Engineers from RMIT University are developing a technique to help underwater technicians by using a modified speargun to efficiently and cheaply test seabed soil.
RMIT University researchers, Professor Majid Nazem and Junlin Rong, have showcased an innovative method for testing soil, potentially streamlining the process for major infrastructure projects.
Specifically, these soil tests are designed to provide critical information to engineers prior to building offshore infrastructure such as windfarms and pipelines.
“These structures require geotechnical information. For instance, an example is the soil friction angle, which reflects how the soil behaves under a large amount of loading. This information helps engineers design structures,” said Rong.
“To obtain this information, the conventional method involves deploying a drilling rig to the site, drilling to determine the soil’s strength, and then converting those measurements to determine the soil friction angles.
“These soil parameters are crucial. What we are doing now is trying to replace some of these tests, which usually require a significant number of tests to gather all the necessary information. This is where we play a role, substituting conventional testing methods.”
Conventionally, the typical method for testing seabed soil involves winching or dropping lightweight or heavy-duty probes – known as penetrometers – from the deck of a support vessel.
However, using these probes comes with a set of challenges in certain contexts.
For wind farm projects in shallower waters, lightweight probes can struggle to penetrate the seabed, while heavy-duty probes, which are effective, can cost up to $200,000 per day.
Nazem and Rong’s method, using a modified speargun, utilises probes attached to a speargun bolt.
“The speargun is designed for challenging underwater environments, making it an ideal inspiration for a geotechnical engineering test device,” said Rong.
“Its mechanism allows for efficient penetration of topsoil, providing easy soil investigation.
“By adapting the speargun’s mechanisms, we can deliver considerable penetration forces, enabling faster geotechnical surveys.”
The RMIT researchers have tested this method by testing different probe tips in a water tank filled with various sand mixtures.
They used an array of sensors and high-speed cameras to capture the results.
According to Rong, the results have demonstrated the device’s potential in field applications.
“In laboratory environments, the device showed considerably greater penetration potential compared to free-falling probes on soil,” he said.
“Notably, in high-density sandy material, the penetration depth was twice that of previously reported values achieved by freely falling probes.
“This breakthrough technique has the potential to revolutionise site investigations for wind farm projects, offering significant time and cost savings while outperforming the embedment achieved by other dynamic penetrometers.”
Rong believes that conventional testing methods, like cone penetration, will remain as the more popular choice.
However, Rong hopes that their device could eventually provide an alternative method for testing, which could subsequently reduce the number of expensive tests needed.
Majid Nazem said the device was now ready for field trials,
“Now that our experiments have demonstrated the device’s ability to achieve considerable embedment depth in dense sand,” he said.
“We are keen to conduct field trials and collaborate with our potential industrial partners to further test its performance for offshore geotechnical engineering applications.”
In the field
Currently, the team is comprised of a project lead or director, Professor Nazem, who coordinates these efforts, while the laboratory partner, Rong, assists with design, planning, and conducting the tests.
Together, they analyse the data and draw conclusions based on their findings.
In addition to their internal team, they collaborate with other institutions such as the University of Melbourne, which helps with design and implementation through its expertise.
“We also work closely with manufacturing and application teams at RMIT, who help us build and test our devices,” said Rong.
“Additionally, the technical staff in RMIT’s heavy structural lab provides valuable support.
“This project is a team effort, and the credit goes to everyone involved, not just me or the project lead.”
The engineers will soon be setting the level for their field tests, expecting their speargun probe to penetrate the seabed to a depth of two to five meters based on their laboratory tests.
However, in their Melbourne-based laboratory, they only used about 25 per cent of the energy of the spearguns due to safety limitations associated with firing the gun indoors.
“We haven’t conducted field tests yet. If we can apply 100 per cent of the energy in the field, we can test further and clarify our assumptions or hypotheses,” said Rong.
“Compared to conventional methods, we need to validate our data, which we are also doing in the lab, but field tests will provide more critical information.”
Field tests will also determine how viable the speargun is when deployed from a support vessel. Rong remains confident based on their preliminary data.
“There are more research questions we need to investigate to determine if this method fits the boats through this kind of testing,” he said.
“However, based on our laboratory test results, we are confident that these methods can provide a viable alternative to current test technologies.”
Rong also hopes to gain support from industry partners, who can then assist the engineers in developing a design for an enhanced shooting mechanism.
“Currently, in the laboratory, we are developing these models as prototypes. In the next stage, if we find suitable collaborators, we aim to further optimise the design and build a deployment rig or shooting mechanism,” he said.
“This could involve either using a remotely controlled vehicle from the seabed or shooting directly from support vessels or smaller ships.”
ROVs, or Remotely Operated Vehicles, are unmanned, remotely controlled submarines used for various underwater tasks.
They’re often used in industries like oil and gas, marine research, and deep-sea exploration.
Rong explained that a similar mechanism to their speargun probe could soon be mounted onto an ROV.
“The remote-controlled vehicles currently used in the industry are typically employed for deepwater construction, where they monitor projects at depths of up to about 1,000 meters,” said Rong.
“These vehicles can carry equipment and allow for remote and safe operation of tests.
“If we were to use a boat for shooting, we would need to assess whether it is feasible to reach the seabed and penetrate the ground effectively from that distance.”
Collaboration with industry
The engineers are pursuing different avenues to obtain partnerships with industry.
“We are participating in a field research conference where we are presenting our technologies and introducing them to the market,” said Rong.
“Currently, we haven’t received much feedback from the industry. However, our goal is to showcase our technologies, generate interest, and explore potential collaborations for future developments.”
Their ultimate goal is to partner with a manufacturer who could enable the engineers to scale-up their device.
“Next, we can scale-up to conduct a full-scale test of this particular design,” said Rong.
“We plan to scale-up and gain a deeper understanding of how the larger equipment will perform.”
Rong expressed excitement about the prospect of obtaining an industry collaborator who can bring their technology to the next stage.
“If there are any potential collaborators or future funders interested, we are eager to engage in bringing these innovative solutions to the geotechnical field,” he said.
“We have everything ready and are prepared to move forward at any time.”