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I would like to respect Dr. Vu Thanh Tu, lecturer in Department of Hydrology and

Water Resources, Thuy Loi University and Dr. Nguyen Quoc Khanh, a majorResearcher of Vietnam Institute of Geosciences and Mineral resources, for theirguidance, advice andexperience to complete this master thesis. Theirconstructive comments, untiring help, guidance and practical suggestions inspired meto accomplish this work successfully.

Besides, I would like to thank Propessors in Hydrology and Water resources facultyand members in the Project "Investigation, assessment and warning zonation forlandslides in the mountainous regions of Vietnam” conducted by Vietnam Institue ofGeosiences and Mineral resources (VIGMR) who supported me in terms of the datacollection and gave me useful advices for my thesis.

I remember all those who have contributed directly or indirectly to

successfully completing my study.

Finally, I must express my very profound gratitude to my family for providing me withunfailing support and continuous encouragement throughout my years of study and

through the process of researching and writing this thesis. This accomplishment wouldnot have been possible without them.

Ha Noi, May 23" 2017

Luu Thanh Binh

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Thereby declare that is the researches have done by myself under the supervisions ofDr. Vu Thanh Tu and Dr. Nguyen Quoc Khanh. The results and conclusions of thethesis are fidelity, which are not copy from any publish sources or any forms. Thereferences documents and relevant sources, the thesis has cited and recorded as

Ha Noi, May 23" 2017

Luu Thanh Binh

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In Viet Nam, there have not been so far comprehensive database of natural disasters in

general as well as landslide in particular, Therefore, although there is an undebatable

considerable achievements in landslide mitigation, these efficiencyhas not been

significant, Consequently, thete is an urgent demand to have implementation of

landslide investigation, In the scope of the State-funded Landslide Project“Investigation, assessment and warning zonation for landslides in the mountainousregions of Vietnam” funding by Vietnam institute of geosciences and mineralresources, an integrated methodology that combining the traditional investigation withmodern technology of remote sensing imagery analysis has been applied and initially‘generating encouragingly achievements. This methodology has extremely utilized the‘available data and resources as well as applying stage of the art technology in order tosupport investigator in field survey. Based on that, the most complete landslidedatabase of characteristics along with causes resulting in landslide process has beenestablished, Within scope of the topic 1g using GIS andfield investigations on scale 1:50.000 in Tuong Duong district, Nghe An province”

is conducted for further study on an integrated method sys m between traditionalinvestigations with moder remote sensing technology has been applied and initiallygiVen good results. This system takes full advantage of available data and resources asWell as applies new technologies to assist investigators in carrying out their work inthe field, Thanks to complete database on characteristics of sliding blocks, as well asits causes has been built,

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1.1.2 Factors affecting slides.

1.2 World-wide researches on geological hazards 201.3 Researches on geological hazards in Vietnam, 23CHAPTER 2. METHODOLOGY

2.1 Process of mapping the current state of landslides 262.2 Field surveys 33CHAPTER 3. DATA COLLECTION AND DATA ANALYSIS

3.1 Data collection

3.2 Data analysis 393.3 Field survey. 48CHAPTER 4. RESULTS AND DISCUSSIO:

4.1 The results of Landslide, interpretation from remote sensing data 314.2 Results of actual landslides survey work. sa4.3 The causes of landslides sẽ4.3.1 Geomorphology, topography factors. sỹ4.3.2 Geological factors 9

4.3.3 Meteorological and hydrological elements 60

4.3.4 Causes from the impact of other types of geological hazards ol4.3.5 Human activities “CONCLUSIONS AND RECOMMENDATIO:

REFERENCES...APPENDIX

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istrict 56

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LIST OF FIGURES

Figure 1, Studied area (Tuong Duong distri he An province) 2

, 2009) and (Chakraborty, 2008)6

Figure 2. Showing different parts of landslide (USG:

Figure 3. Falling slide (falling rocks) 1Figure 4. Uptuming slide 8Figure 5. Rotational slides 9Figure 6. Translational slides 10Figure 7.Complex slide lôFigure 8. Debris flow RFigure 9. Flank shape 16Figure 10. Conceptual framework 2Figure 11. Stereoscopic for the same area created from aerial image (above) and

satellite image (below) with DEM 28Figure 12. Hill shade 29Figure 13. a) Checking landslide interpretation in the field; b) Compared landslideinterpretation with 3D model 32Figure 14. Outline of satellite image interpretation processing 40Figure 15. Crack on road edge and slope. 49Figure 16. Cracks / predicted slopes of sliding blocks in Tan Xa area 50Figure 17. Comparison of interpretation sliding points with 3D digital modkl...Š1Figure 18. Expected landslide interpreting from remote sensing 5Figure 19. Landslide type classification by commune administrative unit s4Figure 20, Landslide frequency by commune administrative unit 35Figure 21. Landslide volume classification by commune administrative unit 35Figure 22. Investigated positions in the field 37Figure 23. Landslide inventory mapping for Tuong Duong district, Nghệ An province

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United States Geological Survey

Gross Domestic Product

Foreign Direct Investment

Digital Elevation Model

Community-Based Disaster Risk Management

Asia Disaster Preparedness Center

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Landslide is one of most common types of natural disasters occurring in mountainousareas of Vietnam. Damage to people, facilities and environment caused by landslide isfoflen more serious than current awareness and assessment of society. In general,studies on landslide have been applied on a large scale, implemented at a small scale,

‘and most of them only provide quantitative forecasting results. Up to now, there have

‘been no surveys, studies and warnings about landslide risk in sufficient detail to betterserve prevention and mitigation of losses (Le Quoc Hung et al., 2014). In order to‘overcome these trictions, it is necessary to develop a comprehensive survey andanalysis program that applies advanced and appropriate methodologies to assess and

‘give warnings about landslide effectively and timely for

<small>a</small>

12 planning and

management of natural disasters in the context of climate change (Tran Tan Van et al.,2002, Nguyen Xuan Khien et al, 2012, Le Quoc Hung et al., 2013, 2014),

So far, Vietnam has not have a full database of natural disasters in general orlandslides in particular. Therefore, prevention of natural disasters to minimize the‘damage caused by landslide in recent years has not been effective although there havebeen many achievements. Therefore, investigation of landslide in mountainous areas

of Vietnam is a very urgent task, Within scope of the topic "Landslide inventory

mapping using GIS and field investigations on scale 1:50.00 in Tuong Duongdistrict, Nghe An province” is conducted for further study on an integrated methodsystem between traditional investigations with modern remote sensing technology haybeen applied and initially given good results. This system takes full advantage ofAvailable data and resources as well as applies new technologies 0 assist investigatorsin carrying out their work in the field. Thanks to complete database on characteristicsOf sliding blocks, as well as its eauses has been built

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Objectives and tasks

- To study the application of integrated method system between GIS technology,remote sensing analysis and field survey for setting up landslide mapping,

- To investigate landslide status, determine causes of landslide in Tuong Duongdistrict, Nghe An province.

