GEOTECHNICAL RISK AND SUSTAINABLE PRACTICES : LESSON LEARNED AND A WAY FORWARD

Transcription

1 GEOTECHNICAL RISK AND SUSTAINABLE PRACTICES : LESSON LEARNED AND A WAY FORWARD IR. ZAINAB BINTI MOHAMED. PhD GEOTECHNICAL ENGINEERING AND GEORISK MANAGEMENT INSTITUTE FOR INFRASTRUCTURE ENGINEERING AND SUSTAINABLE MANAGEMENT. UNIVERSITI TEKNOLOGI MARA, MALAYSIA zaina556@perak.uitm.edu.my 1

2 Presentation Outline 1.0 Introduction 2.0 Geotechnical Risk Assessment 3.0 Stability of Slope 4.0 Case studies 5.0 Lesson Learned 6.0 Way Forward 2

3 1.0 INTRODUCTION Geotechnical Engineering : involves a study of geomaterial properties and behaviour when subjected to various types of forces. Quantifying and applying the soil mechanics/rock mechanics principles to the design of earth structures ( Das,2006) Rock Mass Classification in Tropics ( Zainab, 2004) Challenges of quantifying weathered rock mass / weak rock masses/ soil like rock like materials Technology and its reliability in quantifying the deterioration of natural materials properties and behaviour in tropics 3

4 ROCK MASS CLASSIFICATION BY WEATHERING GRADE FOR ENGINEERING WORK ( Zainab 2004) soil mechanics No mechanics Weathered/weak rock rock mechanics 4

5 Physical weathering Chemical weathering 5

6 No Mechanics 6

7 Slope hazard Generally, the main factors which contribute to landslide are geomorphological process, physical processes, ground conditions, man-made activities, climate change and global warming effect. Geotechnical assessment on 52 slopes identified the most frequent factor of slope instability are slope material, discontinuity ( rock state),slope geometry, slope distress, rainfall intensity, drainage system ( surface run-off), mode of slope failure and slope stabilization technique The urban development encroaching into highland is at risk of landslides. However, the 2014 Cameron Highland and Kelantan landslides and mud flow had diverse scenario Record of the past forty year incidences of slope hazard in Malaysia had killed more than 500 peoples with estimated billions of economic loss 7

8 Slope Failure events 1971-April

9 2.0 Geotechnical Risk Assessment Identify causal factors for hazard, model risk, understanding the hazard and improve reliability of system Most common model use in engineering field is Causal model for risk and reliability assessment a) Hazards Analysis: hazard identification, hazard to engineering system, their causes and severity of consequences b) Risk Mapping : identify the potential area of failure and mark it. c) Risk Rating : method to rate the risk ( number or colour code ) for the hazard d) Consequence-to-life category rating : situation where the facilities are located e) Improve Reliability of system / Mitigation within the expected risk zone 9

10 3.0 Stability of Slope Stability of slope : determine based on the interplay between driving forces and resisting forces. Driving forces ( weight & gravity ) promote downslope movement of material, whereas resisting forces ( shear resistances) deter movement. W FOS = Resisting Forces (Ʈ ) Driving Forces ( W ) Ʈ FOS > 1 SAFE? FOS < 1 UNSAFE 10

11 FOS variation as a function of time i) Stable slopes - margin of stability is sufficiently high to withstand all destabilizing forces. ii) Marginally stable slopes which fail at some time in response to the destabilizing forces at certain level iii) Actively unstable slopes - which destabilizing forces produce continuous or intermittent movement 11

12 FOS Probability distribution curves MODES OF SOIL SLOPE FAILURE 3 stability stages must be seen to be part of a continuum, The probability of failure being minute at the stable end of the spectrum, but Increasing through the marginally stable range to reach certainly in the actively unstable stage 12

13 The three stability stages provide a useful framework for understanding the causal factors of landslides and classifying them into two groups on the basis of their function: i) Preparatory causal factors which make the slope susceptible to movement without actually initiating it and thereby tending to place the slope in a marginally stable state. ii) Triggering causal factors which initiate movement. The causal factors shift the slope from a marginally stable to an actively unstable state. A particular causal factor may perform either or both functions, depending on its degree of activity and the margin of stability 13

