MIL-HDBK-1003/8A
surface water is expected to accumulate and remain for long periods in the
soil surrounding the system.
3.2.3.3
Class C, Moderate. The water table is expected to never be above
the bottom of the system, but surface water is expected to accumulate and
remain for short periods in the soil surrounding the system.
3.2.3.4
Class D, Mild. The water table is expected never to be above the
bottom of the system and surface water is not expected to accumulate or remain
in the soil surrounding the system.
3.2.4
Analyzing Site Classification for Application of Pre-Engineered
Underground System. The Federal Agency Committee on Underground Heat
Distribution Systems has reviewed and approved systems by suppliers. Each
system is defined in the brochure approved by the Committee. No system may be
installed without prior approval as given in the brochure. The letter of
certification contained in the conduit system brochure stipulates the approved
site classification. A system approved for higher classification is
acceptable for use in lower classifications. For example, Class A is
acceptable for Classes B, C, and D, etc.
3.2.5
Analyzing Site Classification for Application of Shallow Concrete
Trench System
3.2.5.1
Soils
a) Fine grained soils (impervious). The highest ground water
level evident during the wettest period of the year should be a minimum of 1
foot (305 mm) below the lowest point of water entry into the concrete shallow
trench system. The lowest point of entry is defined as the joint between the
concrete trench wall and concrete trench bottom. The concrete trench bottom
will be continuous with no openings. The above condition will ensure that
constructability of the concrete shallow trench is practical and that
potential infiltration of water into the shallow trench will be negligible.
Open drainage ways, swales, or swampy/boggy areas will preclude use of a
concrete shallow trench system because of ground water level guidance in Table
5. The concrete shallow trench system must be rerouted or regraded to bring
the concrete trench out of the unsuitable conditions. Have the geotechnical
engineer who performed the detailed site classification survey provide
regrading instructions. The designer will ensure that the fill will remain
stable and will not be subject to future wash-outs. If the specific site
conditions are such that these alternatives are not viable, consider
aboveground low profile or a direct buried system of the prefabricated or
preengineered type in accordance with NFGS-02694 for these areas.
b) Coarse grained soils (semipervious/pervious). The ground water
level during the wettest period of the year should be at least 1 foot (305 mm)
below the lowest point of water entry into the concrete shallow trench system.
21
Previous Page