<small>= To make a landslide map at scale 1/50,000 in Tuong Duong district, Nghe An</small>

Features of terrain, geomorphology and hydrology

‘Tuong Duong is a mountainous district in western part of Nghe An province with area

of 2.812km2 with quite complex terrain, high mountain range and huge segments,

<small>=I borders Laos and Que Phong district in the north and northwest</small>

It borders Laos in the south and southwest

<small>~ borders Con Cuong district in the east and southeast</small>

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~ It borders Ky Son District in the west.

River networkin this area is quite erowded, including Lam river with a length ofnearly 50 kms. Upstream of the Lam River is divided into two sub-branches of NamMo River inthe southwest and Nam Non River in the northwest, and a large basin in

as Cha Ha River, Chang“Trang Stream, Nam Chon Stream, Khao Stream, Co Stream.... These are both difficultthe north of the district. Also there are also small streams s

for traffic in the area and potential risk for flash flood.

Traffic, humanity

‘Traffic network in this area is underdeveloped ausing many difficulties for travelling,National highway 7A runs across the district, This is the main traffic network toconnect the western area of Nghe An province with other parts of the region. In

addition, provineial highway 487 conneets National Highway 7A and National Road

48 to other districts in the northwest of Nghe An province. In addition to the above-mentioned roads, Lam River is also a major transport route, There are also inter-‘commune roads, border roads, but generally the roads are very winding, many slopes,sloping height of 10 to 50m, easy to slip in rainy seasons.

‘The population of the district, 68,441 people, with 18 administrative unit includingmany ethnic groups such as Kinh, Thai, Hmong, Tay, Odu, Khomu, ete. Thepopulation density is unevenly distributed, mostly crowded in. Hoa Binh town areaand along the National Highway 7. The main occupations are small agriculturalproduction, small scale production and trading. In addition, there are residential arethat focus on commune centers and small clusters along the road. The H’Mong andKhomu ethnic groups mainly live in mountainsides, streams and river banks. They livein big villages or small villages with outdated lifestyles. Culture and economy of thesemountainous ethnic groups is still underdeveloped. Up to now, about two thirds of thepopulation in the district have no access to national power network

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Tuong Duong is directly affected by the climate in southwest of Nghe An province,characterized by tropical monsoon climate with two distinct seasons, Rainy seasons:{rom April to October. Dry seasons: from November to March of next year.

Average temperature varies from

exceeds 23oC; Month with the highest temperature is July: 39-41°C; The month with

C, there is 6 months which its temperature

the lowest temperature is January: 8°C

‘Average rainfall is 1,450 mm, but unevenly distributed in space and time (in Ca riverupstream from Cua Rao upward, rainy seasons start and end in 3 months including‘August, September and October, annual average rainfall is only 1,350 mm. Ca riverdownstream from Cua Rao downward, rainy seasons start from July and end inSeptember, annual average rainfall is over 2,000 mm ).

Affected by a part of southwest wind (from Laos) appearing from April to August,causing dry and hot clmate in some areas of the district (Cua Rao area, Xa Luong‘commune are considered as hottest area in Indochina),

Geological features

In this area, base rocks are mainly quart bars-sericite, sandstone, siltstone, sericite,clay shale in Ca river formation (03-S1,.), siltstone, Huoi Nhỉ clay shale formation($2-DIi,), Nam Tam (D1-2n0, clay limestone, siliceous shale, clay shale in La Kheformation (Cly). sandstone, siltstone, shale cliff are classified to thin layerintercalation of acreage of Dong Trau Acid formation (T2,s), Sandstone of Khe BoFormation (Ny) and Quaternary sediment of Quaternary formation (Q),

Tectonic activity in the area occurs quite strong, main fault system of the Ca River

runs along in the Northwest - South Bast, leading to some other faults forming a large

crushed zone so that landslide risk is quite high.

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CHAPTER 1. LITERATURE REVIEW

1.1 Types of landslides and causes

Landslide is a natural hazards phenomenon, under influence of geodynamic processes,causing slope instability (called slope in general) leading to slope shift (matter),destroying all related things on its way, Landslide occurs when rock mass becomeunbalanced, sliding forces exceed friction forces. It is clear that landslide processes are

the products of changes in geomorphological, hydrological and geological

morphological conditions. Changes in conditions are made by geodynamic processes,plant development, land use, human activities, as well as frequency, intensity ofsedimentation and vibration, According to Varnes (1984), the term "landslide"includes all the sliding phenomenon on a slope surface. These phenomena include

phenomena that do not actually slip like rock falling and muddy flows.

‘There are many systems of classification of landslide in which two systems are widelyused, especially given by Hutchinson (1968), Skempton and Hutchinson (1969) andVarnes (1958, 1978, and 1984) in westem countries. Both systems are grouped in formof shifting but differ from shifting states. Slope displacement generally begins with thedestruction of shear force, creating sliding surfaces that are boundaries of shear zonebut in sliding form, the shifting is the extrusion, flowing under pressure. Choice of

classification system depends on the purpose of the study is to analyze the condition of,

sliding mass destruction or the interpretation of the displacement results of the slidingblock. The Varnes classi ion system is easy to use and discussed at InternationalAssociation of Engineering Geology (IAEG) on sliding (1990) and the published inglossary of landslides in many languages. The Varnes landslide classification system

(1978 and 1984) highlights the type of displacement and material type. In fact, any

sliding block is classified and described using two material phrases and type of

displacement. The sliding classification method is listed in Table 1, and the sliding

body is described in Figure 2.

