Peak friction angle estimation from joint roughness coefficient of discontinuities of limestone in Peninsular Malaysia

The peak friction angle (φpeak) roughness of discontinuity surfaces is a value that is fundamental to the understanding of shear strength of geological discontinuities, considering its importance in determining the mechanical properties of the discontinuity surface. It is however, both time and cost demanding to determine the peak friction angle as it requires an extensive series of laboratory tests. This paper 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 in a field survey study, and applying the fore mentioned empirical correlation. A total of 1967 tilt tests and JRC measurements were conducted in the laboratory to determine the peak friction angles of rough limestone discontinuity surfaces. The experimental results were analyzed and correlated to establish a polynomial equation of φpeak = -0.0635JRC2 + 3.95JRC + 25.2 with coefficient of determination (R2) of 0.99. The laboratory results were also compared with theoretical results calculated from Barton’s linear equation. The results shown that estimation of peak friction angles were more accurate using the newly proposed polynomial equation since the percentage differences between measured and calculated peak friction angles is less than 6% compared to estimation from Barton’s linear equation where the percentage of differences is less than 11%. The proposed correlation offers a practical method for estimation of peak friction angles of discontinuity surfaces of limestone from measurement of JRC in the field

Assessment of ultimate bearing capacity based on the Hoek-Brown failure criterion

The ultimate bearing capacity is an essential requirement in design quantification for shallow foundations especially for structures built on large rock masses. In many engineering projects, structures built on foundation of heavily jointed rock masses may face issues such as instability and sudden catastrophic rock slope failure. Determination of the ultimate bearing capacity (Qult) of foundations resting on rock mass has traditionally been determined by employing several strength criterions. One of the accepted and widely implemented methods is to use the Hoek-Brown failure criterion 2002, where the required parameters are determined from a rock mass classification system, Geological Strength Index (GSI). This paper defines an assessment for ultimate bearing capacity (Qult) based on the Hoek-Brown failure criterion 2002 for a granitic rock slope beneath a 20 m diameter concrete water tank at Bandar Mahkota Cheras, Kajang, Selangor. Based on the Hoek-Brown failure criterion 2002, the ultimate bearing capacity (Qult) of rock mass was 7.91 MPa. The actual stress acting on the rock mass was 0.32 MPa. The assessment showed that the rock mass is safe since the ultimate bearing capacity (Qult) is 24.7 times higher than the actual stress acting on the rock mass

Rock Slope Stability Assessment of Limestone Hills in Northern Kinta Valley, Ipoh, Perak, Malaysia

The uniqueness of karsttopography in Kinta Valley lies with the spectacular shape of the steep-sided limestone towers. However, theinstability ofthese hillslopes may affect the vulnerability of the surrounding area. Thus, this study was conducted with the objective to investigate the failure modes of 9 slopes in the vicinity ofnorthernKinta Valley, Ipoh, Perak. There were two types of failure modes identified in the study area,which are planar and wedge failures. Planar failures were identified on slope GL3of Gunung Lang and slope GR3of Gunung Rapat with the dip direction and dip angle of 280⁰/79⁰ and 004⁰/ 64⁰ respectively. Two wedge failures were identified on slope QXL1of Qing Xing Ling, Taman Saikat with dip direction and dip angle of 252⁰/82⁰ and 302⁰/74⁰ respectively. A wedge failure was identified on slope GL3 for Gunung Lang, slope GR1, slope GR3 for Gunung Rapat and slope QXL2 for Qing Xing Ling,Taman Saikat. The dip direction and dip angle for the respective wedges failure were 345⁰/65⁰, 036⁰/ 49⁰, 006⁰/ 64⁰ and 025⁰/60⁰. No failure was identified on slope GL1, and slope GL2,forGunung Lang and slope GR2, and slope GR4forGunungRapat

