Equation 6.26 should only be used when the pile spacing is equal to or greater then 3D. Using a value
of 3Dto account for the anticipated wedge-type failure of the soil as the pile laterally deflects is probably an acceptable assumption for medium to dense sand. For loose sand, the pile may simply laterally
punch into the sand, much like a punching shear failure for the bearing capacity of shallow foundations
on loose sands. Hence for nondisplacement (i.e., cast-in-place piles) and low-displacement piles in loose
sands, it may be appropriate to only multiply the result from Eq. 6.25 by the width of the pile, or: