Empirical equations established for estimating the rock strength of the working face based on the cutting forces of a tunnel boring machines (TBM) are further examined and discussed with respect to the dominant factors affecting TBM performance. Constants in the equations are related to TBM-specific parameters such as excavation (tunnel) diameter, cutter diameter, and cutter distance. The relationship between the constants and the TBM specifications is examined in this study on the basis of data collected at ten tunnels, and it is found that the constants are most strongly influenced by the cutter diameter and tunnel diameter.

Zur Schatzung der Gesteinsfestigkeit an der Arbeitsflache ermittelte empirische Gleichungen, die auf den Schneidekraften von Tunnelbohrmaschinen (TBM) beruhen, wurden weiter im Hinblick auf die vorherrschenden, die Leistung der TBM beeinflussenden Faktoren hin untersucht und diskutiert. In der Gleichung enthaltene Konstanten werden zu den TBM-spezifischen Parametern wie Auschachtungs- (Tunnel) Durchmesser, Schneidendurchmesser und Schachtlange in Beziehung gesetzt. Die Beziehung zwischen diesen Konstanten und den technischen Daten der TBM wird in dieser Studie auf der Basis der bei 10 Tunnelbauten gesammelten Daten untersucht. Dabei wurde gefunden, dass diese Konstanten am starksten von den Durchmessern der Schneiden und der Tunnel beeinflusst werden.

Cette etude examine et discute les equations empiriques permettant d'estimer la resistance de la roche attaquee aux forces de coupe des tunneliers dans le cadre de l'etude des facteurs dominants affectant les performances des tunneliers. Les constantes de ces equations concernent les paramètres specifiques des tunneliers comme le diamètre d'excavation (du tunnel), le diamètre du couteau et la distance de coupe. Cette etude examine le rapport entre ces constantes et les caracteristiques techniques des tunneliers d'après des donnees collectees dans dix tunnels et elle conclut que ces constantes sont principalement influencees par le diamètre du couteau et le diamètre du tunnel.

1. Introduction

In a previous paper (Fukui and Okubo, 1999), the present authors proposed a method for estimating the rock strength of the working face based on TBM cutting forces (thrust and torque) and cutting depth. The method was found to be promising for real-time in-situ estimation of rock strength, with rock strength calculated by this method found to be consistent with the strength obtained by bedrock surveys and Schmidt-hammer rebound hardness tests at several tunnels. The proposed method represents a useful technique for selecting the most appropriate supporting pattern for rapidly changing rock mass characteristics, thereby preventing accidents and reducing construction time and expense.

However, as the constants in the equations for estimating strength are dependent on the TBM specifications, the equations cannot be readily customized for tunnels in the planning stage. In this study, mechanical excavation data for ten tunnels is analyzed with respect to the relationship between these constants and the TBM specifications in order to develop guidelines for establishing constants for new tunnels.

2. Equations for Estimating Rock Strength

The fundamental relationships derived based on excavation tests as reported previously are as follows.(Equation in full paper) where p is the cutting depth and σc is the rock strength.

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