• Journal of Korean Tunnelling and Underground Space Association
• /
• v.9 no.3
• /
• pp.241-250
• /
• 2007

During enlarging an existing tunnel under operation, unexpected excessive overbreaks and large cavities around the tunnel were found. It was an issue that they might influence the stability the new tunnel. The overbreaks and cavities are assumed that they were attributed to excessive blasting under the condition of insufficient ground investigation. To enlarge the existing tunnel safely, therefore, a remedy measure for the overbreaks and cavities is suggested.

• Tunnel and Underground Space
• /
• v.30 no.1
• /
• pp.63-75
• /
• 2020

When tunnel is excavated via drilling and blasting, the excessive overbreak is the primary cause of personal or equipment safety hazards and increasing the cost of the tunnel operation owing to additional ground supports such as shotcrete. The practical management of overbreak is extremely difficult due to the complex causative mechanism of it. The study examines the relationship between rock mass characteristics (unsupported face condition, uniaxial compressive strength, face weathering and alteration, discontinuities- frequency, condition and angle between discontinuities and tunnel contour) and the depth of overbreak through using feed-forward artificial neuron networks. Then, Overbreak Resistance Factor (ORF) has been developed based on the weights of rock mass parameters to the overbreak phenomenon. Also, a new concept of tunnel overbreak management system using ORF has been suggested.