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TERRESTERIAL LASER SCANNING METHOD IN ROCK SLOPE DATA ACQUISITION – ADVANTAGES AND LIMITATIONS IN MALAYSIAN TROPICAL TERRAIN

BY: MOHAMAD FARUQ SYAHMI MD ARIPIN

INTRODUCTION

Terrestrial Laser Scanner (TLS) becoming common now for rock slope stability assessment. The popularity of the method is highly contributed by the density, rapid data acquisition and high accuracy. However, user should keep in mind that TLS is just like any other tools such as Geophysical equipment. Therefore, it is susceptible to errors and limitations, especially in tropical climate country such as Malaysia. This paper is discussing the advantages and limitation of TLS method. 

ADVANTAGES

  1. Reduce time consumed in data acquisition phase, 
  2. Out of reach data can be measured, 
  3. Minimal equipment error, 
  4. Able to collect millions of point cloud data for more accurate weighted discontinuity set. 

DISADVANTAGES 

  1. Required more time in data processing and analysis stage, 
  2. Resolution and truncation highly dependent on site conditions and rock mass condition, 
  3. Difficulty in data acquisition on Grade IV and Grade V weathered rock and highly fractured rock. 
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Figure 1: TLS field data acquisition, processing, characterization, and analysis stage.
Figure 1: TLS field data acquisition, processing, characterization, and analysis stage.

LIMITATION 

The limitations of TLS are extensively discussed by M. Sturzenegger et. al. (2007) where the effect of the limitation can be reduce significantly if the fundamental of the TLS is understood. 

  • Occlusion occurs when some of the rock faces is unable to be scanned due to the unfavourable position of the laser scanner which restrict the data acquisition on the rock slope discontinuity features 
Figure 2: Effect of occlusion which caused shadow and loss of data.
Figure 2: Effect of occlusion which caused shadow and loss of data.
  • Truncation occurs when the exposure of discontinuity is less than the available resolution of the 3D TLS. Features such as joints and bedding planes with low exposure make it difficult for the scanner to detect the discontinuity. 
Figure 3: Rock slope with low relief discontinuity plane can caused truncation where the exposed plane is below the TLS resolution.
Figure 3: Rock slope with low relief discontinuity plane can caused truncation where the exposed plane is below the TLS resolution.
  • Censoring occurs due to a surface that appears only partly on a rock face with the part of it hidden within the rock face which result to underestimation of the persistence of discontinuities. 
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  • Orientation bias occurs when the scanner line of sight (LOS) is parallel to the orientation of the discontinuity. Frequently these daylighting discontinuities give great influence in the stability of the slope.
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ISSUES IN MALAYSIAN TROPICAL TERRAIN 

Tropical climate in Malaysia contributed greatly to the terrain condition causing the limitations to occur. 

  1. High rain intensity causing high weathering grade and erosion,m 
  2. High water table causing dense vegetation growth, 
  3. Effects of relict structures in weathered rocks contribute to the failure. 
Figure 6: Typical slope conditions in tropical climate country such as Malaysia.
Figure 6: Typical slope conditions in tropical climate country such as Malaysia.

RECOMMENDATION 

Several recommendation are outlined in this paper to reduce the effects of the limitations: 

  • Multiple TLS scanner position.  
Figure 7: Illustration of the laser can elevation bias. (a) Rock face showing bedding joints, (b) Positions of the laser scanner at two different elevation with respect to the rock face, (c) Stereonet obtained from the upper position, on which bedding joints do not appear, (d) Stereonet obtained from the lower position showing poles representing the bedding joints (inside the black circle). (Sturzenegger et al., 2007)
Figure 7: Illustration of the laser can elevation bias. (a) Rock face showing bedding joints, (b) Positions of the laser scanner at two different elevation with respect to the rock face, (c) Stereonet obtained from the upper position, on which bedding joints do not appear, (d) Stereonet obtained from the lower position showing poles representing the bedding joints (inside the black circle). (Sturzenegger et al., 2007)
  • UAV LiDAR 
    • This method has the same principle as basic LiDAR method such as TLS, the difference is in that UAV LiDAR is all-direction mobile while TLS is mounted on the ground.  
    • Application of UAV LiDAR can greatly increase the resolution and coverage of the data thus eliminate most of the limitation from TLS method. 
  • Counter checking with scanline (conventional) method. 
    • Scanline method should never be neglected in any way possible. Scanline will provide the visual identification on the actual discontinuity plane in order differentiate from blasting cracks, drill hole, rock bolt, soil nail, or anything that can be mistakenly inferred during point cloud data processing phase thus can be filtered out. 
Figure 8: Scanline method in discontinuity mapping of rock slope (ISRM, 1978)
Figure 8: Scanline method in discontinuity mapping of rock slope (ISRM, 1978)

CONCLUSION 

The fundamentals of TLS data acquisition is very important to understand in order to reduce the limitations and improving the quality of data acquisition: Malaysian tropical terrain is susceptible to the conditions that may increase the limitation of TLS, hence, experienced geologist must understand the said site conditions to plan ahead the fieldwork. 

rockbg

GEOLOGICAL TERRAIN MAPPING PRACTICE AS INDUSTRIAL STANDARD

BY: AFIQ FARHAN ABDUL RAHIM
MOHAMAD FARUQ SYAHMI MD ARIPIN

INTRODUCTION

A check on GTM practice has been conducted under Newton-Ungku Omar Fund Initiative with gradual improved methods implemented on several GTM projects as pioneer. 

