Hengxing Lan

RockFall analyst: A GIS extension for three-dimensional and spatially distributed rockfall hazard modeling

Geographic information system (GIS) modeling is used in combination with three-dimensional (3D) rockfall process modeling to assess rockfall hazards. A GIS extension, RockFall Analyst (RA), which is capable of effectively handling large amounts of geospatial information relative to rockfall behaviors, has been developed in ArcGIS using ArcObjects and C#. The 3D rockfall model considers dynamic processes on a cell plane basis. It uses inputs of distributed parameters in terms of raster and polygon features created in GIS. Two major components are included in RA: particle-based rockfall process modeling and geostatistics-based rockfall raster modeling. Rockfall process simulation results, 3D rockfall trajectories and their velocity features either for point seeders or polyline seeders are stored in 3D shape files. Distributed raster modeling, based on 3D rockfall trajectories and a spatial geostatistical technique, represents the distribution of spatial frequency, the flying and/or bouncing height, and the kinetic energy of falling rocks. A distribution of rockfall hazard can be created by taking these rockfall characteristics into account. A barrier analysis tool is also provided in RA to aid barrier design. An application of these modeling techniques to a case study is provided. The RA has been tested in ArcGIS 8.2, 8.3, 9.0 and 9.1.

Engineering and geological characteristics of granite weathering profiles in South China

Granite weathering profiles are widely distributed in South China. Their engineering and geological characteristics are major geotechnical subjects that are important in the design and construction of civil engineering projects. This paper presents a summary of the weathering characteristics and zoning of granite weathering profiles in South China and discusses their engineering and geological properties. A five-grade scheme has been adopted in the zoning of a granite weathering profile. Studies have shown that the completely weathered granites (CWG) in South China have the following characteristics: low moisture content, low to medium plasticity (W-L = 22.5-39.0%; I-p = 6.5-11.8%), medium void ratio (0.36-1.29), weak shrinkage and medium compressibility (a(1-2) = 0.24-0.8 MPa-1) and high shear strength (phi = 20-30degrees; c = 20-40 KPa). The CWGs are usually at a low or high plastic state and most of them are over-consolidated soils. A majority of the physical and mechanical properties have good statistical correlations with the degree of weathering. The data presented in the paper are important in geotechnical engineering projects such as slope stability evaluation in China

Evolution of In Situ Rock Mass Damage Induced by Mechanical-Thermal Loading

To understand and predict the in situ brittle rock mass damage process induced by a coupled thermo-mechanical loading, the knowledge of rock mass yielding strength, scaling relationship between laboratory and in situ and microstructure characterization is required. Difficulties have been recognized due to the seldom availability of in situ experiment and appropriate numerical methodologies. The Äspö Pillar Stability Experiment was used to monitor the evolution of rock mass damage in a pillar of rock separating two 1.75-m diameter vertical boreholes. The loading of the pillar was controlled using the in situ stresses, excavation geometry, and locally increasing the rock temperature. The induced loading resulted in a complex discontinuum process that involved fracture initiation, propagation, interaction and buckling, all dominated by a tensile mechanism. Tracking this damage process was carried out in two steps. Initially, a three-dimensional numerical model was used to generate the stresses from the excavation geometry and thermal loading. The plane strain stresses, at selected locations where detailed displacement monitoring was available, were then used to track the evolution of damage caused by these induced stresses. The grain-based discrete element modeling approach described in Lan et al. (2010), which captures the grain scale heterogeneity of the rock, was used to establish the extent of damage. Good agreement was found between the predicted and measured temperatures and displacements. The grain-based model provided new insights into the progressive failure process.

