Lessons from Full-and Partial-Face Excavation in Difficult Rock Conditions

Summary

Abstract

The selection between full-face and partial-face excavation methods is a decisive factor in the success and efficiency of conventional tunnelling projects. This choice is shaped by a complex interplay of geological and geotechnical rock mass conditions, environmental and urban constraints, regional design and construction standards, and permissible surface settlement thresholds. Each excavation method imposes distinct implications for project cost, schedule, and safety, highlighting the critical importance of informed decision-making during the early design phase. Over the years, continuous advancements in construction materials, excavation machinery, numerical modelling, and real-time monitoring technologies have significantly enhanced the feasibility of full-face excavation. These advancements enable the safe and efficient construction of tunnels with cross-sectional areas exceeding 150 m², pushing the limits of conventional tunnelling. Nonetheless, partial-face excavation remains an essential and often preferred strategy when staged excavation is required to ensure ground stability, manage deformations, or address specific site constraints. This study presents a comparative analysis of full-face and partial-face excavation methods, drawing on selected complex case histories from one of the major Alpine base tunnels and international projects under low overburden. Critical factors, including rock mass properties, excavation techniques, tunnel geometry, alignment, and construction sequencing, are evaluated to identify their influence on method selection and project outcomes. The case studies provide valuable insights into the practical advantages, limitations, and applicability of each approach, establishing a reference framework for conventional tunnelling practice in challenging geological and urban contexts. The paper highlights key considerations for optimizing excavation strategy, balancing safety, cost, and schedule, and leveraging modern construction technologies, providing engineers with guidance to select the most effective excavation method for complex tunnelling scenarios.