RELATED DOCUMENTS

  1. JMG (2010) Garis Panduan Pemetaan Geologi Terain (JMG.GP.06). Jabatan Mineral dan Geosains Malaysia. Kuala Lumpur. 73p.
  2. GCO (1989) Geotechnical Area Studies Programme: Territory of Hong Kong. Geotechnical Control Office. Hong Kong. 346p. 

TECHNICAL RECOMMENDATIONS 

A proposed workflow is presented in Figure 1. The proposed workflow comprises of three main investigation components which can be conducted simultaneously, namely: 

  1. Geological Terrain Mapping (Annex A) 
  2. Geohazards Assessment (Annex B) 
  3. Engineering Geology Assessment (Annex C) 

which are separated into 5 stages of investigation, namely: 

  1. Stage 1: Preliminary Study 
  2. Stage 2: Field Data Acquisition 
  3. Stage 3: Data Management and Processing 
  4. Stage 4: Auditing and Verification 
  5. Stage 5: Final Report / Product 
  1.  
Figure 1: Proposed workflow for GTM practice with three main investigation components: Terrain Mapping, Geohazards Assessment and Engineering Geological Assessment.
Figure 1: Proposed workflow for GTM practice with three main investigation components: Terrain Mapping, Geohazards Assessment and Engineering Geological Assessment.

ANNEX A – GEOLOGICAL TERRAIN MAPPING

Terrain mapping aims to map the geomorphology related to Area of Interest (AOI) and its potential constraints towards planned development. The outcome of terrain mapping serves as general guidance for geotechnical works in proposed developments as in JMG.GP.06 – Table 8. 

Terrain mapping utilizes polygons (in vector-type GIS data), with each polygon shall consist of terrain attributes as in JMG.GP.06 – Table 1. 

The methodology in this technical guidance note serves as a supplementary document to guide geologist with adherence to procedure in JMG.GP.06 – section 3.0. 

Figure 2: Proposed polygon demarcation workflow, with priority to demarcate the polygons regarding geomorphology first before other attributes. (i) delineate the catchment boundaries – ridge, crest and peak, (ii) delineating the drainage valley, (iii) refining the geomorphology based on terrain shapes, (iv) dividing polygons based on slope gradient, (v) refining polygons based on activity and erosion attributes based on satellite imagery, and (vi) draft Terrain Classification Map with attribute codes from polygon demarcations.
Figure 2: Proposed polygon demarcation workflow, with priority to demarcate the polygons regarding geomorphology first before other attributes. (i) delineate the catchment boundaries – ridge, crest and peak, (ii) delineating the drainage valley, (iii) refining the geomorphology based on terrain shapes, (iv) dividing polygons based on slope gradient, (v) refining polygons based on activity and erosion attributes based on satellite imagery, and (vi) draft Terrain Classification Map with attribute codes from polygon demarcations.

ANNEX B – GEOHAZARDS ASSESSMENT  

Geohazards assessment has been included in JMG.GP.06 yet was briefly shown on the workflow without much elaboration. 

Geohazards assessment must cover the extent of sub-catchment where AOI is located. Therefore, the study must be extended upstream or downstream from AOI, without limiting the study to AOI only. 

Each geohazards (landslide, debris flow, or flood) constitutes a different approach, a competent geologist is needed for such assessment. 

Interpretation of geohazards from topographic data. However, identifying geohazards feature including landslide scarp and body might be tricky especially in relic structures. The following map may prove helpful for geohazards identification: 

  • Hillshade Map (Figure B-1) 
  • Topographic Openness Map 
  • Slope Gradient Map 
Figure 3: Hillshade map generated from topographic data, showing the relief of topography and any geohazards feature in study area. Demarcation of different components in a recent debris flow occurrence, highlighting its (i) source area, (ii) transportation area, and (iii) depositional area.
Figure 3: Hillshade map generated from topographic data, showing the relief of topography and any geohazards feature in study area. Demarcation of different components in a recent debris flow occurrence, highlighting its (i) source area, (ii) transportation area, and (iii) depositional area.

Geohazards interpretation shall be drawn on map. The followings are recommended ways of representing geohazards on map: 

  • Landslide: Identified landslide geohazards shall be demarcated in polygons, which each landslide is separated into two polygons – source area (scarp) and deposit area (body). 
  • Debris flow: Requiring a more comprehensive approach to study the catchment type, where each identified debris flow is separated into three polygons (components) – source area (landslide or other debris flow triggering source), transportation area, and deposition area. 
  • Rock falls: Run rock fall runout simulations or general 1H from rock slope rule as recommended by JMG. The rock fall affected area is demarcated in polygon while rock slope is shown in a polyline. 
  • Flood: Based on previous flood records, map the probable extent of flood in polygon. 

ANNEX A – ENGINEERING GEOLOGICAL ASSESSMENT  

Engineering geological assessment aims to identify engineering geology and geotechnical issues associated with geology in AOI. 

