Environmental Geology of Limestone in Malaysia

TAN Boon-Kong Geology Programme, Faculty of Science & Technology, Universiti Kebangsaan Malaysia, Bangi, Malaysia

Abstract This paper provides an overview of the engineering geology of limestone. Limestone is of rather wide occurrence in Malaysia. It is interesting in view of the unique landforms and karstic features that are encountered in limestone terrains, e.g. steep, subvertical limestone cliffs rising abruptly and majestically above the ground surface and highly variable and pinnacled subterranean limestone bedrock. The karstic features and associated engineering geological problems of both the limestone hills and the bedrock are discussed in the paper. Rockfalls, sinkholes, cavities, etc. are some of the common engineering geological problems associated with limestone terrains. Some local case studies are provided as illustrations. Finally the rock mechanical properties of limestone is discussed at the end of the paper. Key words: engineering geology, limestone, Malaysia

1 Introduction

Limestone is a sedimentary rock consisting mainly of the mineral calcite (calcium carbonate, CaCO3). The other common mineral in limestone is dolomite [CaMg (CO3):]. Common impurities in limestone include chert (microcrystalline, cryptocrystalline quartz or amorphous silica, SiO2), clay, organic matter and iron oxides. Limestone is unique since it is soluble in even slightly acidic waters, such as carbonic acid formed from the dissolution of carbon dioxide in water. The end results of the solution of limestone are a host of karstic features, such as cavities, caves, solution slots, pinnacled bedrock, stalactites/stalagmites, basal notches and overhangs in limestone cliffs. In addition, residual soils left over in the dissolution of limestone are so-called terra rossa or residual red clays mantling the limestone bedrock. These are accumulations of the insoluble residues or impurities of the limestone, comprising silica, organic matter, clays, iron oxides, etc. Limestone is metamorphosed into marble, i.e. a metamorphic rock consisting predominantly of fine to coarse-grained recrystallised calcite and dolomite. Due to recrystallisation, the crystals have interlocking or sutured boundaries forming a mosaic, hence increasing the density and strength of the rock. Many of the limestone formations in Malaysia have actually been metamorphosed into marble. For example, the limestone formations in the Klang Valley (K.L. area) and the Kinta Valley (Ipoh area) are strictly all marble. However, marble also shows the same

54 solution features and behaviour as in limestone. This paper thus includes limestone and marble, and for ease of presentation, they will be jointly referred to as limestone. Limestone is of rather wide occurrence in Malaysia. In Peninsular Malaysia, the major occurrences are in the Klang Valley, the Kinta Valley, Kedah-Perlis (including the Langkawi Islands), Kelantan (Gua Musang area), and Pahang. In these aforementioned areas, limestone occurs as majestic, precipitous cliffs as well as extensive bedrock formations. No limestone hills occur in the southern regions of Peninsular Malaysia (Johor, Melaka), and at one time it was thought that limestone does not occur at all in the southern region of Peninsular Malaysia. However, in recent site investigations, boreholes, mostly associated with various engineering construction projects, have encountered limestone bedrock in some parts of Johor as well as parts of Singapore Island. For example, the Tangkak vegetable farm area is underlain by extensive limestone bedrock, as revealed by boreholes drilled for the North-South Expressway in the Tangkak area. The Second Link Crossing joining Johor to Singapore is also underlain by extensive limestone bedrock. Similarly, the Tuas region and others in Singapore Island also have limestone bedrock. Sabah and Sarawak have extensive limestone formations occurring in the forms of numerous limestone hills and bedrock. The examples are the famous Mulu Caves and the Niah Caves of Sarawak, which are of world fame in terms of cave formations and exploration (speleology). They are also of geo-touristic value. The formations of limestone hills and their associated cave systems have been the subject of numerous studies. The interested reader is referred to Bulletin 6 by Wilford (1964) on the geology of the Sarawak and Sabah caves. The memoir by Ingham and Bradford (1960) also provides interesting reading on the geology of the limestone hills (including Gua Tempurung) and bedrock in the Kinta Valley. Similarly, the memoir by Jones (1978) discusses the limestone formations in Kedah-Perlis and the Langkawi Islands.

