A traffic-alleviating project in one of Cemex USA's key markets has required mixer truck drivers to execute inordinate back-up distances to unload mixes. The project to which the company is supplying 65,000 yd. of specialty ready mixed concrete is the fourth bore of the Caldecott Tunnel, connecting Oakland to Orinda, Calif. However, in order to transport the material inside the tunnel, mixer trucks had to be driven 3,000 ft. in reverse on a narrow one-lane road.
Cemex’s experienced drivers have been able to make this maneuver safely hundreds of times throughout the project, providing 24-hour service for several months. The tunnel addition is expected to significantly cut traffic delays for thousands of daily commuters. Excavation and construction work began in 2010, and the tunnel is expected to open for traffic in late 2013.
The fourth bore requires excavation dimensions 50-ft. wide and 40-ft. high, roadway clearance of 16.75 ft. in height, and concrete roadway paving 29-in. thick. The project is being executed using a Sequential Excavation Method (known as the New Austrian Tunneling Method) that requires Cemex to supply specialty concrete shotcrete, which is applied using a construction technique where the material is pumped pneumatically on a surface at a high speed.
This allows it to be used on any type or shape of surface, including vertical and overhead areas. Cemex is providing a tailor-made shotcrete mix with extremely low shrinkage, custom formulated to work with the special machinery used to pump it long distances into the tunnel. In this sequential method, short sections of tunnel are excavated, then supported with shotcrete, steel girders and rock dowels.
Upon its completion, the fourth bore will function as the nerve center for the Caldecott Tunnel. Among the features of the fourth bore is a fire prevention and response system with a linear heat detector, carbon monoxide and nitrogen oxide detectors, and evacuation passages.
Additionally, the bore is designated as a regional lifeline structure, and is designed to reopen to emergency traffic within 72 hours of a major earthquake and will be equipped with strong seismic monitors to gather information that will be sent to the California Geological Survey to help predict future earthquakes.
“Cemex is proud to work with local and federal governments to help enhance the country’s infrastructure,” said company President Karl H. Watson, Jr. “As the U.S. construction sector continues to recover, we look forward to remaining the provider of choice for major infrastructure projects around the country.”