RECLAMATION OF MINED-OUT PONDS IN THE KINTA VALLEY FOR HOUSING DEVELOPMENT

There were about 70,000 hectares of land in the Kinta Valley under mining leases in the early 1990s just before the slump in the tin mining industry. Most of these land were mined either by the open cast palong or dredging method and what is left from these mining activities are dumps of loose, unconsolidated tailing sand, some with lenses of slurry slime and more than a thousand abandoned ponds. These ponds vary in sizes from as small as a few tens of square metres to as large as about 45 hectares.
In recent years, as a result of planned development in the state, a large number of these ponds had been reclaimed for the construction of housing estates, industrial parks and related infrastructures. Notable examples are the development of the housing estates and industrial parks in the Pengkalan-Lahat and Gopeng-Kampar areas. The conventional methods of reclamation which include (a) the lowering of water level and emplacement of fill material, (b) the displacement method and (c) containment method, are widely practiced. However, such reclaimed ground often entrap soft slime lenses and with the passing of time, show differential settlements, resulting in cracks in the buildings and often leading to the weakening of the structures. In addition, the latter two methods are not environment-friendly, as slurry slime are removed from the ponds and are deposited into some nearby ponds.
Researches carried out showed that an environment-friendly method of reclamation involves the flocculation of the slurry slime with either Natural Organic Polymer-CaCl2 or Polyvinyl Acetate. The flocculated slime is then admixed with soil. The admixing of flocculated slime with soil results in a marked increase in the solids concentration and bearing strength and a decrease in the voids ratio and moisture content.
This technique is economically viable if the depth of the slurry slime to be flocculated is less than 5 metres for ponds with water depths of up to 5 metres. For ponds of 7 to 11 metres and 15 metres, the thickness of the slime has to be less than 3 metres and 2 metres respectively.