I-280 Culvert Replacement (EA 04-0V250)

Caltrans proposes removing and replacing a culvert system on the Interstate (I-) 280 southbound separation to State Route (SR-) 87 in Santa Clara County from post mile (PM) R2.8 to R3.0. There is a substantial amount of water seeping through the pavement and depressed areas between the two drainage inlets (Dis) on the asphalt concrete (AC) pavement. Based on visual inspections of the site and review of the as-builts, the settlement and cracks is likely due to the failure of the underdrain pipes. The underdrains have limited capacity as they are partially filled with soil, corroded, and at some locations are fully blocked, causing water seepage through the roadway surface. The foundation soils are migrating into the underdrain system and as a result, cavities and settlement have been created. To prevent the underdrain system from migrating into the water seepage, the existing underdrain will be removed and replaced with a new system consisting of 10” Perforated PVC pile (PPP) (Refer to D102 in 2022 Standard Plans), and a Class 3 Permeable Material (PM) drainage layer under the shoulder with a length of 330’ to draw down the inflow of the groundwater. Trenching of the roadway will be required to access the underdrain. The foundation soils under the pavement will be strengthened using compaction grouting in combination with sodium silicate, which is a fast-acting chemical setting agent. Before the construction of the new underdrain, the compaction grouting will be used within the limits of the settled areas to an approximate depth of 20 feet. The roadway will then be repaved with hot mix asphalt (HMA). Traffic control will be required during construction.