10th Asian Regional Conference of IAEG (2015)

Case study of the soundness diagnostic method by monitoring the time-dependent
behaviour around the tunnel ground
Hiroumi NIWA(1), Kenji OKAZAKI(2), Hideyuki MURAYAMA(3), Yoshihiko ITO(2),Terukatsu SASAYA(3), Toshiyuki KURAHASHI(2)(1) Fujita Corporation, Japan
E-mail:hiroumi.niwa@fujita.co.jp(2) Public Works Research Institute, Civil Engineering Research Institute for Cold Region, Japan(3) Fujita Corporation, Japan
Abstract
The time-dependent deformation after the completion of tunnel construction hasbecome a serious social issue in Japan. One of the problems is that most of thesedeformations could not be discovered by conventional rock evaluation methods. Therefore,a more rational method for rock estimation and maintenance systems required. A diagnostic
method is required that is able to provide constant and reproducible monitoring fromconstruction stage to maintenance stage. And it is necessary that any such method isapplicable to in-use tunnels without harmful damage of structures, and can be carried out
rapidly. We are carrying out a study to develop a diagnostic method to estimate thesoundness of tunnel ground from time-dependent behavior from the perspective of geology,
mineralogy and geophysics in an actual tunnel with time-dependent deformation. From theresults of a series of laboratory tests and field experiments, we found it is possible toestimate the soundness of tunnel ground using seismic velocity. Moreover according to
drilling survey, the seismic velocity is sensitive to current geological conditions. And thesoundness of tunnel ground may be evaluated by a decrease in the ratio of surface seismic
velocity to that deep zone. It is confirmed that decrease in P-wave velocity in the zone with
time-dependent deformation is higher than other zones.
Keywords: time-dependent behavior, seismic refraction survey, soundness diagnostic method,P-wave velocity
1.

Introduction

pavement and there is no diagnostic method forassessing these time-dependent behaviours at present(JSCE, 2005). Thus a new method is needed toevaluate the soundness of tunnel ground until its
maintenance phase. For maintenance use, the new
diagnostic method is required to enable continuous
observation in tunnels that are in service.
We are undertaking a project study focused onthese time-dependent behaviours of rock mass fromthe perspective of geology, mineralogy andgeophysics. In previous paper, we reported that it
might be a useful index to observe the time relatedchanges of seismic velocity as a result of bothlaboratory experiments and field experiments (Niwaet al., 2015a). This paper describes the result of field
experiment of actual tunnel with time-dependent
deformation and the result of case study evaluating
the soundness of tunnel ground using seismicvelocity.

In Japan, much of the infrastructure was built
during a period of rapid economic growth between
the 1950’s and 1970’s, and maintenance of these
aging structures is becoming a serious social issue.
Recently, continuous ground degradations such as
squeezing and swelling with time-dependent
behaviour have led to damage of the linings or floor
heaving in several in-service tunnels (JSCE, 2013,
Sakuma et al., 2009). These time-dependent
deformations in tunnels may cause serious social andeconomic losses such as an accident involving users
and a traffic closure caused by lack of required
clearance. Moreover, countermeasures in in-service
tunnels are usually expensive and quite disruptive as
they often require reinforcement or the addition of an
invert arch. However, it is difficult to observe directly
degrading ground conditions behind a lining or1

10th Asian Regional Conference of IAEG (2015)

2.

Diagnostic method

2.1 Concept of the diagnostic method
It is known that the stress released by excavatinga rock mass often results in changes of physicalproperties such as strength reduction. Fig. 1 shows
the concept of a diagnostic method using seismicvelocity. This concept is based on the idea that thephysical properties of rock mass should change as it
degrades. For a rock mass that doesn’t show
time-dependent behaviour, the seismic velocity may
show no decrease apart for a potential small decrease
due to initial degradation during the construction
phase. As the rock masses with time-dependentbahaviour, the seismic velocity may show continual
decrease until late phase of maintenance stage. Basedon this concept, it may be possible to evaluate thesoundness of rock mass around a tunnel bycontinuous monitoring of seismic velocity.

Fig. 1 Concept of diagnostic method using seismicvelocity

2.2 Outline of applied tunnel
The tunnels in this study are a pair of roadtunnels in Hokkaido Japan. The first is the original
tunnel in which time-dependent deformation has been
occurring for the more than 30 years since completion,
the other is a newly constructed relief tunnel. In theremainder of this paper we call the initial tunnel “Oldtunnel” and the relief tunnel “New tunnel” The Old
tunnel was completed in 1977 using the timbering
support method and has length of approximately 1.9km. The New tunnel was completed in 2014 with
NATM and the length is approximately 3.0 km. The

geology of both tunnels is mostly hydrothermallyaltered Neogene andesite or dacite (Okazaki, et al.,2015).
The Old tunnel has 5 sections of time-dependent
deformation as shown in Fig. 2. Thesetime-dependent deformations initially occurred
rapidly in the No.4 block with over 300 mm floor
heaving and a side wall extrusion within three yearsof completion. Though several series ofcountermeasures were taken, some slow-speed
deformation is still occurring. On the other hand,though no time-dependent deformation was observed

