topcon电池:Environmental Geology of Limestone in Malaysia5

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.
60
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.