a) Take soil resistivity readings along the conduit line (in
accordance with Table 4).
b) A cathodic protection system is required to protect metallic
piping systems and manholes. This applies to all sites where soil resistivity
is less than 30,000 ohms per cubic centimeter (ohm-cm), where stray direct
currents can be detected underground or where underground corrosion, due to
local soil conditions, has been found to be severe.
Soil Corrosiveness Classification. Have an experienced corrosion
engineer make the classification based on a field survey of the site carried
out in accordance with recognized guidelines for conducting such surveys.
Classify the soil at the site as corrosive or noncorrosive on the basis of the
a) Corrosive: The soil resistivity is less than 30,000 ohms-
b) Noncorrosive: The soil resistivity is 30,000 ohm-cm or greater
Soil Stability. During the above survey, observe and note the soil
stability. Use NAVFAC DM-7.01 for criteria. Note areas of unstable soil on
the site plans depicting the distribution route.
Soil Load-Bearing Capacity. As a part of the project designer's
survey, have an experienced soils engineer investigate the load-bearing
qualities of the soil in which the system will be installed. Identify the
location and nature of potential soils problems. Depending on the nature of
the problem, the designer may choose to reroute the line, use a combination of
concrete shallow trench, direct buried, or aboveground low-profile systems, or
elect to over-excavate and replace with nonexpensive fill.
Site Classification. Base selection of the conduit system type on
the underground water conditions at the project site as defined in Tables 4,
5, and 6 for Class A, B, C, or D application corresponding to underground
water conditions ranging from severe to mild, respectively.
Class A, Severe. The water table is expected to be frequently
above the bottom of the system or the water table is expected to be
occasionally above the bottom of the system and surface water is expected to
accumulate and remain for long periods in the soil surrounding the system.
Class B, Bad. The water table is expected to be occasionally above
the bottom of the system and surface water is expected to accumulate and
remain for short periods (or not at all) in the soil surrounding the system or
the water table is expected never to be above the bottom of the system but