Jinge Wang

Mapping Urban Bare Land Automatically from Landsat Imagery with a Simple Index

In recent years, hundreds of Earth observation satellites have been launched to collect massive amounts of remote sensing images. However, the considerable cost and time to process the significant amount of data have become the greatest obstacle between data and knowledge. In order to accelerate the transformation from remote sensing images to urban thematic maps, a strategy to map the bare land automatically from Landsat imagery was developed and assessed in this study. First, a normalized difference bare land index (NBLI) was presented to maximally differentiate bare land from other land types in Wuhan City, China. Then, an unsupervised classifier was employed to extract the bare land from the NBLI image without training samples or self-assigned thresholds. Experimental results showed good performance on overall accuracy (92%), kappa coefficient (0.84), area ratio (1.1321), and match rate (83.96%), respectively. Results in multiple years disclosed that bare lands in the study site gradually moved from inner loops to the outer loops since 2007, in two main directions. This study demonstrated that the proposed method was an accurate and reliable option to extract the bare land, which led to a promising approach to mapping urban land use/land cover (LULC) automatically with simple indices.

Rainfall characteristics for anisotropic conductivity of unsaturated soil slopes

The purpose of this study was to investigate the effects of the anisotropic ratio on the stability of slopes using the reliability index approach. A numerical analysis of the relationship between the three rainfall patterns, advanced, normal and delayed, and the anisotropic ratios was designed. This study also considered three different soil properties (sand, silt, and clay) to simulate rain infiltration. In this study, probability analysis was used to evaluate the stability of unsaturated soil slopes. The finite element computer program Geo-Studio was used to simulate the process of rainwater infiltrating a slope. The pore-water pressure results evaluated from seepage analysis (SEEP/W) were imported into the slope stability program (SLOPE/W). Results for the anisotropic ratio of hydraulic conductivity indicate that when the anisotropic ratios become higher, the reduction in the reliability index is insignificant. In addition, the simulation results indicated that when saturated hydraulic conductivity (ks) was less than rainfall intensities (I), the percentage probability of the occurrence of a landslide was larger than when ks was greater than I. Finally, in the cases of anisotropic ks, stability of the high ratio soil slopes was not found to be sensitive to the reliability index variation during the simulation period. Moreover, when ks was greater than I, slope stability decreased earlier than was the case in the opposite situation.

An Approach to Obtain Saturated Hydraulic Conductivity of Reservoir Landslide

The response of the seepage field to the reservoir water level change greatly depends on the saturated hydraulic conductivity of reservoir landslides, which plays a critical role in their evolution processes. Currently, in situ tests and laboratory tests are the main approaches to obtain hydraulic conductivity. However, both of these methods have obvious drawbacks (e.g., size and location limitations); thus, the test results cannot be directly adopted for solving many geotechnical engineering problems that are of great inhomogeneity. To overcome these drawbacks, a back-analysis approach is proposed in this paper to obtain the saturated hydraulic conductivity based on groundwater observation. This approach includes three main steps: (1) develop a saturated–unsaturated seepage model based on field investigation; (2) use the Generalized Regression Neural Networks method to establish a non-linear mapping relation between saturated hydraulic conductivities and groundwater levels; and (3) employ the Genetic Algorithm method to search for the optimum solution for hydraulic conductivity under which the calculated groundwater levels in the seepage model fit best with the observational groundwater levels. Furthermore, this approach is applied to back analyze the hydraulic conductivities of the riverside slump I# in the Huangtupo landslide, which is volumetrically the largest reservoir landslide in the Three Gorges Reservoir area in China. The observational groundwater levels that are used to back analyze the hydraulic conductivities are the result of a response of the whole landslide to the reservoir water level change. Consequently, this approach overcomes the aforementioned limitations in the tests, and the results provide more reliable references for studying reservoir landslides.

Introduction to the Badong Field Test Site for Landslide Research in the Three Gorges Reservoir Area of China

The initial impoundment and periodic water level variation may change the balance of geological environment of the reservoir area and bring different kinds of geohazards. Reservoir induced landslides typify such hazards that present challenges to the long-time operation of the Three Gorges Water Conservancy and Hydropower Project of China. The Huangtupo landslide, with multiple sliding stages and masses, is one of the largest and most destructive landslides still deforming in the Three Gorges Reservoir area. From 2008, we take the Huangtupo landslide as a typical case, and build a large field test site to provide an unprecedented opportunity for the research on the evaluation and prevention of reservoir induced landslides. The test site is composed with a tunnel group with a total length of 1.1 km and a series of monitoring system on both earth surface and underground. Through the tunnel group and multiple monitoring systems, visitors can directly enter the Huangtupo No.1 riverside sliding mass to closely observe the bedrock, sliding zone, and sliding mass, and also operate related scientific experiments and deep monitoring, such as large scale in-situ mechanical tests, underground hydrological tests, deep stress, deformation and environment monitoring. Now, the test site becomes an important site for international research, education, and academic communication about geohazards.

Residual-state creep of clastic soil in a reactivated slow-moving landslide in the Three Gorges Reservoir Region, China

We study the creep properties of clastic soil in residual state. The intact samples are taken from a reactivated slow-moving landslide in the Three Gorges Reservoir Region, China. Firstly, the patterns of the landslide movement are analysed based on recent monitoring data, which indicate that the soil within the shear zone is undergoing two deformation processes: a creep phase, characterised by different creep rates, and a dormant phase. We then study the creep behaviour of the soil samples through a series of ring shear creep tests under various shear stress conditions. The creep response depends strongly on the ratio of the shear stress to the residual strength, and the normal effective stress, whereas the creep rate decreases due to strength regain. The long-term strength of the clastic soil is close to the residual strength. Therefore, the residual strength obtained from conventional shear test, which is less time consuming than creep test, can be used in long-term stability analyses of creeping landslides.

Study on Morphological Characteristics of Coarse Particles in Sliding Zones of Huangtupo Landslide in Three Gorges Reservoir Area, China

The coarse particles (defined as particle size between 0.25 mm and 2 mm here) in sliding zones of Huangtupo landslide in Three Gorges Reservoir Area are taken as study objects. Particle size distribution and particle profiles of samples are firstly obtained through sieving tests and digital imaging respectively. Combined with fractal theory, the fractal dimensions of particle size distributions and particle profiles are calculated quantitatively. Scanning electron microscopy and energy disperse spectroscopy are employed to capture the micrograph and test the mineral composition of samples. Tests and analysis results indicate that the particle size distributions and profiles of samples have fractal characteristics, and the fractal dimensions can be used as quantitative analytical index for the evolution of sliding zones. As the continuous development of sliding zones, the particle mass – size fractal dimension increase and the profile fractal dimension decrease. The special surface characteristics of particles can also indirectly reflect the stress and deformation conditions during the failure and evolution of the sliding zones.