Session: 10-03-01: Piles, Spudcans and Others

Submission Number: 155384

An Electrokinetic Approach for Reducing Spudcan Base Suction 

Extraction of mobile jack-up rigs’ spudcan foundations in soft clay sediments is a time-consuming process. Suction at the base of an installed spudcan dictates the extraction resistance. Consequently, any reduction of the base suction will ease the extraction process and reduce offshore time and hence cost. Previous research revealed that the loss of the base suction may reduce extraction resistance. This paper experimented the potential of using electrokinetic phenomena such as electrode reaction and electroosmosis for reducing the base suction. Electrolysis of pore water is occurred by electrode reaction when the electric current is applied via electrode inserted into saturated clay deposit. This resulted in formation of a gas layer (and hence gap) underneath the base of the spudcan, and crack through the clay deposit. To evaluate the effectiveness at creating a thin gas layer and forming crack at reducing the base suction, several model tests employing electrokinetic phenomena were conducted by using newly proposed method for applying electric current to spudcan. These tests focused on observing gas generation around an installed full-spudcan and crack formation through the kaolin clay deposits to evaluate the potential of reducing base suction. A microfocus X-ray CT scanner was used for imaging.

The results of the experiment showed that the new method was effective for applying current to the entire embedded spudcan, where the anode was set in the solution above the ground and the spudcan served as the cathode. The results of X-ray micro tomography imaging indicated that gas and crack generated around the spudcan and shaft that could potentially reduce the base suction. The calculation for the corresponding prototype scale indicated that the generated gas volume decreased with increasing depth. Additionally, the total energy consumption at this scale was 2 kWh, which was relatively low compared to the operational energy requirements of ships. By increasing the anode area, the voltage applied in the seawater can be reduced, leading to further energy savings. Therefore, if this method proves effective for spudcan extraction, it could significantly shorten the extraction time compared to the conventional method, resulting in substantial energy savings.

In summary, the results for this study confirm that the base suction can be reduced through the formation of a thin gas layer and/or cracks. The weight of the backfilled soil column above the spudcan can also be reduced as the soil column above the spudcan peels away from the shaft. Instead of conventional pumping water through the nozzles for breaking the base suction and digging or reverse circulating the soil above the spudcan, only thing will be required is applying electric current. Critically, total extraction (offshore) time will be much shorter and hence significantly cheaper.

Presenting Author: Yuri Sugiyama National Institute of Maritime, Port and Aviation Technology Port and Airport Research Institute

Presenting Author Biography: Yuri Sugiyama is a researcher at the Port and Airport Research Institute. Her research focuses on marine geotechnology and its application to geotechnical engineering. Her prior work explored soil/water/gas coupled modeling considering dissolved gas, constitutive modeling of clay mineral alteration, and disturbances during the sampling of soil specimens from deep seabed ground. Recently, she has shifted her focus to technological developments, including ground improvement, clay consolidation, and the spudcan extraction method using electrokinetic treatment.