A MASSIVE piling rig will drive piles more than 60 metres below the riverbed as part of the new $342 million Nowra bridge project.
Anyone crossing the Shoalhaven River can't have missed the massive metal monsters on the south western side of the river being used as part of the project.
Some of the pylons will be up to 60 metres below the riverbed.
Already a number of pylons have been put into place on the southern riverbank.
Piles create a foundation for the bridge by connecting the piers to a layer of solid rock below and there will be 39 piles for the new bridge and 10 smaller temporary piles to build the foundation of the casting yard on the southern side of the river.
The piling method used depends on the soil or rock type and the load the pile will support.
Piles are generally either bored or driven into the ground using cranes, piling rigs, vibrating or drop hammers.
On the project, Fulton Hogan will be using both steel driven piles and bored piles filled with concrete.
The northern most pier will be constructed using the bored pile methodology.
This method is used as the depth to rock is around 10 metres below the river bed.
Bored piles will involve placing a steel casing, from which the soil and rock within the casing is bored and drilled out and removed.
The casing is then filled with reinforced concrete to provide the load capacity for the bridge.
Driven piles will be required at all other piers across the river, where the depth to rock is up to 60 metres below the riverbed.
Driven piles are built by vibrating and hammering steel casings through the river's sediment layers and into the rock layer deep below the river.
These casings will come in two segments of up to 30 metres in length and welded together during the placement operation.
Once hammered deep below the riverbed, a portion of the river sediment inside the top segment of the casing will be excavated and replaced with reinforced concrete.
After construction of the bridge piles, a reinforced concrete pile cap is placed over the group of piles, from which the pier extends up to the bridge deck.
Land piling has started with river piling due to start in late March 2021 and weather permitting is expected to be complete by late 2021.
Piling activities will occur during standard working hours - Monday to Friday between 7am and 6pm and Saturday between 8am and 1pm.
Some piling activities, particularly during hammering of the piles into the rock, may generate high noise greater than 75 dB(A) - weighted decibels, relative loudness of sounds in air as perceived by the human ear.
These activities will only be carried out Monday to Friday between 8am and 6pm and Saturday between 8am and 1pm.
Where higher noise generating (above 85 dB(A)) activities occur, will be undertaken in blocks of no more than three hours, with at least one hour break before restarting.
Driven piles involve using a vibrator and impact hammer to push the steel case to the required depth.
This activity is continuous, noisy, and vibration will be felt in the surrounding area.
Piling activities may generate noise between 75 and 110 dB(A).
Vibration in the surrounding area will be felt from the energy transmitted through the ground from the piling vibrator and hammer.
The level of ground vibration will vary depending on local terrain, geology, groundwater, weather and the distance from the work.
Ground vibration will generally move faster and at a higher frequency in rock compared to soil and reduces in strength as the distance increases from the work.
Ground vibration is measured by Peak Particle Velocity (PPV) in millimetres per second (mm/s). Ground vibration is generally considered with respect to two aspects: human comfort property impact - either structural or cosmetic.
While everyone's perception and tolerance levels are different, the human body is sensitive to small levels of vibration, with most people able to feel vibration levels under 0.5mm/sec.
A common concern is that ground vibration will cause damage to property and structures. Cosmetic damage, such as small hairline cracks, can occur to residential properties or light commercial-type buildings, when the level reaches about 50mm/s.
Depending on the structure type and condition, structural damage is not expected until vibration levels exceed 100mm/s.
Before the start of construction, property condition reports were prepared for all properties expected to receive vibration from the project.
These reports are used to assist in considering whether property damage has occurred.
Noise monitoring is carried out to assess the impact of construction activities against existing noise levels. This is carried out monthly and for specific activities.
Vibration monitoring is carried out when new work starts and throughout the duration of any work that creates vibration.
Both noise and vibration monitoring will be carried out for all piling work.
The temporary rock platform on the southern side of the river has been completed.
Affectionately nicknamed Fulton Hogan Island by some locals, the platform will provide a working area for bridge piling and foundation work in the southern half of the river, where the water is shallow.
It will allow the piling rig and crawler cranes to operate safely to build the new bridge.
The platform will be removed once the the bridge is completed and some of the material will be reused elsewhere on the project.
During this work the northbound bridge footpath will be temporarily closed due to noise associated with piling, with pedestrians and cyclists detoured onto the southbound bridge path.
Signage will be in place during the temporary closures.
For the safety of workers and river users, there will be marine exclusion zones that will be marked by safety buoys and signage during piling work and pier construction.
Access along the Shoalhaven River will be maintained, with at least one navigation span open at all times during river work.
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