Experimental Study On Microwave Fracturing Of Hard Rock

Footsteps to explore and study new methods for rock breakage and tunneling never stop.At present,traditional borehole-blasting method and mechanical breaking method still play a dominant role,the two methods accounting for more than 90%.However,borehole-blasting method has big original rock disturbance and low construction accuracy.Mechanical breaking method could overcome the shortcomings of borehole-blasting method,while for hard rocks,serious tool wear,large amount of maintenance and low penetration are the main problems.In many newly-developing rock breaking methods,microwave fracturing technology for hard rock is considered one of the most promising methods.It can be used to a single crushing technics and assist rock breakage,to solve the tool wear problem of mechanical breaking method.Significantly,it has important research significance for exploring new methods for rock breakage and tunneling.In the paper,a large number of experimental studies on mechanism and effect of microwave fracturing hard rock and the mechanical properties of different rocks after microwave treatment were conducted by a multimode cavity with frequency of 2450 MHz.The microwave absorption capacity of main rock-forming minerals,the influence of heating path on the effect of hard rock fragmentation and the influence of microwave irradiation on mechanical properties of different hard rocks were studied.Based on the mechanism of microwave breaking rock,a new microwave fracturing equipment was researched.Laboratory and field test were conducted to study the fracturing effect.The main research contents are as follows:(1)Quartz,potassium feldspar,albite,calcite,black mica,white mica,hornblende,enstatite,and olivine were treated by microwave.The microwave absorption capacity of the rock-forming minerals were estimated and classified by heating rate and temperature increment.Based on SEM-EDX elemental analysis and composition distribution,the reaction mechanism between rock-forming minerals and microwave was analysed.(2)Different microwave heating paths produce different heating effects.Microwave heating tests were conducted to basalt samples with different power levels and irradiation time.Uniaxial compressive strength and P-wave velocity were measured before and after microwave treatment.The influence of heating path on the fracturing effect of basalt were studied,and the results can make some guidance to engineering applications.(3)Microwave heating of basalt,granite and sandstone with different power levels and irradiation time were followed by conventional mechanical strength(uniaxial compressive,Brazilian tensile and point load strengths),deformation and P-wave velocity tests.The influence of microwave irradiation on strength,deformation,wave velocity,firmness and rock crushing work ratio etc.were studied.The influence of power level and sample dimension on fracturing effect of hard rock were studied,too.(4)Water has a strong microwave absorption capacity which within rock will influence the microwave absorption capacity of rock.So it has important research significance to study the microwave absorption and mechanical properties of water saturated hard rocks.Microwave heating of dry and water saturated basalt,granite and sandstone samples were followed by conventional mechanical tests.The influence of water on mechanical properties of hard rock after microwave treatment were studied.(5)Current microwave tests are always conducted in an industrial microwave oven either with a single mode or multimode cavity in the laboratory,which limited the engineering application of this technology.A new microwave fracturing equipment was researched to study the surface fracturing and borehole fracturing effect of hard rock.A microwave thermal-mechanical coupling loading system combined the microwave fracturing equipment with a rock mechanical test system,which was used to study the influence of uniaxial stress on fracturing and damage properties of hard rock.(6)Microwave fracturing test of basalt in Baihetan underground powerhouse was conducted by the new microwave fracturing equipment.Digital borehole camera and ultrasound velocity were measured before and after microwave irradiation to study the fracturing effect of engineering rock mass.