Engineering Geology 117 (2011) 159–169

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Engineering Geology

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Re-evaluation of rock core logging for the prediction of preferred orientations of karstin the Kuala Lumpur Limestone Formation

Hareyani Zabidi a,⁎, Michael Henry De Freitas b

a School of Materials and Mineral Resources Engineering, Universiti Sains Malaysia, 14300 Nibong Tebal, Penang, Malaysiab Department of Civil and Environmental Engineering, Skempton Building, Imperial College, SW7 2AZ, London, United Kingdom

⁎ Corresponding author. Tel.: +60 135016293; fax: +E-mail address: srhareyani.zabidi@eng.usm.my (H. Z

0013-7952/$ – see front matter © 2010 Elsevier B.V. Aldoi:10.1016/j.enggeo.2010.10.006

a b s t r a c t

a r t i c l e i n f o

Article history:Received 17 December 2009Received in revised form 9 August 2010Accepted 9 October 2010Available online 16 October 2010

Keywords:LimestoneKarstRQDSMART tunnelRose diagramKuala Lumpur

Based on the relationship between the geological structures and river patterns, the preliminary prediction ofthe karstic features in the Kuala Lumpur Limestone Formation, based on the existing geological, map appearsto be directed between N030° to 070° and N120° to 150°. The factual evidence of this occurrence is obtainedfrom investigation in the field: first, using the two sites exposed for construction of the SMART tunnel underKuala Lumpur and second, based on the SMART tunnel project rock cores recovery. Amuch detailed predictionwas made by re-evaluating the TCR, RQD and SCR values. The reassessment of these values enables the drilledground to be classified into four different qualities of rock mass: good quality limestone; moderate qualitylimestone; weathered limestone; and fully developed void-like karst. According to this new classificationsystem, the tunnel appears to align generally in the heavily karstified limestone in the northern section andmassive good quality limestone in the southern section of the study area; which is represented as rosediagrams. The evidence for this analysis is given and the methods used for these studies are explained.

60 45941011.abidi).

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1. Introduction

In Malaysia, limestone caves extensively outcrop in the northernhalf of the Peninsular Malaysia, such as in Langkawi Islands, northernPerlis, Kinta Valley in Perak and Klang Valley in Kuala Lumpur.Although these limestone formations vary considerably in geologicalage and tectonic setting, they are very similar in chemical composi-tion; being dense, recrystallised, and massive with little impurities;and, by having these properties, the formations are more likely todevelop karst landscape and large caverns within them (Gobbett,1965). The features can be seen well developed in limestoneformation at many of the previously exposed open hydraulic tinmines in Perak and Kuala Lumpur (Yeap, 1987).

In contrast to any other karst formations in the country, karstterrain in Kuala Lumpur is a home for many big foundations of highand heavy buildings, thus, it is so important to understand itsexistence (Pollalis, 2002). Karst in Kuala Lumpur could simply bedivided into two groups based on its morphology. The first group issurface karst and the second is buried karst where the latter group isthe dominant type of karst that occurs in Kuala Lumpur (Yeap, 1985).Batu Caves at the northern part of Kuala Lumpur represents thesurface karst, and towers vertically above a flat alluvial plain of KlangValley. However, Batu Caves represents only 1% of the whole karst

formation developed in the area. Buried karst occurs as a bedrock anddominates the sub-surface of Kuala Lumpur Valley. According toWaltham and Fookes (2003), the highly irregular topography oflimestone formation, which is classified as extreme karst (kV), wasfirst discovered buried beneath the alluvium layer. This happenedwhen they were exposed to the air between 1970's and mid 1980's inthe tin mines that were found scattered around Ipoh and KualaLumpur, and for the first time, were presented as highly irregular sub-surface rockhead and fractured rock mass of buried karst (Fig. 1) (Tan,1985; Yeap, 1985). Deep borehole records from construction sites inthe city confirm its occurrences (Mitchell, 1985; Tan et al., 1985).

Upon the discovery of highly variable karst formation from the tinmining activities, extensive studies were carried out, with most ofeffort looking specifically at the process and the time-scale at whichkarst had developed. Yeap (1985) attempted to classify the karsticfeatures into 5 significant groups based on the physical andmorphological characterization. This classification is also in goodagreement with the 5 stages of karst evolution proposed by Yeap(1987). Based on the observations carried out by Yeap (1985, 1987,1993) at the previously open tinmines around the Kuala Lumpur area,it was believed that the karstification process occurred beneath apermeable layer of sediment that was later eroded to expose thekarstic formations to the air before later being buried once againunder alluvium. This is verified by Tan (1986a,b, 1987) in morespecific study areas, where he pointed out the presence of a very softsoil zone, where the SPT value is 0, located immediately above thelimestone bedrock below themuch younger formation; the Kenny Hill

Fig. 1. (a) Sungai Way Mine, Kuala Lumpur (picture from Yeap, 1985). The irregular top surfaces of the Kuala Lumpur Formation were revealed during the tin mining exploration;(b) high pinnacles of the limestone rock surface in Kuala Lumpur (picture from Tan, 1985).

