PURPOSE: To perform easy and reliable civil engineerign works at a very soft ground and in water, by a method wherein right and left wheel devices are coupled to a car body, and an elevation control mechanism, which elevates the wheel device, is installed.

CONSTITUTION: Wheel devices 5, which are self-running and of watertight structure, and disposed on both side of a car body 1. A civil engineering machine frame 11 is mounted to a truck frame 6 of the device 5 by means of a trunnion 13, and a civil engineering machine B is mounted to the frame 11 by means of a sliding frame 19, a civil engineering plate 20, a retainer member 21, and a civil engineering mechanism B. First and second links 25 and 28 coupled together by means of a pin 31 are mounted to the frame 6 and the car body 1, a rod 34 of an elevating cylinder 33 is coupled to an intermediate bracket 24 of the second link 28 by means of a pin member 35 to form an elevation control mechanism A. At a very soft ground on land, the bottom of the car body 1 as well as the devices 5 is earthed to perform works, and when it is used in water, the devices 5 are lowered and brought into contact with the bottom of the sea to start works.