| Mineral resources are one of the main engines for China's economic growth,and It is an important pillar of our efforts to build a world-class powerhouse,Its strategic significance is self-evident.Therefore,since the founding of our country,mineral resources have used and exploitation upward trend.Due to the long-term mining and the continuous increase in the industrialization and mechanization of the country,most of the shallow mineral resources are gradually depleted.The country's mineral resources strategy has gradually shifted from the shallow to the deep.However,after entering the deep mining,various geological conditions have become more complicated,mining has become more difficult,and dangerous factors have increased.As a result,the safety issues of many projects need to be solved.Taking open-pit mining as an example,it is the main mining method for our country's metal mines.With the increase in the scale of mining and the depth of mining,the problem of large deformation of high and steep slopes becomes increasingly prominent,eventually leading to slope instability and other potential dangers.Increased,which poses a great threat to people and equipment.Because the slope deformation is not easy to detect,and when the slope reaches a slippery state,there are various reasons that affect the final damage.Therefore,it is not enough to ensure the stability of the slope only by controlling the influencing factors.Maximize the protection of slopes and surrounding rocks before disasters occur.At present,the protection and monitoring methods of open pit slopes at home and abroad are anchor cables as the main carriers.The extensive application of anchor cable in engineering is not only low cost,convenient and simple,but also has strong mechanical properties(the bearing capacity,deformation,etc.)and these mechanical parameters determine the effectiveness of anchor reinforcements.The slope height increases with the increase of the mining depth,the surface of the rock mass increases,the gravitational potential energy increases,the joints develop fully,and the influence of natural factors and human factors increases,resulting in a large deformation of the slope and stability greatly reduced,these unfavorable factors impose higher requirements on the anchor cable.For the traditional anchor cable,due to the limitations of the material itself and its own structural defects,it cannot be well adapted to the large deformation damage caused by the surrounding rock,and the support was invalidated.In view of the limitations of the mechanical properties of the traditional anchorage cable and the seriousness of the engineering environment,it is urgent to develop the support cable with supernormal mechanical properties,and build a new constitutive relation of the nonlinear rock mass,and then form a complete set of anchorage cable supporting system suitable for large deformation of rock mass.In 2011,the team of Academician He Shichao at the State Key Laboratory of the Deep State(Beijing)team developed a constant-resistance anchor cable with high constant resistance,large elongation,strong energy absorption,and a negative Poisson's ratio effect on the overall structure,abbreviated as NPR anchor.Since the development of NPR anchors,a series of experiments have been conducted in the laboratory,including static experiments and dynamic experiments,and have been successfully applied to the stability monitoring and control of many open-pit mine slopes with remarkable results.By summing up the research results of the past years and combining a large number of experiments,it has been found that so far there has been no research:First,the study of the deformation of the varistor in the NPR cable,the movement of the constant resistance body in the varistor,the negative Poisson's ratio of the NPR cable,and the energy absorption characteristics;Second,establish an elasto-plastic mechanical model suitable for the NPR anchor cable deformation state.At present,the design of the NPR cable for the specific constant resistance is based on the experience and the two-dimensional elastic theory.In practice,the constant resistance of the NPR cable is produced by the interaction between the constant resistance and the constant resistance body.In this process,the rheostat is not only elastically deformed,but also undergoes some plastic deformation.Among them,the plastic deformation has the greatest effect on the constant resistance.It is a three-dimensional elastoplastic mechanical model is established,and its accuracy is verified.It provides some theoretical support for subsequent design of constant resistance;Third,Depth analysis of several key factors affecting the constant resistance of NPR anchor cables.Constant resistance is one of the core factors that determine the energy absorption of NPR anchor cables,and it is also an important mechanical parameter for effective reinforcement of surrounding rock masses.Therefore,it is very important to study several parameters that affect constant resistance for designing NPR anchor cables with different constant resistances;Fourth,according to the scientific concept of“predicting deep geological tectonic activities and effectively controlling local active faults”proposed by Academician He Manchao,it is urgently necessary to break the deformation length of existing NPR anchors,increase the energy absorption level,and design a reasonable anchor structure guarantee,constant resistance stability.In view of the above four aspects,the study in this paper takes the static characteristics of NPR anchor cables as the breakthrough point,adopts working principle analysis,exploration of deformation laws,derivation of elastoplastic mechanics theory,structural innovation,and analysis of geometric dimensions,and through a series of indoor The combination of statics and simulation analysis.The contents and main conclusions of the various parts of this paper are as follows:First,the