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Table 1. Varnas Sliding Classification System (1978, 1984)‘Type of materials

Ps fasacnat fick sing | Dàn Mek | Tạm Mạ

Cross cuneat | Crosaliing | Debris eros siting] LMẢ - cm

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from small cleavage facet or overturn parts of materials or when the nose of the cliffprotrudes into the sea under the effect of waves or riverbed erosion leading to brokenlegs causing loss of adhesive force (Figure 3)

Figure 3. Falling slide (falling rocks)

Soil, rocks are likely to fall free in high steep slopes. In contrast, the material will fallto the surface of the slope very strongly if the slope is less than this value (Ritchie,

1963). The destruction of this type depends on the properties of the materials, the

clasticity and falling of a part of the terial (Hungr and Evans, 1988), and spillagemay also be shattered upon collision. On long slopes, the falling will move down inroll form with short bounce and gradually reduce the range of impact on the slopebelow. At localized sloping locations, some of the material may bounce off to create

free-fall motion with bouncing and spinning (Hungr and Evans, 1988).

Upturned slide (also known as dropping

‘The upturned/dropping type is a phenomenon when a sloping piece of land (roof,stone) is turned over, falling off the slope with a focus around a point or a hypotheticalaxis, The upturning/dropping process can be impacted by gravity into the mass oflandslide in the material forming fractures forming the upstream slope or under the

action of water, ice that exists in the tock (Figure 4).

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Figure 4. Upturning slide

Top upturning is broken blocks at the top of the slope below the sliding block. Deepupturning often occur in large, steep sedimentary rock masses caused by the swiveling

of the mass of debris, resulting in shearing that starts at the top of the rock (Goodman

and Bray, 1976). Upturning under the nose of the surface is a phenomenon that causes

the partial slope of the slope due to the weight of the slope itself. This destruction is

also called roof nose, The formation of cracks in the top of the sliding block is a highlypathogenic agent and causes landslide stress (Goodman and Bray, 1976). This is a

complex type of erosion, not only in rock formations, but also in clumps of muddy feet

under the influence of the river.

Rotational slide

Rotational slide is the phenomenon of blocks of rock, which are displaced by the

surface of the hypothetical concave surface. If the destruction surface (in eross section)

is cylindrical or eyeloid, then during sliding, the deformation within the sliding blockis less, the rock composition is not disturbed. When the sliding occurs, the sliding headshifls mainly vertically, the sloping surface above the sliding block tends to produce asloping backward gradient (Figure 5),

Rotational slide occurs in homogeneous materials, which are often mote intense than

other types of displacement. However, in nature material is rarely homogeneous, thesloping displacement in these materials often occurs unevenly and intermittently inlayers of material, When digging a sloping roof can also cause slipping. The mainslope at the top of rotational slide is almost vertically, without any support, the slide

can cause the sliding of this part

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Sometimes, side edges of the decaying surface have a large slope leading to the

displacement of flanks downward, increasing the load on the sliding block. The

penetration of water into the sliding head increases the humidity of the material,

making surface break down as well as increasing the weight of the sliding mass that

facilitates easy sliding

Translational slide

Translational slide is the phenomenon of sliding mass passing down through a surfacethat is flat or slightly rugged. Translational slide are generally shallower than

rotational slide, D/L ratio of this slide occurs in the soil is usually less than 0.1

(Skempton and Hutchinson, 1969). Destroying surfaces are usually shaped in theshape of wide troughs in cross section (Hutchinson, 1988). In contrast, the rotationalsliding surfaces tend to restore the sliding mass to equilibrium (Figure 6)

In this slide type, the continuous sliding block can break apart in part if the velocity ofmovement or the humidity is increased, the block is broken and can then betransformed into a flowing form, resulting in more accurate debris flows. Translational

slides are usually accompanied by intermittent signs such as faults, fissures, layering,

‘or contact layer between base rock is weathering layer above. Intermittent translationalslide in simple form on rocks called rock sliding (Panet, 1969) or flat slide.

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Figure 6, Translational slidesComplex slide

This isan intermediate slide between rotational slide and translational slide. The D/L.

ratio is also intermediate once between the (wo types (Skempton and Hutchinson,1969). The destroying surface in this type has a steeper but thinner slope. The sliding

surface is a complex fracture pattern, depending on the internal deformation and

surface tension stresses within the material range and the results in the formation ofintermediate ramps, its slope is sharply reduced on the surface of the deformation‘material, sinking to ereate trenches and compressed areas. This type of slide usually‘occurs when structure of sliding block have presence of weak soil or weathering claylayer resulting in intermediate slides that control the movement and produce aComplex slide surface (Hutchinson 1988 ). Depending on materials and particularity

of the slope, Complex slide is also known as mudslide and flows.

Figure 7.Complex slide

(2) Intermediate slide between rotational side and translational slide

{b) Landslide (Complex slide - between rotational slide and flat slide)

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“The term Swelling was introduced in engineering geology by Terzaghi and Peck(1948) to describe sudden displacement of water carrying mud and sand covered byhomogeneous clay. One of these types of destruction occurs when a layer of clay orwet sand becomes moist and softer, and is more resistant to the flow of water and tothe compression of the hips by the weight of the upper layers (Dana, 1877). Thisexplains the phenomenon of a stable steep slope in the long run can be destroyed andmoved unexpectedly. The destroying surface of this form is not the surface with thelargest stress load, such as normal slippage, that is destroyed by the liquefaction orjection of soft materials than the sheath

Debris Flows

Debris flows are continuous, spatial movement in which the short-lived forms ofcross-sections are not maintained for a long time. The velocity distribution feature inthe displacement block is similar to that of the liquid flow. The gradual change fromsliding to flowing depends on the amount of water in the soil, the mobility and theextent of the sliding mass. Slipping, debris slide can become extremely rapid debrisunder certain conditions,

Varnes (1978) used the terms earth flow and slow earth flow to describe slowermoving of dry land flows and resulting in sticky soils (usually known as clay orweathering from the base rock) with moderate slope, sufficient humidity, Open-slopedebris flows ereate a pathway to move down into the valley to form sloping topsoil orcreate sinuous channels, Normally, coarse-grained materials can form a conduit orform as a bed through a slope. The formation of earth flow is often associated with

rain and flood, which occurs immediately after floods due to unusually heavy rain,

‘with moving material sometimes being rolled in meters. Soils on steep slopes do notexist, The vegetation facilitates the formation of debris flows through the erosion ofthe bottom, sometimes creating reservoirs that increase the energy of this debrisstream, The process of sometimes displacement of raw materials into a natural dykeforms the formation of hanging systems, which threatens to collapse into the conduit

in

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when impact shocks occur, Streams of matter can extend up to several kilometersbefore depositing small particles on the entire conduit,

Figure 8. Debris flow

Debris flow is a kind of slide with a larger, more agitated, faster than open-slope

debris. Historically, a debris in Huascaran (Peru) created between 50 million and 100

million cubic meters of soil, rock, ice, snow at speeds up to 100 meters per second intoawide area (Varnes, 1978)

Another form of this type of movement is called bedrock flow, which is characterizedby continental distortion in the earth's surface such as deep slides, which move very

slowly along the cutting surface and not connected due to the folding process. It is

clear that flows can also be started from sliding processes on the base rock or shale,which can be classified as a Complex slide.

