PENGARUH JARAK DAN POLA PREFABRICATED VERTICAL DRAIN (PVD) PADA PERBAIKAN TANAH LEMPUNG LUNAK = EFFECT OF DISTANCE AND PATTERN OF PREFABRICATED VERTICAL DRAIN FOR IMPROVEMENT OF SOFT CLAY SOIL - Aspara, Wimpie Agoeng Noegroho (BPPT, 2016)