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1.
A hybrid discrete-continuum approach has been presented in this paper to simulate water flow in the near and far fields of deformable fractured rocks. In the near field, the discrete model is used; while in the far field, the equivalent continuum model is employed. The discrete element method (with the static relaxation algorithm) is used in the near field and the boundary integral equation method in the far field. Along the interface of these two domains, both mechanical and hydraulic compatibility conditions are satisfied. Fully coupled hydro-mechanical analysis can be conducted in the combined near and far fields. Application to a dam foundation problem has demonstrated the capability of the developed approach. 相似文献
2.
卫国 《地球科学与环境学报》1989,(3)
本文研究美国学者P.Bankston和R.J.McGovern提出的一个公开问题—数直线R中那些子集分划R?研究表明,R中的每一个0一维子集都分划R;对月中的1一维子集;本文给出了开集、闭集以及具有某种散性的子集分划R的充分必要条件。 相似文献
3.
This paper presents a three-dimensional (3D) continuum nonlinear analysis of the Meloland Road Overpass (MRO) near El Centro, California. The modeling methodology and the computational tools are discussed in detail. The performance of the computational model is evaluated by comparing the computed responses with the responses recorded at the bridge site during the 1979 Imperial Valley and 2010 El Mayor-Cucapah earthquakes. Amongst the recorded earthquake events at the bridge site, these two events caused the strongest shaking. The comparison shows that the 3D model is potentially an effective tool for detailed analysis of a full bridge system including foundation soils, pile foundations, embankments, supporting columns, and the bridge structure itself in a unified system without relying on any ancillary models such as Winkler springs. Additional response parameters such as displacements, rockings, and bending moments are also evaluated although none of these was measured during the seismic events. 相似文献
4.
Water-removed spectra increase the retrieval accuracy when estimating savanna grass nitrogen and phosphorus concentrations 总被引：2，自引：0，他引：2
Abel Ramoelo Andrew K. SkidmoreMartin Schlerf Renaud MathieuIgnas M.A. Heitkönig 《ISPRS Journal of Photogrammetry and Remote Sensing》2011,66(4):408-417
Information about the distribution of grass foliar nitrogen (N) and phosphorus (P) is important for understanding rangeland vitality and for facilitating the effective management of wildlife and livestock. Water absorption effects in the near-infrared (NIR) and shortwave-infrared (SWIR) regions pose a challenge for nutrient estimation using remote sensing. The aim of this study was to test the utility of water-removed (WR) spectra in combination with partial least-squares regression (PLSR) and stepwise multiple linear regression (SMLR) to estimate foliar N and P, compared to spectral transformation techniques such as first derivative, continuum removal and log-transformed (Log(1/R)) spectra. The study was based on a greenhouse experiment with a savanna grass species (Digitaria eriantha). Spectral measurements were made using a spectrometer. The D. eriantha was cut, dried and chemically analyzed for foliar N and P concentrations. WR spectra were determined by calculating the residual from the modelled leaf water spectra using a nonlinear spectral matching technique and observed leaf spectra. Results indicated that the WR spectra yielded a higher N retrieval accuracy than a traditional first derivative transformation (R2=0.84, RMSE = 0.28) compared to R2=0.59, RMSE = 0.45 for PLSR. Similar trends were observed for SMLR. The highest P retrieval accuracy was derived from WR spectra using SMLR (R2=0.64, RMSE = 0.067), while the traditional first derivative and continuum removal resulted in lower accuracy. Only when using PLSR did the first derivative result in a higher P retrieval accuracy (R2=0.47, RMSE = 0.07) than the WR spectra (R2=0.43, RMSE = 0.070). It was concluded that the water removal technique is a promising technique to minimize the perturbing effect of foliar water content when estimating grass nutrient concentrations. 相似文献
5.
The model proposed in this article relates permeability to porosity measurements that can easily be performed in the laboratory. The pore size distribution (PSD) curve is updated with strains and damage. The updated volumetric fractions of natural pores and cracks are introduced in the expression of permeability. Contrary to classical permeability models based on PSD integrations, the model proposed in this article accounts for possible changes in the porosity modes: one mode for undamaged samples and two modes for cracked samples. The proposed approach also accounts for varying states of damage, as opposed to classical fracture network models, in which the cracks pattern is fixed. The only material parameters that are required to describe the microstructure are the lower and upper bounds of the pores size for both natural pores and cracks. All the other PSD parameters involved in the model are related to macroscopic parameters that can easily be determined in the laboratory, such as the initial void ratio. The framework proposed in this article can be used in any damage constitutive model to determine the permeability of a brittle porous medium. Drained triaxial compression tests have been simulated. Before cracks initiation, permeability decreases while the larger natural pores are getting squeezed. After the occurrence of damage, permeability grows due to the increase of cracks density. The model performs well to represent the influence of the confining pressure on damage evolution and permeability variations. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
6.
