Investigation Methods and Procedures - Geotechnical Engineering Investigation - page 37

Preparation is first on a preliminary basis; a final map is prepared after site reconnais-
sance and, preferably, after at least some subsurface investigation. To aid in reconnais-
sance, all significant cuts and other surface exposures should be noted on the map, as well
as areas of questionable conditions.

Assessment of Mapped Conditions
Soil formations : Soils may be geologically classified by their origin and mode of occurrence
(Chapter 7), the engineering significance of which lies in the characteristic properties
common to the various classes. Therefore, if a soil formation is classed in terms of origin
and mode of occurrence, preliminary judgments can be made regarding their influence on
construction.
Rock formations : The various rock types have characteristic engineering properties and
structural features, either as originally formed or as deformed by tectonic or other geologic
activity. When attacked by weathering agents they decompose to form characteristic soil
types as described in Chapter 6. The identification of rock-mass features allows the for-
mulation of preliminary judgments regarding their influence on construction.

Three examples of engineering geology maps illustrate the approach:

1. A proposed new community in a region of glacial soils is illustrated in Figure

2.15. Conditions may be generally interpreted for engineering purposes solely on
the basis of the soil types, classified geologically as follows:
(a) Foundation conditions : RX, GT — good support all loads; GK — good support
moderate loads; GL, GT/GL-possible suitable support for light to moderate

FIGURE 2.15
Preliminary engineering geology map of Bromont, Quebec, Canada. Conditions may be generally interpreted