The influence of soil layering and penetrometer diameter on penetration resistance

Methods employing cone penetration test (CPT) data for site characterisation and foundation design have continued to evolve as use of the CPT grows worldwide. Research to assist the development of such methods has included penetration testing in a laboratory environment where the presence of thin soil layers in samples has highlighted the need for improved understanding of the influence of penetrometer size. This paper presents the results of a systematic experimental investigation of the relationship between the penetration resistance, penetrometer diameter, and relative strength of the soil layers in two-layered sand–sand and sand–clay profiles. The results combined with other high quality experimental results reported in the literature are used to quantify the influence of the strength of the layers on the cone resistance at the boundary of two layers as well as on the nature of the sensing and development sections of the cone profile. These observations inform modifications to the Boulanger and DeJong filtering method, with the primary objective of developing a consistent approach for the prediction of ultimate end bearing resistance of driven piles in layered stratigraphy. Examples using different diameter penetrometers in the field and in multi-layered deposits created in the laboratory illustrate the suitability of these modifications.