This paper presents a study on an ancient river-damming landslide in the SE Tibet Plateau, China, with a focus on time-dependent gravitational creep leading to slope failure associated with progressive fragmentation during motion. Field investigation shows that the landslide, with an estimated volume of 4.9?×?107 m3, is a translational toe buckling slide. Outcrops of landslide deposits, buckling, toe shear, residual landslide dam, and lacustrine sediments are distributed at the slope base. The landslide deposits formed a landslide dam over 60 m high and at one time blocked the Jinsha River. Optically stimulated luminescence dating for the lacustrine sediments indicates that the landslide occurred at least 2,600 years ago. To investigate the progressive evolution and failure behavior of the landslide, numerical simulations using the distinct element method are conducted. The results show that the evolution of the landslide could be divided into three stages: a time-dependent gravitational creep process, rapid failure, and granular flow deposition. It probably began as a long-term gravitationally induced buckling of amphibolite rock slabs along a weak interlayer composed of mica schist which was followed by progressive fragmentation during flow-like motion, evolving into a flow-like movement, which deposited sediments in the river valley. According to numerical modeling results, the rapid failure stage lasted 35 s from the onset of sudden failure to final deposition, with an estimated maximum movement rate of 26.8 m/s. The simulated topography is close to the post-landslide topography. Based on field investigation and numerical simulation, it can be found that the mica schist interlayer and bedding planes are responsible for the slope instability, while strong toe erosion caused by the Jinsha River caused the layered rock mass to buckle intensively. Rainfall or an earthquake cannot be ruled out as a potential trigger of the landslide, considering the climate condition and the seismic activity on centennial to millennial timescales in the study area.
相似文献A primal C0-conforming virtual element discretization for the approximation of the bidimensional two-phase flow of immiscible fluids in porous media using general polygonal meshes is discussed. This work investigates the potentialities of the Virtual Element Method (VEM) in solving this specific problem of immiscible fluids in porous media involving a time-dependent coupled system of non-linear partial differential equations. The performance of the fully discrete scheme is thoroughly analysed testing it on general meshes considering both a regular problem and more realistic benchmark problems that are of interest for physical and engineering applications.
相似文献Time is one of the often-neglected factors in the assessment of the erratic failure of shale rock. Laboratory-creep experiments showed that constant stress induces time-dependent failure in brittle shale. However, the microscopic reason for time-dependent deformation in shale is still unknown. In the current study, triaxial creep and recovery experiments showed that the brittle shale specimens exhibit viscoelastic and viscoplastic creep deformation at constant stress state. In addition, the X-ray computed tomography scan of Marcellus shale showed that the shale specimens contained significant volume of preexisting microcracks. The statistical correlation among permanent strain during the triaxial experiment and stress-induced change in the three-dimensional geometry of microcracks showed that the microcracking is the microscopic reason for viscoplastic creep deformation in shale. In addition to the time and level of constant differential stress, factors such as orientation of bedding planes and specimen heterogeneity also influence the nature of creep deformation.
相似文献Rainfall-induced slope instabilities are ubiquitous in nature, but simulation of this type of hazards with centrifuge modelling still poses difficulties. In this paper, we introduce a rainfall device for initiating slope failure in a medium-sized centrifuge. This rainfall system is simple, robust and affordable. An array of perforated hoses is placed close above the model slope surface to generate the raindrops. The rainfall intensity depends on the centrifuge acceleration and the flow rate of the water supply, which is controlled by the size and number of the tiny pinholes in the hose walls. The rainfall intensities that are tested range from 2.5–30 mm/h, covering the intensity range of moderate, heavy and torrential rainfall events. Our model test with rainfall-induced slope failure shows that this system is capable of generating relatively uniform rainfall of wide intensities and leads to various patterns of slope failure.
