발파진동 및 비산충격에 대한 광주 안정성 분석

Abstract

These days, mining industry prefers underground development for large mining because of exhaustive minning resources and environmental pollution and large drafts and mining cavities thanks to extensive distribution of heavy excavation machines. In a mining design, to control collapse of cavities and secure stability, design of cavities and pillars are considered as very important. Pillars separate cavities while controlling deformation of rock mass and are categorized according to their roles as follows: support pillars, protective pillars, and control pillars. As such pillars are designed and excavated based on empirical formulas, when roofs or side walls collapse in mining, mining works are retreated or rocks in front of collapsed area are abandoned and major resources are buried, which causes lower economic profits and stability. In blasting work for mining, blasting vibration, flyrocks and fatigue behaviors may cause deformation or destruction of pillars, and collapse of mining cavities. Therefore, it is very important to secure stability of pillars against shock vibration, and blasting vibration delivered through the ground. For the stable blasting design, we have to examine lithology of blasting sides of cavities and identify patterns of blasting design and deformation behaviors of pillars by blasting vibration and shock vibration of flyrocks. Therefore, this study investigated discontinuity of cavities and carried rock mass evaluations and lab experiments to identify physical and chemical characteristics of rocks in study area. And we obtained a prediction equation of blasting vibration through instrumentation for underground cavities and analysed excavation damaged zones. For measurement of convergence of pillar, we installed six instruments at three places(upper, middle and bottom) of pillar crossing at right angles to investigate deformation of pillar due to excavation of mining cavities, and obtained theoretical shock vibration imposed on pillar through fragmentation analysis and measurement of flyrock distance. To examine the influence of pillar in underground mining blasting, we carried a finite element analysis and compared the result with prediction equation of blasting vibration, and shock vibration of flyrock when a impact was imposed on pillar and theoretical shock vibration. Blasting vibration at theoretical throwing distance of flyrock(16.34 m) in underground mining cavities was estimated to be 18.92 and when distance(14.59 m) from working face to pillar is applied to a prediction equation of blasting vibration, vibration was calculated to be 22.47 cm/s. Theoretical shock vibration when flyrock with maximum particle size(F100) collided with the left sidewall of pillar, was calculated to be 16.96 cm/s. It indicates that 75 % level of vibration against the blasting vibration prediction equation. As a results of numerical analysis, maximum value of blasting vibration at pillar was 32.67 cm/s, which highly indicates against blasting vibration prediction equation. Maximum shock vibration obtained through a numerical analysis on the time when flyrock collided with pillar was 15.22 cm/s, which indicates that about 90 % level of vibration against theoretical shock vibration and 68 % level of vibration against blasting vibration prediction equation. In comparison with the blasting vibration and shock vibration by pillar size(width/height) through finite element analysis, blasting vibration velocity decreased when pillar size increased from 0.25 to 0.92, variation of blasting vibration velocity when pillar size is greater than 1.08 was slighted. Shock vibration velocity greatly decreased when pillar size increased from 0.25 to 0.42, variation of shock vibration velocity when pillar size is greater than 0.58 was slighted. Through the equation of relationship between pillar size and maximum vibration velocity at left sidewall of pillar, it enable user to estimate pillar size by damage levels(Langefors and Kilhstrom, 1973). In comparison with the prediction equation of blasting vibration through in-situ instrumentation and regression analysis, shock vibration in case flyrock collided with pillar was predicted to be lower, which indicates that influence of blasting vibration is greater than shock vibration of flyrock. However, in blasting at very near distance from pillar, actual shock load on pillar by flyrocks is great and in consideration of total particle size and superposition effect of shock vibration, as it is expected shock vibration to pillar will increase, it should be considered as an important factor in design of pillars. At underground mining cavities, blasting design should consider application of blasting vibration prediction equation, theoretical shock vibration of flyrocks and shock vibration imposed on pillars obtained through a numerical analysis, which will contribute to increased stability of adjacent pillars, and proper identification of the influence of blasting vibration and shock vibration of flyrocks on rock mass and artificial structures such as pillars, drafts and tunnels.