ᐅ Berlin-style temporary retaining structure for securing the excavation pit
Created on: 21 Sep 2023 10:54
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Bayernbors
Hello everyone,
There are several issues with the excavation at our construction project. The general contractor (GC) says the planned house is large (2 semi-detached houses, each 11 by 7 meters (36 by 23 feet)) and the plot is small (~450 m² (4844 ft²)), which brings some technical challenges.
The work on the excavation started with the demolition of the old house, as it already had a basement.
The worst part is that we discovered all these problems gradually, not as originally planned:
1) First, it turned out that the edges of the excavation were unstable, requiring support for the crane, so a crane foundation was built.
2) Secondly, it was found that the plot was still too small for the crane, and a permit was needed to place the crane partially on the sidewalk.
The first two steps were completed by the end of June, and then work was completely halted (except for the crane setup).
At the end of August, my new neighbors contacted me and were concerned because they saw that the sides of the excavation were slipping more and more, causing the excavation to slope toward their property and compromising the slope’s stability.
At this point, the GC said they had already discussed this issue with the relevant authorities. They suggested increasing the slope of the excavation, but this proposal was rejected because it would affect the sidewalk.
The only remaining solution was then to provide a bond to secure the stability of the sidewalk.
After an additional geotechnical investigation, it was determined that sheet piling is required on all sides, not just along the sidewalk.
My questions are:
Does all this make sense?
Is it normal to discover these issues so late? Does it really take about three months to reach this conclusion? Should I hold the GC accountable for these delays?
Note: At the end of June, I agreed with the GC that the house should be completed by the end of February 2024, as our contract states: “The contractor commits to delivering the project ready for occupancy within 8 months from the start of excavation, weather permitting.”
Finally, how much more time should I expect to complete this Berliner trench sheet pile installation and finally begin construction?
I have read online that the costs could be several tens of thousands— is that realistic?
Thank you very much.
Best regards
There are several issues with the excavation at our construction project. The general contractor (GC) says the planned house is large (2 semi-detached houses, each 11 by 7 meters (36 by 23 feet)) and the plot is small (~450 m² (4844 ft²)), which brings some technical challenges.
The work on the excavation started with the demolition of the old house, as it already had a basement.
The worst part is that we discovered all these problems gradually, not as originally planned:
1) First, it turned out that the edges of the excavation were unstable, requiring support for the crane, so a crane foundation was built.
2) Secondly, it was found that the plot was still too small for the crane, and a permit was needed to place the crane partially on the sidewalk.
The first two steps were completed by the end of June, and then work was completely halted (except for the crane setup).
At the end of August, my new neighbors contacted me and were concerned because they saw that the sides of the excavation were slipping more and more, causing the excavation to slope toward their property and compromising the slope’s stability.
At this point, the GC said they had already discussed this issue with the relevant authorities. They suggested increasing the slope of the excavation, but this proposal was rejected because it would affect the sidewalk.
The only remaining solution was then to provide a bond to secure the stability of the sidewalk.
After an additional geotechnical investigation, it was determined that sheet piling is required on all sides, not just along the sidewalk.
My questions are:
Does all this make sense?
Is it normal to discover these issues so late? Does it really take about three months to reach this conclusion? Should I hold the GC accountable for these delays?
Note: At the end of June, I agreed with the GC that the house should be completed by the end of February 2024, as our contract states: “The contractor commits to delivering the project ready for occupancy within 8 months from the start of excavation, weather permitting.”
Finally, how much more time should I expect to complete this Berliner trench sheet pile installation and finally begin construction?
I have read online that the costs could be several tens of thousands— is that realistic?
Thank you very much.
Best regards
Bayernbors schrieb:
The general contractor has covered one side of the excavation so far, but I’m not sure how useful that really is. For that one side, it helps somewhat. Pun intended: overall, it’s still only a half measure.
Bayernbors schrieb:
She just says that the site is very challenging and something like, “Who could have known about all these problems from the start?” What is the site manager’s professional background?
https://www.instagram.com/11antgmxde/
https://www.linkedin.com/company/bauen-jetzt/
Bayernbors schrieb:
She only says that the plot is very challenging and something like: "Who could have known about all these problems from the start"!Bayernbors schrieb:
After an additional soil investigationWas there a prior geotechnical report? Did the general contractor request one before the demolition? How did the neighbor fare? Did they have one? Was it communicated?
