Mr LUGG - 1998-10-13
My question concerns the Adelaide River bridge. I understand there is now an interim report ready from expert consultants, and I ask the minister if he is in a position to outline the reasons why the bridge collapsed and when it might be back in service?
ANSWER
Madam Speaker, I have indeed received an interim report. We are still awaiting the final report from Sinclair Knight Mertz. They were commissioned to investigate the possible causes of the partial collapse of the bridge. They are recognised experts in corrosion and have provided an interim report which indicates that corrosion at a rate of 7 times than expected had completely eaten through the base of at least 2 piles of pier 6 on the Adelaide River bridge.
When the final report has been received the information will be made available to engineers operating in similar areas so that these issues can be addressed in future and similar designs can be taken into consideration in the construction of such future projects.
The interim report details 5 contributing causes that have been identified for the severe corrosion of the steel piles. They are: Abrasion - screen velocities range from 1 metre per second in the dry season to 3.5 metres per second in the monsoon season, and sediments carried by the water have abraded the pile coatings and have continuously removed protection against corrosion as they would have formed, thus accelerating the corrosion. Sulfide mud - mud removed at the bridge site has been significant over the past 30 years. The oxygen rich fresh water of successive flood seasons has carried the mud away from the river bed in the vicinity of the bridge and in doing so has exposed sulphides. Oxidisation has led to the production of weak sulphuric acid which has a direct chemical attack on the piles, and this one here is, and I won’t make the same mistake as I did in the Katherine River where I confused orgasms and organisms, but there is in fact extensive colonies of sulphate reducing bacteria found on the piles. These bacteria cling to the pile steel and seem to be more prevalent on bare steel sections of the pile than the coating sections. They may in fact contribute to the degradation of the coral tar epoxy coating system itself. The by-products of the sulphur reducing bacteria ...
Mr Bailey: Didn’t anyone check for 20 years?
Mr COULTER: No it’s not something that people said: ‘Let’s jump into the Adelaide River and go down and see if we have got any sulphite reducing bacteria alive down there’.
Mr Bailey: So you wait until it falls down …
Madam SPEAKER: Order!
Mr COULTER: The by-products of sulphate - well they do not all have the hindsight that you have.
A member interjecting.
Mr COULTER: Obviously you are a very wise person.
The by-products of sulphate reducing bacteria include a sulphide slime, which is a low pH and, therefore, attacks the steel resulting in large pit corrosion behind the mushroom-like head of each colony. So we actually have a bacteria down there that is eating the steel away. The fourth is the galvanic action within piles which is electrolysis, and the galvanic action between the pile groups.
Madam Speaker, the bridge is expected to be open to all traffic at the end of October. Initially it will be a single lane only, while the new bitumen is laid and linemarking and guard rails are completed, but all works are expected to be completed in mid to late November. What we have now done is to go out and do extensive testing right across the Northern Territory of any structure, anywhere, that is in the ground, including Alice Springs, because of the salt movements within the Alice Springs area. So we have checked water towers and electric piles, electric posts, anything that is in the ground.
We do, of course, have to look at a number of other bridges in the Northern Territory now, as a result of obtaining this information. Bridges like the South Alligator and the Vic River will certainly be tested now that we know what is happening in these areas. They have similar conditions. We do not believe that the same problems would exist, for example, in the Mary River which has more fresh water, it has a different sand, and we think that that probably is not facing the same turmoil as the Adelaide River bridge piles actually faced.
It is interesting and I will make the following comments. I would like to thank all those people who have been working on the bridge day and night to get the bridge opened. They have done a fantastic job. It has cost us a lot more than what we originally thought it would but it really is a tribute to the engineers and the people out there who have dedicated a fair bit of their lives in recent months to getting this bridge opened. But when you are up against a kind of steel eating bacteria - the Northern Territory certainly has some anomalies which you probably wouldn’t find in many other parts of the world.
