抄録
The Reclaimed area of the Urayasu district in Chiba Prefecture is composed of an alluvial deposit of more than 40 meters depth. This alluvial deposit consists of an upper sand layer 15 meters thick (N Value 0〜15) and a lower silty clay with depth of 25 meters or more (N Value 0〜5). Successive ground settlements measuring 7〜11cm per year have occurred due to compressive consolidation. Through the alluvium, four steel piles of φ600×14 were driven into a diluvial stratum. Then, for the past 2 years, the axial forces due to the surrounding soil settlement have been measured. The results are summarized as follows : (1) Maximum axial force is 320 ton in a 50 meters pile, and 200 ton in a 40 meters pile. (2) These axial forces result from the negative frictions caused by consolidation of the lower silty clay. Friction stress τ of the lower silty clay is equivalent to 0.3δ^^-_v, which is well known. (3) Friction stress τ of the upper sand is unexpectedly smaller than that of AIJ recommendation (τ=3+N/5), and evaluated as τ=N/10 at most.
