Method for evaluation of geological strength index of carbonate cliff rocks: Coupled hyperspectral-digital borehole image technique

The deterioration of unstable rock mass raised interest in evaluating rock mass quality. However, the traditional evaluation method for the geological strength index (GSI) primarily emphasizes the rock structure and characteristics of discontinuities. It ignores the influence of mineral composition and shows a deficiency in assessing the integrity coefficient. In this context, hyperspectral imaging and digital panoramic borehole camera technologies are applied to analyze the mineral content and integrity of rock mass. Based on the carbonate mineral content and fissure area ratio, the strength reduction factor and integrity coefficient are calculated to improve the GSI evaluation method. According to the results of mineral classification and fissure identification, the strength reduction factor and integrity coefficient increase with the depth of rock mass. The rock mass GSI calculated by the improved method is mainly concentrated between 40 and 60, which is close to the calculation results of the traditional method. The GSI error rates obtained by the two methods are mostly less than 10%, indicating the rationality of the hyperspectral-digital borehole image coupled evaluation method. Moreover, the sensitivity of the fissure area ratio ( S r ) to GSI is greater than that of the strength reduction factor ( α ), which means the proposed GSI is suitable for rocks with significant fissure development. The improved method reduces the influence of subjective factors and provides a reliable index for the deterioration evaluation of rock mass. • The mineral content of core is classified by hyperspectral image. • The fissures of rock mass are identified by digital panoramic borehole image. • The GSI is improved according to the mineral content and fissure area ratio. • The parameter sensitivity of fissure area ratio is greatest in proposed GSI method.