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Formation. This soft soil zone was interpreted as a weatheredlimestone formation which was possibly weakened by dissolutionafter being covered by the Kenny Hill Formation, and overlain bymuch harder or stiffer layer of soils from the Kenny Hill Formation(SPT=30–50 or even greater).

A systematic presentation of engineering geological data in theform of a hazard map is a useful tool in urban planning, particularlyin a highly developed karstic area, as in Kuala Lumpur. Currentlypractice of depending heavily on borehole drilling to study thecomplexity of the ground in Kuala Lumpur is risky and incorrect, asmuch of the commercial centre of Kuala Lumpur is founded on theheavily karstified limestone of the Kuala Lumpur LimestoneFormation and boreholes give no guarantee of finding all thekarst; and, this has always been a challenge for engineers working inKuala Lumpur (Mitchell, 1985; Gue and Tan, 2001; Abdullah,2004a). Around the world, various studies, ranging from cavemapping, geophysical survey and borehole drilling, have beenconducted to understand and further predict the extremely complexsystem of the underground cavities (Epting et al., 2009). Currentstudies on the underground karst were largely based on the caveresearch and expose outcrops seen at road cuts, mines or quarrieswith most of the studies looking at the known distributions ofsinkholes in predicting the future occurrences of sinkholes in theareas of interest (Gao et al., 2005; Brinkman et al., 2008; Bruno et al.,2008; Guerrero et al., 2008). Nonetheless, in the recent years, manyavailable logged boreholes were recovered from karst terrain asmore engineering structures in the urban area are in demand. Theanalysed data is improved by advanced technology that has createdborehole imagery to study the solution conduits in karst aquifersand other karst features (Manda and Gross, 2005; Papadimitriouet al., 2008).

However, boreholes are commonly drilled in a less systematicpattern of distribution to form spatial coexistence between twoboreholes logs, and this should be taken into consideration ininterpreting karst (Urban and Rzonca, 2009). Commonly conductedin the geotechnical study, borehole logs are mainly used to deduce thevertical profile and the distribution of strata in studied area underlainby bedded sequences of rocks. In the karst study, mapping of theunderground cavities commonly utilises several techniques ofgeophysical survey which provides much comprehensive and thor-oughly information on the characteristics of the underground karstterrain compared to drilling alone. Boreholes are commonly used forground validating purposes and hydrogeological observations (Sudhaet al., 2009). Pesendorfer and Loew (2009) and Filipponi et al. (2009)studied the groundwater networks, looking into the potential inflows

into the studied engineering structures and hence, characterizing thehydraulic properties of the ground.

Research conducted for the last 50 years had shown that thedevelopment of a dissolution cavity is more likely to follow somepreferred orientations and patterns. These variations were observedto follow the significant patterns of variables involved, such as thestructural geology, topography, mineralogy, sedimentology andpalaeoclimate. Parts of these relationships and observations havebeen well written by many researchers in Malaysia, for example, theyattempted to link the close relationship of karst formation with thegeological structures and drainage patterns, by which the predictionof karst can bemade by analysing the stream trellis form in the ground(Tjia, 1970, 1996). However, many authors did not consider thepossibility of quantitatively studying the karst formation and ratherlikely to make a straight forward depiction of the studied rock mass,leaving the currently available method of karst prediction to be alonedetected by borehole drillings. Hence, the main objective of this paperis to do the methodology self-checked analysis by quantitativelyidentifying the distribution of the karst cavity formed in the KualaLumpur Limestone Formation using the so obtained borehole logs ofthe SMART tunnel project. In this study, the geometry of the karstsystem was directly observed from the quality of recovered cores,whereas the hydraulic properties were analysed from the installedpiezometer readings. This is the second phase of analysis followingthe first paper written by Zabidi and deFreitas (2006), where theprediction of karst orientations in Kuala Lumpur were deduced fromthe map study and later verified by field observations carried out atthe two previously exposed sites for the SMART construction.

