Alluvial plain of the coast of Kum river tail were found as being mostly consisted of weak foundation. The settlement of the ground, density and change of moisture content which were formed by the load due the construction of earth works were disclossed by the field investigations and laboratory tests. The results are as follow, 1) Banking materials are SM and soft soil stratum is CL. 2) Field moisture content; Wf=19-1.37c c; percentage of clay (less than 0.005mm) 3) optimum water content and maximum density of banking materials; rt=2.15$mid$0.0165W(12%<W>24%) 4) Density and moisture coutent of banking materials; rt=2.146-0.0095W (8%<W>50%) 5) Density and moisture content of weak foundation; rt=2.06-0. 007W After construction (20%<W>50%) Befor construction (40%<W>60%) 6) Load and settlement of weak foundation; Everage settlement ratio; 12% of actual load p Maximum settlement ratio; 19% of actual load p Minimum settlement ratio: 5% of actual load p 7) Relation of cohesion and unconfined compression test value; c=1/2qu (qu<0.5kg/$ extrm{cm}^2$) c=1/3qu (qu<0.5kg/$ extrm{cm}^2$)