10th Asian Regional Conference of IAEG (2015)

Relationship between Groundwater Flow and Internal Structure of Landslide Massby Combined Geophysical Survey Method
Gen FURUYA(1), Akira SUEMINE(2) , Jun’ya HONDA(3) and Gonghui WANG(4)(1) Faculty of Engineering, Toyama Prefectural University, Japan
E-mail:gfuruya@pu-toyama.ac.jp(2) Former, Disaster Prevention Research Institute, Kyoto University, Japan(3) Toyama Prefecture Government, Japan(4) Disaster Prevention Research Institute, Kyoto University, Japan
Abstract
In this study, we performed two geophysical survey methods, 1-m-depth groundtemperature survey and surface-wave seismic survey, in Nishi-ikawa landslide, for better
understanding relationship between the dynamics of groundwater flow and internal
structure of landslide mass. We installed 31 thermocouples at the 1 m depth along 3 crosssurvey lines on the landslide, and has been continuously monitoring. In this paper, wepointed out the E-line in this landslide, and found that the distribution of groundwater flow
was vein-like. Furthermore, we carried out surface-wave seismic geophysical survey at thislines. We pointed out phenomena by these surveys as following: (1) in the rainy summer
season, the ground temperature briefly changes associating with the rainfall-infiltration
process, but goes back to almost the same temperature as that of the isothermal layer at the
1 m depth. This indicates that groundwater in this landslide may have two differing sources.
(2) Veins groundwater flow are located on those areas with low shear wave velocity as
revealed by the surface-wave seismic geophysical survey. Especially, there is one
monitoring point (E7) at which 1 m depth ground temperature lowered after each heavy rain.
Decreasing behavior is consistent with the increasing of water level observed in a borehole
nearby. Therefore, we concluded that groundwater from isothermal layer increases along
weak structure zone in the landslide mass.
Keywords: 1-m depth ground temperature, surface-wave, heavy rain, borehole water level,
extruding flow
1.

Introduction

crystalline schist area. The variation of groundtemperature at one meter depth was caused by inflow
of groundwater (increase of borehole water level) in
deep layer (approximately isothermal layer) fromresults of these methods.

It is well known that in many cases the landslide
movement is regulated by variation of groundwater.
There are many cases the groundwater in landslide
mass is shown as a water surface profile. However, it
seems that actual groundwater flow exists as vein-likeshape in a natural slope (e.g. Takeuchi, 1980; Furuya
et al, 2006). It seems that such groundwater flow iscontrolled by internal structure of landslide mass.
Therefore, detecting of location and behavior ingroundwater flow are needed to evaluate detailed
slope stability.
In this study, we carried out two geophysicalsurvey methods, continuous monitoring of groundtemperature at the depth of one meter andsurface-wave seismic survey, at the Nishi-ikawa
landslide to clarify relationship between groundwaterflow and internal structure of landslide mass in the2.

Test site

Nishi-ikawa landslide is located in the middle of
Shikoku Island, southwestern Japan shown in Fig. 1.
This landslide was reactivated by the cutting on thelower part of an old landslide. The Nishi-ikawa
landslide consists mainly of green schist and partiallyof pelitic schist where had been well studied throughdrillings and various monitoring since 1973 (Suemine
et al, 1980; Suemine, 2004). Maximum depth of thislandslide mass is approximately 16 m by estimated bypipe strain gauge monitoring. The 1-m-depth ground1

10th Asian Regional Conference of IAEG (2015)

temperature survey had also been carried out on
January 2000 to examine the location of veins ofgroundwater flow (Furuya et al., 2013). In Fig. 1,
those areas with the ground temperature being higher
than the average one meter depth ground temperature(8.5˚C) were highlighted and estimated to be theveins of groundwater flow (Furuya et al., 2013).
Especially, over 9.0˚C, high temperature area, isindicated by arrows, which is direction of estimatedvein of groundwater flow. Furthermore, continuous
monitoring of ground temperature at the same depth
has been carried out at three survey lines (C, E, and I
line (shown in Fig. 1)) since 30 April 2010 (Furuya etal., 2014).

