PURPOSE: To construct monolithic continuous cement trench walls and sills by utilizing the same soil material as an excavated material as aggregate for impermeability.

CONSTITUTION: The method comprises the following steps in a continuous cycle. a) excavating a trench or channel 13 by means of a cutter 14 fitted to a moving excavating machine 10; b) extracting the soil excavated in the trench 13; c) transferring the extracted soil into a conveyor belt 21 interposed between the cutter 14 and a container 22, 34 provided with disgregating members 23, 35 for crumbling the extracted soil and mixing it with a consolidating agent so as to form with the extracted and crumbled soil a plastic and homogeneous mix; d) casing continuously the mix from said container 22 to the excavated trench or channel 13.