ROCK SLOPE STABILITY ASSESSMENT OF LIMESTONE HILLS, SOUTHERN KINTA VALLEY, IPOH, PERAK, MALAYSIA

The uniqueness of the karst topography of Kinta Valley is the result of the spectacular shaped steep-sided limestone towers. The instability of these hillslopes however, may affect the vulnerability of the surrounding area. This paper presents the results of slope stability assessment by using kinematic analysis to investigate the possible failure modes of 7 slopes in Gua Naga Mas (GNM1, GNM2 and GNM3), Gua Kandu (GK1, GK2 and GK3) and Gua Tempurung (GT) located in the southern part of the Kinta Valley, Ipoh, Perak. From the results of the slope stability assessment, it was determined that planar failure and wedge failure were the main failure modes. The GNM1 slope of Gua Naga Mas consist of four wedge failures and a planar failure with dip directions/dip angles of 005⁰/54⁰, 354⁰/59⁰, 124⁰/52⁰, 360⁰/50⁰ and 063⁰/70⁰ respectively. The GNM2 slope consists of a wedge failure with the dip direction/dip angle of 021⁰/64⁰. Two wedge failures and a planar failure were identified on slope GNM3 with the respective dip directions/dip angles of 336⁰/49⁰, 301⁰/68⁰ and 270⁰/71⁰. The GK1 slope for Gua Kandu consists of wedge and planar failures with dip directions/dip angles of 231⁰/49⁰ and 217⁰/49⁰ respectively. The mode of failure at GK2 slope was identified as wedge failure with the dip direction/dip angle of 154⁰/44⁰. No mode of failure was identified on slope of GK3. Slope GT of Gua Tempurung was identified to have two wedge failures with dip directions/dip angles of 011⁰/49⁰ and 321⁰/48⁰ respectively

Correlation of Dynamic and Static Young’s Modulus for Limestone

The application of rock mechanics in the area of geotechnical engineering is important especially, in describing the strength of rock material for essessing the stability of excavations, foundations and slopes in rock. In this study, the characterization of the rock material was investigated through the Young’s modulus parameter, which describes the relationship between the stress applied to the rock material and the resulting strain. For an elastic and homogeneous solid, the measurement of Young’s modulus can be determined either from the static or dynamic measurements. Numerous studies outline the differences between the Young's modulus obtained from static and dynamic measurement in the laboratory. Comparatively, the measurement using static methods are more direct and realistic, as it describes the behaviour of rock deformation until failure occurs. The dynamic methods are more versatile and continuous, as they rely solely on the measurement of elastic wave velocities. However, one of the most notable disadvantages of rock material characterization by means of dynamic methods is that it overestimates the failure of rock material when compared to its actual value. With this in mind, the aim of this study is to obtain the measurements of Young’s modulus using both the static and dynamic methods. Based on the comparison made, an empirical equation of Est = 0.9264 (Edy) + 0.4976 with coefficient of determination, R2 of 0.8 is obtained for estimating the static Young’s modulus for limestone. The equation is applicable in situation where static measurement could not be carried out, and also serves as reliable estimation of Young’s modulus from dynamic measurement

A systematic approach of rock slope stability assessment: a case study at Gunung Kandu, Gopeng, Perak, Malaysia

The stability of the limestone cliff at Gunung Kandu, Gopeng, Perak, Malaysia was assessed based on the Slope Mass Rating (SMR) system on 53 cross sections of the Gunung Kandu hill slopes. The slopes of Gunung Kandu were identified as class I (very good) to IV (poor). The kinematic analysis showed that 12 out of 53 hill slopes of Gunung Kandu were identified as having potential wedge, planar and toppling failures. The assessment showed that the stability of the western flanks can be classified as stable to unstable with the probability of failure from 0.2 to 0.6. The stability of the eastern and southern flanks range from very stable to partially stable with the probability of failure from 0.0 to 0.4. While the stability of northern flanks are from very stable to stable with the probability of failure of 0.0 - 0.2. This systematic approach offers a practical method especially for large area of rock slope stability assessment and the results from probability of failure values will help engineers to design adequate mitigation measures

Stability assessment of limestone cave: Batu Caves, Selangor, Malaysia

The limestone hill of Batu Caves is slowly being turned into a recreation park for slope climbing, base jumping and cave exploring. Quantitative assessment on the stability of the cave is essential to ensure the safety of tourists and visitors. The aim of this study was to quantitatively assess the stability of Gua Damai, Batu Caves, Selangor, Malaysia by using the Q system for rock mass classification, together with other factors such as cave width and thickness of the cave roof. The stability of the limestone cave wall was evaluated using Slope Mass Rating (SMR). A discontinuity survey conducted along the slopes beneath the opening of the cave showed that the rock mass comprised of four major joint sets labeled as J1, J2, J3, and J4 with the dip directions and angles of 110˚/73˚, 325˚/87˚, 243˚/39˚ and 054˚/30˚, respectively. The result of kinematic analysis showed that the dip direction/dip angle of a potential wedge failure was 051˚/59˚. By referring to the ratio of cave roof thickness with cave width, the results showed that the cave is stable. Based on the relationship between Q system and the cave width, the stabilities of Section 4 of Gua Damai is stable while Section 1, 2, 3, 5, 6, 7 and 8 require supports. Based on SMR, the cave walls stability at Portion c, d, and f were not stable while Portion a, b, e and g were stable. Overall, the most stable part of the cave is Section 4 followed by Sections 5 and 2. Sections 1, 3 and 8 are moderately stable while Sections 6 and 7 have poor stability