2 Limestone Hills

2.1 General karsttic features Limestone hills are characteristically steep-sided, with subvertical to overhanging cliffs. The base of limestone hills also often exhibit deep horizontal notches or undercuts due to dissolution by streams, groundwater or swamp water. Though they might appear massive when viewed from the side, most limestone hills are actually "riddled" with numerous caverns and cave systems. The interior of file limestone hill mass may also be pock- marked with deep hollows or solution sinkholes or dolines, locally called "wangs". These are visible from the ak or from aerial photographs, e.g. Wang Pisang of Gunung Rapat, Ipoh. The famous cave systems include the Batu Caves (K.L.), the Gua Tempurung and Sam Poh Tong in Ipoh, the Mulu and Niah

55 Caves in Sarawak, etc. Limestone hills are of all sizes and heights. They are actually the remnants of the limestone formation which has been degraded/dissolved, and the collapse of the limestone cliffs contributes to the reduction in the size of the limestone hills. In a previous survey of the limestone hills in the Kinta Valley, for example, some 40 limestone hills of various sizes have been recorded (Tan, 1988). While some limestone hills are "massive" and spatially extensive, e.g.G. Rapat, G. Tempuruing - G. Rajah massif, others appear as slender, needle-like limestone hill pinnacles, the notable example being the so-called Tambun Tower (Tan, 1998a). Intersecting or criss-crossing the limestone hills are various geologic structures or fractures such as joints and faults, and together with the intrinsic bedding planes of the limestone, these geologic structures control the stability of the cliffs, the formations and orientations of caves and cave systems and other dissolution features.

2.2 Rockfalls

56 Rockfalls and rockslides are major engineering geologic problems associated with limestone hills. The steep-subvertical and often overhanging limestone cliffs are potentially hazardous in terms of rock slope stability, and numerous major incidences of rockfalls have been investigated and documented by the Geological Survey Department in the past (e.g. Shu et al., 1981; Shu and Lai, 1980). In the survey of limestone hills in the Kinta Valley area, numerous minor occurrences of rockfalls and potential rockfall sites were also documented by me (Tan, 1988), in addition to the major ones previously documented by the Geosurvey. Besides structural control by joints, faults and bedding planes, other significant contributing factors to rockfalls include blasting operations in nearby quarries (vibrations and gas expansions into fracture planes).

2.3 Rockfall hazards zonation--the Tambun Hills An investigation into the potential rockfall hazards in the limestone hills of the Tambun area has been conducted recently (Tan, 1998b). The objectives of the study

57 were to identify and categorise the various limestone cliffs into various hazards zones, so as to aid in the planning of development and construction around these hitlls. The methodology adopted involved ranking the various cliff faces in terms of stability by considering both the geological structures and the solution features. A 3-zone classification scheme was used to denote stable/low hazard, moderately stable/moderate hazard, and unstable/high hazard zones, producing a hazard zonation

58 map for planning purposes. Some typical results of the study are shown in Table 1 and Fig. 1.Details can also be referred to in Tan (1998b). Among other things, one of the conclusions of the study was that the north-south-trending bedding planes of the limestone hills in the Tambun area are the major structural features controlling the morphology and the stability of the cliff faces. The so-called Tambun Tower is one good example.

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3 Limestone Bedrock

Limestone bedrock is perhaps even more important from the view-point of engineering constructions such as buildings and roads. The various bedrock features affect the construction works directly; they can also affect structures sited in limestone terrains in the future (long term effects) many years after the completion of the project.

3.1 Pinnacled bedrock surface The highly variable and pinnacled limestone bedrock surface and its associated problems are now well known and well documented (e.g. Tan and Batchelor, 1981; Ting, 1985; Chan, 1986; Tan, 1987). Exposures in old mine pits provide the best opportunity to observe the myriad forms of limestone pinnacles and troughs. The Bandar Sunway/Sunway Lagoon area exhibits some classic examples of limestone pinnacles, arches, etc.

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It is interesting to note the generally deep depths to limestone bedrock in the Kuala Lumpur area as compared to those in the Ipoh area, as revealed by a study of borehole data in the two regions (Fig.2, Tan, 1993). Depths to bedrock are around 20 m in the Ipoh area, as compared to 30-50 m in the K.L. region. Overhangs in the limestone

61 pinnacles would be harder to detect as it involves coring through the "nose" of the overhang. They are critical since the overhangs are underlain by soft sediments or soils. Mitchell (1985) provides a good example of the limestone pinnacle overhang at the Pan Pacific Hotel site in K.L.

3.2 Linear trenches in bedrock Long, linear trenches can sometimes be observed traversing limestone bedrock surfaces. Such trenches are the results of dissolution of limestone along major joints or faults. The interesting thing about the long, linear trenches is that they are often the sites of numerous sinkholes "popping up" along the trenches. To look at it in another way, the localities of several sinkholes in an area are often aligned along definite lines corresponding to the trends of major joints or faults dissecting the bedrock. Once again, exposures in old or operating mine pits or bedrock quarries provide the best opportunity to view these long, linear trenches. As the widths of the trenches are often limited, say, a couple of metres only, the sinkholes appearing along the trenches thus have small diameters of a couple of metres only -- a common observation with regard to the diameters of sinkholes. At the intersection of two trenches, however, the sinkholes that develop would be of larger diameter than usual, say 5-10 m.

