Open Cut - Slope Stability

[slickdeals]

Are there recommended rules of thumb for slopes (1:1, 1.5:1, 2:1, H:V) for different soil types? I have come across an OSHA document that addresses this, but wanted to know if there were others. Are there mathematical ways to calculate it, and if so, what parameters would be needed?

What is the normal practice for benching an open cut? I have seen documents mentioning 1.2m vertical before a bench is required. Are there any good documents that address generic requirements?

 

[cvg]

the best way I have found is to ask a qualified geotechnical engineer to make a recommendation for the excavation slope and any required benches. OSHA regulations are intended for construction safety. Long term stability, operation and maintenance of cut slopes require a more rigourous engineering approach.

 

[RFreund]

To calculate it - you would perform a slope stability (aka global stability if you deal with retaining walls) calculation. However this requires knowing the soil properties (mainly effective friction angle and cohesion). A little cohesion can have a large impact in the calculation so it best to get these values from a geotech.
I'd be curious if there were any 'rules of thumb' for different soils.

EIT

http://www.HowToEngineer.com

 

[Riggly]

CVG makes a valid point: OSHA give these guidelines for construction safety (Sands 2:1, clays: 1:1, silts 1.5:1 (type A, B, and C soils). There is also a height restriction. Beyond a certain depth they recommend a geotechnical engineer. Shallower depth needs a 'competent person'. I had a booklet on benching for construction, but I believe someone borrowed it for take, and I can't remember the author. Anyway, as CVG stated on long term you will need an experience geotech, because knowing the soil parameters and condition affecting the slope stability requires a little experience for reliabilit.

 

[Hoaokapohaku]

You might look at your local grading ordinance. Sometimes local ordinances have maximum allowable slopes based on worst-case soil conditions in that locality with geotech engineering required for anything steeper.