The critical stage in the evaluation of rainfall-induced landslide failure is in formulating reasonable models to better simulate spatiotemporal changes of slopes in the hilly terrains. A physically based model can take into account the contribution of rainfall infiltration and shear strength of saturated soil layer, and therefore help revealing the landslide formation mechanisms. This paper presents a physically based approach to simulate the landslide process triggered by rainstorm. On the basis of previous solutions, we select the simplified infiltration model Slope-Infiltration-Distributed Equilibrium (SLIDE) to illustrate the dynamical relations between factor of safety (FS) and accumulation of rainfall over time. This model is tested with three representative landslide events in the southwest, southeast, and south central of China during rainstorm. Results show that the time of landslide failure predicted from the SLIDE model is consistent with the reality. Meanwhile, this paper illustrates the differences of FS among the different slope gradients in the vicinity of same soil texture and relationship between FS and rainfall accumulation. This work formulates a methodology of rainstorm-induced landslide evaluation and improves upon the existing landslide prediction methods.
This paper focuses on the estimation of the maximum impact force of dry granular flow upon a rock shed using a coupled discrete element method (DEM) and finite element method (FEM). The dry granular flow is modeled as an assembly of discrete particles, and the rock shed is modeled by applying the FEM. The coupled DEM–FEM approach calibrated with a small-scale physical experiment is used to simulate the movement of a dry granular flow impacting the rock shed. Full-scale numerical modeling based on the field model is constructed to estimate the maximum impact force of dry granular flow on a rock shed. Based on the numerical results, three key stages of the impact process are identified: startup streams slippery, impact, and pile-up. The sensitivities of bulk density, impact height, slope angle, cushion thickness, and friction coefficient to the maximum impact force are 1, 0.63, 2.68, 0.09, and 0.73, respectively, in the benchmark model, and the parameters with high sensitivities should be given priority in the design of rock sheds. Moreover, an evaluation formula of maximum impact force is obtained and based on the numerical results and Buckingham's principle.
In this thesis, an attempt is made to derive a mathematical model describing the packing behavior based on generalized Hele Shaw flow for a purely viscous and compressible fluid in thin cavity under nonisothermal conditions. Reasonable and necessary assumptions and simplifications are introduced after thorough and detailed analysis of the packing stage, the material properties are described accurately as well. The finite element technique is employed to treat the pressure and temperature field in the streamwise direction, however, an implicit finite difference scheme is used to obtain temperature distribution in the gapwise direction. In the end, comparision of the predicted and experimental pressure trace over the packing stage for PS is presented. The two agree quite well with each other and the accuracy of the present simulation has been verified.
The heat island effect of major cities around the world and the associated environmental and ecological problems have become more and more serious with the global warming and the speedup of urbanization process. In the view of geological and environmental protection, this paper analyzes the causes and characteristics of urban heat island effect and its impact on the geological environment. I In particular, this paper focuses on the variation of soil engineering properties that arise from the effect and corresponding disaster effect. Furthermore, this paper presents four key scientific issues: i.e., soil temperature changes, moisture migration laws in the soil, the variation of soil engineering properties and the geological disaster effect in the urban heat island. The paper also analyzes their detailed research contents. This paper points out the great theoretical and practical significance for understanding urban heat island effect on soil engineering properties, urban geological disaster prevention and reduction, and the urban sustainable development.
Fast accumulation of soil organic matter (SOM) following forest restoration shifted from cropland has been widely reported, but how the pools and molecular composition change across soil aggregate fractions remains unclear. In this study, undisturbed topsoil (0–10 cm) samples were collected across a decadal chronosequence of forest stands (RL10, RL20 and RL40) restored for 10, 20 and 40 years following maize cropland (CL) abandonment in a karst terrain of Guizhou, Southwest China. SOM changes were explored using the size and density fractionation of water-stable aggregates, 13C isotopic signalling and biomarker analyses as well as 13C solid-state NMR assays. Compared to that of CL, SOM content was increased by 24%, 79% and 181%, mass proportion of macroaggregates increased by 136%, 179% and 250%, and particulate organic matter (POM) increased by 13%, 108% and 382%, respectively at RL10, RL20 and RL40. With biomarker analyses, the relative abundances of plant-derived organics (lignin, cutin, suberin, wax and phytosterols), mostly protected in aggregates, increased, while those of microbe-derived OC, predominantly mineral bound, decreased in response to prolonged forest restoration. Calculated as per the Shannon diversity index (H'), changes in SOM pool complexity and molecular diversity were parallel to the SOM accumulation trend. The pool size ratio of POM to MAOM (mineral-associated organic matter) and the molecular abundance ratio of PL (plant-derived lipids) to ML (microbe-derived lipids) appeared to be indicative of SOM accumulation following forest restoration. With prolonged forest restoration, the topsoil OM shifted from microbial MAOM dominance to plant-derived POM dominance. Furthermore, the great topsoil OM enhancement in restored forest stands was shaped by pool complexity and molecular diversity changes with the complex interactions among plant-microbial-mineral assemblages in the karst topsoil. Both the pool complexity and molecular diversity of SOM should be considered in addressing carbon sequestration with forest restoration concerning the functioning of soil ecosystems and services under global change pressures.
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