HGM02-01

会場:101B

時間:5 月 26 日 11:00-11:15

Assessment of weathering grades for different chemical and geomechanical properties; A
Sri Lankan case study
Assessment of weathering grades for different chemical and geomechanical properties; A
Sri Lankan case study
Udagedara Dashan T.1∗ ; 小口 千明 2 ; GUNATILAKE Jagath K.3
UDAGEDARA, Dashan T.1∗ ; OGUCHI, Chiaki T.2 ; GUNATILAKE, Jagath K.3
1
1

Uva Welassa University, Saitama University, 2 Saitama University, 3 University of Peradeniya
Uva Welassa University, Saitama University, 2 Saitama University, 3 University of Peradeniya

Having a better understanding of the weathering grade of rock materials is highly beneficial in the perspective of civil engineering and geology. The classification of weathering grades can be performed based on the chemical, physical, mineralogical,
textural and strength properties of rocks. Among those, the use of chemical components to classify weathering grades is not very
promising for all types of rocks. Based on the mobility of elements various chemical indices for weathering grades have beenformulated. Most of those indices are based on experiments of weathered acidic igneous rocks under humid and well drained
environments. There are only a few indices formulated for sedimentary and metamorphic rocks, so the use of chemical weathering indices for the classification of weathered metamorphic rocks would not be convincing. However, the use of physical andstrength properties for the assessment of weathering grades is comparatively convenient. A better variation of those properties
with respect to weathering grades is resultant irrespective to rock type. Therefore, this study focuses on assessing weathering
indices using physical, strength and chemical properties of a selected metamorphic rock and evaluating the correlation among
the indices derived from those properties.
Fresh and weathered rocks of garnet-sillimanite gneiss were selected from the Samanalawewa Hydropower Project. Weathering grades were visually assessed initially, then confirmed with physical and strength properties using tests on dry density, watercontent, ignition loss, point load strength and slake durability. Whole rock geochemical data were used to calculate weathering
indices.
Physical and strength properties show a marked difference with weathering grades. However, chemical indices are not very
convincing. Silica-Titania, Product index and Ruxton ratio show a gradual variation with weathering grades. Mobiles index also
shows an acceptable variation. However, the modified weathering potential index, which was formulated for metamorphic rocks,
Parker index, which was formulated for all types of rocks, do not show a gradual variation with weathering grades. Chemicalindex of alteration and weathering (CIA and CIW) do not show a recognizable variation with weathering grades. Physical andstrength properties show good correlation with most of chemical indices. In addition, most chemical weathering indices show
good correlation with each other. The Lixiviation index is the one shows weak correlation with most of other chemical weathering
indices. The failure of some indices in showing a good correlation can be accounted for the heterogeneity of garnet-sillimanite
gneiss.

キーワード: Weathering grades, Rock weathering, Chemical weathering index
Keywords: Weathering grades, Rock weathering, Chemical weathering index

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HGM02-02

会場:101B

時間:5 月 26 日 11:15-11:30

柱状節理の発達した花崗斑岩の皮殻を伴う球状風化過程
Spheroidal weathering process of granite porphyry with columnar joints to form corestones covered with rindlets
平田 康人 1∗ ; 千木良 雅弘 2 ; 陳 友晴 3
HIRATA, Yasuto1∗ ; CHIGIRA, Masahiro2 ; CHEN, Youqing3
1

京都大学大学院理学研究科, 2 京都大学防災研究所, 3 京都大学大学院エネルギー科学研究科
Graduate School of Science, Kyoto University, 2 Disaster Prevention Research Institute, Kyoto University, 3 Graduate School ofEnergy Science, Kyoto University
1

