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The interaction between soil and geotextile is essential for the performance of reinforced soil. This study reveals the microscopic mechanism of interface shear between sand and geotextile based on the discrete element method (DEM). The surface characteristics of geotextile are simulated by overlapped particles. The micromechanical parameters of sand, geotextile, and interface are calibrated effectively using laboratory test results. Three types of shear tests on the sand-geotextile interface are simulated; namely, interface direct shear test (IDST), double-sided interface shear test (D_IST), and interface direct shear test with periodic boundary (PBST). For IDST, the results show that the thickness of shear band is 2.4--3.0 times the average particle diameter ([D.sub.50]); the contact force, percentage of sliding contact, and contact normal anisotropy inside the shear band are larger than those outside the shear band, whereas the coordination number is smaller inside the shear band. The mechanical response of D_IST is similar to that of IDST. However, D_IST has a shear band thickness of 3.0[D.sub.50], and greater coordination number, percentage of sliding contact, and contact normal anisotropy. The results of PBST indicate that the peak stress and the shear band no longer appear without boundary constraint and the contact distribution is uniform. Key words: geotextile, geosynthetic, direct shear test, discrete element method (DEM), microscale. L'interaction entre le sol et le geotextile est essentielle pour la performance des sols renforces. Cette etude revele le mecanisme microscopique du cisaillement d'interface entre le sable et le geotextile base sur la methode des elements discrets (MED). Les caracteristiques de surface du geotextile sont simulees par des particules qui se chevauchent. Les parametres micromecaniques du sable, du geotextile et de l'interface sont etalonnes efficacement a l'aide des resultats d'essais en laboratoire. Trois types d'essais de cisaillement sur interface sable-geotextile sont simules, a savoir l'essai de cisaillement direct par interface (<>), l'essai de cisaillement par interface double face (<< D_IST>>) et l'essai de cisaillement direct par interface avec limite periodique (<< PBST >>). Pour IDST, les resultats montrent que l'epaisseur de la bande de cisaillement est de 2,4~3,0 fois le diametre moyen des particules ([D.sub.50]); la force de contact, le pourcentage de contact glissant et l'anisotropie normale de contact dans la bande de cisaillement sont superieurs a ceux de l'exterieur alors que le nombre de coordination est inferieur dans la bande de cisaillement. La reponse mecanique de D_IST est similaire a celle d'IDST. Cependant, D_IST a une epaisseur de bande de cisaillement de 3,0[D.sub.50] et un indice de coordination, un pourcentage de contact glissant et une anisotropie normale de contact superieurs. Les resultats de PBST indiquent que la contrainte maximale et la bande de cisaillement n'apparaissent plus sans contrainte de limite et que la distribution des contacts est uniforme. [Traduit par la Redaction] Mots-cles: geotextile, geosynthetique, essai de cisaillement direct, methode des elements discrets (MED), micro-echelle., 1. Introduction Geotextile is one of the most widely used geosynthetics in geotechnical engineering practices, such as slopes, roadbeds, landfills, and embankments (Giroud and Noiray 1981; Rowe and Soderman 1985; [...]

Flowslides are rapid gravity-driven flows of sediment-water mixture that typically occur following slope failures in soils, tailings, and municipal solid wastes, but the progressive state transition during the evolution of flowslides is still unclear. In this study, a practical method which couples elastic-plastic constitutive equations and Bingham fluid equations by a progressive transition criterion is developed within the framework of smoothed particle hydrodynamics (SPH). The elastic-plastic constitutive equations describe the mechanical behavior at a solid-like state and that at a fluid-like state is described by Bingham fluid equations. The progressive state transition can be described by a transition factor, which is governed by the degree of saturation and shear strain rate according to the experimental data. Transient seepage flow is also introduced into the SPH framework to describe the effect of water content on the evolution of flowslides. An infiltration boundary method based on ghost particles and smooth function symmetry is proposed to precisely model the rainfall infiltration process. The experimental data of ring shear tests and flume test are adopted to successfully verify the performance of the method, which can reasonably simulate the complicated solid-fluid transition processes. The method is further applied to simulate a full scale catastrophic flowslide at Payatas Landfill. As the overlying pressure on the slip surface increases, the material reaches the yield state. During the postfailure stage, the material at the slip surface first changes into an elastic-plastic state, and then partially transforms into a fluid-like state, leading to the large deformation of the failure material. The proposed method can contribute to a better understanding of the evolution of flowslides and is an applicable tool for hazard assessment. [ABSTRACT FROM AUTHOR]

