Abstract
The process of evaluating rock mass strength requires that major structural features such as joints that influence rock strength are considered. In carbonate rock masses, however, the strength of the rock mass is largely dependent on intact rock strength and structural features play a secondary role. Laboratory experiments on porous rock have shown that intact rock strength reduces with increasing porosity, which has a direct effect on the rock mass strength. Rock porosity has however not been well accounted for in rock mass characterization methods currently in use. This research applies the modified GSI method for carbonate rock masses which is based on a combination of GSI and total porosity. The main aim is to quantify the GSI with respect to rock porosity which is a direct indicator of the state of karstification, as an inherent feature that affects rock mass strength. An empirical equation is proposed whereby the GSI as observed in the field is modified by a natural log of the value of porosity, giving rise to a modified GSI (GSIm). The GSIm together with laboratory properties of rock is used to determine the properties of Vipingo coral limestone from RocLab software. A deterministic parametric slope stability analysis is done using the finite element software Phase 2 with the rock mass properties as input parameters. The analysis results point to a direct dependence of the slope stability on slope angle, slope height and rock mass strength of the lithological unit. The graphs make a useful design guide for slopes engineered in this type of rock mass.
Highlights
Determination of rock mass mechanical properties is crucial for geoengineering works in civil applications such as tunnels, slopes, foundations and mining operations, both surface and underground
Laboratory experiments on porous rock have shown that intact rock strength reduces with increasing porosity, which has a direct effect on the rock mass strength
The main aim is to quantify the Geological strength index (GSI) with respect to rock porosity which is a direct indicator of the state of karstification, as an inherent feature that affects rock mass strength
Summary
Determination of rock mass mechanical properties is crucial for geoengineering works in civil applications such as tunnels, slopes, foundations and mining operations, both surface and underground. The originally developed rock mass classification systems of RMR and Q-system served the purpose quite well in conjunction with the Hoek-Brown failure criterion. The RMR system and Q-system relied on RQD which is difficult to obtain for weak rock masses due to very poor core recovery. The Geological strength index (GSI) developed by Evert Hoek [1] became a suitable alternative classification system based on geological observation of rock mass properties. A lot more research studies and modifications have been conducted by different researchers on various aspects of the GSI system to take care of weak, jointed, and heterogenous rock masses [2]
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