Another special form of flows is volcanic material debris. Formed from voleanic ashdeposited on the volcanic slope with low consolidation, movement under the effect of

water flows from fractured lakes, condensation of steam, precipitation of water

particles along with ice melting on top of volcanoes (Voight, 1990),

1.1.2 Factors affecting slides

Landslide phenomenon is thought to be related to the relationship between shearstrength of soil and rock formed on the slope to their gravity. A slippage occurs when

2

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the balance of the relationship is tilted toward gravity. This relationship can be alteredby natural and human influences. Factors that affect slope stability and slip events arevaried and very different, interacting in a very complex way (Varnes, 1984)According to Sidle and Ochiai (2006), natural elements can be divided into five

‘groups: soil strength, soil chemistry, mineralogy; Geology; geomorphology;

hydrology; and seismics,

Geological factors

Stability of the slope is related to different types of lithology (Sidle and Ochiai, 2006),and this strong or weak relationship is highly dependent on each type of lithology(Skempton and Delorey, 1957; Thomson, 1971; Sawnston, 1978; Shimokawa et al.,1989; Yokota and Iwamatsu, 1999; Derbyshire et al., 2000; D'Amato Avanzi et al,2004; Wakatsuki et al., 2005). Weathering often modifies lithological, mineral andhydrological properties of lithologies, so weathering is also an important factor for thestability of the slope in all environmental conditions (Maharaj, 1995). Yokota andIwamatsu, 1999; Chigira, 2002; Wakatsuki et al., 2005).

Another important geological factor in the study of sliding catastrophe is the unstablelayering order. This occurs when rock mass displacement on the class surface istriggered when the gap pressure develops at the interface between the two differentlithologies (cg between sandstone and clayst ‘or when stability of clay sediment is‘weakened by the permeability of water through the lithological la x (Krgjei et al2002). Therefore, landslides often occur when there occurs heavy rain. In general, fourlypes of unstable classifications are identified: (1) intercalation between hard and softrocks; (2) Soil is highly modified and highly permeable to a low permeability; (3) thinlayers of soil lying on base stone; (4) Cap rock (with crack) is located on thick‘weathering rocks.

Relative stability of soil and rock is largely influenced by tectonic activities in the past

and current weathering (eg, in studies by Julian and Anthony, 1996; E1 Khattabi andCarlier, 2004). In particular, tectonic activities also play a role in slope stabilitythrough fracturing, cracking and structural deformation (Ibetsgerger, 1996; Pachauri et

B

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al 1998), Fractures and lineaments are often researched in landslide hazard

‘Mechanical, chemical and mineralogical factors of soil

“The mechanical, chemical and mineralogical factors of the soil are closely related to

nature and balance of the soil. Shear resistance is one of the most important

al stability of theslopes. It does not have a certain value but is greatly influenced by the load action thatmechanical properties that greatly influences the natural and art

‘occurs on the slope that is most likely due to the effect of water content in the soil. Theshear resistance is basically expressed as a function of the vertical pressure on the

sliding surface (ơ), consolidation force (c), and inside friction angle (ø). The

relationship between these components to other natural features of the soil has alsobeen introduced in numerous works such as Terzaghi and Peck (1967), Wu andSangrey (1978), Fredlund and Rahardjo (1993),

Another important natural feature is the clay content in the soil. Clay minerals as thechemical weathering product of rock are so important. There are numerous studies thathave checked the relationship between some specific clay minerals with sliding

patter

s and slope sei sitivity of steep slopes

al., 2002). Clay accumulation in residual cracks has also been linked to slip events (eg,(eg, in Yatsu, 1966, Duzgoren- Aydin et

in studies by Prior and Ho, 1972; Parry et al., 2000). Clay mineralogy and chemistrymay also provide indications regarding the states of potential slip surfaces (Matsuura,

1985; Shuzui, 2001; Zheng et al. 2002; Wen et al., 2004).

Cac yếu tổ cơ học, hóa học và khống học của đất có liên quan rất chat chẽ đến cáctính chất tự nhiên và trạng thi cân bằng của đt. Cường độ cắt là một trong những đặc

tinh eo học rit quan trọng có ảnh hưởng lớn đến độ ổn định tự nhiên và nhân tạo của

sắc sườn đốc. Nó khơng có một giá tị nhất định nhưng lại bị ảnh hưởng rit lớn bởi

các hoại đột 18 tải trọng xây ra trên sườn mã nhất là do ảnh hưởng của lượng nước

trong dit. Cường độ cắt đất cơ bản được biểu điễn như là một ham số của áp lực thingđứng lên mặt trượt (G),lực cổ kết (c), và góc ma sát rong (g). Mỗi quan hệ giữa cácthành phin này đối với các đặc tinh tự nhiên khác của đất cũng đã được giới thiệu

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trong rit nhiều cúc công trinh như của Terzaghi và Peck (1967), Wu và Sangrey

(1978), Fredlund và Rahardjo (1993).

