1、翻译部分Numerical modelling of the effects of weak immediate roof lithology on coal mine roadway stabilityAbstract: The stability and associated design of roof reinforcement requirements of tunnels driven in United Kingdom. Coal Measures strata is directly related to the engineering characteristics of t
2、he immediate roof lithology and the effects of redistribution of the in-situ stress. Numerical modelling carried out by the authors has been used to simulate the widely observed detrimental effects of both high horizontal stress and weak immediate roof lithology on tunnel roof stability. Different n
3、umerical modelling techniques, such as continuum, discontinuum and hybrid finite element-discrete element codes, have been used tomodel the deformational behavior of Coal Measures strata and are discussed in the context of specific case examples to highlight their application and suitability formode
4、lling of weak rock. The modelled results demonstrate that the thickness of the relatively weak mudstone in the roof of the tunnel has a significant influence on the extent of failure and, ultimately, the need for additional reinforcement.1. IntroductionUntil recently 5 mines worked the Barnsley seam
5、 in the Selby Complex (Wistow, Stillingfleet, Riccall, Whitemoor and North Selby). The seam dips at approximately 7 to the North-East, ranging in depth from 250 mWest of the Wistow Mine to in excess of 1200 m East of the North Selby Mine. Typical seam thickness varies from 3.5 m in the West to 1.8 m
6、 in the East of the Selby Coalfield. The roof strata typically consist of an immediate, relatively weak mudstone (up to 1 m thick) overlain by more competent silty mudstones, siltstones and sandstones. The mudstone thickness varies across the Coalfield, ranging from non-existent due to high energy d
7、epositional river channels where the sandstone lies directly above the seam to an extensive thickness of greater than 4 m. Typical tunnel or roadway dimensions are 3.5 m high by 5.0 m wide.The successful implementation and subsequent use of roofbolting in United Kingdom coal mine tunnels have provid
8、ed a large database of tunnel deformation monitoring information, including in-situ measurement of strata behaviour, tunnel deformation and reinforcement performance. Kent et al. (1999) provided a summary of the analysis and interpretation of deformation monitoring data from across the Selby Complex
9、 during the period 1988 to 1994. The database provided an ideal opportunity to investigate how geological and stress variations affect the stability and deformational behaviour of tunnels driven through Coal Measures strata. The data were established for tunnels on drivage, prior to face retreat and
10、 any additional deformation associated with longwall extraction. Detailed analysis of the database confirmed that the stability and associated design of roof reinforcement requirements of tunnels driven in United Kingdom Coal Measures strata is directly related to the lithology of the immediate roof
11、 of the excavation and the redistribution of the in-situ stress caused by creation of the excavation (Hurt (1992), Kent (1996), Kent et al. (1999) and Siddall and Gale (1992). For example, significant increase in tunnel roof deformation is observed when excavations are driven perpendicular to the ma
12、ximum horizontal principal stress direction. Tunnels driven at an angle to the in-situ stress field suffer asymmetrical deformation, with pronounced observed stress effects that require additional reinforcement for stability. These observed effects include the formation of “guttering” or excessive b
13、ulging/bulking of the immediate roof. The thickness of the relatively weak mudstone in the roof of the tunnel has a significant influence on the extent of failure and, ultimately, the need for additional reinforcement. Recent numerical modelling carried out by, or undertaken as part of research supe
14、rvised by the authors over the last fifteen years has provided a wide range of case examples and different applications of use of numerical methods to model weak rock behaviour. This has involved the use of a combination of continuum, discontinuum and hybrid methods, where the choice of the numerica
15、l method adopted took into consideration the capabilities and limitations of the software. The factors considered included: choice of appropriate input parameters such as material constitutive criteria, whether there is a need to model discontinuity behaviour, what failure mechanism is being simulat
16、ed and whether or not there is a need for two or three-dimensional analysis. The modelling has been used to simulate the widely observed detrimental effects of both high horizontal stress and weak immediate roof lithology on tunnel roof stability, using specific case examples taken from the Selby Coalfield. The detrimental effects of weak roof lithology on tunnel roof behaviour are demonstrated using both 2 and 3-dimensional numerical modelling. The examples concentrate on th
