Tolerances in tunnelling - small cause and great effect / Toleranzen im Tunnelbau - kleine Ursache mit großer Wirkung

Tolerance is defined as the permissible deviation from the specified dimensions, since dimensions cannot be produced exactly. This is particularly relevant in tunnelling, where refurbishment contracts requiring the breaking out of the inner lining of the tunnel and the construction of a new lining will be of increasing significance in the future. Adding the upper and the lower limiting deviations gives the dimensional tolerance (tolerance range), by which the tunnel cross-section has to be over-excavated in order to maintain the structure gauge. The Austrian standards ÖNORM B 2203-1:2001, 2203-2:2005 and 2110:2009 provide for the tolerances to be specified, but do not define the areas of responsibility. Details of dimensional tolerances (± values) for tunnelling are defined in the RVS 09.01.43 (9.34) "Construction of inner lining concrete". Under the currently valid regulations, careful attention should be paid in design and tendering to clear provisions and the demarcation of the spheres of responsibility of client and contractor. When existing inner linings are broken out and tolerances are taken into account, attention also needs to be paid to the structural stability of the remaining inner lining.