Dissertations / Theses on the topic 'Landsliding'

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Kyoto University (京都大学)
0048
新制・論文博士
博士(理学)
乙第10072号
論理博第1351号
新制||理||1115(附属図書館)
UT51-99-G549
(主査)教授 奥西 一夫, 教授 千木良 雅弘, 教授 佐々 恭二
学位規則第4条第2項該当

Disasters can occur without warning and severely test society’s capacity to cope, significantly altering the relationship between society and the built and natural environments. The scale of a disaster is a direct function of the pre-event actions and decisions taken by society. Poor pre-event planning is a major contributor to disaster, while effective pre-event planning can substantially reduce, and perhaps even avoid, the disaster. Developing and undertaking effective planning is therefore a vital component of disaster risk management in order to achieve meaningful societal resilience. Disaster scenarios present arguably the best and most effective basis to plan an effective emergency response to future disasters. For effective emergency response planning, disaster scenarios must be as realistic as possible. Yet for disasters resulting from natural hazards, intricately linked secondary hazards and effects make development of realistic scenarios difficult. This is specially true for large earthquakes in mountainous terrain. The primary aim of this thesis is therefore to establish a detailed and realistic disaster scenario for a Mw8.0 earthquake on the plate boundary Alpine fault in the South Island of New Zealand with specific emphasis on secondary effects. Geologic evidence of re-historic earthquakes on this fault suggest widespread and large-scale landsliding has resulted throughout the Southern Alps, yet, currently, no attempts to quantitatively model this landsliding have been undertaken. This thesis therefore provides a first attempt at quantitative assessments of the likely scale and impacts of landsliding from a future Mw8.0 Alpine fault earthquake. Modelling coseismic landsliding in regions lacking historic inventories and geotechnical data (e.g. New Zealand) is challenging. The regional factors that control the spatial distribution of landsliding however, are shown herein to be similar across different environments. Observations from the 1994 Northridge, 1999 Chi-Chi, and 2008 Wenchuan earthquakes identified MM intensity, slope angle and position, and distance from active faults and streams as factors controlling the spatial distribution of landsliding. Using fuzzy logic in GIS, these factors are able to successfully model the spatial distribution of coseismic landsliding from both the 2003 and 2009 Fiordland earthquakes in New Zealand. This method can therefore be applied to estimate the scale of landsliding from scenario earthquakes such as an Alpine fault event. Applied to an Mw8.0 Alpine fault earthquake, this suggests that coseismic landsliding could affect an area >50,000 km2 with likely between 40,000 and 110,000 landslides occurring. Between 1,400 and 4,000 of these are expected to present a major hazard. The environmental impacts from this landsliding would be severe, particularly in west-draining river catchments, and sediment supply to rivers in some catchments may exceed 50 years of background rates. Up to 2 km3 of total landslide debris is expected, and this will have serious and long-term consequences. Fluvial remobilisation of this material could result in average aggradation depths on active alluvial fans and floodplains of 1 m, with maximum depths substantially larger. This is of particular concern to the agriculture industry, which relies on the fertile soils on many of the active alluvial fans affected. This thesis also investigated the potential impacts from such landsliding on critical infrastructure. The State Highway and electrical transmission networks are shown to be particularly exposed. Up to 2,000 wooden pole and 30 steel pylon supports for the transmission network are highly exposed, resulting in >23,000 people in the West Coast region being exposed to power loss. At least 240 km of road also has high exposure, primarily on SH6 between Hokitika and Haast, and on Arthur’s and Lewis Passes. More than 2,750 local residents in Westland District are exposed to isolation by road as a result. The Grey River valley region is identified as the most critical section of the State Highway network and pre-event mitigation is strongly recommended to ensure the road and bridges here can withstand strong shaking and liquefaction hazards. If this section of the network can remain functional post-earthquake, the emergency response could be based out of Wellington using Nelson as a forward operating base with direct road access to some of the worst-affected locations. However, loss of functionality of this section of road will result in >24,000 people becoming isolated across almost the entire West Coast region. This thesis demonstrates the importance and potential value of pre-event emergency response planning, both for the South Island community for an Alpine fault earthquake, and globally for all such hazards. The case study presented demonstrates that realistic estimates of potential coseismic landsliding and its impacts are possible, and the methods developed herein can be applied to other large mountainous earthquakes. A model for developing disaster scenarios in collaboration with a wide range of societal groups is presented and shown to be an effective method for emergency response planning, and is applicable to any hazard and location globally. This thesis is therefore a significant contribution towards understanding mountainous earthquake hazards and emergency response planning.

