Key Engineering Materials Vols. 306-308

Abstract: Mohr-Coulomb model is a perfect elastoplastic model. It only considers the variation of material strength with lateral compressive stress, but doesn’t consider the variation of elastic modulus with lateral compressive stress and stress level and this is accordant with the true characteristic of geological material. The elasticity modulus in Mohr-Coulomb model was modified by employing the processing method of tangential modulus in Duncan-Chang nonlinear elastic model. In modified model, the stress-strain curve in elastic phrase behaves as hyperbola. In order to embed the modified model in FLAC3D program (Fast Lagrangian Analysis of Continua in 3 Dimensions), a preprocessing program was written and was employed to analyze numerically the bearing capacity of rigid piles loaded laterally.

Abstract: There are several different yield surfaces of Drucker-Prager yield criterion which corresponds to Mohr-Coulomb yield criterion in principal stress space. The different yield surfaces are determined by parameters in Drucker-Prager criterion. The influence of the different parameters on computational results is discussed in the paper, and the use of the equivalent Drucker-Prager criterion to Mohr-Coulomb criterion is suggested when elastoplastic analysis is performed in engineering problems.

Abstract: The power house of Yantan extended hydropower project, with complex geological conditions such as fault f211 below the power house and quartzite on top of it, is a huge underground cavern with large span and high wall. In order to evaluate the stability of the power house surrounded by such complex geological structure, the numerical simulation excavation of power house with different location schemes were studied by the elasto-plastic 2D FEM method. The deformation and evolutive process of the stress with the progress of excavation were analyzed. On the condition ensuring the whole stability of surrounding rock mass, comparison optimization analyses were conducted on the power house location scheme. The rational location scheme was demonstrated. The final analyses results show that: (1) The mechanical properties of quartzite and its relative location to the power house has no obvious influence to the stability of surrounding rock mass.(2) The f211 is the main bad geological structure which affect the stability of power house. (3) The case of moving 10m upward of power house is the most rational scheme for the whole stability of power house. (4) The Supporting measures, which would has an obvious effect in controlling the influence on the stability of surrounding rock mass by weak geological structure, are suggested at the out-crop of f211.

Abstract: The progressive failure process of a layer rock slope under explosions is simulated using two-dimensional Universal Distinct Element Code (UDEC). It is shown that the failure process of the slope can be divided into three phases, the formation and growth of local failure area as well as coalescence of sliding plane. In addition, the displacement components of a critical point of the slope are also suggested to be a progressive process.

Abstract: This present paper describes the process and methods of the numerical analysis, including yielding criterion, 3-D geometrical model, rock mass mechanical parameters, initial geostress field, method to simulate excavation process, simulation method for supporting structures. Then, the paper gives the computational results of rock deformation and stability for the large cavern group and comparisons for three cases: with no supporting structures; with bolts and shotcrete lining but no prestress-cables and with all the supporting structures of bolts, cables and lining. Finally, the paper reaches several conclusions.

Abstract: A brief description is given to the visco-plastic constitutive model of 3-D FLAC software and some treating methods for the numerical analysis. The excavation steps and the exerting time of excavation loads are determined in the light of the real construction process. The rockmass mechanical parameters are determined according to back analysis of in-situ measured displacement data. The analysis results of displacement and stability of the opening complex surrounding rocks in the construction process and in a long period of time after excavation completion are given.

Abstract: Basic mechanical behaviors of rocks at different temperatures and with different moistures are required to be investigated for studying and designing rock engineering in cold regions. In this paper, two typical rocks, i.e., red sandstone and shale sampled from Jiangxi and Hubei in China, respectively, are tested by uniaxial and triaxial compressive tests at different temperatures ranging from 20°C to -20°C and in dry and fully saturated states. The test results show the different behaviors of them. The values of the uniaxial and triaxial compressive strengths, Young’s modulus, cohesion, and friction angle, increase with the lowering of the testing temperatures, but the tendencies are different for these two kinds of rock.

Abstract: By use of complex variable theory, formulae for tangential stress on ellipse edge are derived. Sub-crack point, opening angle and maximal tangential stress on ellipse edge are studied under uniaxial compression, biaxial compression, or uniaxial compression and crack water pressure separately. Based on the maximal tension stress criterion, formulas of maximal tangential stress and critical load are presented. The results show that sub-crack point, opening angle, maximal tangential stress and critical load are varied with different aspect ratio and different inclined angle. Meanwhile, the most dangerous inclined angle is obtained.

Abstract: Based on the field geology survey data, the probability distribution function of joint aperture was analyzed and the availability of the fitting data was verified. The joint aperture data observed the previous fitted function can be generated in the process of joint simulation. The seepage of rock mass is proportional to the third power of joint’s aperture. It is much more reasonable and feasible to analyze the permeability tensor of rock mass with the previous generated data. At the same time, the method comprehensively considered the effect of joint’s orientation, aperture, scale and their distribution.

Abstract: In the classical Coulomb’s earth pressure theory, the failure surface in the backfilled clay behind rigid retaining wall in slope engineering is assumed a plane. However, it has been proved by a number of laboratory and field tests that this failure surface is actually a curving surface. In this paper, based on the vertical differential element method and the variational principle, a new analytic solution to determine the actual failure surface in the backfilled clay is derived, and the effects of the backfilled clay’s properties as well as the effects of the retaining wall’s smoothness are discussed. The result obtained from the proposed approach is compared with Coulomb’s earth pressure theory.