Long Term Cyclic Stability of Shallow Helical Anchors in a Hydraulically Placed Sand-Paper

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The study investigates the static and long-term cyclic uplift performance of shallow helical anchors in very loose, saturated sand placed hydraulically. Ten anchor tests—two static and eight cyclic—were conducted using 152 mm and 254 mm diameter anchors, with cyclic tests lasting up to 44,157 cycles. Soil conditions were assessed using cone penetration and laboratory tests.<br /><br />Static uplift capacities were consistent with a model based on a vertically lifted soil wedge. During cyclic loading, anchors accumulated displacement and lost embedment; cyclic failure generally occurred when the reduced resistance associated with embedment loss approached the anchor’s static capacity at its current depth. The loose sand showed slightly greater displacement accumulation than previously tested medium-dense sand.<br /><br />Two-way cycling, which included compression as well as uplift, caused greater displacement accumulation than one-way uplift cycling—up to 3.2 times greater. An empirical displacement-accumulation model represented test behavior reasonably well until normalized displacement reached approximately 0.1–0.3 times the anchor diameter. Beyond this range, displacement rates increased sharply, indicating potential progressive failure.<br /><br />The authors used the model to develop cyclic stability diagrams for different cycle counts. Defining stability as displacement below 0.1 anchor diameter produced boundaries that generally agreed with test results and can help assess long-term performance. However, the model does not capture the transition to accelerating displacement, and some tests stable through tens of thousands of cycles may have failed if continued. Further testing, particularly for one-way loading, is needed.

Keywords

helical anchors

uplift performance

cyclic loading

shallow anchors

saturated sand

static capacity

embedment loss

displacement accumulation

cyclic stability

soil wedge model