3.3 Cavities in limestone bedrock Cavities in the limestone bedrock are of major concern to foundation engineers. They occur at various depths, i.e. in multi-levels, and are of various sizes/thicknesses. A survey of cavity sizes based on borehole data in the Ipoh area showed that they are mostly < 3 m in thickness (Table 2, Tan, 1988). Ting (1985) and Ting et al. (1993) also concluded that the most common cavity size is < 1m. In any case, occasional large cavities >3 m can still be encountered at a particular site. Thus, the detection and determination of the detailed configuration of the cavities and cavity system at a particular construction site are major efforts in a site investigation programme, in particular where high-rise buildings are being planned and constructed. Three dimensional physical models have been used to depict and decipher the intricate nature and extent of the cavities and the bedrock profile. A recent high-rise project in the K.L. area witnessed the tremendous efforts put in to detect the cavities in the limestone bedrock by employing > 100 boreholes on a close-grid boring pattern. Numerous cavities, some at multi-levels, were detected through those efforts. The number of boreholes for high-rise buildings underlain by limestone bedrock are in the order of 100's, e.g. the Petronas Twin Towers have ~400 deep boreholes (Tarique Azam, 1996). The formation of cavities in the limestone bedrock is related to the fluctuations of

62 the groundwater level. Cavities are developed mostly within the zone of groundwater level fluctuation, and it is reasonable to expect that deeper down below the zone of active groundwater fluctuation, cavity formation would be limited. The exposures at the Bandar Sunway Quarry (bedrock) seem to support such an idea that below a certain depth the limestone bedrock is massive (although jointed) without cavities or other solution features. Nearer the surface, large cavities, solution arches, pinnacles etc. are observed. For the K.L. region, it would be reasonable to postulate that below a certain Reduced Level (RiL), the limestone bedrock would not contain any cavities. The determination of this R.L. would require a meticulous compilation of all borehole data in limestone in the K.L. region--something that has not been attempted to date! Fig. 3 illustrates the development of cavities/caves in relation to limestone hills as suggested by Wilford (1964), which is perhaps also applicable to limestone bedrock.

63 3.4 Slumped zone One of the unique features of the limestone bedrock terrain is the occurrence of the so-called slumped zone or collapsed weak soil zone immediately above the limestone bedrock surface. The formation and identification of this slumped zone has been discussed by Tan and Ch'ng (1986). It has been encountered in numerous high-rise building sites in K.L. since the early 1980's (e.g. Chan and Hon, 1985; Ting, 1985), and also recently at the K.L.C.C. Petronas Twin Towers site (Tarique Azam, 1996). Recognition of the presence of the slumped zone is via its very low S.P.T. N values of ~0 as limestone bedrock surface is approached. Overlying the slumped zone can be much stiffer soils with N=30-50 or more, such as the residual soils of the Kenny Hill formation in the K.L. area. Fig. 4 shows some typical examples. In the K.L. area, the slumped zone often occurs close to the Kenny Hill formation--Limestone contact zones. Similar occurrences have been reported in other limestone areas, e.g. Ipoh (Tan, 1988) and Hong Kong (Pascal, 1987).

3.5 Sinkholes Sinkholes are the main crux of the problem in a limestone bedrock terrain. The formation or emergence of a sinkhole is usually very sudden and unpredictable, and as such, its consequences can be catastrophic. Thus, the reporting and documentation of sinkholes swallowing parts of a road, a house, etc. are too common indeed. While the inherent karstic features of the limestone bedrock (such as pinnacled profiles, cavities and linear trenches) all contribute or provide the geologic settings for the development of sinkholes, other man-made factors or activities such as dewatering of groundwater level by pumping, dewatering of deep excavations or basements and open-cast mining can trigger the formation or emergence of sinkholes. The documented cases of sinkholes in the Kinta and Klang valleys include the Bt. Merah/Menglembu area in Ipoh (Shu, 1982, 1986; Chow et al.,1996), Serdang Lama in K.L. (Shu, 1986) etc. The emergence of sinkholes in the Bt. Merah area continues till today (1999), as reported frequently in the local press. Similarly, in the recent construction of the K.L.C. C. Petronas Twin Towers project, several sinkholes also "popped up", including a major one that damaged a nearby bungalow. An interesting study on the occurrences of sinkholes (>100 in number) in the Bau area, Kuching Division in Sarawak was conducted in 1993-1994. Unfortunately, the results of the study cannot be presented here for the time being (CONFIDENTIAL!) --perhaps some time in the near future, hopefully?