A membrane effect often occurs in geosynthetic-reinforced structures, where subsoil may have voids or sinkholes. An analytical model is proposed to estimate membrane effect of a geosynthetic reinforcement subjected to localized sinkholes. The upper interface friction in the subsided area and vertical deformation of supporting soil in the anchorage area are considered simultaneously. The maximum geosynthetic strain and maximum surface settlement, serving as key design points, can be determined. Based on the proposed method verified using a full-scale experiment, a parametric study is conducted. The results show that ignoring upper interface friction results in significant undervaluation of maximum geosynthetic strain, and ignoring vertical deformation of supporting soil leads to obvious undervaluation of maximum surface settlement. A practical design framework is also proposed and it is an applicable tool for preliminary design of geosynthetic-reinforced structures, especially for cases with soft ground. Key words: geosynthetic, membrane effect, arching effect, maximum strain, maximum surface settlement. L'effet de membrane se produit souvent dans les structures renforcees par geosynthetique, ou le sous-sol peut avoir des vides ou des gouffres. Un modele analytique est propose pour estimer l'effet membranaire du renforcement geosynthetique soumis a des gouffres localises. La friction de l'interface superieure dans la zone abaissee et la deformation verticale du sol de soutien dans la zone d'ancrage sont considerees simultanement. La deformation geosynthetique maximale et le tassement maximal de la surface servant de points de conception cle peuvent etre determines. Basee sur la methode proposee verifiee en utilisant une experience a grande echelle, une etude parametrique est menee. Les resultats montrent que le fait de ne pas tenir compte de la friction de l'interface superieure entraine une sous-evaluation significative de la deformation geosynthetique maximale, et que de ne pas tenir compte de la deformation verticale du sol de support entraine une sous-evaluation evidente du tassement superficiel maximal. Un cadre de conception pratique est egalement propose et il s'agit d'un outil applicable pour la conception preliminaire de structures renforcees par geosynthetique, en particulier pour les cas avec sol meuble. [Traduit par la Redaction] Mots-cles : geosynthetique, effet membranaire, effet d'arche, souche maximale, reglement de surface maximum., Introduction Geosynthetic-reinforced structures are extensively used in geotechnical engineering. In such a structure where subsoil may have voids or sinkholes, membrane effect often occurs along with soil arching (e.g., Giroud [...]

Apart from the estimation of magnitudes of precipitation, floods and storm surges, modelling of storm water flows in a densely populated urban area is required for designing coping strategies and making decisions. Incorporating surface runoff and conduit flow modelling capabilities has enabled the prediction of urban flood hazards. This study synthesises methodologies for simulating flood processes and evaluating flood hazards in urban environment. Existing models and their associated uncertainties are summarised, and state-of-the-art techniques to build up a numerical model for simulating urban floods and the applications to specific cases are illustrated. A schematic framework for urban flood hazard prediction is proposed, within which multi-source observation retrieval, physics-based modelling, parameter optimisation, uncertainty estimation, model-observation fusion, evaluation of compound effects of multiple factors and digital twin techniques are included. The major challenges and uncertainties in flood process modelling originate from input data, model structures, validation processes and compounding effects. Multidisciplinary techniques for estimating the input data and enhancing the efficiency and accuracy of the flood evaluation should be developed. Great efforts are needed in understanding the process-dependent indicators, coupled modelling and data-model assimilation. Determining the probability of compound floods and understanding the driving factors are also essential for evaluating flood risks. [ABSTRACT FROM AUTHOR]

Recently, a lot of open source e-learning platforms have been offered for free in the Internet. We thus incorporate the intelligent diagnosis and assessment tool into an open software e-learning platform developed for programming language courses, wherein the proposed learning diagnosis assessment tools based on text mining and machine learning techniques are employed to alleviate the loading of the teachers. Experiments were conducted in two introductory-undergraduate programming courses to examine the effectiveness of the proposed diagnosis and assessment tools. The learners' work including the source code and comments were processed by the proposed text mining and machine learning techniques. This system also provides immediate feedback and high-quality evaluation results to guide the learners with poor performance. Our experimental results reveal that the proposed work can effectively assist the low-ability learners. (Contains 6 tables and 13 figures.)

