Interactions of overburden failure zones due to mu

Authors: Wanghua Sui Yuan Hang Luxing Ma Zhaoyang Wu Yongjie Zhou Guoqing Long Lianbo Wei

Publish Date: 2014/09/27

Volume: 74, Issue: 3, Pages: 1019-1035

PDF Link

Abstract

This paper presents an investigation on the interactions of overburden failure zones induced by the mining of adjacent coal seams using the longwall caving method Overburden failure is an important factor in safety assessments in the fields of mining engineering geology and safety geology especially when mining under water bodies In this study the influence of the thickness and properties of the interburden between seams on the development and interactions of caving and fractured water flow zones are investigated by using in situ measurements scale model testing and numerical simulations The height of the fractured water flow zones in the scale model tests and numerical simulations are basically in good agreement with measurements after mining of the upper and lower seams of Seam No 3 in the Cuizhuang Coalmine Therefore the scale tests and numerical simulations in the study are verified The results show that interaction and superposition between two close distance seams cannot be ignored when the ratio h/M of the interburden thickness h to the cutting height of the lower seam M is less than a defined critical value A dividing line Line D has been proposed to judge whether the interactions exist When the M h/M points are located above Line D the caving zone induced by excavation of the lower seam will not propagate to the caving zone induced by the upper seam Otherwise for the M h/M points below Line D the interactions and superposition of the overburden failure must be considered when predicting the heights of the caving and fractured water flow zonesCoal deposition is usually in the form of multiple seams with different interburden thicknesses and geologies Much research on the interactions of strata stress and deformation due to multiple seam mining have been carried out for roomandpillar and longwall panels since the 1980s Mark 2007 Mark et al 2007 Some of the earlier research mainly focused on roomandpillar mining It was found that subsidence and pillar load transfer are two of the typical interactions between adjacent coal beds Chekan et al 1986 An evaluation model for the probability of multiple seam mining success was proposed by Chanda 1989 Chekan et al 1988 found that the ratio of the overburden to interburden thickness is a key factor influencing load transfer Later multiple seam interactions associated with longwall mining or interactions between roomandpillar and longwall panels were investigated with a focus on their complex multipleseam stress and displacement interactions Chekan et al 1989 Heasley and Akinkugbe 2005 Porathur et al 2013 Results demonstrated that during multipleseam excavations it is important to protect the overlying workable seams and minimize surface subsidenceThe longwall top coal caving LTCC method is an effective mining approach that originated in Europe and has been widely and successfully used in China Overburden stress distribution top coal caving and fracturing mechanisms and evaluations and interaction between strata movement and hydraulic supports have attracted much attention and have been thoroughly studied since the LTCC method increased in popularity Xie et al 1999 Yasitli and Unver 2005 Humphries and Poulsen 2008 Alehossein and Poulsen 2010 Vakili and Hebblewhite 2010 Khanal et al 2011 Swift 2013 Gao et al 2014 In recent years research on the influence of the LTCC method on closedistance seam mining has been carried out by investigating overburden failure and stress distributions using in situ measurements numerical simulations and scale model testing Yang et al 2008 Luan et al 2010 Zhang and Zhang 2010 Guo 2011 Xu et al 2013 Results show that interactions on overburden failure during the excavation of closedistance seams are enhanced by the superposition between the floor damage zone of the upper seam and the roof caving zone of the lower seam This superposition results in increases in the height of the caving and fractured water flow zones of the lower seam which are greater than those induced by singleseam mining under similar conditionsPrevious studies in the literature revealed some characteristics of the interactions of overburden failure and subsidence induced by the mining of closedistance seams The damaged interburden and/or caving rocks of the upper seam due to longwall mining constitutes part of the roof of the lower seam It has been found that the influence of upper seam mining on the stress deformation and failure of lower seam mining is reduced with increasing interburden thickness However the understanding on overburden failure due to multiple seam mining falls short of that on single seam mining especially in terms of the LTCC method Some issues require more profound studies and understanding such as how multiple seams interact during caving mining to the extent that the thickness and properties of the interburden influence interactions and how mining sequences and directions of recovery influence interactions To this end the main purpose of this study is to investigate the influence of the thickness and geological engineering properties of the interburden between two close seams on the interactions of overburden caving and fracturing based on a case study of Seam No 3 including the upper and lower seams of the Permian Shanxi Formation in the Cuizhuang Coalmine Shandong China

Keywords: