1739
Cutting tool wear prognosis and management of wear-related risks for Mix-Shield
TBM in soft ground
Prévision d’usure des outils de coupe et management des risques liés à l’usure pour Mix-Shield
TBM en terrain meuble
Köppl F.
Herrenknecht AG, Schwanau, Germany,
Thuro K.
Technische Universität München, Lehrstuhl für Ingenieurgeologie, Munich, Germany
ABSTRACT: The wear of cutting tools is a major issue in Mix-Shield tunneling in soft ground, because it is the most common reason
for intermission of advance. Thereby the costs for the downtime commonly exceed the costs for the changed cutting tools. However,
due to the inaccessibility of the processes involved and the variety of influencing factors, there are no prognosis tools available, that
provide reliable information on cutting tool life. With the detailed data analysis of 18 Mix-Shield TBM drives, this paper takes an em-
pirical approach to tool wear in soft ground. The data analysis results in a qualification and quantification of the relevant influencing
factors on cutter tool life. This leads to a prognosis model for cutter life in soft ground for Mix-Shield TBM, based on empirical corre-
lations with soil parameters and TBM design and advance parameters. For a realistic approach the model is completed by an engineer-
ing process to translate the cutter life into distances for intermission of advance and required amount of cutting tools to be changed.
RÉSUMÉ: L’usure des outils de coupe est un sujet majeur lors de l’excavation en mode Mix-Shield car elle est la raison principale
des interventions hyperbares. En effet, les coûts des interventions hyperbares sont souvent supérieurs aux coûts des outils remplacés.
A cause de la difficulté d’accés au processus d’excavation et la diversité des facteurs influents, il n’existe pas d’outil de prévision ana-
lytique ou empirique permettant d’obtenir des informations fiables sur la durée de vie des outils. Avec une analyse détaillée concer-
nant 18 tunnels forés avec des TBM Mix-Shield, ce document sert de base pour une approche empirique concernant l’usure des outils
de coupe en terrain meuble.Les résultats reposent sur l’analyse quantitative et qualitative de tous les facteurs ayant une influence sur
la durée de vie des outils. L’exploration de ces résultats mène à un modèle de prévision de la durée de vie des outils de coupe en ter-
rain meuble pour TBM Mix-Shield bàse sur des corrélations empiriques des paramètres géologiques, de forage et du design du TBM.
Pour une approche réaliste, le modèle intégrant un process d’ingénierie, permet de convertir la durée de vie de outils en distance pour
les interventions hyperbares ainsi que la détermination du nombre d’outils à changer.
KEYWORDS: Mix-Shield TBM, cutting tools, wear, soft ground, wear prognosis, risk management.
1 INTRODUCTION
The changing of cutting tools on Mix-Shield TBMs is either
either done at fixed positions with prearranged grout blocks or
with hyperbaric works in the excavation chamber. Therefor ad-
vance is intermitted and the bentonite suspension is partly re-
placed by compressed air, which maintains the support of the
excavation face while the tools are changed manually. The posi-
tion for the interventions and the obtainable length of the inter-
vals between the interventions is determined by the wear of the
cutting tools. At the same time the boundary conditions in the
projects are often critical for hyperbaric interventions, e.g. due
to high support pressure, or overlying infrastructure. Conse-
quently careful and foresighted planning of the interventions is
necessary in order to avoid such critical areas.
In contrast to this, there are no models available, which al-
low for a reliable prognosis of the tool life (K
ÖHLER
et al. 2011). Insights on tribological mechanisms on metal sur-
faces are widely available, but neither analytical models
(B
ERETITSCH
1992), index tests for the abrasivity of soils
(N
ILSEN
et al. 2006a,b,c, T
HURO
et al. 2006, T
HURO
& K
ÄSLING
2009, J
AKOBSEN
& D
AHL
2010, G
HARAHBAGH
et al. 2011), nor
empirical analyses of individual projects (G
WILDIS
et al. 2011)
have resulted in sufficient correlation with the actual wear on
Mix-Shield TBMs.
The research presented in this paper therefore focuses on the
empirical analysis of tool wear data from reference projects em-
ploying Mix-Shield TBMs. The analysis results in the identifi-
cation and quantification of the relevant influencing factors on
tool life and therefore enables a prognosis of the tool life for
Mix-Shield TBMs in soft ground. The tool life can then be used
in an engineering process to determine the position of the neces-
sary interventions
I
, the intervals
b
I
and the necessary amount of
tools to be changed
n
t
.
2 DATA ANALYSIS
2.1
Basic data
For the data analysis 10 reference projects employing 13 Mix
shield TBMs for 18 drives were researched. The related tool
change data are summarized in tab.1.
Table 1. Overview of the raw tool change data researched in the ref-
erence projects.
Soil type
Volume
Disc Cutters
Scrapers
DIN EN 14688 T1
[m³]
[pcs.]
[pcs.]
Clay & Silt
2.843.645
212
327
Sand
1.281.604
238
937
Gravel
1.188.783
1.180
1.336
Total:
5.314.031
1.630
2.600