Initially part of thematic map component in JMG.GP.06, the engineering geological assessment shall stand alone as a comprehensive investigation, with multiple outputs including engineering geological model and map. 

Comprehensive engineering geological judgement based on preliminary study and field investigations must be done with emphasis on the following engineering geological issues: 

  • Engineering geological properties of soil and rock with its distribution within AOI and its implication towards any geotechnical works done on site. 
  • Weathering profile and depth of each layer  based on field observations and borehole / geophysical data from SI and its implication towards any geotechnical works done on site. 
  • Structural geology (bedding / schistocity plane / fault or other discontinuities within rock or soil mass found on site) of study area and its influence towards any future geotechnical works. 
  • Groundwater and surface water regime on site. General groundwater table shall be established based on SI data, while surface water flow regime can be established from field investigations. The implication of groundwater and surface water regime towards future geotechnical works shall be highlighted. 
  • Potential instabilities on site (also addressed in geohazards assessment) and its implications toward any geotechnical works done on site. 
  • Other engineering geological features found on site that potentially influence (or act as constraints) towards future geotechnical works on site. 
Figure 4: Engineering geological model of a study area, highlighting issues under and above surface, and relationship between engineering geological properties and human activities.
Figure 4: Engineering geological model of a study area, highlighting issues under and above surface, and relationship between engineering geological properties and human activities.
rockbg

DEVELOPMENT OF GEOSCIENCE INFORMATION FOR AREA BUSINESS CONTINUITY PLAN

BY: MOHAMAD FARUQ SYAHMI MD ARIPIN

INTRODUCTION

As part of the Disaster Resilient Cities: Forecasting Local Level Climate Extremes and Physical Hazards for Kuala Lumpur project funded by Newton-Ungku Omar, Geomapping Technology Sdn. Bhd. was assigned to develop Technical Guidance Note (TGN) on Development of Geoscience Information for Area Business Continuity Plan (Area BCP). The pilot study on Area Business Continuity Plan is in Kuala Lumpur. 

RELATED DOCUMENTS

  • Malaysian Standard (2007) MS 1920:2007: Business Continuity Management – Framework. 36p 
  • International Organization for Standardization (2012) ISO22301:2012: Societal security — Business continuity management systems — Requirements 
  • JICA Study Team (2015) Planning Guide for Area Business Continuity (Area BCM Toolkits), Version 2

TECHNICAL RECOMMENDATIONS 

A proposed workflow is presented in Figure 1. The proposed workflow comprised of three main components which can be conducted concurrently, namely: 

  1. Formulation of Area BCP (Annex A) 
  2. Geohazard and Risk Assessment (Annex B) 
  3. Urban Geology Map (Annex C) 
  1.  
Figure 1: Proposed workflow for geoscience information development of Area BCP (Modified after JICA Report 2004)
Figure 1: Proposed workflow for geoscience information development of Area BCP (Modified after JICA Report 2004)

DATA COLLECTION AND COLLATION

Implementation and formulation of Area BCP required the following geographic information to be collected and analysed: 

  1. Geophysical hazard inventory map, 
  2. Digitized industrial agglomerated area map, 
  3. Transport, infrastructure and lifeline utilities map, 
  4. Legal framework for disaster risk management and BCP, 
  5. Current state of BCP implementation 

Most of the existing data are readily available and archived by the relevant authorities, government agencies, and/or municipal councils.

Table 1: Data requirement for Area BCP in construction of GIS database modified from Hitoshi Baba et al. (2014)
Table 1: Data requirement for Area BCP in construction of GIS database modified from Hitoshi Baba et al. (2014)

ANNEX A – FORMULATION OF AREA BCP / AREA BCM  

Business Continuity Plan (BCP) 

  • Business Continuity Plan (BCP) relates the management and business continuity between individuals and organizations.  
  • BCP can be referred to as the development of a recovery framework or a strategy plan in preparedness of emergency, high risk event or natural disaster. 
  • In addition, the BCP is able to realize the sustainable development of the area as it ensures that industrial development of an area is not threatened further despite the disaster (JICA 2014). 
  • A survey conducted by NISER’s ISMS Survey in 2003 shows that only 52 % of Malaysian organizations are currently practicing Disaster Recovery Planning (DRP) while 37% are implementing BCP (Jalil 2004). These figures imply generally that the level of BCP implementation in Malaysia is still at a relatively infant stage. 

Area Business Continuity Plan (Area BCP)

  • The Area BCP is a framework and guide of disaster risk management by stakeholders. Such stakeholders include individual companies, industrial area administrators, local authorities and infrastructure administrators to continue the business of the industrial agglomerated area as a whole. 
  • The geographical scope of the Area BCP depends on the local situation or the size of the of stakeholder’s coordination, so that the scope of the Area BCP may be an industrial park, an industrial agglomerated area or even a nation. 
  • The Area BCP should be coordinated with the BCP of each party in such a way as to complement critical information required to quantify damages or share business resources for both public and private parties. 
  • Each BCP should refer the Area BCP to identify limitations in the area, considering the Recovery Time Objective (RTO) of the business resources and planning the recovery initiatives. 
  • Hence, the developed Area BCP should be looped back to BCP for continuous reviewing and monitoring for future improvements. 

