Soil shear resistance on burried pipe

[warrenw]

I have a question I was hoping someone could help me with.
What I have is an 18" steel pipe (27 ft. long) that is lying on grade with 9" to 18" of loose gravel fill over it. The pipe will expand due to thermal growth and I need to determine the resistance that the fill will produce.
What I have done is calcuate the weight of fill over the pipe (120pcf) plus the weight of fill on the sloping sides of the pipe (wedge) at an angle of 30 deg. plus the weight of the pipe itself. I assumed that this vertical load will produce a horizontal resistence by a sliding shear friction factor of o.55.
Horizontal Resistance = (weight)*(lenght)*0.55
Does this seem reasonable??
Thanks for your help
warren

 

[ishvaaag]

I assume you try to do normal force multiplied per a friction factor of 0.55. Both your pressure of the soil against the buried pipe and friction factors are rough approximations.

Your friction factor seems not ilogical yet as per AASHTO is not the safe one, at 22 deg at much in table 5.5.5B, or about 0.40

Then, the weight thing may be more, for you have the soil force above and the same plus the pipe's weight as reaction below. This also happens for anchoring plates for reinforced earth.

... yet it is not reliable. Once heating has forced outwards the pipe, arcing action plus chemical binding may cause that the actual friction comes only from the pipe plus content's weight.

Then this better be accounted as a distributed friction along the length.