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SEISMIC AND GEOTECHNICAL STUDIES - KUNDASANG

posted Apr 21, 2012, 2:39 AM by jeffery jim   [ updated Jul 7, 2016, 10:25 AM ]

INTRODUCTION

Sabah is the state in Malaysia which experiences the most occurrences of earthquake and seismic activities in comparison to the other states. There are 78 occurrences of earthquake since 1897 where the 1976 and 1991 caused the worst damages to the surrounding infrastructures. Sabah have 3 main seismic zone namely the Central-North (Ranau Zone), the Labuk Bay – Sandakan Basin Zone, and the Dent – Semporna Peninsular Zone. 

The site is located at the Central-North area which is regarded as highly instable as wells as situated in the K1 sector in the Kundasang Landslide Complex. Thus, the possible development should undergo scrutinyin a desktop study before detail studies prior to development.


SEISMIC AND EARTHQUAKE

The proposed site is currently situated at the area which is regarded highly active with seismic activities and to make it complicated, these fault lines are sitting close to the proposed site. The 1991 earthquake (three) epicenters are located relative close to the site as well. Amongst the clear devastation of due to this earthquake are the infrastructure and the structure of the SMK Kundasang which is situated 500 meter away from the site.

The followings are the illustrations of the 1991 earthquake’s epicenters which are located within 20-30 kilometer from the proposed site with the magnitude of 5.1 Richter scale.

In order to get accurate reading, a field observation and data gathering could assist in composing and producing an appropriate contour map for PGA of the said area. Another method could be employ on design of any structure should allow for 180 gals or 0.18g for design. For safety, it is recommended that design should allow for 0.45g.

Seismic resistance features shall be recommended and incorporated in the resort layout planning, architectural and structural design.


GEOLOGY

The proposed site is sitting on the Eocene Trusmadi Formation with the predominantly Oligocene-Lower Miocene West Crocker Formation relatively close on the eastward of Kundasang. Among the most critical issues lies on the geological properties of the proposed site would be the existing of major faults surrounding it. Since the site its located on the Kundasang Landslide Complex with rapid development within the vicinity, the additional faults would be one of the parameters which might initiate the other geotechnical failure (to be discussed in the geotechical section of this report).

Currently, there are two active faults at Kundasang, namely the Lobou-lobou Fault (Left Lateral strike-slip, trending N20°E) and the Mensaban Fault (Normal Oblique, striking WNW-ESE). The Lobou-lobou fault and Mensaban fault crossing the Kundasang Landslide complex and relatively close to the proposed site. These faults are believed to be crossing less than 100 meter from the site had caused tremendous damages to properties and affected the socio-economy of the inhabitants within the area.

There are Threefundamental causes for ground instability were identified:-
Original earth material of the Oligocene submarine chaotic deposits (mapped by most previous
reporters as Trusmadi Formation, Figure 2a), 
The Kundasang area being located within the WNW-trending wide and Quaternary Mensaban fault zone, 
The still rising Kinabalu pluton that may have disturbed the isostatic equilibrium and causes local normal faulting as adjustment.

The above map clearly indicate the past events and the possible reoccurrences where the site might exposed to;-
As the erosion/landslide deposit area from the higher area (located at Westward),
To erode/side together with other masses down Eastward, and
Exposed to rock and boulders from Westward.


SOIL TYPES

The soil type plays an important role to pre-determine the possibilities of geotechnical behavior of the surrounding.

The existing is situated on the Crocker type of Soil association however it is to be reminded that the proposed site also situated close to the boundary of Trusmadi Soil association at the North and the Pinosuk Soil association on the East side of the proposed site.


Key Association     Landform Parent Material             Main Soil Units

47 Crocker     Mountains Sandstone and Mudstone OrthicAcrisols [1]; Chromic and 
                                                                                        DystricCambisols [1]; Lithosol [1]
50 Trusmadi     Mountains Sandstone and Mudstone Gleyic and OrthicAcrisols [1]; 
                                                                                        GleyicPodzols [8]; HumicGleysol [2]; 
                                                                                        DystricHistosol [10]; Lithosol [1]
18 Pinosuk     Plateau         Sandstone and Mudstone GleyicPodzol [8]; Gleyic and 
                                                                                        OrthicAcrisols [1]; Humic and 
                                                                                        DystricGleysols [6].

Hence this would actually conclude the type of soils available at the site would be of majority Orthic and GleyicAcrisols.

From this table and site condition and a cross reference to Rating Value for Landslide susceptibility Analysis (LSA), the Trusmadi and Pinosuk association where DystricGleysols, GleyicPodzols and DystricHistosol soil units are those which are highly susceptible to landslide.


GEOTECHNIC

The significant of the proposed site does not only placed itself at one of the hotspot area which is sitting close to the boundary of sector K1 and sector K4 of the Kundasang Landslide Complex (which comprises of 6 sectors and 6 landslide systems). Each of this complex’s sector (the landslide system) consist of mass valued at 1.5 up to 5 million m3 with varies movement rate. Therefore, it is important to understand the existing scenario and to study, to valuate and to determine the projected and propagated movement with known knowledge of the localized issues.

Based on Detailed field observation on geodynamic features (since 1999 to est. 2007), the proposed site is surrounded by scarps or slopes or cliffs in sector K1 with some seepage or ponding spots surrounding it at the south and at the Northeast in less than 50 meter away.

The latest development of housing or resort at the eastern side would also propagate possible dynamic in ground movement due changing water level or other geotechnical factors.


SUMMARY

The followings are the summary for the desktop study;-

  • The proposed site is located at a critical area which is dynamically unstable and might pose danger to inhabitants if counter measures are not taken in all aspect during pre-development, development and post development.
  • Soil Investigations and geological studies should be performed prior to any perusal for design and submission. Aside from that, there is a high possibility that EIA would be required as part of the pre-requisite in submission and documentation prior to construction.
  • The proposed alignment, orientation of buildings and infrastructures; and other aesthetic features should be a complimentary to all hazard posed to the development.


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