!Rangkuman UCS With Strain Gauge

UCS can calculates both the rock strength and estimates measures axial and lateral deformation of the rock specimen.

The modulus of compressibility can be estimated from the axial curve.

Poisson’s ratio can be estimated from the two strain curves.

Usually two strain gauges are attached with glue in the middle (height wise) of the specimen in diametrically opposite positions.

The strain gauges should be perfectly aligned with the axial axis of the specimen.

Glue to attach the strain gauge called gauge cement.

In practice, three different ways to estimating the modulus of elasticity, are used,

1. Tangential modulus, where d/d at 50% of maximum stress2. Average modulus, where d/d estimated from average curve3. Secant modulus, which is the slope of the straight line from zero strain and intersecting the

curves at 50% of maximum stress

These moduli, often assumed as modulus of elasticity, in fact, they are the modulus of deformation!

In order to estimate the “true” modulus of elasticity a reloading sequence must be performed.

if UCT is conducted with measurement on axial strain (a) and horizontal strain (r) through installing a pair of strain gauges, besides UCS, several important parameters pertaining to rock deformation such as strain at failure (f), Young’s modulus (E) and Poisson’s ratio (ν), can be obtained

http://www.uq.edu.au/geomechanics/rockmech.htmlRock Testing Capabilities

The Geomechanics Laboratory within the School of Civil Engineering at The University of Queensland offers a range of rock testing, including the following:

o Static testing:o Unconfined Compressive Strength without or with strain-gaugingo Indirect Tensile Strength (Brazilian or loading disc)o Fracture Toughnesso Shore Sclerescope Hardness

o Cyclic testing:o Applied to any of the above tests

o Quantitative and qualitative analyses:o Backscatter and secondary electron imaging using Scanning Electron Microscope (SEM)o X-Ray Diffraction analysis using the Energy Dispersion Spectrometry (EDS) technique

UNIAXIAL COMPRESSIVE STRENGTHSample preparation

Sample preparation may require coring and trimming to form cylindrical test specimens conforming to ISRM recommendations (see Figure 1; that is, cylindrical specimens 54 mm in diameter by 134 mm high to give a height to diameter ratio of 2.5 to 3.0, a ratio of specimen diameter to that of the largest rock grain greater than 10:1, and having the ends of the specimen flat to within 0.02 mm).

Figure 1. Brisbane tuff specimens prepared for UCS testing

Specimens may be strain-gauged (and wired) with 2 lateral and 2 axial CEA-06-500UW-350 model Micro Measurements Division (USA) brand strain gauges per specimen (see Figure 2), for measuring both axial (longitudinal) and circumferential strain to determine Young's modulus and Poisson's Ratio.

Figure 2. Strain-gauged Brisbane tuff UCS specimensTesting

Unconfined Compressive Strength (UCS) testing is carried out using a digitally-controlled INSTRON testing machine (see Figure 3), with measurement of the applied stress, overall sample height, and strain gauges (if fitted), and with reporting of the stress/strain plot, UCS, Secant Modulus (at 50% of UCS), and Young's Modulus and Poisson's Ratio (if strain-gauged).

Figure 3. UCS testing of strain-gauged Brisbane tuff specimen