| Rock is the object of direct contact with underground engineering.The research on the deformation and damage of rock is not only an important topic of rock mechanics,but also plays an important role in the prevention and safety of accidents in the actual production and construction of underground engineering.In this paper,yellow sandstone is taken as the research object.The uniaxial compression damage acoustic emission monitoring experiment and digital speckle observation experiment are carried out by using DISP acoustic emissionsystemandDICdigitalspecklesystem.The three-dimensional destruction process of rock is carried out by RFPA~3DD numerical simulation software.The purpose of the simulation is to comprehensively study the three-dimensional failure process and acoustic emission characteristics of the yellow sandstone.The variation law of acoustic emission time domain and frequency domain parameters,the number of acoustic emission events,energy characteristics and three-dimensional distribution characteristics,the evolution of deformation field during rock failure process and the three-dimensional space failure process of rock are analyzed.The main conclusions drawn are as follows:(1)The displacement field and strain field of the uniaxial compression deformation process of the yellow sandstone are non-uniformly evolved,and the zoning phenomenon of the deformation field of different states will occur.The position and area of the deformation field will change continuously with the loading,when it is close to the rock damage.At the junction between different partitions of the displacement field,the rock is prone to rupture,and the partition of the strain field is gradually transformed into a localized zone.The location of the localized zone of the strain field is often the potential rupture position when the rock is destroyed.The non-uniform evolution of the displacement field and the strain field is the non-uniformity of the rock material and the nonlinear failure of the rock when it is loaded.(2)In the uniaxial compression failure process of the yellow sandstone,the acoustic emission ringing count and absolute energy appear in large quantities,and the cumulative ringing count and accumulated absolute energy will explode.It is worth noting that the ringing count and absolute energy are active during the initial stage of loading,because the structural defects or weak areas in the rock have been significantly damaged,and the stress drop appears in the corresponding position of the stress curve.In the uniaxial compression failure process,the yellow sandstone always has a large number of amplitude signals of 45dB-55dB.The duration of the signal is mostly above 300μs.When the rock reaches the damage,the number of high amplitude signals will increase greatly,and the duration will also increase.Significantly elevated.(3)The main frequency of the uniaxial compression failure process of the yellow sandstone has obvious segmentation,mainly concentrated in the five frequency bands of 98KHz-102KHz,148KHz-150KHz,225KHz-250KHz,270KHz-280KHz,290KHz-320KHz,among which 98KHz-102KHz,225KHz-The acoustic emission signals of the three frequency bands of 250KHz and290KHz-320KHz are relatively large throughout the loading process.As the stress increases and the loading process progresses,the proportion of the main frequency signal of the acoustic emission high frequency band will gradually increase.The variation of the number and distribution of the main frequency signals in different frequency bands is different from the internal damage type of the rock,the accumulation of damage and the stress state.The reaction is related.The loading and failure process of the yellow sandstone will gradually increase with the increase of the stress,and the distribution range of the average frequency and the center frequency will increase before and after the rock failure.(4)In the uniaxial compression failure process of the yellow sandstone,the acoustic emission event will explode in the position where the stress drop occurs,and the number of acoustic emission events will increase at the initial stage,corresponding to the damage of the original structure or weak zone inside the rock,stress 0.2.The number of rock acoustic emission events in the two stages of-0.4σc and 0.4-0.6σc is small,and the growth rate is very slow,which is the quiet period of the acoustic emission event.The large number of rock cracks are generated,developed and penetrated,which will generate a large number of acoustic emission events in the corresponding damaged areas.High-energy and medium-energy acoustic emission events are sensitive to cracks and weak areas inside the rock,which can cause obvious damage to the rock.In addition to being sensitive to large cracks that cause significant damage to rocks,low-energy acoustic emission events can also respond well to damages such as closure and compaction of microcracks within the rock,friction between material particles,and throughout the process of stress growth.Low-energy acoustic emission events are always present,and their distribution not only corresponds to the location of the macroscopic cracks of the rock,but also exists in the interior of the rock and other locations on the surface and has a certain number of distributions.The number,energy characteristics and three-dimensional distribution characteristics of acoustic emission events of rock during loading deformation have a good characterization of the space-time development of rock internal cracks and the accumulation and evaluation of rock damage.(5)The numerical simulation of RFPA~3DD in the process of rock three-dimensional space damage shows that rock failure is a process of unit damage and crack initiation,development,collection and penetration,and macroscopic damage is formed.The expansion and penetration of cracks is a three-dimensional development process from rock.Cracks on the surface are difficult to judge the development of cracks inside the rock.The surface cracks may gradually spread from the surface to other surfaces or the interior of the rock.It is also possible that the damage inside the rock accumulates and the internal cracks gradually reach the surface.One or several cracks in the rock failure process play a major role in the development of the failure process,and the final macroscopic fracture is determined by the development of the main crack.Some of the lower strength particles,cement or mineral components of the rock itself are broken first,and these broken units tend to be crack initiation sites.The damage of the rock will occur simultaneously on the surface and inside the rock.The crack on the surface will gradually expand to the inside,and the internal damage will gradually form a connection with the surface crack.(6)The acoustic emission events of rock failure process are closely related to crack initiation,development,collection and damage of rock materials.Acoustic emission events are mainly distributed near the rock crack surface and the damaged area.The acoustic emission events generated by compaction and closure of micro-cracks and pores in the compaction stage are low.The initiation,development and collection and penetration of cracks will generate a large number of acoustic emission events,and the energy of acoustic emission events is higher than the initial stage.The energy of the acoustic emission event generated by the acoustic crack closure inside the rock,the acoustic emission event energy at the intersection of the crack is obviously higher than other locations,and it is related to the damage and damage of the rock at the intersection of the crack.Generally,the damage inside the rock is large.The energy of the acoustic emission event corresponding to the damage is also higher.The acoustic emission monitoring experiment of rock failure process and the numerical simulation of RFPA~3DD have a good consistency about the distribution characteristics and energy characteristics of acoustic emission events.Both of them can be used as mutual verification and supplement in rock failure experiments.(7)The maximum principal stress of the rock failure process will be concentrated and will gradually change with the loading.The maximum principal stress is the concentration of tensile stress and the minimum principal stress concentration has a great influence on the crack initiation of rock crack.The damage of rock failure process occurs randomly on the rock surface and inside at the initial stage of loading.Cracks will start and develop from the damage unit as the loading progresses.When the cracks form and join and connect,the rock damage is mainly caused by the crack and nearby units.The damage to the unit that is away from the crack location is reduced.A large number of damages occur in the unit near the intersection where the crack occurs,especially in the interior of the rock.It is difficult to judge the damage inside the rock only from the development of the surface crack. |
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