Process of Area BCP/Area BCM

  • Area BCP formulation conducted by JICA study team which facilitated stakeholder discussion to take steps as Figure 2 developed by a team which refers to the standard ISO22301 procedure. 

 

Figure 2: Steps to formulate Area BCP and to implement Area BCM. Source: Hitoshi Baba et al. (2014)
Figure 2: Steps to formulate Area BCP and to implement Area BCM. Source: Hitoshi Baba et al. (2014)

ANNEX B – GEOHAZARD AND RISK ASSESSMENT

There are two ways to determine the target disaster situation: first, by evaluating past experiences in the area, and second, by performing numerical hazard assessments and risk assessments. 

If the region has experienced the business interruption(s) in the past due to natural hazard(s), it is highly likely that in the immediate future, the same type(s) of hazard will occur at the same or greater scale (Hitoshi Baba et al., 2014). If work group members decide to consider past hazard(s) as the object hazard(s) for preparation, the disaster history of past events can be used as target situation(s). When the area has encountered multiple types of hazards, the working group may choose one type for the first Area BCM cycle, and others for the following Area BCM cycles. 

In the case that the area may not have accurate records of the past disaster(s), it is important to evaluate or assess the area’s prevalent hazard which may disturb business operations, the magnitude of the hazard, and the risks of disaster caused by the hazard. The following analyses are necessary. 

  • Identify predominant risk caused by natural hazard, 
  • Target setting of disaster scale, 
  • Hazard assessment of the area, 
  • Vulnerability assessment and risk analysis of the area. 
Figure 3: Steps to formulate Area BCP and to implement Area BCM. Source: Hitoshi Baba et al. (2014)
Figure 3: Steps to formulate Area BCP and to implement Area BCM. Source: Hitoshi Baba et al. (2014)

ANNEX C – URBAN GEOLOGY MAP 

Urban geology was defined by Culshaw (2012) as study of the interaction of human and natural processes with the geological environment in urbanised areas, and the resulting impacts, and the provision of the necessary geo-information to enable sustainable development, regeneration and conservation. Urban Geology Map incorporate the following information in one easy to understand map. 

  1. Geomorphology, 
  2. Surface and Subsurface Geology. 
  3. Engineering Geology, 
  4. Hydrogeology, 
  5. Hazards and Geoenvironment. 
rockbg

ROCK FALL HAZARD ASSESSMENT AND RISK ZONING OF GUUNG PONDOK, PADANG RENGAS, PERAK

NATURE OF PROJECT: ROCK FALL HAZARD
CLIENT: PERAK HANJOONG SIMEN SDN BHD
LOCATION: PADANG RENGAS, PERAK

INTRODUCTION

Gunung Pondok consists of limestone that could give the risk to the people who live close to the hill. There are several villages nearby the east hill of Gunung Pondok namely Kampung Sungai Ati, Kampung Pondok, Kampung Pulau, and Kampung Padang Rengas.  Light Detection and Ranging (LiDAR) and geological field survey were conducted to assess the physical characteristics of the Gunung Pondok (east hill). The LiDAR field data acquisitions were conducted using Terrestrial Laser Scanning (TLS) and Unmanned Aerial Vehicle (UAV) method. The geological discontinuities mapping, and identification of rock material were conducted using the scanline method and Point Load Index Tests at three outcrops, namely GP1, GP2, and GP3. The surveys were performed from 9th to 22nd September 2016. 

Figure 1: Gunung Pondok Hazard Hill
Figure 1: Gunung Pondok Hazard Hill
Figure 2: Site condition of Gunung Pondok for TLS data capturing
Figure 2: Site condition of Gunung Pondok for TLS data capturing

RESULTS AND DISCUSSION 

i) LiDAR Survey

LiDAR survey that was conducted provides the Digital Elevation Model (DEM) of the hazard hill. Several factor maps were generated such as hillshade map, elevation map, contour map, slope gradient map, slope aspect map as well as aerial photograph. These maps were used in rockfall trajectory analysis to visualize the running distance of the rock. Based on the LiDAR survey, a natural hazard hill estimated dimension of the total unstable rock mass being 100m long, 110m wide and 80m height with estimated weight of 2.38 million ton of limestone rock.   

 

ii) Discontinuity Mapping and Kinematic  Analysis

Discontinuity mapping and kinematic analysis conducted to determine the behavior of rock discontinuities (bedding, joint, fault) that effects the stability of the hill. The potential failures at the site were wedge failure, planar failure and toppling failure. Two (2) cavities were also identified near the base of hazard hill. The results of the analysis utilized in rock mass classifications based on Slope Mass Rating (SMR) method.  

Figure 3: Location of outcrop GP1, GP2 and GP3, Gunung Pondok, Padang Rengas Perak
Figure 3: Location of outcrop GP1, GP2 and GP3, Gunung Pondok, Padang Rengas Perak

iii) Slope Mass Rating (SMR) 

Slope Mass Rating (SMR) assessment was conducted utilizing the results from kinematic analysis, discontinuity mapping and point load test. Based on the analysis, the probability of failure of the slope ranged from 0.2 (stable) to 0.9 (completely unstable).  