相似文献Explosives are still the cheapest source of breaking rock in the mining or tunnelling operation and can be applied in varying geological conditions. It generates various troubles such as ground vibration, air overpressure, and fly rocks. It is well known that the maximum charge per delay (MCPD) has to be optimum for safe blasting and can be achieved through trial blasts, which is a complicated and costly process. Therefore, it is required to reduce the number of trial blasts. In this study, a total of 18 blasts were conducted in an underground coal mine and were simulated using similar ground conditions using Ansys software. The Peak particle velocity values obtained in the mines and through the models were compared. The error in PPV found between the actual and predicted by simulation is less than 15%. It can help us design the MCPD in rock excavation operations, visualise damages using simulation in Ansys software, and economical compared to field trials.
相似文献This paper presents a coupled finite and discrete-element model (FEM and DEM) to simulate internal erosion. The model is based on ICY, an interface between COMSOL, an FEM engine, and YADE, a DEM code. With this model, smaller DEM subdomains are generated to simulate particle displacements at the grain scale. Particles in these small subdomains are subjected to buoyancy, gravity, drag and contact forces for short time steps (0.1 s). The DEM subdomains provide the macroscale (continuum) model with a particle flux distribution. Through a mass conservation equation, the flux distribution allows changes in porosity, hydraulic conductivity and hydraulic gradient to be evaluated for the same time steps at a larger, continuum scale. The updated hydraulic gradients from the continuum model provide the DEM subdomains with updated hydrodynamic forces based on a coarse-grid method. The number of particles in the DEM subdomains is also updated based on the new porosity distribution. The hierarchical multiscale model (HMM) was validated with the simulation of suffusion. Results for the proposed HMM algorithm are consistent with results based on a DEM model incorporating the full sample and simulation duration. The proposed HMM algorithm could enable the modelling of internal erosion for soil volumes that are too large to be modelled with a single DEM subdomain.
相似文献Metocean conditions during hurricanes are defined by multiple parameters (e.g., significant wave height and surge height) that vary in time with significant auto- and cross-correlation. In many cases, the nature of the variation of these characteristics in time is important to design and assess the risk to offshore structures, but a persistent problem is that measurements are sparse and time history simulations using metocean models are computationally onerous. Surrogate modeling is an appealing approach to ease the computational burden of metocean modeling; however, modeling the time-dependency of metocean conditions using surrogate models is challenging because the conditions at one time instant are dependent on not only the conditions at that instant but also on the conditions at previous time instances. In this paper, time-dependent surrogate modeling of significant wave height, peak wave period, peak wave direction, and storm surge is explored using a database of metocean conditions at an offshore site. Three types of surrogate models, including Kriging, multilayer perceptron (MLP), and recurrent neural network with gated recurrent unit (RNN-GRU), are evaluated, with two different time-dependent structures considered for the Kriging model and two training set sizes for the MLP model, resulting in a total of five models evaluated in this paper. The performance of the models is compared in terms of accuracy and sensitivity toward hyperparameters, and the MLP and RNN-GRU models are demonstrated to have extraordinary prediction performance in this context.
相似文献We present the results of numerical simulation for impacts of relatively small asteroids and ice bodies of 30–100 m in size, decelerated in the atmosphere and exploding before they reach the surface, but still producing seismic effects due to the impact wave reaching the surface. The calculated magnitudes fall within the range of 4 to 6, and average seismic efficiency of these events is 2.5 × 10–5. The results obtained allow the seismic hazard from impacts of cosmic bodies to be estimated.
相似文献The MétéEAU Nappes water-resource-management tool is presented. It is usable on the aquifer or part-of-aquifer scale for real-time observation of the state of the groundwater resource, and it is already operating in France. This online decision support tool is also able to predict the state of the resource in the short- and mid-terms. The paper explains the use of the tool in a case study in the Authion Valley, in the north-west of France, chosen for its context of tension surrounding the groundwater resource resulting from high volumes of abstraction for irrigation. The results of the simulation highlight the advantages of MétéEAU Nappes as a tool for prediction and simulation of the state of the groundwater resource. The results also show the advantages of this type of tool for water resource management, such as supplying local actors with reliable and real-time observations of the aquifer and providing forecasts to anticipate possible water shortage.
