November 24, 2020

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David Espinoza and Lucas de Melo Coauthored an Article About Reinforced Soil Structures Over Soft Foundations for the International Journal of Geoengineering Case Histories

David Espinoza, Ph.D., P.E., (Maryland) and Lucas de Melo, Ph.D., P.E., (Maryland) coauthored an article entitled “Application of Hybrid Drained-Undrained Model for Analyzing the Stability of Reinforced Soil Structures Over Soft Foundations with Prefabricated Vertical Drains” for publication in the International Journal of Geoengineering Case Histories on November 19, 2020.

Their coauthors were Chunling Li, Soil and Land Use Technology and Ranjiv Gupta, Freeport-McMoRan.

David Espinoza is a Senior Principal Geoenvironmental Engineer based in Maryland focused on foundation design over soft soils, design of containment facilities (e.g., municipal solid waste, mining tailings, coal-combustion residuals), closure of containment facilities (e.g., tailing storage facilities) and more recently, financial evaluation of infrastructure investments taking into consideration physical risks such as climate change.

Lucas de Melo is a Senior Principal Engineer based in Maryland with more than 20 years of experience in dams and mining related projects, geotechnical design and field studies, risk quantification, hazardous materials remediation; and in the design of coal ash disposal sites, solid waste management facilities, and capping systems for site closures.

The International Journal of Geoengineering Case Histories is an official journal of the International Society for Soil Mechanics and Geotechnical Engineering (ISSMGE), the premier scientific organization for geotechnical engineering worldwide. The Case Histories Journal covers the broad area of practice in geotechnical engineering (soils and rocks), including geotechnical earthquake engineering, environmental geotechnics and engineering geology, and energy geo-construction.

The ISSMGE is the pre-eminent professional body representing the interests and activities of Engineers, Academics and Contractors all over the world that actively participate in geotechnical engineering.


Prefabricated Vertical Drains (PVDs) are typically used for embankment construction over saturated soft cohesive soil deposits to accelerate consolidation and reduce construction time in the field. PVDs accelerate consolidation of thick soil deposits by reducing the drainage path from tens of meters to 1-2 meters depending on PVD spacing in the field. Current design methodologies typically consider the increase of shear strength due to accelerated consolidation, but still use undrained shear strength for the entire cohesive soil layer even after PVD’s are installed. However, for cases in which PVDs are closely spaced, which allows excess pore water pressure to dissipate relatively fast, the assumption of undrained conditions for design may be overly conservative and, in some cases, this assumption may render an embankment construction unfeasible, unless additional ground improvement techniques are used to significantly enhance the foundation strength. This paper presents a Hybrid Drained-Undrained (HDU) model for construction of embankments over soft soils that accounts for the improved soil drainage conditions after installation of PVDs in the assessment of the shear strength used for design. A field case study is presented where the HDU methodology was used for the design of a 2.4-km long MSE berm constructed over a PVD-improved soft soil site, allowing for significant cost savings. The HDU approach was implemented using limit equilibrium models during the design stages to analyze the global stability of the MSE berm at different stages. Finite element models calibrated using field monitoring data collected during construction showed factors of safety comparable with that calculated using the HDU approach, which further supports the suitability of the HDU approach for PVD design.

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