Figure 4: Slope stability distribution at eastern hill of Gunung Pondok, Padang Rengas, Perak
Figure 4: Slope stability distribution at eastern hill of Gunung Pondok, Padang Rengas, Perak

iv) Rock Fall Trajectory and Hazard Zoning

The 875m length slope was divided into 43 sections (25m differences) which are CH0 to CH875 to be simulated. The rockfall trajectory analysis conducted based on Colorado Rockfall Simulation Program (CRSP) and Lump Mass Method. The CRSP and Lump Mass Method were developed based on equation of motion to estimate energy, velocity, and height of bouncing of rock.  The analysis shows that the maximum rolling distance for slope ranged from 56m to 440m from slope toe. The rock blocks from slope CH188, CH213, CH475, CH500, CH513, CH525, CH538, CH550, CH563, CH575, CH588, CH688, CH700, CH713, CH725, CH738, CH763, CH775, CH788, CH800, CH813, CH825 and CH838 were simulated to fall toward Kampung Sungai Ati.  

Figure 5: Example of rockfall run out analysis conducted by using Rocfall software
Figure 5: Example of rockfall run out analysis conducted by using Rocfall software

The hazard zones were determined based on the results of rock fall analysis and Guideline by JMG (2013). The hazard zones divided into three (3) zones which are high hazard zone, intermediate hazard zone and low hazard zone. Distance of high hazard zone, intermediate hazard zone and low hazard zone in entire study areas were ranging from 56 m to 440 m, 12 m to 473 m and 381 m to 566 m. The distance of high hazard zone is the maximum rolling distance. The distance of intermediate hazard zone was calculated by minus the 1.5 times of height of slope (1.5H) with maximum rolling distance of rock fall. The distance of low hazard zone is equal to the 1.5 times of height of slope, H. 

Figure 6: Hazard zones and slope stability distribution for Gunung Pondok, Padang Rengas, Perak
Figure 6: Hazard zones and slope stability distribution for Gunung Pondok, Padang Rengas, Perak

SUGGESTION AND RECOMMENDATION

The results of the analysis have been presented to the State’s Exco in 2016. The state together with the Perak Hanjong management are on negotiation to choose the best method to avoid harm to the people.  As for GMT, based on the results and analysis, the long-term best mitigation measure to reduce the risk from the hazard hill is to establish and demarcate a buffer zone around the hazard hill.   

CONCLUSION 

The hazard assessments of 49 slopes (875 m) using Slope Mass Rating (SMR) rock mass classification suggested that the probability of failure of slopes at study area ranging from 0.2 to 0.9. The total width of slope with probability of failure of 0.2, 0.4, 0.6 and 0.9 are 200.25 m, 337.25 m, 281.25 m and 56.25 m respectively. The stability of slopes varies from Completely Unstable to Stable. The rock fall analysis recommended that the maximum rolling distances for slope ranging from 56 m to 440 m from slope toe. The rock fall simulation results suggested that the distance of high hazard zone, intermediate hazard zone and low hazard zone in this study area were ranging from 56 m to 440 m, 12 m to 473 m and 381 m to 566 m. 

rockbg

ENGINEERING GEOLOGY ASSESSMENT FOR PROPOSED PERMANENT STABILIZATION FOR GRANITE ROCK SLOPE IN MALAYSIA

NATURE OF PROJECT: ENGINEERING GEOLOGY AND ROCK SLOPE STABILITY ASSESSMENT
DURATION: 4 MONTHS
DURATION: AUG 2018

BACKGROUND AND METHODOLOGY

Geomapping Technology Sdn. Bhd. undertook the assessment on engineering geological assessement and rock slope stability mapping at Bukit Lanjan, Selangor. The lithology of the cut slope consists of granitic rock mass with weathering Grade I to Grade III. Due to the nature of the outcrop, engineering geology assessments is conducted to obtain optimal engineering geological data for comprehensive analysis for rock slope stability. The engineering geological survey methods are: 

  • Discontinuity Survey: Scanline survey and Terrestrial Laser Scanning (TLS) 
  • Airborne survey using UAV/drone 
  • Kinematic analysis 
  • Rock Mass Rating (RMR) and Slope Mass Rating (SMR) 
  • Modified Geological Strength Index (GSI) 

RESULTS AND DISCUSSION 

Based on discontinuity mapping, multiple potential failures were identified using kinematic analysis which was represented potential instabilities on site. The demarcated potential failure is depicted as the major potential failure mode. Each major potential failure blocks were labeled with unique ID and analyzed with limit equilibrium method.  

Rock masses were assigned   RMR and SMR rating based on the parameters acquired from the mapping survey. The orientations of potential failure plane were used in readjustment factor in SMR analysis. Based on SMR classification, the slopes were identified as Class II (Stable), Class III (Partially Stable) and Class IV (Potentially Unstable).

Figure 1: Oblique aerial photograph showing identified potential instabilities and it is given ID.
Figure 1: Oblique aerial photograph showing identified potential instabilities and it is given ID.

The rock masses were also analysed using modified GSI method and the results shows good correlation with RMR (Bieniawski,1989). 

Figure 2: Results of TLS point cloud data processed in Coltop3D showing characterized discontinuity sets.
Figure 2: Results of TLS point cloud data processed in Coltop3D showing characterized discontinuity sets.

