Abstract Description: The deep foundations industry provides a variety of cutoff and barrier wall installation techniques. Each technique has its specific features and application limits. The paper presents four case histories demonstrating how techniques can be tailored and/or combined to create the best value for dam and levee owners.
The Herbert Hoover Dike Rehabilitation project required the installation of a cutoff wall with depths up to 65 feet into an existing levee. The sandy embankment was partially underlain by an organic layer and interbedded layers of Florida limestone, sandstone/cemented sands, sands, silts and clays. This allowed the owner to use a performance-based specification allowing multiple cutoff wall systems. BAUER Foundation Corp. (BFC) as one of the contractors selected a combination of pre-treatment and cutter soil mixing, while applying two different pre-treatments based on ground conditions.
A cutoff wall with a depth of up to 142 feet and minimum 2 feet of bedrock embedment was needed for the East St. Louis Deep Cutoff Wall project, another levee remediation. Based on experience with similar conditions on preceding close-by cutoff wall projects, the owner specified a panel wall with self-hardening slurry backfill. Thus, main task for the contractor was to optimize equipment, tooling, panel layout and mix design of the backfill to provide the best value while maintaining excavation safety and meeting quality requirements.
The Rosshaupten Dam rehabilitation project included the installation of a plastic concrete cutoff wall up to 230 feet deep. The cutoff wall extents through the dam embankment up to 138 feet into bedrock. As the reservoir had to remain impounded and out of concern for slurry losses, the wall was installed as diaphragm wall executed with single-bite panels. To improve the condition of embankment soils and bedrock damaged by seepage and to prevent slurry losses, the contractor BAUER Spezialtiefbau GmbH chose a pretreatment with tube a manchette (TAM) and rock grouting, respectively.
At the Center Hill Dam Rehabilitation project, the owner specified an up to 300 feet deep barrier wall as element wall with concrete backfill. While both a secant and panel (or optionally a hybrid approach) had to be tested on site, contractor BFC elected to install the production barrier wall using a panel-only approach. The contractor furthermore chose to install a mandatory encasement wall, which represented a pre-treatment of the clay embankment and soil rock interface, in shallow areas using large-diameter secants and in deeper areas as panel-only wall.
Learning Objectives:
Get to know several cutoff and barrier wall systems.
Learn how ground conditions, depth and other factors impact the selection of the wall systems.
Learn how techniques can be tailored and/or combined to the project needs.
