Evaluasi kebutuhan tulangan pile cap terhadap variasi karakteristik tanah lempung: studi kasus proyek Nilam Central Plant

Abstract

The design of pile caps as transition elements between the upper structure load and the pile foundation system is highly dependent on the mechanical characteristics of the supporting soil. Pile caps play a critical role in pile foundation systems, functioning as structural elements that transfer loads from superstructure columns to a group of piles beneath. Soil variability, both vertically and laterally, poses a significant challenge in foundation design, particularly in pile group systems where load distribution relies on the collective behavior of the pile cap. In soft clay conditions, differences in subsoil stiffness often lead to eccentric load transfer due to uneven pile reactions, generating additional bending moments and increasing the structural reinforcement demand. This study aims to evaluate the influence of soil elastic modulus (E) variation on the flexural reinforcement requirements of pile caps, using eccentricity as a derived analytical parameter. The elastic modulus values ranged from 1.75 MPa to 45 MPa, based on the classification of in-situ soft clay conditions. A static analytical approach was employed to calculate load eccentricity, resulting bending moments, required steel area, and corresponding reinforcement weight. The results show that a decrease in E significantly amplifies eccentricity and bending moments, leading to up to a fourfold increase in reinforcement requirements under extremely soft soil conditions. At the lowest E value, the required reinforcement reached 1714.68 mm² with a weight of 258.80 kg, while at the highest E value, it dropped to only 146.97 mm² and 28.76 kg. These findings underscore the necessity of explicitly incorporating soil stiffness into pile cap design to ensure structural efficiency and to avoid overdesign.