Mohd Ashraf Mohamad Ismail

Rock Overstressing in Deep Tunnel Excavation of Pahang-Selangor Raw Water Transfer Project

Tunneling under high overburden and in-situ stress may cause tunnel instability because of rock overstressing. Evaluating overstressing in deep hard rocks is crucial to minimize excavation risks. The excavation of the Pahang-Selangor Raw Water Transfer Tunnel is evaluated in this study. A potential overstressing problem is expected at a tunnel depth more than 500 m. Therefore, the possibility of rock overstressing is assessed based on the evaluations of in-situ stress measurement, rock strength, and actual observations during the tunnel excavation. An analytical method is used to analyze the behavior of the tunnel under high overburden stress based on rock strength and tangential stress factors. The empirical assessment approach to the observation of actual overstressing appeared to be valid for the prediction of overstressing. These approaches facilitate the reasonable prediction of tunnel behavior under different rock conditions, support systems, and overburden stresses, which serve as useful tools in the observational design and construction method of long and deep tunnels.

Subsurface Characterization Using Ground and Underwater Resistivity Techniques for Groundwater Abstraction

A geophysical method was used in studying the subsurface profile for investigating the aquifer existence at Jenderam Hilir, Selangor, Malaysia. The 2-D electrical resistivity technique is to determine the presence of aquifer suitable for groundwater abstraction. Resistivity was measured through an ABEM SAS 4000 Terrameter and ABEM Terrameter LS. 2-D electrical-imaging resistivity data of subsurface profile for each survey line were calculated inverse modelling, validate by borehole data which showed the lithology: sandy clay to sandy silt sediments more than 3 m deep, composed of alternating layers of silty and sand. The aquifer potential are mostly in silty sand zones which resistivity value should be within 60-800 ohm-m. Based on interpretation, a potential water-bearing aquifer was located at a depth of 3 m and below which is good agreement with interpreted results. 2-D underwater resistivity survey lines were conducted across the ground and river. Resistivity image was interpreted as silty sand under the river bed, which the subsurface aquifer on land has a physical contact with surface water. Result has shown that ground and underwater resistivity technique can be used as alternative method in finding a good location for groundwater abstraction.

Rock Mass Classification System Used for Pahang-Selangor Raw Water Transfer Tunnel

The recent Pahang-Selangor raw water transfer tunnel project had resulted in a large amount of rock mass classification data for the assessment of the rock mass class required for the design of tunnel support system. In this project, a rock mass classification by Japan Highway Public Corporation (JH) has been used to assess the rock mass class using geological mapping and geological documentation of the tunnel face and the side walls of the excavated tunnels. Although JH classification had been used for this project, other forms of classification using different criteria from Rock Mass Rating (RMR) and Q-System have also been widely used for tunnelling project all over the world. Since there have been few studies on the relationships among such different criteria of the classification systems, this study mainly focuses on the comparison between the JH and RMR classification systems for the water transfer tunnel. From the correlation analysis among the criteria used in both JH and RMR classification systems, there is higher correlation if the rock mass is in relatively good condition. It was also found that there is less consistency between JH and RMR classifications in the region of ‘poor rock’. However, the correlation between both classification systems is still considered suitable to be used in this tunnelling project.

Systemic Approach to Elevation Data Acquisition for Geophysical Survey Alignments in Hilly Terrains Using UAVs

This study is about systematic approach to photogrammetric survey that is applicable in the extraction of elevation data for geophysical surveys in hilly terrains using Unmanned Aerial Vehicles (UAVs). The outcome will be to acquire high-quality geophysical data from areas where elevations vary by locating the best survey lines. The study area is located at the proposed construction site for the development of a water reservoir and related infrastructure in Kampus Pauh Putra, Universiti Malaysia Perlis. Seismic refraction surveys were carried out for the modelling of the subsurface for detailed site investigations. Study were carried out to identify the accuracy of the digital elevation model (DEM) produced from an UAV. At 100 m altitude (flying height), over 135 overlapping images were acquired using a DJI Phantom 3 quadcopter. All acquired images were processed for automatic 3D photoreconstruction using Agisoft PhotoScan digital photogrammetric software, which was applied to all photogrammetric stages. The products generated included a 3D model, dense point cloud, mesh surface, digital orthophoto, and DEM. In validating the accuracy of the produced DEM, the coordinates of the selected ground control point (GCP) of the survey line in the imaging area were extracted from the generated DEM with the aid of Global Mapper software. These coordinates were compared with the GCPs obtained using a real-time kinematic global positioning system. The maximum percentage of difference between GCP’s and photogrammetry survey is 13.3 %. UAVs are suitable for acquiring elevation data for geophysical surveys which can save time and cost.

Preliminary Investigation on the Behavior of Pore Air Pressure During Rainfall Infiltration

This paper focused on the preliminary investigation of pore air pressure behaviour during rainfall infiltration in order to substantiate the mechanism of rainfall induced slope failure. The actual behaviour or pore air pressure during infiltration is yet to be clearly understood as it is regularly assumed as atmospheric. Numerical modelling of one dimensional (1D) soil column was utilized in this study to provide a preliminary insight of this highlighted uncertainty. Parametric study was performed by using rainfall intensities of 1.85 x 10-3m/s and 1.16 x 10-4m/s applied on glass beads to simulate intense and modest rainfall conditions. Analysis results show that the high rainfall intensity causes more development of pore air pressure compared to low rainfall intensity. This is because at high rainfall intensity, the rainwater cannot replace the pore air smoothly thus confining the pore air. Therefore, the effect of pore air pressure has to be taken into consideration particularly during heavy rainfall.