In this study, a high density of logged boreholes, drilled for theconstruction of the Stormwater Management and Road Tunnel(SMART), provides a great opportunity to quantitatively analyse thesub-surface cavity karst (Fig. 2). TheMalaysian Government proposedthe construction of the SMART project on account of the frequency offlooding in Kuala Lumpur over the past three years; the cityexperiences frequent flash floods from the Klang River during themonsoon season because it is situated at the confluence of the KlangRiver and the Gombak River (Abdullah, 2004b; Klados and Yeoh,2004; Krause et al., 2004; Tunnel and Tunnelling, 2005). Thisinnovative solution involves a dual-purpose tunnel, which will notjust be used to control the volume of flood water coming into the citycentre during the rainy season but will also be used as an automobilecorridor to reduce traffic congestion at the southern gateway of KualaLumpur during the dry season. The tunnel has a total length of 9.7 km;the central 3 km section of the tunnel doubles up as a two-deck toalleviate traffic congestion in central Kuala Lumpur.

Fig. 2. SMART alignment, crossing between Ampang at the northern section and Taman Desa at the southern section of Kuala Lumpur.

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2. Geology of Kuala Lumpur and its relationship withkarst formation

Kuala Lumpur is located in Peninsular Malaysia, lies on a flat alluvialplain within the broad valley of the Klang River, bounded by high hillspredominantly of granitic rock to the west and east. The main river ofthe study area is the Klang River that drains a catchment area ofapproximately 1288 km2, and traverses a distance of nearly 120 km.Generally, Kuala Lumpur has a uniformly high air temperaturethroughout the year, averaging between 25 °C and 28 °C with 80%humidity. The climate is strongly affected by the speed and direction ofair streams which sweep across the Peninsular Malaysia twice a year,blowing fromthe southeast and thenortheast direction, and responsiblefor two interchangeable seasons each year: monsoonal and trans-monsoonal that carry with them strong wind and heavy rainfall.

Fig. 3 shows the location and geologic setting of the SMART tunnelalignment between Ampang at the northern section and Taman Desaat the southern end of Kuala Lumpur. The bedrock geology of thestudy area consists of sediments ranging in age from MiddleOrdovician to possibly Permian, and a granitic body intruded duringthe Late Triassic. The oldest of the sequence is the HawthorndenFormation (Middle Ordovician toMiddle Silurian), amixture of quartz –mica amphibolites and carbonaceous schists, phyllites and quartzites –overlain by the Kuala Lumpur Limestone Formation (Middle Silurian toLower-Middle Devonian) (Gobbett, 1964). The overlying Kuala LumpurLimestone Formation is composed of fine to coarse grained, white togrey, predominantly recrystallised limestones, with local developmentsof dolomitic limestone and dolomites, all with few impurities. TheseLower Palaeozoic formations experienced their first phase of foldingduring theDevonian to form east–west fold axes. An extensive period ofuplift, weathering and erosion followed during which karst developedin the Kuala Lumpur Limestone Formation.

These Lower Palaeozoic formations are overlain unconformably bythe shales, mudstones and sandstones of the Kenny Hill Formation,which accumulated towards the end of the Carboniferous and the startof the Permian. These sediments were folded by a second tectonicorogeny during the Late Triassic. This strongly deformed the LowerPalaeozoic rocks to produce the metamorphic grades now seen andfolded strata to follow a north–south trend. The Lower Palaeozoicsequence has bedding dips that are commonly steep and overturned,contrastingwith themoregentledipsof theKennyHill Formationwhich

lies over them.The country rockwas then intrudedbygranite, estimatedto be either broadly contemporaneouswith or younger than the secondphase of folding, occurring towards the Late Triassic. The last period ofdeformation isNE–SWandNW–SE trending faulting,whichhas affectedall the formations, including the granite. The fault zones of the AmpangFault, trendingatN285°, and theGombakFault, atN200°, havemarkedlydisplaced the Kuala Lumpur Limestone Formation and can be expectedto have affected its hydraulic conductivity. Paton (1964) believed thatthe presence of mature karstic features, as distinct from the palaeo-karst, in this area is the result of climate in the present and recent past.The rock head karst is generally believed to have developed during theQuaternary, although it is possible that considerable dissolution alsooccurred prior to the deposition of the Permo-Carboniferous Kenny HillFormation; this paleo-landscape has been buried by alluvium to formthe current landscape of Kuala Lumpur (Chan and Hong, 1985).