system introduced the concept of NPR anchor cable support,that is,coupling NPR anchor cable and surrounding rock into a system,using its high-constant resistance to resist the residual external force load of the surrounding rock,using its large deformation characteristics to control the degree of deformation of the surrounding rock,the excess deformation energy in the surrounding rock can be absorbed by its energy absorption characteristics,so as to ensure that the NPR anchor stays in a stable state without fracture failure.Further,by analyzing the energy balance equations of NPR anchors and rock masses,it is concluded that"any rock mass of engineering geological structure,after coupled support with NPR anchors,will have the same mechanical properties as NPR support material."in conclusion.Second,in order to analyze and study the static properties of NPR anchor cables,He Manchao developed HWL-2000 constant resistance large deformation anchor cable static tensile experimental system.In this paper,the composition,component parameters and rationality of tensile rate of the NPR anchor cable static tensile test system are described and analyzed in detail.Through the experimental system,the NPR anchor cable was tested,the basic parameters of the test piece,the experimental preparation and experimental methods,and the experimental process were described in detail,and the phenomenon appeared in the experimental results was analyzed scientifically.In this paper,the NPR anchor cable specimens of 1000mm length(constant resistor)are taken as the object of study.The constant resistance change of the NPR cable during the tension process,the strain rule of the varistor,and the change law of the expansion are described in detail,static/dynamic negative Poisson's ratio and energy absorption and other mechanical parameters change.Discover the following three points from the experimental results:First,during the process of large deformation of NPR anchors,the same strain law will occur at each unit point of the surface of the rheostat.The reason for the formation of this law is related to the motion of the constant resistance body;Secondly,By coMParing the measurement before and after the radial test of the rheostat and the self-developed radial measuring equipment,the expansion law of the NPR cable is obtained,effective demonstration of the negative Poisson's ratio effect of NPR anchors;Third,the NPR anchor cable was measured by a thermal infrared imager and a laser thermometer,and its superior energy absorption characteristics were visually verified.Third,NPR anchor cable constant resistance is one of the factors that affect the state of energy absorption,so in the design of a specific constant resistance NPR anchor cable can not rely on experience alone,but also need a reasonable theoretical formula with it.After analyzing the NPR anchor cable,it is different from the pure Lame problem and the thin-walled cylinder problem.It is necessary to discuss the approximator of the constant-resistance device as a thick-walled cylinder,and establish three-dimensional and two-dimensional elasto-plastic mechanics models for NPR anchor cables.At the same time,the actual geometric parameters of all NPR cables are substituted into the theoretical constant resistance value,and coMPared with the tensile experimental values,it is found that the constant resistance value obtained by the three-dimensional elastic-plastic mechanical model is closer to the actual force value,and it provides some theoretical support for designing NPR anchors.Fourth,through the establishment of three-dimensional elasto-plastic mechanical model,it is found that the key factors affecting the constant resistance of NPR anchor cables are:The strength of the rheostat material,the geometry of the rheostat(thickness,inner and outer diameters,etc.),the angle of the inclined surface of the constant resistance body,the plane length of the constant resistance body,and the friction coefficient,etc.These changes in the parameters are constant to the NPR anchor cable resistance has a very big i MPact.For this reason,the maximum constant resistance value of NPR anchor cable is obtained by optimizing each parameter and it has certain reference value for designing NPR anchors.Fifth,In order to conscientiously implement the scientific concept of"prediction of deep geological fault activity and control of local geological activity faults"proposed by Academician He Manchao,the research group put forward higher requirements for the energy absorption capability of NPR anchor cables.For the first time,a breakthrough experiment was conducted on the stability of the NPR anchor cable deformation and constant resistance.From the original 1000mm~2000mm tensile strength and 495kN~547kN constant resistance,which are gradually increased to the deformation of 3000mm~4000mm and the constant resistance of 550kN~723.7kN,and increase the energy absorption effect from the original4.21?10~5~1.09?10~6 J to the4000mm deformation3.2?10~6J.At the same time,the structure of the constant resistance body is designed,make the constant resistance of the NPR anchor cable is increased,and the same law of fluctuation as the NPR anchor is presented in the mechanics law,which ensures the stability of the constant resistance.In summary,the NPR anchor cable has good mechanical properties and exhibits a certain negative Poisson's ratio effect through static tensile tests.The NPR anchor cable is put into the engineering practice,its superior mechanical properties can not only absorb the excess deformation energy in the rock body,but also have a good control effect on the large nonlinear deformation of the rock mass,so that the maximum degree of maintenance is good,and take the rock mass stability and integrity,and it has a positive effect on mine safety and sustainable development.It has significant social and economic benefits. |
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