Applied Mechanics and Materials Vols. 90-93

Abstract: A new method to analyze the seismic stability of the cut soil slope is suggested in this study. In the method, the limiting equilibrium theory and the stress analyzing method are used. The stress acceptability criterion is based on the limited strength of soil. Two basic assumptions are given in the method. One is that the slip surface can be replaced by a series of straight lines. The other is that the interslice boundary is an inclined plane. Three balance equations for any slice, which are two for force equilibrium and one for moment equilibrium, are proposed. An iterative method, which solves the balance equations from the first slice to the last slice, is also suggested. In the new method, the slip surface is not predefined, but is obtained slice by slice going from downhill to uphill in terms of the force and moment balance equations of the slice.

Abstract: Through carrying out the experiments of unit pile model to simulate the different force conditions of bored pile buried in different depth of soil,and combining with the finite element numerical simulation, This paper studies the bored pile ultimate friction resistance of the soil depth effect, and provides reference for engineering design and scientific information.

Abstract: Now, pneumatic rotary anchor roofbolter is widely used in the underground. Pneumatic rock driller is mainly operated in hard rock tunnel, but it often exists in the phenomenon of hard rock and soft rock sections alternately. The result is occured in the replacement of drilling rigs and drilling tools, to produce a great deal of inconvenience. This not only affects seriously anchorage operating speed, but also increases production costs and brings insecurities factors of replacing driller. This study analyzes the performance and parameters of traditional rock rigs & roofbolter. Mechanical Model is established on the basis of studying rock breaking mechanism. Drilling parameters are comprehensively evaluated. It is put forword of specific rotary-impact function of pneumatic anchor rock driller. On this basis, specific rotary-impact function of pneumatic anchor rock driller has been systematically studied.

Abstract: In the process of deep tunnel excavation, the surrounding rock mass, which often endures high initial geo-stress, is in the state of typical unloading. As the adjustment of stress induced by excavation, rock mass behaves a peculiar kind of mechanical deformation characteristics, different from those in loading conditions. As thus, a series of representative unloading tests on hard granite from DaGangShan power station in China, which is being excavation at 1500 meters deep below earth surface, are carried out to simulate dynamically excavation process for studying the peculiar mechanical deformation characteristics. On the basis of unloading tests, a series of research results are acquired as follows： (1) Under unloading condition, lateral deformation occurs in the unloading direction and volumetric strain changes from compression deformation to dilation deformation. (2) Under unloading condition, hard granites behave brittle failure and Mogi-coulomb criterion can well describe the failure characteristics. (3) According to curves of unloading tests, the constitutive model is deduced for simulation analysis.

Abstract: In practical projects, foundations or roadbeds soil is usually in complex initial stress states, and deformation and settlement may happen caused by earthquakes or other dynamic loadings. Since conventional laboratory soil test cannot authentically reproduce dynamic behaviors of soils under complex initial consolidation stress conditions, dynamic deformation behaviors of compacted loess is conducted under complex initial stress conditions through remodeled DTC-199 torsional cyclic load triaxial apparatus. The paper systematically investigated the effects of different initial stress state, such as average principal stress p₀ , the angle of initial principal stress α₀ and the initial intermediate principal stress coefficient b₀, etc. on dynamic shear modulus G_d and damping ratio λ. Results show that: (1) To the same γ_d , G_d increases with the increase of p₀ but the α₀ and b₀ have no influence on G_d. (2) The α₀ has a little influence on λ and the p₀ and b0 have no influence on λ.

Abstract: Fault is one of the most important factors affecting tunnel instability. As a significant and casual construction of Jinping II hydropower station, when the drain tunnel is excavated at depth of 1600 m, rockbursts and water inrush induced by several huge faults and zone of fracture have restricted the development of the whole construction. In this paper, a progressive failure progress numerical analysis code-RFPA (abbreviated from Rock Failure Process Analysis) is applied to investigate the influence of faults on tunnel instability and damaged zones. Numerical simulation is performed to analyze the stress distribution and wreck regions of the tunnel, and the results are consistent with the phenomena obtained from field observation. Moreover, the effects of fault characteristics and positions on the construction mechanical response are studied in details. Some distribution rules of surrounding rock stress of deep-buried tunnel are summarized to provide the reasonable references to TBM excavation and post-support of the drain tunnel, as well as the design and construction of similar engineering in future.

