Long-term settlement analysis of soft ground improved with the preloading method and centrifugal model tests for validation

¹ Civil Engineering Department, Toyo Construction Co., Ltd., Tokyo, Japan
² Division of Civil Engineering, Faculty of Engineering, Hokkaido University, Sapporo, Japan

^* Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Abstract

Preloading is widely used to reduce residual settlement in soft clays, but practical procedures for predicting long-term deformation after preload removal and reloading remain limited. This paper proposes a practical method based on the isotache concept, in which the consolidation yield pressure is uniquely related to the visco-plastic strain rate. The formulation for loading is extended to unloading and reloading so that complex load histories are treated within a single framework. Primary consolidation is solved using an axisymmetric consolidation equation, while time-dependent deformation is evaluated with an isotache constitutive model. The two calculations are updated sequentially in an uncoupled manner, avoiding a fully coupled implementation while maintaining computational efficiency. Centrifuge model tests were conducted in a cylindrical container with well-defined drainage and stress boundaries, and post-unloading behavior was monitored for over 48 h. The effects of removal timing (degree of consolidation), vertical drains, and initial stress level were examined parametrically. The tests showed elastic rebound and negative excess pore water pressure at unloading, followed by continued swelling or time-dependent resettlement after dissipation. The analysis qualitatively reproduced these responses, demonstrating applicability to moderate unloading conditions (OCR ≤ 1.4).