The flexibility of the NATM approach as illustrated by Dr. Sauer and Partners' 'NATM Tool Box' means that it can be adapted in all geotechnical conditions. Ground conditioning/improvements such as jet grouting, ground freezing, grouted pipe spiling or Barrel Vault Methods are also available to stabilise the face. The application of the Doorframe Slab Method, a semi Cut & Cover construction method also allows very shallow tunnel alignments. The Caisson Method, for example provides a safe and cost effective alternative to Immersed Tube tunnels.