Indeed this is, I think, the first time that this bacteria has been found in the tropics. It is known to exist in other more temperate regions and this is the first discovery of it here.
ANSWER
Madam Speaker, I have indeed received an interim report. We are still awaiting the final report from Sinclair Knight Mertz. They were commissioned to investigate the possible causes of the partial collapse of the bridge. They are recognised experts in corrosion and have provided an interim report which indicates that corrosion at a rate of 7 times than expected had completely eaten through the base of at least 2 piles of pier 6 on the Adelaide River bridge.
When the final report has been received the information will be made available to engineers operating in similar areas so that these issues can be addressed in future and similar designs can be taken into consideration in the construction of such future projects.
The interim report details 5 contributing causes that have been identified for the severe corrosion of the steel piles. They are: Abrasion - screen velocities range from 1 metre per second in the dry season to 3.5 metres per second in the monsoon season, and sediments carried by the water have abraded the pile coatings and have continuously removed protection against corrosion as they would have formed, thus accelerating the corrosion. Sulfide mud - mud removed at the bridge site has been significant over the past 30 years. The oxygen rich fresh water of successive flood seasons has carried the mud away from the river bed in the vicinity of the bridge and in doing so has exposed sulphides. Oxidisation has led to the production of weak sulphuric acid which has a direct chemical attack on the piles, and this one here is, and I won’t make the same mistake as I did in the Katherine River where I confused orgasms and organisms, but there is in fact extensive colonies of sulphate reducing bacteria found on the piles. These bacteria cling to the pile steel and seem to be more prevalent on bare steel sections of the pile than the coating sections. They may in fact contribute to the degradation of the coral tar epoxy coating system itself. The by-products of the sulphur reducing bacteria ...
Mr Bailey: Didn’t anyone check for 20 years?
Mr COULTER: No it’s not something that people said: ‘Let’s jump into the Adelaide River and go down and see if we have got any sulphite reducing bacteria alive down there’.
Mr Bailey: So you wait until it falls down …
Madam SPEAKER: Order!
Mr COULTER: The by-products of sulphate - well they do not all have the hindsight that you have.
A member interjecting.
Mr COULTER: Obviously you are a very wise person.
The by-products of sulphate reducing bacteria include a sulphide slime, which is a low pH and, therefore, attacks the steel resulting in large pit corrosion behind the mushroom-like head of each colony. So we actually have a bacteria down there that is eating the steel away. The fourth is the galvanic action within piles which is electrolysis, and the galvanic action between the pile groups.
Madam Speaker, the bridge is expected to be open to all traffic at the end of October. Initially it will be a single lane only, while the new bitumen is laid and linemarking and guard rails are completed, but all works are expected to be completed in mid to late November. What we have now done is to go out and do extensive testing right across the Northern Territory of any structure, anywhere, that is in the ground, including Alice Springs, because of the salt movements within the Alice Springs area. So we have checked water towers and electric piles, electric posts, anything that is in the ground.
We do, of course, have to look at a number of other bridges in the Northern Territory now, as a result of obtaining this information. Bridges like the South Alligator and the Vic River will certainly be tested now that we know what is happening in these areas. They have similar conditions. We do not believe that the same problems would exist, for example, in the Mary River which has more fresh water, it has a different sand, and we think that that probably is not facing the same turmoil as the Adelaide River bridge piles actually faced.
It is interesting and I will make the following comments. I would like to thank all those people who have been working on the bridge day and night to get the bridge opened. They have done a fantastic job. It has cost us a lot more than what we originally thought it would but it really is a tribute to the engineers and the people out there who have dedicated a fair bit of their lives in recent months to getting this bridge opened. But when you are up against a kind of steel eating bacteria - the Northern Territory certainly has some anomalies which you probably wouldn’t find in many other parts of the world.
Indeed this is, I think, the first time that this bacteria has been found in the tropics. It is known to exist in other more temperate regions and this is the first discovery of it here.
Last updated: 09 Aug 2016