Fig. 2 Geologic cross section and survey line of Old tunnel and New tunnel

210th Asian Regional Conference of IAEG (2015)

for now in the New tunnel, there are 2 sections thatshowed an initial deformation of invert arch with
about 100 mm floor heaving had occurred. Thisrequired re-excavation work and the replacement ofsupport member.

degree angle. Each shot is stacked 3 times at eachshot point in order to improve S/N ratio. The surveyline is 450 m length in the New tunnel, 1,500m in theOld tunnel. The interval of receivers is 6.0m, and theinterval of shot points is 3.0m- 6.0m. The
configurations of the shot and receiver in both tunnels
are shown in Fig.3. In the Old tunnel, single spread ofsurvey line consists of 100 geophones over 594m andthe whole survey is conducted while moving thespread with 150m lap. Using the above equipment,
we finished seismic refraction survey without any
damage to tunnel structures and were able to keep
one lane of the tunnel open to traffic.
We applied tomographic analysis to the dataobtained. To determine most probable initial model,
we initially carried out a tomographic analysis using
fifty randomly generated velocity models andaveraged those fifty results.

2.3 Seismic refraction survey
A seismic refraction survey was carried out inboth tunnels in order to evaluate the soundness oftunnel ground. In the New tunnel, it was conducted
on a freshly paved floor immediately after
construction before use. Whilst, in the Old tunnel, it
was conducted after closure after opening of the Newtunnel.
We used a hydraulic impactor as the seismic
source and MEMS (Micro electro mechanicalsystems) sensors as seismic receivers. The recording
system was a SERCEL 428XL DSU. The receiver
was set on a tripod stand in order to ensure stabilityon the pavement. The hydraulic impactor was used to
avoid damages to the pavement as a non-blasting
seismic source. MEMS sensors enabled down-sizingof the survey equipment and to reduce the hours
needed for receiver handling (Niwa et al., 2015b).
P-wave generation was achieved using a vertical shotand S-wave generation using an inclined shot at a 35

2.4 Drilling survey
The drilling survey was conducted in the Old
tunnel in order to grasp the geological distribution
and condition of altered rock. Initially, several shortdrillings of less than 5m length were carried out as abrief survey. The equipment used for short drillings
was a portable core drilling machine normally used

Fig.3 Configuration of shot points and receiver points

310th Asian Regional Conference of IAEG (2015)

for concrete core sampling. Employed short drillingsystem were specially arranged in order to be able touse the core sampler which commonly usedgeological survey drillings. The short drillings are
conducted in horizontal direction from side wall oftunnel as shown in photo. 1. Because this equipment
is easy to set it up, it is able to achieve the maximum
5m depth in less than half a day. And long horizontal
and vertical drillings carried out as part of a detailed
survey of the No.4 block. The equipment used forlong drilling was the hydraulic rotary drillingmachine usually used for tunnel advanced drilling.
The survey length is 40m for horizontal drilling and30m for vertical drilling.
3.

Photo. 1 The equipment of short drilling survey(Murayama et al., 2015), the survey result showscoincident tendency. On the other hand, in the New
tunnel, a certain level of loosening must be going on
due to initial discontinuous deformation in the zoneof deformation 1 and 2. However the decreased levelof seismic velocity is relatively less in the New tunnel
than the Old tunnel.
We carried out several drilling surveys in order tobetter understand the geological distribution of theOld tunnel. The drilling survey confirmed that thegeology of the Old tunnel consists mainly of alteredandesitic rock including pyroclastic rock. Fig.5 shows
the geological condition observed in each of thedrilling samples. As shown in Fig.5, the geology
around the No.4 block is strongly altered to clayey
condition. Though it is unclear whether these clayey
conditions caused the tunnel deformation or whether
a huge deformation in the tunnel made geology

Results and discussion

3.1 Survey results
Fig.4 shows the vertical distribution of seismic
velocity obtained by the seismic refraction survey ofboth tunnels. It also shows the section where initial
and time-dependent deformations had occurred. The
deformation of New tunnel is mainly discontinuous
initial floor heaving after completion of invert arch.
And the deformation of the Old tunnel is continuoustime-dependent deformation in No.1 to No.5 block.
As shown in Fig.4, P-wave velocity is relatively
lower between No.1 and No.5 block in which thetime-dependent deformation was observed. While,P-wave velocity of north side of Old tunnel and New
tunnel is higher than No.1 to No.5 block. As several
significant deformations such as floor heaving andside wall extrusion are observed in No.4 block

Fig.4 Results of seismic refraction survey in New tunnel and Old tunnel

410th Asian Regional Conference of IAEG (2015)

Fig. 5 Geological condition and P-wave velocity of Old tunnel

Fig. 6 Decrease rate of P-wave velocity of Old tunnel and New tunnel
clayey, it was confirmed that the seismic velocity issensitive to current geological conditions.

