Design of Shallow Foundations for Tidal-Stream Energy Structures-Paper

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The study investigates the horizontal resistance of shallow, gravity-based foundations for tidal-stream turbines placed on exposed rock. Because tidal currents impose large horizontal loads and design guidance for rock–foundation sliding resistance is limited, developers may use excessive ballast, increasing cost and installation difficulty.<br /><br />Researchers conducted combined vertical and horizontal load tests on a 1:3-scale, 90-degree conical steel footing at a quarry in Nova Scotia. The weathered basalt site was selected as a geological analogue for offshore deployment conditions. Tests varied footing penetration and vertical loading to assess their effects on lateral capacity.<br /><br />The results show that penetration into the rock is critical. A footing resting on the rock surface, without embedment, achieved a peak horizontal-to-vertical load ratio (H/V) of about 0.67. Embedded tests reached substantially higher ratios, with a maximum of 1.82. Embedment also changed the failure mechanism: embedded footings mobilized resistance through rock chipping and formation of a groove, while a non-embedded footing was governed mainly by interface friction. The achievable H/V ratio also depended on applied vertical load.<br /><br />The authors conclude that site-specific field testing may help establish design resistance and optimize foundation ballast. However, results are affected by scale and rock-mass characteristics, including jointing and fracture spacing, so they cannot be transferred directly to full-scale structures. Further research is recommended on alternative cone angles and combined vertical–horizontal–moment loading.

Keywords

tidal-stream turbines

shallow foundations

horizontal resistance

gravity-based foundations

rock–foundation sliding

conical steel footing

embedment

rock chipping

vertical load ratio

field testing