Prioritizing Systemic Risk Factors of Substandard Construction in South Korean Apartment Projects Using a Modified Delphi and Risk-Matrix Approach

Abstract

Recent large-scale collapses at South Korean apartment construction sites have highlighted the need to examine technical and systemic risk factors in an integrated manner. This study identifies and prioritizes expert-perceived systemic risk factors associated with substandard construction and develops a professional-perception-based risk prioritization framework for the South Korean apartment-construction context. An initial set of 57 preliminary factors derived from literature and document review was refined to 26 core factors through a two-round modified Delphi process involving a 15-member expert panel. The 26 factors were subsequently evaluated by 42 construction professionals using the relative importance index (RII) and a two-dimensional risk matrix based on perceived occurrence frequency and severity. “Aging and shortage of skilled workers” ranked first in overall importance (RII = 0.871) and risk priority (RI = 19.25), followed by “Excessive schedule pressure” (RI = 18.43) and “Lowest-bid system and low-price competition” (RI = 18.26). Using the adopted operational criterion of RI ≥ 15 within the four-level 5 × 5 risk-matrix classification, seven factors were classified in the Extreme-Risk Zone. In contrast, “Missing rebar (omitted shear reinforcement)” showed the highest perceived severity (S = 4.810) but lower perceived occurrence frequency (F = 2.500), yielding RI = 12.02 and classification in the High-Risk Zone. The highest-priority profile centered on workforce capacity, schedule and procurement pressure, subcontracting governance, concrete quality and curing, and multilingual communication. These findings represent structured professional perceptions rather than observed failure frequencies or causal estimates and require further validation using project- and incident-level data.