INTRODUCTION

During the past decade or so, development of the Kuala Lumpur metropolitan area has been very rapid, in particular with regards to the new surge of highrise buildings that have been erected and those that are currently under construction. This rapid increase in the number of highrise buildings is anticipated to continue with perhaps even greater ferocity into the near future.

As larger and taller buildings are being planned and constructed, site investigations for the foundations have naturally become more thorough. Of particular relevance to the Kuala Lumpur metropolitan area is the occurrence of large tracts of limestone bedrock underlying the city and its vicinities. Site investigations have time and again revealed the existence of numerous underground solution channels, cavities, sinkholes, etc. that are associated with the limestone bedrock, as is typical of advance karst development in tropical terranes.

This paper presents a case study of foundation problems in limestone in the Kuala Lumpur area.

GEOLOGIC SETTING

Kuala Lumpur is located within the Klang Valley which is underlain quite extensively by limestone bedrock. The bedrock is frequently exposed in gravel pump mines exploiting alluvial tin. Just north of the city, the limestone rises to form an isolated hill locally known as the Batu Caves. The Kuala Lumpur Limestone is underlain by the Hawthornden Schist, and overlain by the Kenny Hill formation (consisting of quartzite and phyllite). The Klang Valley is bounded on the east and west by granitic ranges. Alluvium overlies a large part of the valley and the 1imestone bedrock.

The stratigraphy of the Klang Valley area is summarised as follows:

The Kuala Lumpur Limestone is estimated to be 1830 metres thick, and consists of finely crystalline grey-cream, thick ly bedded, variably dolomitic and calcitic limestone(strictly marble since the rock has been metamorphosed and recrystallised). It is in the Kuala Lumpur Limestone that foundation problems, especially for highrise buildings, occur and thorough site investigations are necessary to delineate the location, distribution and orientation of the underground solution channels, cavities and sinkholes to avoid future foundation problems, as illustrated by the following example.

SITE INVESTIGATIONS FOR A PROPOSED HIGHHISE BUILDING

The Proposed highrise building is located in downtown Kuala Lumpur. From the geologic man, it was indicated that this site is on the limestone formation (Figure 1) and as such, a series of bore holes were put in. These boreholes were aimed at determining the depth to the bedrock(which is pinnacled and thus uneven in limestone), as well as the existence of cavities at various levels and their extensions or interconnections. As the project involves a superstructure over twenty storey high, it was essential to found the piles on sound, massive bedrock of sufficient thickness. The cavities were thus investigated thoroughly. Coring or dri11ing was terminated only if at least 4.5 metres of solid rock has been encountered. The spacing of the boreholes(located mainly at proposed pile locations) was of the order of several metres(2–3 metres).

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