Subsurface Characterization using Geophysical Seismic Refraction Survey for Slope Stabilization Design with Soil Nailing

The application of geophysical seismic refraction for slope stabilization design using soil nailing method was demonstrated in this study. The potential weak layer of the study area is first identify prior to determining the appropriate length and location of the soil nail. A total of 7 seismic refraction survey lines were conducted at the study area with standard procedures. The refraction data were then analyzed by using the Pickwin and Plotrefa computer software package to obtain the seismic velocity profiles distribution. These results were correlated with the complementary borehole data to interpret the subsurface profile of the study area. It has been identified that layer 1 to 3 is the potential weak zone susceptible to slope failure. Hence, soil nails should be installed to transfer the tensile load from the less stable layer 3 to the more stable layer 4. The soil-nail interaction will provide a reinforcing action to the soil mass thereby increasing the stability of the slope.

Rippability Assessment of Weathered Sedimentary Rock Mass using Seismic Refraction Methods

Rippability or ease of excavation in sedimentary rocks is a significant aspect of the preliminary work of any civil engineering project. Rippability assessment was performed in this study to select an available ripping machine to rip off earth materials using the seismic velocity chart provided by Caterpillar. The research area is located at the proposed construction site for the development of a water reservoir and related infrastructure in Kampus Pauh Putra, Universiti Malaysia Perlis. The research was aimed at obtaining seismic velocity, P-wave (Vp) using a seismic refraction method to produce a 2D tomography model. A 2D seismic model was used to delineate the layers into the velocity profile. The conventional geotechnical method of using a borehole was integrated with the seismic velocity method to provide appropriate correlation. The correlated data can be used to categorize machineries for excavation activities based on the available systematic analysis procedure to predict rock rippability. The seismic velocity profile obtained was used to interpret rock layers within the ranges labelled as rippable, marginal, and non-rippable. Based on the seismic velocity method the site can be classified into loose sand stone to moderately weathered rock. Laboratory test results shows that the site’s rock material falls between low strength and high strength. Results suggest that Caterpillar’s smallest ripper, namely, D8R, can successfully excavate materials based on the test results integration from seismic velocity method and laboratory test.

Analysis of Infiltration-Suction Response in Unsaturated Residual Soil Slope in Gelugor, Penang

Rainfall infiltration on residual soil slope may impair slope stability by altering the pore-water pressure in the soil. A study has been carried out on unsaturated residual soil slope in Gelugor, Penang to determine the changes in matric suction of residual soils at different depth due to rainwater infiltration. The sequence of this study includes the site investigation, field instrumentation, laboratory experiment and numerical modeling. Void ratio and porosity of soil were found to be decreasing with depth while the bulk density and dry density of soil increased due to lower porosity of soil at greater depth. Soil infiltration rate and matric suction of all depths decrease with the increase of volumetric water content as well as the degree of saturation. Numerical modeling was used to verify and predict the relationship between infiltration-suction response and degree of saturation. Numerical models can be used to integrate the rainfall scenarios into quantitative landslide hazard assessments. Thus, development plans and mitigation measures can be designed for estimated impacts from hazard assessments based on collected data.

Soil Compaction Assessment Using Spectral Analysis of Surface Waves (SASW)

Compaction is a process of soil densification in earthworks via by pressing the soil particles with air being expelled from the soil mass, thereby increasing its unit weight. Thus, it is important to evaluate the quality of soil compaction as prescribed in the technical requirement. SASW method is widely used for estimating material properties in layered structures based on the dispersion characteristics of Rayleigh Waves. The small scale at dimension area of 1.0 m width x 1.0 m length x 0.9 m depth was excavated and back filled with laterite soil. The soil was compacted for every layer at 0.3 m thickness. Each layer of soil compaction was conducted compaction test using core cutter methods and SASW test to determine the density and shear wave velocity. The phase velocity for layer 1 was between 112 m/s and 114 m/s, layer 2 was between 67 m/s and 74 m/s and layer 3 was between 74 m/s and 97 m/s. The result shows that the compacted soil layers are not fulfilled the quality of compacted soil layers where supposedly the expected shear wave velocity for the compacted layers should be higher than 180 m/s which is classified as stiff soil.

Preparedness of fire safety in underground train station: Comparison between train operators in Malaysia with other operators from the developed countries

The purpose of this paper is to compare the fire evacuation plan and preparation at the underground train stations in the different countries. The methodology for this study was using the extended questionnaire survey to investigate the Rapid Rail Sdn Bhd, Malaysia’s fire safety plan and preparation at the underground train stations. There were four sections in the questionnaire which included (i) background of the respondents, (ii) the details on the train stations, safety instruction and fire evacuation exercises (iii) technical systems, installation and equipment at the underground stations and (iv) procedures and technical changes related to fire safety that had been applied by the operators. Previously, the respondents from the different train operator services in the developed countries had completed the questionnaires. This paper extends the response from the Rapid Rail Sdn Bhd to compare the emergency procedures and preparation for fire event with the developed countries. As a result, this study f...