Maungatapu Peninsula is a northeast trending peninsula located within the Tauranga Basin covering an area of 1.6km². Maungatapu is underlain by a sequence of volcanic tephras, ashes and fluvial deposits derived both locally and from the Taupo Volcanic Zone. In late May 1995 three landslides occurred at 83, 85 and 89 Te Hono Street, and again in late December 1995 at 330 Maungatapu Road. The purpose of this study was to carry out a geotechnical investigation of these landslides, and to establish the mechanisms that produce cliff failure on the Peninsula. Landslides were identified from aerial photographic interpretation and engineering geological mapping at a scale of 1:5000, and were classified as, 1) probable large scale block failures, 2) piping-triggered block failures, 3) wave erosion triggered block failures, and 4) colluvium/topsoil failures. Geotechnical core logging at a scale of 1:50 identified a number of stratigraphic units including the Post-Rotoehu Ash Tephras, Rotoehu Ash, Palaeosol, Hamilton Ash, Pahoia Tephras, Cross-bedded sequence, Upper Bounding Aquitard, Aquifer, and Lower Bounding Aquitard. The total thickness of the sequences are approximately 15m, and failures in 1995 were associated with a piping failure within the aquifer and lower section of the Crossbedded sequence triggering a block landslide. Geotechnical testing involved both field and laboratory testing to characterise the various stratigraphic units present within the logged cliff faces. In-situ shear strength testing indicated variable strength through out the profile, with the Palaeosol demonstrating the highest shear strength, and the Aquifer the lowest. This relationship was also confirmed by unconsolidated undrained triaxial laboratory testing. Clay mineralogy analysis indicated that the main constituent clays present were mixed layer 7 & 10 Å Halloysite and Allophanes. Atterberg Limit testing demonstrated a range of plasticities from low to very high. Direct shear testing indicated low cohesions and high friction angles for the Cross-bedded sequence and Aquifer, and a moderate cohesion and friction angle for the Lower Bounding Aquitard. Dispersion and Erodibility testing showed the Post-Rotoehu Ash Tephras, Rotoehu Ash, and Palaeosol to be non-dispersive and non-erodible, whilst the Cross-bedded sequence was dispersive and highly erodible. Both in-situ and laboratory permeability testing indicated low permeabilities associated with the stratigraphic units of the Peninsula. From field and laboratory investigations a hydrogeological model was developed to explain the fast lag times delineated by plots of piezometric water level response to rainfall. The hydrogeological model combined components of a "defect controlled permeability model" and a "hydraulic head response model". The "defect controlled permeability model" indicates that these fast lag times can be produced by soakage water permeating through high permeability flow pathways such as exfoliation defects, fractures, and heavy bioturbation structures. The "hydraulic head response model" involves the rapid transferral of a pressure wave along the Aquifer and lower section of the Cross-bedded sequence in response to changes in the hydraulic head of the Peninsula due to recharge within a much larger catchment of approximately 5km² Stability analysis using a non-circular failure mode was conducted for an increasing phreatic surface and landslide block size. The phreatic surface was related to piezometric water levels and showed that with an increase in the phreatic surface there was a decreased in the factor of safety by 0.1 from 1.0 to 0.9. Increasing the landslide block size was undertaken to determine whether larger blocks were likely to fail. From calculations it was concluded that failure of blocks greater than 10m back from the cliff edge were unlikely for the piping triggered model. Two principal conclusions can be drawn from this study. Firstly a 2H:1V slope line projected back up to the Peninsula's surface from the base of the cliff delineating a geotechnical assessment zone is not a correct representation of the failure types threatening cliff top properties. Therefore, this assessment criteria should be reassessed, and a policy adopted where by any future development on a cliff top property should require a geotechnical report if deemed necessary by the Consents Officer from evidence of slope failures in adjoining properties or other evidence of instability on site. The second conclusion is that it takes approximately two months of double the average rainfall to produce adverse pore water conditions at the cliff edges where a rainfall event can trigger a piping-triggered block slide such.

