TAJUL ANUAR JAMALUDDIN

Geology Programme

Faculty of Science & Technology

Universiti Kebangsaan Malaysia

Bangi Selangor

LARGE-SCALE LANDSLIDES IN

MOUNTAINOUS TERRAIN OF MALAYSIA –

SOME CASE STUDIES

INTRODUCTION

• Landslides are not only a significant natural disaster but they also contribute to the

geomorphic reshaping of the mountain landscape.

• When large mountain slopes are investigated, slow moving creep-like landslide

masses can be found very commonly, which we refer to here in this paper as large -

scale landslides.

• Such landslides have a long history of occurrence, and they generally affect the river

courses, influence the geomorphology, growth of vegetation as well as activity and

livelihood of local communities.

• In many cases, large-scale landslides possess very slow movements (e.g., a few to

few tens of centimetres a year), and specialised instruments, such as inclinometers,

extensometers, GPS installations, etc. may be necessary to understand that they are

in fact moving.

LARGE SCALE LANDSLIDE - DEFINITION

• huge land masses in natural slopes that have pronominally moved in the past, in most

cases goes back from hundreds to thousands of years ago, and which still retain the

original slope form without completely collapsing as in ordinary rain-induced slope

failures.

• Large-scale landslides usually involved deep-seated soil-and-rock mass creep, debris

creep and all creep-related active landslides or relict landslide masses.

• Landslide volume >50,000 cubic meter.

• Many large-scale landslides are earthquake-induced; e.g.

Sichuan EQ, Padang EQ, etc..

LARGE SCALE LANDSLIDES

LARGE SCALE LANDSLIDES IN MALAYSIA

• Malaysia did not experienced strong/major earthquakes; but large-scale landslides are still

existed; and they are mainly gravity-induced coupled with heavy and prolonged rainfall.

• Large-scale landslides usually involved deep-seated soil-and-rock mass creep, debris creep

and all creep-related active landslides or relict landslide masses.

• An important aspect of dealing with large-scale landslides is to understand their distribution,

pattern and behaviour based on geological and geomorphological features as well as from the

impacted infrastructures built on them.

• This paper attempts to present a scenario of large-scale landslide hazards identification and

disaster risks mitigation measures from some case studies in Malaysia; namely:

• Kundasang Sabah,

• Teluk Datai Langkawi, and

• Gunung Pass Perak,

• The term "landslide" describes a wide variety of processes that result in the downward

and outward movement of slope-forming materials including rock, soil, artificial fill, or a

combination of these (USGS Fact Sheet 2004-3072).

• Like other structures produce by gravitational forces, landslides are neotectonic

structures. Neotectonic structures can mimic tectonic structures.

• Fundamental Concepts of Geology is usually applicable when studying landslides; e.g.

• Doctrin of Uniformitarianism - “The present is the key to the past”

• Pumpelly’s Rule – Small structures are a key to and mimic the styles and

orientations of larger structures of the same generation within a particular area.

• Law of Cross-cutting relationships – the younger cuts the older structures.

• Law of Superposition - the oldest strata will be at the bottom of the sequence

• Law of Original horizontality - layers of sediment are originally deposited

horizontally under the action of gravity.

• Landslides produce “neotectonic structures”, thus identiying “neotectonic structures”

associated with landslide is the key to unravel large-scale landslides.

GEOLOGY OF LANDSLIDES

LARGE-SCALE LANDSLIDE MORPHOLOGY

An old, large-scale landslide in Malaysia (Kundasang, Sabah).

670m

Large-scale landslides – Hazards Identification

• Arcuate headscarp

• Hummocky topography

• Deflection of river course

Geomorphological features of a large-scale landslide – Kundasang, Sabah

Large-scale landslides – Hazards Identification

A A’

A’ A

• Anomalous benches

• Arcuate headscarp scars

• Hummocky topography

The topographic expression of deep-seated slides is characterized by Y-shaped tributaries, anomalous benches and arcuate headscarp evacuation scars.