紀伊半島南東部の花崗斑岩山地には，厚い風化帯があり，花崗斑岩の基盤岩が直径 0.4-1.5 m の球形のコアストンに風化し，コアストンの表面に鱗状の層 (皮殻) が生じている．この風化現象は球状風化と呼ばれ，その際の皮殻は化学的風化によって剥離した結果であると古くから考えられている．しかしながら，皮殻形成の際の化学的変質に伴う物理的性質の変化や亀裂発達の過程は解明されていなかった．そこで，その中新世の熊野酸性岩類の花崗斑岩を対象にして，地表踏査と露頭観察，ならびに採取試料の表面観察と鉱物-化学的分析，物理的性質の測定を行った．その結果，次のように球状風化が進んでいることが分かった．花崗斑岩は 2-6 m 間隔のほぼ鉛直の柱状節理をもち，地表付近では，斜面に沿ったシーティング節理に切られて角柱のブロックになる．球状風化は，柱状節理やシーティング節理から褐色化 (酸化) が進むことにより始まる．コアストンの半径に因らず，褐色帯は 2.5-5 cm の厚さであり，最もコアストン側の皮殻が 3.5-5cm の厚さであることから，褐色帯が約 5 cm の厚さを超えると剥離が生じると考えられる．薄片観察や X 線回折分析によれば，黄鉄鉱や緑泥石の酸化と水酸化鉄の形成が褐色化の際に生じる．褐色化が進むにつれて，細孔が水酸化鉄に充填されていることや微小亀裂が褐色前線と平行に形成されていることが紫外線照射のもとで行う蛍光観察によって明らかになった．また，褐色帯や皮殻内部に認められる亀裂は，鉄の水酸化物とバーミキュライトとの集合体に収束する傾向があり，0.5-2 cm 間隔で鱗状を成す．褐色帯では，P 波速度は最大 10%速くなったが，褐色境界と平行な面の圧裂引張強度は低下した．これらの物理的性質の変化は，細孔充填と亀裂発達の影響であると考えられる．岩石の密度と化学組成を用いたマスバランス計算によれば，褐色帯や内側の皮殻では未だに体積膨張は認められなかったが，亀裂がさらに増加した外側の皮殻では 20%，マサでは 80 ％，未風化岩よりも体積増加を示した．以上の結果は，亀裂発達と皮殻の剥離の原因が鉄の水酸化物の間隙への沈殿に伴う体積膨張であることを示唆している．また，マスバランス計算は化学成
分が褐色帯と皮殻，マサで，構成鉱物の変化と調和的に溶脱されていることを示した．酸素の拡散と溶脱によって，コアストンは皮殻を次々と生じて小さくなりつつ，節理に近い皮殻は斜長石を失い，内部に亀裂を発達させる．皮殻は最終的にマサになり，マサ中に皮殻に包まれたコアストンが生じる．
キーワード: 球状風化, 風化皮膜, 花崗斑岩, 亀裂, 酸化, P 波速度
Keywords: spheroidal weathering, weathering rind, granite porphyry, crack, oxidation, P-wave velocity

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HGM02-03

会場:101B

時間:5 月 26 日 11:30-11:45

石造建造物におけるバイオ風化とバイオプロテクションに関する議論
Regarding to the arguing issue; Bioweathering vs Bioprotection in stone historical buildings
宋 苑瑞 1∗ ; 藁谷 哲也 2 ; 小口 千明 1
SONG, Wonsuh1∗ ; WARAGAI, Tetsuya2 ; OGUCHI, Chiaki1
1

埼玉大学大学院理工学研究科, 2 日本大学文理学部地理学科
Graduate School of Science and Engineering, Saitama University, 2 Depart of Geography, College of Humanities and Sciences,
Nihon University
1

The Angkor complex is the one of the greatest cultural heritages in the world. It is constructed in the early 12th century, designated as a world cultural heritage by UNESCO in 1992. The temples at the Angkor complex are mainly made of sandstone andlaterite. However, due to the tropical climate, plants, lichens and various microorganisms are growing well on the rock surface.
Black crusts are also easily found on the stone surface. Biological factors are considered as a damage factors for the heritage.
The studies suggested that how it can be removed without destroying the substrate efficiently.
We sampled Angkor sandstone covered by black crust at the Angkor Wat and Bayon temples, Angkor complex, and observed
the section and the surface of the rock sample by using SEM. Surfaces of the samples are not polished in order to observe theoriginal condition. The depth of the black crust is up to 1 mm. Many filamentous materials were found on the black crust. Average energy-dispersive X-ray spectroscopy data of the black crusts shows that over 70 % of the surface materials are compoundsof carbon. And 15% of the mass are made of SiO2 . It seems that these materials are hyphae. The shape of the hypha is likea thread and its size is few µm in diameter and up to several centimeters in length. Black crusts are consisted of elements andcompounds of carbon, Na, Mg, Al, Si, Cl, K, Ca, and Fe.
The answer of the controversy question “Do lichens on the historical building protect it or not?” is not fixed. It protects
while weathers. It depends on the time scale and the surroundings. We have to focus on the timing of the lichen fall off. Under
the lichen coverage, rocks may be protected. When the lichen fall off, it may have lower surface than lichen-free rock surface.
Weathering is in progress and is a result of previous process under various facts, not only biological factors but wet-dry cycle,
various salt and so on. This is the reason why it is hard to judge whether lichens should be removed or not. We have to check all
the environmental data such as temperature, humidity, direction, insolation, rainfall frequency, human effect, weathering degreeetc. and decide to remove or not. Therefore, field survey and evaluation standard are needed. Further research has to be continued
to find out the better and proper way of conservation for the historical sites as Angkor monument.