conducted when the ground temperature difference
between the normal ground temperature at a depth of
1 m and the flowing groundwater temperature
exceeds 2.5˚C on summer and winter seasons in the
mid-latitude. We installed 29 thermocouples at threemonitoring lines since 2010 which based on theestimated result of the 1-m depth ground temperature
survey and two additional thermocouples at east andwest part of point E6 since 2013 (Fig. 1). The
monitoring was performed as following:• In each survey line, the interval between eachmonitoring point is 10 meters. However, 5 metersinterval from E5 to E7. Total measurement points
are 31.
• Using sensors are T-type thermocouple. These are
installed at the depth of one meter in eachmeasurement point. The temperature measuring
range is -40~ +125 ˚C with a precision of ±0.5˚C.
• Maximum sampling interval is 2 seconds for all
the 31 points.
The measurement has been carried out since 30 April
2010. However, there are missing data resulting fromthe disconnection by animals, lightning damages orother factors in the monitoring period.
In this study, we used precipitation data of the
Ikeda dam site monitoring station, Ministry of Land,
Infrastructure, Transport and Tourism, which was
located 2.5 km far from the Nishi-ikawa landslide. In
addition, we used record of borehole water level at
No. 4 (recorded on chart paper) to examine therelationship between 1-m-depth ground temperature
at the point E7 and behavior of groundwater level.
3.2 Surface-wave seismic survey
To investigate the internal structure of thelandslide mass, we carried out the surface-wave
seismic survey known as multichannel analysis of
this wave at the E line for ground temperaturemonitoring in 2014. We used 24 geophones (NaturalFrequency: 4.5 Hz) in this survey. These were set on
2 meters intervals along the monitoring line of groundtemperature, and wooden hammer (approximately 8kg) was used for exciter of seismic motion. The
hummer points were outside of measurement line andalso intermediate between the geophones. After then,profile of the underground structure was estimated by
exclusive software. The equipment and software were
following:•Seismograph: McSEIS-SXW 24ch type K (OYO
Corporation).
• Software: SeisImager_e (ditto).

Fig. 1 Plan of the Nishi-ikawa landslide
3.

Methodology

3.1 Continuous monitoring of ground temperature
The principle of detecting groundwater flow bysoil temperature monitoring, details are described in
Takeuchi (1980), is based on the monitoring thedifferences in the 1 m depth ground temperatures
disturbed by veins of groundwater. Furuya et al.
(2014) re-explained that the ground temperature in
the vicinity of the groundwater vein tends to be lower
than the average ground temperature from summer toautumn because flowing groundwater temperature islower than normal ground temperature at a depth of 1
m. In contrast, the ground temperature in the vicinityof the groundwater tends to be higher in winter tospring as compared to the temperature of thesurrounding ground because flowing groundwatertemperature is higher than normal ground temperature
at a depth of 1 m. Takeuchi (1980) has pointed outthat 1-m-depth ground-temperature surveys can be

4.

Results and Discussion

4.1 Variation of ground temperature at the one
meter depth in heavy rain
Furuya et al. (2014) have pointed out ground2

10th Asian Regional Conference of IAEG (2015)

temperature at the depth of one meter in the point I1
and E7 were decreasing after a heavy rain in summer
season, and these phenomenon might be effected byvein of groundwater flow. We focus the hourly dataat the point E7 where locates near water levelmonitoring in borehole No. 4.
Fig. 2 shows the result of hourly time serieschanges relationship between ground temperature atthe point E7, precipitation, and borehole water levelat the No. 4 for the period of 19 June to 14 July 2013.
In this figure, the heavy rain occur on 19 to 21 June
(Cumulative precipitation is 149mm). The normal
ground temperature at the depth of 1 m without
effected by groundwater flow is increasing period in a
mid-latitude area of north hemisphere during thisperiod. The ground temperature at the point E7 isincreasing 20 to 21 June. After increasing, thistemperature is decreasing approximately 11 days
except 26 June with a slightly strong rainfall. On theother hand, increasing borehole water level at the No.

