PROJECT

Exploring the riverbed strength of the Swan River

Exploring the riverbed strength of the Swan River

Status: Complete

Researchers

  • Fiona Chow
    Adjunct Professor, Centre for Offshore Foundations System, UWA
  • Shiaohuey Chow
    Research Fellow, Oceans Graduate School, UWA
  • Conleth O'Loughlin
    Associate Professor, Oceans Graduate School, UWA
  • Vincent Goh
  • Rian McIlduff

Project Summary

Free-fall penetrometers are instrumented projectiles that are deployed by allowing them to free fall in water and embed into the target sediment. The use of free-fall penetrometers in offshore geotechnical site investigation has gained increased interest, particularly in characterising the soil strength of shallow seabed.  This is crucial for applications such as pipeline design and submarine landslide surveying. Compared to the conventional approach of using a large survey vessel and a mechanical system for pushing a penetrometer into the seabed, free-fall penetrometers offer a cheaper and quicker way to survey the seabed, with potentially equal accuracy if the tools are designed and interpreted correctly. Two prototype free-fall penetrometers (free-fall sphere and cone penetrometers) were developed at the Centre of Offshore Foundation Systems, UWA.  This project assessed the performance of the new prototypes, their improvement and optimisation, and the validation of their interpretation methods by conducting field trials in the Swan River.

Project updates

Preliminary field trials conducted using a dummy free-fall penetrometer

Preliminary field trials were conducted in early October 2016 using a dummy free-fall penetrometer at a few locations along Swan River to establish the field deployment procedure. In addition, desk study was carried out with actual test site (i.e. East Perth) identified and existing soil investigation data obtained from relevant industry and government bodies.  Actual field test of the two free-fall prototypes (free-fall sphere and cone penetrometers) at the East Perth was completed in late February 2017.

 

Figure 1:  Free-fall cone penetrometer

Figure 2:   Instrumented free-fall sphere

Figure 3:   Field trails at Swan River using a dummy free-fall penetrometer 

 

East Perth Field Expedition Near the New Perth Stadium

On Friday 5 May 2017, field tests using the two free-fall penetrometers were successfully conducted at the East Perth site by Vincent, Rian and Shiaohuey. The cone and sphere free-fall penetrometers with different masses were deployed using different fall heights from a CSIRO research vessel, the BF Ryan. The penetrometers were able to embed up to 2.3 m into the riverbed. The embedment depth of the penetrometer is found to increase with increasing penetrometer mass and impact velocity. The undrained shear strength estimation of the Swan River sediments using the free-fall penetrometers are coming soon!

Figure 4:  Rian (Left), Vincent (Middle) and Shiaohuey (Right) conducting field tests using instrumented spherical and cone free fall penetrometers.