3. Method of analysis

In this study, an almost continuous profile of the Kuala LumpurLimestone Formation along the 9.7 km tunnel is provided by therecords of boreholes drilled during the site investigation for theSMART project, thus offers a good opportunity to study the groundcondition of karst features along the line (T&T, 2005). Due to thesedemanding ground conditions, extensive site investigation along thetunnel alignment was necessary, comprising around 500 drillings ofdeep sub-surface investigations with drilling up to a maximum depthof 50 m below ground level (BGL), in addition to a resistivity surveywas carried out before and during the construction of the tunnel. Thecollection of borehole records used in this study was largely based onthe drilling and logging carried out by several private geotechnicalcompanies in Kuala Lumpur, appointed by the Malaysian's govern-ment and also a company joint-venture pact between Gamuda Berhadand Malaysia Mining Corporation Berhad (MMC). These logs werereanalysed during this study to re-assess the Solid Core Recovery(SCR), Total Core Recovery (TCR) and Rock Quality Designation (RQD)so that a quantitative measure of the quality of the ground can bedetermined. Using the values so obtained, the ground is re-classifiedinto four different qualities of rock mass, ranging from very good tovery poor. Based on this classification and the position of theboreholes, a percentage of karst per unit area seen in plans, couldbe calculated, which was then presented as rose diagrams.

Fig. 3. A simplified version of the geological map of Selangor, Sheet 94 (Yin, 1967). The valley area is composed of the Hawthornden Formation, the Kuala Lumpur LimestoneFormation, the Kenny Hill Formation and granitic body.

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In the two aligned borehole analysis, good quality of the ground isrepresented as small values on a rose diagram, whereas poor qualityground, which is thus expected to containmuch karst, is represented bylarge values. However, as the boreholes were drilled at differentspacings and at different depths, a further analysis is required toproduce a representative value per unit area seen in plan. Thus, an areaanalysis was carried out, using the three nearest borehole method ofcalculation; a modified version of the Thiessen Polygon method; this ispresented in the secondpart of thepaper. In this analysis, thepercentageof karst was defined in any area by the three closest boreholes. Theboreholes along the alignmentweregrouped intofivedifferent sections:the North Bound section; the Jalan Kampung Pandan section; theKampung Pandan Roundabout section; the South Bound section and theTaman Desa section; each of the sections contains different clusters ofboreholes which can be used to form several different triangles, eachjoined by the three nearest boreholes, as mentioned above.

The calculated karst percentage obtained from the analysis wasplotted against per unit area to give a profile of the ground in terms ofarea along the alignment. Having considered the horizontal variabletowards the karstification, the next step was the assessment of karstin a volume of the ground, where the vertical variable was studied. Inthis analysis, the same triangles were used to check the volume ofkarst developed as were used to calculate its presence per unit area;the results obtained were presented as the fraction of karst plottedagainst the volume of the ground.

4. Factual data from the SMART tunnel project

From field observation, the buried karst landscape of the KualaLumpur Limestone Formation can be further grouped into two classesin accordance to its dimensions and characteristics: a Karst Scale 1

(K1) which is well developed creating a highly irregular level of rockbelow the alluvium, varying in elevation by tens of meters over tens ofmeters and containing numerous voids, many of which have collapsedand are partially filled, and a Karst Scale 2 (K2) which is much smallerand concentrated on fractures which have developed an openness(measured in centimeters) and freshness that suggest that it is stillactively developing. The existence of two different groups of karst inthe area was recorded from the mapping of two localities exposedduring the construction of the SMART tunnel: the North Junction Boxin Kampung Pandan Roundabout and the South Junction Box in SungaiBesi (Zabidi, 2008).

The construction extends the existing borehole data and permits adetailed study of such karst to be conducted, since the Kuala LumpurLimestone Formation is the predominant geological formation at thetunnel level throughout the route. Nonetheless, this data is muchbetter in some places than in others. The drilling was done inaccordance with BS 5930, 1981, whereas the core logging was carriedout with reference to BS 5930:, 1999. The quality of rock drilled outfrom the ground was measured by the Total Core Recovery (TCR),Solid Core Recovery (SCR) and Rock Quality Designation (RQD), inaddition to description of the rock and the fractures according to BS5930:, 1999.

5. SMART tunnel rock core recovery

The Northbound and the Southbound section of the tunnel werenamed in reference to the advancement of TBM to the north and southof the Kampung Pandan Roundabout (Fig. 4). The cores drilled fromthe Northbound tunnel section can generally be classified as heavilykarstified; this is largely based on the quality of the recovered core.Poor recovery was often encountered, especially in the Kampung

Fig. 4. A general map of the SMART tunnel alignment. The location of boreholes is shown in different clusters of boreholes.

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Berembang area, near to the Klang Holding Pond construction site,and in the Jalan Kampung Pandan, at the North Junction Box site. Inthe Kampung Berembang site, 12 boreholes, with a horizontaldistance between them less than 10 m, revealed a very poor recovery,lots of cavities and broken material. The ground condition becomesextremely unpredictable as the rock mass change over a shortdistance between much karstified grounds to solid massive rock.Further down to the south, close to the Kampung Pandan Roundabout,on the discovery of the poor ground conditions from the first stagedrilling carried out in the area, further deep drilling, consisting ofclosely spaced probes at a distance less than 10 m and at depth morethan 40 m BGL was carried out during the construction of the tunnel(Zabidi, 2008).

