Settlement due to adjacent excavations
Settlement due to adjacent excavations
(OP)
Engineers,
I am looking for references which can provide information about settlements and cracks in structures due to adjacent excavations.
My case is next to a house was made a 8 ft o 10 ft excavation on a loose to medium dense sand material. The wall of the house is 20 ft off the edge of the excavation (surprisely, it was a sloped excavation, looked around 0.8h to 1v, and did not fail).
House owners said they started to notice damages on the house once the excavation was made.
Thanks.
I am looking for references which can provide information about settlements and cracks in structures due to adjacent excavations.
My case is next to a house was made a 8 ft o 10 ft excavation on a loose to medium dense sand material. The wall of the house is 20 ft off the edge of the excavation (surprisely, it was a sloped excavation, looked around 0.8h to 1v, and did not fail).
House owners said they started to notice damages on the house once the excavation was made.
Thanks.





RE: Settlement due to adjacent excavations
I would ackknowlede their concerns and tell them you will get a building surveys to make some measurements. I.e floor plane survey, crack monitoring.
What type of foundations is it on? Where is the water table, any dewatering? How long is it was the excavation open for?
RE: Settlement due to adjacent excavations
The occupants probably paid more attention to cracks and other anomalies that already existed in the structure but went unnoticed.
Cracks can often be evaluated for their cause and, to some degree, their age. I have seen this many times over the years. Some are legitimate....most are not.
RE: Settlement due to adjacent excavations
EireChch,
Using a phi of 26 deg (N between 6 and 12), 45 + phi/2 (measured from the horizontal), is 58 degrees, which results in about 4 feet of the wall. I don't think it is that far.
There is a separate team working on the measurements, such as floor survey and crack monitoring.
The foundation is a simple concrete wall footing (continuous footing) on top of a stem wall. No dewatering, WL was no detected in 10 feet borings. The excavation was open for about 1 month.
Ron,
I agree with you, many homeowners react to these situations once they notice something weird is going on next to their properties. But this is not the case. What happened was contractor did the excavation but halfway they noticed few cracks were showing up at the adjacent house, then contractor decided to back fill the excavation in order to avoid more damages.
I got few more questions:
1 - Other than the 45+phi/2 approach, in order to know if the footing would or would not notice there was any excavation nearby, there are few other approaches such as
a) Bousinnesq pressure isobars (I did a quick check and using this one the footing would not be affected by the excavation) and
b) the 45 deg method which is drawing a 45 deg line from the edge of the footing and check if it intersects the excavated wall (in this case, i did a quick calc, and it is about 10 feet below the bottom of the excavation).
2 - How would you take into account the time in which the excavation was open?. I mean, what is the difference is the excavation is open for 1 month and for 1 year?.
RE: Settlement due to adjacent excavations
Best to avoid by doing a pre-construction review of adjacent structures.
Dik
RE: Settlement due to adjacent excavations
RE: Settlement due to adjacent excavations
Dik
RE: Settlement due to adjacent excavations
RE: Settlement due to adjacent excavations
58 degress from horizontal results in top of failure wedge being rougly 13ft from the adjacent structure. You have measured from vertical.
RE: Settlement due to adjacent excavations
No WL level detected in 10 ft deep borings. I am sure Water table is not that far from the 10 feet depth. No dewatering operations were performed.
EireChch
You are correct, it is 13 ft off the structure, so should be fine.
Just to confirm, Would you also use Bousinessq pressure charts in order to verify if stresses could be felt by the adjacent structure?. or with the 45+phi/2, measured from the horizontal, you think it is more than enough?.
RE: Settlement due to adjacent excavations
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RE: Settlement due to adjacent excavations
RE: Settlement due to adjacent excavations
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RE: Settlement due to adjacent excavations