Causes and mitigation of delay and cost overrun in deep excavations supported by soil nailing and ground anchoring: a mixed-methods study from Iran

Purpose Deep excavation projects supported by soil nailing and ground anchoring systems are increasingly prevalent in densely urbanized metropolitan areas, yet remain understudied in construction management research. This study investigates the primary causes of delay and cost overrun in such projects, drawing on empirical data from Iran. Design/methodology/approach A mixed-methods approach was adopted, combining a PRISMA-guided systematic review of 431 international publications with expert interviews and consultations involving 25 industry professionals and structured questionnaires administered to contractors, consultants and owners. Delay factors were evaluated using impact indices, likelihood of occurrence, and overall significance, with root cause analysis pursued to the fourth causal level in key cases. Findings Constraints related to neighboring structures and underground facilities emerged as the most critical drivers, followed by inadequacies in geotechnical investigation. Stakeholder responsibility analysis attributed approximately 38.0% of factors to owners, 37.7% to contractors and 15.9% to consultants. A practical mitigation framework was developed, integrating insights from the systematic review, prior case studies and expert judgement. Regional conditions and sample size constraints may limit transferability. Originality/value This is the first study to apply a PRISMA-guided systematic review of 431 publications specifically to soil nailing and ground anchoring systems, combined with multi-level root cause analysis and structured stakeholder attribution, offering targeted guidance for Iranian urban deep excavation projects and transferable implications for similarly urbanizing economies.