Expansive Soils

GEOL 4093

Risk Asssessment

Expansive Soils

• Also called shrink-swell soils

• Expand greatly when saturated with water

• Expansion largely due to chemical attraction of water molecules between layers of clay minerals called smectites.

Hydrocompaction

• Expansive clays can also dry out and decrease in volume

• Hydrocompaction is the process of shrinkage and/or collapse from water loss

Expansion of a single smectite grain as a result of the addition of water between clay layers. From Murck et al., 1997, Dangerous Earth.

The type of structural damage that can result from soil expansion beneath a building. From Murck et al., 1997,

Dangerous Earth.

Other Types of Soils

• In addition to expansive clays, other soils can decrease in volume (compact)– Water-saturated organic peat– Sensitive soils

Sensitive Clays. The “house of cards” structure (A) often results from rapid deposition. Structural change (B) can result from disturbance such as shaking in an earthquake (liquefaction). The results is a volume decrease and settling or subsidence. From Murck et al., 1997, Dangerous Earth.

Engineering Geology

• Check out Richard Meehan’s web site

• www.dnai.com/~meehan/rlmce/expan/master.html

• He is an engineering geologist with a great deal of information on the problem of expansive soils and how to deal with it

Typical problems and one solution when dealing with compaction. See www.dnai.com/~meehan/rlmce/expan/master.html.

Dealing with slope problems. See www.dnai.com/~meehan/rlmce/expan/master.html.

Typical setting for future problems, and dealing with it by having deep pilings. See www.dnai.com/~meehan/rlmce/expan/master.html.

Simple load removal can cause expansion problems. This might occur during mining, for example. See www.dnai.com/~meehan/rlmce/expan/master.html.

National Resource Conservation Service (part of USDA) Map, Phoenix area.

National Resource Conservation Service (part of USDA) Map, Tuscon area.

Perhaps the world’s most famous example of problems with compacting soils.