‘To begin with the Ground Levelling Party comprised about 800 men, but it steadily expanded until every fit man was included, together with many who were far from fit. Survivors of the Thailand railway were numbered among them. The work consisted of nothing more or less than shifting hill to swamp.
Their bodies almost totally unprotected from the burning heat of the sun and the glare of the pulverised flat of the airstrip, the men toiled at the hillsides, excavating the soil and rock and loading it into hand trucks. These were pushed along the network of narrow-gauge railway lines to the edge of the swamp where the spoil was tipped. When one considers the grossly undernourished condition of the men, most of whom weighed less than two-thirds of their normal weight, and the fact that they were working for between ten and twelve hours a day in gruelling heat, it is truly remarkable what they achieved.’
Source: http://ukmamsoba.org/changi.htm