Large-scale Landslides – Hazards Identification

LIVING IN A LANDSLIDE…

Kampung Dumpiring Atas, Kundasang

CASE STUDY #1- KUNDASANG LANDSLIDE COMPLEX

• The Kundasang area as a whole is sited on a large-scale landslide complex. The “Kundasang Landslide Complex” consisted of a number of km-scale, active, landslide systems and it has been identified as the first natural large-scale landslide phenomena ever reported in Malaysia (Komoo, et al. 2005).

Understanding A Landslide Complex

Unit

System

Complex

An individual landslide/ slope failure, small scale.

A number of landslide units, geologically, hidrogeologically/ geomorphologically related to each other.

A region of instability consisting of a number of landslide systems.

Landslide Complex

• Unit

• System

• Complex

The small structures are a key

to and mimic the styles and

orientations of larger

structures of the same

generation within a particular

area – Pumpelly’s Rule

KUNDASANG LANDSLIDE COMPLEX

• The impacts of the ground movement in Kundasang has given rise to some environmental and socio-economic issues; e.g.

• loss of lives,

• damaged properties and infrastructures,

• psychological pressures,

• disputes on land boundaries,

• land degradation and etc.

LANDSLIDE HAZARDS IDENTIFICATION – Damaged Structures

Abondoned damaged rigid buildings due to ground movements

Disrupted electric supply.

Burst water pipe which requires regular repair works.

Burst water tank due to lateral deformation caused by ground movement.

LANDSLIDE HAZARDS IDENTIFICATION – Damaged Utilities

LANDSLIDE HAZARDS IDENTIFICATION

Dislocated and subsided road pavement

LANDSLIDE HAZARDS IDENTIFICATION

One of the tension cracks that cut trough the school

compound

Uplifted retaining wall

Slanted fence

• Distribution and boundary

of the landslide systems.

• Bagkground : aerial

photographs taken in

2001.

Regional survey & aerial photographs interpretation

2003

LANDSLIDE

IDENTIFICATION

• Based on API, field mapping and association of the geodynamic features; at least 6 systems of major landslides were identified.

LARGE-SCALE LANDSLIDE HAZARDS MITIGATION

• Issues & Challenges:

• As land development and human activities in Kundasang grows rapidly, the issues on integrating resources and environmental management and socio-economic development needs to be systematically explored to effectively reduce losses from landslides and other impacts of the ground movements.

• Integrated Landslide Risk Management:

• In general, the recommended approach covers several major elements, spanning a continuum from research to the formulation and implementation of policy and mitigation. These include: a) landslide hazards identification and assessments, c) real-time monitoring, d) loss assessment, e) information collection, interpretation and dissemination, f) guidelines and training, g) public awareness and education, h) implementation of loss reduction/mitigation measures, and i) disater preparedness and emergency response.

GOVERNANCE

• Restricting development in landslide-prone areas

• Revised land-use planning

• Standardizing codes for excavation, land clearing, construction and new

development.

• Protecting existing development

RECOMMENDED SOLUTION

….to overcome problems of large-scale landslide.

Landslide behaviour – its getting bigger and bigger with time….

…the landslide rear and side scarps would grow bigger and propagate backwards (upstream) and laterally ……

LANDSLIDE HEAD PROPAGATES UPSTREAM AND SIDEWARDS

…. Property losses and damages increased yearly. This kind of large-scale landslide is difficult to stop because of deep-seated and very long slding plane.

LANDSLIDE HEAD PROPAGATES UPSTREAM AND SIDEWARDS

The rate of movement might be reduced if the ground water level be lowered down below the level of the sliding plane. This can be achieved by pumping out water regularly from the suitably designed pumping wells on the slope and adequate surface drainage system. The draw up water can be utilised for domestic and agricultural purposes! At the downstream area, where the sliding plane is shallower, suitably desinged reataining walls can be constructed to stop the ground movement and to protect the existing infrastructures.

PU

MPIN

G W

ELL

PU

MPIN

G W

ELL

PU

MPIN

G W

ELL

RETAINING WALL

CONCRETE-LINED DRAIN

The pumping rate should be closely monitored, recharge and discharge rate should be in equilibrium. Otherwise problems of land subsidence might start to surface!

