Analysis of Rock Tension Anchors for Mat Foundation

[MrEngineerUS]

I have been tasked with analyzing a mat foundation of a rectangular concrete tank (about 130'x125'x16' tall). The issue is half the tank will be filled during service and rock anchors are installed along nearly all the wall locations (including interior walls) to guard against buoyancy. The tank is bearing on a layer of compacted stone over rock.

I'm having trouble determining an accurate approximation of the pressure distribution and anchor tensions for this offset loading condition. I initially thought I could look at this as if it were a pile group (just analyzing for tension instead of compression in the anchors). However, with a typical pile cap the piles can take both the tension and compression reactions. In this case, the anchors take tension but the mat can be assumed to resist the bearing pressure as it normally would. In addition, the fact the anchors are not on a uniform grid but follow the plan of the wall layout makes it more challenging as well.

So, it seems as if it is more of a bearing plate/anchor bolt type analysis to me but I'm not sure where to start. Does anyone have any advice or references they can provide?

Thank you!

 

[PEinc]

To resist tank buoyancy, the tiedown anchors should be spread over the area of the mat slab. This will reduce the required thickness and reinforcing steel in the mat. If you place the tiedown anchors only under the tank's walls, the mat slab will need to be strong enough to span the width and or length between walls. Spanning between wall requires a much stronger mat slab than if the tiedown anchors are spaced about 10 to 15 feet on center over the mat area. Either way, the total anchor force needed to resist uplift will be the same, as should the total number of anchors.

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