Bayernbors schrieb:
Work on the excavation started with the demolition of the old house, since it already had a basement.Did the basement have to be removed? Could it not have been left in place?In my humble opinion, the general contractor (or main contractor) should have already known what kind of ground they were going to build on. However, obtaining a geotechnical report is the responsibility of the client.
Are you the clients? Or did you purchase the house including the land from the developer?
Eight months is very tight. For your own sake, don’t make the mistake of pushing too hard—and don’t cancel the lease yet.
H
hanghaus202326 Sep 2023 19:19I only see information from the ground investigation report here. There is no planned excavation pit, nor any shoring (sheet piling) planned.
Why? It should be clear to everyone that a guarantee does not solve the problem. It should also be clear to your site manager and you by now that an unsupported excavation pit can and will affect the road. The costs for the repair must be borne by the party responsible.
It would have helped if the problem had been resolved quickly.
Bayernbors schrieb:
That is not entirely clear. What do you think should have been done in this case?
The municipality also closed the roads (fully or partially) because the road’s stability can no longer be guaranteed (at least that is their position).
Why? It should be clear to everyone that a guarantee does not solve the problem. It should also be clear to your site manager and you by now that an unsupported excavation pit can and will affect the road. The costs for the repair must be borne by the party responsible.
It would have helped if the problem had been resolved quickly.
Bayernbors schrieb:
When I check again, it seems the excavation pit has exposed the neighbor's foundation to the east (they appear to have no basement). This is a two-story house on a slab-on-grade foundation. The slab is already cantilevered in the area above the installed membrane below.
The exterior walls rest on it and place bending loads on the slab.
This is a matter of urgent concern, with a risk of structural failure of the house 😱
My summary of what I understood can be summed up in five letters: "nothing" (and even here I am not entirely sure).
The original poster (OP) and their building partner have received a building permit here that I already do not understand: the land register excerpt shows the neighboring house No. 18 on plot 367/21 and the previous building on the OP’s property in a location that suggests the neighbor’s previous boundary setback was applied. I cannot even verify the simple boundary setback to the neighbor here. Then I read about a basement of the existing building, which I do not recall being mentioned in the OP’s previous thread – so this unexpected deep demolition surprised me. I see here an "excavation pit" as if for a basement of the semi-detached house: the slope appears to contain a working space, which seems overly generous to me if it were only for a deep demolition. Not that I assumed the previous building had no basement—but I did assume this for the new building. So I had indeed expected a deep demolition rather than mere backfilling of the existing basement, but then with proper securing using sheet piling or similar measures, of course, to prevent the unintended creation of a working space between the deep demolition and the neighboring boundary. I am surprised that I, as a construction advisor (a professional, but theoretically inclined), am thinking further here than a builder (for whom this should be standard practice). Furthermore, I am surprised that this "excavation pit" might actually be a genuine building pit (for the new basement), because otherwise it should have been filled and compacted immediately or almost simultaneously.
So I am assuming here a regrettably architect-free planning process: that is, they apparently approached a general contractor (GC) who then unrealistically planned the still-built property virtually like a grading layer. If I were at the building authority, I would have at least made the building permit conditional on the submission of a demolition schedule. This looks to me like such a textbook case of deception that I have initial suspicion that the mayor of @goalkeeper might have found a new area of activity here. Ceterum censeo, the tax rate on thoughtlessness urgently needs to be raised.
https://www.instagram.com/11antgmxde/
https://www.linkedin.com/company/bauen-jetzt/
The original poster (OP) and their building partner have received a building permit here that I already do not understand: the land register excerpt shows the neighboring house No. 18 on plot 367/21 and the previous building on the OP’s property in a location that suggests the neighbor’s previous boundary setback was applied. I cannot even verify the simple boundary setback to the neighbor here. Then I read about a basement of the existing building, which I do not recall being mentioned in the OP’s previous thread – so this unexpected deep demolition surprised me. I see here an "excavation pit" as if for a basement of the semi-detached house: the slope appears to contain a working space, which seems overly generous to me if it were only for a deep demolition. Not that I assumed the previous building had no basement—but I did assume this for the new building. So I had indeed expected a deep demolition rather than mere backfilling of the existing basement, but then with proper securing using sheet piling or similar measures, of course, to prevent the unintended creation of a working space between the deep demolition and the neighboring boundary. I am surprised that I, as a construction advisor (a professional, but theoretically inclined), am thinking further here than a builder (for whom this should be standard practice). Furthermore, I am surprised that this "excavation pit" might actually be a genuine building pit (for the new basement), because otherwise it should have been filled and compacted immediately or almost simultaneously.
