PURPOSE: To reduce the size of cores and to decrease the number of piles so as to increase resistance to side pressure by placing lines of hollow soil cement piles on the outside of a line of core-containing soil cement piles, and driving a well point into the ground between both lines of piles for pumping up underground water.

CONSTITUTION: In a portion of a small excavation depth surrounding a low- water-pressure area A, a line of normal soil cement piles (a) is provided while steel cores (b) of H-section are inserted into every one soil cement pile (a). Double lines of soil cement piles are provided on the outer periphery of a high- water-pressure area B and up to a position a predetermined distance into the area A from both ends of the area B; i.e., the lines 2 of hollow soil cement piles are placed at a predetermined distance D to the outside of the line of core-containing soil cement piles obtained by insertion of the steel cores (b) of H-section into the soil cement piles (a). A well point 30 is driven to a predetermined depth into the ground between both lines 1, 2 of piles to pump up underground water.