Comparative Study of Piled Raft and Deep Foundation Systems for a 13-Storey Academic Building in Surabaya

Abstract

Foundation selection for a multistorey building on soft ground is governed not only by pile capacity, but also by settlement, load sharing, construction constraints, and cost. This paper compares the original deep-foundation design for an academic building in Surabaya with two piled-raft alternatives. The building has 13 main floors, one roof level, and an overall height of 56 m. The original system comprises 251 driven piles, 0.60 m in diameter and 30 m long, connected by 1.20 m thick pile caps. Each piled-raft alternative uses a 1.00 m thick raft and 269 piles of the same diameter, but with a reduced length of 20 m and a spacing of 2.40 m. The alternatives differ only in pile type: bored or driven. Borehole BH-01 gives an average N-SPT value of 4.42, and the site is treated as Site Class SE. ETABS 21 was used to obtain the superstructure reactions, the Meyerhof method was applied to estimate axial pile capacity, and PLAXIS 2D was used to study soil-foundation deformation. The total vertical reaction is 17,232.02 tons, while the maximum pile reaction under gravity and earthquake loading is 163.92 tons. Allowable capacities are 173.87 tons for the bored pile and 189.48 tons for the driven pile. PLAXIS settlements are 37.5 mm and 36.7 mm for the two piled rafts, compared with 243.2 mm for the raft without piles. Within the reported cost scope, the driven-pile raft has the lowest estimate at IDR 7.79 billion and provides the most favourable overall result, although vibration, construction quality, and field verification remain important in the final selection.