Bieniawski's Rock Mass Rating Research Articles

Systematic Approach to Sustainable Rock Slope Stability Evaluation

Geological discontinuities play an important role in the evaluation of rock slope stability. Romana's Slope Mass Rating (SMR) system provides a methodology to quantify rock slope stability. Employing Bieniawski's Rock Mass Rating (RMR) to classify the rock mass of an investigated slope, SMR enables an objective determination of the rating adjustment values based on discontinuity orientation-slope orientation, respective dips angles and slope excavation methods. However the surface roughness of the discontinuities and their peak friction angles (αp) that are fundamental in determining rock slope stability are not directly considered in this evaluation. A more sustainable approach to rock slope stability assessment proposed here combines the SMR determination with the determination of the peak friction angle, αp of the discontinuity surfaces. Based on this proposal, the potential for slope failure can be quantified as follows: if SMR predicts failure and dip angle of the discontinuity (βi) > the peak friction angle (αp) the slope has a very high failure potential; if SMR predicts failure and βi < αp, the slope has intermediate failure potential; if the slope is stable according to SMR & βi > αp, the slope has low failure potential and if stable according to SMR and βi < αp, the slope can be considered as stable.

Machine learning techniques applied to the construction of a new geomechanical quality index

Given the non-existence of a standard quality index for ornamental slate, granite and marble blocks, classical classification methods such as Bieniawski's rock mass rating (RMR) and Barton's Q System are typically used, very much unquestioningly and indiscriminately. These methods, however, were originally designed for a different purpose, namely to identify and solve stability problems in underground excavations. Furthermore, they rely on pre-established parametric formulas that do not necessarily coincide in terms of criteria with rock quality experts. In fact, the fit between both perspectives has never been properly evaluated. In this article, we propose a quality index for ornamental rock constructed using machine learning techniques (support vector machines (SVMs)) to model the quality grade allocation procedure as applied by the expert. This quality index is composed of a set of logical rules consisting of mathematical inequalities in relevant ornamental quality variables. Nonetheless, the fact that the SVMs have the drawback of being difficult to interpret complicates the process of extracting the quality rules used by an expert. To overcome this drawback, we used classification and regression trees (CARTs) trained using SVM output.

Geological and geotechnical investigations of Loharinag-Pala Hydroelectric Project, Garhwal Himalaya, Uttarakhand

The project area, forming a part of Bhagirathi valley, exposed rocks classed as central Himalayan crystallines and are medium to high grade metamorphics. The rock types exposed are feldspathic gneisses, quartz-biotite schists, garnet-biotite schist, biotite gneisses, migmatites and amphibolites. To design the rock support for the underground structures of desilting chambers, HRT, surge shaft, pressure shafts, power house, TRT and for the foundations of barrage and intake of desilting chambers, rock mass classifications was attempted following the methods of Bieniawski Rock Mass Rating (RMR) Classification and Tunnelling Quality Index (Q) of Barton et al. RMR technique involves collection of data on rock strength, RQD (%), spacing of discontinuities, condition of discontinuities and groundwater condition, while the ‘Q’ involves collection of data on RQD (%), joint set numbers (Jn), joint roughness number (Jr), joint alternation number (Ja), joint water reduction factor (Jw) and stress reduction factors (SRF). The permeability test in the overburden was done by the constant head method, while in the bed rock portion conducted by packer test. The result indicates that the rock masses of the area fall under the good, fair and poor rock quality. Augen gneiss of power house area is coming under the category of moderately strong rock as proved by deformability characteristics and strength parameter. On the basis of above study recommendations have been made for the proper and safe construction of the project components.

Effect of shape of underground openings on boundary stresses

As soon as an underground excavation is made, the in situ stresses within the rock mass gets disturbed and redistribution of stresses takes place. As such, the stresses around an underground opening would be different from the pre-excavation stresses, i.e., in situ stresses. A zone of disturbed stresses is formed around an opening and generally known as 'zone of influence'. The extent of zone varies from rock to rock. For a very good and strong rock this zone is small, where as for weak rocks it is large. In other words, if the induced stresses due to tunnelling do not exceed the in situ strength of the rock mass, the surrounding rock mass remains in an elastic state and the zone of influence is limited. However, when the induced stress is more than the strength of the rock mass, the rock fails and the condition is popularly known as squeezing ground condition. The boundary stresses around an underground opening govern the stability of underground opening. It has been studied by Hoek and Brown (1982) that the shape of underground opening does affect the boundary stresses around an underground opening. To carry forward the work, a Research Project was awarded to the author by Ministry of Water Resources, Government of India. Parametric study has been carried out to obtain the influence of shape of underground openings on maximum boundary stress. In addition to five different shapes of the opening, various other parameters used for the study are tunnel depth, in situ stresses, uniaxial crushing strength of intact rock material, and Bieniawski's rock mass rating. The analyses for various values of all these parameters have been performed using numerical analysis code FALC3D. The maximum boundary stresses at the roof have been obtained and simple equations are developed for estimating the maximum boundary stresses. The analysis shows that the curves for horse-shoe and circular shapes are almost superimposing indicating that the roof stresses at the centre of the opening in these two shapes are almost same. Using the equations, maximum boundary stress can be estimated. Using the failure criterion of Sheorey (1997), safety factor contours for all the models have been plotted and the minimum safety factor values (fmin) at the roof have been obtained. Using fmin, in situ stress ratio k, depth of underground opening, rock mass rating RMR and laboratory crushing strength, rc, finally different equations have been developed for each shape to estimate the minimum factor of safety value in the roof of the opening. (A) Reprinted with permission from Elsevier. For the covering abstract see ITRD E124500.

Influence of air-deck blasting on fragmentation in jointed rocks in an open-pit manganese mine

The influence of air-deck blasting on fragmentation in jointed rock masses of a manganese open-pit mine has been investigated. It is revealed that air-deck blasting improves the degree of fragmentation and produces more uniform fragmentation compared with conventional blasting. Mean fragment size (MFS) reduces from a range of 0.36–1.0 m to a range of 0.27–0.51 m. Fragmentation index (FI) and blast-induced fragmentation increase from 1.38 to 4.34 and from 37–65% to 66–100% respectively. Empirical correlations have been developed to estimate MFS and FI from conventional and air-deck blasting on the basis of Bieniawski's rock mass rating, powder factor and ratio of spacing to burden. Results indicate that air-deck blasting could be more effective in very low to low strength moderately jointed rock masses than in medium strength highly jointed rock masses.

TOOMPEA HILL STABILITY ANALYSIS

On Toompea Hill situated in the center of Tallinn there are several natural, ancient architectural and historical monuments. It has become apparent that the processes in the rock mass caused an unfavorable environmental side effect accompanied by significant subsidence of the Toompea Hill. Identification of the reasons of the Toompea Hill's subsidence and opening the physical substance of these processes is the main aim of the present work. For the feasibility study stability problems were investigated. Accordingly, it was decided to perform numerical modeling analysis using two-dimensional Fast Lagrangian Analysis of Continua (FLAG - program) (1). It is suitable for stability analysis, for parametric and sensitivity studies. For the first time, preliminary calculations before the modeling have been proposed. This method enabled to simplify and quicken the further modeling. It was made by means of conventional calculation methods, using theoretical formulas. The utility of preliminary calculations was clearlyproved. At first, little field information was available to estimate the rock mass properties. For this estimation, geological data were used. The rock mass properties were selected, based on Bieniawski's rock mass rating (RMR) (2).