Offshore renewable energy is top of mind for NC State researchers looking to advance clean energy sources. From wind turbines to wave energy devices, the seafloor is the new horizon for sustainable energy.

“These technologies are essential for advancing both national and global clean energy goals and supporting the transition to a low-carbon future,” Neda Jamaleddin, post-doctoral research scholar in the Department of Civil, Construction and Environmental Engineering (CCEE), said.

Jamaleddin is part of a team that recently investigated a new anchoring method for offshore applications that eliminates the need for large equipment. The method, called Remote Anchoring and MicroPiling (RAMP), was developed by Makai Ocean Engineering, which partnered with NC State researchers through a project supported by the U.S. Department of Energy’s Advanced Research Projects Agency–Energy (ARPA-E). 

Jamaleddin, Associate Professor Ghadir Haikal and Distinguished Professor Mohammed Gabr have conducted several studies investigating the RAMP system, specifically hollow-bar micropile anchors for offshore renewable energy applications.

Remote Anchoring and MicroPiling (RAMP)

This new method can potentially reduce the cost of offshore renewable energy installations and enable the deployment of these devices in areas that were otherwise inaccessible.

In the RAMP system, foundational elements are remotely installed into the seabed. These foundational elements, called hollow-bar micropiles, range from 100 to 300 millimeters in diameter and have a hollow core.

“For hollow-bar micropiles, drilling and high-pressure grouting are integrated into a single step,” Jamaleddin explained. “It enables faster installation and improved productivity.”

While hollow-bar micropiles are widely used on land, they have yet to be fully adapted for offshore applications. Before being widely adopted in unpredictable oceanic environments, their performance must be carefully evaluated. That’s where researchers from NC State come in.

Testing the RAMP System

The NC State research team examined how high-pressure grouting used in the RAMP system affects the axial pullout capacity of hollow-bar micropiles. Axial pullout capacity is the maximum tensile force a foundation element can withstand before being pulled out of the seabed. 

“If the applied tensile load exceeds the axial pullout capacity, the anchor could be pulled out of the seabed,” Jamaleddin said. 

The team developed a numerical model using PLAXIS 3D, a 3D geotechnical software, and validated it against field test data.

“I saw very similar trends and results compared with the field test data,” Jamaleddin said. “That gave me a baseline for my numerical modeling and from there, I conducted a parametric study, changing different parameters to see how they affected the results.”

This modeling process was complex, as it involved three elements: the micropile, the soil and the interface between them. As pressurized grout is injected, it enlarges the drilled cavity and redistributes stresses in the surrounding soil and along the grout–soil interface.  

Through these analyses, the researchers found that the installation process can both strengthen a micropile and affect a larger area of soil around it. They found that micropiles installed in denser sand or with greater grout-induced expansion have a higher pullout capacity. However, when several micropiles are placed too close together, the affected areas of soil can overlap, making the whole group of micropiles less efficient. 

“The findings suggest that current spacing guidelines may need to be reconsidered,” Jamaleddin said. 

Overall, the researchers said more studies are needed to develop design guidelines for micropiles that take installation effects into account.

Why it’s Important

By eliminating the need for large equipment, the RAMP system has the potential to be used in deep-water locations and across a range of seabed conditions, from rock to soft clay, potentially reducing the installation costs of offshore renewable energy devices such as wind turbines and wave energy converters. This particular study focused specifically on hollow-bar micropiles installed in saturated sand. 

“I’d like to see clean, renewable-energy systems become more accessible around the world,” Jamaleddin said. “That is something I truly hope to see one day.”

This subsequent NC State study was supported by the North Carolina Renewable Ocean Energy Program (NCROEP). The researchers’ findings were recently published in Ocean Engineering, titled “Installation effects on the axial pullout capacity of hollow-bar micropiles in saturated sand.”

This post was originally published in Civil, Construction and Environmental Engineering.