Mechanism of Overbreak and Underbreak Induced by Tunnel Blasting and Control Methods

Abstract Controlling overbreak and underbreak during tunnel blasting is a critical challenge, as it directly impacts excavation quality and safety. This study provides an in‐depth analysis of the effects of surrounding rock geology, cross‐section specifications, and construction conditions on overbreak and underbreak. The mechanisms underlying blasting‐induced overbreak and underbreak are elucidated, revealing that conventional methods—such as controlling drilling angles and ensuring appropriate charge spacing—remain limited, particularly for long advances. To address these limitations, this study introduces a geometric control method employing both long and short holes, with derived theoretical formulas. Case study validations demonstrate that this computerized control method can swiftly determine critical parameters such as collar positions, drilling angles, and hole lengths, offering precise theoretical guidance for on‐site drilling operations. The proposed method has shown significant effectiveness in controlling over‐break and underbreak.