Physical classifications and engineering characteristics of in situ boulders in tropically weathered granite

The issues of boulder in tropically weathered granitic rock masses have roused a lot of problems and risks to the work performances and design quality in civil engineering. Although the presence of in situ boulder could be predicted through several methods and classified in several weathering classification schemes, the behaviour of tropically weathered in situ boulder is not well understood. The aim of this study is to establish physical classification and engineering characteristics of granite boulders and to catalogue the boulders in tropical weathering profile. A total of 46 panels of granitic profile consist of 88 in situ boulders from five quarry sites located in Johor, Malaysia were investigated involving several field and laboratory test programs. The field test programs conducted include geological field mapping, discontinuity survey and classification of physical characteristics of boulder as well as its surrounding material in various weathering zones. The physical characteristics examined include occurrence of boulders in moderately to completely weathered zone, shape, size and rindlets characteristics from respective weathering zone. The laboratory test programs involve determination of physico-mechanical properties and mineralogical analysis. The field study revealed five dominant weathering profiles with different significant types of weathering zone and occurrence of in situ boulder. This finding indicated that in situ boulder is the main character in the formation of heterogeneous zone in weathering profile especially in the moderately weathered (Zone 3), highly weathered (Zone 4) and completely weathered zone (Zone 5). The angularity, size and rindlets characteristics of the boulder from moderately to completely weathering zones significantly differ from each other. Due to these significant differences, the in situ boulders formed in completely, highly and moderately weathered zones are classified into three major types, namely Type A, Type B and Type C, respectively. Boulder Type A is surrounded by double rindlets zones which classified as inner and outer rindlets, while boulder Type B possess single rindlets zone which is classified as inner rindlets. On the other hand, boulder Type C has no rindlets and it is surrounded by joints and fractures. The differences in physical characteristics of boulders Type A, B and C could be used to predict their existence in different weathering zones. The result obtained from the laboratory study revealed the physico-mechanical properties which include dry density, porosity, durability, strength and permeability of rindlets and saprolites found in completely weathered zone showed significant variance compared to highly and moderately weathered zone. In conclusion, the in situ boulders formed in moderately to completely weathered zones possessed significant variance of physical and mechanical characteristics which can be used as an indicator in weathering classification and engineering design purposes

Effect of Surcharges to The Stability of Mechanically Stabilized Earth Wall Using Finite Element Method: Back Analysis Study Case in Senai City Airport

Abstract: Mechanically Stabilized Earth (MSE) wall is a composite retaining structure construction made up of alternating layers of compacted backfill and soil reinforcing components. Surcharges on top of MSE wall is one of the factors that can lead to the failure of the MSE wall. In Senai City Airport, a MSE wall with high 9 m and length up to 400 m has been constructed. However, the effect of various surcharges of the MSE wall slope did not well investigate and was poorly understood. This study aims to investigate the effect of surcharge to the stress behaviour and the factor of safety of Mechanically Stabilized Earth Wall (MSE) wall using Finite Element Method (FEM). The study conducted using different loads in order to determine the stress behaviour and the safety factor of MSE wall using PLAXIS software. The geometry and parameters of sandy silt slope of Senai City Airport, Senai, Johor was taken from design consultant and previous soil investigation report, respectively. The soil parameters were used in this study are the unit weight of the soil, cohesion, Poisson Ratio, Young Modulus and the friction angle. This study gave the best result in order to determine the effect of surcharges to the behaviour of stress and safety factor of MSE wall. The highest total displacement was at 100 kN with total displacement 19.23m with 0.884 factor of safety. This study revealed the effect of various surcharges on the behaviour of stress and factor of safety of the MSE wall. The increase of surcharge increased the stress behind the wall and increased the factor of safety (FOS) when the loads was increased

Electrical resistivity and induced polarization techniques for groundwater exploration

Abstract: Electrical resistivity and induced polarization surveys have been conducted for groundwater exploration at two different sites of geological aged i.e. Carboniferous and Quaternary. This study discussed the earth materials resistivity and chargeability for metasedimentary rock and unconsolidated sediment for groundwater exploration at Kampung Jongok Batu, Dungun and Kampung Paya Rawa, Besut, respectively. For this study Terrameter LS2, cable, electrode, cable connector, battery and remote cable are tools for measurement. The spacing between electrodes is 5 m, maximum length of spread line is 400 m and using Pole-Dipole protocol. Via comparing between the resistivity and chargeability values able to provide better interpretation for ground water exploration for metasedimentary rock and unconsolidated quaternary sediment. The result shows the important of chargeability for refining the resistivity value for locating the groundwater position.Â

