Comparative Consolidation Behaviour and Statistical Characterization of Settlement Variability of Soft Soils from Three Selected Sites in Lagos, Nigeria

Abstract

Accurate prediction of consolidation settlement is fundamental to the serviceability design of foundations on soft cohesive soils. Although numerous studies have reported consolidation characteristics of soft soils, most investigations have focused on deterministic evaluation of individual consolidation parameters, with limited attention to statistical characterization of settlement variability from laboratory measurements. This study presents a comparative investigation of consolidation behaviour and settlement variability of soft cohesive soils obtained from Palm Grove Estate, GRA Ikeja, and Shonibare Estate in Lagos, Nigeria. One-dimensional consolidation tests were conducted in accordance with ASTM D2435/D2435M using undisturbed cohesive soil samples. The coefficient of consolidation (Cv), coefficient of volume compressibility (mv), void ratio (e), permeability (k), and primary consolidation settlement were determined under vertical loading from 50–100 to 400–800 kN/m². Settlement variability was characterized using the arithmetic mean, standard deviation, and coefficient of variation (COV) from repeated laboratory measurements. Results showed that mv decreased by approximately 60–63%, while Cv reduced by 32–41% with increasing effective stress. Permeability decreased by approximately 70–75%, with reductions in void ratio, confirming continuous densification of the soil skeleton during consolidation. Despite these reductions, primary consolidation settlement increased systematically with applied loading, attaining maximum average values of 84 mm, 74 mm, 136 mm, and 61 mm for Palm Grove Estate, GRA Ikeja (1.5 m), GRA Ikeja (3.0 m), and Shonibare Estate, respectively. The calculated COV ranged from 7.11% to 19.67%, indicating low to moderate variability and good repeatability of the laboratory measurements. The study demonstrates that settlement behaviour is governed by soil compressibility, effective stress increment, and the thickness adopted for settlement analysis rather than compressibility alone. Integrating deterministic consolidation analysis with statistical characterization of settlement variability provides clearer interpretation of laboratory settlement behaviour and offers a practical framework for improving confidence in serviceability-based foundation design for soft cohesive soils in urbanizing environments.