Soil spatial variability has a significant impact on the reliability of geotechnical structures. In particular, the horizontal variability is important for linear infrastructure, which has only limited vertical height and width, but extensive length. Due to depositional and geological processes, the variability is often substantially different in the vertical and lateral directions. This variability can be characterised by a spatial correlation length, or scale of fluctuation, which is a measure of how significantly soil properties are correlated in space. An analysis of the reliability of such a measure has been undertaken using synthetic data, leading to a design chart which quantifies the statistical uncertainty in the scale of fluctuation for specific site investigation designs, which can be an important input for probabilistic analyses of the structure response. Moreover, practical guidance for site investigation design is proposed which can reduce the statistical uncertainty. The method has been applied to a real site investigation comprising a row of 29 closely spaced cone penetration tests (CPTs), within a larger site investigation of 100 CPTs, and applied to a simple design calculation for a long embankment to illustrate the impact on slope stability assessment. The site investigation data are made available to add to the limited amount of detailed data in this field.
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- Site investigation
- Statistical analysis