Project: CID West Branch
Phase I of the West Branch consisted of the construction of a new main trunk sewer in Mulberry Street extending from the Santa Fe Pump Station south to Bruce Forrester Viaduct. Beginning at the existing 10-foot diameter concrete Slough Sewer at its intersection with the alley located immediately south of Woodswether Road, the new 12’ x 8’ cast in place reinforced concrete box culvert was connected to a new rock box constructed under a separate city project over the Slough Sewer. This segment, running down the alley from Santa Fe Street to Mulberry Street, was cast in place to minimize the number of joints in the Corps of Engineers critical zone behind the Missouri River levee and floodwall. At Mulberry Street, the sewer turned south in Mulberry Street to a point 500’ south of the levee centerline, where it changed from a cast in place section to a precast section. At the intersection of the alley and Mulberry Street where the box culvert turned south, the trench was shored with secant piles, due to the proximity and physical condition of the adjacent existing buildings. Just south of the location where the box culvert switched to precast construction, the 12’ x 8’ box culvert transitioned to a 12’ x 6’ box culvert. This section then extended south to the end of the project at a point just to the south of the reconstructed Bruce Forrester Viaduct.
In order to construct the new box culvert in Mulberry Street, the existing cast iron water main was removed and replaced with a new 8” polywrapped ductile iron water main. In addition, an existing 36” combined sewer which crossed the proposed alignment of the box culvert was realigned and lowered.
The West Branch - Phase II CID storm sewer project begins at the end of the previously completed Phase I project. At the beginning of this phase of the project, a 14’ x 8 ‘ structure was constructed to provide access for cleaning of the sewer and to transition from the existing box culvert to an 84” diameter reinforced concrete pipe. The 84” pipe extended southward to the north side of the existing Union Pacific Railroad right-of-way, where it reduced to a 72” diameter steel pipe, which was bored and jacked under the two mainline and one spur tracks of the railroad for a length of 120 feet. All of the boring and jacking operations were performed with the railroad open for traffic. For corrosion protection, the inside of the steel pipe was sandblasted and coated with a ceramic epoxy coating after installation was complete.
From the south side of the railroad right-of-way to 11th Street, 72” diameter reinforced concrete pipe was used for the storm sewer. From 11th street to 13th Street, 6’ x 4’ reinforced concrete box culvert was used for the storm sewer. Transition structures which also functioned as junction boxes were constructed at each roadway intersection. This segment also included construction of the sewer under the 12th Street viaduct, a three level bridge constructed in approximately 1912. Under the viaduct, there was only about 14 feet of clearance to the underside of the lowest level of the viaduct. At 13th Street, the storm sewer turned west for one block to hickory Street, where it ended. This segment used 36” diameter reinforced concrete pipe. All along the entire project, the existing inlets were disconnected from the existing combined sewer system and connected to the new storm sewer. Additional inlets were installed as needed to provide adequate drainage. Due to favorable bidding conditions, it was decided to add new 36” diameter reinforced concrete pipe storm sewers in St. Louis Avenue, Union Avenue and 11th Street from Mulberry Street west to Hickory Street, and in Union Avenue and 11th Street from Mulberry Street east toward Santa Fe Street to the construction project. These storm sewer lines were primarily field engineered during their installation.
Since the project area has been developed for so long, it was necessary to modify a number of existing utilities to accommodate the new storm sewer construction, and to update the existing infrastructure. Existing steel gas mains were replaced and relocated, and existing telephone lines were relocated to clear the alignment of the new storm sewer. In Mulberry Street from Forrester Viaduct to 12th Street, the existing 8” and 4” water mains were abandoned, and a new 8” ductile iron pipe water main was constructed. The construction of the new storm sewer also required the construction of a new sanitary sewer main in 11th Street from Hickory Street to Mulberry Street and in Mulberry Street from 11th Street to St Louis Avenue to provide service connections from a number of buildings on the east side of Mulberry Street whose existing service connections crossed Mulberry Street and conflicted with the new storm sewer. This new 18” ductile iron pipe sewer was constructed between the new storm sewer and the existing buildings on the east side of Mulberry Street.
Because of the size and scope of the storm sewer installation and the utility relocations along Mulberry Street, it was necessary to completely remove and reconstruct all of Mulberry Street throughout the project limits, including roadway pavement, curb and gutter, sidewalks, drive approaches, and handicapped access ramps. The storm sewer trench in 13th Street was reconstructed with full depth asphalt pavement and the entire street received an new asphalt overlay. The existing roadway pavement on the other side streets, where storm sewer was added during the construction of the project, was removed down to the existing concrete subbase, and nine inches of new asphalt pavement was placed. Complicating the project were schedule limitations imposed on the project by the funding sources for the project. These limitations required that the construction be completed, and the final closeout paperwork be submitted and approved on only 5 months from the start of construction. In order to meet this ambitious and aggressive schedule, the contractor chose to work around the clock seven days a week for approximately three months, during the installation of all of the piping.