Below Grade Beam

I have a 4' wide beam at about 7' below grade. What kind of load should I design the beam for? It seems that considering the whole 7'x4' of soil is quite a lot. Can I assume arch action like designing lintel?

 

[Ron]

Need to know what else the beam is supporting. For only the soil condition, you cannot consider arching as in masonry. Soil type and properties will dictate the loading, but essentially all of the overburden will have to be considered as loading the beam, in addition to whatever other loads are on it.

 

[Rowland33]

You need a soils investigation to depth equal to at least twice the width of the beam below its soffit. Then ask a Geotec for his recommended allowable bearing pressure. After which you will be able to sleep well at nights.

 

The beam is pile supported.

 

[breaks]

Ron is absolutely correct, you cannot assume arching action with soil. In fact, you may want to assume quite the opposite - an extra weight from soil at a 15-degree angle from the vertical on either side of the beam. This 15-degree "slice" of soil is sometimes taken into account when designing cantilever retaining walls and could apply here, depending on the soil characteristics.

At the very least, you should design the beam for the loading from the soil directly above the beam, as well as any additional structure loads.

 

[Rowland33]

If it's pile supported, I agree with' breaks'.