An engineering geomorphological investigation of the Esk River catchment has been undertaken to quantify the relationships between the valley's geomorphic evolution, the many 1-10km2 deep-seated landslides present within the catchment, and a significant flood event that inundated the lower valley in April 1938. The identification of key geomorphic processes enabled the assessment of catchment's geomorphic stability, the development of generalised models for landsliding, and the delineation of a pre-disposed zone of instability. This information is then applied to assess key geomorphic controls on the flood event. The region lies within the forearc basin of the obliquely convergent Hikurangi Margin, and is underlain by soft, gently eastward dipping Pliocene marine strata. Structurally it is dominated by its close proximity to the Mohaka Fault, as well as two westward-dipping blind thrusts beneath the valley identified in this study: the Wakarara Fault – Trelinnoe Sector, and the Eastern Patoka Fault. Evidence from seismic reflection surveys indicates that these have both been active since the early Mangapanian (2.8 - 3.2 Ma), and an analysis of stream longitudinal profiles and plan form suggests limited displacement may have taken place within the last 10,000 years. A survey of rock mass defects within a representative sample area in the centre of the valley highlights four sub-vertical joint sets; conjugate sets strike 153° and 246°, and another sub-parallel to the folding strikes 033°. These defects correlate well with lineaments identified in aerial and satellite photographs and are attributed to extension of the sediments across the top of fault-propagated folds. The generally low power streams have exploited these defects and highly incised channels now run almost exclusively along them. Deep-seated landslides occur generally within the area of folding and their extents are defined by lineaments inferred to correspond to persistent joints in the rock mass. The slides are translational, and are facilitated by up to 80m of incision - ongoing since the abandonment of an extensive terrace inferred to be Ohakean (18-10ka) in age. Basal failure surfaces commonly dip at angles as low as 6°, and a combination of tectonically induced flexural shears sub-parallel to bedding and very low shear strength tuffaceous horizons are inferred to provide planes of sufficiently low shear strength to facilitate failure. While most deep-seated landslides appear active, there is no evidence to suggest they were substantially affected by recent major tectonic (e.g. 1931 Ms7.8 Hawke's Bay Earthquake) or climatic events (e.g. 1938 c.1 :1000yr Esk Valley Storm). The headwaters of the catchment are located on the Maungaharuru Range. This rises from 500m - l300m and provides baseflow to the Esk River. Extensive deep-seated landslides dominate the eastern face of the range. These are inferred to have been triggered by the removal of lateral support at the foot of the range following significant incision and denudation in the last interglacial c.125ka. A deep-seated gravitational slope deformation is proposed to extend to 1.2km below sea level, and provide a driving mechanism for the slides. While the 1938 Esk Valley flood was primarily a result of an exceptional three day storm event, suspended sediment load was also an important factor. This is inferred to have resulted primarily from channel erosion in soft colluvial sediments on the Maungaharuru Range. Combined with significant sediment load from shallow landsliding and possible tectonic subsidence preconditioning the lower reaches of the aggradational valley, this lead to c.1 m of silt being deposited in the lower reaches of the aggradational valley. Rapid stream incision in response to uplift in 1931 and aggradation in 1938 is returning the lower reach of the river to grade and decreasing the flood hazard.