Trends, prospects and challenges in quantifying flow and transport through fractured rocks 总被引：25，自引：7，他引：18
Shlomo P. Neuman 《Hydrogeology Journal》2005,13(1):124-147
7.
《Geomechanics and Geoengineering》2013,8(3):183-196
An analysis is developed to determine the response of laterally loaded piles in layered elastic media. The differential equations governing pile deflections in different layers due to a concentrated static force and/or moment acting at the pile head are obtained using the principle of minimum potential energy and calculus of variations. The differential equations are solved analytically using the method of initial parameters. Pile deflection, slope of the deformed axis of the pile, bending moment and shear force can be reliably obtained by this method for the entire pile length. The input parameters needed for the analysis are the pile geometry and the elastic constants of the soil and pile. It is observed that soil layering has a definite impact on pile response and must be taken into account for proper analysis and design. The analysis forms the basis for future formulations that can consider stress–strain nonlinearity. 相似文献
8.
《Geomechanics and Geoengineering》2013,8(2):105-118
Nature as described by classical mechanics is governed by a set of physical laws in the balanced form of various physical entities, including mass, linear and angular momenta, energy, and entropy (entropy inequality). These laws must be obeyed in the development of any theory of applied mechanics. In soil mechanics, one deals with porous material composed of solids and fluids strongly interacting with each other. Within the framework of continuum mechanics, materials are assumed to be infinitesimally continuous, which renders an unavoidable hypothesis for soil. That is, each of the solid, liquid, and gaseous phases can be treated as a ‘smeared’ medium superimposed by and interacting with other constituents at the same infinitesimal point. Such treatment, however, requires the fundamental balance laws be recast into more elaborative forms involving microstructural effects (inter-phase actions). This paper introduces such a continuum framework based on existing theories of immiscible mixtures. To accommodate the pre-flow response, in the present work, the energy terms attributable to shear deformation and spin, allied with a coupling effect, are included. In the framework, a set of extended effective stresses is defined; indicating that the soil skeleton has an effective stiffness, which may still be positive-definite after failure. The framework is general and may pave a way for solving practical geotechnical problems covering both pre- and post-failure stages. 相似文献
9.
This paper evaluates the commonly used substructuring method for analysis of bridge systems where the bridge is divided into two sub-systems: the bridge superstructure and the substructure including the pile foundations, abutments, and soil. Modeling of the soil-structure interaction (SSI) in the system is simplified by replacing the pile foundations, abutments, and soil with sets of independent equivalent linear springs and dashpots at the base of the superstructure. The main objective of the paper is to examine how well the substructuring method simulates the seismic response of a bridge system. The baseline data required for the evaluation process is derived from analyzing a fully-coupled continuum bridge model, already validated for the instrumented two-span Meloland Road Overpass. The same bridge system is also simulated using the substructuring method. The results from both approaches are compared, and it is shown that the differences between them can be significant. The substructuring method consistently overestimates the pier base shear forces and bending moments and the pier top deflections. Moreover, the spectral response of the bridge structure is mispredicted. The analyses are repeated for a three-span bridge system subjected to several ground motions, leading to a similar observation as before. Hence, the current state of practice for simulating seismic SSI in bridges using the substructure model is shown to be too simplified to capture the major mechanisms involved in SSI. 相似文献
10.
This paper focuses on the mechanisms taking place in a granular platform supported by piles in soft soil. Several modelling approaches were explored. A two-dimensional small scale model test using the Taylor–Schneebeli soil analogue was first developed and the experimental results were compared to a discrete element model using the particle code PFC. The validation of this numerical approach allowed the parametric study to be extended numerically. Parametric studies were also performed on continuum model using the finite-difference code FLAC. Comparison of the parametric studies performed on each modelling approach underlined some differences and lead to a consideration on the macro- and micromechanical parameters. 相似文献