10th Asian Regional Conference of IAEG (2015)

Verification of swelling and landslides of smectite-bearing ground due tohydrothermal alteration in non-volcanic region
Eiji TAMURA(1) and Shuichi HASEGAWA(2)(1) Yonden Consultants Co. Inc., Japan
E-mail:e-tamura@yon-c.co.jp(2) Kagawa University, Japan
Abstract
Bedrock deterioration by hydrothermal alteration has been overlooked in previous
geological investigations in non-volcanic regions, and has been interpreted as fault gouge or
fault breccia instead. Firstly, this paper describes the swelling characteristic of smectite
bearing ground generated by hydrothermal alteration. Next, it shows that there are
discernible hydrothermal alteration zones along the Median Tectonic Line in central
Shikoku. The hydrothermal alteration zones mainly consist of smectite bearing clay aroundthe intrusive rhyolite body of the middle Miocene. Hydrothermal alteration generatedegradation of the bedrock and the smectite bearing clay cause the unexpected landslide in
a cut slope constructed several years ago. In addition, using the cation exchange capacity
test it has been shown that the smectite produced from hydrothermal alteration in the
Shikoku area is of the Ca-type.
Keywords: hydrothermal alteration, bedrock deterioration, smectite, swelling, Ca-type1.

Introduction

produced by hydrothermal alteration due to theigneous activity in the middle Miocene (Hasegawa, etal., 2001a). It is pointed out that this should be thecause for the troubles during construction works suchas unexpected landslides on cut ground slope (Tamura
et al., 2007b), large landslides in ancient era(Hasegawa, et al., 2001a), large displacements in thetunneling (Hasegawa, et al., 2006), and heaving of cut
ground (Tamura et al., 2007a).
Smectite is generated not only by a hydrothermal
alteration but also due to weathering. It is importantto verify if the origin of smectite depended onhydrothermal alteration as this can give important
knowledge of the distribution of smectite-bearing
ground. Unfortunately, such verification is not carriedout enough.
In this paper, we present the swellingcharacteristic of smectite-bearing ground, based on
in-situ data. This case shows the occurrence of theheaving of a cut caused only by the change inthickness of the overburden load due to theconstruction the cut and thus, can be used to properly

Ground heaving can cause the deformation ofbuildings set up directly on cut-ground, landslides
due to the bedrock deterioration and larger
displacements in tunnels. The heaving of a dam
foundation composed of shale (Goodman, 1993), theheaving of ground in residential area composed ofshale (Meehan, 1975）and the heaving of ground at aresidential area due to the crystal pressure of gypsum(Oyama et al., 1998), etc. have been reported. In
tunneling, heaving is referred to as squeezing ground,and has been extensively studied and investigated. In
tunnel deformation, two effects, deformation due toswelling smectite and deformation due to insufficientstrength of the rock can overlap. Discerning both
effects is difficult. Although the cause of heaving isdue to the swelling of smectite in many cases, there isalmost no research about heaving of foundations due
to swelling of smectite using in-site data.
In Shikoku, a hydrothermal alteration zone withexpansive clay minerals including smectite wasformed around the intrusive body or along the fault

110th Asian Regional Conference of IAEG (2015)