Một đặc tin tự nhiên quan trong khác nữa là hàm lượng sét trong đất. Các khoảngchit sét là sin phẩm phong hóa hóa học của đất đá rt quan trong. Có rất nhiều cácnghiên cứu đã thử nghiệm liên hệ giữa một số các khoảng chất sét cụ thể với các kiểu.trượt và sự nhạy cảm đối với trượt lờ của các sườn đốc (Vi dụ trong các nghiễn cứu

cia Yatsu, 1966; Duzgoren-Aydin và nnk, 2002). Sự ích ty sét trong các khe nứt tầndr cũng được liê hệ với các sự cổ trượt (vi dụ trong các nghiên cứu của Prior và Ho,

1913; Parry và nn, 2000). Khoáng học ớt và hóa học sét cũng có thé cung cắp nhữngdấu hiệu liên quan đến các trạng thái của các mặt trượt tiềm năng (Matsuura, 1985;

Shuzui, 2001; Zheng và nk, 2002; Wen và nok, 200),Geomorphological factors

Slope is closely related to starting of slippage. In the majority of slides studies,

slippage was seen as a major sliding or sliding trigger (eg, Lohnes and Handy, 1968;

Swanston, 1973; Ballard and Willington, 1975) .Sometimes slope angle is considered4s an index of slope stability, and in GIS it can be computed in numerical and spatialterms (O'Neill and Mark, 1987; Gao , 1993)

In addition, environmental dynamies factors have a great influence on landslide. Forexample, fast-moving blocks and debris flow may even appear in areas with lowsloped angles. This proves that the geomorphologic, geological, hydrological and soil

factors are dee factors for the stability of the slope.

Flank shapes

“The flank shapes have great influence on the stability of the slopes in sloping terrain

<due to the concentration of water or division of water on the surface of the flanks andsubsoil of the flank. According to the geomorphology-hydrogeaphic unit, there arethree basic flanks: divergentéconvex, plannar/straight and convex/eoncave. In general,the convex flank is the most stable slope in steep terrain, following by straight flankand the least stable one is the concave flank. The reason is that the topographic

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structure has a great influence on the concentration or division of water on the surfacefof the flanks and under the surface of the flanks. The concave form tends toconcentrate the water below the surface of the flank on small areas of the flanks, andthus the pressure of the water in the holes increases rapidly in the event of long:

rain, When hole pressure is formed in the cavities, the soil cutting force will drop to a

critical value and a sliding fault may occur. Thus, cavities are sensitive to the onset ofdebris slipping or slide (Hack and Goodlett, 1960; Dietrich and Dunne, 1978, Benda,1990).

(1) - Convex flank (2) - Straight flank (3) -Coneave flank

Figure 9. Flank shapeAspect

Aspect has a strong influence on hydrological processes through evaporation, andtherefore affects the weathering and growth processes of the plant on the flanks,especially for dry environment (Sidle and Ochiai, 2006). Such features are likely toincrease slope instability (Churchill, 1982; Gao, 1993; Hylland and Lowe, 1997; Lanet al., 2004)

Statistical relationships between elevation and landslide phenomena have beeninvestigated in many works (eg, Pachauri and Pant, 1992; Lineback Gritzner et al.,2001; Dai and Lee, 2002). In general, elevation is often associated with landslidethrough other factors such as slope, lithology, weathering, rainfall, surface movement,

soil thickness and land use. For example, mountainous areas often face enormous

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Hydrological factors

Hydrological factors also play an important role in the onset of slippage. Some of themost remarkable hydrological processes are rainfall (distribution of space and time ofrainfall), soil infiltration (and potentials of surface flows), horizontal and verticaldisplacements in lithology, evaporation, etc.

Spatial distribution of rainfall is closely related to the onset of slippage (Campbell,1966; So, 1971, Starkel, 1976) through the effect of the formation of porous waterpressure on unsteady flanks (Slide and Swanston, 1982; Slide, 1984; Iverson andMajor, 1987; Tsukamoto and Ohta, 1988). Some scientists consider one of the fourattributes associated with rainfall as factors that cause slippage: total rainfall, intensityof rainfall in a short time, rainfall during storms and stormy period. However, it hasnot been determined what type of rainfall attribute is most relevant to landslidephenomenon. Some people have argued that the intensity of rainfall in short term is themost decisive factor, others suggest that there is a link between slippage incidents andrainfall over a long period.

Hydrographic characteristics of weathered soil and base rock

Hydrological characteris of the soil that affect slope stability can influence the rate

at which the water moves into the slope as well as its ability to retain water. In

addition, the structure, density and direction of cracks in the base rock and other‘underlying materials also play a eritical role in whether the water from the top soilpenetrates below or underneath from topsoil

[At microscopic rate, velocity of water in the soil on the slope is characterized by

‘ransmitivity (K), the amount of water that flows below the surface on a hydraulic

grai 1. Clay and soil with very small voids usually have much smaller K value thancoarser soils. Furthermore, to demonstrate the permeability of the soil in wet butunsaturated conditions, it ary to evaluate the unsaturated K values,

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“The rate of water flow in soil of a layer confined in unstable terrain forms governslong-term water conductivity and therefore also affects the moisture content of uppershell (Sidle et al. 1985). When a permeable layer

pressure of the voids can be recast and lead to instability of the slope (Hardenbickerretained in a clayey substrate, the

and Grunert, 2001). In addition, the high voids of relatively deep layers of soil on very

steep slopes can become unstable after prolonged periods of rainfall, despite theincreased pressure of voids (Sidle and Ochiai, 2006).

Water penetration

The concept of water penetration is related to amount of water actually into soil anddepends on physical, biological, terrain and farming factors as well as the speed of‘water distribution (ie, intensity of rain or speed of ice melting). Water penetration is

related to maximum amount of water or potential water going into soil ata given point

in time (Water penetration is always greater than or equal to the permeation rate). Theinfiltration rate of water into the soil is greatly affected by the soils naturalcharacte ies (ie, Void ratio, water transport into soil, distribution of void size, flownetwork), vegetation, farming practices, icy conditions, and terrain conditions. It hasbes

of the flanks (Horton, 1993),

shown that the water penetration rate has an indirect relationship to the stability

Flow under surface layer

Due to flow processes under the surface that govern the movement of water flow onflank that have been penetrated, these processes affect the characteristics of the waterpressure distribution gap in both space and time. Frequent currents in soil (Tsukamotoet al, 1982; Sidle et aL, 2000a, 2001; Uchida et al., 2001) and under base rock(Montgomery et al., 1997; Uchida et al., 2003; Sidle and Chigira, 2004)

