Stub Pier Stabilization Performance-Paper

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The paper describes an emergency landslide repair on U.S. Route 50 in Cincinnati, Ohio, where deep movement along a bedrock shear plane had damaged the roadway and forced the closure of three lanes. Because a conventional tieback-anchored drilled-pier wall was too costly and time-consuming, Terracon and the Ohio Department of Transportation installed 154 closely spaced “stub piers” in 2005.<br /><br />The 30- and 36-inch-diameter shafts were socketed into bedrock. Their steel reinforcement extended from the shaft bottoms to roughly 15–20 feet above bedrock, but stopped about 30–35 feet below the ground surface. The reinforced sections acted as shear elements, with soil arching intended to make the piers function as a wall. The design targeted a short-term slope safety factor of about 1.2. Installation and roadway reopening took less than three months, at a reported cost of approximately $500,000 in 2005—estimated at one-quarter to one-third the cost of the tieback alternative.<br /><br />Instrumentation monitored movement, earth pressure, and steel strain. After 11 years, readings indicated that the piers had successfully interrupted the original deep-seated movement and performed better than anticipated. At two monitored piers, measured deflections near the top of the steel were substantially lower than LPILE predictions; deflections near bedrock closely matched predictions. Estimated lateral loads needed to reproduce observed movement were about 50–55% of the original design assumptions.<br /><br />The authors conclude that stub piers can be an effective, economical solution for landslides with deep shear planes, potentially lasting well beyond their intended temporary service. However, the method is not suitable for every site; shallow instability and long-term movement must also be assessed. They recommend careful instrumentation, consideration of creep and surface impacts, and numerical analysis of soil–structure interaction.

Keywords

landslide repair

stub piers

U.S. Route 50

Cincinnati Ohio

bedrock shear plane

drilled-pier wall

slope stabilization

earth pressure monitoring

soil arching

soil-structure interaction