Application of a Comprehensive Rock Slope Stability Assessment Approach for Selected Malaysian Granitic Rock Slopes (Pengaplikasian Pendekatan Penilaian Kestabilan Cerun Batu Komprehensif untuk Cerun Batu Granit Malaysia yang Terpilih)

In Malaysia, rock slope stability analysis has been largely confined to kinematic analysis with rock mass rating systems as assessment tools for stability analysis. While this method addresses the fundamental issues of rock slope stability including identifying potential failure modes, an information gap still exists between geologists and engineers in designing proper mitigation measures for rock slopes. This paper aims to address this issue by incorporating several methodologies, including kinematic analysis, slope mass rating and the Barton-Bandis criterion for the limit equilibrium method. Four rock slopes with potential instabilities namely KSA, KSB, LHA, and LHB were studied. KSA and KSB were located near Kajang, Selangor while LHA and LHB were located near Rawang, Selangor. Each slope exhibits multiple potential failures, with attention given on sliding-type failures in planar or wedge form. A slope mass rating value was assigned to each potential failure based on rock mass ratingbasic and the slope mass rating based on readjustments for discontinuity orientation and excavation method. Factor of safety from limit equilibrium method show potentially unstable blocks and failed blocks (Factor of Safety <1.00) with confirmation on site. Water filling of discontinuity apertures plays an important role in destabilizing rock blocks, especially in wet conditions experienced in Malaysia’s tropical climate. Several geometries are identified as potentially unstable due to low slope mass rating (Class V) and factor of safety of <1.2, such as planar J5 and wedge J2*J5 at KSA, wedge forming with sets J3, J4 and fault plane at KSB, planar J2 at LHA, and wedge J3*J4 at LHB. Stabilization structures such as rock bolts can be better designed with the determined factor of safety values coupled with relevant geological and geotechnical inputs. In this comprehensive rock slope stability assessment approach, limit equilibrium method serves as a useful method in analyzing rock slope stability to complement kinematic analysis and stability ratings often used in Malaysia

Seismic Interpretation and Reservoir Static Model: A Case Study in Block MFK, Riau Province, Indonesia

MFK Block was located between Kampar and Rokan Hulu, Riau Province and 135 from Pekanbaru City, Indonesia. There are 33 wells in Field X, MFK Block with 27 active wells. This field has an area of about 79.65 km² that located in Central Sumatra Basin. The field was discovered in 1976 and began to be produced in January 1979. Our research is focused on AK reservoir intervals, which is also part of Bekasap formation. The main aims of this study are to interpret field structure model, determine the distribution of reservoir properties, develop static reservoir model for field as a reference for field performance enhancement, estimate oil reserves in the field reservoir, and the prospect of hydrocarbons in the AK reservoir. The available data are 2D seismic data, mudlog descriptions, well log data, and perforation data. The methods used in this study are stratigraphic sequences, electrofacies analysis, geological structure analysis, static reservoir modelling, and estimation of hydrocarbon reserve volumes. Based on mudlog and electrofacies analysis, the study interval was arranged into 2 lithofacies units, namely sand channel and sand bar. The depostion environment of Bekasap Formation is estuarine environments. The interval of the study has an association of fasies moving northeast to southwest. Based on the results of property reservoir analysis, facies that have good reservoir quality is sand channel facies. Based on the static modeling method approach, the estimated stock tank oil initially in place (STOIIP) for AK reservoir interval is 728 MBBL

Use of ultrasonic velocity travel time to estimate uniaxial compressive strength of granite and schist in Malaysia

The uniaxial compressive strength (UCS) is one of the most common mechanical parameters required in geotechnical engineering to characterize the compressive strength of rock material. Measurements of UCS are expensive, time consuming, destructive and thus, not favorable in the presence of limited samples. Therefore, a simple yet practical application is needed for the estimation of UCS. This research presents two correlations to predict UCS values for granite and schist by using ultrasonic velocity travel time (tp ) from ultrasonic tests. The validity of the practical approach presented in this research is confirmed based on the strong correlations developed from the experimental tests conducted. For the entire data set, the correlation between UCS and ultrasonic velocity travel time was expressed as UCS = 217.2 e-0.016(tp) for granite and UCS = 1110.6 e-0.037(tp) for schist and the coefficient of determination (R2 ) value for both granite and schist is 0.93. These correlations may be useful for applications related to geotechnical engineering designs