10th Asian Regional Conference of IAEG (2015)

The effective way to mitigate landslide by groundwater survey measuring groundtemperature
Tadashi YASUDA(1) and Atsuo TAKEUCHI(1)(1)Natural Groundwater Research Institute, Japan
E-mail:yassann.25.1@gmail.com
Abstract
Recently, there are many natural disasters such as landslide caused by heavy rain fall,
which supply groundwater to make slope unstable and landslide occur. The groundwaterespecially subsurface flow can raise water pressure to lift the bottom face of landslide, andalso may move landslide block. Consequently, it’s very important to know how thegroundwater which is related to the landslide flows. So we have surveyed the ground waterflow in landslide area measuring ground temperature. This measuring method is called theground temperature measuring survey which mainly consists of 1m depth temperature
measurement and Multi temperature logging. In this paper, we are explaining the groundtemperature measuring survey method and its principle firstly, then introducing a case studyof the landslide survey using this method, and finally, considering its effectiveness forlandslide survey and mitigation work.
Keywords: landslide, groundwater, ground temperature, groundwater vein stream,
1m depth ground temperature measurement, Multi temperature logging,
1.

Introduction
Landslide is caused by heavy rain fall, which
supply groundwater to make slope unstable andlandslide movement occur. The groundwaterespecially subsurface flow can raise water pressure tolift to the bottom face of landslide, and also may movelandslide block. Consequently, it’s very important toknow how the groundwater which is related to thelandslide flows. So, we have surveyed the groundwater flow in landslide sites measuring groundtemperature. This measuring method is called theground temperature measuring survey which mainly
consists of 1m depth temperature measuring and Multi
temperature logging. In this paper, we will introduce
the method, a case study and will consider its
effectiveness of surveying and mitigation work forlandslide.

that is groundwater level is lowered by withdrawing it,
the lifting force will be decreased and, consequently
the landslide movement will be stopped or stabilized .
Fig.2 shows schema of making landslide more stable
bywithdrawing
groundwaterfromwheregroundwater flows (Yasuda and Takeuchi, 2012).
That makes groundwater level lower and landslide
more stable.

2.

Fig. 1 Schema of groundwater flow in landslide blockLandslide and Groundwater
Landslide is generally classified into somecategories by type of movement and material. In
narrow meaning, it is defined as mass movement onslope, where is, in depth, a distinct zone of weakness
that separates the overlying soil mass that is landslide
block from stable underlying soil or rock. Fig.1
shows schema of groundwater flow around landslide
block (Yasuda and Takeuchi, 2012). Groundwaterflows into the zone to develop pressure to lift themass and make it slide. If the pressure of groundwater

Fig. 2 Schema of landslide stabilization bywithdrawing groundwater

1

10th Asian Regional Conference of IAEG (2015)

3.

Groundwater Survey

3.2 Multi temperature logging
Multi temperature logging is an advanced
groundwater exploration in a bore hole to detect thedepth of groundwater vein stream by measuring
temperature as shown Fig.4. The implementation ofthe logging is as following;[1] Measuring temperature of natural state in the hole.
[2] Pouring hot water into the hole
[3] Putting the probe with sensors in the hole.
[4] Adjusting temperature of each depth to be equal.
[5] Measuring every 1 to 5 min for half an hour
Then, the relation of temperature returning rate
to depth is obtained. The rate is equal to {(Thetemperature at 0min – The one at certain time) / (Theone at 0min – The one of natural state)}. Thegroundwater vein stream is detected as the point offaster turning back to natural state, which means highreturning rate on the graph. The rate being more than
60% per half an hour is reliable evidence ofgroundwater flowing (Takeuchi, 1996).

3.1 Ground temperature measuring
Here, we introduce the groundwater survey
measuring ground temperature. If groundwatertemperature is different from ground temperature, it
can be known where groundwater flows. To know
distribution of planar groundwater flow, it is effective
to measure distribution of ground temperature. On theother hand, to know that of vertical groundwater flow,
it is meaningful to detect the groundwater vein stream
in a borehole by Multi temperature logging.
Generally in landslide area, groundwater doesn’t flow
uniformly but streams like a vein (Takeuchi, 1996).
So we call it groundwater vein stream.
3.1 1m depth ground temperature measurement
If the depth of measuring is 1m, the temperature
condition is considered constant within a few days.
This is reason why 1m depth ground temperature
measurement is general method of groundtemperature measurement. Fig.3 shows theory of 1m
depth ground temperature measurement (Takeuchi,2013). In principle, normal 1m depth groundtemperature is higher/lower than groundwatertemperatureinsummer/winterrespectively.
Groundwater vein stream is detected by thedifference between the ground temperature and thegroundwater temperature. In case of implementing
the measurement should be done as follows;[1] Calibrating sensor.
[2] Measuring ground temperature[3] Estimating normal 1m depth ground temperature:[4] Measuring groundwater temperature.
[5] Rectifying deviation due to land condition
Then the planar distribution of groundwater veinstream is obtained by drawing isothermal lines on aplanar figure.