14 4.0 CASE STUDY 1 Geotechnical and Geological Risk Assessment at Batu caves, Selayang. PARCEL 2 : Kg. Sri Gombak Indah, Kg. Sri Gombak Indah Tambahan, Kg. Wira Damai and Pusat Seni Silat Lincah SCOPE OF STUDY i) Assessment of hazard and risk of Limestone Rock Cliff. ii) Demarcation of risk zone around rock cliff for development control. iii) Evaluation of existing development and proposing mitigation and stabilization measure for limestone rock cliff. 14

15 Georisk : Geological risk occurs from geological events that create a negative impact to human, property and environment. ( Anon 2013) Problem Batu Caves Geohazards: potential events caused by geological conditions of limestone rock cliff and limestone subsurface cavity which causing serious threats to human lives, property, the natural and built environment Approach Engineering Risk and Reliability Study: identify causal factors for hazards; model risk use in engineering field to better understanding the hazards and improve reliability of system Solution Sustainable Geotechnical Practice: Geotechnical practice requires that natural risk and activities to be identified, quantified and analyse its consequences to provide mitigation measures against geohazards. 15

16 PARCEL 2 PARCEL 1 PARCEL 3 16

17 PARCEL 2. 17

18 Parcel 2 Typical Limestone rock face 18

19 Parcel 2 Kg. Sri Gombak Indah, Kg. Sri Gombak Indah Tambahan, Kg. Wira Damai and Pusat Seni Silat Lincah. Coverage area of hectars. Slope parameter 2400 m, height m Methods of statement : TLS of the whole limestone rock cliff, discontinuity mapping of rock slope face, geomechanical assessment of rock mass, geotechnical risk analysis The geotechnical risk and consequences analysis were carried out to identify and classify the geohazard towards public safety as well as providing information for purpose of future development. 19

20 Parcel 2 ; TLS output Limestone Rock cliff boundary without contour showing slope sections for rockfall simulation 20

21 Parcel 2 Rock mass assessment and rockfall analysis S59 Most critical slope, maximum rolling distance 10.7 m (red), Unstable slope, One deep wedge failure 21

22 i. Unstable rock cliff; A4 and A5 ( blue). ii. Partially stable rock cliif; B5, B6, B7 iii. Land lots lay in the red zone, A4, A5, B5,B6, B7 are highly at risk of rockfall hazard iv. All red shaded lots and black shaded lots lay in medium risk zone v. Yellow shaded lots, a few lay in high risk zone but many in medium risk zone vi. Unstable slopes along A1, A2,A3 and Partially stable slopes at B1, B2,B3,B4 has no information on land use plan 22

23 Parcel 2 is densely populated. Residential nearest to the toe of the cliff ( 17 m) must be given immediate attention. Hard engineering solution is not recommended unless the area is totally evacuated a. High Risk Hazards Zone 1. The high risk red zone should be made as buffer zone for future rockfall hazard 2. The land owner/authority should consider not to allow for any development in the high risk red zone especially involving risk to potential loss of life 3. Routine slope inspection/monitoring to detect any changes to rock cliff instability as recommended by JKR Slope Maintenance Guidelines. 23

24 Slope maintenance inspections and their follow-up works/actions ( GEO) or JKR Slope Maintenance Guidelines. 24

25 2014 Cameron Highland Disaster Cameron Highland was developed in the 1930s, is one of the oldest tourist spots in Malaysia. Disaster occurred almost every monsoon season of the year ( in/yr). Year 2014 was the worst, however has been predicted. File picture courtesy of Malaysian Fire and Rescue Department, December 30,

26 Business as usual Nov 6th 2014 Kuala Terla :Continuous heavy rains about 4 hrs, 2 landslides n mudslide. One died 4 injured Oct 2013 Bertam valley: mudslide claimed 4 lives, 100 houses destroyed 26

27 Preliminary Review: A study on The Development of the Hill Stations in Peninsula Malaysia was conducted in May 2001 Purpose is to formulate guidelines and recommendations for the sustainable development of six hill stations in Peninsular Malaysia, one of it was Cameron Highlands Cameron Highlands occupies an area of ha and with a population of about 30,000, is the largest hill station in Malaysia. 27