Throughout the alpine domain, shallow landslides represent a serious geologic hazard, often causing severe damages to infrastructures, private properties, natural resources and in the most catastrophic events, threatening human lives. Landslides are a major factor of landscape evolution in mountainous and hilly regions and represent a critical issue for mountainous land management, since they cause loss of pastoral lands. In several alpine contexts, shallow landsliding distribution is strictly connected to the presence and condition of vegetation on the slopes. With the aid of high-resolution satellite images, it's possible to divide automatically the mountainous territory in land cover classes, which contribute with different magnitude to the stability of the slopes. The aim of this research is to combine EO (Earth Observation) land cover maps with ground-based measurements of the land cover properties. In order to achieve this goal, a new procedure has been developed to automatically detect grass mantle degradation patterns from satellite images. Moreover, innovative surveying techniques and instruments are tested to measure in situ the shear strength of grass mantle and the geomechanical and geotechnical properties of these alpine soils. Shallow landsliding distribution is assessed with the aid of physically based models, which use the EO-based map to distribute the resistance parameters across the landscape.
In tutto l'arco alpino, le frane superficiali rappresentano un rischio estremamente attuale che ogni anno causa ingenti danni alle infrastrutture, alle proprietà e, nei casi più tragici, provocano perdite umane. Le frane superficiali rappresentano un importante fattore di evoluzione del paesaggio alpino in quanto provocano perdita di suolo e modificano quindi la distribuzione dei terreni adibiti al pascolo. L'analisi dei meccanismi di innesco delle frane superficiali e la loro distribuzione, deve essere condotta partendo da una profonda conoscenza dei parametri geomeccanici che caratterizzano il suolo e soprassuolo. Nell'area di studio, un bacino montano situato tra i 1900 e i 2400 m s.l.m., la maggior parte dei versanti è ricoperta da un fitto manto erboso, il Nardetum; questa copertura vegetale tuttavia, presenta degli evidenti pattern di degradazione, causati dall'intesa attività pastorizia. Nelle zone in cui il manto erboso è danneggiato, le resistenze calano drasticamente, aumentando quindi la vulnerabilità al franamento superficiale. L'obiettivo di questo lavoro è quello di combinare la suddivisione del territorio, fatta attraverso tecniche di classificazione automatica delle immagini satellitari alle proprietà geomeccaniche e geotecniche delle diverse coperture. La caratterizzazione di queste proprietà del suolo e soprassuolo è stata condotta utilizzando sia strumenti e metodi tradizionali, sia tecniche innovative e strumenti sperimentali. Infine per studiare la distribuzione delle frane superficiali, i dati raccolti in campagna e suddivisi nelle diverse classi di copertura, sono stati inseriti in modelli di stabilità dei versanti.

Following the 22 February 2011, MW 6.2 earthquake located on a fault beneath the Port Hills of Christchurch, fissuring of up to several hundred metres in length was observed in the loess and loess-colluvium of foot-slope positions in north-facing valleys of the Port Hills. The fissuring was observed in all major valleys, occurred at similar low altitudes, showing a contour-parallel orientation and often accompanied by both lateral compression/extension features and spring formation in the valley floor below. Fissuring locations studied in depth included Bowenvale Valley, Hillsborough Valley, Huntlywood Terrace–Lucas Lane, Bridle Path Road, and Maffeys Road–La Costa Lane. Investigations into loess soil, its properties and mannerisms, as well as international examples of its failure were undertaken, including study of the Loess Plateau of China, the Teton Dam, and palaeo-fissuring on Banks Peninsula. These investigations lead to the conclusion that loess has the propensity to fail, often due to the infiltration of water, the presence of which can lead to its instantaneous disaggregation. Literature study and laboratory analysis of Port Hills loess concluded that is has the ability to be stable in steep, sub-vertical escarpments, and often has a sub-vertically jointed internal structure and has a peak shear strength when dry. Values for cohesion, c (kPa) and the internal friction angle, ϕ (degrees) of Port Hills loess were established. The c values for the 40 Rapaki Road, 3 Glenview Terrace loess samples were 13.4 kPa and 19.7 kPa, respectively. The corresponding ϕ values were thought unusually high, at 42.0° and 43.4°.The analysed loess behaved very plastically, with little or no peak strength visible in the plots as the test went almost directly to residual strength. A geophysics resistivity survey showed an area of low resistivity which likely corresponds to a zone of saturated clayey loess/loess colluvium, indicating a high water table in the area. This is consistent with the appearances of local springs which are located towards the northern end of each distinct section of fissure trace and chemical analysis shows that they are sourced from the Port Hills volcanics. Port Hills fissuring may be sub-divided into three categories, Category A, Category B, and Category C, each characterised by distinctive features of the fissures. Category A includes fissures which display evidence of, spring formation, tunnel-gullying, and lateral spreading-like behaviour or quasi-toppling. These fissures are several metres down-slope of the loess-bedrock interface, and are in valleys containing a loess-colluvium fill. Category B fissures are in wider valleys than those in Category A, and the valleys contain estuarine silty sediments which liquefied during the earthquake. Category C fissures occurred at higher elevations than the fissures in the preceding categories, being almost coincident with bedrock outcropping. It is believed that the mechanism responsible for causing the fissuring is a complex combination of three mechanisms: the trampoline effect, bedrock fracturing, and lateral spreading. These three mechanisms can be applied in varying degrees to each of the fissuring sites in categories A, B, and C, in order to provide explanation for the observations made at each. Toppling failure can describe the soil movement as a consequence of the a three causative mechanisms, and provides insight into the movement of the loess. Intra-loess water coursing and tunnel gullying is thought to have encouraged and exacerbated the fissuring, while not being the driving force per se. Incipient landsliding is considered to be the least likely of the possible fissuring interpretations.