Urgent landslide susceptibility assessment in the 2013 Lushan earthquake-impacted area, Sichuan Province, China

The Lushan earthquake with magnitude Ms 7.0 (Mw 6.6, USGS) in Sichuan Province, China, triggered a large number of landslides, which seriously aggravated the earthquake’s destructive consequences. This paper mainly focuses on the methodology of the urgent landslide susceptibility assessment right after the earthquake. The detailed landslide inventory (including 5,688 landslides) is prepared by means of urgent post-earthquake landslide field survey, landslide remote sensing interpretation of multi-source remote sensing images including high-resolution unmanned aerial vehicle images and historical landslide archives. Ten remarkable causative factors for landslide occurrence have been selected to conduct the landslide susceptibility assessment, including earthquake intensity, landslide density and slope gradient. An integration assessment approach is developed to facilitate the effective urgent post-earthquake landslide susceptibility assessment using three methods: factor sensitivity analysis, analytical hierarchy process and factor-weighted overlay. Such integration can effectively reduce the subjectivity and uncertainty resulting from using single method. The validation evaluation using the area under curve suggests the landslide susceptibility assessment results have satisfactory accuracy, and the suggested methodology is effective for the urgent post-earthquake landslide susceptibility assessment. The study results reveal that earthquake intensity and slope gradient are the two most important causative factors for post-earthquake landslide occurrence in the Lushan earthquake-impacted area. The dominant slope gradient and slope aspect with relatively higher landslide frequency are 45°–50° and south-east direction, respectively. The intense earthquake impact increased the dominant slope gradient of landslide spatial distribution, and the thrust campaign of seismogenic fault with strike NE–SW made south-east direction as the dominant slope aspect of the landslide spatial distribution. The locations with very high and high landslide susceptibility are mainly distributed in the regions with higher earthquake intensity and adverse terrain conditions, such as Shuangshi town and Longmen town of Lushan county and Muping town of Baoxing county. The study results are expected to provide a beneficial reference for the landslide prevention and infrastructure reconstruction after the Lushan earthquake.

Spatial hazard analysis and prediction on rainfall-induced landslide using GIS

The application of landslide hazard model coupled with GIS provides an effective means to spatial hazard analysis and prediction on rainfall-induced landslides. A modified SINMAP model is established based upon the systematic investigation on previous GIS-based landslide analysis models. By integrating the landslide deterministic model with the hydrological distribution model based on DEM, this model deeply studied the effect of underground water distribution due to rainfall on the slope stability and landslide occurrence, including the effect of dynamic water pressure resulting from the down slope seepage process as well as that of static water pressure. Its applicability has been testified on the Xiaojiang watershed, the rainfall-induced landslides widespread area in Southeast China. Detailed discussion was carried out on the spatial distribution characteristics of landslide hazard and its extending trend, as well as the quantitative relationship between landslide hazard with precipitation, slope angle and specific catchment area in the Xiaojiang watershed. And the precipitation threshold for landslide occurrence was estimated. These analytical results are proved useful for geohazard control and engineering decision-making in the Xiaojiang watershed.

A modified frequency ratio method for landslide susceptibility assessment

The frequency ratio method is one of the most widely adopted methods for landslide susceptibility assessment. However, due to the obligatory classifications of landslide-related factors with continuous factor values, the conventional frequency ratio method is complicated by a discontinuity problem of the frequency ratio values and a subjectivity problem. This paper has modified the conventional frequency ratio method and developed a handy geographical information system extension that implements the modified method. Through calculating the frequency ratios for every “identical normalized factor value” instead of for every “factor class,” the modified method radically increased the continuity of frequency ratio values and reduced the subjectivity accompanied by the classifications of factors. An automatic and quick assessment of landslide susceptibility becomes possible because the calculations of frequency ratios for different factors in the modified method are constrained by only two uniform parameters (precision and bin width). Two case studies were adopted to inspect the performances of the modified method. From a quantitative point of view, the modified method derives landslide susceptibility models having slightly larger AUC values than the conventional method. From a qualitative point of view, the modified method gives much more detailed variations of frequency ratio with factor value and, as a result, can reveal characteristic fluctuations of frequency ratio and can smoothen the spatial discontinuity of the landslide susceptibility map derived by the conventional method. In practice, this modified frequency ratio method is expected to benefit the landslide susceptibility assessment and get further evaluations in the meantime.

