Papers by Author: Ning Li

Abstract: It is increasingly recognized around the world that the landscape needs more sustainable planning and management. It often needs new tools to effectively apply the principles, planning and management of sustainable development. Therefore, when planning for sustainable development, the ecological knowledge is essential.

Abstract: With the developing of integrated circuit(IC) technique, improving of integration level, reducing of feature size and increasing the wafer size, the stringent requirements for global planarization during IC fabrication are raised. During chemical mechanical polishing(CMP) of multilevel interconnect for IC, there are obvious influence of the polishing quality on performances of the device．CMP slurry is one of the important factors of influencing the polishing quality. In this work, the stability of tungsten plug CMP slurry for IC multilevel interconnect was studied. Through experiment, interaction between the components in the CMP slurry was analyzed, and stable slurry with optimized polishing parameters to achieve higher removal rate were defined．

Abstract: The Main factors affecting the stability of underground caverns are selected, including the rock mechanical parameters (elastic modulus, Poisson ratio, cohesion and internal friction angle) and initial ground stress parameter (lateral pressure coefficient). Numerical test method is adopted to analyze each parameter’s sensitivity to surrounding rock displacement. Sensitivity formula making each values comparable is established. The sensitivity distribution laws are obtained, and then each parameter’s quantitative effect on displacement is discussed. This work has prominent guiding significance to engineering designs.

Abstract: This paper presents the combination method between geological radar and video surveillance in the tunnel geological prediction, in case the randomness in judgment for the target body prone in the current geological advanced prediction. In order to improve the accuracy, this method conducts geological advanced prediction by comprehensive of geological radar, geological and construction information. In order to verify the effect of this method, we conducted a field trial in the Yululing tunnel. The field trial results are very well. And the accuracy of geological advanced prediction has been improved. This method reached the expected target for the accuracy which we want to improve of geological advanced prediction.

Abstract: Aiming at frost heave problem existing in tunnel construction with artificial horizontal ground freezing in coastal areas, this paper puts forward an equivalent load method for frost heave simulation and a nonlinear deformation simulation method for soil around frost wall. Employing the numerical test method, the designing parameters’ influence on ground frost heave is studied systematically. These parameters include depth of tunnel, frozen wall thickness, excavation radius of tunnel and frost heaving ratio. Furthermore, some measures are proposed to reduce ground frost heave.

Abstract: Fractured rock mass is one of the most important engineering materials for civil engineering in rock mass and rock layer, and has special failure model and constitutive relationship different from other man-made materials. A new numerical model is introduced and applied in studying the deformation, strength, and the failure mode of fractured rock mass, with the consideration of the damaged plasticity theory for intact rock, and joints distribution in fractured rock mass. A series of numerical experiments on jointed rock mass samples are performed to verify the validity of the new numerical model for fractured rock sample. Some feature datum from lab experiment is used to compare the results from numerical tests by the new model. According to these results, the initiation and propagation of induced fracture, and the failure mode of the fractured rock mass samples, are agreed with their associated feature datum by lab experiments.

Abstract: Based on the Generalized Plastic Mechanics (GPM) and strain gradient-dependence of yield surfaces, the differential expressions of the volumetric and shear plastic strains are constructed, then the Generalized Gradient-dependent Plastic Mechanics (GGPM) is established to describe the strain localization characteristics and the basic mechanics characteristics of geo-materials. In order to discretize the controlling equations and the boundary conditions of analyses filed, an increment functional in which the displacement and plastic multipliers are independent variables was constructed to build up the variational principle of GGPM. Both the displacement and the plastical factor are discretized in space. A set of non-linear equations taking the displacements and the plastic factors of nodes as the unknown variables are obtained to solve the new proposed mechanic model. The boundary condition and the increment algorithm are also given. The numerical examples indicate that: (1) when strain localization appears,the plastic shear strain and the plastic volumetric strain mainly concentrate in localization band; (2) the mesh- dependency does not appear any more when the size of mesh changes; (3) when the parameters reflecting localization increase,the width of the strain localization band will be wider obviously.

Abstract: More and more engineering practice indicates rock mass is prone to lose its stability through crack coalescence under dynamic loading, such as blasting and earthquake. However, the crack coalescence pattern of rock specimens containing two or more flaws has not been studied comprehensively under dynamic loading. In this paper, the mechanism of the crack coalescence and peak strength of sandstone-like materials containing two parallel flaws are studied under uniaxial static and dynamic loading with strain rates 1.7×10-5 s-1 and 1.7×10-1 s-1. Through the comparisons of the propagation length, coalescence pattern of the cracks and strength increase of the pre-cracked specimens under static and dynamic loading, the dynamic response of the crack coalescence is found different from static loading under different geometric setting of the flaws. The inertia effect of the crack propagation is revealed under dynamic loading, that is to say, the growth of the secondary cracks tends to the original propagation direction, and the direct and immediate coalescence is taken place easily between two pre-existing flaws, which is different from the kinking coalescence under static loading. So, the inertia effect of the crack propagation is regarded as the main cause of the strength increase of the brittle material under dynamic loading for medium strain rates. In virtue of the explanation, another cause of the mode II shear fracture occurred under earthquake is opened out.