Stressors and Soil Contamination - Sustainable Practices in Geoenvironmental Engineering - page 33

• Other actions classed under the hydraulic stressor grouping could include those
associated with loods, droughts (lack of water as a hydraulic stressor), exces-
sive rainfall and water availability detrimental to agricultural productivity, etc.
(adverse impact).
2.2.1.2 Mechanical
The common types of stressors included in the mechanical group that act on soils are those
that produce pressures and stresses in a soil mass. Natural stressor sources are earth-
quakes and avalanches, whereas anthropogenic sources include those activities associated
with resource exploitation, agroindustry, primary and secondary industries, constructed
facilities, and activities related to urbanization. The impacts generated by the stressors in
the mechanical group include (Yong et al., 2012):
• Direct loading from a solid mass such as an overlying structure, e.g., a bridge abut-
ment and foundation footings for a structure, or facility. Resultant effects in the
affected soil include.
• Collapse of overlying structure due to failure of the soil to support the applied
load (adverse impact).
• Settlement of the overlying structure due to consolidation, secondary com-
pression, and/or creep of the supporting soil (adverse impact).
• Pressures on a soil mass as a result of actions related to water movement, e.g.,
swelling pressure in conined swelling soils, loss of bonding in collapsing soils,
and pressures developed in the soil in unstable slopes.
• For swelling soils under overlying structures, swelling pressure could under-
mine stable support of the structures, thereby causing collapse of the structure
(adverse impact).
• For collapsing soils, sudden or gradual loss of particle bonding mechanisms
will result in collapse of soil structure.
• For unstable slopes, instability of the slope will result in slope movement or
slope failure (adverse impact).
• Soil freezing and frost heaving pressures resulting from formation of ice lenses.
Although these impacts can be reckoned as the results of stressors classifying under
the thermal group, their inclusion in this portion of the discussion shows that not all
stressor sources reside solely in one single category. The consequent effects of soil
freezing and developed frost heaving pressures are, in a manner of speaking, similar
in principle to those experienced with swelling soils. In the case of ice lens formation,
the consequent effects from subsequent thawing of the ice lens can be severe if ice
lenses formed in the freezing stage have created signiicant frost heaving in the soil.
2.2.1.3 Thermal
The thermal group of stressors generate heat or cooling in soils. The natural stressor source
is the summer-winter cycle. A signiicant anthropogenic source is canisters containing
high-level radioactive wastes embedded in underground repositories generating heat over