Figure 3-9. Structure of a well-graded soil
quantitative determination of soil trafficability are detailed in TM 5-330. A broad overview of those procedures is
discussed in the following paragraphs.
(1) Preliminary Information. Before an in-depth quantitative analysis of soil trafficability can begin,
some preliminary information must be considered.
(a) Conditions for Sampling. Ideally, field sampling of soils for trafficability purposes takes place
under the soil's worst natural condition. If testing under these circumstances is not possible, then the worst
trafficability condition must be extrapolated from data concerning the soil type, topography, climate, and weather.
(b) Identification of Soil Type. Using established field classification or remote collection
techniques, existing soil types are determined according to the USCS.
(c) Identification of Critical Layer. The layer within a given soil profile that has the greatest
impact on trafficability is called the critical layer. As shown in table 3-3, the depth