英文原文
Numerical simulation of coal am joints and stiffness effects on coal bumps
Yangdongjiang, yixinzhao, jiezhu
China University of Mining and Technology (beijing)
Beijing, PRC 100083
jiangyd@ yixin_
chinazhujie@163.com
Abstract
The numerical approach to translatory coal bumps analysis is ud to examine the effects of joint and coal am stiffness on the outburst velocity, deformation magnitude of the opening wall and plastic zone length in the coal am. A ries of tests are performed by v
arying the joint dip angles, spacing normal to joint tracks, joint block size and coal am stiffness ratio to the surrounding rock. Results of joint and coal am stiffness effects analysis indicate that joint dip angle, interval spacing, block size and coal am stiffness ratio have profound influences on coal bumps.
The increasing of interval spacing and joint block size can generate larger roadway deformation, lower roadway deformation velocity and longer plastic region in the coal am. Higher stiffness ratio can also result in larger deformation, higher deformation velocity of opening wall. Coal bumps conditions deteriorate as the dip angle rotated to 90 degree or the elastic zones disappear in the whole active zone of coal am for different spacing distributions..
Keywords: Coal bumps, numerical simulation, joint, translatory
1、INTRODUCTION
Underground coal bumps is one of the catastrophic mine failures result from sudden rele
as of energy. With the enormous amounts of relead energy, coal bumps may cast veral tons of coal mas openings horizontally, which always result in destruction and collap of roadways, damage of facility even death and injury to the miners. The phenomenon of coal bumps can be found in various kin roadway shape. Coal bumps throws out large quantity of coal from the wall and then the roadway will be clod over hundreds of meters.
The rearch is financially supported by Rearch Fund for the Doctoral Program of Higher Education under grant No. 20030290001.
2、MECHANISM OF COAL BUMPS
Generally speaking, coal bumps can be classified (Rice, 1935) into two types: One is pressure bumps which are caud when strong and brittle coal pillars or portions of pillars and loaded beyond their load-carrying capacity resulting in sudden and violent failure. The other is shock bumps, which are attributed to rupturing of strong strata above the coal am. [3~4]
In fact, most coal bumps occurred like translatory rock bursts (Lippmann, 1989), which result in coal am projecting dynamically into the excavation and the excavation can be clod over hundreds of meters. The qualitative description of the mechanism of coal bumps is shown in Figure 1.
At pre-excavation state, the primitive overburden pressure q acting on the coal am can be assumed to be at static friction elastic state, shown in Figure 2(a). However, after the roadway is mined out, the primitive vertical pressure exerted on the am over the width of the excavation should be transferred onto the am adjacent to the excavation [5].The
vertical pressure distribution after excavation is shown in Figure 2(b). Perturbations in the original litho static stress field caud by the excavation can, therefore, result in coal/joint failure on the am horizons. Thus, the coal am can be divided into three distinct zones: the pressure relief zone A, maximum static equilibrium zone B and the primitive overburden pressure zone C.
The mining induced ismic, detonations or other activities may cau waves and unstable crack propagation in the coal am and surrounding rock. This will cau decre
a of normal stress and increa of shearing stress to the interfaces between the coal am and the adjacent overlying and underlying rock layers. The effects may convert the sticking friction into a sliding friction. Moreover, at the active zones, the coal am near the excavation will be an active plastic region. Only when the whole active zones are transferred to be one active plastic region at some condition, the coal bumps are more likely to occur. Once the coal bumps occur, coal at A zone and portion of B zone will translatory eject to the roadways.
3、NUMERICAL SIMULATION TECHNIQUE
3.1 Numerical Modeling
Numerical modeling using UDEC version 3.0 (ITASCA, 1996) has been carried out for Tangshan coal mine in order to investigate stability of 12 coal am on 14th level. Numerical models were developed for analyzing the effects of three main parameters of joint on coal bumps. The geometry of the two-dimensional 40m40m model studied is shown in Figure 3. According to the mining depth and overlying strata situation, the origin
al litho static stress of 21 Mpa is impod on the top boundary of the mechanical model. Moreover, the tectonic stress is 25 Mpa loaded on the left and right boundary horizontally.
3.2 Geo-Material Properties
In current numerical modeling, the Mohr-Coulomb model was adopted. For all cas, the mechanical properties for coal am and both the roof and floor rock are listed as the following, coal am: elastic modulus 5.9 Gpa, passions ratio 0.34; the roof and floor rock: elastic modulus 36 Gpa and passions ratio 0.28.
