| Bolt support has become an indispensable support method in the field of geotechnical engineering.Traditional bolts often break and fail,which can not be applied to geotechnical engineering with large deformation and instability.In view of this,Prof.Manchao He had designed and developed constant resistance and large deformation(CRLD)bolt with negative Possion's ration in 2010.This bolt has been successfully applied in coal mine,slope and other engineering fields,and it has achieved good practical results.In this paper,the basic method of numerical test is used to further study the support mechanism of CRLD bolt under various working conditions.The main research contents are as follows:(1)The absorbable energy equation of CRLD bolt has been obtained.When the absorbable energy of CRLD bolt is equal to the energy released from the surrounding rock mass,the CRLD bolt can be inserted into the surrounding rock mass to achieve the goal of "deformation in resistance,resistance in deformation and absorbing energy by constant resistance characteristic to prevent disasters".(2)In order to study the tensile mechanical properties of CRLD bolts,the numerical simulation of the tensile strength of the CRLD bolt was carried out by RFPA static software.The experimental results show that the maximum plastic strain is 12 times of the maximum value of elastic strain after constant resistance tensile fracture,and the stress value fluctuates in the range of 345.07—347.26MPa during plastic deformation,and the fluctuation is stable.It shows the bolt has good constant resistance characteristics.The results of numerical experiments are in good agreement with Prof.Manchao He laboratory test results,which verifies the accuracy and reliability of the numerical test method.Based on this,the numerical method is used to study the interaction principle of CRLD bolt and surrounding rock under loading,analysis of stress characteristics and deformation and failure characteristics of anchored rock mass,and comparative analysis of the support effect of traditional bolt and CRLD bolt.It is shown by test results that the supporting effect of the constant resistance bolt is better than that of the traditional bolt.When CRLD bolt is added to rock mass with a certain thickness,many cracking phenomena occur in rock mass,and a large number of shear mode acoustic emissions are generated on the surface of the anchor,but this bolt is not broken.The CRDL bolt with bamboo knot effect has great constant resistance(mainly reflected in the large plastic deformation that can occur with the deformation of surrounding rock after the bolt is stressed)and lateral expansion characteristics of negative Passion's ratio,which greatly improves the anchoring role of the bolt.Based on the above principle,when negative Passion's ratio is at different positions on the rod,this kind of anchor has the anchoring function of full-length anchor,end anchor and multi-point wedge expansion.(3)The RFPA static-dynamic coupling version software is adopted to study the support effects of traditional bolt and CRLD bolt under static and dynamic loads.Through numerical comparison tests,it can be known that the CRLD bolt can effectively control the deformation amount and deformation rate of the laneway surrounding rock,reduce the total number and growth rate of accumulated acoustic emission,reduce the stress on the elements in the model and protect the stability of the laneway.This paper verifies that the constant resistance bolt has better impact resistance mechanical properties than traditional bolt,and provides an effective way to prevent and control dynamic disasters such as rock burst.(4)The precursory information of sliding failure of faults and slopes is analyzed,that is,"stress sudden drop,catastrophe occurs".Before the fault sliding failure,the number of acoustic emission and the acoustic emission energy increase slightly,which is opposite to the stress.Before the sliding failure of the slope,it can be seen that the stress decreases from the maximum value and the AE curves begin to show a significant rise,the two curves display opposite laws.(5)The all-weather continuous real-time monitoring is carried out during the drilling and detonating process of Yangshan tunnel in Menghua railway,and the waveform characteristics of the microseismic event are analyzed.Through the recorded microseismic monitoring datas,the relationship between the deterioration of the rock mass and the microseismic activity is discussed in the process of large deformation and failure of tunnel roof.Research results show the microseismic monitoring system can be used to detect precursor information of tunnel roof damage,namely the frequency of microseismic events and microseismic energy appear"lull" and "active period" during the whole failure process,and there are two peaks in the whole process,it is accompanied by the destruction of surrounding rock,when the second peak occurs;The damage range and strength of the surrounding rock can be delineated by the space time magnitude distribution of the microseismic events and microseismic events density nephogram.According to the geological conditions of Yangshan tunnel,a numerical model is established to analyze the influence of CRLD bolts on the tunnel surrounding rock.The numerical simulation results show that the quantity and energy of acoustic emission are greatly reduced,which restrains the deformation and failure of the surrounding rock roof. |
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