Underwater Caisson Repair at Naval Shipyard

Problem

At Newport News Shipbuilding, engineers hoped to find a modern solution for a problem that took over one hundred years to develop. When the facility was constructed in the 1890’s, wooden piles were driven to support structural columns that framed the mammoth facility. Over the intervening years the wooden piles began to deteriorate, leading to a loss of column bearing capacity and reduced lateral strength. As the facility continues to serve as a critical piece of national security infrastructure, a thoughtful, measured solution needed to be found to stabilize the structural columns and ensure many more years of uninterrupted shipbuilding activities.

Analysis

Engineers conducted a full analysis of the situation to identify all the factors that contributed to the problem with the structural columns at the shipyard. It was determined that the loss of column stability was the result of a fluctuating water table, aged and untreated piles that had deteriorated over time, and environmental contamination. All these factors led to the evident loss of bearing and lateral support and were the main drivers of the settlement taking place beneath the structural columns.

Solution

Because all repair options at the facility were subject to strict environmental and space constraints, a list of choices was prepared for the shipyard. Engineers discussed the use of jet grouting, helical anchors, cementitious compaction grouting, and the URETEK Deep Injection® (UDI) process. UDI was selected because among the available options it involved no impact on shipyard operations, and because URETEK’s 486 Star® polymer was completely resistant to environmental contaminants. A demonstration project by URETEK helped make the case for UDI, and the significant cost advantage of UDI over the alternative repair options sealed the deal.

Result

URETEK crews mobilized to the site and began the project by conducting extensive Dynamic Cone Penetrometer (DCP) testing to gather soil data and formulate a specific injection plan. With a targeted plan in place, workers installed injection probes and then began a series of static and dynamic load injections around the affected columns. Following UDI, additional DCP testing confirmed that the soils in proximity to the stability columns had been stabilized, and spot excavation and inspection at a test column confirmed that the polymer was widely dispersed as intended. The engineers at Newport News Shipbuilding were satisfied with the results and pleased with URETEK’s approach to the project.

URETEK Deep Injection® (UDI)

Widely referenced throughout our industry, UDI involves the injection of structural polymer into base and subgrade soils to increase the load bearing capacity. This is achieved by injecting the polymer through small holes drilled directly through the pavement structure to depths determined by site-specific analysis. Our URETEK 486 Star® material flows easily into voids and weak zones within the soil mass below. Through a controlled chemical reaction, the expanding polymer compacts surrounding soils and applies a controlled pressure on targeted areas of the affected pavement above. If needed, a multi-injection design plan is utilized to gently return the pavement to its original grade. The composite material quickly cures into a strong, dimensionally stable, and water-resistant geo-material, providing years of reliable service.

URETEK 486 Star®

URETEK 486 Star® polymer is a two-component, high-density, expanding thermoset polyurethane system. It was developed to be the ideal solution for under-sealing, void filling, lifting of settled pavement, stabilization and stiffening of weak soils, and for encapsulating and sealing buried infrastructure. URETEK 486 Star® is environmentally inert, non-toxic, and resists underground water erosion or weakening due to its industry-leading hydrophobic properties.

Shipyard Repair
Shipyard Repair
URETEK crew injected polymer at the base of a structural column
Shipyard Excavation
Excavation near a test column showed good dispersion of polymer