Environmental Engineering Reference
In-Depth Information
Figure 3.12.
Variation of unconfined compressive strength of schist with angle between the foliation
planes and applied loads (Trudinger, 1973).
occurred in the samples loaded at about 45° to the foliation. This result is typical of schis-
tose rocks.
3.4.2
Weathered products and profiles developed in schistose rock
Schistose rocks vary widely in their susceptibility to chemical weathering. Varieties rich in
quartz are very resistant and, at the other extreme, rocks rich in clay minerals or chlorite
are very susceptible. Because of this, no typical weathered profile exists for all schistose
rocks. However many schistose rock masses consist of layers (parallel to the foliation) of
varying susceptibilities to weathering. Thus weathering often tends to exaggerate the
strength anisotrophy of such masses and the upper surface of fresh rock often has a deeply
slotted or serrated shape, as shown in
Figure 3.13
.
Schists which are rich in micaceous minerals (biotite, muscovite or chlorite) tend to
form micaceous silty or clayey soils when extremely weathered. The silty varieties are
often of low
in situ
density and are highly erodible by water or wind. Also they tend to be
hydrophobic, making dust control difficult on construction sites.
Even when fresh or only partly weathered, the more micaceous, fissile schists usually
produce much dust due to abrasion during handling and trafficking.
