Technical Description:
• Aluminum Structural Plate
• Span: 14-ft. 0-in.
• Rise: 7-ft. 3-in.
• Length: 49.5 ft.
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In late July 2018, flooding conditions in the state of Pennsylvania were so severe that Governor Tom Wolf declared a proclamation of disaster emergency. Damage was extensive throughout the state and especially in the Borough of Huntingdon. As an example, the heavy, days-long rain event caused the soil above the culvert to subside and the eventual collapse of an existing structure over Muddy Run near Crawford Apartments at Ninth and Moore Streets.
"After the multi-day rain event, there was a huge hole that developed," said Interim Borough Manager Dan Varner. "A large section collapsed and there was a 90% blockage of Muddy Run."
After the damage was reported to Pennsylvania's Emergency Management Agency (PEMA), the agency as well as the Federal Emergency Management Agency (FEMA), surveyed the site to determine eligibility for financial assistance. The subsidence, which was first reported in November 2017, was caused by stormwater runoff which, in turn, damaged the structure's footings. The borough was already working with the Department of Environmental Protection (DEP) to fix it, but once the damage was declared an emergency, the project was fast-tracked.
"We were already working to replace this section of culvert due to structural instability, but the project was expedited when the culvert failed due to heavy rains on July 26," stated Kyle Lantzy, P.E., Structural Engineer with GHD, the project's engineer. "Contech Engineered Solutions was able to expedite the procurement of an aluminum culvert, which provided a quick and easy installation at a relatively small site."
GHD and Contech determined that the fastest and most economical solution was a 14'-0" span x 7'-3" rise Aluminum Structural Plate (ALSP), 49.5' in length. In addition to providing a quick time frame for manufacturing and installation, the ALSP structure also provided many advantages over other products considered. Its light weight added to the ease of installation as compared to other types of structures. It weighed 1/50 as much as reinforced concrete pipe which reduced equipment costs and allowed for easy handling of pre-assembled sections within the tight trench constraints.
Contracted to complete the repairs, HRI, Inc. installed the ALSP carefully, taking care not to damage the surrounding utilities or the structural integrity of the existing stone arch. The excavation was approximately 18’ deep and required a large track excavator not only to reach the depths of the excavation, but also to install large trench boxes to keep the excavation from collapsing. Once the boxes were installed, a temporary bypass pump operation was installed to divert the stream around the new concrete flow channel until the concrete reached acceptable strengths. During this cure time, HRI assembled the arch on site. After the concrete had cured, the bypass was terminated and the stream flowed as intended through the new structure. HRI was then able to lower large sections of the arch into place on the concrete foundation.
"When HRI was contacted about this project, we were not only excited to work alongside both a great engineer and owner, but also to work on such a unique project," stated Travis Boyd, Senior Project Manager with HRI. "As the project's contractor, we faced many logistical challenges in regards to modifying existing crews and work schedules in order to free up manpower and equipment, while also ensuring that we could procure all the necessary materials, all within a short time frame."
After the arch was installed, a surprisingly challenging part of the project occurred during backfilling. Not only was a select material needed, but it also needed to be compacted to a specific density. To achieve this, HRI placed the select backfill material in 8” lifts and then, after compaction, took a density test in multiple locations prior to placing the next lift. In order to achieve the desired results, HRI had to raise the trench boxes at controlled heights to allow for the next lift of material to be installed, while also not allowing the existing excavation to come in on the select material. All in all, it took just over one month to complete the project.
"As Project Manager, I appreciated how quickly GHD and Contech's representative worked together to identify the best product for this application and place the order," concluded Ann Reynolds, Project Manager with GHD. "The Borough purchased the arch directly to expedite delivery. In the meantime, HRI mobilized to the site and began preparations for the installation. Every party communicated and cooperated for a successful outcome, and the culvert performed perfectly through the rest of the unprecedented precipitation in 2018 that affected Pennsylvania."
Technical Description:
• Aluminum Structural Plate
• Span: 14-ft. 0-in.
• Rise: 7-ft. 3-in.
• Length: 49.5 ft.
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