Hang Zhou Li

Experimental Study on Shear Strength Characteristics and Stress-Strain Relationship of Loess

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.

A Nonlinear Constitutive Model for Soil under Complex Stress State

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.

Analysis of Slope Failure Mechanisms Considering Micropile-Soil Interaction

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.

Wedge Stability in the Roof of a Non-Circular Tunnel

A closed-form solution is presented for the calculation of the stability of a wedge in the roof of a tunnel. The stability of the wedge is investigated using a two-stage relaxation procedure. A polynomial function is used to fit the horizontal induced stress along the axis of the noncircular tunnel based on the numerical results. The effect of the ratio K of the horizontal-to-vertical in situ stress on the internal horizontal force is investigated. The influences of the normal and shear stiffness and the far field stress on the stability of the wedge are investigated. The results indicate that the stiffness and far field stress have significant effect on the stability of the wedge.

Accounting Problems of Safety Investment of Enterprise in China

The situation of the safety production of enterprise is very severe in China due to the insufficient safety investment. The accounting has unique effect if using it to manage the safety investment activity. However, the accounting function in safety investment of enterprise in China does not effectively mobilized. Based on the factors, Current situation of accounting of safety investment of enterprise in China is analyzed. The accounting problems of safety investment are investigated. The improvement measures of accounting of safety investment are proposed.

Constitutive Model of Strain Softening for Soft Rock

This paper aims to study the strain softening behavior of soft rock. A modified equation of unified strength theory is proposed that is convenient to be applied in geotechnical engineering where compression is customarily taken as positive. And also the limit line on deviatoric plane of this modified equation is derived and introduced into the three dimensional (3D) elastic viscoplastic constitutive model of Yin and Graham. Parameters of the model are determined from experiments of the diatom soft rock specimens. Numerical simulations are performed to compare the strain softening behavior predicted in this paper and triaxial experimental results. Simulation results show that the proposed model can accurately describe the strain softening of soft rock.

Effects of Soil Properties Uncertainty on Reliability Index of Slope

A probabilistic analysis procedure and related algorithms were based on the Monte Carlo simulation method that considers the variability of soil properties in this paper. A homogenous slope example provide insight into the effects of uncertainty due to the variability of soil properties on slope stability .Taking soil parameters cohesion c, friction angle, gravity γ as the basic random variables, the reliability index are calculated using Monte Carlo simulation method taking into account the uncertainties of these basic random variables. The calculated results are compared for four recognized methods of slope stability, which are Ordinary method, simplified Bishop method, simplified Janbu method and Morgenstern Price method. And the influence of soil parameters’ probability distribution model (i.e. the normal distribution and the log–normal distribution), variation coefficient, mean value, correlation between parameters on the reliability index of slope is discussed. The study shows that different soil properties have different influence degree on the reliability index with regard to the slope reliability analysis.

STUDY ON STRESS-STRAIN RELATIONSHIP OF LOESS BASED ON TWIN SHEAR UNIFIED DAMAGE CONSTITUTIVE MODEL

To investigate the change of loess stress state, a series of triaxial shear tests were performed on normal consolidation and over consolidation loess. From the test results, the stress-strain relationships of loess were obtained and discussed. Based on unified strength theory, the statistical damage constitutive equation was obtained under triaxial stress state assuming distribution statistical probability of micro-units strength. Then the proposed formulation was adopted to study on stress-strain constitutive relationships of loess and to simulate consolidation undrained triaxial test and consolidation drained triaxial test for normal consolidated and over-consolidated specimens. Compared between experimental and theoretical results, it was shown that the proposed constitutive model can well describe stress-strain relationship of loess, whatever the characteristic of strain softening or stain hardening.

Unified Three-Dimensional Revision of Modified Cam Clay Model

According to unified strength parameters obtained from unified strength theory, the slope of critical state line is modified to reflect critical states of different geomaterials under general stress states. Yield function that can consider the effect of the third deviatoricic invariant is proposed, and an elasto-plastic constitutive model is established by adopting non-associated flow rules; furthermore, methods of overcoming singular points on the yield surface are discussed. The proposed model is verified by true triaxial tests of clay, and results show that the model can well predict stress-strain relationships.