Factors affecting overbreak in large tunnels excavated by the drilling and blasting method

In underground construction, especially when excavating through hard rock, the drilling and blasting method is preferred. The disadvantage of this method is the frequent occurrence of exceeding the designed excavation area (overbreak). This is a significant concern for both construction managers and contractors, as it affects economic and technical indicators, including the volume of drilling, excavating, and support work, as well as the durability and stability of the structure over time. Specifically, overbreak not only increases the volume of excavation and transportation but, more importantly, increases the volume of concrete reinforcement for the tunnel lining and shotcrete, affecting the working conditions of the lining and surrounding rock mass. Overbreak in underground construction depends on many different factors. The factors can be divided into objective and subjective elements. Objective factors include the geological conditions of the rock mass, encompassing its properties, fracture orientation, and evaluation indices. Subjective factors focus on the drilling technology and excavation length. The results show that rock mass quality, such as the RMR index, fracture characteristics, and excavation length, significantly influences the overbreak coefficient.

How to Cite

Chu, T.Viet and Dao, C.Van 2026. Factors affecting overbreak in large tunnels excavated by the drilling and blasting method (in Vietnamese). Journal of Mining and Earth Sciences. 67, 5 (Oct, 2026), 84-94. DOI:https://doi.org/10.46326/JMES.2026.67(5).07.

References

Bieniawski, Z. T. (1977). Geomechanics classification of rock mass and its application in tunneling. ISRM.

Bulychev, N. S. (1989). Cơ học công trình ngầm. M. (tiếng Nga).

Đào, V. C., Nguyễn, Q. P., Nguyễn, P. N. và nnk. (1999). Báo cáo tổng kết đề tài cấp Bộ: Nghiên cứu xác định hệ số thừa tiết diện các hầm tuyến năng lượng thủy điện Yaly.

Müller, L. (1970). The rock mechanics of underground construction. Proceedings of the 2nd Congress of the International Society for Rock Mechanics, Vienna: Springer-Verlag, 3, 691-702.

Müller, L. (1976). Geomechanical principles in tunneling. International Journal of Rock Mechanics and Mining Sciences and Geomechanics Abstracts, 13(4), 123-140.

Müller, L. (1978). New Austrian Tunnelling Method (NATM). Tunnelling ’78: Proceedings of the 3rd International Tunnelling Conference, London: Institution of Mining and Metallurgy, 381-392.

Phan, Đ. Đ. (1999). Xây dựng công trình ngầm thủy điện Hòa Bình. Nhà xuất bản Xây dựng.

Singh, B. (1972). Influence of rock joints on blast fragmentation and tunnel stability. International Journal of Rock Mechanics and Mining Sciences, 9(5), 345-356.

Singh, S. P., Xavier, P. (2005). Causes, impact and control of overbreak in underground excavations. Tunnelling and Underground Space Technology, 20 (1), 63-71.

Tariq, S. M., and Worsey, P. N. (1996). An investigation into the effect of varying joint aperture and nature of surface on pre-splitting. In: Proceedings of the 12th Annual Symposium on Explosives and Blasting Research, International Society of Explosives Engineers (ISEE), February 4–8, 1996, Orlando, FL, USA, pp. 186–195.

Terzaghi, K. (1946). Rock defects and load-bearing capacity in tunnels. Journal of the Boston Society of Civil Engineers, 33, 93-122.

Wahlstrom, J. (1973). Stability analysis of underground openings in jointed rock. Tunneling ’73: Proceedings of the International Tunneling Conference, London: Institution of Mining and Metallurgy, 45-58.

Worsey, P. N., Farmer, I. W., and G. D. Matheson. (1981). The Mechanics of Pre-Splitting In Discontinuous Rock. The 22nd U.S. Symposium on Rock Mechanics (USRMS), Cambridge, Massachusetts, June 1981.

Worsey, P. N., and Qu, S. (1987). Effect of joint separation and filling on pre-split blasting. In: Proceedings of the 3rd Mini-Symposium on Explosives and Blasting Research, Society of Explosives Engineers (ISEE), February 5–6, 1987, Miami, FL, USA, pp. 26–40.

Johansen, J., and Mathiesen, C.F. (2000). Modern Trends in Tunnelling and Blast Design (1st ed.). CRC Press. https://doi.org/10.1201/9781003762201.

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