the method of converting clayey or silty soil into stable and solid underground columns or piles suitable for carrying a building structure , comprises first the drilling of bores of a diameter considerably smaller than the external diameter of the column or pile to be created , to a predetermined depth , and secondly directing a focused laser beam gradually across the entire surface of each bore by mechanical and optical means , in such a manner that each point of the bore surface is irradiated and heated at an intensity sufficient for converting the soil surrounding the bore into a solid permanent mass of a predetermined thickness measured from the bore surface , which mass retains its strength and is resistant to moisture and temperature .