CONCLUSION 

Empirical method and rating systems such as kinematic analysis, Rock Mass Rating, Slope Mass Rating, and Geological Strength Index are very useful in determine the rock mass rating for mitigation works. However, limit equilibrium analysis will provide more information on slope stability in specific condition. 

rockbg

BOULDER MAPPING FOR ELEVATED HIGHWAY CONSTRUCTION IN GRANITE HILL AT AMPANG JAYA

NATURE OF PROJECT: GEOLOGICAL & GEOHAZARDS ASSESSMENT
CLIENT: PROJEK LINTASAN SUNGAI BESI – ULU KELANG SDN BHD
DURATION: DEC 2017 – MAR 2018

INTRODUCTION 

SUKE is a 24.4km, three-lane, dual-carriageway, elevated expressway running from Sri Petaling to Ulu Kelang. It has 14 interchanges and reaches out to over 60 residential areas as well as connects to major highways and roads in Kuala Lumpur. SUKE will serve as a viable alternative to MRR2 highway by minimizing traffic congestion in Cheras, Pandan Indah, and Ampang, as a direct link for a new greater growth city such as Kajang, Segambut, and Kepong and as an effective and high capacity traffic dispersal scheme for eastern Klang Valley areas. At package CB1 (B7 & B8), the proposed highway alignment is in close distance with the residential houses of Taman Saga. Boulder fall hazard is one of the geological problems encountered at this location.  

Figure 1: The highway alignment in close distance with residential houses.
Figure 1: The highway alignment in close distance with residential houses.

BOULDER MAPPING 

Boulder mapping was conducted on hilly terrain with several streams flow down the slope towards depression areas close to Taman Saga. The boulder mapping was conducted to map the location and condition of the boulders and recommend suitable remedial type. The mapping methodology was adopted from the suggestion of Au and Chan (1991) and  engineering judgment based on available records. Besides, the field observation is important to study the hazard posed by the boulders.  Six (6) criteria were considered for this boulder mapping which are; i) Boulder location, ii) Embedded depth, iii) Boulder shape, iv) Boulder size, v) Local slope angle, and vi) Vegetation density.  

RESULTS 

There are two (2) areas of boulders accumulation exist in the project site which are; i) The boulders on the slope face near to Taman Saga: which have the potential of boulders fall as its located on the slope steeper than 35°. In fact, there also incidents of boulders fall during construction due to excavation works. ii) The boulders located along the stream channels in the forest reserve which prone to debris flow hazards. 

Figure 2: Distribution of boulders on the slope face and along stream channel
Figure 2: Distribution of boulders on the slope face and along stream channel

RECOMMENDATIONS 

Conceptual recommendations were suggested at this particular area such as stabilization/scaling (boulders on a slope) and installation of flexible protection net (boulders along the streams) to mitigate this issue as shown in Figure 3. Hence, the boulder mapping execution is very crucial at any locations that face the same problems with Taman Saga, especially on granitic rocks area. 

Figure 3: Suggested recommendations for the boulders hazard
Figure 3: Suggested recommendations for the boulders hazard
rockbg

GROUNDWATER MODELING IN SG MUDA BASIN, KEDAH

NATURE OF PROJECT: BASIN SCALE MODELLING FOR GROUNDWATER RESOURCE DEVELOPMENT
CLIENT: JABATAN MINERAL DAN GEOSAINS MALAYSIA (JMG) KEDAH / PERLIS / PULAU PINANG
DURATION: JUNE – NOV 2018

INTRODUCTION 

Muda Basin in Kedah and its neighboring states of Pulau Pinang as well as a part of the state of Perlis are faced with the problem of water shortage which persist year in year out. Jabatan Mineral Dan Geosains Malaysia (JMG) is faced with the task to resolve the problem.  Systematical evaluation of the groundwater potentials in the Basin is carried out by JMG. For this purpose, JMG Kedah/Perlis/Pulau Pinang awarded the groundwater modelling project to Geomapping Technology (GMT) Sdn. Bhd. to develop a groundwater flow model for the aquifer at Sungai Muda Basin (4,210 km2). The primary objective is to estimate the groundwater reserve and maximum sustainable extractions from the aquifer to support technical decision for planning and groundwater resource development of the Basin.

METHODOLOGY 

The approach used in this study include: 

  • Desktop review and previous data gathering 
  • Data processing and management using state-of-the-art software e.g. ArcGIS, Rockworks, Surfer and Aquifer Test to aid groundwater development.
  • Numerical Modelling  

 The three-dimensional numerical code, Modular finite-differential flow (MODFLOW) by U.S. Geological Survey was used for finite differential solutions for the reserve estimates, ZONE BUDGET was used to assess the availability of groundwater in six (6) zones and sub-catchment. Data were integrated on the platform of Visual MODFLOW flex software. 

CONCEPTUAL MODEL 

Three (3) hydrostratigraphic unit were considered for Muda Basin. This comprises of two aquifer system: (i) upper aquifer and (ii) fractured bedrock aquifer. The layers are: one unconfined layer at the top of the model (Layer 1:Quarternary Alluvium), one semi-confined layer (convertible from confined to unconfined) that defines the main Muda Basin aquifer (Layer 2:coarse sands and weathered rocks) and lastly one confined, underlying fractured bedrock aquifer (Layer 3) from Semanggol (sandstone/siltstone, shale), Mahang (shale, sandstone) Baling (shale, siltstone, sandstone , limestone) and Granite Formations.  

