SR68 Midland Road Emergency Landslide Repair: Let’s Try Something Different-PPT Presentation

PPT Presentation

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The presentation describes the emergency repair of a landslide affecting State Route 68 (SR 68) and adjacent Norfolk Southern Railroad tracks in Beaver County, Pennsylvania. The area has experienced long-term soil creep and recurring roadway and track displacement. In July 2018, PennDOT closed the eastbound lane after pavement damage raised safety concerns.<br /><br />Extensive earlier investigations by L.R. Kimball and Golder Associates included borings, rock coring, inclinometers, piezometers, seismic surveys, and other testing. The site lies in landslide-susceptible shale and sandstone formations, with no identified mineable coal seams or oil and gas wells. Engineers used the accumulated monitoring data to model the existing creep condition and assess remediation options.<br /><br />Alternatives considered included groundwater lowering, lightweight fill, stone columns, and deep soil mixing (DSM). DSM was selected as the preferred approach, with modeled stability performance better than the other options. The project was completed in 2019–2020 for approximately $3.5 million, including $2.5 million for the slide area.<br /><br />The contractor proposed an alternate DSM layout using seven-foot-diameter columns. Because performance depended on achieving consistent strength and mixing, the project included bench-scale testing, field validation panels, production monitoring, wet-grab sampling, and verification coring. Acceptance requirements specified a minimum 28-day unconfined compressive strength of 115 psi, with additional criteria for the proportion of results meeting strength targets and for treatment uniformity.<br /><br />Construction findings highlighted the importance of precise depth and elevation controls, since equipment initially measured depth from the ground surface, and of adequate mixing time at the column base. The project was completed on schedule despite a COVID-related shutdown. Key lessons included using prior investigation data effectively, validating construction methods before production, and maintaining robust quality-control and verification procedures.

Keywords

landslide repair

State Route 68

PennDOT

Beaver County

deep soil mixing

Norfolk Southern Railroad

slope stability

groundwater lowering

quality control

unconfined compressive strength