1、A method for the design of longwall gateroad roof supportW. LawrenceaGeowork Engineering, Emerald, QLD, AustraliaAbstract:A longwall gateroad roof support design method for roadway development and panel extraction is demonstrated. It is a hybrid numerical and empirical method called gateroad roof su
2、pport model (GRSM), where specification of roof support comes from charts or equations. GRSM defines suggested rof support densities by linking a rock-mass classification with an index of mining-induced stress, using a large empirical database of Bowen Basin mining experience. Inherent in the develo
3、pment of GRSM is a rock-mass classification scheme applicable to coal measure strata. Coal mine roof rating (CMRR) is an established and robust coal industry standard, while the geological strength index (GSI) may also be used to determine rock-mass geomechanical properties. An elastic three-dimensi
4、onal numerical model was established to calculate an index of mining induced stress, for both roadway development and longwall retreat. Equations to calculate stress index derived from the numerical modelling have been developed. An industry standard method of quantifying roof support is adopted as
5、a base template (GRSUP). The statistical analyses indicated that an improved quantification of installed support can be gained by simple modifications to the standard formulation of GRSUP. The position of the mathematically determined stable/failed boundary in the design charts can be changed depend
6、ing on design criteria and specified risk.Keywords: Coal mine; Roof control; Support; Design1. IntroductionLongwall gateroad strata stability is essential to ensure uninterrupted production. In Central Queenslands Bowen Basin, immediate gateroad roof lithology varies from coal to weak interlaminated
7、 material, to strong almost massive sandstone, with localised areas of weak fault affected strata. It is usual for roof conditions within any one mine to vary significantly. Typically, longwall mines in the Bowen Basin have specified gateroad roof support based on past practice. Modifications to gat
8、eroad support are generally reactive, due to encountered difficult strata conditions, and less proactive. Current gateroad support design approaches have limitations, which have restricted their applicability and adoption as mine site design tools. A prototype for an improved gateroad support design
9、 methodology has been developed that is integrated and systematic, based on rock engineering principals, but requires engineering judgement and experience 1. There were several broad objectives for the design methodology. A consistent and unambiguous definition of strata conditions and behaviour was
10、 required. Gateroad roof support needed to be assessed and specified. The method had to provide design calculations and justification for compliance and statutory purposes, and could serve as a framework for a mine strata management system. Mine site support designers must be able to readily use the
11、 method to manage uncertainty and risk. The method must be able to be reviewed, modified and expanded.2. Current roof support design methods for longwall gateroadsNumerous roof support design methods have been proposed over the years, but none have gained widespread acceptance by the coal mining ind
12、ustry 2. There are empirical databases, some proprietary, based on industry practice, which specify gateroad primary and secondary support densities, using a statistical approach 3 and 4. Analytical methods are not appropriate when rock-mass yield due to high mining induced stresses occurs, but may
13、be applicable and adapted to low stress environments 5. The application of complex post-yield numerical modelling in the design process for excavation support is valid although contentious, and requires a more comprehensive justification and better industry understanding of its strength and limitati
14、ons 6. The complete mathematical representation of rock-mass properties and behaviour is a complex issue, which is still outside the capability of current numerical modelling code 6.Engineers and mathematicians do not have the current capability to fully define rock-mass geomechanical properties and
15、 their mathematical representation. Elasticplastic numerical modelling is a useful tool if used appropriately. It is not exclusively correct or unique, or always superior to other available and accepted design techniques. These aspects have been recognised during recent collaborative Australian Coal
16、 Association Research Program research on longwall microseismics 7, where it was considered that current 3D numerical models lack sufficient validated constitutive relationships, and are forced to make compromises when dealing with complex rock-mass behaviour.Simplified elastic numerical methods 8 and 9 have merit and are certainly applicable for more massive sedimentary rock-masses 5. An assessment of their applicability to weaker, laminated clastic
