Page 29 - Trench and Excavation

the bottom dry. Rather, the bottom will be mud. Also, the discharge line must be dumping the
pumped water far enough from the trench that it does not run right back in.

Water Diversion
Water can also enter the trench from the surface of the ground. It can come from a pre-existing
body of water near the trench or from rain run-off. In most cases, this water will be controlled
through diversion and diking. Diversion of water means to re-direct the natural drainage of surface
water in a way that keeps it from entering the trench or weakening the walls of the trench. If an
excavation intersects a stream, the stream can be re-routed by digging an artificial waterway.

Dikes and Berms

Berms also can keep the excavation area free of surface water by placing a barrier between the
excavation area and the surface water. Berms can be used to re-route bodies of water or can be
constructed around the excavation to keep surface water from entering.

The berm should be constructed to resist water infiltration. The use of well-compacted impervious
materials which are free of large rocks or clumps is desired. It should be sloped at a 2H: 1V rate
to prevent sloughing. This means that the width of the dike will be four times its height. Erosion
should also be controlled with an outer covering of rock or riprap.

The berm should be constructed high enough to accommodate all the anticipated water. Water
running over the top of the berm will quickly cause the berm to fail. The height of the berm should
be 1.5 times the anticipated height of the water. Therefore, if a berm is to hold back 2 feet of
water, it should be at least 3 feet high and 12 feet wide.

Stability of Adjacent Structures

Any time excavation operations are close to or under the foundation or footing of an existing
structure, the stability of that structure could be jeopardized. Therefore, when such an operation
is contemplated, the Competent Person must assure the stability of the structure and worker
safety by providing support systems that will assure that the structure will not collapse. That
support may include underpinning, bracing, shoring, cribbing, or some other effective means. This
may also be the time to solicit the advice of the RPE.

The RPE must be consulted if the excavation will involve removal of soil from below a base or
footing of a foundation or retaining wall if that removal could reasonably pose a hazard to workers.
The exception to this is if the excavation is made in stable rock or a support system has already
been provided. In either case, the advice of a RPE should still be sought. Removal of soil from
under a sidewalk, pavement or other surface structure is also prohibited unless appropriate
protective systems are being used.

Underground Installations

Probably the largest, unexpected cost to a contractor is the inadvertent cutting of a utility pipe or
communication cable. Additionally, most insurance companies will not pay for this type of damage
if the location of the utility or cable had not been previously identified. Many explosions have
occurred when natural gas lines are ruptured. It then makes good safety sense and economic
sense to locate utility and communication assets prior to digging.

Trench & Excavation
Competent Person Training P3 Safety Solutions LLC
Page 29