Flotation calcs.
Flotation calcs.
(OP)
What is the usual flood recurrence used to check flotation of structures? What safety factors are associated with what periods of occurence? Also, can you recommend references that address bouyancy checks?






RE: Flotation calcs.
Once the flood return period is set (say 1 in 30 year flood) then you will have your design water level from your hydrograph. The minimum factor of safety you need to prevent buoyancy at this floodwater level is 1.1. This may seem low, but water is a known fluid of specific density (which changes very little). Also, note that 1.1 is a MINIMUM factor of safety.
Regards
Andy Machon
RE: Flotation calcs.
If there is any water expected, design for water 1/4 of depth of structure below ground surface.
Water may come from burst mains, climatic change etc., so design for the "water expected" situation, or provide external drainage system. Alternatively advise the client against having a basement.
RE: Flotation calcs.
RE: Flotation calcs.
Flood reccurence of say 1:5 is okay. The water table fluctuation will allow u to fix the maximum level. Piezometer can be installed on site for monitoring this.
Depending on the location where u intend/propose to carry out construction, your local meteorolgical dept. will give u sufficient information on flooding propensity.
Water table during any flood allows for 100% saturation of the soil. But water above the ground level assists.
Factor of safety for buoyancy check should be taken as 2.
This takes into account probable rise in gwt.
Resisting forces against vertical upthrust is the weight of the building. For small structures this is sometimes a problem. The upthrust is actually surface area of the building that interfaces with the ground X the depth of maximum water table X 10kN/m3.
For basements, provision of relief drains become important if it has slab on grade with joints.
(Also look for articles or reference on pore water dissipation.)