congaree slide

Rail Bridge Pier Stabilization

Columbia, SC

congaree featured

The Job

This project was a capital repair to a bridge pier for a Class I railroad serving the Port of Charleston, SC.

The Challenge

The Congaree River south east of Columbia, South Carolina frequently sees high flow events, inundating the surrounding low country. At the transition from timber trestle to a bridge, the first bridge pier was originally constructed of stone, bearing on a timber pile supported timber mat. Over time, the river channel migrated and began to expose the timber substructure and scour below the pier.

The nearest road was more than four miles away through impassible swamp, so all work had to be performed from the river, and all material had to be pumped across the bridge, a distance of approximately 600 feet. Due to the compressive nature of the underlying materials, any backfill material needed to be as light as possible, but due to the high likelihood of flooding, couldn’t contribute significant potential uplift.

The Solution

To address the scour, minimize additional load to the underlying soils, and ensure long term stability of the structure, a third party consultant designed a two tier sheet pile jacket for the structure, and specified the backfill material as 65lb/cuft cellular concrete for the lower segment, and approximately 45lb/cuft cellular concrete for the upper segment.

CJGeo designed mixes which would meet these requirements, be pumpable 600LF, tolerate the high vibration environment from the more than 12 trains per day, and facilitate a short installation timeframe.

After the general contractor installed the first level of sheet piling and dewatered the area, CJGeo placed approximately 150CY of 65lb/cuft material. The second, smaller diameter, ring of steel was installed, and CJGeo then filled the annular space between it and the necked down pier with 45lb/cuft material.

The cellular concrete was installed over a period of four days onsite.