Measurements of Infiltration Rates in Compacted Urban Soils

Previous research (Pitt, et al. 1999) has identified significant reductions in infiltration rates in disturbed urban soils. More than 150 prior tests were conducted in predominately sandy and clayey urban soils in the Birmingham and Mobile, Alabama, areas. Infiltration in clayey soils was found to be affected by an interaction of soil moisture and compaction, while infiltration in sandy soils was affected by soil compaction alone. The tests reported here were conducted under more controlled laboratory conditions and represent a wider range of soil textures and specific soil density values. METHOD Laboratory permeability test setups were used to measure infiltration rates associated with different soils having different textures and compactions. These tests differed from normal permeability tests in that high-resolution observations were made at the beginning of the tests to observe the initial infiltration behavior. The tests were run for up to 20 days, although most were completed (when steady low rates were observed) within 3 or 4 days. Test samples were prepared by mixing known quantities of sand, silt, and clay to correspond to defined soil textures, as shown in Table 1. The initial sample moistures were determined and water was added to bring the initial soil moistures to about 8%, per standard procedures (ASTM Dl140-54), reflecting typical "dry" soil conditions and to allow water movement through the soil columns. Table 2 lists the actual soil moisture levels at the beginning of the tests. Three methods were used to determine the effect of compaction on infiltration: hand compaction, Modified Proctor Compaction, and Standard Proctor Compaction. Both