Deltaic soil behavior classification using CPTu records—Proposed approach and applied to fifty-four case histories

ABSTRACT

For the past four decades, the CPT has played a key role in onshore and offshore soil investigations. One of the main applications of cone penetration test (CPT) is the soil behavioral classification. Most of the developed methods for soil identification using CPT and CPTu (piezocone) data are well categorized for common soils, such as clays, silts, and sands. Soils with low resistance or more compressibility generally involve problems in geotechnical engineering practice and construction projects. Consequently, these unusual deposits require further evaluation and more detailed data. Five major groups of problematic soils including: liquefiable, sensitive, peaty, collapsible, and expansive soils have been considered in this study. One hundred and forty CPT and CPTu test records were collected from fifteen countries. Sixty-one of the records are related to difficult soils. A brief comparison is performed for currently used soil behavioral classification charts, such as by Campanella et al. (1985), Robertson (1990), Jefferies and Davies (1991) and Eslami and Fellenius (1997). Analysis based on CPT data indicates that a few commonly used charts recognize relatively well problematic deposits. However, further studies are needed to increase the accuracy and capability of methods. Existing charts have some problems due to the limitations of the nature of rectangular charts based on two axes. A new format of classification chart, i.e., triangular form containing cone tip resistance (q_c), sleeve friction (f_s), and pore pressure (u₂) is proposed for soil identification which can be realized in practice. The proposed chart with more accuracy and less scattering of data than the previous charts is able to identify soil types particularly for deltaic soils.

KEYWORDS:

• CPT and CPTu database
• problematic soils
• soil behavior classification (SBC)
• triangular chart