Project At-a-Glance
- Project was entirely restricted to the road’s right-of-way, requiring careful coordination of activities.
- Brierley designed high-mobility mix to allow mitigation under road surface.
- Barrier grout was used ensure high-mobility grout remained in targeted area of subsurface (under the road).
- Two notable sinkholes developed to the surface during construction requiring over-excavation, backfilling and compaction.
Recognition
- “Western State Award” Abandoned Mine Lands Reclamation Award
Office of Surface Mining Reclamation and Enforcement, 2024
Situated atop the Hanna No. 3 Mine, CR 297 serves as the secondary and emergency access roadway from US Hwy 287 to the communities of Hanna and Elmo. Dozens of historic subsidence events recorded in the Hanna No. 3 Mine impacted the useability of this important roadway to the point its use was restricted. The solution to bring CR 297 back into service was to inject over 28,000 cubic yards of void-fill grout into the mine workings below a 3,700-foot stretch of this important corridor during a 5-month period.
Grout mix design and injection strategy was critical. Using high mobility grout with moderate injection pressure ensures the grout’s capacity to infill compromised overburden material subject to continued settlement, rather than mitigating a specific mine void after a collapse or failure. Strategic injection of low mobility grout created in-situ barriers to help restrict the flow of grout to the target area thus optimizing infilling potential while reducing excess grout flow beyond the intended mitigation area.
Utilizing drone based orthomosiac mapping and LiDAR during project construction, Brierley Associates was able to define areas that were subject to historic undermining and local water shed characteristics that resulted in redirection of a culvert to prevent surface water erosion.
To protect high priority structures within the project area a structural monitoring program was implemented for the Bill Coffman Bridge crossing the UPRR tracks, as well as the tracks themselves. Automated Motorized Total Stations (AMTS) were used to report data readings which were continuously monitored by Brierley representatives. No movement of the bridge deck, abutments, or bridge apron were recorded during mitigation actions. Structural monitoring was also implemented for a 60-inch CMP culvert acting as secondary storm-water drainage through the historic tributary of Big Ditch. Brierley’s pre-construction inspection identified signs of deformation in the culvert. To reduce the potential of further damage to the culvert during construction activities 14 laser-tilt sensors were placed along the culvert alignment. The collected data was available in real time through GeoInstruments QuickView data visualization application that runs on GeoCloud servers. This laser tilt sensor data was continuously monitored by Brierley representatives during operations occurring within 500 feet of the culvert.
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