In contrast, a much better quality rock mass was recovered outfrom the South Bound tunnel section with one or two exceptionallocations, e.g. the Sungai Besi Junction Box and the Taman DesaReservoir Pond, where the rock cores are heavily weathered andfractured. Other than those two locations, the boreholes consistentlyrevealed cores that have percentages more than 90% of TCR, SCR andRQD values. The drilled limestones weremassive, dense and show fewfractures in comparison to the limestones drilled from the NorthBound tunnel section; and this profile of core logs was in goodagreement with the exposed rock sections mapped in the SouthJunction Box located in Sungai Besi.

The analysis started with a comprehensive study of almost allborehole logs obtained from the rock core drilling carried out for theSMART tunnel; leaving out biased data. This was done by having leftout all the boreholes drilled in a single line as the data is biased to the

directions of the line of boreholes. The values of RQD, SCR and TCRwere chosen to independently describe the quality of the grounddrilled along the alignment and further used to calculate thepercentage of existing sub-surface karst, where the drilled rock corewas classified into four different qualities of rock mass: good qualitylimestone; moderate quality limestone; weathered limestone andfully developed void-like karst. For every closely spaced cluster ofboreholes, the percentage of karst per unit area was measuredbetween two boreholes in any given direction; the percentage of karstwas represented as rose diagrams.

5.1. The SCR, RQD and TCR values

Following BS 5930:, 1999, the Total Core Recovery (TCR) is definedas the percentage ratio of the core recovered (either solid or non-intact) to the total length of each core run. The Solid Core Recovery(SCR) is referred to as the percentage ratio of the solid core recoveredto the total length of each core run, whereas the Rock QualityDesignation (RQD) is defined as the ratio of the total length of thesolid core (the SCR definition) pieces each greater than 100 mmbetween natural (not drilling induced) discontinuities, to the lengthof core run. For the purpose of this study, the BS 5930:, 1999classification of TCR, SCR and RQD is neither detailed nor specificenough in definition to explain the complex nature of the karsticlandscape of the Kuala Lumpur Limestone Formation. To analyse theborehole logs quantitatively a further classification and practicaldefinition on the quality of the limestone rock has been made in orderto define the presence or absence of such smaller scale (K2) karst; this

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was largely based on the Solid Core Recovery (SCR), the Rock QualityDesignation (RQD) and the Total Core Recovery (TCR), as theclassification is the most practical and available system to date forinterpreting the quality of rock mass drilled from the ground.Additional input can also be obtained by the core photos taken fromthe sites, and this may allow for the re-checking of the core log to becarried out. In this classification system, the range of percentages foreach group was chosen after checking and re-assessing all therecorded boreholes by comparing their core logs with their photos.

In this analysis, the presence of what might be palaeokarst andmodern karst in the recovered limestonewas defined as karst andwasanalysed every 1.5 m length of the core. The problem here wasdetecting small scale karst (K2). Large scale karst (K1) was mainlydetected by TCR and had shown much consistence values of highpercentages of recovery throughout the exercise; detection of smallscale karst cavity was less significant to compare to this percentage.The TCR value was analysed by measuring up the total depth ofdrillings and largely used to assess the overall profile of the ground;the value is a combination of soft soil and hard rock materials, asdefined in BS 5930:, 1999. Within the recovered core there could besmall scale karst (K2); this would be reflected in SCR and RQD. Thismuch smaller scale of karst concentrated on fractures can directly beinterpreted from these two percentages as the SCR has onlyconsidered the solid or hard rock materials and the RQD representsthe quality of the recovered hard rock; either as an intact mass or

Table 1New classification system of quantifying the borehole log, using the SCR and RDQ values. Thand RQD (after BS 5930:, 1999).

broken pieces of rock. Hence, these two have been used to grade thelimestone into 4 types; Table 1 illustrates the re-classification.

1. SCR 100% to 70%: RQD 100% to 35%. Good quality rock.2. SCR 69%–50%: RQD 100%–35%. Moderate quality rock.3. SCR 69% to 50%: RQD 34% to 0%. This is taken as “weathered”

limestone, where weathering has opened discontinuities andhence represented areas of the ground having great potential tocontain well developed small scale karst. In this class, a muchhigher percentage of SCR was used in comparison to the RQD giventhat the recovered core within this value shows good recovery ofsolid rock, but frequently as a non-intact mass; broken pieces ofrock less than 100 mm long result to the lowering of the RQD value.

