Abstract

Point load test (PLT) is a widely used indirect method to estimate the unconfined compressive strength (UCS) of rocks in geotechnical practice. The test consists of loading a rock specimen between two conical platens until failure occurs in order to calculate the point load strength index (Is(50)). Its main advantages are the simplicity of the test, the flexibility in terms of the specimen's shape and size, the low cost and the possibility of being performed in the laboratory or the field. In this line, many authors have obtained correlations between Is(50) and UCS for different rock types. However, limited works have been conducted in soft or weak rocks such as porous building stones with UCS values lower than 40 MPa and very few studies have examined the relationship between Is(50) and elastic Young´s modulus (Est) or the water saturation effect on these properties and the corresponding correlations. This study tries to close these gaps by stablishing correlation functions to infer UCS and Est in term of Is(50) for porous building stones from Alicante (Spain) in dry and saturated conditions. Concerning the results, significant correlations were obtained for dry, saturated and both dry and saturated specimens, demonstrating the applicability of PLT to predict the strength and the deformability of these rock materials. Finally, the findings were also compared with other previous studies.

1 Introduction

Uniaxial compressive strength (UCS) and static Young´s modulus (Est) are the two most important mechanical properties of rocks for its practical value and relevance in mining, geotechnical and civil engineering projects performed in rock environment. UCS is frequently used in geomechanical classifications of rock mass like RMR (Rock Mass Rating) proposed by Bieniawski (1975) and Q (rock mass quality index) introduced by Barton et al. (1974), which are commonly utilised in designing of tunnels, slopes and foundations. However, despite testing procedures to measure these mechanical parameters are fairly simple, they are relatively expensive and time consuming (Kahraman 2014). Furthermore, obtaining specimens with the geometry required by standard is difficult or impossible in soft rocks or very jointed rock masses. For these reasons, indirect tests are very useful to estimate strength and deformability for preliminary projects. In this line, point load test index (IS(50)) has been frequently used for the prediction of UCS value due to its many advantages as the testing ease, the simplicity of sample preparation due to the flexibility in terms of size and shape of specimens that can be used, and the feasibility to be used in the field as well as in the laboratory (Singh et al. 2012).

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