WARTA GEOLOGI GEOLOGICAL SOCIETY OF MALAYSIA PERSATUAN GEOLOGI MALAYSIA Jilid 47 APRIL Volume 47 No. 1 2021 No. 1 ISSN 0126 - 5539; e-ISSN 2682 - 7549 PP2509/07/2013(032786) RM 70.50 Warta Geologi PERSATUAN GEOLOGI MALAYSIA Editor Wan Hasiah Abdullah Geological Society of Malaysia Geological Society of Malaysia, Malaysia Council 2020/2021 Editorial Board Azman A. Ghani President : Abd. 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This photograph, taken by Yusuf Madi, is the winner of GSM National Geology Photography Competition 2020/2021 CATATAN GEOLOGI GEOLOGICAL NOTES DOI : https://doi.org/10.7186/wg471202101 Ultrasonic pulse velocities and dynamic elastic constants of sandstones from the Semanggol Formation, Beris Dam, Kedah Darul Aman J. K. Raj No. 83, Jalan Burhanuddin Helmi 2, Taman Tun Dr. Ismail, 60000 Kuala Lumpur, Malaysia Author email address: [email protected] Abstract: The main Beris Dam is founded on a sequence of thick bedded conglomerates and pebbly to fine grained sandstones with minor mudstone mapped as the Semanggol Formation of Triassic age. Ultrasonic pulse measurements show velocities of compressional and shear waves through the sandstones to increase with decreasing grain size; the pebbly sandstone with velocities of 2.210, and 5.171, km/s, and the coarse grained sandstone with velocities of 2.477, and 5.612, km/s, respectively. The medium grained sandstones have compressional and shear wave velocities of 2.457, and 5.793, km/s and the fine grained sandstones, velocities of 2.572, and 5.867 km/s, respectively. Dynamic elastic constants computed from the ultrasonic velocities also increase in values with decreasing grain size; Poisson’s ratio varying from 0.36 to 0.39, the modulus of elasticity from 35.076 to 48.210 GPa, the bulk modulus from 52.260 to 67.362 GPa and the modulus of rigidity from 12.637 to 17.468 GPa. Increasing velocities and elastic constants with decreasing grain size are considered to result from a denser arrangement of constituent grains as shown by increasing dry unit weights. Comparison with the results of an unconfined compression test on a fine grained sandstone indicate that the ultrasonic elastic constants are good approximations of static elastic constants. Keywords: Ultrasonic pulse velocities, elastic constants, Semanggol Formation INTRODUCTION audible range are used in determination of the velocities, Properties of rock material are usually only considered the calculated constants are termed ultrasonic elastic from the point of view of their reaction to static stresses, constants (ASTM, 1976; AIT, 1981). It is to be noted that i.e. the stresses to which a structure in rock would normally these ultrasonic constants, and wave velocities often do be subjected. However, during the construction phase of not agree with those determined by static laboratory, or engineering projects, and possibly later if earthquakes or in situ methods (ASTM, 1976). The ultrasonic method, nuclear explosions are considered, a rock material may be however, has the advantage that it is a non-destructive subject to transient dynamic loading from the action of technique and allows for preliminary prediction of the explosives, often exceeding by many orders of magnitude elastic properties of rock material. any static stress to which it may be subjected (Farmer, A number of studies involving the ultrasonic method 1968). The way in which a rock material may accept or have been carried out in Malaysia; Raj (1996) showing reject these dynamic stresses is of direct importance to the compressional and shear wave velocities as well as design of structures and towards this end, a knowledge dynamic elastic constants of igneous rocks from the Ajil of its dynamic elastic constants is extremely useful area to be dependent upon inherent mineral compositions (Farmer, 1968). and textures. The ultrasonic method furthermore, Various methods are available for determination of determined a compressional wave velocity of 6.046 km/s the dynamic elastic constants of rock material; the most for a porphyritic hypersthene micro-diorite from Tawau common laboratory method involving their calculation (Raj, 2004a), whilst a meta-rhyolitic tuff from the Dinding from measurements of the propagation velocities of Schist was shown to be an anisotropic rock material with compressional and shear waves (ASTM, 1976). Such a compressional wave velocities of 5.616, and 3.973, km/ calculation procedure is possible in view of the fact that sec, parallel, and perpendicular, to foliation, respectively the existence and velocity of all body waves in an elastic (Raj, 2004b). medium is a function of its density and elasticity (Obert Goh et al. (2016) determined the ultrasonic pulse & Duvall, 1976). Where pulse frequencies above the velocities of compressional waves through some 70 ISSN 0126–5539; e-ISSN 2682-7549 Warta Geologi, Vol. 47, No. 1, April 2021, pp. 1–8 J. K. Raj granite, and 24 schist, specimens cored from samples after measurement of the shear wave velocities, a thin collected at various locations in Peninsular Malaysia. film of grease was applied on the core ends to ensure Unconfined compression tests of the cores then led to good contact with the transducers. proposal of two empirical relationships that were said After determination of the compressional and shear to predict the uniaxial compressive strength from the wave velocities, several dynamic elastic constants were compressional wave velocity. calculated based on formulae provided in standard Nurul Huda et al. (2019) determined the ultrasonic laboratory manuals as those of the American Society pulse velocities of compressional and shear waves through for Testing and Materials (ASTM, 1976) and the Asian eight sandstone cores from the Kenny Hill Formation. Institute of Technology (AIT, 1981). It is to be noted Unconfined compression tests of the cores then allowed that these formulae are based on assumption of a linear determination of the uniaxial compressive strengths as relationship between applied stress and the resulting well as modulus of elasticity, shear modulus and bulk strain; an elastic medium being one in which all strain modulus. Regression analyses were said to yield good is instantaneously and totally recoverable on removal correlations between compressional wave velocities and of the applied stress (Farmer, 1968). In such a medium, static elastic constants. the existence and velocity of all body waves is thus a In this short note, the compressional and shear wave function of its density (or unit weight) and elasticity; velocities of ultrasonic pulses through sandstones from the the propagation velocities of compressional, and shear, Triassic Semanggol Formation are presented.