Evaluation of Changes to Soil Suction Resulting from Residential Development

When new development occurs in arid regions, the boundary conditions and in particular the amount of water applied to the soil is usually changed. This change in the boundary condition at the surface can induce a change in the soil suction profile. In the case where the soils underlying structures exhibit volume change in response to a change in soil suction, a change in the soil suction can in turn induce volume change in the soil. As a consequence, the degree (amount by which the suction changes) and extent (depth over which a change occurs) of soil suction change are of interest to designers developing recommendations for many aspects of new construction, including grading, floor and foundation support, and landscaping. A series of suction measurements are reported for samples recovered from over 30 sites in the Denver metropolitan area where single-family residential structures have been in-place between 7 and 62 years. Samples were obtained to depths of approximately 12 meters. A companion set of results are presented for sites at which no development has yet occurred. In general, comparison of these results suggests that residential development affects the underlying soil suction profile in complex ways. In several cases, no effect can be observed. In most, suction decreased in the upper 3 to 7 meters, and in a few cases deeper wetting was suggested. The depth of suction decrease did not correlate to the age of the structure. However, operating characteristics, in particular landscaping choices and watering policies, have a significant influence over the degree and extent of suction changes.