Full scale trial of rock bag filter units
AMC Search conducts independent assessment of a full scale trial on the performance of Rock Bag Filter Units
November 16, 2023
AMC Search was commissioned by Project Material Pty Ltd to provide an independent assessment of a full-scale trial on the performance of AquaRock Bags® Filter Units as an alternative to conventional rock armour to provide scour protection against wash generated by bow and stern propulsion units from ships and tug vessels.
Rock bag filter units can be placed on the revetment and bottom of the berth pocket to prevent undermining of quay wall structures or scour around piles.
Project Material organised the use of Pacific Tug’s Cape Mac tug located at their Brisbane Pacific Marine Base to conduct full-scale trials on the performance of the 4 t and 8 t rock bags.
The aim of the trial was to use the thrusters of the tug boat as a power source to determine the point at which the rock bags fail, or are dislodged from the constructed revetment and base in the following configurations:
- Stability for the 4 t and 8 t rock bags on a 1V:2H slope
- Potential for uplift of the 4 t and 8 t rock bags on a flat surface when
- The tug is located seaward of the bags
- The tug is located above the bags
- Stability for the 8 t rock bags when stacked as an unsupported vertical wall
- Smaller 2 t AquaRock bags® used for localised scour protection and ground preparation
The trials were conducted on the 7th of October 2022, with the Cape Mac utilising both engines to thrust water towards the rock bags.
The water velocities were measured at the revetment using an acoustic doppler velocimeter (ADV). However, during one of the runs, submerged debris impacted the ADV damaging the probe and eventually ceased to operate for the final configuration.
As a result, the maximum water velocity from the tug was estimated at 5.3 m/s from data received from the damaged ADV, shown in the Table below.
* Note: ADP Instrument was damaged for these measurements
** Note: Water velocity assumed equal to the recorded velocities in Case B
During the testing, hydrographic surveys were conducted to measure the movement of the rock bags and surrounding riverbed. These surveys showed minimal movement of the 4 t and 8 t rock bags in all three configurations, as well as the surrounding 2 t rock bags, from the direct and indirect tug wash in velocities up to an estimated 5.3 m/s.
Therefore, this trial showed that the AquaRock Bag® units are suitable to be installed as scour protection in berth pockets, around piles and on revetments, as well as revetment armour units in water velocities up to 5.3 m/s with minimal movement.
Results from the trial were presented by AMC Search Consulting Engineer Gabriel Tooker at Coasts and Ports 2023 and his presentation and full paper can be downloaded for further reading.
Video footage shows the full scale trial underway with the Pacific Mac tug used as a power source to test the performance of rock bag filter units as an alternative to conventional rock armour to provide scour protection against wash generated by bow and stern propulsion units from ships and tug vessels.
The trial showed that rock bag filter units are suitable to be installed as scour protection in berth pockets, around piles and on revetments, as well as revetment armour units in water velocities up to 5.3 m/s with minimal movement.
