ABSTRACT
Soil strength can occur in various forms or expressions, such as compressive strength, shear
strength, and tensile strength, etc. There are many different soil strength measurement tech-
niques, most of which originate from a specific applied soil test requirement. Soil tillage
operation will often include a number of directional forces that the soil’s strength resists until
it breaks. The compressive strength resists tool insertion, the shear strength resists action of
crushing soil by lateral forces, and the tensile strength resists the breakage of soil, which involves
pulling it apart at the edge of tillage tines. While the ability of the soil to sustain traffic or support
a building relates to compressibility and compressive strength, as discussed in Chapter 59, the
soil strength associated with root penetration or tillage tool resistance can be conveniently
ascertained by a penetrometer, which measures penetration resistance of a device inserted
in the soil (most often a vertically oriented measure). The strength of soil to resist landslide
and some forms of erosion, for example, is better expressed by techniques that explicitly
measure the shear of the soil (a planar measure), such as standard sheargraph techniques.