active right-lateral fault.
The Inner zone is composed of the Ryoke-belt,
and from north to south the Outer zone is composedof the Sanbagawa belt, the Chichibu belt, and the
Shimanto belt. The Ryoke belt is composed of the
Izumi group, in which Cretaceous granite is
uncomformably overlain by Late Cretaceous
sedimentary rocks. The Sanbagawa belt is composedof high-pressure intermediate-type metamorphic rock,and the Chichibu belt is a Jurassic accretionary
complex, composed mainly of sandstone andmudstone. The Shimanto belt is mainly composed ofa Cretaceous accretionary complex on the north side,
and a Paleogene accretionary complex mainly on thesouth side.
In Shikoku, not only the intrusive rocks ofrhyolite of the middle Miocene distributed along theMTL, but granite and rhyolite are also scatteredthroughout the Inner zone or the Outer zone. Theserocks indicate K-Ar age of about 13 to 15Ma, withmany of them concentrated around 14Ma (Shinjoe
and Sumii, 2000 etc.). The hydrothermal alteration
zone, which shows the combination of mineral of theevaluate the swelling characteristic of smectite.
Next, we present the case of hydrothermal
alteration around the intrusive rock consisting ofrhyolite of the middle Miocene along the Median
Tectonic Line (MTL) in Shikoku. It shows that thegeneration of expansive clay minerals such as
smectite is closely related to the intrusive rock andthe extension of hydrothermal alteration of the fault
and its surrounding ground. Notably, it shows that the
bedrock classification of the deep undergrounddeclines due to hydrothermal alteration, resulting in
bedrockdeterioration
includingprogressedargillation.
Furthermore, the exchangeable cation of smectite
generated by the hydrothermal alteration on Shikoku
is the Ca2+-based Ca type.
2.

Geological setting and distribution ofhydrothermal alteration
The geology in Shikoku is divided by the MTL
into the northern Inner zone and the southern Outerzone, and the zonation of the following geologicalbelts extends east and west (Fig. 1). The MTL is an

Heaving site described in
Chapter 3

Fig.1 Geological map of Shikoku and heaving site (described in
Chapter 3)2

10th Asian Regional Conference of IAEG (2015)

smectite zone, is distributed in the region without
distribution of the intrusive rocks beyond the region
along the MTL, as well as in the region near the
intrusive rocks of rhyolite of the middle Miocene(Hasegawa et. al., 2001b).

fracture zone
The heaved pelitic schist fracture zone iscomposed of sandy clay or clayey sand having adensity of soil particles of 2.701 to 2.770g/cm3, a unit
weight of 22.9 to 23.3kN/m3, a natural water content
of 5.3 to 7.6%, and a clay content of 7 to 42%. The
fine fraction of this crush zone is mainly composed ofmuscovite and chlorite, and contains a large amountof smectite which is expansive clay mineral. Smectite
content is between 10 to 15% in the pelitic schist
fracture zone and approximately 27% in the basic
schist fracture zone.
The swelling pressure of the fracture zone was
30 to 60kN/m2 in the pelitic schist crush zone and
90 to 130kN/m2 in basic schist fracture zone. For
both samples, the swelling reaction during thelaboratory test occurred immediately after theinundation and finished within approximately 30
minutes, which shows the swelling reaction
occurred immediately under a forced wet-state(Left figure in Fig. 2).
In the swelling test, the swelling pressure wasmeasured at four-level loading pressures. The
swelling pressure of the pelitic schist fracture zone
is 0 to 11% under the loading pressure of 0 to 98
kN/m2. A negative correlation was found between
the loading and the swelling pressures as shown in
the right figure in Fig. 2. The maximum swellingpressure in the right figure in Fig.2 is 160kN/m2,
which is equivalent to the overburden thickness of
7.5 m.

3. Swelling characteristic and upheaval
mechanism of smectite-bearing crush zone
3.1 Case of heaving of a cut in smectite-bearing
fracture zone
This chapter explains the swelling characteristic
and upheaval mechanism of a smectite-bearing
fracture zone for a case in which a concrete
foundation built in a cut in the Sanbagawa belt in
Shikoku that heaved 66mm in the seven years after
the foundation was constructed (Tamura et al., 2007a,Fig. 1). The fracture zone is 20 m in width, and it isinclined 50 degrees from the level. The heaving of the
cut in this case was caused only by the conditions of
the cut.
The investigation site is located in the pelitic
schist area at the southern edge of the Sanbagawa beltof the Shikoku region. The heaving ground is the cut
has a thickness of 25 m and is composed mainly ofpelitic schist and partially of basic schist fracturezones. The site is within a fresh bedrock area whose
overlying bedrock with a thickness of 25 m wasremoved and is close to the large fault in the
Sanbagawa southern edge. Therefore, smectite at thesite is assumed to be generated by hydrothermal
alteration.

