THE ORIGIN AND PROPERTIES OF BOULDERY CLAY IN SINGAPORE

This paper discusses distribution, nature, behaviour, strength and properties of Bouldery Clay in Singapore. The Bouldery Clay in this location is a stiff to hard landslide material with randomly distributed sandstone boulders. The soil matrix consists of silty and sandy clay. The boulders vary in shape and size as well as the degree of weathering. The Bouldery Clay can be as deep as 120 m below the present ground surface. Bouldery Clay is mainly found in and around the central business district of Singapore and many of the high-rise buildings have been constructed on or in this formation. The Bouldery Clay is postulated to have originated from a series of landslides along faults. Some of the faults could be observed on a map from 1819. The strength of the soil matrix has been investigated by standard penetration tests, pressuremeter tests and plate load tests. The average undrained shear strength is 1.0 MPa. The average modulus of elasticity of this material is 280 MPa as determined from the unloading-reloading curves from the plate load tests conducted in the horizontal direction.