Measured Drill Hole Verticality

The verticality of 70 high-quality sample boreholes drilled at 7 sites with a variety of subsurface conditions is evaluated. The depths of the boreholes range from 100 ft to about 1,070 ft. Verticality is expressed as the ratio of the horizontal offset at the bottom of the borehole to the vertical depth of the borehole. The results show distinctly different average values of offset to depth ratios for soil sites and hard rock sites. These differences are discussed, and offset versus depth for the two boreholes with the largest offsets are plotted and conclusions drawn.