Shoring Requirmenets for Building Excavation

[SiPaul]

We have a plan to excavate to a depth of about 7' below grade for building foundations. The excavations are 45'-70' wide and about 10' from a roadway. They are from 70'-200' long (one of the sites will be a multi-family complex). The buildings are slab-on-grade and the deep excavations are really to compensate for soft soils.

This is, of course, not a trench situation but I would assume that OSHSA requirements for excavations over 4' deep would apply. Is there any situation where shoring (or benching, sloping,et) would not be required? Could we fill to within 4' of grade and remove the shoring?

Also - the proximity to the roadway may be a concern. We are planning for, at a mimimum, saftey fence but would chain link be more appropriate for fall protection and general pedestrian safety? Would jersey barriers be required to 'protect' or vehicular traffic? Any standards for barriers between construction sites and pedestrian/vehicular traffic.

 

[singingk]

You have to give more informations about the ground and groundwater situation before anybody can give you further advice.

 

[SiPaul]

We anticpate groundwater around 7-9'. This is from the soil borings.

 

[singingk]

What are the results of the borings concerning the ground? You posted 'bout some soft strata above..

 

[PEinc]

You asked, "Is there any situation where shoring (or benching, sloping,et) would not be required?"

Yes, you would not necessarily need sheeting if you can safely open cut the site according to OSHA regulations.

Check local DOT standards for traffic barrier requirements. However, as singingk said, you have not provided enough information for anyone to give you proper advice.

 

[SiPaul]

The soil borings have generally classified the material as "fill" typical of an urban area. We have had other excavations where the soil was generally soft. In some places it was quite weak but the contractors were able to excavate without shoring. They may have been down 9-10' without any shoring (we were not overseeing construction for that area).

I have been around numerous excavations where the contractor has taken upon himself the work without any substantial shoring. This is bad practice, but it does give rise to a practical question of when, if at all, one could safely excavate in these conditions. It would seem a question of degree of risk (and not a safe gamble!), for a contractor to undertake any work without proper shoring. I could see in a rocky situation that it may be possible, but given the soft soil it defies logic that the excavations could stay open for any appreciable amount of time.

 

[civilperson]

Remote controlled and wire directed machines allow unbenched excavations by keeping the workers out of the excavation.

 

[Riggly]

Excavation support is NOT required, except you are limited by right-of-way or other obstruction, and provided that the excavation is less than 20'(>20ft must require design by engineer). However,if you are not using shoring, OSHA's requirement is that you must cut back the slope or bench in accordance to whether the soil is Class 'A', 'B' or 'C' soils. Note if the soils are layered, each layer has to be benched at least to the maximum allowable slope. In addition there must be ladders placed at least 25' for egress.

http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=STANDARDS&p_id=10932

 

[GrumpyG]

Many times I have tried to minimize the amount of shoring on a project. With a tight site condition, the room gained by shoring becomes a valuable and necessary area for stocking materials. Attempting to save money on shoring also may result in an unsafe condition.

 

[Mickney]

How did the geotechnical firm determine the consistency of the "soft" soils? If strictly based on SPT testing, the close proximity to groundwater may have impacted the SPT testing. I practice in the Piedmont and many times our competitors go strictly on blow-counts alone. When SPT testing is performed close to groundwater, the high soil moisture sometimes yields a lower SPT value than the actual soil strength. We usually supplement our SPT testing with shear-vane or pressuremeter testing in these situations.

Anyway, for the question of shoring or not shoring, engage your geotechnical engineer to run slope stability analysis for various side slope configurations. Specialty laboratory testing will be required. Use OSHA requirements for the starting point for slope configurations.