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Overbreak in a tunnel is

  • A.excavation beyond the intended profile
  • B.excavation falling short of the intended profile
  • C.the volume of concrete lining placed per metre
  • D.the advance achieved in a single blasting round

Answer: A

Correct answer: excavation beyond the intended profile

Overbreak is rock removed outside the designed line, whether by blast damage or by blocks falling from the crown. It costs money twice over: the material must be mucked out and the resulting void filled with lining concrete. Controlled perimeter blasting exists chiefly to limit it.

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