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TECHNICAL GUIDANCE NOTE

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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. 

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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.
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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) 
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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. 
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