Accreting soil system with horizontal drainage layers (HDLs) widely exists in engineering practices. With the existence of HDLs, each soil layer undergoes two stages: layer formation stage and surcharge loading stage. The methods proposed by Gibson and Zheng et al. are adopted to derive the analytical solution for the layer formation stage, while the separation of variables method and Duhamel's principle are combined to develop that for the surcharge loading stage. The solution is verified against two existing analytical solutions and a numerical model. Parametric studies are then conducted to investigate the consolidation characteristics. Given a certain design height of accreting soil system, an upper limit of the maximum excess pore-water pressure (ULMP) is observed with HDLs if consolidation coefficient is large enough or accreting rate is small enough. When ignoring the interlayer formation interval, ULMP is inversely proportional to the consolidation coefficient and proportional to the accreting rate and the square of layer thickness. A prediction method for the time when ULMP appears is provided considering the influence of accreting rate, layer thickness, and consolidation coefficient. A design chart for reference value of the maximum layer thickness is also proposed. [ABSTRACT FROM AUTHOR]

Horizontal drains can effectively accelerate the consolidation of soils. In this study, an analytical model for the consolidation of a multilayered soil system with horizontal drainage pipes is developed first. A virtual semipermeable layer containing the drainage pipes is introduced to simplify the analysis. A semipermeability coefficient (R) is then adopted to describe the drainage capacity of the virtual semipermeable layer. The analytical solution is derived following separation of variables method and Duhamel's principle, which is verified by two existing analytical solutions in literature from different aspects. By comparing the results calculated by the analytical solution and numerical model, an efficient method is proposed to relate the arrangement of drainage pipes and R. The method is effective if the layer thickness is large enough compared with the pipe diameter and the pipe spacing is not too small. Based on the equivalent method, a preliminary design method of the horizontal drainage pipes is also proposed. [ABSTRACT FROM AUTHOR]

Summary: In this paper, a thermodynamic model is developed for predicting the performance of a beta‐type Stirling heat pump with rhombic drive mechanism for water heater and the model is validated by a 1‐kW class prototype Stirling heat pump. In the present model, the working space is divided into expansion space, heat absorber, regenerator, heat rejecter and compression space. The pressure, mass and temperature variations of working fluid in each working space are predicted. The temperature variation of wall boundary is also taken into consideration. The temperature of working fluid in each working space and the temperature of wall boundary are obtained by solving energy equations simultaneously. Eventually, the pressure of working fluid in each working space can be corrected by using empirical formula of pressure drop. All the thermal properties of working fluid and wall boundary in each working space at each time step can be obtained by repeating the above process. Then, the performance of heat pump such as absorbing heat, rejecting heat, indicated power and COP can be calculated. A series of experimental measurements and comparisons are also conducted for validating present model. The results show that the prototype heat pump can produce 904 W heating power and 38°C hot water under 1 LPM water flow rate with 5 bar helium at 1000 rpm. [ABSTRACT FROM AUTHOR]

Abstract Heat-bonded nonwoven geotextiles (HBNGs) made from synthetic fibers are widely used in engineering practices. One of the challenges on the way is to link the properties of fibers and the fabric's microstructure to the deformation and failure mechanisms of HBNGs. In this study, a random distribution geometry method was developed to reproduce the complex fibrous structure of HBNG. A piecewise linear model was adopted to reproduce the nonlinear stress-strain relationships of single fibers. The present method has been successfully applied in the simulation of uniaxial and biaxial tensile tests and puncture test. The orientation distribution of fibers and the mechanical behaviors (e.g., deformation, strain localization, force-strain relationship) of HBNG specimen were reasonably simulated. Specifically, the hourglass shape during uniaxial tensile test, the axisymmetric deformation pattern during biaxial tensile test and the trumpet shape during puncture test were all well reproduced. The present method provides an applicable tool to study the complicated mechanical behaviors of HBNG and is also helpful to obtain a better understanding of its deformation and failure mechanisms. [ABSTRACT FROM AUTHOR]