‘great control on development of void pressure on flanks and thus affect the onset ofin make a

slippage phenomena,

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Pore water pressure

In general, pore pressure is usually formed temporarily in lithologic groundwatermirrors and is related to initiation or promotion of sliding faults. Sloping faults withsliding faults are particularly sensitive to the development of groundwater mirrors dueto the convergence of surface currents (Anderson and Burt, 1978; Pierson, 1980b;‘Tsukamoto etal 1982; Tsuboyama et al.. 2000)

Influence of vegetation

Vegetation often increase slope stability in two ways: (1) by removing soil moisturethrough evaporation and (2) by creating cohesion of roots into soil (Gray andMegahan, 1981; O'Loughlin and Ziemer, 1982, Riestenberg and Sovornick-Dunford,1983; Greenway, 1987). As a consequence, vegetation is also seen as a major factoraffecting sliding phenomena. Some of the effects of vegetation on hydrological andmechanical processes that affect the stability of the slopes include:

<small>+ Limitation of rainfall due to vegetation, thus promoting evaporation and</small>

reducing water infiltration (Satterlund, 1972; Greenway, 1987)

+ Root system absorbs water from soil physiologically (through evaporation)leading (0 a reduction in soil moisture (Dingman, 1994)

= Root system of large trees makes shells underlying layer firmly attached to

Seismies is also one of the major factors that trigger slippage. The majority of past

slippage is triggered by seismic events and those events are more and more frequentand often unexpected. Sliding type triggered by most common earthquakes includerock fall phenomenon on the slopes. In fact, any type of slipping can occur, including

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rapid falling making broken debris, slow and sticky slipping, block slipping and earthflows (Keefer, 2002). Falling rocks, crumbling stones and flows are most commonsliding phenomena triggered by earthquakes, and flow phenomena are capable oftransporting material in most farthest distance. Only one type of slide is considered the

only one related to earthquakes is the phenomenon of sliding due to swelling; This

type of slide can cause cracks or subsiding. Swelling is related to temporary loss ofdurabi of sand components and humus components acting as a lubricant solution.This can increase destructive effect of major earthquakes,

‘The biggest and most devastating landslides are known to be related to volcanoes.They usually occur when a volcano erupts or as ä result of the movement of sediments,formed by volea <small>vity,</small>

* Cutting down trees increases the potential for soil erosion and weakens the root's

ability to retain soil, thereby reducing evaporation

* Vibration occurring due to natural phenomena (such as earthquakes) or man-madeactivities (due to machine operations, blasting ..)

1.2 World-wide researches on geological hazards

AS United Nation chose ninetieth decade as International Decade for DisasterMitigation, disaster investigations seemed to have been motivated and demonstrated avery strong development. Large global projects may be referred to as "Methods of riskassessment for urban areas in prevention of seismic disasters” ended in 2000,"Earthquake and Megacities Initiative” End of 2002, "Role of Local Governments in

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In developed countries and some countries in the region such as the United States,Canada, Britain, France, Russia, New Zealand, Hong Kong, Taiwan, landslidesurveying has been conducted for two decades. Along with the rapid development ofinformation technology, most of surveying work has been done automatically to detectand give alerts accurately and in a timely manner and has significantly contributed tominimize loss of life and property caused by landslide accidents. Automatic landslidehhazard surveying system can accurately predict destructive movement. It is moreimportant that the surveying system also evaluates effectiveness of anti-skid works tohelp designers make additional adjustments to suit reality.

‘There have been a lot of investigations on the process of landslide has been conductedin detail, Especially in some countries ike the United States, Canada, Britain, France,Australia, India, China, ete where annual losses caused by landslide valued millions oftoday, thedollars, landslide surveying system have been established closely. However

<small>most c</small> mon method used for assessing and forecasting landslide risk is still

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controversy, There are now many different ways to divide the different methods ofsliding studies with varying levels of detail. However, the main methods currentlyused by scientists around the world can be grouped into three groups of methods:

1 Id survey method: commonly related to evaluation of geotechnical,geomorphological, engineering geological and geological researchers.

2. Modeling method: commonly conducted in laboratories to establish mathematirelationship between sliding components and likelihood of landslides.

3. Information integration method in geographic information system (GIS), combinedwith statistical algorithm, neural network, fuzzy logic algorithms, geneticalgorithms, ete, © evaluate and establish map of landslide risk forecast

Among three groups of methods above, the first two methods have high accuracy forevaluating the possibility of landslide in si gle sliding blocks, but they are noteffective to asses the possibility of slipping of a certain area. Also cost of these‘methods is also large. Currently, the third method is being used widely in the worldand is highly effective in solving the problems of assessing possibility of landslideoccurrence, however, combination between information layers in GIS and algorithmsfor ing possibilty of landslide in specific areas is still controversial and there isno agreement among scientists. Then there is no uniform method and it continues torequire scientists to spend more time and effort on research,

In recent few years, the application of remote sensing (RS) and geographical —geological information system and its theories and views to the geological field have

sven positive effects in the work of geological investigation in general and assessment

of geological disaster in particular. In the world, remote sensing analysis combined

with GIS analysis is considered to be one of the most effective methods in

investigating and controlling landslides and environmental protection. Combination ofimage processing and geological data processing such as geological map, tectonicdata, weathering, hydrology, ete. by GIS processing technology generates synthetic‘models (Tran Tan Van, 2002, Nguyen Trong Yem, 2006, Nguyen Thi Hai Van, 2001Nguyen Thanh Long, 2009 ..) are very useful for investigating and evaluatinglandslides.

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1.3 Researches on geological hazards in Vietnam.

