Goh Thian Lai

A Systematic Approach for the Quantification of Rock Slope Stability

Slope Mass Rating (SMR) quantifies the adjustment factors of Rock Mass Rating (RMR) for cut slope stability evaluation. However, the discontinuities surface roughness in spite of being a fundamental parameter influencing the peak friction angles (αp) of discontinuities is not considered. Therefore, a systematic cut rock slope stability evaluation proposed here is based on the use of αp of discontinuities and together with the results of SMR classification. The potential for slope failure can be summarised as follows: if SMR predicts failure and dip angle of discontinuity (βi) > αp, the slope has a very high failure potential; if SMR predicts failure and βi αp, the slope has low failure potential and if stable according to SMR and βi < αp, the slope is stable. This approach has an additional advantage since the joint roughness determination using tilt testing is relative low cost and does not require complicated testing methods.

A Low Cost Alternative Approach to Geological Discontinuity Roughness Quantification

The surface roughness of geological discontinuities can be considered a key parameter in the evaluation of the stability of structures constructed within rock masses. Several different methodologies can be applied to determine this parameter and they vary in their complexity. The aim of this study is to correlate the peak friction angle (ϕp) of discontinuity planes of fresh bedrock with the Joint Roughness Coefficient, JRC. A simple low cost approach is presented based on the determination of JRC and the application of derived polynomial equations to determine the peak friction angle, ϕp from the surface roughness from geological discontinuities for the major lithologies found in Peninsula Malaysia. Eight thousand six hundred and seven tilt tests were conducted to obtain the correlations between peak friction angles with JRC of granite, schist, limestone, quartzite and sandstone. The respective polynomial equations are as follows: for granite ϕp= −0.071 JRC2 + 3.56 JRC + 35.6° for schist ϕp = −0.022 JRC2 + 3.21 JRC + 28.1° for limestone ϕp= −0.0635 JRC2 + 3.95 JRC + 25.2° for quartzite ϕp = −0.083 JRC2 + 4.17 JRC + 27.6° for sandstone ϕp = 0.0424 JRC2 + 1.13 JRC + 29.2° For all the derived polynomials, the coefficient of determination, R2 was greater than 0.9. The JRC can be determined as part of an engineering geological investigation and the respective polynomial applied to determine the peak friction angle, ϕp for the specific lithology.

The geomechanical strength of carbonate rock in Kinta valley, Ipoh, Perak Malaysia

The stability of both cut rocks and underground openings were influenced by the geomechanical strength of rock materials, while the strength characteristics are influenced by both material characteristics and the condition of weathering. This paper present a systematic approach to quantify the rock material strength characteristics for material failure and material & discontinuities failure by using uniaxial compressive strength, point load strength index and Brazilian tensile strength for carbonate rocks. Statistical analysis of the results at 95 percent confidence level showed that the mean value of compressive strength, point load strength index and Brazilian tensile strength for with material failure and material & discontinuities failure were 76.8 ± 4.5 and 41.2 ± 4.1 MPa with standard deviation of 15.2 and 6.5 MPa, respectively. The point load strength index for material failure and material & discontinuities failure were 3.1 ± 0.2 MPa and 1.8 ± 0.3 MPa with standard deviation of 0.9 and 0.6 MPa, respectively. The Brazilian tensile strength with material failure and material & discontinuities failure were 7.1 ± 0.3 MPa and 4.1 ± 0.3 MPa with standard deviation of 1.4 and 0.6 MPa, respectively. The results of this research revealed that the geomechanical strengths of rock material of carbonate rocks for material & discontinuities failure deteriorates approximately ½ from material failure.

Development of empirical correlation of peak friction angle with surface roughness of discontinuities using tilt test

The significant influence of surface roughness of discontinuity surfaces is a quantity that is fundamental to the understanding of shear strength of geological discontinuities. This is due to reason that the shear strength of geological discontinuities greatly influenced the mechanical behavior of a rock mass especially in stability evaluation of tunnel, foundation, and natural slopes. In evaluating the stability of these structures, the study of peak friction angle (Φpeak) of rough discontinuity surfaces has become more prominent seeing that the shear strength is a pivotal factor causing failures. The measurement of peak friction angle however, requires an extensive series of laboratory tests which are both time and cost demanding. With that in mind, this publication presents an approach in the form of an experimentally determined polynomial equation to estimate peak friction angle of limestone discontinuity surfaces by measuring the Joint Roughness Coefficient (JRC) values from tilt tests, and applying ...