Application of Innovative Underreamed Ground Anchorages with Capsule-Paper

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The paper presents an innovative underreamed ground anchorage system designed to provide high pullout capacity, reliable construction quality, and lower cost. Its key component is an enlarged cylindrical body (ECB) formed inside an inflatable capsule at the base of the anchor. The capsule is installed with tendons and inflated with cement grout, allowing the enlarged body’s dimensions and grout volume to be controlled. The system is intended for applications including deep excavations, anti-uplift foundations, and slope protection.<br /><br />Model tests found a strain-hardening load–displacement response. Rather than causing overall soil failure, uplift produces localized shear and compaction around the ECB. Base resistance provides the dominant share of capacity: in tests with embedment-to-diameter ratios above 4.5, it accounted for at least 80% of total pullout resistance.<br /><br />The authors describe a combined construction method using jet grouting followed by capsule expansion. Injecting a specified grout volume helps control the ECB’s size and strength and improves installation quality across varied ground conditions.<br /><br />A case study of a large development in Kaifeng used 4,450 anchors to resist groundwater uplift. Compared with a tension-pile alternative, the project anticipated cost savings exceeding 30% and a reduction in construction time from 100 to 45 days. Preliminary tests achieved 1,200 kN ultimate capacity; in acceptance tests, 43 of 44 anchors had displacements below 90 mm at the specified test load. The paper also reports broader project experience in China, with typical cost reductions of 10–20% and reduced use of steel strand and cement.

Keywords

underreamed ground anchorage

enlarged cylindrical body

pullout resistance

cement grout

inflatable capsule

jet grouting

ground anchor

uplift foundation

slope protection

cost savings