碩士
國立中央大學
應用地質研究所
92
Frequent crustal movements and subtropical climate lead to the high sliding potential of many slopes in Taiwan, area slope stability analysis offers valuable design data to urban planning and large scale engineering projects. This study aims to analyze the factors that will contribute to sliding potential respectively, and an integrated evaluation is proposed for Takeng, Taichung. Factors with different grading and weighting are quantified statistically, GIS is used to process large spatial data, and a practical and efficient method in evaluating area slope stability is presented. Factors contributing sliding potential are extracted from topographic maps, geologic maps, and all the available sources. Field geological investigation and Schmidt hammer impact tests are conducted as an assistance. Grading and weighting of the factors are quantified by inverse analysis, all the data are then proceed to a further integrated calculation to obtain the landslide susceptibility map of the area. The basic concept in the analysis is to set each grid point as (x,y,z) where x and y are the coordinates, z is the evaluating grade of a certain factor. By integrating all the effects from other factors, a new z-value representing its sliding potential grade will thus be obtained. Study results show that the sliding in the middle and west parts of the area is mainly affected by fault structure, that in the northeast part is highly related to rock properties, while sliding in central and east parts is the results of strong weathering and erosion. Rock strengths in the area are evaluated from Schmidt hammer rebound values, high rock strength distribution lies in the locations with topographic highs. The result show that the high topography can be reflected as high rock induration.

The Ottawa/Gatineau region has significant deposits of sensitive glacial marine clay. As these deposits have risen due to isostatic rebound, these materials have been incised by various watercourses, carving river valleys throughout the region. The slopes of these river banks are susceptible to retrogressive slides with significant travel distances. A novel method of monitoring changes in these landslides has been developed and is explained in this thesis. Using a tethered blimp as an aerial photo platform, high resolution digital elevations models (DEM) with accuracies of ±0.49m on vegetated slopes have been created using photogrammetry. These DEMs have been created for a several photos sets taken over time. This allows changes over time to be monitored. The use of ground control points (GCP) allows for the complete three dimensional movement of discrete points to be monitored over time. The photogrammetric DEM have been compared to similar DEM derived from LiDAR surveying. By complimenting these surveys with historical aerial photos it is possible to develop better models of landslide failure processes, which will ultimately provide better predictions of movements and failure. When movements and failures can accurately be predicted it will then be possible to better manage the risk associated with these landslides events.
Thesis (Master, Civil Engineering) -- Queen's University, 2012-01-30 16:20:27.13

The mobility of sediment in steep mountain rivers controls the denudation rate and height of mountain ranges worldwide. Sediment movement within the steepest terrain often occurs as catastrophic shallow landsliding, posing significant hazards to those living downstream. Despite the importance of steep channels, our observations of sediment transport are mostly limited to rivers with slopes of less than 2°. This prevents us from predicting the runoff required to transport sediment throughout most of the drainage network and from knowing the mode of transport that should dominate (dilute river transport vs. landsliding). I performed a series of laboratory experiments in an artificial river with an adjustable slope to test the flow depths required to transport sediment on slopes up to the dry angle of repose. Counterintuitively, sediment becomes harder to move on steeper slopes by dilute river processes. Laboratory observations of flow hydraulics and field observations of cobble stability reveal that this reduced mobility is a hydraulic effect resulting from the shallow flows that are inherent to steep channels. In experiments that were conducted at slopes steeper than half of the dry angle of repose, sediment was more easily transported by shallow landsliding than dilute river processes. Within this landsliding regime, sediment was again observed to be more stable than predicted by traditional theory. Documentation of these experimental failures with high-speed video revealed that failures occur with a characteristic length scale that is shorter than predicted, and that these short failures experience a strong buttressing force at their downstream margin. These results suggest that landslide length scales consistently with width, and also provides new expectations for the saturation level required to initiate failures. Ultimately, these experiments provide us with expectations of the flow depth required to transport sediment throughout the entire drainage network, and also allow us to partition the drainage network into river-dominated and landslide-dominated regimes.