RETAINING WALL

PU

MPIN

G W

ELL

PU

MPIN

G W

ELL

PU

MPIN

G W

ELL

CONCRETE-LINED DRAIN

CONCRETE-LINED DRAIN

RETAINING WALL (CONTIGOUS BORED-PILE

WALL)

BEDROCK

…..After several months/years, it is expected that the water table would be reduced and thus the movement of the landslides could be drastically reduced and stopped.

RETAINING WALL

PU

MPIN

G W

ELL

PU

MPIN

G W

ELL

PU

MPIN

G W

ELL

CONCRETE-LINED DRAIN

CONCRETE-LINED DRAIN

RETAINING WALL (CONTIGOUS BORED-PILE

WALL)

BEDROCK

STRUCTURAL MITIGATION

STRUCTURAL MITIGATION – CBP WALL

Lessons Learnt From Kundasang Landslides

• Geological and geotechnical inputs should always be optimised in addressing the landslide problems in Kundasang.

• Public awareness, their understanding on the hazards and risks of the landslide; understanding their socio-economic needs and capability; their perception as well as their participation in vulnerability reduction measures, albeit small, is vitally important to achieve integrated and sustainable landslide hazards management.

• Scientific and technical information have to be packaged and streamlined based on stakeholders ability and capacity to address the threat and impact of the landslide hazards.

• Scientific, Technical and Socio-Economic inputs should be integrated to ensure a sucessful landslide hazards management.

CASE STUDY #2– DEVELOPMENT IN SUSPECTED LARGE-SCALE LANDSLIDE

• An exclusive hotel was developed in a scenic bay; without knowing that severe damages to its only access road is due to inherited ground/slope instability.

• Denser vegetation cover

• Hummocky topography

• Arcuate main scarp

GEOLOGY OF THE LANDSLIDE DEPOSITS

THE MACHINCHANG LANDSLIDE COMPLEX (??...)

TELUK

DATAI

• Marked contrast in the vegetation cover.

• Landslide areas have denser vegetation

• Spoon-shaped, arcuate head scarp morphology.

• Sandy beaches coves (?)

Large-scale, natural landslides:

LESSONS FROM DATAI CASE STUDY

• Landslide are commonly have denser/thicker vegetation cover because of;

• thicker soil profile which allow for sturdy growth of bigger and taller trees.

• High moisture content and better rate of infiltration as well as percolation of ground water

• Loose soil texture – good for vegetation growth

• The large-scale landslides (system) are commonly associated with:

• A number of smaller landslides (units).

• Arcuate, spoon-shaped main scarp

• Hummocky topography over the moved masses/body

• Chaotic, dismembered rocks masses, poorly sorted debris and colluvium deposit.

• Deep-seated sliding plane, unstable ground and problematic to the infrastructures built on them.

• Large scale landslides along a coast line have a significant control on the coastal morphology, closely related to the occurrence of sandy beaches cove/bay.

Photo 1: Early. 1999

Photo 2: Sept. 1999

CASE STUDY #2: THE CUT SLOPE AT GUNUNG PASS, PERAK

• Gunung Pass is located between CH23000-CH24500 of hilly road linking

Simpang Pulai and Pos Selim In Perak to Blue Valley Cameron Highland,

Pahang.

• The construction of the 35km road was started in 1997 and was expected to

be completed in 2000. Having confronted with serious and numerous

landslides/slope failures, the opening of the road was delayed to 2004, but

construction and slope rehabilitation works at Gunung Pass were still

continuing at that time.

• The largest landslide was in the cut slope at Gunung Pass.

• This case study, which was conducted in 2005, involved a detailed geological

mapping was attempted to investigate the causes for the massive and active

landslide.

Case Study #2: The Cut Slope At Gunung Pass, Perak

Photo 1: Early. 1999

Photo 2: Sept. 1999

Photo 3 : August 2000

Photo 4 : October 2001

The Cut Slope At Gunung Pass (CH 23000 – CH 24500)

Photo 5 : as in 2002

The Cut Slope At Gunung Pass (CH 23000 – CH 24500)

Photo 6 : August 2003

Photo 7: June 2004

Photo 8 : February 2005

Photo 9: Jun 2007

Geodynamic Features • Failure scarps above the moved

bodies.

