Theoretical and Experimental Investigation on Underwater Ground Anchors-Article

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The study evaluates underwater ground anchors as a cost-effective way to reinforce existing wharves when harbour deepening would otherwise require disruptive reconstruction or longer sheet piles. At Ravenna’s SAPIR terminal, engineers developed and tested a remotely operated installation system using advancing jet grouting.<br /><br />The U.W.A. system installs steel tie rods from the shore using a robotic drilling and injection unit. High-pressure cement grout forms a roughly 40 cm diameter bonded column around the anchor. The test anchors were 18–21 m long, with active bonded lengths of about 16 m. Their design capacity was governed by the steel bars’ 630 kN yield load; the estimated resistance of the soil-bonded bulb was 1,000 kN.<br /><br />Seven anchors were installed in 2010: three at 5 m depth to assess equipment performance under hydrostatic pressure and four at 8 m to test the project design depth. Load tests included operating loads of 300 kN and loads up to or above 630 kN. A nonlinear soil–anchor interaction model was used to predict load–elongation behaviour and was compared with measured results.<br /><br />Installation and load testing were successful. At the operating load, measured elongations were consistent with predicted values—approximately 5–6 mm—and at 630 kN they were generally around 15–20 mm. The measured response supported the model’s assumptions about soil resistance and stiffness. Where failures occurred at higher loads, they involved couplings or bar bending, rather than failure of the bonded anchor.<br /><br />The findings indicate that remotely installed underwater anchors can provide reliable, relatively low-deformation reinforcement at depths where wharf stresses are greatest. The technology may also support higher-capacity or additional anchor rows, subject to checks of the wharf structure and site geotechnical conditions.

Keywords

underwater ground anchors

wharf reinforcement

jet grouting

remote installation

tie rods

soil-anchor interaction

load testing

Ravenna SAPIR terminal

anchorage capacity

geotechnical engineering