USE OF SHOTCRETE FOR TUNNELLING IN DIFFICULT GROUNDS

The use of shotcrete in Europe is discussed. Experience in the use of shotcrete in a hydroelectric plan tunnel in Italy is described. Special reinforced shotcrete was used to line the tunnel immediately after excavation. The reinforcement consisted of steel mesh ribs placed at distances varying from 0.5 to 1.20 m and completed by secondary rods and by a large steel mesh behind the steel mesh ribs. Details are outlined of this construction which, subsequent studies indicate, was completely successful. A second project is detailed which consisted of road tunnels which underpassed built-up zones and garden zones. The ground consisted of various types of argillaceous slates inserted with chalky sandstone strata, some part of which were greatly decomposed and others totally decomposed. The problems presented in this particular situation could be solved only by the shotcrete system. A section in which the shotcrete ring was the only support of the tunnel up to the completion of the excavation works (2 years later), was continuously tested by survey of bench marks installed from 5 up to 7 on a part of the steel mesh ribs. The maximum subsidences (on single bench marks) were of +0.30 mm after 272 days and of +0.416 mm after 242 days at another point. These data confirm the validity of the shotcrete method. Comparisons are made of the results of the shotcrete method with those constructed according to traditional methods. The successful use of the shotcrete method for the construction of the Milan Subway System (1967-1970) is described. Attention is drawn to certain points which are of importance for the shotcreting method. Shotcrete must be applied only where the ground characteristics require it. The widths employed must be adequate to support the ground. The steel mesh ribs and metal support must be distributed and placed in such a way that they will be integrated in a resistant, calculable complex with the shotcrete. The components of the concrete must incorporate an ideal and accurate granulation for the kind and percent of accelerators employed.

Media Info

  • Pagination: p. 79-95

Subject/Index Terms

Filing Info

  • Accession Number: 00263687
  • Record Type: Publication
  • Report/Paper Numbers: SP-45 Conf. Proc
  • Contract Numbers: H0111881
  • Files: TRIS
  • Created Date: Dec 19 1981 12:00AM