3.3 Mechanism of heaving of a smectite-bearing
fracture zone in the cut

3.2 Geotechnical behavior of a smectite-bearing

Fig. 2 Example of swelling pressure test of pelitic schist crush zone (left figure) and correlation
between loading pressure and swelling rate in crush zone (right figure)3

10th Asian Regional Conference of IAEG (2015)

The mechanism of heaving of smectite-bearing
fracture zone in the cut ground can be summarized asfollows.
In the smectite-bearing fracture zone, overburdenpressure of about 600kN/m2, which is equivalent to
the ground overburden thickness of about 25 m, wasreleased through excavation. Swelling occurred in thesmectite-bearing fracture zone. This resulted inupheaval of the concrete foundation on the fracturezone. It is assumed that the swelling reaction
continues to the depth at which the overburden andthe swelling pressures are balanced is reached, after
the swelling of smectite finishes. Measuring ofunderground displacement by borehole inclinometerusing a CCD camera revealed that the undergroundswelling reached a depth of approximately 7.5 m(Tamura et al., 2007a). Because this is consistent withswelling of the fracture zone when a loading pressureof not more than 160kN/m2, which is equivalent to
the overburden of 7.5 m, is applied, thereforeswelling can be determined to not progress deeper
than 8 m. Namely, it can be considered that thisfracture zone has a swelled to an amountcorresponding to the overburden.
As shown above, it is assumed that removal of
overburden by a large excavation causes a swelling
reaction based on the swelling of smectite near the
ground's surface in the fracture zone having the
expansive capacity. The swelling reaction extends
downwards over several years and finally finishes atthe depth in which the overburden and the swellingpressures are balanced.

4. Hydrothermal alteration and landslide along
the MTL
4.1 Hydrothermal alteration and fault gouge along
the MTL
Along the MTL in Shikoku, from Kawanoe,
Shikoku-chuou-city, Ehime prefecture, which is thecenter of Shikoku (Fig. 3), westward, the rhyolite andandesite belonging to the Ishizuchi group of Miocene
intrude into the fracture zone of the MTL and its
surrounding area, as a result, hydrothermal alteration
occurred.
Hasegawa et al. (2001a, 2001b) and Tamura et al.
(2001) reported that the fault gouge along the
intrusive rock of the MTL contains tridymite,
dolomite and magnesite, as well as smectite andillite-smectite mixed-layer mineral and reported thatthose mineral composition had been produced byhydrothermal alteration.
In this chapter, the state of bedrock deterioration
by hydrothermal alteration on the cut ground slope
along the MTL is described as previously by Tamura
et al. (2007b). In addition, the case of the low-angle
landslide predisposed by the hydrothermal alteration
originated smectite-bearing clay is presented. An
landslide occurred five years after the construction of
the cut, and was preceded by heavy rain.
4.2 The bedrock deterioration due tohydrothermal alteration observed on the cut
slope

Fig.3 Locations of alteration zone(A) and landslide(B) along the MTL in Shikoku

4

10th Asian Regional Conference of IAEG (2015)

Fig.4 Geology of cut slope in Iyomishima region,
Ehime prefecture(modified after Tamura et al., 2007a)Fig.5 Rock mass classification and distribution
clay minerals of cut slope(modified after Tamura et al., 2007a)

The location of the bedrock deterioration in the
Iyomishima region is close to the Ishizuchi fault of
the Median Tectonic Line active faults system. The
cut slope has a height of about 40 m. The geology of
the cut ground slope is composed mainly of pelitic
schist of the Sanbagawa belt. Rhyolite with a width ofabout 2 m, belonging to the Ishizuchi group of the
middle Miocene intrudes into the lowest part of cut
slope (Fig. 4)..
The geology from the top to fourth cut slope in
the cut slope is composed of weathered rocks andclassified as CL-class ground according to the rockmass classification by CRIEPI (Japan Society ofEngineering Geology, 1992). The fifth and sixth cut
slopes are composed of D-class ground (Fig. 5). The
D-class ground is subdivided into DH class mainly inclast form, DM class mainly in small fragment form
and with argillation and DL class in clay form.
On this cut slope, its deep underground, which isless weathered, shows argillation that has progressed
further than its weathered ground surface. The
rhyolite body in the 6th cut slope shows strong
argillation itself, as well as causing argillation to its
surrounding schist. Furthermore, an altered clay zone