キーワード: アンコールワット寺院, 石造文化財, 保存修復, 地衣類, 生物風化
Keywords: Angkor Wat, stone cultural heritage, conservation, lichen, biological weathering

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HGM02-04

会場:101B

時間:5 月 26 日 11:45-12:00

Accumulation of radioactivity inside Yoshimi archeological heritage
Accumulation of radioactivity inside Yoshimi archeological heritage
RAJIB, Mohammad1∗ ; KODAMA, Shogo1 ; SONG, Wonsuh2 ; OGUCHI, Chiaki T.2
RAJIB, Mohammad1∗ ; KODAMA, Shogo1 ; SONG, Wonsuh2 ; OGUCHI, Chiaki T.2
1

Graduate School of Science and Engineering, Saitama University, 2 Department of Civil and Environmental Engineering,
Saitama University
1
Graduate School of Science and Engineering, Saitama University, 2 Department of Civil and Environmental Engineering,
Saitama University
The Hundred Caves of Yoshimi is a cluster of ancient grave caves dug on the cliff made of tuffaceous sandstone located in
Yoshimi town, Saitama. It was designated as a national historic site on March 7, 1923. Built between late 6th century and late
7th century, the caves were initially made for only the blood royal and other big powerful families but later used for large scaleof underground munition factory. At present, the area is used for tourist attraction. Continuous survey has revealed that the caves
are heavily affected by salt weathering, mostly by gypsum. However, seasonal changes have also been observed in salt formation.
As part of that survey, accumulation of natural radioactivity, significantly anomalous than background level, has been observed
inside some of the caves of Yoshimi. The survey has been carried out to all accessible caves and radioactivity was measured by
Horiba Radi PA-1000 radiation monitor within 2-5 cm of the wall. Radioactivity was found to be as high as 0.119 micro sievert
per hour in some of the walls which is more than twice of the natural radioactivity found at the entrance of the area. This amountis marginally higher than the radiation dose limits for general public. Having similar rock type in all the caves, the reason ofsuch accumulation of radioactivity is lichen formation in the inside walls which is a known bio-accumulator of radioactivity.
Though studied walls are still out of reach of tourists visiting Yoshimi caves, spreading of lichen to other walls might increase
the radioactivity risk. Such accumulation of radioactivity also needs to be considered if other caves are opened for tourists infuture. Specific source of radioactivity also needs to be investigated through detail survey.
キーワード: Natural Radioactivity, Yoshimi caves, Weathering, Lichen, Bio-accumulator, Radiation dose
Keywords: Natural Radioactivity, Yoshimi caves, Weathering, Lichen, Bio-accumulator, Radiation dose

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HGM02-05

会場:101B

時間:5 月 26 日 14:15-14:30

韓国マノ山における岩塊流の形成プロセス
Formation processes of block stream in Mt. Maneo, South Korea
瀬戸 真之 1∗ ; Kim Song-Hyun2 ; 田中 幸哉 2
SETO, Masayuki1∗ ; KIM, Song-hyun2 ; TANAKA, Yukiya2
1
1

