In recent years, the engineering community has witnessed significant advancements in our understanding of subterranean infrastructure and its complex interactions with the surrounding geological environment. Among the pressing challenges are the behaviors of tunnels constructed twinwise beneath the earth’s surface, especially when subjected to varying soil conditions and structural reinforcements such as pile foundations. A groundbreaking study authored by Pham, VV., Do, NA., Osinski, P., and colleagues—soon to be published in Environmental Earth Sciences—delves deeply into the intricate dynamics governing the behavior of twin circular tunnels, emphasizing the influence of both pile foundation designs and soil constitutive models amidst the critical deconfinement process.
This seminal research confronts the pivotal problem of how different soil models interplay with pile foundations to affect the mechanical response of adjacent twin tunnels. At the heart of subterranean structural design, engineers must confront the challenge that soils are not merely passive mediums but exhibit nonlinear, time-dependent constitutive characteristics that significantly influence tunnel stability and deformation. Incorporating advanced soil constitutive models such as elastoplasticity and critical state frameworks allows for a more realistic simulation of how soils behave under loading and unloading conditions, especially during tunnel excavation stages that inevitably involve deconfinement—the reduction in lateral earth pressure once the soil is disturbed.
Amongst the compelling motivations for this study is the rising necessity for urban subterranean infrastructure that not only maximizes available underground space but also ensures long-term safety and sustainability. Twin tunnels—utilized often in transportation and utility conduits—present particular complexities, given that the structural interaction between two circular cavities and the surrounding soil leads to stress redistribution, potential deformation, and challenges for foundational support. The inclusion of pile foundations, which are deep vertical elements designed to transfer loads to stable soil strata, introduces additional layers of complexity. How these foundations interact with soil mechanics and tunnel envelopes is essential knowledge for practitioners aiming to mitigate risks associated with settlement, soil failure, or structural collapse.
Pham and colleagues employed sophisticated numerical modeling techniques to simulate the behavior of twin tunnels under various conditions, observing how different soil constitutive models influence stress paths and deformation patterns. The study importantly extends beyond simplistic elastic models, which often fail to capture soil yielding and plastic deformations, opting instead for robust elastoplastic formulations that accommodate the hysteresis and post-peak softening behavior exhibited by soils during excavation. This nuanced approach brings to light the critical stages wherein deconfinement effects dominate, allowing for better predictive capabilities in tunnel design and risk assessment.
The findings reveal that the choice of soil constitutive model drastically alters the predicted stress distribution around the tunnels. For instance, models incorporating strain-softening and critical state concepts better represent localized failure zones and more realistically capture the development of plastic zones adjacent to tunnel linings. Such insights underscore the importance of using advanced soil models to ensure the fidelity of numerical simulations; overlooking these factors may lead to underestimations of ground deformation and consequent structural damage.
Pile foundations, as the second protagonist of this study, demonstrate their indispensable role in enhancing tunnel stability in soft or weak soil conditions. The interaction between piles and soil effectively modifies the load transfer mechanisms, increasing overall system stiffness and limiting excessive ground movements. However, their performance is deeply intertwined with soil behavior during deconfinement. The research illustrates that in certain soil regimes, poorly designed pile arrangements may result in stress concentrations or unintended soil-structure interactions that could compromise tunnel integrity.
One of the most remarkable contributions of this study is its detailed treatment of the deconfinement process. Traditionally, tunnel excavation models considered soil pressures as largely static or immediately adjusted to excavation stages. However, the reality involves a temporal reduction in lateral confinement, provoking significant transient phenomena including stress relaxation, strain localization, and pore pressure fluctuations. By integrating these dynamic, time-dependent effects into their models, the authors offer a more holistic perspective that aligns closely with observed field behavior.
The study’s implications extend far beyond academic curiosity, as they provide foundational groundwork for engineers in urban planning and subterranean construction. By meticulously characterizing how twin tunnels respond to varying soil properties and structural reinforcements, the paper sets a new benchmark for designing robust underground infrastructures capable of withstanding complex geomechanical challenges. Such advances are crucial for expanding metropolitan networks, facilitating resource extraction, and safeguarding infrastructures against natural hazards and anthropogenic stresses.
Importantly, the research also underscores the necessity for interdisciplinary collaboration—combining geotechnical engineering, computational mechanics, and materials science—to devise comprehensive predictive tools. The soil constitutive models used in this study are the product of decades of experimental testing and theoretical refinement, while pile foundation design benefits from iterative feedback between geotechnical investigations and structural engineering principles. This synergy embodies the future direction of underground construction, where data-driven, physics-informed models accelerate innovation and safety.
Moreover, in an era increasingly conscious of environmental impacts, understanding soil-tunnel-pile interactions helps mitigate the risks of subsidence, groundwater contamination, and ecosystem disruption. Tunnels constructed without adequate attention to soil behavior can inadvertently trigger surface anomalies or environmental degradation. This research equips engineers with the insights necessary not just to design safer tunnels but to preserve the delicate balance of the environment above.
From a methodological standpoint, the authors implemented advanced finite element analyses, validating their models against experimental data and case studies. The parametric investigations delineate how varying pile lengths, diameters, and spatial configurations affect the stress regimes, revealing optimized designs that minimize adverse ground movements while maximizing structural resilience. This quantitative narrative furnishes a practical roadmap adaptable to diverse geotechnical scenarios.
The twin tunnel configuration, while common in metro and sewage systems, presents unique challenges related to spatial constraints and proximity-induced stress interactions, topics thoroughly probed in the paper. The coupled soil-pile-tunnel system’s nonlinear behavior requires meticulous calibration of material parameters—such as cohesion, friction angle, elasticity modulus, and dilation angle—to accurately reproduce field conditions. The study’s comprehensive sensitivity analyses provide invaluable insights into critical thresholds beyond which design modifications are imperative.
Another striking aspect lies in the examination of time-dependent phenomena, such as creep and consolidation, which influence long-term tunnel stability. The recognition that soil deconfinement leads to progressive rearrangement of soil grains challenges conventional instantaneous excavation assumptions and points toward more sophisticated staging and monitoring protocols during construction. Real-time data integration and adaptive construction methodologies may emerge as natural extensions of this research.
In conclusion, the work by Pham, VV., Do, NA., Osinski, P., and their team marks a significant milestone in subterranean engineering research. By simultaneously considering pile foundation effects and advanced soil constitutive models during the deconfinement process, the study pushes the envelope on predictive accuracy for twin tunnel behavior. Its findings promise to influence design standards, construction practices, and safety regulations worldwide, fostering resilient infrastructural development in increasingly urbanized and geologically complex regions.
The publication represents a clarion call to engineers, geoscientists, and policymakers to embrace integrative, data-informed, and physics-based approaches in underground construction. As cities grow downward as much as they do upward, mastering the subterranean domain through innovations such as those presented in this study will be vital. The future of safe, sustainable, and smart urban infrastructure emerges from the deep understanding of soil-structure interactions that this research so compellingly advances.
Subject of Research: Behavior of twin circular tunnels considering pile foundation and soil constitutive models during the deconfinement process.
Article Title: Effect of the pile foundation and soil constitutive models on the behavior of twin circular tunnels considering the deconfinement process.
Article References:
Pham, VV., Do, NA., Osinski, P. et al. Effect of the pile foundation and soil constitutive models on the behavior of twin circular tunnels considering the deconfinement process. Environ Earth Sci 84, 364 (2025). https://doi.org/10.1007/s12665-025-12365-3
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