Abstract
This paper presents a study of the spatial variability of the cone resistance in a medium dense sand deposit in Norway. Spatial variability studies have been done earlier for clay deposits, but there are few results available for sands. To bridge this gap and to compare the spatial variability of sand and clay, the in situ cone resistance measured with the piezocone at the Oysand benchmark site near Trondheim was studied. Corrected cone resistances qt derived from the measured cone resistance and pore pressure measurements were used to establish the autocorrelation structure of the Oysand deposit. The qt data were examined visually and conclusions were drawn on the data that should be analyzed. A depth interval of 7 to 12 m was selected for spatial variability further analysis. The scale of fluctuation was identified. Several autocorrelation functions were considered, and the single exponential function was found to be the one offering the best autocorrelation. The spatial variability in the vertical and horizontal directions was analyzed statistically, using three different approaches, the auto-correlation fitting, maximum likelihood estimation and simplified Vanmarcke method. The results indicate short autocorrelation distances of 3 m or less in the horizontal direction, suggesting a very variable sand at the Oysand site. These horizontal autocorrelation distances are much shorter than those obtained for clays. In the vertical direction the scale of fluctuation was less than one meter, as obtained for other soils.
Highlights
The engineering properties of a soil always exhibit variation from point to point within a soil volume
This paper presents a study of the spatial variability of the cone resistance in a medium dense sand deposit in Norway
In the vertical direction the scale of fluctuation was less than one meter, as obtained for other soils
Summary
The engineering properties of a soil always exhibit variation from point to point within a soil volume. It is of interest to quantify the spatial variability in order to assess its importance, help plan future soil investigations and, if possible, reduce the uncertainty in a property by spatial averaging. This paper quantifies the spatial variability of the cone resistance in a sand deposit. Little information exists on the spatial variability of sands and silts. Even when closely spaced, can show large variability. Quantifying the distance over which the soil parameters in a sand are correlated can help plan site investigations and reduce the uncertainty in the soil parameters derived from the piezocone test. The variability in the corrected cone resistance is analyzed through first a visual inspection of the data, and second a calculation of the spatial correlation structure
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