Standard Penetration Test

SPT? – A better approach to site characterization of residual soils using other In-Situ tests Roger A. Failmezger1, Daniel Rom2, Stacy B. Ziegler3

Sound geotechnical design requires a thorough quantification of soil properties. Engineers must determine the average values and variability of those properties. They must use tests that assess the site variability but minimize the parasitic test variability. The more variable the site is, the higher the risk is and therefore the more conservative the design should be. The contrary is also true. After determining the average and standard deviation values of the soil properties, the engineer can provide a design at a level of computed risk that is acceptable to the owner. Where heterogeneous conditions prevail, which is often the case for residual soils, a large number of accurate tests is required. The chosen test should measure or model the property of interest. Heterogeneous conditions are best characterized using near continuous testing, such as dilatometer or piezocone. A dilatometer test (DMT) is a static deformation test and is useful for predicting settlement. The piezocone (CPTU) is a model of a pile and is good for predicting vertical capacity of piles. Often exploration budgets are only large enough to perform a field program with associated laboratory testing consisting of routine index testing and a limited number of consolidation and triaxial tests. While consolidation and triaxial tests are practical for homogeneous conditions, it is not cost-effective to perform

1

President of In-Situ Soil Testing, L.C., 2762 White Chapel Road, Lancaster, VA 22503, email: insitusoil @ prodigy.net

2

President of Piedmont Geotechnical, Inc., 14735 Wrights Lane, Waterford, VA 20197, email: danrom @ ix.netcom.com

3

Engineer at Duffield Associates, Inc., 5400 Limestone Road, Wilmington, DE 19808, email: stacy@duffnet.com

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Failmezger, Rom, Ziegler

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enough of these tests to be representative...