Arching effects for a 0.4MPa lean mix

[HanStrulo]

Hi Everyone

I am designing a soldier pile system for a shoring. I have W beams in 1m diameter lean mix of 0.4MPA. I want to consider the arching effect for the passive calculations but I am afraid the lean mix might be too weak.

Is there any reference (or from your own experience) to the minimum strength of lean mix/concrete that guarantees That the arching factor will be in effect? and that the width used to calculate passive resistance is not just the width of the W beam but the entire 1m diameter?

Thank you very much

 

[EireChch]

We assume arching in most soils, even if its a H pile driven into the ground. A 1m dia of 0.4MPa will definitely provide arching.

Arching is a very real thing that happens in all soils.

 

[hokie66]

How do you proportion 0.4 MPa lean mix? That is not really concrete. Do you have any cement in it at all? That won't provide corosion protection for the steel. 5 MPa is usually the lower limit for something to be called concrete, but that is not structural concrete.

 

[PEinc]

We specify 0.7 MPa (100 psi) lean mix flowable fill for our drilled-in soldier beam projects, both temporary and permanent, unless owner/agency specifications require stronger concrete. We also fill the entire drill hole. Unless the soil around the embedded portion of the soldier beam is soft, we use 3b as the passive width of the soldier beam toe where b is the diameter of the drill hole. Per FHWA's Geotechnical Engineering Circular No. 4, Ground Anchors and Anchored Systems, Sec. 6.5.1, Corrosion and Protection of Steel Soldier Beams and Sheet Piles; "Below the excavation subgrade, drilled-in soldier beams are surrounded by either lean-mix or structural concrete and therefore are not considered susceptible to corrosion." Per Sec. 5.5.2.1, Soldier Beam and Lagging Walls; "For drilled-in soldier beams backfilled with lean-mix concrete, the full diameter of the beam may be used for lateral resistance calculations provided the lean-mix concrete has a compressive strength of no less than 0.36 MPa." FYI, 0.35 MPa = 51 psi. EDIT: This same FHWA section says, "In cohesionless soils and for drained conditions in cohesive soils, passive resistance is assumed to be developed over three times the soldier beam width, b, with a magnitude determined using the Rankine passive earth pressure coefficient."

http://www.PeirceEngineering.com

 

[BigH]

If anyone is interested, there is an interesting paper along these lines in one of the Pan-Am Geotechnical Conferences back in, I'd say, the mid-1960s by John Seychuk. I have the paper somewhere . . . will try to find