A massive concrete foundation mat pour for a multiuse building complex in Newport Beach, California, presented contractors with a challenge. The mat, which varies from 3.5 to 8 feet thick, had to be placed over a quagmire 21 feet below sea level. To prepare the extremely wet site for concrete placement, workers first dewatered the area. After stabilizing the soil, they capped the area with a 4-inch-thick concrete water barrier topped with rolls of bentonite. Later, the bentonite was extended up the subgrade walls and coated with shotcrete.
It was decided that the concrete would be placed by pump overnight in a 16-hour, monolithic pour. The 71,000-square-foot mat pour required a fleet of five truck-mounted pumps each having 170-foot boom extensions. To meet the 16-hour placement schedule, each pump had to have an output capability averaging 92 cubic yards of concrete per hour. Lack of space at the jobsite limited the maximum pump output capacity to an average of 128 cubic yards, a number still high enough to easily complete the pour within the designated time frame. To keep the pour on schedule, 130 ready mix trucks from four central-mix plants were required, each carrying a 9.5-yard load. Fourteen haul-away containers on lowboy trailers were used to cart off the excess ready mixed concrete. Just 11.5 hours after beginning the pour, the project was completed.