is observed from the rhyolite with argillation on the
6th cut slope toward the 5th to 3th cut slopes crossing
the schistosity.
The clay zone of rhyolite and basic schist at theth
6 layer matches the sliding surface of smalllandslide caused by the cut.
X-ray diffraction reveals that the part withargillation, when comparing with the mineralcomposition of the fragment of a basic schist or
rhyolite, is characterized by containing more
expansive clay mineral of smectite and achlorite-smectite mixed-layer mineral. In particular,smectite and chlorite-smectite mixed-layer mineral
are located mainly near the rhyolite observed on thebottom of the cut slope that is less affected byweathering, as shown in Fig. 5.
4.3 Unexpected low-angle landslide caused on a
cut slope constructed five years earlier
In the east region of Shikoku, intrusive rhyolite
is not observed along the MTL, however,hydrothermal alteration occur similarly as observed in
the west and central regions of Shikoku. Shown
below are the cases in which altered sandstone5

10th Asian Regional Conference of IAEG (2015)

cut slope. This geological condition results in a
structure that is difficult to drain the ground water.
The gray-white clay (A in Fig. 7) on the top of thesliding surface originates from sandstone and iscomposed mainly of quartz and chlorite. Smectite, an
expansive clay mineral, is observed in the gray-whiteclay. The black clay (B in Fig. 7) on the fault crushzone originates from mudstone at the end point iscomposed of illite-smectite mixed-layer mineral.
The features of the landslide at this site are as
follows: it has a high sliding speed and a large sliding
amount similar to a collapse, however, the sliding
gradient is as low as 22 degrees, and deformation of
the rock slide is more like a landslide than a collapse.
Also, the landslide occurred suddenly several years
after cut ground. The occurrence of such an
unexpected landslide is considered to be caused by
the smectite-bearing altered sandstone, which is an
expansive clay mineral with weak strength due tohydrothermal alteration, and the presence of fissure
dipping towards the face of the slope (Tamura et al.,2007b).

generated by hydrothermal alteration have developed
sliding surface and caused unexpected landslides on a
cut slope 5 years earlier.
The landslide site in the Donari region, Awa-city,
Tokushima prefecture, is a cut slope which iscomposed of the Izumi group along the Hikino faultof the MTL active faults system (Fig. 3). It is anexpress highway cut slope that was cut 5 years earlier.
After continuous rain with precipitation of 83.5 mm
for 2 consecutive days, a landslide of weathered rock,70 m in width, 80 m in length and 10 m in slide-depth,
having a volume of 26,000 m3 occurred (Tamura et al.,2007b). The landslide created a head cliff 10 m inheight at the top after about 1 hour. The soil mass had
slide downwards by about 8 m.
The cut slope where the landslide occurred wascomposed of 7 benches, each 7 m in height, and thecut gradient was 1:1.5. The sum total of slope heightwas 50 m (Fig. 6). The landslide occurred from the 2th
to 7th cut bench. The sliding materials consisted ofweathered altered sandstones of the Izumi group.
As shown in Fig. 7, the geology of the landslide
is composed of weathered sandstone towards the top
and mudstone below. The sandstone layer is brownish
and is about 10 m thick. The boundary of both layers
is composed of the white-cloudy altered sandstone
with a system of fissure dipping towards the face ofslope with a low angle, creating the sliding surface.
The altered sandstone is 1 to 2 m in thickness andincludes many white-gray clay veins. The thicknessof the landslide is about 10m. The black mudstonelayer has a fault fracture zone at the end point of the5.

