Evaluation of geo-mechanical properties of very weak and weak rock materials by using non-destructive techniques: Ultrasonic pulse velocity measurements and reflectance spectroscopy

• The geo-mechanical properties of very weak–weak rock materials were investigated.
• Different genetic rocks types were defined by using the reflectance spectroscopy.
• The empirical equations of Vp-UCS and Vp-Ei were obtained for each rock type.

The main purpose of this study is to evaluate the geo-mechanical properties of very weak and weak rock materials by using ultrasonic pulse velocity measurements and considering specifically detailed mineralogical compositions. For the purpose, P-wave velocity (Vp) measurements of 66 core samples of the sedimentary rocks including claystones and mudstones collected from Firuzkoy area of Istanbul (Turkey) were carried out. Unconfined Compressive Strength (UCS) tests were then conducted. The axial deformations recorded during the UCS tests were also evaluated and the elastic moduli of the rock materials (Ei) were calculated. Statistical relations were investigated between the values of P-wave velocity measurements and the UCS and Ei. In order to evaluate the effects of detailed mineralogical compositions on the prediction performances of the empirical equations Vp-UCS and Vp-Ei, the reflectance spectroscopy was introduced. 1035 spectral measurements were taken from smooth and fresh surfaces of the failed core samples. Different genetic rock types were defined according to crystal field effect and charge transfer absorptions of transition elements, and water and OH vibrational spectral diagnostics. The statistical relations were reinvestigated, and the individual empirical equations were reproduced for each genetic rock type. The mean values of the multiple coefficients of correlations (R) were obtained to be 0.904 and 0.916 for the equations of Vp-UCS and Vp-Ei. Considering the maximum values of R, the increment rates for the values of the explained variances reach up to 14.3% and 13.5% for the equations, respectively. Additionally, according to the results of the analysis of variance (ANOVA) evaluations, the empirical equations of Vp-UCS and Vp-Ei reproduced for each genetic rock type were found to be statistically significant at the significance level of 0.05. As a consequence, the non-destructive techniques Vp measurements and reflectance spectroscopy could be efficiently used together for the evaluation of the geo-mechanical properties of very weak and weak rock materials in particular.