This document aims to offer a guide to the methods for tunnel face stability assessment in mechanized tunnelling and to provide a best practice guideline for face support pressure calculations. Furthermore, the document intends to help with the choice between available calculation methods depending on the expected ground conditions.

This document consists of seven chapters in total, excluding introduction. The second chapter introduces the general aim of a tunnel face stability assessment and briefly describes soft ground mechanized tunnelling technology with a focus on the tunnel face stability. The German safety concept regarding the face stability assessment is outlined in the third chapter. Following this, the most important scientific approaches dealing with face stability calculations are discussed, in chapter 4 focusing on support pressure due to earth pressure at the tunnel face and in chapter 5 summarizing support pressure due to groundwater pressure. The most relevant calculation methods for shield tunnelling practice are presented in detail in chapter 6. Additional aspects regarding face stability are discussed in chapter 7. Two examples of face support pressure calculations are provided at the end of this document in chapter 8.