碩士
國立成功大學
土木工程學系
106
On September 28, 2016, due to the typhoon Megi, mudstone slope failed in in Yanchao district, Kaohsiung city, which damaged a building and buried three lives. To investigate the mechanism of the rainfall-induced mudstone landsliding, the field investigation was used to evaluate the geological conditions of the study area and the experiments were conducted to obtain the characteristics of geomaterials. Then, finite element analysis (FEA) and discrete element analysis (DEA) were employed to explore the driving mechanism in the prefailure regime and the dynamic runout process in the postfailure regime, respectively. In FEA, the driving mechanism was revealed in terms of the pore water pressures, saturations, and displacement of the sliding zone. The onset of the rainfall-induced landsliding was found by the rapid change of source displacement (RCSD). The result indicated that the variation of saturation and pore water pressure at the monitor points near the surface was earlier than other locations, because rainfall first passes through the monitoring points near the surface; The likely failure timing was ascertained as 28 hr from the beginning of the typhoon rainfall. In DEA, based on the result of the FEA, the estimated seepage force was obtained. To account for water infiltration associated with the dynamic runout process of the landsliding and reconstruct the dynamic runout process of the landsliding, the reduced sliding friction coefficient in DEA was examined. Based on the results, satisfactory agreement between the numerical analysis and landslide behavior was realized. Water infiltration and transition in steepness play significant roles in the behavior of the dynamic runout process. The landsliding exhibited a maximum speed of 4.41 m/s and decelerated as it reached a gentler slope. Overall, the study indicated that the combination of FEA and DEA can be utilized to investigate the failure mechanism of landslides and provide useful insights. The approach can be a high potential to investigate many other geotechnical problems and help us better understand their mechanism.

碩士
逢甲大學
環境資訊科技研究所
93
With the increasing of population and economic, the flats ground became lessen. Developing of mountainside became a trend ,but the stability of ground was destroyed. Hence every typhoon and torrential rain usually cause collapsed and mudflows on mountainside area which was seriously harm local residents. IF we can predict which area is dangerous than others, we can prevent disasters and reduce attacks. Nan-Quin road is the main tourism road in Xin-Zhu. Where never happened any serious natural disasters. But during Elly typhoon, happened about ten disasters between Xhu-Dong and Song-Ben. That section is main road to Wu-Feng village. Considering the important of tourism and inhabits, we use this section as object in the research. Using two different satellite images and NDVI values to judge where happen collapsed. Combine collapse image and every trend factor image, we can get each factor’s level and damage situation. And we can divide the road into six levels: stabile, low, low-medium, medium, medium-high and high. Finally we draw the trend of collapsing map for government departments. In the research we find slope, geology and height have greater influence of stability. Each factor we can sort in large to small as follow: slope, geology, height, land-using, aspect, distance to water and distance to road. Whole research area mostly distribute in medium trend area. High trend area distribute around rivers.

碩士
國立中興大學
水土保持學系
88
The objective of this research is to study the soil water characteristics on Chiu-fen-er-shan landslidung area. The soil texture on the experimental field includes sandy loam, sand clay loam, and clay. The water retention curves of different soil texture were determined by measured water content and water potential .The model suggested by Van Genuchten was applied to express the water characteristics of these soils. The parameters of this model of different soil texture were determined with the experimental data by curve fitting technology. The equations of water characteristic curves of different soil samples are as following: Sample 1. θ(h) = 0.03483+0.46617/[1+(αh)1.15]0.1304 Sample 2. θ(h) = 0.03484+0.39116/[1+(αh)1.45]0.3103 Sample 3. θ(h) = 0.03151+0.38349/[1+(αh)1.15]0.1304 Sample 4. θ(h) = 0.03168+0.36432/[1+(αh)1.15]0.1304 Sample 5. θ(h) = 0.03336+0.39764/[1+(αh)1.55]0.3548 Sample 6. θ(h) = 0.03388+0.41712/[1+(αh)1.40]0.2857 Sample 7. θ(h) = 0.02451+0.40449/[1+(αh)1.50]0.3333 The theory developed by Mualem was used to predict the unsaturated hydraulic conductivity.

