sliding between the shank bar and the sleeve pipe owing to the internal force of the shank exceeding the constant resistance of the CRLD bolt.In the stage of elastic recovery,the shank and the sleeve are again relatively static and rebound and oscillate together.(2)In view of the CRLD bolt possessing different force conditions and movement situations under the different impact load,the impact load is divided into three categories:elastic impact load,stable impact load,and unstable impact load.Under the elastic impact load,the shank and the sleeve have no relative sliding.The CRLD bolt is elastically tensed and compressed and eventually returns to its original state.However,under the stable impact load and unstabel impact load,the CRLD bolt exports structural deformation with the relative slipping between the shank and the sleeve,and finally stabilizes at a certain amount of elongation(i.e.the slipping elongation).The essential difference between the stable and unstable impact load is that:under the stable impact load,no structural deformation will occur after the impact load ends;under the unstable impact load,the structural deformation will still occur after the impact load ends.2.The connection between each other of the combined CRLD bolts highly needs to be investigated due to the coupling support of the roadway in the engineering excavation.The dynamic models of the double parallel-connected CRLD bolts under the three types of impact load are theoretically established and the theoretical results are experimentally verified with the impact tensile tests on the CRLD bolts samples.Under the elastic impact load and stable impact load,the load-displacement curves of the CRLD bolts are characterized by the returning back(i.e.the curves have the part with a negative gradient).The difference is that:under the elastic impact load,the displacement eventually returns to the starting point so as to form a closed curve;under the stable impact load,the displacement finally does not return to the origin point with the structural defonnation and no closed curve is formed.In addition,under the unstable impact load,the load-displacement curve has no returning back due to the displacement continues to increase after the load completing.3.The mechanical behaviors of the rock mass anchored with CRLD bolt under different loads(such as constant load,ascending-type load,sinusoidal load and step load)are obtained,which are based on the physical model of the anchored rock mass.(1)The rock mass anchored with CRLD bolt undergoes three processes of initial stage,slip stage and stick stage,and then enters the periodic slip-stick stages until the anchored rock mass failed.In the initial phase,the rock mass is anchored by the elastic deformation of the CRLD bolt.Once the internal force of the CRLD bolt exceeds the constant resistance,the shank and the sleeve slide relatively to each other and the anchored rock mass enters the slide phase.In the slip phase,the deformation of the anchored rock mass maintains unchanged,while the internal force of the CRLD bolt is declining and the force of the rock mass is relaxed.After the relative sliding stops,the anchored rock mass begins the stick phase and the support is again provided by the elastic deformation of the CRLD bolt.As the deformation continues to increase,the anchored rock mass periodically slides and sticks until it eventually breaks down.(2)The mechanical behaviors of the rock mass anchored with CRLD bolt have great difference under the different loads.Under the constant load,the strain of the anchored rock mass is increasing whereas the strain rate is decreasing,and the stress is reducing in a step shape.Under the ascending-type load,the strain of the anchored rock mass is increasing whereas the strain rate is approximately zero,and the stress is rising in a sawtooth shape.Under the sinusoidal load,the strain and stress of the anchored rock mass both possesses the fluctuating characteristics,and the strain has a slightly rising trend while the stress has a slightly descending trend.Under the step load,the strain of the anchored rock mass is increasing and the stress changes in a concave-convex shape.(3)The mechanical behaviors of the rock mass anchored with CRLD bolt are compared with those of the rock mass anchored with rebar bolt under each different load.The growth rate of the strain for the rock mass anchored by CRLD bolt is gradually decreasing due to the existence of slip stage,so that the CRLD bolt can control the doformation of rock mass more effectively than the rebar bolt under the same conditions.On the other hand,the stress of the rock mass anchored by CRLD bolt is declining with the sliding,which relieves the supporting burden of the CRLD bolt,so that the CRLD bolt can provide a longer safety duration than the rebar bolt.4.The force and deformation of the rock mass anchored with CRLD bolts/cables and rebar bolts/cables are monitored and recorded in the return air roadway of 6-S204 mining face.The theoretical model and results are verified by the engineering analysis.(1)The force of the rock mass anchored by rebar bolts/cables is equivalent to the inputting load because rebar bolts/cables entirely rely on the deformation of the material itself to provide support.However,the force of the rock mass anchored by CRLD bolts/cables is reduced due to the output with structural deformation for the CRLD bolts/cables.(2)The deformations of the rock mass anchored by CRLD bolts/cables and rebar bolts/cables both increase with time.However,in the slip phase for the rock mass anchored by CRLD bolts/cables,the relative slide between the shank and sleeve belongs to the itself deformation of the internal structure for the CRLD bolts/cables,which does not cause the increase of the deformation for the anchored rock mass.Therefore,the growth rate of the deformation for the rock mass anchored by CRLD bolts/cables is slowed down,which indicates that the deformation of the rock mass anchored by CRLD bolts/cables is less than that of the rock mass anchored by rebar bolts/cables in the same duration.5.The physical model experiment of the roadway anchored by CRLD bolts/cables is conducted based on the return air roadway in the 121302 mining face of the Kouzidong Mine.The theoretical model and results are verified by the experimental analysis.The force and deformation of the simulated rock mass anchored with CRLD bolts/cables are deeply investigated in the effective support stage.During the stress loading period,the force of the anchored rock mass is no longer a linear increase whereas possessing a phased decline,which reduces the growth rate of the force so that the force increases in a sawtooth shape.During the stress holding period,the force of the anchored rock mass does not keep constant and the phased decline also occurs so that the force decreases in a step shape.On the other hand,the deformation of the anchored rock mass first increases linearly and then increases with the strain rate decreasing. |
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