| In recent years,people are faced with many problems of high temperature rock projects,such as hot dry geothermal extraction,deep mining of mineral resources,underground coal and oil shale gasification,deep geological disposal of nuclear waste,and rock mass engineering experienced fire.In order to analyse the stability and security of those kinds of rock projects,people need to master physical,mechanical and permeability characteristics of rocks experienced different temperature.At the same time,the excavation rate is slow and the tool wear is serious when TBM works in hard rock tunnel.Considering that microwave irradiation heating can decrease the strength and the friction property of rocks,microwave assisted mechanical rock breaking can improve excavation efficiency of TBM and reduce its tool wear,which has a good prospect of application.In this paper,we studied the physical characteristics(mass,volume,density and porosity),ultrasonic characteristics,permeability,mechanical characteristics(uniaxial compressive strength,elastic modulus and the Brazilian splitting tensile strength)and mineral characteristics(mineral species,content,particle size and connection mode)of sandstone and granite experienced different temperature by the traditional heating method.Considering the good prospect of microwave assisted mechanical rock breaking in hard rock excavation of TBM,besides the idexes above,this paper aso studied the friction characteristics and the brittleness index of the granite by microwave heating method.The main conclusions are as follows:(1)With the increase of temperature,the mass and density of sandstone and granite decrease and the decrease rate increases,while the volume and porosity decrease first and then increase.The mass of sandstone decreases significantly more than the granite,while the change range of granite 's volume and porosity is much more than the sandstone.The decrease of the sandstone 's density depends on the change of volume and mass,while the decrease of granite mainly depends on the increase of volume.And the change trend of porosity is similar to the volume.(2)With the increase of temperature,the P-wave velocity of sandstone and granite decreases and the decrease rate of granite is bigger.The decrease rate of sandstone's velocity is small after heated on 100? to 200?,and the decrease rate is big after heated on 400? to 800?,while the velocity of granite decreases linearly.(3)The permeability of sandstone and granite is almost unchanged when heated on 100? and 200?.The permeability of sandstone increases quickly between 400?and 600?,and increases slowly between 600? and 800?,while the permeability of granite increases quickly between 200? and 800?.And the permeability of sandstone increases by one order of magnitude from 25? to 800?,while the permeability of granite increases by three orders of magnitude from 25? to 800?.(4)The uniaxial compressive strength,elastic modulus and Brazil splitting tensile strength increase first and then decrease with the increase of temperature,while the corresponding indexes of granite decrease.(5)With the increase of temperature,the mineral composition,content,particle size of the sandstone and granite are not obviously changed,however,the contact form of the quartz of the sandstone is changed from point and line contact to linear and concave contact,and the fractures of the quartz and feldspar minerals of the granite increase gradually.(6)When heated by microwave,the appearance,physical characteristics,ultrasonic characteristic,permeability,mechanical characteristics and mineral of granite have the same change rules with the granite heated by traditional heating method,which are both thermal cracking and have a same mechanism of failure.The friction property of granite decreases gradually when heated by microwave,and the life of tool wear improve 0.33,0.96,2.66 times after heating 12 min?18 min and 24 min by microwave.The brittleness index of granite greatly increases after microwave heating,which can improve the efficiency of TBM. |
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