Hi,
I am just looking for some thoughts on a project that I am working on. I am involved in the construction of a large football stadium. The stadium is being constructed on poor quality ground and underneath the structure has been piled.
The stadium has 16 lift shaft cores located around the pitch.Initially the main survey company on site established bench marks on 2 of the cores, the first 2 to begin construction. The benchmarks were traversed into site form know datum. However since the start of the job (12 months) these 2 cores have dropped 25mm and the RL of these bench marks has not been updated. The proceeding 14 other cores were traversed into site as per the original method. These cores have settled to varying levels with the minimum settlement being 10mm. The main survey company is using the marks located on the cores as the issued primary control to the other survey companies onsite. This essentially means that there would be up to 15mm discrepancy between 2 vertical control marks. We have been told by the client surveyor to blend the 15mm out between the cores through the structural steel.
A surveyor for the company I am involved with however does not think this is correct and as the stadium continues to settle we keep updating the benchmarks. Every time we update the benchmarks however we are in essence 'stretching' the building as all of the steel that we have installed up until now becomes low every time we update.
Has anyone any thoughts on this? Thanks in advance.
LODGER87, post: 373624, member: 11742 wrote: Hi,
I am just looking for some thoughts on a project that I am working on. I am involved in the construction of a large football stadium. The stadium is being constructed on poor quality ground and underneath the structure has been piled.
The stadium has 16 lift shaft cores located around the pitch.Initially the main survey company on site established bench marks on 2 of the cores, the first 2 to begin construction. The benchmarks were traversed into site form know datum. However since the start of the job (12 months) these 2 cores have dropped 25mm and the RL of these bench marks has not been updated. The proceeding 14 other cores were traversed into site as per the original method. These cores have settled to varying levels with the minimum settlement being 10mm. The main survey company is using the marks located on the cores as the issued primary control to the other survey companies onsite. This essentially means that there would be up to 15mm discrepancy between 2 vertical control marks. We have been told by the client surveyor to blend the 15mm out between the cores through the structural steel.
A surveyor for the company I am involved with however does not think this is correct and as the stadium continues to settle we keep updating the benchmarks. Every time we update the benchmarks however we are in essence 'stretching' the building as all of the steel that we have installed up until now becomes low every time we update.
Has anyone any thoughts on this? Thanks in advance.
This is in the UK? It doesn't cast us in a good light!
Holding settling benchmarks will only cause confusion, to say the least. How can you ever do an as-built properly?
I am assuming there are cast in plates in the cores that have cleats (angle brackets) welded onto them and they then receive the steelwork.
1) Maintain benchmarks in stable positions, outside the stadium
2) Precise level in and monitor the settlement of the cores. Update benchmarks inside regularly, issue to subbies in writing ,and dated.
3) As-built cleats and other cast in items from benchmarks regularly transferred in from outside with the caveat that they are susceptible to settlement of the core. The benchmarks used and the date and values used should be recorded with the as-built.
4) Main contractor's surveyor should then issue new levels for any construction if required (in writing, and dated). He/she can then do as much "blending" as they want.
None of the above will happen though as the main contractors surveyor would then be taking responsibility and liability for any problems caused by the differential settlement. They will happily let you do it on a verbal, and you pick up any problems.
squowse, post: 373629, member: 7109 wrote: This is in the UK? It doesn't cast us in a good light!
Holding settling benchmarks will only cause confusion, to say the least. How can you ever do an as-built properly?
I am assuming there are cast in plates in the cores that have cleats (angle brackets) welded onto them and they then receive the steelwork.1) Maintain benchmarks in stable positions, outside the stadium
2) Precise level in and monitor the settlement of the cores. Update benchmarks inside regularly, issue to subbies in writing ,and dated.
3) As-built cleats and other cast in items from benchmarks regularly transferred in from outside with the caveat that they are susceptible to settlement of the core. The benchmarks used and the date and values used should be recorded with the as-built.
4) Main contractor's surveyor should then issue new levels for any construction if required (in writing, and dated). He/she can then do as much "blending" as they want.None of the above will happen though as the main contractors surveyor would then be taking responsibility and liability for any problems caused by the differential settlement. They will happily let you do it on a verbal, and you pick up any problems.
Thanks for the response squowse. You hit the nail on the head. It is causing huge confusion especially as the main contractor has their head in the sand and doesn't want to know about it.
The main contractor surveyor has been monitoring the settlement of the cores twice monthly and the survey data shows on average 2-3mm settlement on the cores each month. We are in a situation now though where we are installing pre-cast stairs adjacent to the cores which have had the most settlement and the steel has been installed for 6 months. Due to this we are having to place additional packers to get the stairs up to design level. The client are asking for reasons as to why the steel is low even though they are aware of the settlement. As you stated above we are being very diligent in recording what control was used and what date.
It just can become a little frustrating when you have a client that knows there stadium is sinking but is surprised when you tell them something is low?!
Document everything and send your data to the Engineer of record. Bring your reports to him/her with a cup of coffee every morning. Be the most irritating June bug you can be. Buzz in his ear every waking moment until this is addressed.
Nobody will remember whose fault this is. Everyone will remember who was on the team. Make them fix it or remove yourself from the project.
I highly agree. This is an issue for the structural engineer... redesign may be needed. Provide the data in a clear format, explain it to them as best you can, wait for their direction. Get yourself out of the decision making loop, put it where it belongs.
This is more a geotechnical problem, and the structural engineer will likely have to burden the headache the most.
These vertical problems will haunt the project persistently.
"wait for their direction. Get yourself out of the decision making loop, put it where it belongs." Big amen to Mr. Ehlert's advice.