相似文献The widely used groundwater flow model MODFLOW offers a range of software packages to simulate the interaction between streams and groundwater in aquifer systems. However, these existing packages lack a general method to address the chaotic simulation sequences of stream segments and require these segments to be ordered by modelers as input to the code. Therefore, it is challenging to simulate a stream network divided into a large number of segments such as a canal irrigation system. In this study, the Streamflow Automatic Routing (SAR) package was developed, and an effective method is proposed to automatically determine the segment simulation sequence. The stream segment order in the SAR input file is arbitrary, which allows modifications of the stream network by removing segments directly and adding segments at the end of the segment group. This mainly includes two processes: scanning all the outlet channels of the water system and calling the recursive algorithm for each outlet channel of the water system. The SAR package was tested using a hypothetical stream–aquifer system and applied to a complex flow field in Aiding Lake of Turpan Basin, China. In the results, a close fitting between the simulation and observations shows that the SAR package precisely simulated the exchange flux between the steams and aquifer. The SAR package can significantly improve the efficiency of simulations in a complex stream network, and it can be widely used as a subroutine package of MODFLOW in agricultural irrigation areas where rivers and canals are interlaced.
相似文献Karst aquifers are very complex due to the presence of dual porosity. Rain–runoff hydrological models are frequently used to characterize these aquifers and assist in their management. The calibration of such models requires knowledge of many parameters, whose quality can be directly related to the quality of the simulation results. The Sacramento Soil Moisture Accounting (SAC-SMA) model includes a number of physically based parameters that permit accurate simulations and predictions of the rain–runoff relationships. Due to common physical characteristics of mature karst structures, expressed by sharp recession limbs of the runoff hydrographs, the calibration of the model becomes relatively simple, and the values of the parameters range within narrow bands. The most sensitive parameters are those related to groundwater storage regulated by the zone of the epikarst. The SAC-SMA model was calibrated for data from the mountainous part of the Louros basin, north-western Greece, which is considered to be representative of such geological formations. Visual assessment of the hydrographs as statistical outcomes revealed that the SAC-SMA model simulated the timing and magnitude of the peak flow and the shape of recession curves well.
相似文献The continuously low efficiencies of flood relief service in responding to flooding disasters in Taiwan highlight a need for research. This service efficiency is negatively influenced by flood relief facility locations and their operational management structure. The Fazih River floodplain has been previously identified as a high-flood-risk area using an analytic hierarchy process. The purpose of this study is to use the location set covering problem and the maximal covering location problem to determine the number of relief facilities required and the maximum covering area of each facility for the case study area of the Fazih River floodplain. The findings showed that covering distances range from 3.0 to 6.6 km and the number of facilities required for improved service efficiency is between 1 and 4.
相似文献Exploitation of gas hydrate requires an improved understanding of the behavior of gassy soil. In this study, a numerical simulation technique is proposed that uses the discrete element method (DEM) to evaluate the undrained mechanical behavior of gassy sand, which consists of three phases—sand particles, water, and gas. The governing equation of gassy sand under undrained condition is derived and incorporated into the DEM simulation, in which gas solution and exsolution are considered. Undrained isotropic unloading and undrained triaxial compression tests on gassy sand samples with dissolved methane and carbon dioxide are simulated. Reasonable consistency is found when the simulation results are compared with experimental observation and theoretical calculation. The simulation highlights the significant influence of the gas solubility on the undrained behavior of gassy sand. The micro-responses of the observed phenomenon are also investigated.
相似文献In collapsible loess area, the negative skin friction of pile foundation will cause many engineering problems such as failure of pile strength and reduction of bearing capacity of pile foundation, which will bring great harm to engineering construction. In order to study the change and distribution law of negative friction of pile foundation in collapsible loess area, the scale model test of negative friction of pile considering loess collapsibility was designed and completed. Through finite element numerical simulation, the test results are verified, and the distribution law of negative friction of pile and the number and position of neutral points are obtained. The test results show that under the condition of immersion, the loess has layered settlement, and there are both negative friction and positive friction on the pile surface, and there are two neutral points. Negative friction drags the pile downward, which makes the axial force of the pile increase obviously. The numerical simulation results verify the feasibility and validity of the test results. The research results of this paper have certain guiding significance for pile foundation design in collapsible loess area.
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