9.5kCY MSE wall backfill

Baltimore, Maryland

The Job

As part of increasing the capacity of Interstate 95 north of Baltimore, Maryland, Express Toll Lanes are being added in the center of the existing roadway.

The Challenge

A 96″ diameter PCCP raw water supply line runs parallel to Interstate 95 along most of the project length. Originally, there was quite a bit of room between the roadway and the water line, however as the interstate has widened, it’s gotten closer and closer to the PCCP water line. As part of this project, there are extensive ramp and embankment sections which are immediately adjacent to the waterline, which is not in a condition to see any increase in loading.

To address this, extensive use of lightweight backfill is required to increase elevations while not increasing loads on the fragile, and very critical, pipe.

The Solution

In order to facilitate construction of a roughly 850LF MSE wall running parallel to the waterline, lightweight backfill was required. Originally designed for backfilling with Lightweight Expanded Shale Aggregate (LESA), CJGeo worked with the contractor to develop a hybrid backfill material of 30lb/cuft cellular concrete and traditional weight 57 stone. The relative depths of the two materials was selected so that the average density of the mass was equal to that of an entirely LESA backfill, which resulted in only needing roughly 2/3 the volume of lightweight backfill material.

Lightweight backfill is rarely less expensive as soil or traditional aggregates. However, by leveraging the very low unit weight of cellular concrete, a blended solution was possible that saved significant amounts of money.