D08

Role of halloysite on the initiation and movement of coseismic landslides occurring on tephra
slopes〇Baichuan Liu, Gonghui Wang

Landslides

occurring

ontephraslopesduringearthquake are normally characterized by their highand the conduction of a series of experimental works.
The details are list below.

mobility and long runout, and usually present
significant hazard to human safety and the built

The first phase of this study is to confirm whether theenvironment. This kind of landslides could be wellsliding surface contains halloysite or not and the shapeexampled by those triggered by the 2016 Kumamotoof halloysite through XRD test, SEM detection andearthquake on Minami Aso area, Kumamoto, and by

TEM detection. By field trip to Minami Aso,

those triggered by the 2018 Hokkaido Eastern Iburi

Kumamoto and Atsuma, Hokkaido, the samples were

Earthquake in the hills near the epicenter. Field study

taken back to the laboratory for testing and detection.

on those landslides revealed that most of theThe results show that: 1) The existence of Halloysite

landslides occurring on tephra slopes are shallow but

has been confirmed in the sliding surfaces for those

destructive, the displaced landslide materials mainly

landslides occurring in Minami Aso area and Atsuma

consist of tephra, and their sliding surfaces are mostly

area. 2) The halloysite in the sample taken fromdeveloped within the weathered tephra layer, where

Minami Aso area presents the shape of tubular one,the water content is very high and a clay mineral ofwhile that in the sample taken from Atsuma area,

halloysite resulting from the weathering of volcanic

Hokkaido shows the shape of platy or crumpled

glass is normally presented. Similar phenomena hadlamellar.

also been reported in the landslides occurring on
tephra slopes in other countries. Therefore, it is

The second phase of this study aims at examining thebelieved that the presence of halloysite has played aeffects of introduction of halloysite on the water

bad effect on the initiation of slope instability and theretention of tephra materials through pF tests. The

post failure movement of the displaced landslide

samples were prepared by adding different contents ofmaterials for these coseismic landslides occurring on

halloysite to the tephra materials taken from Minami

tephra slopes. Nevertheless, the role of halloysite on

Aso area, Kumamoto, or to the silica sand sample.

the initiation and the movement of landslide remains

Field examination on the weathered tephra layer withhas not been clarified, although some research basedformation of halloysite and the results of pF tests

on case studies had been conducted and someindicate that: 1) the weathered tephra layer withpreliminary results had been achieved. Hence, thisformation of Halloysite normally maintains high water

study aims at clarifying the role of halloysite on thecontent under natural conditions. 2) The sample

initiation and movement of landslides occurring on

containing halloysite showed higher water retention

tephra slopes, through field investigation of some

capacity then the mixture of tephra with fine silica

landslides triggered by recent earthquakes in Japan,

sand. Namely, besides the small particle size,

halloysite's special structure may elevate the potential

higher brittleness index, which means that the soilof water retention capacity.

layer containing halloysite may suffer from higher
post failure mobility. 3) Halloysite reduced the energy

The third phase of this study involves in examining

required for shear failure in denser soils. This means

effect of halloysite on the shear behavior of tephrathat given the earthquake motion being the same,material. The program includes: 1) Using a in situ

landslides on tephra slopes containing high content of

direct shear box to perform shear tests on samples inhalloysite may be easier to be triggered. 4) Halloysitedisturbed or undisturbed states with natural water

reduced the energy required for sliding rapidly.

content on the landslide field. 2) Making mixture of

Therefore, potential energy can be converted into

tephra materials with different content of halloysite or

kinetic energy faster and then elevate the sliding

with different contents of fine silica sand, andmobility.

conducting undrained ring shear tests on thesemixtures in saturated state with different initial

In summary, through these above-mentioned works, itdensities. The tests results show that: 1) Addinghas been clarified that introduction of halloysite in thehalloysite to tephra material changes the peak shear

tephra can elevate the water retention capacity such

resistance of the sample. As the halloysite content

that the tephra can be in high water content state inincreases, the peak shear resistance decreases.

natural condition. Introduction of halloysite does not

However, the peak shear strength for the mixture ofaffect the peak shear strength of tephra materials, but

tephra with 10% of silica powder became small andcan elevate the liquefaction potential, such that thebecame greater with further increase of the silica

shear failure could be easily triggered and the mobility

powder. 2) The sample containing halloysite showed aof displaced landslide material be elevated.