Evaluation of the Stress State in Two Adjacent Backfilled Stopes Within an Elasto-Plastic Rock Mass

Abstract

Backfill is used in the mining industry to improve the stability of underground openings and reduce the environmental impact due to the surface disposal of mine wastes. A critical issue for the design of backfilled stopes is the determination of the stress state in the backfill and surrounding rock mass. In recent years, much work has been conducted to assess the stresses in isolated backfilled stopes. Recent work performed by the authors indicates that the stress distribution in a backfilled stope may also be affected by the excavation of an adjacent opening. So far however, simulations of neighbouring stopes have been based on an elastic behavior for the rock mass, which may not reflect its actual response (especially under large stresses). This paper presents key results obtained from numerical simulations of two backfilled stopes excavated in sequence in an elasto-plastic rock mass. The simulations results illustrate the effects of the non-linear rock mass response and of other characteristics including stopes geometry (size and spacing) and depth, natural stress state, and backfill properties. These results indicate that, although arching effects tend to develop in all narrow stopes, the stress distribution in adjacent openings can be quite different for elastic or elasto-plastic rock mass behavior. The results presented here also illustrate the similarities and differences between the behavior of a single backfilled stope and of two adjacent stopes, depending on the rock mass properties and overall characteristics of the system. Keywords Adjacent stopes Á Mine backfill Á Rock mass Á Stresses Á Numerical modelling Á Elastic Á Elasto-plastic behavior List of symbols B Stope width (m) c 0 Cohesion of backfill (kPa) c rm Cohesion of rock (kPa) D Distance between stopes (or pillar width) (m) E Backfill modulus (MPa) E r Rock mass elastic modulus (GPa) E rm Rock mass deformation modulus (GPa) h Depth (m) in the backfill H Stope height (m) K Earth pressure coefficient in the backfill (-) K a Rankine's active earth pressure coefficient K o Earth pressure coefficient at rest K r Earth pressure coefficient for the natural stresses in the rock mass z Depth at the base of the stope (m) Dd h Maximum difference between the horizontal displacements (cm)

Required strength estimation of a cemented backfill with the front wall exposed and back wall pressured

“…Previous studies have shown that the numerical analyses are very helpful to understand the mechanical response of backfilled stope (Rankine, 2004;Pirapakaran and Sivakugan, 2007;Li and Aubertin, 2009b;Veenstra, 2013;Falaknaz, 2014;Falaknaz et al, 2015aFalaknaz et al, , 2015bFalaknaz et al, , 2015cLi and Aubertin, 2014;Liu, 2017;Liu et al, 2016aLiu et al, , 2016bLiu et al, , 2017Yang et al, 2017a). In this study, FLAC 3D is used to analyse the stability of the exposed backfill.…”

“…Numerous recent studies have shown that this solution can be valid when the stopes are very large in plane and small in height. For most cases, the arching effect has to be considered for estimating the stresses in backfilled stopes (Aubertin et al, 2003;Li et al, 2003Li et al, , 2005Li and Aubertin, 2009a, 2009bThompson et al, 2012;Falaknaz et al, 2015aFalaknaz et al, , 2015bFalaknaz et al, , 2015cLiu et al, 2016bLiu et al, , 2017. As the arching effect was neglected in the calculation of the lateral pressure along the two side walls and stability analysis of the exposed cemented backfill, the solution of Yang et al (2015) can be rewritten as follows for estimating the minimum required cohesion (FS = 1) of the cemented backfill:…”

Geomechanical Modeling of Stress and Fracture Distribution during Contractional Fault-Related Folding

“…Many studies have found that fractures often develop around fault zones and anticlinal core, and that fracture spacing is positively correlated with regional differential stress [12] [13] [14]. Some researchers have suggested that lithology and combination of fractures may be more significant than regional stress [15] [16] [17] [18] [19].…”