In Vietnam, types of geological hazards have been studied since 1960s of last century.In last few years, as some of the geological hazards have occurred each year andcaused a ot of serious damage to people and property, the research on geologicalhazards has been paid more attention, Scientific works include: Nguyen Trong Yem etal, (1995, 1998, 1999, 2004, 2006), Tran Trong Hue et al, (2006), Vu Cao Minh et al(1996, 2000), Dinh Van Toan et al. (2003), Nguyen Quoc Thanh et al (2006, 2008) ofInstitute of Geology (Ministry of Science and Technology); Nguyen Dinh Vinh, LeDuc Tuu (1995), Nguyen Thanh Son (1996), ... under Ministry of Transportation;Pham Kha Quyen, Nguyen Dinh Uy (1996). Do Tuyet (1999), Tran Tan Van et al(2002), Vu Thanh Tam et a. (2005), Nguyen Thi Hai Van et af. Institute of Geotogicaland Mineral Res ch - Ministry of Natural Resources and Environment; Nguyen Duc‘Thai (1998), Dao Van Thinh et al. (2004), Department of Geology and Minerals,al. (2001) underUniversity of Mining and Geology, Ministry of Education and Training, ete

ch as landslides, flood, flash flood,Ministry of Natural Resources and Environment, Nguyen Van Lam

“The resu of geological hazards researches

mudflow, etc. have been achieved remarkably and have established maps of geologicalhazards and classification of geological hazards areas of different scales, specificallyevaluating the impact of geological hazards on important constructions and residentialareas, ete and identifying the factors that influence the geological hazards. In additionto contribution to planning and appropriate use of territorial resources, this result haspractical significance in orienting the construction of urban areas and socio-economic

centers in mountainous areas of Vietnam. Many works have scientific approaches,

logical explanations to find the factors that govern the processes of geological hazards,delineate potential risk forecasts and suggest mitigation measures for sustainabledevelopment of the region's socio-economic development.

However, these studies have only conducted on very small ratio for a large area, themethod of evaluating landslide zoning is only reasonable with percentage of studies,‘There are a number of studies that have applied GIS and remote sensing models tosynthesize and give high accuracy landslide forecast at a rate of 1/200,000 to 1/50,000.‘There is, however, a large shortage of research topics at rate of more than 1/25,000 for

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4 small area, which may suggest appropriate research methods for detailed areas withlarge seale, used for calculating models, delimiting geological hazards risk in theseplaces

Focusing on cities in mountainous areas in the northern of Vietnam, geologicalsurveys have been catried out in urban areas such as Son La, Dien Bien, Lai Chau(Cao Son Xuyen, 1996), Viet Tri, Yen Bai, Lao Cai (Tran Minh, 1997), Hoa Bình1999), Thai Nguyen (Nguyen Van Nghia, 2000), Lang Son, Cao(Nguyen Thi Tai

Bang, Ha Giang, Tuyen Quang (Nguyen Ba Binh, 2000)... However, the authors onlycarries out a preliminary survey and assessment of current state of the geologicalhazards as one of basic investigations of geological survey in addition to aspects schas geomorphology, neo . geology, engineering geology, environmentalgeology, hydrogeology, sơil and weathering. Zoning work on forecasts andassessments of geological hazards risks for these urban areas has not been completelyaddressed.

Due small scale of investigation research, not mentioning risk of geological hazards,the results are mainly generalized. Zoning study and giving geological hazards

be limite

prevention

measures for specific areas are possibility of applying isonly orientation for large areas. Measures for geological hazards prevention andmitigation have not been convinced so that implementation of these measures is noteffective,

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CHAPTER 2. METHODOLOGY

Kk of Future‘The geological hazard currently, is based on the theory that locations at

geological hazards will appear in such areas that share the same conditions thatgeological hazards use to happened in the past. Therefore, the geological hazard mapmaking and the precise identification of locations that have been oceurting are thekeys to divide risky geological hazard zones for study. At present, the establishmentsof geological hazards maps are conducted in four following methods

+ Data collections«Field survey

+ Satellite images analyzing

* Combination of data collections, field survey and analyzing satelite imagesIn whieh:

+ Data collection methods often use the information of geological hazard from the

previous studies by interviews, questionnaires... or information collected from the

public about the landslides that have occurred in the past and the occasions are‘occurring, After that, all the information is displayed on the map to show the status of‘geological hazard in the study zone.

* Field survey method is conducted bygeologists including: describing, marking andcircling the areas that are undergoing landslides, floods, flash floods, riverbankerosion... are observed during the studying real fields.

«The method of satelite imagery analysis is also widely used because through temporal satellite imagery, the detection of a geological hazard at different times canbe easily identified. Besides, with the recent launch of a series of high-resolutionsatellite imagery, the identification of a geological hazard is more accurate and fasterthan that of field surveys. At present, some remote sensing images are used to identifythe locations and the space of slide points such as aerial photos, SPOT images,IKONOS, QUICKBIRD, ASTER, LANDSAT, LANDSAT ETM, MERIS. However,aerial photography is still the preferred method because of its economic efficiency and

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high accuracy.

+ The method of combining data collection, satellite imagery analysis and fieldsurvey is used by many scientists nowadays. The limitations of each above Sindividualmethods are fixed. In addition, the results obtained from this method also reflect the

status and partial risky of geological hazard in the studied field

2. 1 Process of mapping the current state of landslides

Process for lands © inventory mapping is be done with 4 steps, including: (Step A)Stereoscopic image generation, (Step B) Surface 3D generation, (Step C)Interpretation of landslide based on the stereoscopic image analysis and surface 3D,(Step D) Checking

advantage of the data source and available resources (aerial photographs, satelite

calibration on field survey (Figure 5). This process tries to take

images of high resolution obtained from Google Earth, topographic maps at scale 110/000, 1:5,000), as well as the application of new remote sensing technology(stereoscopic image, model) to accelerate the time to decipher in the room, as well astime in the field, since implementation costs are lowered significantly.

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corresponding, to each image, to create the effect of image depth. To view 3D,

glasses we need 2 colours, with cach colour glasses are opposites, usually red andblue.

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Figure 11. Stereoscopic for the same area created from aerial image (above) andsatellite image (below) with DEM

Step B. 3D Hillshade generation

In the landslide inventory mapping, digital elevation model (DEM) data play animportant role. Landslide interpretation on the surface 3D topography based on thegeomorphological characteris of landslide or changes in the flow system.

Therefore, the parameters extracted from the DEM as slopes, hillshade, topographicroughness, and uneven levels is very important, In that map the terrain unevenshadows when combined with the surface creates hillshade 3D, making clearly thegeomorphological characteristics of the surface topography (Figure 12)

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Figure 12. Hill shade

‘Step C. The process of landslide area interpretation

Visual image interpretation is a step in the processing of remote sensing information.

This is a necessary, and can be applied in many different research areas such as

forestry, agriculture, environment... However, to carry out visual image interpretationoutside support of tools such as computers, software etc. also need to base theinterpretation, this is the key to interpretation, The key to interpreting the signs,characterized to distinguish an object, is set primarily based on experience and

Knowledge of the interpretation expert, Typically, the interpretation of such factors

tone image, the size, shape, color, pattern etc. and the relationship with the

surrounding objects will be particularly interested in factors associated with the

shooting time or photography season formed the key to interpretation.

