What is it about?
Soft clay continues to settle slowly even after construction is completed. This long-term movement, known as creep settlement, can damage roads, buildings, utilities, and other infrastructure. A common method for improving soft soil is vacuum preloading. In this method, vacuum pressure and vertical drains are used to compress the soil before the permanent structure or operational load is applied. Most of the settlement therefore occurs during ground improvement rather than after construction. This paper investigates how much preload is needed to control the remaining settlement, especially when creep is considered.
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Why is it important?
Indonesian design guidance commonly uses a preloading load equal to 1.20 times the operational load. However, the study found that this value may not be sufficient to keep long-term settlement below the commonly adopted limit of 20 mm per year, particularly for soft soils that experience significant creep. The results suggest that engineers should consider using a higher load ratio, generally between 1.30 and 1.50, depending on the soil conditions.
Perspectives
Soft soils may continue to settle for many years after construction because of creep. Vacuum preloading can reduce this problem by compressing the soil before the permanent load is applied. However, this study found that the commonly used preload-to-operational-load ratio of 1.20 may not always be sufficient. A ratio of approximately 1.30–1.50 was generally required to limit annual post-construction settlement to 20 mm when creep was considered. The study also introduces a new load ratio coefficient that combines soil properties, soft-soil thickness, vertical-drain spacing, drainage pattern, and loading conditions to estimate long-term settlement. The publication highlights that achieving a high degree of primary consolidation alone does not necessarily guarantee acceptable long-term performance. From a practical perspective, the findings may help engineers design more reliable ground-improvement systems for roads, reclamation areas, industrial developments, and other infrastructure built over soft clay. The proposed method should be used together with site investigation, field monitoring, and project-specific calibration, particularly when applied outside the soil conditions examined in this study.
Aswin Lim
Universitas Katolik Parahyangan
Read the Original
This page is a summary of: Investigation of creep behavior of soft soil during and after vacuum preloading, Rock and Soil Mechanics, May 2026, Tsinghua University Press,
DOI: 10.26599/rsm.2025.00239.
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