surface seismic velocity to deep zone.
The decrease rate of P-wave velocity of No.1 toNo.5 block and non-deformed zone of the Old tunnel
and the zone of initial deformation 1 and 2 of theNew tunnel is shown in Fig. 6. The horizontal axis
indicates conceptually the time from tunnel
excavation. And it also shows the decrease rate of
P-wave velocity just before collapse obtained bylaboratory tests using the New tunnel samples (Niwaet al., 2015a). As shown in Fig.6, the decrease rate of
P-wave velocity of No.1 to No.5 block with
time-dependent deformation is estimated 25% to 44%.
While, the decrease rate of P-wave velocity of theother zone with no time-dependent deformation is 8%
to 16%. Thus, it is confirmed that the decrease rate of

3.2 Soundness evaluation of tunnel groundIf the decrease of P-wave velocity due to thetime-dependent deformation or the loosening by
stress release from the excavated surface, the seismic
velocity in the deeper zone may be assumed to beindicate the original seismic velocity of groundbecause it is far from influence of the excavation. In
other words, the surface part having lower seismic
velocity originally had higher velocity but it
decreased as tunnel excavation work progressed.
Based on this assumption, the soundness of tunnel
ground can be evaluated by a decrease in the ratio of510th Asian Regional Conference of IAEG (2015)

P-wave velocity in the zone with time-dependent
deformation is higher than that in the other zones.
And it is suggested that the threshold of this tunnel
ground may exist between 16% and 25%.
Furthermore the maximum decrease rate of P-wave
velocity is 44% in the No.4 block. The current
decrease rate of P-wave velocity in the Old tunnel isrelatively lower than that obtained by laboratory test
just before collapse, though direct comparison ofvalues of seismic velocity may not be valid becauseof difference of measuring method between field andlaboratory.
4.

Hokkaido Regional Development Bureau of theMinistry of Land, Infrastructure, Transport andTourism. This research was implemented withsupport from the “Construction Technology Researchand Development Subsidy Program” of the Ministryof Land, Infrastructure, Transport and Tourism forthe “Development of Geological Evaluation andDiagnostic Techniques for Deteriorating Tunnels
with Deformation”.
References
JSCE (Japan Society of Civil Engineers) (2005):
Tunnel library 14 Tunnel maintenance in Japan,
pp.52-55. (in Japanese)
JSCE (Japan Society of Civil Engineers) (2013):
Tunnel library 25 Invert for mountain tunnels-Design, Construction and maintenance, pp.295-319(in Japanese)
Murayama, H., Niwa, H., Ito, Y. (2015): Project
study of tunnels with time-dependent behavior –Records of planning and construction, ITA WTC2015 Congress and 41th general assembly,(Submitting)Niwa, H., Murayama, H., Okazaki, K., Obinata, A.,
and Ito, Y. (2015a): An experimental study forevaluation of tunnel ground health using
time-dependent changes of seismic velocity,
Proceedings of the 43rd symposium on rockmechanics, pp.25-30. (in Japanese)Niwa, H., Murayama, H., Okazaki, K. (2015b):
Project study of tunnels with time-dependent
behavior – A diagnostic method using seismicvelocity, ITA WTC 2015 Congress and 41th general
assembly, (Submitting)Okazaki, K., Niwa, H., Murayama, H., and Ito, Y.
(2015): Consideration of the mineralogicalcharacteristics and time-dependent behaviour of thehydrothermal altered andesite, Proceedings of the43rd symposium on rock mechanics, pp.170-175. (inJapanese)
Sakuma, S., Sugawara, N., Tada, M. (2009): Tunnel
invert restoration of sudden heaving deformation inservice -Yamagata expressway Sakazukiyama
tunnel (in-bound line), Tunnels and undergroundVol.53 No.3, pp.27-31.

Conclusions

We carried out a series of experiments in thelaboratory and in two actual tunnels, aiming toevaluate the soundness of tunnel ground using
seismic velocity. The conclusions of this paper aresummarized as follows.
1) The seismic velocity is relatively lower in thesections in which time-dependent deformation wasobserved.
2) According to drilling surveys, the seismic
velocity responds to current geological condition.
3) The soundness of tunnel ground can beevaluated by a decrease in the ratio of surface seismic
velocity to deep zone.
4) It is confirmed that the decrease rate of P-wave
velocity in the zone with time-dependent deformation
is higher than other zones.
We are now conducting continuous monitoring of
the environment in the Old tunnel such as groundwater pressure, air and ground temperature, humidity.
And analysis of mineral composition of rock is also
conducted. Through these studies, we aim to explain
the mechanism of time-dependent behavior of rockmass now on.
Acknowledgements
We would like to express our appreciation to theStudy Committee on Measurement Technology for
Tunnel Deformation Surveys for helping us with thecompilation of the research results by providing
valuable opinions. Also, regarding investigation, wereceived a great deal of cooperation from those at the6