The Slope Failure of Weathered Granite Boulders by Using the Finite Element Method

An assessment of weathered granite profile of a research area at Mukim Senai, Kulai, Johor was conducted using PLAXIS 2D method. The slope stability of weathered granite is closely related to the geometric strength of the slope, slope height, soil type (sand or clay), slope gradient and depth to determine factor of safety. The aim of this research is to model and determine the factor of safety of the weathered granite slope with homogeneous characteristics using Plaxis 2D. In addition, it also aims to analyses and correlate the effect of shapes, size and distribution of boulders to the safety factor of the slope. Finite Element Method (FEM)) had been used through the application of PLAXIS 2D software. By comparing between the 2 methods that have been analyzed, safety factors for the slopes analyzed together with groundwater data is less safe. The Safety Factor has found less than 1.5 indicates a slope prone to landslides

Back Analysis and Potential Remedial Approach for Failure Slope at Bukit Nanas, Kuala Lumpur

This study aims to validate the design parameters and stability of the slopes failure and propose acceptable remedial work by assessing the slope stability in Bukit Nanas, center of Kuala Lumpur. The slopes’ height is around 40 and 60 m with the gradient around 30°-45°. Totally 7 boreholes be carried out and the pertinent engineering properties were analyzed from laboratory testing and back analysis (in situ test). An established computer program SLOPE/W was used to carry out for slope stability analysis. The analysis method adopted was Morgenstern-Price’s Method. Based on the result of the field investigation and numerical analysis, the model of lowest factor of safety (FOS) that evaluated from the existing slope in critical section were selected and recommended for remedial work. Two option of remedial slope design had been proposed. The first option is soil nailing with grid beam and proposed drain while the second option is hybrid anchor with grid beam and proposed drain. Both options are used to improve the slope stability, but first option had been chosen as higher FOS and more efficient option. This remedial approach based on the main cause of slope failure in Malaysia can applied as reference in future slope remedial design

Integral application of electrical resistivity tomography, geochemistry and borehole data in groundwater seepage assessment

Electrical resistivity tomography (ERT) has increasingly adopted as an alternative approach in engineering, environmental and archeological studies. In the past, several limitation of conventional method in groundwater mapping was always relative to the high cost, time consuming and limited data coverage. Hence, this study adopted an ERT in order to identify the unknown problematic zone due to the excessive groundwater seepage occurrences. During data acquisition, five (five) ERT spread lines was conducted using ABEM SAS4000 equipment set. Then, field raw data was processed using RES2DINV and ROCKWORKS software to generate 2-D and 3- D of the inverse model resistivity section respectively. Engineering properties and information related to the borehole and geochemistry results was also used for interpretation and verification purposes. Geochemistry test was performed to identify groundwater sources using Atomic Absorption Spectrometer (AAS) and Ion Chromatography (IC) in order to determine the elements of cation (sodium, potassium, calcium and magnesium) and anions (chloride, bicarbonate, nitrate and sulfate) respectively. Based on ERT results, it was found that low electrical resistivity value (10 ~ 100 Ωm) which commonly associated to groundwater was detected at ground surface (0 m) until greater depth (> 10 m). Furthermore, it was found that the groundwater was classified as Ca-HCO that indicates the water was originally come from a typical shallow of the fresh groundwater. Finally, this study has successfully demonstrate that the integral application of ERT, geochemistry and borehole data was applicable to produced comprehensive outcome with particular reference to the problematic groundwater seepage assessment

Classification on shape of granitoid boulder based on size and surface roughness from various weathering zones for site investigation purposes

Boulder is often posed challenges to earthwork activities such as cut slope and foundation excavation especially in tropical weathered rock like Malaysia. In addition, the guidelines for hard material or rock excavation related to boulder provided by Department of Works Malaysia (JKR) are limited and there is a need to be revised. Therefore, this study aims to establish a classification chart of boulder's shape in different weathering zones for site investigation purposes. The parameters of size, volume and characteristics of surface roughness from moderately to completely weathered zone were measured and analysed statistically. Results of this study show that the increase of weathering zone from zone 3 to 5 significantly reducing the size and volume of boulder with reduction of 27% and 38.3%, respectively. Boulder in Zone 3 to Zone 5 can be classified into six typical sphericities: very flat, flat, sub- flat, sub-spherical, spherical and well-spherical. The results also revealed that the physical parameters of boulder can be classified into six classes based on Roundness Ratio (Rr) and Surface Roughness Index (SRI). Based on these results, a boulder shape classification chart was developed and useful as a guideline for engineering application especially in soil investigation purposes