Interpretation of soil deformation characteristics based on in-situ test: A comprehensive review

In-situ testing methods have become indispensable for evaluating soil deformation properties in geotechnical engineering, offering a means to characterize soil stiffness under true field conditions. Accurate in-situ characterization of soil deformation parameters is crucial for advanced geotechnical analysis, particularly in understanding soil stiffness across various strain levels. Traditional laboratory tests are limited by sample disturbance, scale effects, and inability to reproduce in-situ stress–strain history, motivating greater reliance on in-situ methods. This review synthesizes the recent development of mechanisms, operational principles, and interpretation of in-situ tests, and provides a systematic analysis of deformation parameters such as Young's modulus, constrained modulus, and shear modulus across various strain ranges. The strong strain-dependent nonlinearity of soil stiffness is proposed with each method capturing moduli at distinct strain levels. The effects of dynamic loading protocols on in-situ soil stiffness are analyzed. A hyperbolic degradation model for the prediction of soil stiffness is illustrated. The prospective future and important insights of the in-situ tests to be utilized in soil deformation properties can be concluded from the review, although some potential technical issues, including defining relevant stress-strain levels, disturbance effects, and strain-dependent nonlinearity, require further study. • In-situ testing methods for soil stiffness characterization in the field. • Deformation parameters across small to intermediate strain levels. • Influence of cyclic loading path, strain-dependent nonlinearity, and stress state on stiffness. • Hyperbolic shear modulus–strain degradation curves in field conditions. • Challenges and prospects of interpreting in-situ stiffness measurements.