Experimental And Numerical Study On Rock Cutting By Conical Picks Of Roadheader

At present,the conventional drilling and blasting method is still widely used in underground engineering excavations such as tunnels and mining roadways.Compared with blasting methods for rock breaking,the non-explosive mechanized rock breaking by conical picks has the advantages of standardized tunnel section forming,controllable digging,and small disturbance to surrounding rock,so it is commonly used in tunneling in soft rock formations.However,when applied to hard rock formations,the conical picks are prone to wear,which increases the repair time and shortens the lifetime,leading to low efficiency and high cost of excavation.Therefore,it is important to study the rock-breaking mechanism of picks and then optimize the design of cut-off parameters to improve the rock-breaking performance and reduce the consumption of picks.In this paper,we first tested the rock physical and mechanical parameters of carbonaceous slate and rhyolitic clastic rock in background mine under indoor conditions,counted and analyzed the structural surface and RQD value of two kinds of rock masses in the field,graded the rock quality by different evaluation methods,laid the foundation for the subsequent research on the mechanism related to the rock cutting.The two main contents of the research on the rock-breaking mechanism of picks are cutting force and cutting specific energy.Based on the TRW-3000 true triaxial electro-hydraulic servo test system and selfdeveloped pick loading platform,indoor linear cutting experiments were conducted on samples of carbonaceous slate and rhyolite clastic rock.The effects of different half pick angles,cutting angles,front angles,back angles,cutting thickness and interception distance on cutting force and cutting specific energy were studied.The experimental results show that the cutting angle incorporates the influence of the front and back angles on the difficulty of cutting the rock with the pick.When the cutting angle is small,the back angle is also small.At this time,due to the serious friction between the rock and the pick,the influence of the back angle on the cutting force is dominant.When the cutting angle is large,the influence of the half pick angle and the front angle on the cutting force is dominant.The cutting force increases linearly with the increase of cutting thickness and interception distance.The experimental results show that the cutting specific energy consumption follows a trend of first decreasing and then increasing with the increase of the hald pick angle and cutting angle.When the cutting angle is 54° and the hald pick angle is 45°,the cutting specific energy is the smallest.In addition,with the increase in cutting thickness,the cutting specific energy consumption decreases exponentially.With the increase of the ratio of interception distance and cutting thickness,the cutting specific energy first decreases and then increases,and there is a minimum specific energy.This optimal specific energy is significantly less than the first cutting specific energy,and the ratio of intercept distance to cutting thickness is 2～3.The study shows that there is a significant synergy between the two adjacent picks,and the minimum specific energy under different combinations is the result of the joint action of the intercept distance and the cutting thickness.Furthermore,a mathematical model of the relationship between cutting force,specific energy and pick geometric parameters was established using regression analysis.Using Vic-2D strain digital image correlation software,the four stages of the failure process under pick rock breaking are discussed,and the mechanism of rock breaking by picks is analyzed in depth.To analyze the dynamic damage process of rocks from a microscopic point of view and to verify the indoor experimental conclusions,the PFC2 D particle flow discrete element software was used to analyze the numerical analysis of pick rock breaking under different half pick angles and cutting angles.For carbonaceous slate,the effects of different confining pressure,different joint inclination angles and loading speed of different frequencies on pick rock breaking were simulated.The results show that under the condition of low confining pressure and precast joints,the application of pick breaking under a certain range of loading frequency can promote rock fragmentation,and the rock interceptability is better.Therefore,methods to improve rock interceptability are proposed,such as pre-excavating pressure relief grooves,pre-drilling pressure relief holes,pre-excavating induced roadways and applying dynamic disturbances.Based on the above research conclusions of rock cutting mechanism,the pick arrangement and installation angle of the cutting head of the boomtype roadheader were optimized.A theoretical formula for the modified intercept distance is proposed and applied to the industrial test of the nonexplosive boring site of the roadheader,which greatly improved the excavation efficiency and reduced the wear of the picks and the full cost of excavation.The research conclusions provided basic support and theoretical basis for the design and selection of roadheaders,the evaluation of cutting performance,and the improvement of rock truncability.