Advanced Materials Research Vols. 594-597

Abstract: The stability of reservoir landslide would be influenced obviously by the fluctuation of water level, especially when the water descends, which is different from common landslide. Due to the unsteady seepage of underground water inside slope caused by the change of water level, the stability analysis of reservoir landslide through fluid-solid coupling is very complicated. At present, most people hold the view qualitatively that the less the permeability coefficient is and the faster the water level changes, the more unfavorable it is to the stability. This view lacks quantitative basis. Based on FEM strength reduction, the paper analyzes the influence of different sets of descending speed and permeability coefficient on the stability of reservoir landslide through fluid-solid coupling analysis. The paper also conducts the relevant analysis on the change of the characteristics of seepage field inside the slope, which provides basis for the study of the failure mechanism and the forecast of reservoir landslide.

Abstract: To indentify the influence of human activities on groundwater chemistry, fifteen groundwater samples, from the mostly exploited aquifers, were collected at Tanghai County. Considering the multivariable statistical method is reliable to study the anthropogenic process affecting groundwater composition especially in the early stage, 10 measured hydrochemical variables were used in factor analysis and hierarchical cluster analysis. Factor 1 included EC, TDS, Cl-, and K+ is interpreted as relating to groundwater salinization. Factor 2 and factor 3 is mostly influenced by the water-rock interactions during the flow path and fertile contamination, respectively. Meanwhile, the Q-mode classification result reveals that the cluster 1 having high factor 1 scores also is related to the over-pumping of groundwater, in accordance with the factor analysis result. Generally, to protect freshwater resources and suitable development of this study, some related measures should be mitigated to limit groundwater mining.

Abstract: The modal analysis of pipes conveying fluid considering the influence of Fluid-Structure Interaction (FSI) is always a topic in flow and solid mechanics fields worth study. Three methods of coupling, the direct FSI method, the one-way FSI method and the bidirectional FSI method, with the velocity’s influence on pipe system’s natural frequency were considered in this study. The results of pipe’s dynamic behavior indicate that the two-way FSI method can get a more reasonable result. Furthermore, when velocity changes in a small range far from critical velocity, velocity makes very little influence on system’s nature frequency. The result was compared with conclusion in the literature and very good agreement was found.

Abstract: Mesh moving scheme is an important issue in many fluid-structure interaction problems. In this paper a new mesh motion technique is presented for the effective treatment of moving mesh. The entire deformation is imposed at each time step and the motion of the internal nodes is governed by a modified Laplace equation. Finite element method is adopted to solve the Laplace equation with elemental Jacobian-based stiffening technique. Nodal coordinates are updated by using the total nodal displacements and initial coordinates. The proposed scheme has been applied to several 2D and 3D test cases involving various mesh types with the mesh quality evaluated by an index called elemental aspect ratio. With these applications, it is demonstrated that the present method still preserves good mesh quality for long-term and large amplitude oscillations or deformations.

Abstract: As a sequel to the study in determining the permeability of the porous media composed of obstacles of different sizes, exhaustive numerical calculations were conducted using the same two-dimensional numerical models of square rods as in the previous study. The models consist of collections of square rod obstacles of two-, three-, four- and five-different sizes. Computations were carried out to reveal the details of microscopic velocity and pressure fields. There results are integrated to find the macroscopic pressure gradients for collections of multi-sized obstacles. The Ergun type general formula has been proposed along with a definition of an effective average size, which, when substituted into the formula, yields a reasonable estimate for the macroscopic pressure drops in multi-sized obstacles.

Abstract: As line well pattern is the main development technique in the thin and poor oil layers of Daqing Oilfield South West Ⅱ PⅠ group, the layers have been idle and the degree of reserve recovery is far less than the region level. In response to these problems, we analyzed the balanced flood performance of various layers and the remaining oil distribution through numerical simulation technique. It shows that, the main remaining oil type of intended layers is caused by voidage-injection imperfection. Considering the needs of the follow-up infill well pattern and tertiary oil recovery, we decided to keep the well network independent and integrated without disturbing the pattern configuration and main mining object of various sets of well pattern. Finally we confirmed to perforate-adding the first infill wells of intended layers to consummate the water flooding regime. Through analyzing the production target of different well pattern optimization programs relatively, it shows that the best program has regular well pattern and large drilled thickness.

Abstract: The finite element heterogeneous multiscale method (FEHM) combined with stochastic collocation method (SCM) called SHMFE is applied to studying the seepage field of naturally heterogeneous multiscale subsurface formations. Kinds of stochastic finite element (SFEM) are mainly computational techniques for the class of problems. But those methods do not report the multiscale nature of the properties of subsurface formations. When the random permeability field is heterogeneous in fine scale comparing to study domain, the simulation by the classic SFEM is not a trivial task. The SHMFE can efficiently solve the problems. In the method, Karhunen-Loµeve (KL) decomposition is used to represent the log hydraulic conductivity Y = lnK^ε in fine scale. The SCM which couples the generalized polynomial chaos is used to make the problem determined, and then the FEHM method is used to solve it. Sparse grid stochastic collocation method is used when KL expansion has many random variables. The numerical examples demonstrate that the SHMFE approach can efficiently simulate the flow in naturally multiscale heterogeneous subsurface formations with relatively lower computational cost comparing with the SFEM methods.

Abstract: According to the characteristics that permeability and elastic modulus vary with stress, the variation of elastic modulus of sandstone change with confining pressure was researched through the triaxial test. And combined with empirical formula proposed by Louis (1967), mathematical model of coupling of seepage and stress fields is established. This study shows that: the groundwater has a relatively great effect on rock stress and deformation and is adverse to the slope stability. The elastic modulus that chang with confining pressure influences a lot on rock deformation, meanwhile, the variation of rock stress changes permeability, therefore groundwater is the main influencing factors.

Abstract: Under influence of heavy rainfall, the Zheng-gang landslide in Gu-Shui hydropower station of China started to have serious deformation. Based on the geological field investigations, the mechanism of rainfall infiltration was qualitatively analyzed previously. The rainfall infiltration reduces shear strength on the slip surface by increasing pore water pressure and the hydrodynamic pressure is generated which increased with the hydraulic gradient and water level, thus resulting in the instability of landslide and increased landslide movement. Secondly, combined with the seepage theory of saturated-unsaturated, quantitative study was carried out on the seepage properties of landslide under rainfall condition. Not only the dynamic sliding mechanism of landslide is revealed, but also the seepage stability was evaluated. The worst stability condition came out 4 days after the rain stopped, and the maximal thickness of perched water up to 6m. The results of stability analysis have agreement with the field observations. Finally, the effective drainage measures were proposed.

Abstract: In order to research the stability of excavation in deep mines under high ground stress, high rock temperature and high karst hydraulic, the interaction of stress field, seepage field and temperature field are discussed through basic constitutive relation, seepage equation, thermometer equation and coupled thermo-hydro-mechanical equation. A numerical model was built to simulate the excavation of deep roadway. The result shows that the simulated ground stress based on three fields coupled is much closer to the field measured value and the change of stress and displacement caused by the excavation are limited which is about same as the later monitoring.