So I am assuming here a regrettably architect-free planning process: that is, they apparently approached a general contractor (GC) who then unrealistically planned the still-built property virtually like a grading layer. If I were at the building authority, I would have at least made the building permit conditional on the submission of a demolition schedule. This looks to me like such a textbook case of deception that I have initial suspicion that the mayor of @goalkeeper might have found a new area of activity here. Ceterum censeo, the tax rate on thoughtlessness urgently needs to be raised.
https://www.instagram.com/11antgmxde/
https://www.linkedin.com/company/bauen-jetzt/
B
Bayernbors27 Sep 2023 10:26ypg schrieb:
Was there a soil survey done beforehand? Did the general contractor request one before the demolition? I don’t think this was done. I asked the architect and general contractor once at the beginning, but the architect said it wasn’t necessary at that time, and I failed to double-check it later 🙁.
ypg schrieb:
Did the basement have to be removed? Couldn’t it have been left in place? Yes, it is located elsewhere and has a different size.
ypg schrieb:
You are the clients, right? Yes.
ypg schrieb:
Eight months will be very tight. For your own sake, don’t make the mistake of putting pressure on anyone — and don’t give notice on your apartment yet. From other threads, I understood that 8 months is normal if work starts in good weather conditions. My main concern has been that starting too late would be problematic because winter is approaching. I’m not sure when exactly to start counting the 8 months.
hanghaus2023 schrieb:
I only see information from the soil report. No planned excavation pit. Also, no planned shoring (sheet piling). Yes, unfortunately I don’t have a plan for the excavation pit. The shoring hasn’t been planned yet either. I am still waiting for that to be done.
hanghaus2023 schrieb:
Why? It should be clear that a guarantee bond doesn’t solve the problem. It should also be clear to your site manager and you that an unsupported excavation pit can damage the street. The costs for any repairs are borne by the responsible party. Sorry, that’s my mistake. I didn’t understand why “guarantee bond” was being mentioned here, then realized I mistakenly used that term in my first post when I actually meant “shoring” — as in the Berliner wall shoring system 🙄
Nida35a schrieb:
This is a two-story house on a slab foundation; the slab is already cantilevered over the area below the installed membrane. The exterior walls rest on it and apply bending loads to the slab. I’m not sure how much load is involved here as it’s a very old prefabricated house, but it definitely seems risky. I also reported this to the general contractor, but it’s strange that this neighbor hasn’t complained so far!
11ant schrieb:
My summary of what I understand can be summed up in five letters: “nothing” (and even that I’m not quite sure of).
So the original poster and their building partner obtained a building permit that I don’t fully understand. The cadastral extract shows the neighboring house No. 18 on parcel 367/21 and the previous building on the poster’s property in a position suggesting a boundary tolerance assumed by the previous property owner. I can’t even verify the basic setback distance to the neighbor here. Then I read about a basement in the existing building, which wasn’t mentioned in the previous thread — so I didn’t expect a deep demolition. Next, I see what looks like an excavation pit for an underground basement of a duplex: the slope seems to provide workspace, which seems quite oversized if it was just for a deep demolition. I wouldn’t have assumed the previous building was without a basement, but I did assume the new building was. I had therefore expected a deep demolition rather than just filling in the old basement, but obviously with shoring (sheet piling, for example) to prevent unwanted excavation space forming between the deep demolition and the neighbor’s boundary.
I’m surprised that I as a building advisor (a professional but basically a theorist here) am thinking further than a building contractor (for whom this should be routine daily practice). Furthermore, I’m surprised that this “excavation pit” might actually be a construction pit for a new basement, because otherwise it should have been backfilled and compacted immediately or simultaneously.
So I assume this is unfortunately an architect-free planning: apparently, they went to a general contractor who virtually planned the still-built property as a simple construction site. If I were at the building authority, I would at least have made the building permit conditional upon submission of a demolition schedule. This looks to me like a textbook case of misleading incompetence to an extent that I suspect the mayor of @goalkeeper may have found a new area of responsibility here. Ceterum censeo: the tax rate on thoughtlessness urgently needs to be raised. The plan was to complete the excavation pit along with the demolition of the old house including the basement without any waiting time.
Due to poor planning (or entirely absent planning), it became apparent during execution that some additional measures had to be carried out which were not anticipated, so the excavation was stopped midway through the work.
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