福島大学, 2 慶熙大学校
Fukushima University, 2 Kyung Hee University

This study revealed that formation processes of slope deposits include block stream near Mt. Maneo, South Korea. Using asatellite image reading from Naver site (http://www.naver.com/) and a field survey, we studied the positional relationship between
the Mt. Maneo block stream and its surrounding terrain, as well as the general shape of the block stream. The satellite image
scale was about 1:5000, which had a resolution sufficient to identify the block stream. Next, we superimposed the interpreted
satellite image on a 1:25000 topographic map, and read the contour lines over the location of the block stream. The plan viewof the block stream on Mt. Maneo has a belt-like shape. The top end of the slope is the steepest, having an incline of around 20
degrees. On examining the contour lines crossing the block stream, the contour lines in the top section are found to be more orless straight and represent an even slope with no obvious ridges or valleys. In the central part of the block stream, the contour
lines are convex in the upslope direction, indicating a wide valley. In the lower section of the block stream, the contour lines areconvex in the downslope direction, indicating the presence of a ridge.
A cross-section of the block stream is visible in the central part of the out crop and can be split into two parts: a matrix offine-grained materials on the northwestern side, and a matrix-free deposit on the other side. For the purpose of this study withrespect to sedimentary facies, we counted the sections having matrix as part of the block stream. In the matrix-free deposit
section, blocks with a larger diameter tend to be concentrated in the lower portion. The overall cross section has an upward
convex shape.
We observed ground water flow and soil saturation by five tensiometers. All observation points were located at the top of blockstream. Depth of the tensiometers were about 30cm. Tensiometers were inserted fine slope deposits at the upper part of the blockstream. Observation period was Jul. 9, 2014 to Jul.14, 2014.We observed that slope deposits were rapidly saturated associatingwith rainfall event. Rain fall event was occurred in Jul. 13, 2014. Rainfall amount was 30mm/day. All tensiometers responded
this rain fall event. Suction was decreased very rapidly at this rainfall event. This means that saturation of soil layer occurredat the head of block stream associating with rainfall event. Water was concentrated in the valley created by this landslide. We
can recognize from observation of suction that the unsolidified weathered fine-grained material forming the landslide block waswashed out by this water flow, leaving only the core stones behind.
We believe that the area of the Mt. Maneo block stream is an old landslide site. This could have been a deep seated landslidethat reached the deep weathering layer of the upper section of Mt. Maneo, and it is thought that a large section of the landslide
block consisted of core stones and weathered fine-grained material.

キーワード: 岩塊流, 形成プロセス, 地すべり, 水文観測, 韓国, マノ山
Keywords: Block stream, Form processes, Landslide, Hydrological survey, South Korea, Mt. Maneo

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HGM02-06

会場:101B

時間:5 月 26 日 14:30-14:45

上高地谷の幅の広い谷底における土砂収支に沖積錐が果たす役割
Roles of alluvial cones in sediment budget in the wide valley floor of the Kamikochi
valley, central Japan
島津 弘 1∗SHIMAZU, Hiroshi1∗
1
1

立正大学
Rissho University

The upper reaches of the River Azusa, flowing down in the Kamikochi valley in the Northern Japan Alps, central Japan, issurrounded by very steep mountain slopes and high mountains which elevation is higher than 2500m. There are many landslides
on the steep mountain slopes, from which debris is supplied to the valleys of the tributaries of the upper River Azusa.
Alluvial cones are the most important features on the valley floor of the upper River Azusa. These are formed at each outletof the tributaries. To clarify the roles of the alluvial cones in the sediment budgets of the upper Azusa basin, landforms of the
alluvial cones were investigated and the sediment linkages between the tributaries and the main river were discussed.
Many debris flow lobes are distributed on the surfaces of the alluvial cones. This shows that the alluvial cones are formed
by debris flow accumulation. Most of the alluvial cones have several levels of terraced surfaces. The cone of a tributary,
Furuikezawa, has four levels of surfaces. Each surface is bordered by terrace cliffs of several meters high. While the mostpart of the lowest surface is covered with newly deposited gravels with pioneer trees younger than 70 years, the other surfaces
are covered with mature forest, the age of some trees are hundreds of years, and dense forest floor vegetation. The channel of
Furuikezawa directly connects with the lowest surface and the surface borders on the main river floodplain with dense riparian
forest. The surface is not contact with the channel of the main river. The lower borders of the terraced surfaces are margined byterrace cliffs which stretch parallel with the direction of the valley of the River Azusa. Other alluvial cones in the Kamikochi
Valley have such similar geomorphological characteristics.
These characteristics of the alluvial cone show the alternation of accumulation of debris flows on the cone surface and lateralerosion of the toe of the cones by the channel shift of the main river. The debris supplied from a tributary basin is stored as its
alluvial cone deposits. When the channel of the River Azusa will be shifted to the alluvial cone, lateral erosion will occur atthe lower end of it. As lowering of the base level the channel of the tributary begin downcutting and the alluvial cone surface
becomes a terrace. Debris produced by the lateral erosion is transported downstream of the main stream.
During the time lag between debris supply to the cone and eroded away from the cone and transport downstream debris became
easily breakable into fine materials.
Alluvial cones on a wide floodplain play important role on sediment transport link between mountain slope and valley floor.
Produced debris from the mountain slopes is not transported directly downstream by the main river. That is an important factor
in basin sediment budgets.
キーワード: 土砂移動プロセス, 沖積錐, 広い氾濫原, 土砂収支, 上高地, 中央日本
Keywords: debris transport process, alluvial cone, wide floodplain, sediment budget, Kamikochi, central Japan

