The Fall & Rise of Infrastructure in a Coal Mining Town

Milliken Infrastructure Solutions

As coal mines beneath Rock Springs, Wyo., collapsed in recent years due to neglect and environmental factors, city officials were challenged with preventing severe damage to private property and public infrastructure.

In 2014, a residential backyard in an upscale Rock Springs neighborhood fell into a sinkhole, swallowing a large brick fireplace and a three-season deck. During the emergency repair, crews discovered a 700-ft-long corrugated metal culvert – 48 in. tall and 72 in. wide at its largest point – that ran through many other backyards. Crews jacked up sections of the pipe and placed sections of new pipe inside the old, but the city still needed an improved long-term repair solution to stop future collapses.

Challenge

After the emergency repairs, city officials inspected the invert of the arched, oval pipe, which was covered with dirt and trash. Only after cleaning operations began could workers determine that the majority of the invert had been completely corroded away. Approximately 18 in. of the underlying soil had been eroded along the full length of the culvert, and 4-by-4 wooden beams supported the pipe in multiple areas. In addition to the invert, many of the joints revealed separations of more than 6 in. The crown had also caved in over a 10-ft section of the structure running directly under a roadway.

City engineers needed a trenchless repair solution to minimize traffic and noise disruption in the neighborhood; save the existing road and backyards; and reduce time and expense to complete the project.

Solution

Milliken Infrastructure Solutions’ GeoSpray geopolymer system was selected as a suitable solution. GeoSpray geopolymer is made of a fiber-reinforced mortar that facilitates the creation of a new structural pipe within the old pipe, improving performance and strength. For this repair, a professional engineer certified GeoSpray geopolymer as a structural rehabilitation.

Before applying GeoSpray geopolymer, workers excavated sand and rocks that filled approximately a third of the pipe. Pressure-washing quickly revealed the pipe’s entire invert had corroded away. Next, timber bracing returned the crown to its original shape, standard Portland cement fill was laid in the invert to replace the missing soil and the damaged joints were repaired.

After establishing the pipe’s basic shape, Inland Pipe Rehabilitation (IPR) applied GeoSpray geopolymer to the culvert in two passes, restoring structural integrity. IPR hand-sprayed the first pass to reinforce the width of the pipe and then achieved the final thickness of 1.5 in. using its proprietary EcoCast Advanced Geopolymer Relining System. GeoSpray geopolymer was applied to the culvert’s inlet and outlet to create a monolithic structure. 

Using this advanced repair technology, the City of Rock Springs was able to take full control of a high-risk situation. The storm culvert was restored to better-than-new condition in less than two weeks while the road above remained open to traffic. As a result of this repair, the lifecycle of the infrastructure is expected to extend by more than 50 years.