Abstract:
Smooth core samples for the laboratory tests cannot always be prepared particularly from weak rocks. Although some simple indirect test methods have been developed to estimate the mechanical properties of rocks, the specimen preparation from soft rock for some indirect tests is still difficult. In order to close this gap, the needle penetration test has been used recently. This study investigates the predictability of physico-mechanical properties of pyroclastic rocks from the needle penetration index (NPI). The block samples of pyroclastic rocks were collected from six different locations of Erciyes (Kayseri) region of Turkey. The needle penetration, the uniaxial compressive strength and tensile strength, density, and porosity tests were carried out on the specimens in the laboratory. The NPI values were correlated to the physico-mechanical properties. Very strong correlations were obtained between the NPI values and rock properties. It was concluded that the physico-mechanical properties of pyroclastic rocks can be predicted from the needle penetration index.
Introduction
The physico-mechanical properties of rocks are used for designing surface and underground structures in rock mass in mining and civil engineering projects. Smooth core samples suggested by standards for the laboratory tests cannot always be prepared particularly from weak and clay-bearing rocks. Some simple indirect test methods such as point load test and block punch index tests have been developed to estimate the mechanical properties of rocks. However, the specimen preparation from weak and clay-bearing rocks is still difficult for these indirect tests. In order to close this gap, the needle penetration test which is a simple and non-destructive index test was developed.
The needle penetration test is a non-destructive index test which is applicable both in the field and laboratory and does not require any special sample preparation [1]. The test has been used for the estimation of physical and mechanical properties of weak or soft rocks. Although some researchers have suggested some correlations between the physico-mechanical rock properties and the needle penetration index (NPI) for weak rocks, the studies are limited on this area. In this study, the predictability of physico-mechanical properties of pyroclastic rocks from the NPI was investigated.