• Widespread tension cracks in the vicinity of the failed section.

• Dilated discontinuities (joints, faults and foliations)

Geodynamic Features

• Broken, dislocated, uplifted, truncated, shifted and sagged berm drains.

Geodynamic Features

• Erosions (rills and gullies)

• Uplifted and protruding slope mass

Geodynamic Features • Uplifted & protruding

slope mass.

STRUCTURAL MAPPING & KINEMATICS STABILITY ASSESSMENTS

Wedge failure due to intersection of J1 and J4, if the slope is steeper than 2:1 (63°)

Planar failure due to the daylighting J3 set (170/40). J4 and J1 acted as the release planes for the planar sliding to occur.

Cross-section

The Discontinuities

The Discontinuities

The Discontinuities

The Discontinuities

Hypothetical geological cross-section of the slope showing the likely

orientation of the discontinuities and probable sliding planes

Failure Mechanism..

Failure Mechanism..

Failure Mechanism..

Failure Mechanism..

GUNUNG PASS, POS SLIM – CAMERON HIGHLAND ROAD

61

Keratan rentas cerun di Km 24.02 Jalanraya Pos Selim – Cameron Highland, menunjukkan orintasi

ketakselanjaran utama yang menyebabkan ketakstabilan dan mendorong kejadian tanah runtuh

berskala besar.

Gunung Pass

2001 Failure

The Probable Underlying Factor….

GUNUNG PASS, POS SLIM – CAMERON HIGHLAND ROAD (Continued)

• The landslide is attributed to:

• Reactivation of old, large-scale landslide

• Unfavourable intersections of discontinuities/joints,

• Highly weathered & heavily jointed rock mass,

• Excessive modification of the original hillslope morphology (stress release) and drastic changes in hidrology/hidrogeologic regime..

• “Chasing the ground” by cutting deeper/higher into the slope could not help to stabilize the slope.

• Lessons learnt:

• The area should have been avoided on the first place

• Geological & geomorphological input should have been fully taken into consideration during the route alignment selection and before as well as during the construction.

• The landslide risk has now become too messy to be handled economically, and the best option is to avoid this hazardous road stretch.

63

DISCUSSION

• The existence of the large-scale landslides were only known after the areas have been developed and extensive and continuing damages to the built infrastructures.

• The underlying factors for the extensive damages were ground movement of a large-scale, deep-seated landslide.

• Lesson learnt: Gomorphological and geological mapping focussing on large-scale landslide hazard identification should be exercised prior to any development planning and design in the hilly/mountainous terrain.

• Avoiding development in large-scale landslide areas should be the best option of a disaster risks pre-mitigation (prevention) measure.

• Even massive and costly engineering measures could not effectively prevent disastrous

damages due to deep-seated large scale landslide.

• Other mitigation options for large-scale landslide:

• Changing of land-use types according to degree of risks.

• Low-impact and low-density development. Buildings and houses should be

adequately designed and sited on carefully selected low-risks zones.

• Structural mitigation measures (drainage, slope protection/stabilisation structures)

tailored to site specific conditions.

• Continuous monitoring & Early Warning System

• Public Awareness

CONCLUSIONS

• The occurrence of large scale landslides is not uncommon in mountainous terrain of Malaysia. Their threats have been recognized and admitted as a major geohazard for hill-side development.

• It is so unfortunate and often too late when the existences of large-scale landslides are only known after the affected areas have been developed and suffered from extensive damages/disasters.

• Unnecessary disasters (& great economic losses) could have been avoided if the large-scale landslide geohazards had been identified and assessed on the first place prior to the developmed. Infrastructural development should be avoided when interfering with deep-seated large-scale landslides.

• Remote sensing imageries (e.g. advanced high density LiDAR data) can be a great tool in identifying this large-scale landslide over a vast area. Therefore, future development over Malaysia’s mountainous area should be closely followed from thorough image analysis and geological studies before it can be implemented.

THANK YOU

Acknowledgment

• SEADPRI, LESTARI, & FST UKM

• JMG Sabah Office

• UTM KL