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StructuralEng
StructuralEng, Consultant
Category: Structural Engineering
Satisfied Customers: 6689
Experience:  Structural Engineer
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Should a structural engineer check what services are underground

Customer Question

Should a structural engineer check what services are underground before making a recommendation for the type of foundation to be used for a house build project?

Who is responsible for sourcing an underground services infrastructure plan, at what stage of the project? A domestic new build in Scotland.

Should this be sourced for every building project where groundworks are planned?

The structural engineer was engaged by the architect on our behalf as the developers

The architect acted as our agent from feasibility through to final payment to the builder

Trial pit investigations were done and a desktop evaluation for old limestone workings in the area to establish mineral stability of the site

A topography survey was done, again instructed by our architect

Thank you
Submitted: 3 years ago.
Category: Structural Engineering
Expert:  StructuralEng replied 3 years ago.

StructuralEng :

Hello.

StructuralEng :

I can help

StructuralEng :

The engineer should be made aware of what services are in place, but he would not be finding this out on his own. This would be provided to him.

StructuralEng :

This could come from the architect or the civil engineer, it really depends how the contract is written and what is in each person's scopes.

StructuralEng :

scope

StructuralEng :

For a house, though, I don't think it would make much of a difference. You would not really be building a house on deep foundations. It would be either a mat foundation or strip footings.

StructuralEng :

With either one, getting utilities through, or under, the foundation is not really a problem.

StructuralEng :

Unless the utilities are existing, then it's another ballgame.

StructuralEng :

And someone needs to figure that out, but it's not the structural engineer.

StructuralEng :

If you could rate my answer, I would appreciate it. I'll be happy to answer additional questions on the topic.

Customer: Thank you. I wrote to the institution of engineers to ask if an underground services infrastructure plan should be obtained or referred to by an engineer is such circumstances, mainly before doing trial pit investigations. They replied to say it is common practice to check this prior to any invasive ground works, including trial pits. The trial pits were dug down to 2 metres.
Customer: Hopefully you just received my reply?
Customer: to add to that, we did not have a civil engineer on site, only the architect. The architect contract with us consisted of him carrying out steps 1-8 of the RIAS scale. From feasibility stage which we would sensibly assume to be classed as fact find of clients requirements and any constraints to build on the site.
Customer: It was discovered when we requested connection via Scottish Water that there is a 685mm public sewer pipe running along side the structure, running below foundations in one corner.
Customer: if the structural engineer is employed to provide preparation of details and design certification for submission to the local authority and is therefore recommending the type of footings or foundation to be used, he should surely need to know what existing services ran below?
Customer: as the architect didn't obtain anything to check under ground etc, I can only assume this wasn't provided to the s/e to help him make an informed decision, nor did he request that information. The same applies to the trial pits?
Customer: also, we have had to have a geo-technical engineers opinion about the threat of load bearing from the structure to the sewer and threat from sewer to structure. He would not do a borehole without checking for u/ground services - he said it would affect insurances - surely the same applies to trial pits?
Customer: had the sewer been identified,a raft foundation rather than strip could have been recommended meaning Scottish water and the planning office may still have permitted the build. As it is, the property is complete, we cannot source indemnity so cannot sign Scottish waters retrospective build over agreement as we can't comply with the conditions. With the sewer in place, the property is worth nothing to a future purchaser. Scottish water can apply to have the structure removed.
StructuralEng : Is there any way you can have the sewer line reroute s around the property so the foundation system is not a concern? What about underpinning the strip footing to provide more of a raft foundation under that area of the home?
StructuralEng : it sounds like a difficult situation.
StructuralEng : Or possibly adding micropiles installed with grade beams to support the strip footing, taking the pressure off the soil. It's a big added expense, but could make the building useable. There has to be some fix that is acceptable to the sewer authority.
Customer: We are almost at the point, after 2 years of stress and trying to do as much investigation as we can for ourselves due to lack of funds, where we have no choice but to seek permission from SW to re-route the sewer. We know they won't want to be bothered but if we fund the re-route which if in line with level of indemnity requested, could be £50-70,00, we hope they will agree. There may of course be a technical reason why the can't but as they specifically asked for cover for all of their costs including this amount in case re-route had to b done if the sewer collapses we would expect this to be logistically possible.
Customer: the sewer is 3 metres from the south east corner if the house, buried 7 metres running along diagonally to below the middle of the foundation in the north east corner at a depth of 10 metres. The strip footing is re-I forced to 1500 at that corner as there is a retaining wall.
Customer: it is not a straight forward site but we built in th garden of our existing house and there is circa 15 metres between the two properties. There is manhole access probably 20 metres to the south, across a stream. The sewer pipe runs below the screen.
StructuralEng :

At least it sounds like you have a direction forward. Even if it's an expensive direction, hopefully it will get you out from under the situation.