Fig. 4 Multi temperature logging and graph obtained
from measurement

Fig. 3 Theory of 1m depth ground temperature
measurement210th Asian Regional Conference of IAEG (2015)

4. Case Studies
We introduce case studies of the survey and also
introduce its mitigation work using the result of themeasuring survey method (Yasuda et.al., 2009).
4.1 The case 1
The landslide situates in the mountain area, 42°30’
north latitude and 140°40’east longitude, the Hidaka
district, Hokkaido Japan. Geology of bed rock is
Kamuikotan metamorphic rocks group such as hard
metamorphic green rocks. The landslide became
active in the summer of 2003 after heavy rainfall
which precipitation was reported 215mm for 3 days
until the rain stopped. Crack opening was 20 cm permonth. The exploring map and the landslide profile
are as shown in Fig.5 and 6, respectively.

They are reflected the result from core boring andgeophysical exploration. The landslide consists ofseveral blocks. The 1m depth ground temperature
measurement was conducted in autumn within thelower right area (Small 2 block) where fountain isfound at the end of the slope. The result of themeasurement was shown in Fig.7. The normal 1m
depth temperature was 11.0 ℃ and groundwatertemperature was 8.0 ℃. Multi Temperature Logging
was also done in bore hole of this area, and the result
was as shown in Fig.8. The groundwater flew as avein stream and connected to the fountains at the endof the slope. The depth was about 10m where thezone of weakness and the sliding face existed. By
these measurements, the information of groundwaterflowing was obtained.

Fig .5 The exploring map of the site3

10th Asian Regional Conference of IAEG (2015)

Fig. 6 The landslide profile (A’-A/B-B’ cross section)

Fig. 7 The planar distribution of 1m depth ground temperature.

4

10th Asian Regional Conference of IAEG (2015)

Fig. 9 Schema of the mitigation work
Fig. 8 The result of Multi Temperature Logging

4.2 The case 2
The site situates at the end of earth flow, at analtitude of 10m, 45°10’ north latitude and 141°20’eastlongitude, the Soya district, Hokkaido Japan.
Geology of bed rock is volcanic rocks and debris
overlies it. The 1m depth ground temperature
measurement was conducted in simmer in order tofind the underflow that could be affected by road
construction. The results are as shown in Fig.10 andFig11, respectively. The normal 1m depth
temperature was 16.5℃ and groundwater temperature
was 7.7℃. In Fig.10, groundwater vein stream wasestimated as a narrow line connecting to fountain,
while Fig.11 shows the lowest peak of thetemperature that is groundwater vein stream of eachline. It means the ground temperature measurement
can considerably provide accurate location ofgroundwater vein stream, as shown in Fig.12.

According to the information got from thegroundwater survey, the mitigation work such as
withdrawing groundwater by drainage boring andwell was conducted, as shown in Fig.9. The concrete
protection work against river erosion was also
constructed. The location was where groundwatervein stream was found. The groundwater withdrawing
work was arranged along the groundwater veinstream. After the mitigation work was constructed,
excessive groundwater drained off, and consequently
active landslide stopped and became stable. The
landslide has been stable since the mitigation work
for more than ten years.

Fig. 10 Ground temperature distribution andgroundwater vein stream

Fig. 11 Ground temperature distribution of each line5

10th Asian Regional Conference of IAEG (2015)

Fig. 12 Result comparing of Seismic/Electrical prospecting and 1m depth ground temperature measurement
5. Discussion and Conclusion
The general groundwater measure is electricalprospecting and sometimes seismic prospecting may
be included. As shown in Fig.12, 1m depth groundtemperature measurement can considerably provide
accurate location of groundwater vein stream while
the general groundwater measure such as electrical orseismic prospecting can detect only apparent weakzone which could contain groundwater andgroundwater vein stream (Takeuchi, 2013). 1m depth
ground temperature measurement is more effectivethat it can narrow sphere of countermeasure muchsmaller than the general groundwater measure. Multi
temperature logging can detect the very point/depthof groundwater vein stream in a borehole.
As mentioned above, the groundwater survey
measuring ground temperature can provide
information of planar distribution of groundwatervein stream by 1m depth ground temperature
measurement and that of vertical one by Multi
temperature logging accurately. In case of landslide
being found, it is effective to perform thegroundwater survey measuring ground temperature
because it can indicate exactly where to do
countermeasure such as withdrawing excessive
groundwater using well and bore hole.
These are the reason why the groundwater survey
measuring ground temperature is effective for
mitigating landslide.

Acknowledgements
The authors would like to express their thanks topersons who concern with this paper. They also
would like to continue to study the groundwater
survey measuring ground temperature.
References
Takeuchi A.(1996) :The surveying method of flowing
groundwater by measuring temperature,
Kokon shoin, 480p. (In Japanese)
Takeuchi A. (2013) :The natural groundwater survey– 1m depth ground temperature measurement –,Kokon shoin, 224p. (In Japanese)
Yasuda T., and Takeuchi A. (2012): Consideration forGroundwater Survey of Landslide area,
T h e abstract of research meeting of the Japan
Landslide society of Hokkaido branch, 2012.
(In Japanese)
Yasuda T., Takeuchi A., Nunokawa S., and Tanaka N(2009): A case of landslide disaster survey
reconfirming effectiveness of geophysicalprospecting, The abstracts of research meetingof the Japan Landslide society of Hokkaido branch,2009. (In Japanese)6