Abstract
Great efforts had been made to use indirect non-destructive tests in the geotechnical evaluation of rocks, especially sandstones, employing different empirical equations. However, most of these equations have been derived from hard and compacted sandstones data; therefore, the focus of this research is on weak and weakly compacted sandstones, aiming firstly to obtain empirical equations for estimating their characteristics, secondly to demonstrate and visualize the correlations between the studied variables, and finally to cluster the studied samples based on their characteristics. To attain these aims, twenty oriented block samples were collected from Nubia sandstone, central Eastern Desert, Golden Triangle area, Egypt. These samples were prepared and tested according to standard test methods, including uniaxial compressive strength (UCS), Brazilian tensile strength (BTS), Schmidt rebound number (SRN), porosity (n), bulk density (ρ), and ultrasonic P-wave velocity (UPV). The loss on ignition (LOI) was also employed as a physicochemical test for classifying the studied samples and indicating pores filling materials. The results revealed that these sandstones are characterized mainly by high n, low ρ, and low UPV values and these give an indication of weakly compacted and weakly cemented sandstone with shallow burial diagenetic conditions. Based on UCS and elastic modulus values, these sandstones are mainly classified as very low strength and highly yielding rocks. The results of regression analysis show satisfactory correlations between physical and mechanical characteristics, indicating the suitability of obtained empirical equations to deduce these properties. Principal component analysis revealed that the LOI, BTS, SRN, and USC have a positive correlation to each other and weakly correlated with ρ and UPV, which positively correlated to each other and negatively correlated to n. The results of agglomerative hierarchical clustering revealed that the studied samples can group into three main clusters depending on their USC, LOI, and n values.
Highlights
Significant efforts had been made to use indirect non-destructive tests instead of direct destructive tests in geotechnical applications, such as tunnels, dams, rock excavation or drilling, roads, slope stability assessment, and building
The results revealed that these sandstones are characterized mainly by high n, low ρ, and low ultrasonic P-wave velocity (UPV) values and these give an indication of weakly compacted and weakly cemented sandstone with shallow burial diagenetic conditions
All wacke litho-type samples belong to G3, while all arenite litho-type samples belong to G2, except the high silica content samples belong to G1
Summary
Significant efforts had been made to use indirect non-destructive tests instead of direct destructive tests in geotechnical applications, such as tunnels, dams, rock excavation or drilling, roads, slope stability assessment, and building This is due to the direct destructive tests, such as the unconfined compressive strength (UCS) test, which are mostly overworked, time consumed and more expensive, as it requires special sample preparation and depends on rigorous standards (Ceryan et al, 2013; Ozcelik, Bayram, & Yasitli, 2013). These direct tests are mostly not suitable for weathered rocks, friable, jointed, foliated, and laminated rocks (Mishra & Basu, 2012). Ultrasonic P-wave velocity (UPV) test for example is one of the essential non-destructive tests, which is employed to investigate some properties of rocks, such as degree of rock weathering (Schmidt, 1951), tensile strength (Hosseini & Shirin, 2015), UCS (Kurtulus et al, 2018), elastic properties (Abdullah et al, 2019), slake durability index (Hosseini, 2016), and the physical properties of rocks (Kurtuluş et al, 2016)
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