Characterization of Autocovariance Parameters for Horizontal and Vertical Trends and Spatial Variabilities from a Three-Dimensional CPT Database

Abstract

This paper compiles a large cone penetration test (CPT) database, named CPT3D/3/2577, to investigate the horizontal and vertical autocovariance structures of soil spatial variation. It contains three CPT parameters (cone tip resistance, sleeve friction, and porewater pressure) from 2,577 soundings taken at 186 sites. Nearly all sites are extracted from the New Zealand Geotechnical Database. The database contains sites with multiple CPTs with known horizontal (x–y) coordinates, so not only the vertical autocovariance parameters [such as scale of fluctuation (SOF) and smoothness] but also the horizontal ones can be investigated. The cone tip resistance data from multiple CPTs at each site are analyzed by a random field model whose trend is explicitly modeled, enabling the characterization of the autocovariance parameters for both the spatial variability part (ε) and trend part (t). The identification results of the 186 sites indicate that the vertical SOF for ε varies in a narrow range, but the ratio of horizontal to vertical SOF for ε varies in a wide range (from 1 to 100). The results also indicate that the horizontal SOF for t is large (easily exceeding tens to hundreds of meters), but the vertical SOF for t is much smaller (sometimes only a few meters). The practical implications of these identification results are also discussed.