Figure 1: Conceptual site model of Muda River Basin Kedah overlain with photo map of the study area
Figure 1: Conceptual site model of Muda River Basin Kedah overlain with photo map of the study area

RESULT & DISCUSSION 

(i) The model performed well with standard error of estimate at 0.29 m, RMSE (9.8 m) and correlation coefficient of 0.92. The regional trend of groundwater is north-southwest towards the coast (Strait of Melaka). (ii) The total flow of groundwater through the Muda Basin is ≈14.1 million m3/day. Groundwater storage (∆s) is ≈11.7 million m3/day (11,766,812.45 m3/day). The Basin is recharge at 180 mm/yr (7.2 % of average annual rainfall of 2477.78mm/yr).  The bulk of recharge comes from rainfall (2,098,631.00 m3/day).  

CONCLUSION 

For groundwater development to be sustainable in the basin, maximum sustainable extraction (safe yield) for Muda River Basin is by making all abstraction less than 50 % of natural recharge. 

rockbg

RESERVE ASSESSMENT STUDY OF UNDERGROUND WATER RESOURCES IN SG KELANG BASIN, SELANGOR

NATURE OF PROJECT: BASIN SCALE MODELLING FOR GROUNDWATER RESOURCE DEVELOPMENT
CLIENT: JABATAN MINERAL DAN GEOSAINS MALAYSIA (JMG) SELANGOR / WILAYAH PERSEKUTUAN
DURATION: JUNE – NOV 2018

INTRODUCTION 

Selangor State in Malaysia have reached a decision that a quick fix to the water deficit  is to develop groundwater as supplementary raw water supply for various users. Groundwater modelling is considered the most valuable and powerful management tool that is useful to effectively perform the complex task. For the basin scale groundwater modelling, Jabatan Mineral Dan Geosains (JMG) Selangor, Malaysia awarded the groundwater modelling project to Geomapping Technology (GMT) Sdn. Bhd. to develop a regional groundwater flow model for the aquifer at Sungai Kelang Basin (1,288 km2). The primary objective is to estimate the groundwater reserve and maximum sustainable extractions from the aquifer to support technical decision for planning and groundwater resource development of the Basin.  

METHODOLOGY 

The approach used in this study include: 

  • Desktop review and previous data gathering 
  • Data processing and management  
  • Field investigation for new data capture
  • Numerical Modelling  

 Modular finite-differential flow (MODFLOW) by U.S. Geological Survey was used for finite differential solutions for the reserve estimates, MODPATH (modular finite differential path lines) and ZONE BUDGET was used to assess the availability of groundwater in five (5) zones and sub-catchment areas.  

REGIONAL CONCEPTUAL MODEL OF KELANG BASIN 

Kelang Basin was modelled as three (3) main hydrostratigraphic unit and comprise of two aquifer system (upper aquifer and fractured bedrock aquifer). The layers comprise of one unconfined layer (Layer 1), one confined upper aquifer (Layer 2) and semi-confined fractured bedrock aquifer (Layer 3).  Layer 1 is Quaternary Alluvium/completely weathered soil (sandy clay /sandy silt). Average thickness is estimated to be 12.3 m. Layer 2 (Alluvium clayey sand/silty sand) is the upper aquifer (10.7 m). Layer 3 is fractured bedrock and comprises of relatively less permeable Kuala Lumpur Limestone Formation, Kenny Hill Formation (mainly sandstone) and Hawthornden Schist Formation (schist, and phyllite). Assumed thickness for the fractured bedrock is 250 m. 

Figure 1: Conceptual site model of Kelang River Basin
Figure 1: Conceptual site model of Kelang River Basin

RESULT & DISCUSSION 

(i) The model calibration performed well: standard error of estimate is 0.47 m, RMSE: 9.56 m and correlation coefficient: 0.78. The regional movement o of groundwater is northwest-southwest towards the west coast (Strait of Melaka). (ii) Total inflow of fresh groundwater to the Basin is ≈6.1 million m3/day (6,132,655 m3/day). Groundwater reserve (∆s) is 589,422.25 m3/day). The Basin is recharged at 260 mm/yr (10.5 % of average annual rainfall of 2465mm/yr).  The bulk of recharge to the aquifer comes from rainfall (918,899.06 m3/day).  

CONCLUSION 

For groundwater development to be sustainable, maximum sustainable extraction for the Basin is recommended at 50 % of natural recharge. 

rockbg

NUMERICAL GROUNDWATER FLOW AND SOLUTE TRANSPORT MODELLING AT FELDA BUKIT GOH, PAHANG

NATURE OF PROJECT: GROUNDWATER FLOW & TRANSPORT MODELLING TO ASSESS THE HYDROGEOCHEMICAL RESPONSE OF ENGINEERED BUFFER (CONDISOIL-BM) IN GROUNDWATER
CLIENT: INDUSTRY CENTRE OF EXCELLENCE (UNIVERSITY MALAYSIA PAHANG)
DURATION: OCT 2017 – FEB 2018

INTRODUCTION 

Groundwater flow and solute transport modelling was conducted on site at FELDA Bukit Goh. The model was used to support an extensive investigation on the applicability of a residue formulation (Condisoil-BM) to be used as an alternative backfill and engineering buffer/soil conditioner for agriculture purposes. There are two main objectives for the groundwater modelling: (i) to provide information on groundwater flow characteristics at the site, (ii) to model the rate and transport of contaminants [Calcium (Ca) and Yttrium (Y)] that may leach from Condisoil-BM. 

