surface and foundation distresses caused by shrinking and swelling soils remain
a national issue. These distresses are
due to changes in soil moisture content caused by three primary sources:
evaporation, transpiration, and water table fluctuations. Expansive clay is particularly vulnerable to
changes in moisture content, which results in shrinking during drying cycles
(desiccation) and swelling during wetting cycles (recharge). Reduced rainfall, higher ambient
temperatures, lower vapor pressure, and wind speed influence the rate of soil desiccation
during the summer months, generally reaching maximum drying in September. The moisture lost during the summer drying
cycle is generally replaced, except in times of drought, during the winter
months and reaches its recharge maximum in the spring. When trees, shrubs, and other vegetation are
present, an additional moisture demand results from transpiration, which is the
transport of water through plants from the roots to the leaves and into the
atmosphere. The transpiration period
begins during the spring and peaks during the summer months, which adds to the
desiccation caused by evaporation. The
process of evaporation and transpiration together is called evapotranspiration.
When yearly rainfall is insufficient, a
zone of permanent desiccation is created, which causes a creep-like effect
where the soil does not return to its original volume resulting in permanent
Moisture changes result from extreme weather events and seasonal variations and these
changes can be worsened by roadway construction procedures such as altering
drainage patterns, eliminating surface water retention areas, constructing
pavements during the dry season, constructing an impermeable surface alters subsurface
evapotranspiration patterns, chemically
stabilizing the soil, planting high water demand vegetation, and constructing
dense embankments with impermeable clays to seal the slopes. As subsidence continues, a point is reached
where the pavement structure and embankment yields and surface distresses such
as cracking and faulting occur generally beginning at the edge of the outside
wheel path and progressing outward towards the shoulder. While some research has been conducted, there
is a great need for assessment guidelines for soil characterization,
environmental factors, and the stress state of the pavement system coupled with
cost effective methods to mitigate shrink/swell distresses.
Nelson, J., Miller, D. (1992). Expansive Soils, Problems and Practice in
Foundation, and Pavement Engineering, John E Wiley and Sons.
Vipulanandan, C., Addison, M., M. Hansen,
(2001). Expansive Clay Soils and
Vegetative Influence on Shallow Foundations: Proceedings of Geo-Institute
Shallow Foundation and Soil Properties Committee Geotechnical Special
Publication Number 115, American Society of Civil Engineers,
Department of the Army USA. (1983), Foundations in Expansive Soils,
Technical Manual TM 5-818-7, September 1983.
Biddle, P.G.. (1998). Tree Root Damage to Buildings, Volumes 1 and 2, Willomead
Roberts, J., Jackson, N, and Smith, M.
(2006). Tree Roots in the Built
Environment, TSO Publications.
Freeman, T., Driscoll, R., and Littlejohn, G.
(2002). Has Your House Got Cracks?,
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McPherson, E. (2000). “Expenditures
Associated with Conflicts between Street Tree Root Growth and Hardscape in
California”, Journal of Arboricultural, 26:
E.G. and Peper, P.J. (1995) Infrastructure repair costs associated with street
trees in 15 cities. In Trees and Building Sites. In Proceedings of and
International Workshop on Trees and Buildings (G.W. Watson and D. Neely eds.),
pp. 49–64. International Society of Arboriculture, Savoy, Ill, USA
E.G. and Peper, P.J. (1996) Costs of infrastructure tree damage to
infrastructure. Arboricultural Journal 20, 143–160.
McPherson, E., Simpson, J., Peper, P., and
Xiao, Q. (1999). “Benefits-Costs Analysis of Modesto’s Municipal Urban Forest”,
Journal of Arboriculture, 25:
McPherson, E., Costello, L., Perry E., and
Peper, P. (2000). Reducing Tree Root
Damage to Sidewalks in California Cities, Division of Agriculture and
Natural Resources, University of California.
Randrup, T., McPherson, E., and Costello, L.
(2001). “A Review of Tree Root Conflicts with Sidewalks, Curbs, and Roads”, Urban Ecosystems, 5:209-225, Kluwer
Crow, P. (2005). The Influence of Soils and Species on Tree Root Depth, Forestry
Kopinga, J., (1994). “Aspects of the Damage
to Asphalt Road Pavings caused by Tree Roots”, Proceedings of the International
Workshop on Tree Root Development in Urban Soils, Published by the
International Society of Arboriculture, 165-178, ISBN/ISSN 1-881956-06-7.
Kristoffersen, P. (1998). “Designing Urban
Pavement Subbases to Support Trees”, Journal
Kristoffersen, P. (1998). “Growing Trees in Road
Foundation Materials”, Arboricultural
MacLeod, R. and Cram W. (1996), “Forces
exerted by Tree Roots”, Arboricultural Advisory and Information Service,
|Source Info:||Louisiana Department of Transportation and Development|
Kevin Gaspard, P.E., Louisiana Transportation Research Center, 4101 Gourrier Ave., Baton Rouge, LA. 70808, Tel. 225-767-9104, Fax. 225-767-9108, email firstname.lastname@example.org
Zhongjie Zhang, PH.D, P.E., Louisiana Transportation Research Center, 4101 Gourrier Ave., Baton Rouge, LA. 70808, Tel. 225-767-9162, Fax. 225-767-9108, email: email@example.com
Gavin Gautreau, P.E., Louisiana Transportation Research Center, 4101 Gourrier Ave., Baton Rouge, LA. 70808, Tel. 225-767-9110, Fax. 225-767-9108, email: firstname.lastname@example.org
AFP60 Committee on Engineering Behavior of Unsaturated Geomaterials
John Siekmeier, P.E. M.ASCE
Committee Research Coordinator
Minnesota Department of Transportation
1400 Gervais Ave., Maplewood, MN 55109-2044