Soil infiltration is a critical component of most urban runoff models. However, it has been well documented that during urbanization, soils are greatly modified, especially related to soil density. Increased soil compaction results in soils that do not behave in a manner predicted by traditional infiltration models. Laboratory and field tests were conducted to investigate detailed infiltration behavior of disturbed urban soils for a variety of soil textures and levels of compaction. The results from traditional permeability tests on several soil groups showed that, as expected, the degree of compaction greatly affected the steady-state infiltration rate. The field tests highlighted the importance of compaction on the infiltration rate of sandy soils, with minimal effect seen from antecedent moisture conditions. For the clayey soils, however, both the compaction level and antecedent moisture conditions were important in determining the steadystate infiltration rate.
The effects of urbanization on soil structure can be extensive. Infiltration of rain water through soils can be greatly reduced, plus the benefits of infiltration and biofiltration devices can be jeopardized. This chapter is a compilation of results from several recent and ongoing research projects that have examined some of these problems, plus possible solutions. Basic infiltration measurements in disturbed urban soils were conducted during the EPA-sponsored project by Pitt, et al. (1999a). The project also examined hydraulic and water quality benefits of amending these soils with organic composts. Prior EPA-funded research examined the potential of groundwater contamination by infiltrating stonmvater (Pitt, et al. 1994, 1996, and 1999b). In addition to the information obtained during these research projects, numerous student projects have also been conduced to examine other aspects of urban soils, especially more detailed tests examining soil density and infiltration during lab-scale tests, and methods and techniques to recover infiltration capacity of urban soils. This chapter is a summary of this information and it is hoped that it will prove useful to both stonnwater practice designers and to modelers.
T raditionally, geotechnical engineers relied on the standard penetration test (SPT) and cone penetration test (CPT) to determine soil stiffness and depth of bedrock. These tests typically involve boring (thus, destructive in nature), which require substantial cost and time. As a result of boring, these tests evaluate the soil stiffness only at a single point, which may or may not be representative of the overall site characteristics, and the soil data interpretation is almost exclusively heuristic. For more elaborate investigation, multiple boreholes may be required, which naturally would drive up the costs involved. It is not uncommon that the clients would limit site borings to numbers insufficient for proper site characterization.For rapid constructions, such as erection of high-voltage power transmission lines for power companies using helical anchors or direct embedded foundations, SPT and CPT may not be economically feasible. Alternative testing techniques that provide quick and accurate assessment of soil stiffness are much needed for these projects.Nondestructive geophysical test techniques that are based on elastic wave propagation of induced stress waves in soil offer attractive alternate options. These methods typically rely on mechanically generated stress waves and high-resolution geophones to pick up ground responses to back-calculate elastic material properties of soil layers, which is done by measuring either the compression or shear wave velocities of each material and then by correlating wave speed to elastic moduli.Since 1999, the Southern Company has conducted extensive research in developing the nondestructive geophysical technique for the design of transmission pole structures. The spectral analysis of surface waves (SASW) test technique is based on the dispersion characteristics of surface waves and consists of making field measurements of surface wave velocities at various frequencies and determining shear wave speed profiles through an inversion process. 1 The Southern Company research involved extensive field pull and SASW tests to establish semiempirical design correlations in order to determine the stabilities of the transmission pole structures.In this article, different practical applications of the SASW method are presented, demonstrating the versatility of the SASW method. The presented case studies are all associated with the construction and erection of transmission line poles and towers. In the first case, SASW was used to determine possible correlation between soil shear wave velocities and anchor-holding capacities. In the second case, soil shear wave velocities were used to determine embedment depth required for directly embedded poles. FUNDAMENTALS OF SASWThe SASW method was developed during the last two decades as an extension of a steady-state Rayleigh wave technique. [1][2][3][4] Using impact excitation and two receivers, the technique relies on the time travel between the two receivers to backcalculate travel velocity. During test, the two receivers are placed in the so...
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