It is my pleasure to introduce this issue of the International Journal of Physical Modelling in Geotechnics, which features three papers that address one of the fundamental problems in the geotechnical domain: deformation. The topics include the deformation behaviour of skirted square footings, wall deformation and ground settlement due to excavation, and tunnel deformation induced by deep braced excavation. The papers in this issue demonstrate how physical and numerical modelling can work hand in hand to advance our understanding of geotechnical problems. They also highlight the continuing efforts in developing innovative modelling techniques, such as transparent soil testing, which enables non-intrusive measurement of soil displacement fields. Collectively, these contributions reaffirm the importance of physical modelling in providing high-quality experimental evidence, validating numerical predictions, and guiding safe and resilient design solutions in complex ground conditions.
The first paper by Das et al. (2025) examined the deformation behaviour of skirted square footings subjected to eccentric loading in granular soil. Using an extensive series of laboratory model tests, the study evaluates the influence of skirt length, footing embedment depth, and load eccentricity on both settlement and rotation. The results show that skirts effectively reduce settlement by confining the soil beneath the footing and limiting lateral deformation, with the most significant improvements observed at the surface condition and diminishing with greater embedment depth. Skirts also mitigate rotation by enhancing resistance against overturning moments, while embedded footings experience lower rotation than surface footings under equivalent loading. Regression-based formulations are proposed to predict settlement and rotation under different conditions, demonstrating strong agreement with experimental data. Comparisons with previous studies further validate the proposed correlations, and a practical design chart is provided for determining skirt length to limit settlement within acceptable thresholds. Complementary finite-element simulations illustrate the failure mechanisms, revealing that skirts promote vertical soil mobilisation under central loading and transform the response under eccentric loading into a combined ‘scoop–wedge’ mechanism. Overall, the study confirms the beneficial role of skirts in reducing excessive foundation deformation and provides valuable experimental evidence to support future model development and validation.
The second paper by Abbas et al. (2025) investigated the influence of surface loading on wall deflection, ground settlement, and lateral earth pressure in deep excavations. Using centrifuge modelling and three-dimensional finite-element analyses, the study systematically examines the effects of load position, area, and magnitude. The findings quantify how surface loading alters excavation response, confirming that loads located within the primary influence zone are most critical. Directional effects are also evident, with load width exerting a stronger impact than load length due to the restraining action at excavation corners. Based on these insights, the authors propose simple correlations for predicting wall deflection and ground settlement under representative conditions. Furthermore, the stiffness influence factor introduced by Abbas et al. (2025) is extended to incorporate surface-loading effects. Validation against experimental results and published case studies demonstrates the reliability of the proposed method, offering a practical framework for excavation design in urban environments.
The third paper by Liu et al. (2025) studied the influence of deep braced excavation on adjacent tunnel deformation using an innovative transparent soil modelling technique combined with particle image velocimetry. The transparent soil technique enables direct visualisation of soil displacement fields, providing detailed insight into tunnel response under excavation-induced unloading. A systematic testing programme examined the effects of horizontal and vertical clearances between the tunnel and foundation pit, as well as soil consolidation pressure, on tunnel deformation. Results show that tunnel deformation increases significantly with excavation depth but decreases with greater separation between tunnel and pit. Vertical distance plays a more critical role than horizontal distance in controlling deformation, while higher soil pre-consolidation pressure enhances stiffness and reduces tunnel displacement. Longitudinal deformation patterns consistently exhibit a unimodal distribution, with peak displacement occurring at the centreline of the excavation. Finite-element simulations using a small-strain soil model validated the experimental results, with close agreement in both trends and magnitudes. The study demonstrates the utility of transparent soil modelling in clarifying excavation–tunnel interaction mechanisms and highlights practical measures to mitigate deformation risks.
Together, these contributions provided new insights into excavation-induced soil and structural deformation, as well as the deformation behaviour of skirted foundations. They extended existing predictive methods and demonstrated the value of physical modelling in advancing knowledge within urban geotechnical engineering. I sincerely hope that the papers in this issue will be of interest and offer useful insights for your research and practice. Finally, I would like to express my gratitude to all authors, reviewers, and the journal’s support team for their continued efforts, which make it possible to maintain the high quality and relevance of this journal. The excellence of the contributions in this issue once again attests to the fundamental role of our dedicated reviewers. I warmly invite you to explore these studies and to reflect on the valuable perspectives they bring to the field of physical modelling in geotechnics.