碩士
國立高雄大學
土木與環境工程學系碩士班
99
The satellite image has following characteristics: short capture period, ability to detect the change of the earth surface rapidly, large coverage, large amount of information, multiple spectra and the ability of repeating observations. Therefore, instead of the traditional method of site investigation, which is limited by weather conditions, expenditure, and traffic situation, the remote sensing technology based on satellite image is gradually used to determine the occurrence locations of landslide disasters and their quantities. In this study, we apply the digital image correlation method to evaluate the correlation of two multi-spectral satellite images before and after disasters. A threshold value is used to determine whether the new landslides occur after the disasters. The effect of applying DIC method to identify the landslide is then discussed. The algorithm of digital images correlation is to find out the highest correlation. However, the change of the earth surface will induce a difference between multi-spectral signal of the satellite images before and after the landslide. Therefore, the DIC method can be easily modified to determine the occurrence of landslides. The position with lower correlation between two images will be found out. There exist also many misjudgment situations in the result We use the characteristics of the Normalized Difference Vegetation Index (NDVI) and the Digital Elevation Model (DEM) to reduce the rate of misjudgment. In this study, the analysis procedure is divided into two steps. The whole area is roughly analyzed with a larger subset at first. Then, the area, which is judged to be a landslide area in the rough analysis, is then closely analyzed with a small subset. The result shows that the accuracy rate can reach 76.58% in the analysis carried out with a big subset 16*16 pixels and threshold value 0.997 in the rough analysis and a small subset 5*5 pixels and threshold value 0.998 in the close analysis. This means that a lot of new occurrence landslide is identified. For reducing the rate of misjudgment, we use NDVI to filter the misjudgment region, which is uncovered before the disaster and vegetative restorative after the disaster. DEM is also applied to filter the misjudgment region, which lies around the smooth riverbed and village. This study shows that DIC method can be applied to identify the landslides based on the satellite images before and after the landslide.

碩士
國立東華大學
自然資源管理研究所
96
Shoufong river is one of branches of Hualien river. Its steep terrain, fragile geology and heavy rainfall characteristics bring flooding, gully, bank erosion and surface erosion. Which has been occurred a great deal of sediment hazards. Relying on the recent advances in SPOT satellite images from year of 1996, 2002, 2005 and 2007 and geographic information system (GIS) techniques, this study aims to map the changes and characteristics of landslide regions. According to the degree of potential hazard from landslides this study grouped four parameters to analysis collapses and vegetation recovery. The four parameters are slope, aspect, elevation and geography. This study provides landslide susceptibility maps by adopting Instability Index Method to analyze the potential of slope collapse. The result of this research reveals that: (1)From year 1996 to 2007, the 5 tremendous collapsed regions are previous collapsed regions. These collapsed regions because of the impact of geography and slope covered with less ratio of vegetation. Furthermore, the scales and scopes of these collapsed regions kept on enlarge. Within consecutive years, sizes of newer collapsed regions are co-related with quantities of rainfall brought about by typhoons. (2)Collapses are happened repeatedly on certain landforms and geographical conditions. (3)It is an effective way for predicting and evaluating potential collapsed regions by using Instability Index method to product landslide susceptibility maps. By analyzing the relationship among collapsed regions the ratio of vegetation cover mostly located at east-south slope. The highest recovering rate of vegetation is flat slop regions and the lower elevation regions. Besides, these recovered regions are located at slopes between 15° and 25° and at elevation below 400 meters. Moreover, the highest recovering rates are made by black schist of Tananao Schist and basic igneous rock. The most significance parameter influence collapses according to Instability Index method, Result of this research shows that geography and slope are mainly cause of the collapses and those collapsed regions are mostly located at slopes between 35° and 45°. Those highest degree of potential collapsed regions are made by argillite, slate and phyllite in lushan formation.