8 - CPT and CPTu for foundation settlement and load–displacement (P-Δ) estimation

Abstract

Because of complexity in soil–foundation interaction and subsoil nonlinear behavior, much uncertainty is involved in the foundation settlement evaluation. On the other hand, CPT is known as a very worthwhile tool due to its repeatability, accuracy, and continuity of the records, presenting the appropriate soil properties. In addition, the CPT records can be utilized in estimating the settlement of the foundations. In this chapter, the basic important methods to estimate foundation settlement using CPT records are represented and assessed, such as the methods presented by Janbu (1967), Meyerhof (1976), and Schmertmann (1978). In addition, some new approaches proposed in the recent years by Malekdoost and Eslami (2011) and Valikhah and Eslami (2017) are described based on soil behavior classification charts developed from CPT soundings. The approaches are based on the Janbu (1967) nonlinear stress–strain method. However, instead of using fixed values for stress exponent (j) and modulus number (m), variable coefficients are used depending on various geomaterial deposits. A data bank has been compiled containing 46 case histories including 22 square, 17 circular, and 7 rectangular foundations with widths varying between 0.3 and 2.4m. The accuracy of the calculations made by available common methods is investigated and discussed. Furthermore, the numerical finite difference analysis using CPT-based stress characteristics method, originally proposed by Valikhah et al. (2018), is introduced for the prediction of the axial load–displacement behavior of shallow and deep foundations in sand. In addition, the proposed approaches can be used in estimation of the settlement of a pile group system based on the equivalent footing concept presented by Terzaghi and Peck (1948).