Abstract: To study the granular soil’s rheological properties, a large triaxial rheological apparatus was developed by assemblying a axial pressure and confining pressure providing equipments for the SZ30-4 large scale triaxial apparatus, and the stability examinations proved that the stability of this pressure providing equipments was competent for granular soil’s rheological tests. The large triaxial rheological apparatus have the axial pressure ranging from 0 to 1.0 MPa, confining pressure of 50kPa, 100kPa, 150kPa, 200kPa, 250kPa and the soil sample dimension of Φ=300mm, h=600mm. A series of granular soil creep tests were executed on this apparatus. The tests discussion shows that stress conditions are the main factors, which affects the creep properties of granular soil. There are different rheological properties at different stress level. eg. at low stress level (S=0.1) for the elastic, at middling stress level (0.20.8) for the non-linear viscous plastic. The total rheological strain nonlinearly increase with stress level increments but linearly increase with confining pressure increments. According to the discussion of redstone granular soil’s creep properties, a rheological component based on hyperbola function was presented, and a nonlinear viscous elastioplastic rheological constitutive model was set up by putting the component and the Burgers model in series. The creep properties analysis shows the rheological model can describe the granular soil’s whole rheological phase well.

Abstract: Tunnel excavation is often done in underground engineering such as civil tunnel construction and mine excavation. The numerical simulation can output colorful results to interpret the tunnel excavation effect more easier. Among all the numerical simulation methods, fast lagrangian explicit finite difference code of continua (FLAC3D) is widely used to solve practical problems, especially in field of elasto-plastic characteristic and construction procedure. So in the present paper, 3 steps of excavations in a tunnel is modeled by FLAC3D to present the stress and displacement distribution, and give guidance for the real practice.

Abstract: Probabilistic slope stability analyses have been adopted in study and geotechnical practice. But there are many misconceptions in the literature. One of these is the evaluation index of slope. The evaluation index will not always have the same meanings for the different slip surfaces. There are five kinds of slip surfaces in probabilistic slope stability analysis: slip surface of minimum factor of safety at mean parameters, mix slip surfaces of minimum factor of safety during each iteration, slip surface of minimum reliability index, slip surface of minimum factor of safety at specific parameters combination and slip surface of minimum factor of safety during each iteration in first order reliability method. For different slip surfaces the evaluation indices may be different. The relation among these evaluation indices is discussed and the applicability of the evaluation index is suggested.

Abstract: The paper proposes a calculation method of soil particles framework structural strength, and provides a new parameter, defined as resistance coefficient, which can quantitatively describe the relationship between active stress and passive stress on soil particles framework. The research of the impact of water content, binding materials content and dry density on structural strength and resistance coefficient is conducted under confined compression test with undisturbed and man-made cement structural loess from Yangling. The research shows that structural strength of loess particles framework increases with the increasing of deformation, and with the same deformation, the structural strength of loess particles framework increases with the increasing of water content ; loess particles framework is sensitive to the weakening role of water. The resistance coefficient is smaller and more instability with the increasing of deformation under high water content conditions. The binding material has significant effect on structural strength and resistance coefficient. Moderate cement mixed with loess particles framework cannot only improve the structural strength but also decrease the sensitivity of loess particles framework to the weakening role of water. By controlling the binding material content, water content and dry density, the structural strength and resistance coefficient of man-made cement structural loess will be the same as the undisturbed loess. Increasing dry density can make the structural strength of loess particles framework higher, but the value and the stability of resistance coefficient of loess particles framework structure with high dry density is lower than that in the initial dry density.