Cation exchange composition of smectite due
to hydrothermal alteration in Shikoku area
Smectite is classified by exchange cation into the

Na-type, whose swelling characteristic is extremely
strong, and the Ca-type, whose swelling characteristic
is relatively weak.
We studied the cation exchange composition ofsmectite-bearing clay which is considered to originate

Fig.6 Plan view of the landslide in the Donari
region, Tokushima pref.
(modified after Tamura et al., 2007b)

Fig.7 Profile of the landslide in Donari region,
Tokushima pref.
(modified after Tamura et al., 2007b)6

10th Asian Regional Conference of IAEG (2015)

from hydrothermal alteration in the Shikoku area,

Ca-type smectite.

using a cation exchange capacity (CEC) test andIn Neogene stratum of the Tohoku area where
Na-type smectite with a strong swelling characteristic
is distributed, the sliding surface average gradient is
as small as 19 degrees (Table 2). The shear strengthof smectite is small compared with other minerals.
Na-type smectite swells strongly and degrades it’sstrength, so that low-angle slides will occur easily. On
the other hand, in the Shikoku area, where landslides
called Shear zone type landslides occur locally,
Ca-type smectite in which the swelling potential isslightly smaller, sliding angles are between 22 to 27
degrees (average 24.5 degrees).
The swelling characteristic of Ca-type smectite issmaller than that of Na-type smectite. Nevertheless,even for Ca-type smectite, deformation such as
ground heaving and unexpected landslides due todegradation of ground strength at the smectite-

X-ray diffraction data to examine the exchange cationof smectite.
CEC test samples consist of clay from the fracturezone which was determined to have originated fromhydrothermal alteration. Origin of these samples arecomposed of granite from the Ryoke belt, andesitefrom the Sanuki group, mudstone and sandstone fromthe Izumi group along the MTL, basic schist from thesouthern margin of the Sanbagawa belt, andsandstone from the Shimanto belt. These samples do
not include zeolite and vermiculite, which havesignificant influence on the CEC value. As shown in
the test results in Table 1, in every sample, theexchange cation is mostly Ca ions and is assessed as

Table 1 Samples on cation exchange capacity test of smectite clay due to hydrothermal alteration in Shikoku(modified after Tamura and Hasegawa (2008))
unit：cmol(＋)/kg
Geology

Mother'srock

RyoukegranitegraniteSanukigroup

andesite

Izumi group mudostonealong MTL
sandstone
margin of
Sanbagawa basic schist
belt
Shimanto belt mudstone

Number of Property ofthe sample
sampleCationexchange
capacity

Exchange- Exchange- Exchange- Exchange- Exchangeable Mg
able K
able Caable cation able Na

Amount of1)

smectite

B-Gr-W2

clay

7.4

6.2

0.8

0.2

4.2

1.0

＋＋

C-Gr-W1

clay

14.9

12.5

0.8

0.2

8.3

3.2

＋＋＋

D-Gr-W1

clay

10.0

8.2

0.9

0.2

5.4

1.7

＋

11.4

13.7

0.8

0.3

9.5

3.1

＋＋

33.9

37.6

0.7

0.4

25.0

11.5

＋＋＋＋

12.3

11.3

0.3

1.3

7.9

1.8

＋＋＋

14.1

14.6

0.4

1.5

8.3

4.4

＋＋

alterated rockF-An-f2
fragmentclay
F-An-W2
Donari
0725D-1
Itano
0725I-1

rock fragmentwith clayrock fragmentwith clay

K-№1

clay

13.1

113

0.6

1.1

101

10.5

＋＋＋

K-№2

clay

16.1

22.6

0.5

1.4

12.2

8.5

＋＋＋＋

Note1) abundance of contents by XRD : ++++ very abundance, +++ abundance, ++ poor, + very poor

Table 2 Regional characteristic of smectite and ground disaster related to smectite in Japan(modified after Tamura and Hasegawa(2008))

