These images, when put together, show a trench approx 200' long, approx 40' wide, and varying in depth from approx 5' at the west end to maybe 15' near the east end. The pictures are taken facing south as I walked the length of the trench from west to east. The white arrows show the location of the exposed portions of the concrete slurry that houses the conduit.
In order to continue digging without undermining the conduit, NIST plans to drive piles and install legging as retainer for the conduit bank.
For those who are interested, I can arrange a site visit and have NIST review the plan with us. Tentatively, we should do this middle of next week, before construction resumes.