Tunnel Probabilistic Structural Analysis Using the FORM

In this paper tunnel probabilistic structural analysis (TuPSA) was performed using the first order reliability method (FORM). In TuPSA, a tunnel performance function is defined according to the boundary between the structural stability and instability. Then the performance function is transformed from original space into the standard normal variable space to obtain the design point, reliability index, and also the probability of tunnel failure. In this method, it is possible to consider the design factors as the dependent or independent random parameters with arbitrary probability distributions. A software code is developed to perform the tunnel probabilistic structural analysis (TuPSA) using the FORM. For validation and verification of TuPSA, a typical tunnel example with random joints orientations as well as mechanical properties has been studied. The results of TuPSA were compared with those obtained from Monte-Carlo simulation. The results show, in spite of deterministic analysis which indicates that the rock blocks are stable, that TuPSA resulted in key-blocks failure with certain probabilities. Comparison between probabilistic and deterministic analyses results indicates that probabilistic results, including the design point and probability of failure, are more rational than deterministic factor of safety

Multi-Scale joints roughness characterization using wavelet and shear modeling

Mechanical behavior prediction of rock joints is very important in the rock mechanics. Many models have been proposed to predict the mechanical behavior of joints at which lack of correct evaluation of effective roughness coefficient has been the most important shortage. In this research, each of the upper and lower profiles of joint surfaces is considered as a 2-dimensional wave. Then, multi-scale decomposition based on wavelet theory has been applied studying on asperities. Upper and lower profiles have been combined to produce a composite surface having asperities characteristics of both joint surfaces. Each of the composed wave components (roughness and undulation) has been characterized with statistical quantity of arithmetic mean deviation (Ra). This procedure of characterizing for 2-dimensional waves has been easily extended to 3-dimensional joint surfaces. Conformity in the results of shear and dilation modeling and laboratory tests satisfactorily verifies success of the proposed procedure

Stabilization of the surface of ZnO films and elimination of the aging effect

Zinc oxide is a promising multifunctional material. The practical use of nano- and polycrystalline ZnO devices faces a serious problem of instability of electrical and luminescent characteristics, due to the adsorption of oxygen by the surface during aging. In this paper, the aging effect in ZnO films and nanorod arrays was studied. It was found that ZnO samples demonstrate different behavior of the degradation process, which corresponds to at least two different types of adsorbing surface sites for O(2), where O(2) adsorption is of a different nature. The first type of surface sites is rapidly depassivated after hydrogen passivation and the aging effect takes place due to these centers. The second type of surface sites has a stable structure after hydrogen passivation and corresponds to HO–ZnO sites. The XPS components of these sites include the Zn2p(3/2) peak at 1022.2 ± 0.2 eV and Zn2p(1/2) peak at 1045.2 ± 0.2 eV, with a part of the XPS O1s peak at 531.5 ± 0.3 eV. The annealing transforms the first type of site into the second one, and the subsequent short-term plasma treatment in hydrogen results in steady passivation, where the degradation of characteristics is practically reduced to zero

Study of structural change in Wyodak coal in high-pressure CO2 by small angle neutron scattering

Small angle neutron scattering (SANS) has been applied to examine the effect of high-pressure CO2 on the structure of Wyodak coal. Significant decrease in the scattering intensities on the exposure of the coal to high-pressure CO2 showed that high-pressure CO2 rapidly gets adsorbed on the coal and reaches to all the pores in the structure. This is confirmed by strong and steep exothermic peaks observed on DSC scans during coal/CO2 interactions. In situ small angle neutron scattering on coal at high-pressure CO2 atmosphere showed an increase in scattering intensities with time suggesting that after adsorption, high-pressure CO2 immediately begins to diffuse into the coal matrix, changes the macromolecular structure of the coal, swells the matrix, and probably creates microporosity in coal structure by extraction of volatile components from coal. Significant decrease in the glass transition temperature of coal caused by high-pressure CO2 also confirms that CO2 at elevated pressures dissolve in the coal matrix, results in significant plasticization and physical rearrangement of the coal's macromolecular structure