Area

SmectiteType ofDistribution exchangeable
cationCapacity ofswelling

Landslide
Average angle Degree of swelling
Division byof cut groundof the slip
geologysurfaceTohoku（green tuff area）

wide area

Na-type andCa-typestrong ～weak

Neogene typelandslide19°

strongShikoku（along large fault）

local area

Ca-typeweak

Shear zone typelandslide22～27°

weak7

10th Asian Regional Conference of IAEG (2015)

Wiley & Sons, Inc., New York, pp.124-127.
Hasegawa, S., Tamura, E., Ohno, U., Kanayama, S.,(2001a): Effect of the Middle Miocenehydrothermal alternation on landslides along theMedian Tectonic Line in Shikoku, Japan, Proc. ofInternational Symposium on Geotechnical andEnvironmental Challenge in Mountainous Terrain(GENSYN-2001), pp.439-448.
Hasegawa, S., Tamura, E., Tsuruta, S., (2001b):
Mid-Miocene hydrothermal alteration as ageological factor of landslides in Shikoku,
Southwest Japan, The 108th annual meeting of Geol.
Soc. Japan, No. O-338, pp.169*.
Hasegawa, S., Yoshida, Y., Akagi, W., Tamura, E.,
Kanbara, D. (2006): Rock mass characterization fortunnelling by the geological history ofhydrothermal alternation and landsliding, IAEG,
paper number 580.
Japan Society of Engineering Geology (1992): Rockmass Classification in Japan, Engineering Geology,
pp.18-19.
Meehan, R. L., Dukes, M. T., and Shires, P. O.
(1975): Case history of expansive claystone damage,J. Geotech. Eng. Div., ASCE101(GT9), pp.933-948.
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Shinjoe H., Sumii, T.（2000） ： Origin of acidic
rocks of outer zone, monthly article Earth, extra
edition No.30, pp.222-226*.
Tamura, E., Hasegawa, S., Ohno, Y. (2001)：MidMiocene hydrothermal alteration along the Median
Tectonic Line in Shikoku, Southwest Japan, The
108th annual meeting of Geol. Soc. Japan No.
O-337, pp.168*.
Tamura, E., Jyonai, A., Matsuzaki, S., Hasegawa,
S.(2007a): Swelling characteristic and upheaval
mechanism of smectite-bearing crush zone in
crystalline schist, Jour. Japan Soc. Eng. Geol.,
Vol.48, No.2, pp.80-89**.
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*: in Japanese,**: in Japanese with English abstract

bearing ground occur. Therefore research todetermine the presence or absence of smectite isimportant.
6. Conclusions
In this paper, the swelling characteristic ofsmectite was verified, based on the cases of groundheaving in smectite-bearing ground formed byhydrothermal alteration. Ground heaving depended
only due to the conditions of the cut. In addition, thehydrothermal alteration around intrusive rhyolitealong the MTL and the generation of smectite clay
and deterioration of bedrock were described.
Furthermore, it was shown that in smectite-bearing
ground, due to much degradation of strength, there
are cases of unexpected landslides, including
low-angle landslides, and sudden landslides occurring
several years after the construction of cuts.
This paper is summarized as follows:
1) In smectite-bearing ground, there is a negative
correlation between the loading pressure and theswelling rate after water absorption, and swelling
progresses to the depth where the stress release of theloading pressure caused by the cut and the smectite's
swelling pressure balance.
2) Along the Median Tectonic Line (MTL) in
Shikoku, due to hydrothermal alteration of the middle
Miocene, smectite and its interstratified minerals
were generated and a hydrothermal alteration zone
composed of a smectite-zone is formed.
3) Hydrothermal alteration causes deterioration andargillation of the bedrock, which favors theoccurrence of landslides.
4) Clay containing smectite produced byhydrothermal alteration or smectite mix-layered
minerals, has small shear strength, can causes
unexpected low-angle slides, and deformation can beobserved as late as several years after the constructionof the cut.
5) Although smectite in the Shikoku area iscomposed of Ca-type smectite which has a swelling
potential slightly smaller than that of the Na-type,caution is required.

References
Goodman, R. E. (1993): Engineering Geology, John

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