4. SCR 49% to 0% and RQD 34% to 0%. This was taken as fully developedvoid-like karst; which revealed little recovery of the solid core withthe occurrence of soft fragments of rock or no recovery of the core.

Using this approach, the same range of SCR percentages, between69% and 50%, but different classes of RQD was used to differentiate thequality of the ground; the RQD is 100%–35% in the moderate quality ofrock whilst 34%–0% in the weathered group of rock. In contrast to thispresentation, different classes of SCR percentages in combination withthe same range of RQD values gave another set of ground qualities;ranges fromgood tomoderate and fromweathered to void karst ground(Table 1). This was basically based on the observation of recovered rockcores at sites, structuralmapping carried out on the excavated rock faces

e quality of recovered cores is classified into four groups according to the values of SCR

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and core photos from the SI report, where a significant drop of rockquality, which is heavilyweathered and broken pieces of rock cores, canbe seen when the SCR value is in between 69% and 50% and the RQDvalue is within 34%–0%. This was basically looking at the significantdifferences the groundmade by just considering the classification aloneand the value was not so good when the TCR was small or the core wasclose to a cavity; in this case the SCR and the RQD values appeared to behigher but the core was poor. This had been cross-checked with thephotos taken at sites. Therefore, to calculate the percentage of karstdeveloped along the general alignment of the tunnel, the last group ofkarst, the SCR 49% to 0% and RQD 34% to 0% was used. This range ofpercentages is assigned to represent the voids given to the poor corerecoveries, containing most of soft fragment of rock and soils. Thesematerials are believed to be the in-filling materials of voids or cavitiesoriginated from the heavily fractured and deformed limestoneformation. It is assumed that these hardmaterials were slowly softenedby the process of weathering that finally changed it into the soft soils.Validation of these percentages has been made through the mappingcarried out at the Kampung Pandan Roundabout or Northbound boxwhere karst is seen to develop at the intersection zone between twovery prominent fracturing systems in the limestone formation.

In Fig. 5, four different rock cores which represent four differentquality of rock mass, are presented, namely here as CP4-4, BH-NVS2,BH2 and Bh3650R. These boreholes are illustrated here as an exampleof the calculation used to quantify the percentage of karst formed inone borehole.

1. In the first borehole of CP4-4, the core was drilled to 27 m BGLwiththe rockhead at 2.80 m BGL, to leave 24.80 m rock core with highvalues of TCR, SCR and RQD; it has 0% of karst and thus to be classedas good quality of rock mass.

2. In the second borehole of BH-NVS2, the total length of the core is30.00 m with 4.60 m of soft soil cover and 25.40 m of rock core. Atotal of 2.40 m length of the low percentage in SCR and RQD hasresulted to the 9.44% of karst within this one borehole.

3. In borehole BH2, the core was drilled much deeper, down to44.00 m BGL, but failed to encounter bedrock; this means that the

Fig. 5. Details of four different rock cores, drilled out from four different areas along the tunnhaving quantified using the new classification system of RQD and SCR values. Elevations ar

rockhead is located deeper down than the rest of the rock in thearea and in this case, the core was labelled as 100% karst.

4. In the fourth borehole of Bh3650R, the core was also classified as100% karst as the revealed rock core contains very low values ofSCR and RQD. The core was drilled at a depth of 28.00 m BGL, therockhead was discovered at 10.80 m BGL to leave the 17.20 m ofthe rock core with very low values of SCR and RQD.

5.2. The percentage of karst between two aligned boreholes

Following this classification system, the original SCR and the RQDvalues between aligned boreholes were re-evaluated for everyborehole location where closely spaced clusters of boreholes existed(boreholes space at distances of between 10 m to 20 m) so thatcomparisons in different directions could be made, in order toproduce a percentage of dissolution in given directions. The finalvalues of SCR and RQD were then plotted as rose diagrams of likelykarst. Directions with small values in these diagrams reflect highvalues of SCR and RQD and are assumed to represent a reasonablygood quality of limestone in which little dissolution might beexpected, whereas directions with large values are expected to bemore likely to contain dissolution that has been better developed. Tothe civil and tunnel engineers all such dissolution is viewed as “karst”.