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HGM02-07

会場:101B

時間:5 月 26 日 14:45-15:00

走古丹バリアースピットの地形発達史から読み解く 根室海峡沿岸域の完新世海面変
動と地殻変動Geomorphological evolution of Hashirikotan barrier spits resulting from seismotectonics
along the southern Kuril Trench
七山 太 1∗ ; 重野 聖之 2 ; 渡辺 和明 1 ; 吉川 秀樹 1 ; 長谷川 健 3 ; 池田 保夫 4 ; 石渡 一人 5 ; 内田 康人 6
NANAYAMA, Futoshi1∗ ; SHIGENO, Kiyoyuki2 ; WATANABE, Kazuaki1 ; YOSHIKAWA, Hideki1 ;HASEGAWA, Takeshi3 ; IKEDA, Yasuo4 ; ISHIWATA, Kazuto5 ; UCHIDA, Yasuhito61

産業技術総合研究所, 2 明治コンサルタント (株), 3 茨城大学, 4 北海道教育大学, 5 別海町郷土資料館, 6 北総研地質研究所
Geological Survey of Japan, AIST, 2 Meiji Consultant Co. Ltd., 3 Ibaraki University, 4 Hokkaido University of Education,
5
Betsukai Museum, 6 Geological Survey of Hokkaido, HRO
1

An active barrier system is developed in the Nemuro Bay area along the Okhotsk Sea in eastern Hokkaido, Japan. This
presently rare feature consists of a lagoon (the Furen-ko lagoon), a flood tidal delta, a barrier, and a tidal inlet that opens into
the outer sea of Nemuro Bay and the Sea of Okhotsk. The Hashirikotan barrier spits are active in the northeastern part of theFuren-ko lagoon, and five spit branches (BS1˜BS5) can be observed clearly. Using geomorphological, sedimentological, andground-penetrating radar methods, we analyzed Holocene sediments near the Furen-ko lowland. We dated them using radiocarbon and tephrochronological methods. The Furen-ko barrier system has been established since 5.5 ka. BS1, the youngest spit
was formed after the 17th century, and BS2 was caused by the last seismic uplift in the 17th century. BS3 was uplifted in the
12˜13th century, and BS4 was caused by seismic uplift in the 9th century. These great earthquakes (Mw8.5˜9.1) have occurredat an approximate 500-year interval along the southern Kuril subduction zone. Coastal areas were raised by 1˜2 m during or
just after the earthquakes due to postseismic displacement. Conversely, land subsidence has been ongoing at a rate of about
1.0 mm/year since the 17th century. We conclude that the geomorphological evolution of the Furen-ko barrier system has been
controlled by the seismotectonics along the Kuril subduction zone.
キーワード: 地形発達史, 走古丹バリアスピット, 地震テクトニクス, 南千島海溝, 東北海道, 北部日本
Keywords: geomorphological evolution, Hashirikotan barrier spit, seismotectonics, southern Kuril trench, eastern Hokkaido,
northern Japan

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