ABSTRACT

The Schmidt hammer was used to obtain the in-situ rebound number on various types of rock mass. Point load rest on lump cores and uni-axial compression test on the intact rock cores were conducted to obtain respective strength parameters in the laboratory. The rock mass covered in the present study were of various types including basaltic-a hard rock types to porous sandstone considered as a weak rock. The various relationships between in-situ rebound number and that with the strength parameters were presented. The outcome of the paper is expected to provide a simple approach for in-situ rock mass characterization using Schmidt hammer.

1 INTRODUCTION

The Schmidt hammer developed in the late 1940's as an index apparatus for non-destructive testing of concrete in-situ, has been widely used in rock mechanics since the early 1960's, mainly for estimating the uni-axial compressive strength and Young's modulus of a rock material (Haramy and DeMarco 1985; O'Rourke 1989; Katz et al. 2000; Yilmaz and Sendir 2002; Goktan and Gunes 2004; Yasar and Erdogan 2004; Basu and Aydin 2004; Aydin and Basu 2005; Fener et al. 2005; Buyuksagis and Goktan 2007). Considering its long history and widespread use, the standard method for the Schmidt hammer test (ISRM 1978; ASTM 2001; IS 1987) might be expected to ensure consistent and reliable results and reproducible correlation's for a given rock type. The earlier studies mainly were concerned with intact rock materials; since studies concerning application of Schmidt hammer to characterize in-situ rock mass is limited. Except studies presented by Sheorey et al. (1984) and Ozkan and Bilim (2008) who applied the in-situ Schmidt hammer test on a coal faces.

The present study has been undertaken to determine if any reproducible pattern of in-situ rebound hammer values exists between it and laboratory rock properties of various rock types. The objective of the present paper is to outline the importance of Schmidt hammer to characterize the in-situ rock mass. The relationship between in-situ rebound number various strength parameters are presented. The outcome of the study is expected to provide a simple approach for in-situ rock mass characterization.

2 TEST APPARATUS AND IT'S APPLICATION

The Schmidt hammer determines the rebound hardness of a test material. The plunger of the hammer is placed against the specimen or insitu rock mass face and is depressed into the hammer by pushing the hammer against the specimen. Energy is stored in a spring, which automatically releases at a prescribed energy level and impact a mass against the plunger. The height of rebound of the mass is hardness. The device is portable and may be used both in the laboratory and field.

Rebound tests on the in-situ rock mass were carried out with a Proceq N-type digital Schmidt hammer with impact energy of 2.207 Nm. The instrument used in the present study was DIGI-SCHMIDT 2000, Model No. ND-3805 with R=81+2. It comprised of the actual hammer and the display unit. Both components belong together and the are calibrated as one unit.

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