Seems like there are more underground utility conflicts than a decade ago, and they are getting harder to deal with.  One signal mast arm pole foundation within a new traffic signal was not cooperating with standard installation techniques.  We had to work around two adjacent utility trenches that had been backfilled with sand.  There was one trench on each side of the new foundation (with adequate clearance) and the sand was caving into the drilled foundation hole and exposing the utility pipes in the trench.  The utility representative on site insisted that the pipes had to be encased in sand.  

Next we had to deal with the groundwater in the bottom of the drilled hole that caused some of the native material on the sides of the hole to cave into the drilled hole.  This drilled hole, which started as 3’ round, was stated by the City’s inspector to have expanded to over 6’ round because of the caving.  The contractor came up with the idea to fill the bottom half of the hole with 2-sack slurry then re-drill the hole though the slurry.  Then to put a 3' round plastic pipe on top of the slurry, and pour the whole foundation.  I found the clause in Section 49 that validates it near the bottom of page 628:

"To control caving, you may enlarge portions of the hole, backfill the hole with slurry cement backfill concrete"

The plastic pipe was allowed by other paragraphs of Sections 49 and 63.   We ended up with the attached detail.