Highway Embankment on Soft Soils Case Study and Lessons Learned

This case study describes failure of an interstate connecting-ramp embankment during construction and investigates performance of the prefabricated vertical drains (PVDs) installed to accelerate consolidation of the weak embankment foundation soils. The weak, fine-grained foundation soil experienced less drainage, and thus less consolidation and strength gain, than expected via the PVDs because of an overestimate of the design horizontal coefficient of consolidation. The inverse analyses show the failure was caused by lower than expected shear strength of the foundation soils and an over estimate of the compacted embankment shear strength. As a result, recommendations to estimate horizontal consolidation properties for PVD design and embankment shear strength parameters or future projects are presented.