Legislative Council, Thursday 28 September 2023

Ms FORREST question to LEADER of the GOVERNMENT in the LEGISLATIVE COUNCIL, Mrs HISCUTT

In a response to a question I asked related to the Cam River bridge on 14 September regarding assessments of the structural integrity of the current bridge and what, if any movement had occurred – the Leader replied:

The bridge supports have been monitored continuously since November 2022 using remote monitoring that provides an alert if the bridge moves beyond predetermined limits. The monitoring sensors have shown that the south side of the repaired pier has moved downwards by 9 millimetres and that the bridge joint will also have opened up in the colder months as the bridge beams contract.

1. What are the predetermined limits of movement;

2. Beyond these predetermined limits, are there any other tolerance limits or measures;
a. If so, what are these limits or measures;

3. What plans are in place to respond to movements outside these predetermined limits of movement to ensure the safety of all bridge users;

4. Is it expected the impacted bridge joint will close in the warmer months as the bridge beams expand; and
a. Is this monitored to ensure the wider gap is only related to this expected expansion; and

5. Does the contract for the new Cam River bridge require the contractor to ensure the river channel is clear of debris, rock and other materials used during the construction of the new bridge and the remedial action to secure the current bridge when damaged by the flood event?

ANSWER:

1.& 2. Management of the bridge will remain an ongoing process, with further assessments as movement occurs. The department will further review the bridge management plan and assess whether any further action may be required should further assessments occur.

The movement is monitored closely with the remote monitoring system and the bridge movement has stabilised. With the current monitoring indicating bridge movement is as expected, there is no other monitoring or limits identified.

2a. Not applicable.

3. The department’s engineers and consultants will assess the impact on the structure if further movement occurs, considering all factors including:
i. The amount of concrete poured around and below the undermined footing.
ii. The redirection of the Cam River flow away from the repaired pier to reduce the risk of further undermining.
iii. The reduction of vehicle travel speed.
iv. The pier columns capacity noting that they were strengthened to a solid concrete pier wall as part of the repairs.

4. Yes, it is expected the gap will close a small amount with the increase in warmer weather over the summer months.

4a. Yes, the sensors on the beams and pier directly below the joint will pick up any significant movements, which will be reflected in the gap width of the joint above.

5. The construction contractor operates under a Construction Environmental Management Plan, which requires that they avoid or minimise any impacts to the environment, including controlling sediment runoff, monitoring water quality, and protecting flora and fauna within the site including the river. Upon completion of the works and opening to traffic, which is expected in April 2024, the old bridge will be demolished, and the contractor will rehabilitate the site, including removal of all materials used during construction and demolition works.

It should be noted that damage to the existing bridge pier during the October 2022 flood event was caused by fast moving flood waters causing material to be washed out from under one of the bridge piers, not by debris or other materials associated with construction of the new bridge striking and damaging the bridge piers.