Caisson and Well Foundation

The hand-dug caisson is technically viable as long as the soil can be left free-standing for the lift height during excavation and the rate of water inflow is low. For the majority of residual soils in Malaysia, this criterion can be satisfied. Application of hand dug caissons can be found mainly on hill slopes and congested sites where conventional piling rigs have accessibility problems. 

The hand-dug caisson thrives in an environment where conventional piling equipment struggles e.g. hill sites and congested sites. Being of relatively large diameter (to be able to fit a worker therein), the caisson has potentially large structural capacity - typically above 500 ton. Where the rockhead is near the ground surface, say less than 20 m, the caisson can be socketted into rock to derive full structural capacity. Caisson construction works well on hill slopes and in residual soil 

In Malaysia, the method has been used in a variety of projects in many different soil types. It has been found to be particularly useful under the following circumstances - 

Caisson construction requires a headroom clearance of less than 3 m (for hfting the bucket). It is generally a quiet process except where breaking through rock. Hence, where foundations are required in areas of low headroom (e.g. under an existing bridge) or where noise restrictions exist (e.g. hospital), hand-dug caissons can be considered. 

The hand-dug caisson has been used in very difficult ground conditions including in cavernous limestone. For example, the 40 storey Menara Kek Seng (Jalan Bukit Bintang, Kuala Lumpur) was founded on 4 m diameter caissons socketted into limestone. The integrity of the founding rock was probed within the caisson and cavity treatment instituted (Yee Yap 1998). 

---