Study On Blasting Damage Characteristics And Safety Threshold Of Surrounding Rock And Backfill In Two-step Mining

During the process of two-step minning in the filling mining method with higher stage and deep holes,the dynamic load produced by frequent blasting in stope inevitably produces dynamic effects such as cumulative damage and vibration in surrounding rock and filling body,and even induces instability failure.Therefore,it is of great theoretical significance and engineering value to carry out the blasting damage characteristics and safety threshold of surrounding rock and filling body under the two-step mining blasting.The paper is based on the cooperative project of Fuzhou University,"Research on stope blasting control technology of-Zijinshan Gold Copper Mine"(No.01051602).In view of the problems during the blasting process of two-step mining in Zijinshan deep copper mine,comprehensive research was carried out by means of theoretical analysis,numerical simulation,model experiment and field industrial experiment.The main research contents and results in the dissertation are as follows:(1)Revised the formula of explosion stress field of spherical charge,the relationship of displacement amplitude and angle of incidence between the incident wave,reflected longitudinal wave,refracted longitudinal wave,reflected wave and refracted wave were studied.The formula for calculating the tensile stress at the interface between rock and backfill is derived by using Starfield superposition method.(2)The transition relation between inner stress field and surface vibration velocity of rock mass under blasting is deduced based on three different approaches,Sadov's formula,elevation amplification effect of blasting vibration velocity,reflection and superposition effect of explosion stress wave.The results of numerical simulation and model experiment show that,the transition relation based on the reflection and superposition effect of explosion stress wave is obviously better than the transition relation based on Sadov's formula and the elevation amplification effect of blasting vibration velocity.(3)The fracture damage criterion of rock was given,and the damage of rock and filling body can be judged under the stress state calculated by the above-mentioned theory.The initial damage variables,the relative damage variables and the damage variables based on the sound velocity variation of rock mass were defined.In addition,it is pointed out that the macroscopic failure process of rock mass caused by blasting dynamic loading is not the result of single blasting operation,but the result of multiple blasting interaction.The damage increment of rock has continuous relativity,based on this,the classical formula of damage increment and cumulative damage was modified.(4)Taking the two-step mining of higher stage filling mining method in Zijinshan deep copper mine as the engineering background,and based on the explosion similarity theory,2 models of multi medium coupling concrete with the same size were designed and fabricated,and the blasting was conducted by nonel tube detonators.In the blasting process,the Blast-Ultra high-speed multi-channel dynamic strain testing system was used to monitor the explosion stress field in different mediums,the PDS-SW acoustic wave tester was used to monitor the sonic wave velocity of different mediums before and after blasting,and the vibration velocity of the model top surface was monitored by Blast-UM blasting vibration meter.The monitoring data were employed to verify and analyze the results of theoretical analysis.(5)Based on the blasting damage and dynamic stress ratio,two methods for determining the safety threshold of blasting vibration were proposed.Therefore,the safety threshold of blasting vibration of the filling body with the cement-sand ratio of 1:8 and'1:10 in Zijinshan deep copper mine were determined to be 5.17cm/s and 5.28cm/s respectively.The safety thresholds of blasting vibration of the surrounding rock in short term roadway,medium term roadway and long term roadway are 18.63cm/s,12.42cm/s and 6.21cm/s,respectively.And the corresponding blasting vibration safety control measures were also given.(6)In view of the air-decked charging blasting can effectively weaken the effect of blasting vibration,the laboratory experiment were carried out for three kinds of holes with the diameter of 90 mm,110 mm,160 mm,and the force law of the air-spacer with the diameter of the hole and the filling height is obtained.Simultaneously,the direct pressure was compared with the impact pressure of the filling process.Then,a scientific and reasonable air-spacer of blasting hole was designed,the application effect is good in the industrial test of stope blasting in Zijinshan deep copper mine.