Key Engineering Materials Vols. 535-536

Abstract: It is fundamental to predict the stress-strain behavior of soils to control the stability of the geotechnical engineering. A Duncan-Chang constitutive model is analyzed and found that it ignores the effect of the intermediate principal stress. A unified strength theory is investigated and revised. The lode parameter is introduced into the unified strength theory. The unified friction angle and cohesion which may reflect the influence of the intermediate principal stress and verified by the polyaxial tests are obtained. The compressive strength revised from the unified strength theory is used to replace the Mohr-Coulomb criterion and introduced into the Duncan-Chang model. A modified constitutive model is proposed, which is verified by the plane strain tests. The result shows that the modified constitutive can reflect the effect of the intermediate principal stress, and the Duncan-Chang model is a special case of the modified model when b=0.

Abstract: A large scale model test was carried out in loess slope, in which the stress and deformation characteristics of slopes reinforced with different arrangements of micropiles were studied. The mechanism of the micropile-soil interaction and the reinforcement effect of micropiles in loess slope were analysed. Based on the scale of in-situ loess slope and the physical mechanics parameters of loess soil, a numerical model was established by using finite difference method. For a reasonable arrangement of micropiles in step-shaped slope, the critical slip surfaces were determined considering the influence of slope inclination, ratio of step height and loading position. The micropiles were arranged in the step-shaped slope based on the critical slip surface, and the relationship between the ultimate bearing capacity of slope and shear strength parameters of loess soil was studied. The maximum shear strain of micropile-soil and moment of micropiles were calculated, and then the mechanism of the micropile-soil interaction was analysed.

Abstract: Lightweight foamed concrete is one kind of new and important runway arresting materials for airplanes and other vehicles. To study its crushing and flowing behavior under different loading rates, an electric-driving screw testing machine, and an Instron VHS 8800 higher strain-rate testing machine are used. Crushing mechanical characteristics, and deformation and failure mode with the density of 0.20g/ccm are systematically analysed, while crushing strain-rate range from 0.001/s to about 102/s. Results show this foamed concrete suffers three stages of deformation during loading, namely elastic region, crushing plateau region and densification region; and it presents very low shear strength. Based on testing results, a phenomenological model is established, and comparing model predictions with experimental results, a good agreement is obtained.

Abstract: This paper mainly concerns the non-linear strength characteristics of the loess. A series of consolidated undrained triaxial tests(CU test) and consolidated drained triaxial tests (CD test) of normal consolidation and over consolidation loess specimens are carried out by using the normal triaxial apparatus of strain control. The stress-strain relationship curves and strength characteristics of loess are investigated and analyzed. The results show that the stress-strain relationship obtained by CU tests appears strain softening, while the stress-strain relationship for CD tests appears strain hardening. Different failure modes have different stress-strain relationships. Furthermore, the results also show that the peak strength, residual strength and residual strength ratio change with the different confining pressure. Based on the triaxial shear tests of normal consolidated loess, the influences of over-consolidated loess on the stress-strain relationships and strength characteristic are discussed. Several conclusions obtained in this paper can be referenced for the loess experimental study.

Abstract: The meso-element equivalent method (MEEM), is developed in the study to investigate the damage process and the macro-mechanical properties of concrete. The Monte Carlo method is adopted to generate the random aggregate structure (RAS) firstly, and then the characteristic element size is applied to divide the RAS into many identical units. Each unit obtained is processed equivalently to be a homogeneous and isotropic unit by the homogenization theory. Some concrete specimens in 2-D and 3-D are undertaken to verify the feasibility and accuracy of the proposed approach. The results indicate the high efficiency and accuracy of the present methodology.

Abstract: Using the elasto-plastic constitutive model and strength reduction technique, the stability of slopes is analyzed by a finite difference numerical package FLAC version 7.0. Shear strain increment is used to identify the failure zone. Unlike the conventional investigation taking the soil strengths as constant parameters, this study deals with random variables of soil strengths by using first order reliability method (FORM). In particular, two-dimensional (2-D) spatial variation unique to soil strengths is investigated in the reliability analysis.