Abstract: The random field theory is one of the most effective tools to study the spatial variability of soil properties. Cone penetration tests with tip resistance and shaft friction measurement for Haitai River Crossing Tunnel project are presented in this paper to study the spatial variation of site soft cohesive soils. The tip resistance and shaft friction of 26 CPT locations are analyzed, and the entire project investigation zone was divided into six areas to study the “point characteristics” of strength parameters. The linearly detrended function was used to obtain the stationary fluctuant component, in order to study the spatial variability of strength parameters, the vertical fluctuation scale is calculated throughout three common correlation functions. The results show that the volume of CPT sampling size and its strength parameters are sensitive to the variation of soil mechanical properties, so it is suitable for evaluating the soil spatial variability, and the variation coefficient can be used to divide soil mechanical properties. In the same soil layer, there is a good linear fitting relationship between the tip resistance and the shaft friction. Compared with the other two correlation functions, Markov function has the highest fitting accuracy and is the best fitting model. The variation range of the tip resistance in the vertical fluctuation scale is 0.60 ~ 0.90 m, as well as shaft friction. However, in general, the vertical correlation distance of the cone tip resistance is slightly larger than that of the shaft friction.

Key words: random field theory, correlation spacing, cone penetration test with tip resistance and shaft friction measurement, haitai river crossing tunnel, spatial variability