Preliminary analysis of rock mass weathering grade using image analysis of CIELAB color space with the validation of Schmidt hammer: A case study

Rock slope instability causes rock slope failure with intense weathering processes in tropical regions. In addition to the various advanced numerical rock slope stability assessment techniques that have been developed thus far, simple evaluation techniques characterizing the rock slope weathering degree based on color changes of the rock surface remain one of the main techniques used by most geologists onto the rock slope stability assessment. The present study proposed a new evaluation method for weathering assessment of the limestone rock slope with computer-assisted image processing technologies to reduce human-induced errors based on a manual characterization process. The color changes of the limestone rock referring the CIELAB color space, which indirectly indicated the differential weathering of the rock mass, were measured in-situ using the FRU colorimeter with a 40 mm aperture. The Schmidt hammer was used to determine the intact rock strength and validate the color changes of the limestone rock to the International Society For Rock Mechanics (ISRM) weathering grade standard. Results indicated that a* and b* correlated strongly with R 2  = 0.7404, underscoring the consistency of the CIEL*a*b color space data obtained in situ. The a* and b* correlated strongly with the uniaxial compressive strength result obtained via the rock Schmidt hammer test, with R 2 of 0.7058 and 0.7011, respectively. The results were verified with the weathering grades analyzed using image analysis technique. In conclusion, the CIELAB color space is an effective tool in the preliminary assessment of rock mass weathering, particularly for slightly vegetated rock slope outcrops.