+ Shape: A typical external characteristic for each object. For example, theconventional rice plantations or polygon-shaped or square, or the sliding wallsemicircle shaped bow, feet sliding blocks form fan-shaped bulge,

+ Pattern: In relation to the arrangement of objects in space. Example as easy toarrangement noticeable spatial tree in the garden of trees in the forest as opposed to

(garden: discrete, forest: large arrays); usually linear highway, faults, fissures.

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+ Tone: The aggregate amount of light reflected by the surface of the object, or in otherwords itis an expression of colour in different intensities. For example, the bare landareas or new are ctation areas are theis landslides occur often bright tone image; vesdark tone image. Thi an important factor to evaluate the age of landslide.

* Texture: As the repetition frequency of the changing image tone, It was created by acollection of very small features of each separate object and it determines that object issmooth or raw structured. Example: Grass with fine-grained structure, coarse grainstructure is usually vegetation canopy.

<small>+ Site: The factors related to the geographical location of the object, this is a</small>

particularly important factor to di

linguish objects is with plants, Since the same signin the image but different locations may be different objects.

* Colour: Satellite image considered @ matrix consisting of numbers and pictures tounderstand the information on the transmission channel is carried out according to thecolour coding of each channel set in accordance with the colour from red (0,74m) ->Purple (04pm). The colour of objects in an image frequently used colourcombinations give the interpretation easier to distinguish objects, Commonly usedcolour spaces are RGB (Red, Green, Blue) and, depending on the purpose of researchWhich the interpretation selected colour combinations so that the object of interest isthe best display.

* Combination of relationship: In relation to some characteristics of the object with theobjects around it.

In addition to the photograph interpretation, it is necessary to have experience andknowledge of topography, geomorphology, land cover and stream network in order toidentify landslide type precisely. The following table describes some interpretationstandardization of objects corresponding to landslide morphology.

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Table 2. Interpretation standardization of objects corresponding to landslidemorphology

Tandsti Interpretation standardization

de type Geomorphology Vegetation Stream

‘Vegetation appearsEasily to idemtfy the exposed | linearly uponbedrock surface scarp linked | bedrock exposed

to the sharp gravel slope (20°- | scarp. Land cover

ToPPlE | 30° slope) and alluvial cone. | density is atthe | Nevins special

Or fractured searp (lager than | low level (almost

50° slope) associated to slide. | bared) upon the

gravel slope.‘There is the rapid change in

slope form, characterized by Contrast to stablethe convex (toe) and concave slope. The low(sliding are). The slope often ability in run off

isin the benched form. Crown Ma drainage or

Rotatio | USUAMY is semictcular form, | Quu tearm dục | mereepted water in

Fal [tess convex Forward. Slide, Se | zock cavity or in

scurp incline backward, the | 7 * the backwardaccumulated material part isin | TU inclined partsthe form of bill and mound. ‘There is lacking

‘The ratio of depth/length is ‘water in the convex

from 0.3 to 0.1, Slope is from scarp.

20° 1o 40"

Crack in crown area, flat slide,

‘The depth is relative lowreaching to the weathering

surface right upon the ‘The area of crown

bedrock. The ratio of and transportation _ | The stream is

Translat | depth/length is lower than 0.1. | is eroded. There is. | deflected or

ional | and the large width, The land cover blocked bytranslational landslide slides | difference in the | materials.as the concrete mass, often | body.

<small>appear nervures running as</small>

parallel linear on the slidesurface

Debris | Material low covers the Targe | Land cover, ‘There is a jumble

Tạ, | ee with the high composition | vegetation are | in the body; the

of mud and cobble in the form buried by debris original stream is

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Landsti Tnerpretation standardization

de ype Geomorphology ‘Vegetation ‘Stream

of fan (alluvial cone), Tlow; sometimes | Blocked or changedaccumulated material in both | there are some big. | by material flow.of valley valve alluvial cone | tree still standing

and toe slope strongly right inflow or tree root

still existsStep D. Checking on the field and 3D digital model

Document preparation for field checking including: landslide interpretation map,stereoscopic images and the equipment necessary to identify landslide on the map andin the field

Figure 13. a) Checking landslide interpretation in the field; b) Compared landslide

interpretation with 3D model

‘The inspection was conducted to evaluate the steps: Identified landslide interpretationpoints on the map and in the field, checking in this position then summary statisties,compare landslide interpretation point on the map with landslide point in the field, the

detection of specific topographic signs arise new landslide point and old landslide, a

preliminary understanding of the causes and factors that promote the failures.

Identification of the landslide in the field and the terrain signs on the stereoscopic

image as the basis to improve the quality and accuracy for the landslide interpretation

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in the office, For those of you who slip deciphered but not accessible in the field, itwill compare by 3D model

2.2 Field surveys

Fieldwork consists of a system of investigated roadways designed in accordance withthe system of roads, rivers, streams, with the purpose of cutting the horizontal

geological structure and direction of terrain forms; covering almost residential areas,

construction complex sites: in addition, the basins in the stream system are ensure tobe controlled. The survey process must meet the below technical requirements:

~ Ensure to collect sufficient information, record phenomena, signs of landslides andrelated information; collect data on planning, planning for economic development -

population, reports of the situation of natural disasters and the prevention of floods ~

storms in areas from specialized agencies, local stated management(province, district,commune level)

- While investigating, ensure the landslides, geological and geological featuresidentification, locations and relationship between sliding blocks and sliding factorsmust be measured and recorded, Collect specimens, check results of interpretation ofremote sensing, geophysical data; circle the area that had occurred. possibly occurred

‘geological hazards and other specific problems.

~ The survey on the current state of slides must meet the requirements:

+ At each studied site, information will be collected and filled out the questionnaires,besides, some key information about sliding blocks and detailed information need toexplain because the questionnaire form is not displayed; included

+ Coordinate, elevation; Geographical location; Relative position with feature

terrains, with nearest recent constructions;

+ The main dimensions of the slide blocks, slide scale, slide types

+ Detaled descriptions of the vegetation cover and coverage;

+ Detaled descriptions of belt of cementation;

<small>‘Photo number, photo shooting positions</small>

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