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For the interested reader and also as a reminder that sinkholes occur world-wide in limestone areas, the following references provide interesting readings: Beck (1984), Beck and William (1987) and Beck (1989). For example, the famous Winter Park sinkhole in central Florida which developed between May 8-13, 1981, had an initial diameter of -106 m and a depth of 30 m! It destroyed various facilities and utilities, including a house, several businesses, several cars and a swimming pool and caused major problems for the city of Winter Park (Jammal, 1984). Fortunately, no personal injuries were involved. Various "schematic models" have been presented by different authors to explain

65 the formation of sinkholes. Some of these schematics are shown in Figs. 5 and 6, cited from Taylor et al. (1989) and Chen and Beck (1989) respectively.

4 Rock Mechanical Properties

Some rock mechanical properties based on testing of limestone rock cores in the laboratory are given in Table 3, cited from Tan and Ch'ng (1987). Additional data are given in Table 4, cited from Raj (1994).

5 Conclusions

This paper provides an overview of the engineering geology of limestone. The karstic features and engineering geologic problems associated with limestone, both limestone hills and bedrock, are now well known. For the case of the limestone bedrock, the need for adequate S.I. (including number of boreholes) cannot be over-emphasised to define and map out accurately the myriad forms of solution features inherent in the limestone bedrock.

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66 205-221. Shu, Y.K., 1982. A sinkhole occurrence in Bt. Merah New Village, Menglembu, Ipoh. Jabatan Penyiasatan Kajibumi Malaysia, Laporan E(F) 1/1982. Shu, Y.K., 1986. Investigations on land subsidence and sinkhole occurrence in the Klang Valley and Kinta Valley in Peninsular Malaysia. In: Proc. LANDPLAN H Conf., K.L., 15-28. Shu, Y.K., and Lai, K.H., 1980. Rockfall at Gunung Cheroh, Ipoh. Geological Survey Malaysia, Geological Papers, 3: 1-9. Shu, Y.K., Chow, W.S., and M. Zakaria, 1981. Rockfall danger related to limestone hills in the Kinta Valley, Perak. In: Annual Report, Geological Survey Malaysia, 1981, 184-197. Tan, B.K., 1987. Geology and urban development of Kuala Lumpur, Malaysia. In: Proc. LANDPLAN 1II Symposium, 15-20 Dec., 1986, Hongkong, 127-140. (published as Geological Society of Hongkong Bulletin No.3, Oct. 1987). Tan, B.K.,1988. Geologi kejuruteraan kawasan sekitaran Ipoh, Perak. (Engineering geology of the Ipoh area, Perak). Laporan Akhir Projek Penyelidikan No.7/86, Sept. 1988, UKM, 74 pp. Tan, B.K., 1990. Subsurface geology of Ipoh area, Perak, Malaysia. In: Proc. Conf. on "Karst Geology in Hongkong",5-7Jan. 1990, Hongkong, 155-166. (published as Geological Society of Hongkong Bulletin no. 4, 1990). Tan, B.K., 1993. Urban geology of Ipoh and Kuala Lumpur. In: Proc. Forum on Urban Geology and Geotechnical Engineering in Construction, IEM-GSM, July is~, 1993, Petaling Jaya, 1-1 to 1-25. Tan, B.K., 1998a. The Tambun Tower--a photographic presentation. Newsletter, Geological Society of Malaysia, 24(3): 133-134. Tan, B.K., 1998b. Engineering geological survey of limestone cliffs in the Tambun area, Perak, Malaysia. In: Proc. 8th IAEG Congress, Vancouver. Sept. 21-25, 1998, Vol. H, 1359-1366. Tan, B.K. and Batchelor, B., 1981. Foundation problems in limestone areas--a case study in Kuala Lumpur, Malaysia. In: Proc. Int. Syrup. On Weak Rocks, ISRM, 21-24 Sept., 1981,Tokyo, 1461-1463. Tarique Azam, 1996. Project KLCC: Geology, soils and foundations. Newsletter, Geol. Soc. Malaysia, .22 (2): 73-74. Ting, W.H., 1985. Foundation in limestone areas of Malaysia. In.Special Lecture, Proc. 8th S.E. Asian Geotech. Conf., Kuala Lumpur, Vol. 11, 124-136. Ting, W.H. (ed.), (undated). Engineering and geology in the Kuala Lumpur area. ESCAP publication. Ting, W.H., Lau L.Y., and Chen, M.S., 1993. Treatment of cavities for piled foundations. In: Proc. Forum on Urban Geology and Geotechnical Engineering in Construction, IEMGSM, July 1st, 1993, Petaling Jaya, 2-1 to 2-14.

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