A cluster of closely spaced boreholes (named as BhA1, Bh-V6, Bh-V5,Bh4053R, Bh4053CL, and Bh4053L) located at Ch4000, near JalanKampung Pandanwas taken here as an example for the calculation usedto present the percentages of karst between two boreholes in any givendirection. All the measurements are shown in Fig. 6; according to thenew system, the six drilled boreholes were classified as follows:

Borehole BhA1 was measured to have 37.77% karst content;borehole Bh-V5 is classed as good quality limestone with 0% karstcontent; borehole Bh-V6 contained 19.26% karst; borehole Bh4053Rcontained the most percentages of karst in the group with 66.31%karst; borehole Bh4053CL also has 0% karst as it was drilled at only10.40 m BGL and Bh4053L had 53.84% karst. The percentage of karstbetween two aligned boreholes for every borehole in the group wascalculated by taking the average percentage of karst within the two

el alignment. Each of the boreholes represents a different quality of the rock core, aftere in meters above sea level.

Fig. 6. Six boreholes from a cluster of closely drilled borehole from the Kampung Pandan Roundabout, the location of boreholes are presented in the above map. The quality of therock core is valued in karst percentage, quantified using the new quantitative system. Elevations are in meters above sea level.

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boreholes in the given direction (Fig. 7, map 1); where each of thedirection is aligned between two drilled boreholes. This six boreholeshad produced 15 different directions of predicted karst percentages,presented in Table 2 (Fig. 7), which were later plotted as a rosediagram, shown in Fig. 7 (rose diagram); and, based on the rosediagram, karst in this area is predicted to have mainly developed inthe N310° and N360° directions.

A similarmethod of calculationwas used tomeasure the percentageof karst for every closely spaced cluster of boreholes drilled along the9.7 km tunnel alignment. In total, 36 clusters of boreholeswere selectedfor this analysis leaving out all the boreholes drilled in a single line as thedata is biased to the directions of the line of boreholes. Even so, theinterpretation carried out is still strongly biased by the obtained data,the drilled boreholes; so, the absence of directions in the rose diagramcould represent the absence of data rather than the absence of karst:with more data it would be possible to resolve the unknown.

6. Discussion

The analysed rose diagrams were drawn along the alignment toprovide an overview of the karst condition beneath the proposed

Fig. 7. The quality of each of the rock core is valued in percentage, as karst percentage, haviboreholes are shown in map 1; the percentage of karst and the direction of the two alignediagram to give the more likely directions of the developed karst; major directions are assumbelieved to represent a good quality of limestone.

alignment (Fig. 8 and 9). These groups of boreholes were divided into5 different sections in accordance to the area of drilling as follows:

(1) First was the North Bound (NB) section, consisting of boreholesdrilled out from the North Bound (NB-A) and another twogroups of boreholes drilled in between of Jalan U Thant andJalan Kampung Pandan (NB-B and NB-C). All three clusters arepresented in Fig. 8. In the first group (NB-A), 12 holes weredrilled near the Klang Holding Basin site, at a distance less than10 m between each of the boreholes; here, the quality of therecovered core log is being reflected by the major directions ofthe rose diagram, which means high percentage of dissolutionfeatures in approximately every direction of the ground. Theother two groups (NB-B and NB-C) show less intensity of karstdevelopment in comparison to NB-A.

(2) Second is the Jalan Kampung Pandan (JKP) section consisting ofseven very closely drilled borehole groups (named here as JKP-Ato JKP-F). The poor recovery of rock cores is presented in rosediagrams as shown in Fig. 8. Here, thedrilling of coreswas carriedout at a distance less than 10 m apart to reveal a very highpercentage of karst, as presented in the major direction of rose

ng quantified using the new quantitative system. 15 different directions of two alignedd boreholes are presented in Table 2. All the measurement are later drawn into a roseed to represent the major dissolution karst features, whereas the minor directions are

Fig. 8. The SMART tunnel alignment, for the north section and its relation to the quality of the ground which might be encountered in one given area, based on the rose diagramanalysis.

167H. Zabidi, M.H. De Freitas / Engineering Geology 117 (2011) 159–169

diagrams, especially in groups JKP-F and JKP-G, where karst isassumed to have developed in all directions defined by theboreholes. In the borehole groups of JKP-A to JKP-D, the drilledcores containedminor percentages of karst, less than 50%, and inthe predicted directions of karst obtained from the map study.

(3) Third is the Kampung Pandan Roundabout (KPR) section(Fig. 8), consisting of six clusters of boreholes (KPR-A to KPR-E). Here, the quality of recovered cores was interpreted as acombination of good and poor ground; these were presented inthe rose diagrams. The less percentage of karst, represented bythe minor direction of the rose diagram, has developed ingroups KPR-D, E and F, whereas the developed major directioncould be seen in groups of KPR-B and KPR-C, particularly inbetween N360° and N040°.

