Abstract: In order to evaluate the anchoring effect and the control failure mode of the umbrellashaped ground anchor in the rapid reinforcement of expansive soil slope failures, and to further increase the anchoring results with permanent corrosion protection, a series of field tests were performed on the umbrella-shaped ground anchors with/without grouts and with various anchoring length. The following results can be obtained: 1. In an anchor grouted length range, the ultimate pullout resistance of the conventional grouted ground anchor demonstrates a linear with the bonding length, while for the grouted umbrella-shaped ground anchor, the pull-out resistance first increases nonlinearly with the increase of displacement rapidly, and then the pull-out resistance increases linearly gradually with the displacement value; 2. Since the adhesion between anchor and the surrounding soils induced by the grouts will reach its ultimate value when the displacement of anchor reaches a critical value, a pre-tension load should be applied on the umbrella-shaped anchors so that the ground anchor can reach a much higher pull-out resistance by mobilizing both the umbrella effect and the grouting effect at the same time. After the grouting of the umbrella-shaped ground anchor, the bonding zone can be integrated so that the bonding zone can have a more uniform stress distribution. When the umbrella-shaped ground anchor reaches the ultimate resistance, it still can maintain the ultimate load; 3. Compared with the conventional ground anchor, which need to have an effective length beyond the sliding zone of 21 meters, only 15 meters are necessary for the grouted umbrella-shaped ground anchor with the same pull-out resistance. It is concluded that the new ground anchor has advantages over the conventional ground anchors and can be used in the rapid response of failures in expansive slopes.

Key words: umbrella-shaped ground anchors, grouted ground anchors, ultimate pullout resistance, anchoring characteristics