Star City Wastewater Treatment Plant

Wastewater Plant Benefits from Doka’s One Supplier Solutions

The 90-foot-tall structure contained true radius walls, sloped radius roof and 45-degree sloped radius hopper floor slab. The customer needed unique solutions that allowed them to pour the structure in a safe and quick manner so they could stay true to the project’s critical path timeline. This project also had very a stringent level of safety requirements.

Doka was able to provide several things in one package for the customer. Through a series of meetings with the contractor and owner, Doka was able to come up with solutions for each of the unique areas of the structure, as well as efficient systems that allowed the structure to be completed on time. Doka provided several additional areas of support, such as engineering, onsite tech support, quick and efficient delivery of the different systems. Doka also offered a level of safety that met the requirements of this unique job and high safety standards of the customer. Ulliman Schutte was able to get all that from one supplier source.

The Challenges

The footprint for this wastewater treatment plant is very narrow, necessitating a very tall, narrow structure for the clarifier. This is a unique structure in that the roof cap slab and the cone shaped hopper floor are both radius and sloped. The sloped roof structure had to be poured before building the 45-degree sloped hopper floor. All shoring material for the roof had to be crane lifted out of a 12-foot opening 95-feet high, and the shoring and formwork for the hopper floor had to be lifted in through the same opening. The 45-degree floor slab was problematic because the hopper had to be a true radius. The walls also had to be a true radius system, not chorded with panels.

The Solution

Doka‘s Radius Top 50 system was used for the radius digester walls with shaping timbers, set on our MF240 platforms. Custom brackets connected the MF240 platforms in a radius configuration, both inside and outside the walls. The Top 50 wall gangs were made to a custom height so the entire clarifier could be poured in five lifts, and provided Doka with an opportunity to pre-assemble all of the radius formwork gangs. An onsite Doka technician helped with platform and formwork assembly.

The solution for the roof cap slab was to use Doka‘s Staxo 100 shoring system to pour a slab that was not only round, but sloped upward to a center opening of 12 feet. This required a platform level or “dance floor” to be constructed just below the roof slab elevation to allow safe access to assemble the radius sloped formwork that set on the shoring. The capability of Staxo to be lifted in tower sections made removal through the small opening easier during stripping.

Access to the upper wall pours and the roof shoring was accomplished using two separate DokaScaff stair towers that allowed for double egress. This met the rigid safety requirements for the jobsite. The most challenging portion of the project is the sloped hopper floor of the clarifier. With a 45-degree slope, the heavy slab had to be poured with a true radius top, because this is a fluid holding vessel, and had limited access. Because the roof slab had to be poured first, all of the material had to be lifted in through the small opening in the roof, and the few small door openings at the base. This was accomplished by using multi-tiered Staxo 100 shoring combined with T-Series spindle struts. The upper portion of the hopper cone was supported by bridge overhang brackets where the hopper met the radius digester walls. The shoring was decked with our Top 50 radius gangs using shaping timbers for both the underside and top of the slab. The hopper cone slab was poured in separate “pie” pieces to make finishing easier.