(4) Fourth is the Sungai Besi (SB) section, consisting of five clustersof boreholes which revealed a very good quality of rock cores(SB-A to SB-E). This data is shown in the rose diagram, Fig. 9.The dominant quality of the rock core is seen inmost of the rosediagrams; karst has minor values, which are less than 30%, andcould represent a very good quality of the ground condition inthe southern section of the tunnel.

(5) Fifth is the Taman Desa (TD) section (Fig. 9), consisting of agood quality of rock cores (TD-A) and a poor quality of rock inthe group of TD-B. The rose diagram of TD-A has minordirections in comparison with the major direction of the rosediagram in TD-B, which is assumed to have developed karst inall directions defined by the location of boreholes.

7. Conclusions

Karst in Kuala Lumpur exists as a part of the bedrock with most ofthe identification performed by borehole drillings and assisted by theindirect method of geophysical investigations. However, in KualaLumpur, the geophysical surveys provided little assistance to theengineers on site in predicting the location of karst. This wasattributed to a high water table and unavoidable levels of backgroundgeophysical noise (electrical and acoustic), leaving the borehole logs,most of the time, to do the prediction alone. Comparing the analysiscarried out in this study with the direct observations in caves orexpose outcrop, as previously carried out by many researchers inMalaysia, might have led to a much better understanding on thedevelopment of karst although the latter approach is a more sensitive

Fig. 9. The SMART tunnel alignment, for the south section and its relation to the quality of the ground which might be encountered in one given area, based on the rose diagramanalysis.

168 H. Zabidi, M.H. De Freitas / Engineering Geology 117 (2011) 159–169

method of analysis compared to recovered rock cores; even byconsidering that the borehole log is a direct method in locating andanalysing the intensity of karstification. But, the karst terrain that wasonce exposed to the air during the active period of mining activities inKuala Lumpur now buried beneath the alluvium layer, makes itimpossible to do a direct comparison. But, data obtained fromborehole log analysis should also represent some limitations as theinterpretation is the result of random sampling over a large volume ofa karstic terrain and this gives no guarantee of finding the karst cavity.Hence, this paper presents some methodology that quantitativelyanalyse the occurrence of the karst cavity using a large collection ofborehole logs that could be used to develop much representativeanalysis of the karst cavity in the future.

In this study, considering the complex system of the karst terrainthat presently exists in the ground, which was confirmed by the poorrock core recoveries, a further classification system is needed toproperly log the rock cores. The currently used classification anddescription of the rock core, based on the RDQ percentage is toogeneral and not specific enough to define the characters of karstobserved, and thus to predict the location and the dimension of karstin the ground. Therefore, in this study, the logged boreholes were re-evaluated with the modified classification system. This modified

method was achieved by combining the values of RQD, SCR and TCR,where a combination of certain ranges of percentages of those threeparameters would represent the level of karstification in the ground.The first quantitative analysis was presented in a rose diagram: thequality of the ground was defined by the percentage of karst, so thedirection with a small karst percentage value has good quality groundand the direction with a large value has poor quality ground. Rosediagrams reflecting good quality ground could be seen formed in thesouthern section of the tunnel, whilst rose diagrams for the northernsection reflect poor quality ground.

This is in good agreement with the orientations of joints and karstsurfaces observed at the two sites previously exposed during theconstruction of the SMART tunnel, the Kampung Pandan Roundaboutor the Northbound box and the Sungai Besi or the Southbound box.The two sites are less than 3 km apart, but a clear division could beseen between the grounds exposed in the two areas. In the North, theground is heavily fractured, strongly deformed and varied greatly inthe pattern of fracturing over a short distance. Frequently found at thesite, mainly in the North Junction Box, is a wet yellow colouredslickensided surface believed to have formed as a result of sheardisplacement and the continuous flow of running water. The studiedrockmass is heavily weathered to form variable features of karst

169H. Zabidi, M.H. De Freitas / Engineering Geology 117 (2011) 159–169

cavities within it. Aligned to these features are joints and major karstsurfaces which were observed to orientate at several preferreddirections, ranging from N030° to N040° and N080° to N100°directions, as obtained from the high percentages of the rose diagramin the northern section of the tunnel. In contrast, the exposed rockmapped in the South was massive, dense and barely touched by thedeformation caused by the repeated regional faulting and folding; thisis in a good agreement with the result obtained from the rose diagramanalysis. The two contrasting characters of the rock mass suggest thatthe current ground conditions might have resulted from two differentmajor activities: the faulting and the granite intrusion. An assumptionmade here is that, effectively, the marbelization of the limestoneformation has strengthened the rock quality; even though therecrystallisation of the limestone might not change the possibility ofthe karstification process.

Acknowledgements

This research project is funded by a grant from the ServiceDepartment of Malaysia and University Sains Malaysia.

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