28 Facts Findings Cameron Highlands is mountainous, most terrain being steeper than 40 degrees, characterized by steep slopes and deep ravines, especially at the higher elevations CH is drained by eight rivers; Sg. Bertam, Sg. Telum and Sg. Lemoi, being the major ones; as well as Sg. Ringlet, Sg Habu, Sg Burong, Sg Tringkap, and Sg Terla. These rivers drain eastward into Sg Pahang. The water quality of the rivers Cameron Highlands has been deteriorating over the years, mainly due to siltation from land clearing for developments, road construction and agriculture. The major land uses in the district of Cameron Highlands are forest (71%) and agriculture (8%). Agriculture activities are largely concentrated in areas such as Kg. Raja - Kuala Terla, Tringkap - Kea Farm, Habu and Ringlet - Lembah Bertam. Farming activities in Lojing started in the 1980 s but has accelerated recently due to better accessibility. 28

29 Forests occupy 50,800 ha of the Cameron Highlands district. About 54% of the forests (38,000 ha) in the district have been gazetted as Permanent Forest Reserve (PFE), and the remaining are state land forest. The PFE is made up of 13 forest reserves. The main economic activities in Cameron Highlands are temperate agriculture and tourism. The agriculture produce includes temperate flowers (378 ha, 1999), vegetables (2,720 ha, 1999), fruits (90 ha, 1999) and tea (2309 ha, 1999). Tourism is an important economic sector in Cameron Highlands ( 305,000 with domestic tourist accounting for 79% yr 2000) The two principal tourism products here are Nature Tourism and Agro- Tourism. 29

30 Treats The volume of solid waste generated in Cameron Highlands is approximately 22 tonnes/day and dumped at a site 3 km away from Tanah Rata, where the waste is accumulated and pushed down a steep slope. The indiscriminate clearing by farmers on the hill slopes for agriculture vast land clearing can threaten the water quality and natural slope stability Unsystematic and indiscriminate agriculture land practices The threat of future landslides is very real in Cameron Highlands if no stringent measures are drawn up on control of opening up of farmland and uncontrolled development 30

31 LESSON LEARNED The geophysical hazard and geophysical risk must prioritize public safety and economic loss that are at risk. The landslide occurrence and consequences are avoidable by critically quantify the uncertainties into engineering design. For slope hazard, a greater weightage in design should be given to the quantitative assessment of geological material variability Recognize the probability of slope stability deterioration with time and in relation to causation through other environmental mechanisms. Advance technology is useful tool to capture large scale data Apply preventive mitigation technique to slope with high risk to instability. 31

32 WAY FORWARD Any highland activities must consider the probability of slope hazard and risk as early as land use planning stage, approval for development, application of slope engineering best practices and slope maintenance For highland high hazard activities, continual geotechnical risk assessment must be imposed to land owner The respective authorities, agencies, practitioners and stakeholders are equally accountable to undertake a more sustainable approach as a solution to landslide mitigation. To adopt a soft engineering solution or environmental friendly technique for preventive landslide mitigation in Malaysia environment. 32

33 Authorities to conduct the enforcement of the respective laws to help control the pollution or soil erosion that is occurring in the hill stations. Qualified and competence human capitals are crucial to conduct an effective management of landslide disaster. Sustainable mitigation measure for large scale high land development may be simple, cheap n basic solution. The comprehensive mitigation design can be developed over time as the high land development progress Educate awareness and participation of local communities in landslide risk disaster management PBRC Multidiscipline WG initiated by JMG inorder to established competent resources to lead the knowledge based national project is acknowledge. 33

34 ACKNOWLEDGEMENT Universiti Teknologi Mara Universiti Kebangsaan Malaysia Universiti Teknologi Malaysia Unit Perancangan Ekonomi Negeri Selangor Jabatan Mineral dan Geosains Selangor/Wilayah Persekutuan Jabatan Perancangan Bandar dan Desa Negeri Selangor Majlis Perbandaran Selayang Pejabat Tanah dan Galian Negeri Selangor ERE Group Consultant Ganding Asli Runding 34

35 THANK YOU 35