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walkereng, Consultant
Category: Structural Engineering
Satisfied Customers: 2943
Experience:  Structural Engineer with over 30 years of experience.
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Ok my question relates to the conversion of a bungalow to a

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Ok my question relates to the conversion of a bungalow to a 2/3 story building.
We plan to place the new floors directly onto the existing foundations for 80% and 20 % will be new foundations for an extension at the back as this would be far cheaper than underpinning or knocking down the property so we want to investigate that fully.
We have measured our foundations and found them to be on average 1 metre being 80cms of brick and 20cms of concrete footing. I don't have the width to the concrete to hand but it is in the region of 15cms.
The soil underneath the property is london clay and seems soft to a novice like me.
We have dug two trial pits and our engineer is asking for a shear vane test which is proving hard to obtain.
My questions are.
1. Do you think it is possible for such foundations to support a second/third story?
2.How important would a shear vane test be in proving that?
3. Is the variation in clay that big that the results would be important.
My questions are
I can help, let me read your question a bit closer
1. Using my judgement, that increase in load on a foundation that was sized for a bungalow could cause problems.2. The shear vane test would be essential to help understand the strength of the existing in place soil on your site.3. There are many types of clay coils with varying characteristics. This would be very cheap insurance to know what you have so you can size footings accordingly.
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Customer: replied 2 years ago.
Many thanks.As you say it could cause problems. With a good shear vane test do you think it is possible that we could show that the existing foundations might be sufficient?

It is possible, but it will all depend on the results of the test. Clay can be very tricky with it's possible shrinkage and swelling characteristics when it gets wet.


Good Luck with your project!