DRAINAGE DESIGN CASE STUDY:

To improve water management and extend the life of reinforced concrete barriers at the Oregon Expressway underpass in Palo Alto, California, Caltrain partnered with George Bianchi Construction and the Peninsula Corridor Joint Powers Board to install a maintainable drainage system using JET Filter weep hole assemblies.

This upgrade ensures hydrostatic pressure relief along a busy transportation corridor used by thousands of daily commuters

Underpass and tunnel walls are frequently exposed to:

• Water accumulation from surface runoff

• Hydrostatic pressure behind concrete walls

• Soil migration or wall cracking due to moisture retention

To ensure the new concrete barriers maintain their integrity, drainage weep holes were specified to release trapped water, minimize erosion, and allow for long-term maintenance access.

As directed in the field, 15 JET Filter JF4SS weep hole assemblies were installed through reinforced concrete barriers at designated points along the Oregon Expressway underpass.

✅ System Specs:

• Part#: JF4SS

• Size: 4” Diameter Open-End ASTM 316/316L Stainless Steel Housing

• Filter Media: Mirafi® Filter-Weave FW 300 Geotextile

• Units Installed: 15

• Purpose: Pressure relief and sediment control behind reinforced concrete

This maintainable drainage system is built for longevity and easy access, especially critical in high-traffic transportation infrastructure like Caltrain underpasses.

Without proper drainage:

• Water collects behind concrete barriers

• Hydrostatic pressure causes wall cracking and shifting

• Maintenance becomes reactive and costly

Maintainable weep hole systems, like JET Filter’s JF4SS, provide a proactive solution that allows for drainage inspections and long-term protection of public infrastructure.