Using ESCS for Soil Amendment in Ports and Waterfront Construction

As a material, lightweight aggregates, like expanded shale, clay and slate (ESCS), can help solve engineering challenges in projects ranging from bridge construction to high rise design and from stormwater management to road preservation. ESCS aggregates also play a unique role in geotechnical engineering—especially for waterfront construction.

These types of projects often require soil stabilization efforts to ensure a site can support additional loads. Because ESCS has a predictably high internal friction angle, can reduce dead loads and lateral forces by half and is water insoluble and chemically inert, it can provide a cost-effective solution for waterfront construction. 

But what physical properties come together to enable ESCS to provide such benefits? And how have geotechnical engineers used this material in past projects?

How ESCS Improves Soil Mechanics

To understand how ESCS supports geotechnical engineering, it is important to know how this material is produced. Raw shale, clay or slates are fired in a rotary kiln at temperatures over 1000° C. During this process, air pockets form. These voids remain as the aggregates vitrify and cool. Once cooled, the ESCS aggregates are graded into highly regulated particle size.

The results of this process provide a few benefits to geotechnical applications. First, the network of voids and particle angularity help ESCS aggregates achieve internal friction values (phi angle) of at least 40 degrees—an quantifiable increase from ordinary geotechnical fills. This, in conjunction with their regulated particle size, can provide soil stabilization projects with a high degree of control.

Secondly, the voids throughout ESCS aggregates reduce their density. This translates to a geotechnical fill that is approximately half the weight of traditional fills. This directly supports waterfront construction by reducing the fill’s dead load and amount of lateral force it exerts on retaining structures and foundation systems. It indirectly supports these projects by reducing the number of shipments of material a project requires, thereby streamlining jobsite planning and mitigating shipping costs.

Using ESCS For Soil Stabilization

Geotechnical engineers have recognized ESCS aggregates as a viable means to support project sites with soft soils. For example, in order to turn what had been an industrial section of downtown Boston into a luxury resort, the project engineers needed to plan extensive soil amendments.

The project team removed 840,000 tons of contaminated soil and dredged 41,000 tons of contaminated sediment. Along the waterfront, they reclaimed a tidal area using sheet pile with lightweight fill behind it. These soil stabilization efforts support the roadways and gardens areas along the project’s harborwalk.

Because of the soft soils along the river, a fill that would minimize loading was needed. The project’s designers chose expanded shale fill with an in place compacted density of half that of ordinary fills and an angle of internal friction of over 40 degrees for this application. As such, ESCS aggregate provided several geotechnical engineering solutions simultaneously.

Creating New Land For Waterfront Construction

Lightweight aggregate provides solutions beyond soil amendment. ESCS can be a vital component in creating land to expand port space. In these projects, ESCS’s physical properties provide a stable and lightweight geotechnical backfill. It also reduces demand on adjacent systems, like sheet pile and other retaining wall systems. On the one hand, this makes achieving port stability easier. On the other, it can reduce the overall cost of land expansion projects. When the structural demand is lowered by using ESCS, the value provided is realized through lower structural component costs such as potentially reducing the gauge and length of combi-wall pipe-pile systems used to create wharfs.

The geotechnical engineering teams behind the cruise terminal expansion at Port Canaveral used ESCS lightweight aggregate to minimize lateral pressure against sheet pile structures. This allowed designers to reduce the gauge and length of the sheet piles resulting in a significant cost savings. In addition, the material does not require special handling or compaction efforts to reduce labor costs. And because it was lightweight, it supported cost-effective shipment. All of these benefits allowed the project to be completed efficiently and within budget.

Solving Geotechnical Engineering Challenges One Port at a Time

ESCS offers several design advantages beyond its reduced density and predictably high internal friction angle. The material is chemically inert, water insoluble, free draining and has a high strength and durability. As such it can support soil amendment in waterside construction and soil stabilization wherever soft soils are a concern.