20A - AA FIRST ST BRIDGE REPLACEMENT PROJECT

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LSA ASSOCIATES, INC. JULY 2010 INITIAL STUDY/MITIGATED NEGATIVE DECLARATION FIRST STREET BRIDGE REPLACEMENT PROJECT CITY OF SANTA ANA 2.4 CONSTRUCTION AND PHASING/STAGING The existing bridge consists of two separate structures (a north structure and a south structure) that have been improved at different times. In addition, it is crucial for First Street to remain operational during construction, so one through-lane in each direction will remain open during project implementation. Therefore, construction of the new bridge will occur in phases, starting with the northern structure. Figure 10 shows an overview of the construction phasing. Figures 11, and 12 show the section views of the construction phasing. Figure 13 shows the final section of the bridge. Phase 1: Northern Structure. Phase l begins with redirecting all traffic onto the existing two lanes (one lane in each direction) of the southern structure. Phase 1 Demolition. The Phase 1 demolition includes portions of northern structures above bridge-bearing elevation (superstructure) and foundation elements (substructure) such as columns, wall piers, footings, and pile caps. The piles and drilled shafts of the existing bridge will be cut off 1 ft below the channel invert elevation. Phase 1 Construction. Construction includes the placement of the new bridge foundation elements (during dry season) as well as upper portions of the bridge (superstructure), including girders and deck construction in the northern portion of the bridge. The placement of the recommended superstructure type (precast bulb-tee girder with cast-in-place concrete deck) of the bridge is not required to be conducted within the dry season. A new retaining wall will be built in the northeast quadrant of the bridge. Phase 2: Southern Structure. After completion of the new northern portion of the bridge, traffic will be routed onto the new bridge, and the southern portion of the bridge will be closed in order to allow for demolition of the existing southern portion of the bridge pier and superstructure. Phase 2 Demolition. The Phase 2 demolition encompasses the same demolition activities as Phase 1, but they will occur in the southern bridge structure. Therefore, Phase 2 demolition includes portions of the southern structure above bridge-bearing elevation (superstructure) and foundation elements (substructure) such as columns, wall piers, footings, and pile caps. The piles and drilled shafts of the existing bridge will be cut off 1 ft below the channel invert elevation. Phase 2 Construction. Phase 2 construction will encompass activities in the southern portion of the bridge, which will be conducted in the dry season. The construction activities will include placement of the pier and foundation elements followed by the placement of the girders and deck construction. A new retaining wall will be built in the southwest quadrant of the bridge. Depth of excavation in the riverbed will not exceed four feet. The project will be completed with the changing of the roadway approaches to meet the alignment of the new bridge. P:\DMJ0701\NlND\2.0 Project Description.doc (07/25/10) 2-13 20A-24