Chengren Xiong

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.

Research on the Characteristics and Slope Deformation Regularity of the Badong Formation in the Three Gorges Reservoir Area

The Three Gorges reservoir area is characterized by widely distributed strata of the Badong formation, in which large-size landslides and deep-reaching loosely consolidated formations are likely to occur. Therefore, it is significant to reveal the mechanism and patterns of the large-size landslides that occur in the Badong formation for a better understanding of the development of the nature of deformation and process of formation of the deep-trending loose-slope stratum in the Wushan, Fengjie, and Badong renewal city zones. In this chapter, the geological characteristics of the rock mass of the Badong formation are analyzed on the basis of a systematic explanation of the rock mass strata, space variation of the lithological combinations as well as the space variation of stratum thickness, and structural deformation of the Badong formation. To demonstrate the basic law of long-term deformation of the Badong formation slopes and the patterns of later stage reformation and landslide evolution, the authors use the Huangtupo landslide as an example, as it is a typical failure in the Badong formation.

Evolution Process of Natural Rock Joint Roughness during Direct Shear Tests

AbstractSurface roughness is one of the most important parameters that have significant influence on the mechanical and hydraulic characteristics of rock joints. To investigate the evolution of surface roughness under normal and shear loads, direct shear tests and numerical modeling based on the discrete-element method (DEM) were performed; bright area percentage (BAP), which places emphasis on the contact areas, was used as an index to describe the roughness. The results demonstrate that the surface roughness of rock joints decreased gradually as the shear displacement increased, and then roughness experienced a significant reduction in the residual stage and remained constant. Furthermore, the evolution of surface roughness was found to depend on the normal stress and shearing direction. Reduction in the degree of joint roughness with high normal loads was lighter than that with lower normal loads, and roughness varied with shear directions. The numerical simulation method proposed in this study has the...

Proof of Nondeterministic Polynomial-Time Complete Problem for Soil Slope-Stability Evaluation

AbstractGenerally, slope-stability evaluation involves two coupled tasks: locating the critical slip surface and calculating its corresponding factor of safety. Various assessment methods have emerged in the past few decades, and the question of whether equivalence exists between these methods has become a controversial issue. Unfortunately, research that explores the roots of the slope-stability problem from the perspective of computational complexity is quite limited. This paper addresses this long-neglected but very important problem by rigorously proving that the evaluation of slope stability is essentially a nondeterministic polynomial-time complete problem, which is computationally one of the most difficult types of problems. A significant achievement of this proof is the inference that equivalence between the limit equilibrium method and the strength reduction method does not exist. The methods used throughout these routine analyses are exactly approximate and will not replace one another completel...

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.

Prediction of landslide runout based on influencing factor analysis

Landslide runout predictions are essential for producing hazard maps and siting mitigation structures. Data from 55 catastrophic historical landslides in the mountainous area of China are used to determine how topography, material, triggering factors, volume, and initial posture of the slide mass influence runout. Plots and regressions between slide mobility, expressed in terms of the equivalent coefficient of friction (ratio of the fall height to the runout distance), and the slide volume show the necessity to exclude data from zones where motion is blocked by steep orthogonal slopes (“T-type topography”) in defining meaningful empirical relationships. Landslide material exerts strong control on runout, with colluvium showing the strongest dependence on slide volume. Rainfall-induced rockslides have higher mobility than gravity-induced rockslides, but rockslides triggered by great earthquakes may have lower mobility than gravity-induced rockslides. The extra sum of squares analysis results demonstrate that slide volume is the dominant predictor for estimating runout, with posture also influencing the runout distance of non-seismic rockslides. These results provide the basis for our new, multiple-factor predictive method for runout distance. The predicted runout distance in the test case was about 115% of the actual distance. This method may enhance the accuracy of runout distance estimates for landslides in the mountainous area of China.

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.

In situ triaxial creep test for investigating deformational properties of gravelly sliding zone soil: example of the Huangtupo 1# landslide, China

In recent years, numerous landslide catastrophes have occurred, generating considerable financial losses and other tolls. The deformational and mechanical properties of sliding zone soil would be in primary significance to landslide research, as the sliding zone basically controls the initiation and mobility of the landslide. An in situ triaxial test was carried out on a sample from the sliding zone of the Huangtupo 1# landslide, a subdivision of the Huangtupo landslide in the Three Gorges area of China. The test results indicate that (a) the sliding zone exhibits low compressibility due to the high rock content (54.3%) and long-time consolidation by the overlying soil mass; (b) only decaying creep occurs without abrupt failure, and a constitutive equation with both linear and nonlinear viscoplastic terms is deduced to accurately fit the test data; (c) the surface with an orientation of 35° presents anisotropic traits in terms of displacement, possibly due to cracks that formed at similar orientations within the sample cube; and (d) the creep behavior of the landslide may be closely related to the properties of the sliding zone soil. When a similar stress magnitude to that of the in situ stress environment is applied to the sample, the sliding zone soil behavior matches the landslide deformative behavior. The test results indicate that the Huangtupo 1# landslide will continue to creep, as interpreted from the deformation traits and structural properties of the sample. However, unavoidable limitations of the test and extreme external factors, namely unexpected rainfall and water fluctuation, cannot be ignored.