Post-earthquake rainfall-triggered slope stability analysis in the Lushan area

The “4.20” Lushan earthquake in Sichuan province, China has induced a large amount of geological hazards and produced abundant loose materials which are prone to post-earthquake rainfall-triggered landslides. A detailed landslide inventory was acquired through post-earthquake emergent field investigation and high resolution remote sensing interpretation. The rainfall analysis was conducted using historical rainfall records during the period from 1951 to 2010. Results indicate that the average annual rainfall distribution is heterogeneous and the largest average annual rainfall occurs in Yucheng district. The Stability Index MAPping (SINMAP) model was adopted to assess and analyze the post-earthquake slope stability under different rainfall scenarios (light rainfall, moderate rainfall, heavy rainfall, and rainstorm). The model parameters were calibrated to reflect the significant influence of strong earthquakes on geological settings. The slope stability maps triggered by different rainfall scenarios were produced at a regional scale. The effect of different rainfall conditions on the slope stability is discussed. The expanding trend of the unstable area was quantitatively assessed with the different critical rainfall intensity. They provide a new insight into the spatial distribution and characteristics of post-earthquake rainfall-triggered landslides in the Lushan seismic area. An increase of rainfall intensity results in a significant increase of unstable area. The heterogeneous distribution of slope instability is strongly correlated with the distribution of earthquake intensity in spite of different rainfall conditions. The results suggest that the both seismic intensity and rainfall are two crucial factors for post-earthquake slope stability. This study provides important references for landslide prevention and mitigation in the Lushan area after earthquake.

Estimating the size and travel distance of Klapperhorn Mountain debris flows for risk analysis along railway, Canada

Debris flows occurring on Klapperhorn Mountain in the Yellowhead Pass in the Canadian Rocky Mountains pose a significant hazard to railway operations at the base of the mountain. The size (volume) and travel distance of these debris flows play an important role in assessing the risk to the railway. GIS analysis, airphoto interpretation together with field work were undertaken on two debris flows located at track mileage 54.0 and 54.3. Characteristics of these two debris flow events were analyzed, including debris flow path morphology and event behavior. Their sizes and travel distances were estimated using an empirical-statistical model (UBCDFLOW) under different initiation conditions. Their potential impact on the railway bridge was evaluated using a bridge blockage ratio.

Reactivation mechanism of ancient giant landslides in the tectonically active zone: a case study in Southwest China

The reactivation mechanism and stability of ancient landslides are the major concerns in the tectonically active zone. A detailed case study has been conducted to examine the reactivation mechanism of ancient landslides in Southwest China by investigating the reactivation process, shear strength and stability. Field investigation suggests that the reactivation of ancient giant slides, such as the Luosiwan slide, is attributed to the cumulative effect of adverse geological, structural condition and intensive artificial processes. However, long-term observation has shown that the ancient giant landslides usually remain stable in the remote area in spite of such adverse conditions. Ring shear tests also indicate high peak shear strength of the sliding zone soils. However, the shear strength decreases significantly once displacement occurs at the toe of giant landslide due to engineering construction. The construction process could be considered as the critical triggering factor for the reactivation of ancient giant landslide, which exerts sudden changes in the forces acting on the slope. Both long-term adverse geological evolution and sudden change in the strength lead to the reactivation of giant landslide. This study also suggests that liquefaction plays an important role in the failure behavior of reactivated ancient landslide. An effective drainage system has to be set up during engineering construction so as to reduce the probability of reactivation of ancient landslides.

Integration of TerraSAR-X and PALSAR PSI for detecting ground deformation

In connection with the detection of various spatial- and temporal-scale ground settlements, an integrated persistent scatterer interferometry (PSI) approach is discussed using multi-source, multi-temporal, and multi-resolution synthetic aperture radar (SAR) data. Based on the comprehensive analysis of characteristics of available radar sensors, two remote-sensing SAR data sets were selected: 1 m resolution X-band TerraSAR-X and 10 m resolution L-band Advanced Land Observing Satellite (ALOS) phased array L-band SAR. ‘Tianjin Binhai New Area’ has become one of the most important economic centres in China, and one of its fast-developing urban areas, Tanggu, was selected as the study area. PSI processing was conducted on both data sets. Substantial validation was performed for PSI results from both data sources using levelling measurement. The overall good agreement confirmed the ground deformation maps derived from both data sets. Integration of PSI results appears to be a potentially significant contribution to solving the problems related to common spatial and temporal gaps when using single-type data sets. Application of both data sets revealed the capability of integrated PSIs to measure ground deformation with strong temporal and spatial variation, thereby improving the interpretation of ground deformation characteristics which increases the confidence of hazard assessment and provides some insight into complex underlying mechanisms.