4 occurs approximately 1 day late compared withground temperature. Decreasing of groundtemperature occurs also approximately 1 day after theincreasing of borehole water level at the No. 4.
Fig. 3 shows the result of time series changes
between same data items for the period of 1 to 31
August 2014. In this figure, the heavy rains occur on
1 to 3 (Cumulative precipitation is 314mm: Typhoon
Nakri) and 9-10 August (Cumulative precipitation is
175mm: Typhoon Halong). There are twice
significant decreasing ground temperature on 2 to 3
and 9 to 11 August. Especially 2 to 3 August,decreasing of ground temperature is 3.65 ˚C (19.40 to
15.75 ˚C) compared with between before start ofincreasing and end of decreasing. In this process,increasing of borehole water level at No. 4 begins alittle after increasing of ground temperature at the
point E7. During 8 to 10 August, variation process of
between borehole water level and ground temperature
is similar to the case of 2 to 3 August.

Fig. 2 Time series change of hourly monitoring results between ground temperature (E7), Borehole
water level (No. 4), and precipitation (19 Jun to 14 July, 2013)

Fig. 3 Time series change of hourly monitoring results between ground temperature (E7), Borehole
water level (No. 4), and precipitation (1 to 31 August, 2014)3

10th Asian Regional Conference of IAEG (2015)

It is recognized that peak value of normal groundtemperature at the depth of 1 m without effected bygroundwater flow in a mid-latitude area of north
hemisphere, especially Japan, appear on August to
September (Takeuchi, 1996). Lowest air temperatureon 5 August in AMeDAS Ikeda by Japan
Meteorological Agency was 22.5 ˚C. Takeuchi (1996)
have been pointed out that isothermal temperature
was 12.49 ˚C at the Nishi-ikawa landslide. Fromthese monitored value, the process of groundtemperature variation is that 1) Increasing process iscaused by infiltration of rainfall from ground surface,2) Decreasing process might be caused by increasing
borehole water level (Expansion of the groundwaterflow vein) in-flowed from deep layer such as
isothermal layer. It is probably to be the same process
on 9 to 10 August 2014 and 16 to 21 June 2013
(shown in Fig. 2).

(approximately under the point E4 to E8), and deeppart (deeper than 5 meter) are distributed to thevertical direction (around under the point E6). From
relative low velocity distribution, this area areevaluated to weak (loose) material zone bycharacteristics of the propagation velocity in amaterial.
4.3 Supply source of groundwater flow to generate
a significant difference of soil temperature
As significant decreasing ground temperature
after heavy rain at the point E7 were monitored, we
dug two test boreholes (Depth: 2.55 m) to confirm
surface ground condition by auger boring at 1.8 m
east side of the point E7 and 1.0 m west side of thispoint on 11 May 2014. Table 1 shows one result
which describe groundwater level of these boreholesby this drilling work. In this table, the east side of thepoint E7 is low groundwater level during 11 to 12
May 2014 (2.55 to 2.38 m). On the other hand, thewest one is high groundwater level on same period(1.27 to 1.25 m). We monitored rate of recovery after
pumping at this borehole, which value is 75 cc/min.
These results means that it doesn’t exist
homogeneous groundwater surface in the mass of
Nishi-ikawa landslide. Furthermore, groundwatertemperature in the east side of the point E7 was 13.5
˚C. This temperature is similar to isothermal
temperature. On the other ward, low temperature ofgroundwater consist in deep layer, normally, isexisting in the shallow layer at the east part of point
E7.
From above survey and monitoring results,
although there are a little effect of rainfall infiltration,
decreasing process of ground temperature at the 1 m
depth during heavy rain is relate increasing

