huangyhg

drilled shaft foundation for sign structures
can anyone tell me what the constant "c" is in equation c13-5 of the aashto standard specifications for structural supports for highway signs, luminaires and traffic signals?
basically, this section illustrates the design of drilled shaft foundations, however, the constant "c" is not defined
out of memory, c usually denotes cohesion and then is taken equal to the unconfined shear strength of the soil, this itself taken half the unconfined compressive strength.
additionally normally 1 or more factors applied to c (reducing the expected cohesion) are introduced to make the calculations that c account reliable.
my copy of that manual doesn't have an equation by that number, however, the 1994 manual shows figure 1.8.2c(4), on page 46, which is a nomograph for computing overturning embedment resistance. in that nomograph "c" is the "post stability factor," and is defined as equal to the column load divided by the soil pressure at the top of the caisson: c=p/s1. i hope this helps to clarify their use of the factor "c."
david
"c" as per the definition is the shear strength of cohesive soil (k/ft2). however, fig. 13.4 (refered to by thaidavid) indicates that "c" is post stability factor and is equal to p/s1. "c" in this case has a unit of s.f.
hence the two constants do not relate.

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