Assessment of cavity formation in the crown during tunnel excavation in the Himalayan region

Chimney failure (crown displacement) in tunnel construction presents a critical concern of tunnelling projects in weaker rock formations at shallow depth of cover. Understanding the mechanisms and implications of chimney failure is of paramount importance for ensuring safe and efficient tunnel excavation, preventing potential hazards, and implementing effective remedial measures to maintain tunnel stability and structural integrity. An attempt has been made in this paper to simulate chimney failure in a tunnel and measured the vertical displacements and stresses in both unsupported and supported tunnels with cavities and compared with the field observations. This paper also discusses the importance of appropriate support strategies and remediation techniques to ensure the stability and structural integrity of tunnels while addressing challenges associated with crown displacement and cavity formation.