15 AUGUST 2005
consisting of a number of excavation and backfilling operations. The excavation material from
the first excavation could be stockpiled for use as backfill in the last excavation. The material
second, etc., phases of the project and thereby eliminate double handing of excavated backfill
for all but the first-phase excavation.
Protection of Exposed Material. If materials that are exposed in areas, such as
walls of a silo shaft, foundation support, or any other area against which concrete will be
placed, are susceptible to deterioration or swell when exposed to the weather, they should be
properly protected as soon after exposure as possible. Depending on the material and
protection requirements, this protection may be pneumatic concrete, asphalt spray, or plastic
membrane In the case of a foundation area, the contractor is required to underexcavate
leaving a cover for protection, as required, until immediately prior to placement of the structure
foundation. Any frost-susceptible materials encountered during excavation should be
protected if the excavation is to be left open during an extended period of freezing weather.
Excavation Record. As the excavation progresses, the project engineer should
keep a daily record of the type of material excavated and the progress made.
Good Construction Practices, and Problems. As mentioned previously, the
problems associated with foundation preparation are greatly reduced by following such proper
excavation procedures as maintaining a dry excavation and planning ahead. The principles of
good foundation preparation are simple, but enforcing the provisions of the specifications
concerning the work is more difficult. Inspection personnel must recognize the importance of
this phase of the work since, if not properly controlled, problems can result.
Stable Foundations. It is most important that a stable foundation be provided.
Thus it may be necessary, particularly in the case of sensitive fine-grained materials, to require
that the final excavation for footings be carefully done with hand tools and that no equipment
be allowed to operate on the final cut surface. To provide a working platform on which to begin
backfill placement on these sensitive materials, it may be necessary to place an initial layer of
Foundations Supported on Rock. If the foundation is to be supported on rock,
the soundness of the exposed rock should be checked by a slaking test (soaking a piece of the
rock in water to determine the resulting degree of deterioration (see paragraph 8-3.2.2), and
visual observation to determine if the rock is in a solid and unshattered condition. If removal of
rock below the foundation level is required, the space should be filled with concrete. A
qualified geological or soils engineer should inspect the area if it is suspected that the material
will deteriorate or swell when exposed to the weather. If necessary, the materials must be
protected from exposure using the methods previously discussed in paragraph 8-4.1.2.