4.2 Internal structure of landslide mass by
surface-wave seismic survey
Fig. 4 shows the result of shear-wave (S wave)
profile at the E line. In this figure, it doesn’t
correspond with between the expansion distances of
surface-wave seismic survey and total length ofmeasurement points of E line. This reason is thatcable for surface-wave seismic survey were set on thesurface. Therefore, the latter length is longer than theformer. There are two high velocity parts(approximately Vs>400 m/s) in the mass. These parts
are possibly consisted with hard material such as
rock/large bolder. On the other hand, relatively low
velocity (approximately 160 to 300 m/s) part isexisted, which surrounded dotted lines. In particular,
shallow part (shallower than 5 meter) of dotted linesarea are distributed to the lateral direction

Table 1 Borehole water level at the both side of point E7
Location / Date
11 May12 MayEast side of the point E7

GL-2.55m

GL-2.38m

West side of the point E7

GL-1.27m

GL-1.25m

Note－
Rate of recovery: 75cc/min

Fig. 4 Result of shear-wave velocity profile at the E line by surface-wave seismic survey

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10th Asian Regional Conference of IAEG (2015)

Fig. 5 Estimated vein of groundwater flow path flow deep layer around the point E7(inflowing) of groundwater from deep layer. Fig. 5
shows presumed increasing of groundwater flow pathfrom deep layer at the E line of Nishi-ikawa landslide.
In this figure, groundwater path from deep layer
should be estimated by white dotted line through inthe relative low velocity (weak) part in the landslide
mass like vein shape. The size of this vein might not
be large by the result of drilling at the both side ofpoint E7. It seems that increasing of the groundwaterfrom deep layer, probably, is extruded effect aspiston-flow like by some force.
5.

temperature and slope failures caused by heavy
rainfall, Shikoku Island, southwestern Japan,
Engineering Geology, Vol.85, ELSEVIER,
pp.332-346.
Furuya, G., Katayama, T., Suemine, A., Kozato, T.,
Watanabe, H., Marui, H., (2013): Application of
the newly frequency domain electromagnetic
method survey in a landslide area, Landslide
Science and Practice, Vol. 2, Early Warning,
Instrumentation and Monitoring, Springer, pp.
169-175.
Furuya, G., Suemine, A., Wang, G., Takano, Y.,
Ichikawa, Y. (2014): Vein of groundwater flow
behavior on a Land-slide by continuous monitoringof ground temperature, Engineering Geology forSociety and Territory -Volume 2 Landslide
Processes, G. Lollino et al. (eds.), pp.151-154,
Springer, DOI 10.1007/978-3-319-09057-3_17.
Suemine, A., Shima, M, Konishi, T. (1980): Someremarks on landslide mechanism (An example offractured zone landslide). Disaster Prevention
Research Institute Annuals. 23(B-1), pp. 345-355(in Japanese with English synopsis).
Suemine (2004): Observational result of groundwatertable at landslide occurrence. Journal of the Japan
Landslide Society, 41(1), pp. 43-48 (in Japanese).
Takeuchi (1980): Method of investigating
groundwater-vein-streams
bymeasuring
one-meter-depth in landslide areas (I). Journal ofJapanese Association of Groundwater hydrology,
22(2), pp. 11-39.
Takeuchi (1996): Method of investigating
groundwater flow by measuring temperature,
Kokon-shoin, 480 p (in Japanese).

Conclusions

We carried out two geophysical survey methods,
1-m-depth ground temperature survey andsurface-wave seismic survey, in Nishi-ikawa
landslide, for better understanding relationshipbetween the dynamics of groundwater flow andinternal structure of landslide mass. These results
found that there is one monitoring point (E7) at which
ground temperature at the one meter depth lowered
after heavy rain. This point located low velocity zone
(weak structure) from surface to deep layer by the
result of surface-wave seismic survey. We concluded
that groundwater from isothermal layer increases
along weak structure in the landslide mass. We willconsider the age of groundwater from deep layer andreproducibility confirmation of phenomenon in the
future study.
Acknowledgements
We wish to thank Dr. A. Takeuchi (Natural
Groundwater Research Institute) for his valuablecomments and kind help in this study.
References
Furuya, G., Suemine, A., Sassa K., Komatsubara T.,
Watanabe N., and Marui H. (2006): Relationshipbetween groundwater flow estimated by soil

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