ABSTRACT
The paper examines the application of a rock mass rippability index to the selection of ripping equipment for a given duty. The majority of current rippability indices fail to account for the fracture strength of the rock mass and the rock abrasive potential. The paper suggests a new rippability index for mining applications taking into account uniaxial tensile strength, degree of weathering, seismic wave velocity, discontinuity spacings and abrasiveness of rock. The application of the new rippability index has been illustrated with several case studies.
1 INTRODUCTION
rock mass characteristics
production requirements
mine geometry and
types of excavating machinery
In surface coal mining operations ground preparation is usually accomplished either by ripping or drilling and blasting operations. Blasting utilizes explosive energy whereas ripping operations use mechanical energy generated by a dozer and transmitted to the ground through a ripper. The advent of larger, heavier and more powerful crawler tractors incorporating improved ripper design and life have resulted in an increase in ripper productivity under difficult ripping conditions. In some surface mining applications in urban environments, increasing environmental constraints on blasting have increased the popularity of ripping as an alternative to blasting. The main factors affecting the selection of the ground preparation technique can be defined in relation to the following factors: The purpose of this paper is to examine the influence of rock mass characteristics on ripper performance and thereby to evolve a selection process for rippers for a given duty. In order to achieve this goal a technique of rock classification based on a rippability index has been introduced. This new rippability index is based on intact and in-situ rock parameters which are correlated to tractor ripper's design capabilities and performance. The application of this technique to the selection of rippers has been demonstrated with a number of case studies carried out in British surface coal mines.
Table 1. Classification of rock mass according to rippability index.(available in full paper)
Figure 1 . Classification of ripper attachable dozers based on power and weight. (available in full paper)
2 CLASSIFICATION OF ROCK MASS ACCORDING TO EASE OF RIPPING
Ripping involves fracturing of rock and the relationship between rock fracture strength and seismic velocity is not clear.
Seismic velocity disregards the rock abrasive potential.
rock type
rock fabric
intact rock strength
rock abrasiveness
degree of weathering
structural features of rock mass
seismic wave velocity
rock intrinsic and other Properties
In the past, the single value of seismic wave velocity has been related to rock rippability has and also been used to predict ripper performance and capital and operating costs (Ateco 1969, Horace and Church 1970a, Horace and Church 1974b, Atkinson 1971, Caterpillar 1982, Adam 1983). These relationships, however, are questionable for the following reasons:In the past, several attempts have also been made to predict rippability using classification systems (Franklin 1970, Weaver 1975, Read et al 1975, Müftuoglu 1983, Smith 1986). None of these aproaches can be used to formulate a rippability index for rock. In a previous paper (Singh et al 1986) the authors have discussed the use of the following parameters in formulating a rippability index:
