DRAINAGE DESIGN CASE STUDY:

At the Naval Base Kitsap in Bangor, Washington, the Tang Road Repair Project was launched to enhance drainage and structural performance behind steel sheet pile retaining walls. The scope included the installation of 73 maintainable weep hole assemblies from JET Filter System, designed to relieve hydrostatic pressure and extend the service life of the roadway and shoreline stabilization system.

This project, filed under WCRO-2023-00351-4, forms part of a larger infrastructure initiative to protect critical base access roads and nearby water bodies from erosion and flooding impacts

The purpose of the Tang Road Repair Project includes:

• Repairing the Tang Road MSE seawall and riprap shoreline protection under pier revetments

• Replacing the asphalt and concrete roadway surface

• Rerouting utilities to support the structural repairs

• Removing the beaver dam impoundment to relieve hydrostatic pressure on the road embankment

• Replacing the existing undersized culvert with a new 25-foot wide by 10-foot high box culvert

• Dredging ~8 feet of sediment from Hunter’s Marsh to restore flow capacity

These improvements aim to protect the road from hydrostatic buildup, enhance long-term drainage functionality, and improve base resilience during heavy rainfall and tidal events.

Following the culvert replacement, MSE wall repairs commenced. The project team executed a hybrid retaining wall stabilization plan using vibratory-driven steel sheet piling on both the landward and seaward sides of the road—no impact pile driving was used.

✅ Key Installation Notes:

• Steel sheet pile driven within 2 feet of the existing wall using two vibratory pile drivers

• Installation below the HTL of Hood Canal totaling approximately 132 linear feet

• Seaward sheets driven in dry conditions below +10.00 feet MLLW, with landward sheets installed under any tide condition

• 73 JF4SS maintainable weep hole assemblies installed through the new sheet pile wall system

✅ Weep Hole Drainage System Details:

• 4” closed-end ASTM 316/316L Stainless Steel Housing

• Mirafi® Filter-Weave FW 300 Geotextile Filter Media

• Designed for flushing access, hydrostatic pressure relief, and long-term durability

The region’s marine conditions and embankment saturation risks required:

• Pressure relief behind MSE and steel walls

• Erosion control from tidal influence and runoff

• Secure soil retention near critical roadways

• Drainage access to prevent future maintenance shutdowns

JET Filter’s maintainable weep hole system ensures flow stability, access for flushing, and protection of the embankment and roadway structure.