Figure 1: Aerial photo (Orthophoto) of study area. Red arrow indicates the excavated area for the emplacement of Condisoil -BM.
Figure 1: Aerial photo (Orthophoto) of study area. Red arrow indicates the excavated area for the emplacement of Condisoil -BM.

MODELLING OF THE SITE

Bukit Goh site is considered as hydrostratigraphic unit comprising one aquifer. Layer 1 (sandy clayey SILT/ silty CLAY) is the top layer. Average thickness is 9m. This is the layer of emplaced Condisoil -BM and the layer assumed to be the unit providing rainfall recharge to the underlying aquifer at Layer 2. The area of emplaced Condisoil-BM has dimensions: 25 x 25m, depth is from 0- 4.85 m bgl. Layer 2 (silty SAND) is the aquifer at the Bukit Goh site and 9m thick.  

Figure 2: Four main hydrostratigraphic unit at Bukit Goh with one aquifer (Layer 2) and Condisoil-BM at the Layer 1 upper section
Figure 2: Four main hydrostratigraphic unit at Bukit Goh with one aquifer (Layer 2) and Condisoil-BM at the Layer 1 upper section

RESULT & DISCUSSION 

The flow at the site generally trend northwest – southeast towards the direction of a local river located outside the boundary of the study area.

Figure 3: simulated groundwater head contours in the Layer 1 (sandy clayey SILT/ silty CLAY, Scenario II -after Condisoil-BM emplacement)
Figure 3: simulated groundwater head contours in the Layer 1 (sandy clayey SILT/ silty CLAY, Scenario II -after Condisoil-BM emplacement)
Figure 4: Transport of Ca contained within the Condisoil-BM location (Layer 1) after 7300 days (20 years).
Figure 4: Transport of Ca contained within the Condisoil-BM location (Layer 1) after 7300 days (20 years).

CONCLUSION 

Ca will reach the aquifer after 20 years (7300 days) under an assumption of zero sorption). The emplaced Condisoil–BM is relatively impermeable and able to restrain the movement of contaminants from reaching the groundwater zones. 

rockbg

NUMERICAL GROUNDWATER FLOW AND SOLUTE TRANSPORT MODELLING FOR THE PROPOSED ONSITE SECURED LANDFILL

NATURE OF PROJECT: GROUNDWATER FLOW & TRANSPORT MODELLING FOR LANDFILL DESIGN / ENVIRONMENT IMPACT ASSESSMENT
CLIENT: LYNAS MALAYSIA SDN BHD
DURATION: FEB – MAR 2019

BACKGROUND AND METHODOLOGY 

Numerical Groundwater flow and solute transport modelling was used to establish the (i) groundwater flow characteristics, (ii) migration of contaminants (Pb, Cr, Zn, Ba and Hg) from the proposed onsite secured Landfill (Prescribed Premise) for Neutralized Underflow (NUF) solids at  Kuantan Malaysia.  

(i) Numerical Modelling Approach – The study applies the advanced method of using computer modelling technique, numerical code Modular finite-differential flow (MODFLOW) for assessment. The transient-state model was used to simulate a worst-case scenario under various assumptions: (i) secured landfills at the site are unlined (non -engineered type), (ii) contaminant are non-reactive i.e. adsorption process is negligible and contaminants are expected to migrate at maximum concentration to groundwater. 

(ii) Model Development – Six hydrostratigraphic layers were modelled comprising of two aquifer systems: 

Table 1: Hydrostratigraphic layers of the area.
Table 1: Hydrostratigraphic layers of the area.

RESULT & DISCUSSION 

Figure 1: Six (6) layers of hydrostratigraphic unit at LAMP site that was used in the model
Figure 1: Six (6) layers of hydrostratigraphic unit at LAMP site that was used in the model

(i) Groundwater movement is northeast –southwest, and north-south towards the earthen waste water retention pond at the site. The flow is outwardly discharging to the South China Sea at the southern part of LAMP site. 

Figure 2: groundwater movement towards the waste water retention pond at the site. The pond is hydraulically connected with the aquifers..
Figure 2: groundwater movement towards the waste water retention pond at the site. The pond is hydraulically connected with the aquifers..

(ii) Contaminant (Pb, Cr, Ba, Hg) will reach the upper aquifer after 3650 days (10 yrs.) of migration and Zn will reach after 730 days (2yrs) under assumptions of unlined landfill (no liner systems).  

Figure 3: Pb migration after 10950 days (30 years) in (Model 2).
Figure 3: Pb migration after 10950 days (30 years) in (Model 2).

CONCLUSION 

The model demonstrates that there is minimal negative impact associated with the landfill design to the environment and surrounding rivers due to double liners, moderate permeability of the aquifer and clay layer absorptive properties to retard the contaminants. 

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