PURPOSE: To efficiently perform a sea bed excavation and a filling back operation without receiving any maritime influence by a method wherein while an excavation operating machine connected with a power line is traveled by means of a signal from a land base, a trench is excavated, and after an electric cable is laid in the trench, it is filled back with the aforementioned excavated sediment and along with this, a mortar is fed from the land.

CONSTITUTION: While an excavation operating machine 3 is traveled on the sea bottom 1 by means of a signal from a control-monitoring-operating board on a land base, an excavated trench 30 having a given depth and width is excavated. And in conjunction with this excavation, an electric cable 26 is laid in the groove 30 and along with this, the excavated sediment 45 is carried to the rear side through a sediment carrying device 33 and a belt conveyor 35 and at the rear side of the main body 13, the trench 30 is filled back. And further, the sediment 45 filled back is mixed with a mortar which is fed from the base through a mortar pipe 11 and a consolidation is performed. Next thereto, after the machine a reaches a destination, the power line 12 is disconnected from the operating machine 3 and after the construction work is over, it is wound up by a power line which in the base.