SR-84 Sinkhole and Culvert Repair DO (EA 4X430)

Caltrans proposes repairing a sinkhole and failed culvert on SR-84 in San Mateo County at post mile 16.07. Maintenance Services discovered the sinkhole on August 4 and Field Maintenance installed a steel plate over the sinkhole temporarily so the lane could be reopened to traffic. The sinkhole extends approximately 4 feet toward the median, 15 feet back toward a cross culvert, and daylighted 20 feet down the slope along the roadway. It was determined that an 18-inch corrugated metal pipe (CMP) cross culvert had failed, causing water to intrude into the roadway subbase. The water seepage resulted in loss of subbase material and eventually crated the sinkhole. The project proposes to first remove the undermined roadway section and loose material from the sinkhole. The sinkhole will be repaired by reconstructing the subbase. The existing damaged section of the 18-inch CMP cross culvert will be removed and replaced with a new culvert section of the same size. The roadway will then be repaved using hot mix asphalt. Traffic control, temporary railing (type K), and a temporary signal will be required during construction.