1023
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
1
Three dimensional discrete element simulation of trapdoor unloading and gravity
flow of sandy granular material
Simulation tridimensionnelle par les éléments distincts du débit de décharge et d
’écoulement
gravitaire du matériau granulaire sableux
N. Kikkawa, K. Itoh & Y. Toyosawa
National Institute of Occupational Safety and Health, Japan
M. J. Pender & R. P. Orense
University of Auckland, New Zealand
ABSTRACT: Reported herein are numerical simulations, using the discrete element method (DEM), of a bed of granular material
having a moveable trapdoor over part of the underlying boundary. Kikumoto & Kishida 2003, and Kikumoto et al. 2003 measured the
vertical stresses on a trapdoor and the adjacent boundaries in tests in which Toyoura sand was used to represent natural ground. The
DEM simulation modelled well the vertical stress measured on the trapdoor when it was moved downward and also the vertical
stresses on the boundaries adjacent to the trapdoor. Next the gravity flow of the sand was calculated when the trapdoor was suddenly
removed; it was found that there was a complex dynamic response in the vertical stress on the boundary immediately adjacent to the
opening created, but only modest changes further away. The motivation for these DEM simulations was the desire to understand
better the processes involved in tunnel construction when there is a partial collapse of the face or the roof near the tunnel face.
Although safety in the excavation of underground openings has improved markedly in recent decades, accident statistics for this type
of work remain a challenge for the Japanese construction industry.
RÉSUMÉ: On présente ici des simulations numériques, à l'aide de la méthode d'éléments distincts (DEM), d'un lit de matériau
granulaire ayant une trappe amovible sur une partie de la limite sous-jacente. Kikumoto & Kishida 2003, Kikumoto et al., 2003 ont
mesuré les contraintes verticales sur une trappe et ses frontières adjacentes dans les essais où le sable de Tayoura a été utilisé pour
représenter le terrain naturel. La simulation par DEM modélise bien la contrainte verticale mesurée sur la trappe quand il a été déplacé
vers le bas et aussi les contraintes verticales sur les frontières adjacentes à la trappe. Ensuite, l'écoulement par gravité du sable a été
modélisé lorsque la trappe a été soudainement retirée. Il a été constaté qu'il y avait une réponse dynamique complexe de la contrainte
verticale sur la limite juste à côté de l'ouverture créée, mais seulement de légères modifications plus loin. La motivation pour ces
simulations de DEM a été de mieux comprendre les processus impliqués dans la construction de tunnels lorsqu'il y a un effondrement
partiel de la face ou sur les cotés près du front du tunnel. Bien que la sécurité dans l
’excavation des
cavités souterraines se soit
nettement améliorée au cours des dernières décennies,
les risques d’
accidents dans ce type d
’opération
demeurent un défi pour
l'industrie de la construction japonaise.
KEYWORDS: tunnel, trapdoor, gravity flow, discrete element method, sand
1 INTRODUCTION
At present, almost all mountain tunnels constructed in Japan are
excavated utilizing the New Austrian Tunneling Method
(NATM). This tunneling method was advocated by Prof.
Rabcewicz from Austria in 1964 (Rabcewicz 1964a, b, 1965).
In Japan, the method has been applied to tunnel construction
since about 1978. On the other hand, tunnels in cities are often
excavated utilizing a Shield Tunneling Method. Since adopting
these methods there has been a substantial decrease in the
number of accidents and fatalities in tunnel construction in
Japan. However, there is still a relatively higher incidence of
accidents during tunnel construction than in the construction
industry in general. In tunnel construction, rock fall events in
rocky ground and partial collapse from the roof and face in
sandy ground are characteristic of the types of accident that
occur.
Rock falls and the partial collapse at the face induce stress
redistribution. This in turn leads to the formation of a ground
arch above the failed roofs with accompanying local stress
increases at the foot of the arch. These increased stresses may
cause the collapse to extend to the whole tunnel itself. This
mode of failure is more likely in sandy ground. Therefore, when
minor to modest collapse occurs it is very important to know
how much the stress at the foot of the ground arch will increase
above the values prior to the collapse.
The stress redistribution induced by lowering of a trapdoor
has been tested and analysed (Terzaghi 1936, Murayama &
Matsuoka 1971, Kikumoto & Kishida 2003, Costa et al 2009
etc.). Murayama & Matsuoka (1971) and Kikumoto & Kishida
(2003) measured the earth pressure on the trapdoor and the
surroundings during the lowering of the trapdoor. The
Kikumoto & Kishida (2003) data are compared with the results
from DEM modelling herein. Costa et al (2009) investigated the
ground deformation mechanisms during lowering of a trapdoor
with various ratios of the sand layer depth to the width of the
trapdoor. They showed when the ratio is low, so modelling a
shallow tunnel, the zone failure is limited to sand adjacent to
and above the trapdoor. On the other hand, when the ratio is
high, which represents a deep tunnel, the failure region is more
widely spread beyond the width of trapdoor.
Earth pressure increases during a gravity flow were analysed
using a two dimensional DEM by Kiyama & Fujimura 1983.
They concluded that the earth pressure on the foot of the ground
arch during the gravity flow is much higher than the static earth
pressure. This finding is confirmed by the results of the DEM
modeling presented in this paper.
Three dimensional discrete ele ent simulation of trapdoor unloading and
gravity flow of sandy granular material
Simulation tridimensionnelle par les éléments distincts du débit de décharge et d’écoulement
gravitaire du matériau granulaire sableux
Kikkawa N., Itoh K., Toyosawa Y.
National Institute of Occupational Safety and Health, Japan
Pender M.J., Orense R.P.
University of Auckland, New Zealand
