Cone penetration test (CPT)-based soil classification and stratification with consideration of data cross-correlation and noises

Abstract

In geotechnical site investigation, Robertson’s soil behavior type (SBT) chart is widely used for soil classification based on two quantities measured during a cone penetration test (CPT), the normalized cone resistance Q_t and the normalized friction ratio F_R. Q_t and F_R are negatively correlated and provide complementary information for soil classification. However, this cross-correlation between Q_t and F_R has not been explicitly modelled in previous studies of subsurface soil classification and stratification using an often-limited number of CPT soundings from a specific site. This study aims to leverage such cross-correlation for improving CPT-based stratification and zonation by a joint sparse representation of Q_t and F_R in a vertical cross-section, as well as quantifying their uncertainty under a Bayesian framework. In addition, direct application of the SBT chart to a vertical cross-section often leads to noisy results (e.g., SBTs fluctuate rapidly and unrealistically within short distances). The noises are subsequently removed mainly by subjective engineering judgment in current practices. In this study, a randomization of input measurements is proposed to filter out the noise and improve computational efficiency simultaneously. Both simulated and real data examples are used to illustrate the proposed method. The results indicate that the proposed method significantly improves accuracy of the soil classification and stratification and automatically removes the noise.