Wei Ya Xu

Discrete Element Simulation of Composite Geomaterial Talus Deposit Based on Digital Image Technology

Talus deposit is often seen in the hydropower projects in the southwest of China. Its mechanical properties are so complex that microscopic structure study is often used to reveal the essence of deformation and damage. The digital image processing technology (DIPT) is introduced to the discrete element simulation of talus deposits. Based on the study of DIPT, a Photo-To-PFC (PTP) automodeling program is developed. It is able to realize the whole process: analyzing and processing the digital image, acquiring the information and establishing the model files. The discrete element model of talus deposit can be established fast and correctly by the PTP from the digital photo on-site. A new way is opened up for the study of the talus deposit. As an example, some talus deposit data of Gushui hydropower station is used, structure model and mechanical properties of talus deposit are studied based on DIPT and PTP. The mechanical properties are studied by the numerical simulation of biaxial compression test. The results show that the gravels and soil mass compress with each other to form a corporate load-carrying body for sharing the external forces. The stress-strain curves show a strain-hardening stage obviously due to the impact of gravels. With the increasing of bond strength among soil particles, the initial elastic modulus and peak strength of talus deposit go up at a certain level; the initial elastic modulus and peak strength increase a lot as the existence of gravels.

Mechanical Parameter Analysis of Rock Material via PLSR Model

Mechanical parameter analysis is a complicated issue since it is influenced by many factors. Closely related with the influencing factors of compressibility coefficients of rock material (sandstone), this article first introduces the way to process partial least square regression (PLSR) analysis. The process of carrying out PLSR is divided into six steps as for analysis and prediction of the regression model, which are data preparation, principle collection, regression model for first principle component, secondary principle analysis, establishment of final regression model and number determination of principal component l. And then introduces PLSR for application of analysis and prediction of compressibility coefficients with 30 experiment samples. Seven prediction samples are carried out by PLSR with the training process of 30 samples. The result shows PLSR has good accuracy in prediction under the condition that the model is properly deprived based on certain experimental samples. Finally, some conclusions are made for further study on both mechanical parameters and partial least square regression method.

Stability Analysis of Steep-High Rock Slope Based on Block Mechanical Theory — Case in Jiangping River Hydropower Station

Due to specific geological conditions, stability of complex high slopes has become one of the key technical problems in hydroelectric project. Especially for steep-high rock slope, it is hard to calculate the stability by normal rigid limit equilibrium method. Steep-high rock slope in Jiangping River hydropower station is taken for example. On the base of study of geological structure and judgment of preferred structure plane, simplified geological model is built up. The main deformation destruction mode and type are analyzed based on block theory, rock mechanics and other basic mechanics while the related critical values are calculated. So slope stability is discussed and corresponding control measures are worked out. This method can be used in following stability research of similar slope.

A Coupled Elastic-Plastic Damage Model for Rock Material

With complex mechanics character and under the action of compression and tension in tri-direction, rock will show coupled plastic-damage mechanism as its basic character. Phenomenological coupled elastic-plastic-damage constitutive model with internal variable is proposed based on thermal mechanics theory, elastic law and macro damage mechanics. Numerical experiments on this model and analyze the model character. The result shows that the coupling model could realize rocks softening behavior brought about by damage and strength enlargement caused by confining pressure increasing.

A Chemo-Elasto-Plastic Coupling Model for Sandstone Considering pH Effect

In this paper, we present a numerical modeling of chemo-mechanical behaviour of sandstone. An internal variable is introduced in this model for the purpose of describing pH effect on elasto-plastic properties. A new chemo-elasto-plastic model is proposed for sandstone. The proposed model is applied to predict material responses in triaxial compression tests of sandstone after soaking in different pH acidic solutions. We concluded with good agreement between numerical simulations and experimental data.

Application of Limit Equilibrium FEM Method to the Slope

The limit equilibrium FEM method is a common method using the result of stresses fields obtained from numerical calculation to get resistant sliding force and driving sliding force on the dangerous sliding surface to analyze the stability of slope. The safety factor is the ratio of resistant sliding force to driving sliding force on the most dangerous sliding surface.When compares limit equilibrium FEM method with the rigid body limit equilibrium method, its applicability needs to be verified. Taking a project as an example, this work uses the two methods to analyze the stability of the slope. After calculating, two different safety factors on the sliding surface were got, and the reasons inducing the difference of the safety factors were analyzed. The result showed the safety factor calculated from the limit equilibrium FEM method is much closer to the real situation especially when some parts of the soil are in plastic state. It is mainly because the limit equilibrium FEM method takes the coordination of deformation into consideration. Then two conditions: nature and rain are calculated to analyzed the slope stability. It made a judgment of the stability of the slope and gave a beneficial conclusion to the project.

A Statistical Damage Constitutive Model for Brittle Rocks Based on the Lade-Duncan Failure Criterion

Micro-unit strength of rock is randomly distributed based on Lemaitres strain equivalence assumptions. The paper presents a method for measuring micro-unit strength taking into account the damage threshold. Assuming that the micro-unit strength obeys the Weibull distribution, combined with the Lade-Duncan failure criterion, a new statistical damage constitutive model for brittle rocks is established and the model parameters m and F0 are determined. The model can simulate the stress-strain relation of full process of rock failure well, especially reflects the influence of different stress on damage threshold and the linear elastic characteristic under low stress for rock. The good accord verifies the validity and feasibility of the new model.

Modeling Coupled Flow-Stress-Damage during Creep Deformation

In order to reflect the tertiary rheological characteristics of hard rocks at the high stress states, a new nonlinear visco-elastic-plastic model is proposed on the basis of linear visco-elastic-plastic model and nonlinear visco-elastic-plasticity. And then the corresponding constitutive model are deduced, which can be used for describing rocks’ long-term strength characteristics and their creep deformational behavior and time-dependent damage under interaction of coupled seepage-stress field in rock engineering. At last, considering the time effect of rock damage in the process of tertiary creep, a coupled seepage -stress creep damage model for investigating the whole creep deformation behavior, including tertiary creep failure process is established, and the related equations governing the evolution of stress, creep damage and rock permeability along with the creep deformation of rock is introduced.

Three Dimensional Numerical Analysis of Deformation and Stability of Zone II of Xiazanri Slope Deposit

Xiazanri Slope is a large-scale deposit slope located at the left bank of Liyuan hydropower station in Southwest China. The construction of the water intake there will form a very high excavation slope. Possible failure modes are analyzed based on geological conditions. Numerical simulation is conducted in FLAC3D to obtain the deformation and failure characteristics of slope under excavation and normal water table conditions. Strength reduction method is used to obtain factor of safety. Results show the overall deposit is stable and attention should be paid to local parts.

Effect of Fly Ash and Lime Treatment on Mechanical and Swell Properties of Dunkirk Dredged Sediments

Traditional approaches such as ocean dumping and inland deposit are unsatisfactory for the management of dredged sediments, in the context of sustainable development. The solidified sediments with fly ash and lime as road base materials are preferred to conserve land and minimize impact to environment. A series of tests, such as compaction tests, tensile strength tests and swell tests, were performed to explore mechanical and swell properties of Dunkirk dredged materials. The fly ash contributes to the considerable increase in elastic modulus and the small increase in tensile strength in the presence of lime. Then the potential of treated sediments as road base material is evaluated. After immersion in water for 4 days, the addition of fly ash can induce a remarkable increase in swell percents in contrast with the lime-based sediments.