Electricity and excavations

2. Existing utilities that cross the pipeline trench prevent shields
from being pulled forward. Pulling and resetting shields
around crossing utilities is time-consuming plus the area
around the crossing utility has to be shored in some other
way. In pit construction any existing line that crosses through
the hole is enough to prevent use of a shield.
Because most water, gas, and electric installations are
within the top 8 ft of the surface, it is possible to remove the
top shield and pull lower shields under the utilities. Shoring
or sloping still needs to be provided above the boxes.
S h o r i n g S y s t e m s S e l e c t e d f r o m Ta b u l a t e d D a t a 389
9.6.2 Shoring Shield Size and Nomenclature
The basic elements and nomenclature of a shoring shield are shown in
Fig. 9.30. Shoring shields and boxes are described by height × length ×
wall thickness. The wall thickness is nominal. Most shields are constructed
with 3/16-in plate “skin” over tube steel ribs so the actual
wall thickness is nominal size +3/8 in. Standard heights are 2, 4, 6, and
10 ft. Standard lengths are in 2-ft increments from 10 to 32 ft. Wall