Optimizing compaction of low-grade embankment soils with non-plastic fines under cyclic traffic loading and seasonal moisture variations

Abstract

In many developing countries in Asia, the scarcity of high-quality natural sands poses a major challenge to the cost-effective construction of road and railway embankments. As a result, there is an increasing need to utilize locally available sandy soils with higher fines contents. These embankments are typically compacted under unsaturated conditions and subsequently subjected to vehicle-induced cyclic loading and saturation fluctuations over time due to seasonal rainfall. However, the long-term performance of such materials under these combined effects remains insufficiently understood.

The cyclic and post-cyclic behavior of compacted sandy soils with varying fines contents was investigated in this study to better understand the soils’ mechanical response and suitability for embankment applications, specifically when subjected to seasonal rainfall and long-term cyclic loading. A comprehensive testing program was conducted, including suction-controlled drained cyclic triaxial tests followed by post-cyclic monotonic loading under both unsaturated and soaked conditions. The results showed that, under unsaturated conditions, increasing compaction significantly reduces the accumulated axial strain while enhancing post-cyclic strength and stiffness. Lower saturation levels lead to higher initial suction, which improves stiffness and post-cyclic strength, especially in soils with higher fines. While soils with higher fines contents display increased post-cyclic strength due to improved suction and interparticle friction, they also experience greater axial strain during cyclic loading, particularly when compacted at low saturation levels due to reduced skeletal stability.

Soaking leads to a notable reduction in post-cyclic strength, especially in soils initially compacted at low saturation levels with high fines contents, despite having higher initial stiffness and suction. This highlights the critical role of suction and fabric stability in maintaining a long-term soil performance. These findings provide practical guidance for optimizing compaction and moisture control in the field, and for supporting the sustainable use of locally available fine-grained soils for embankment construction under cyclic loading and environmental changes.