Customer: i did ask questions about kind of underpinning or re-in forcemeat at the outset but it fell on deaf ears.nif we really find ourselves with no option to re-route we will explore your ideas - I suspect the cost will be similar to the re-route.
StructuralEng :

Underpinning is an expensive process. Adding piles and grade beams is also an expensive process. They are options out of a difficult situation, but they do cost quite a bit.

Customer: i don't know if you have any experience of sewers, but we were thinking we should try to find some kind of consultant sewer technician to perhaps look at he sewer plans and advise whether it would be possible to re-route initially and then approach SW with a proposal. W would also us this person to engage the approved SW contractors and over see the project. An added cost but we are worried that if SW say no to us we have no knowledge whether it is technically possible and we could be charged any amount which could escalate a the works progress. Do you think this would be worth considering?
Customer: coukd you p,
StructuralEng :

I always recommend engaging a professional (not a contractor) for your own peace of mind. An engineer has no vested interest in having you pay more than necessary for the work.

StructuralEng :

I don't do anything with sewers, but I'm sure a civil or mechanical engineer could help you.

Customer: please answer my question about whether th s/e providing his services for preparation of the building warrant would include the type if foundation to be used. If yes, do you agree that he would need to make a fully informed decision and therefore should have needed to know what was underground?
StructuralEng :

The SE would typically design the foundations based on recommendations from a geotechnical engineer for the foundation type. The SE generally has a good idea of what type of foundation is needed, and is in line with the geotechnical recommendations. The SE can't make assumptions about what is underground. He is relying on others who have knowledge of this to alert him. It would generally be the responsibility of the prime contract (usually the architect) to find out himself or engage someone to find out.

Customer: going back to the sewer, it's the restricted access that SW are concerned about. Our structure is of negligible threat to the sewer but we have no control over the sewer collapsing. Their build Over agreement includes a standard security condition that virtually means their permission would have to be granted to a lender which in this market basically kills any re-sale - even if we could sign the agreement th value is severely impaired. Who wants to live in a house that could collapse to one side at any time?
Customer: going back to your last comment - there is no mention of a geotechnical engineer being used by the s/e. although there was a comment about soil tests being required. When w questioned the architect in person, he said our solicitors, the planning office should have made checks and we should have told him. He seemed to think the topography survey was sufficient for his purposes as it would have shown manholes. What I don 't understand is how can it be deemed safe to place a design and thrn a building on a plot of land without checking if there are not just sewers but power lines and other hazards below ground? Surely this should be a fundamental part of the feasibility process but I can't find anyone who simply can say - yes if course that needs to be done other wise there coukd b a health & safety issue and xx should have done it - even if that someone should have been me I just need to know.
StructuralEng :

In the US, you're supposed to call the utilities before any digging happens to find out where things are. If you don't do it, you really own whatever problems come up.

StructuralEng :

I would expect the prime contract to take the lead on this.

Customer: i think it will come down to a court decision because even if this isn't something that would be done ordinarily, the architect asked on first visit if we knew what was underground - we said we had no clue but brought to his attention our concerns about a virgin media cable that was only a couple of inches below ground. As he asked this question specifically I believe he had a duty if care to investigate but that is just my view. Planning have explained why they did not consult with SW and this has been accepted as correct. I think the architect just assumed that as planning had been granted on the plot 25 years earlier everything was ok. But actually this matter should never have reached even step 2 which is the design because there were constraints to building on the site, had that been discovered by the professional we employed. Sorry to go on but you can imagine how terrible this is for us. I coukd never have imagined I would be in a situation where I would hope and pray that someone would want me to pay out £50,000 to make a problem go away.
StructuralEng :

He dropped the ball on that one.

Customer: Thank you for listening and for your replies.
StructuralEng, Consultant
Satisfied Customers: 6689
Experience: Structural Engineer
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