Experimental Investigation on Failure Modes and Mechanical Properties of Rock-Like Specimens with a Grout-Infilled Flaw under Triaxial Compression

Flaws existing in rock mass are one of the main factors resulting in the instability of rock mass. Epoxy resin is often used to reinforce fractured rock mass. However, few researches focused on mechanical properties of the specimens with a resin-infilled flaw under triaxial compression. Therefore, in this research, epoxy resin was selected as the grouting material, and triaxial compression tests were conducted on the rock-like specimens with a grout-infilled flaw having different geometries. This study draws some new conclusions. The high confining pressure suppresses the generation of tensile cracks, and the failure mode changes from tensile-shear failure to shear failure as the confining pressure increases. Grouting with epoxy resin leads to the improvement of peak strengths of the specimens under triaxial compression. The reinforcement effect of epoxy resin is better for the specimens having a large flaw length and those under a relatively low confining pressure. Grouting with epoxy resin reduces the internal friction angle of the samples but improves their cohesion. This research may provide some useful insights for understanding the mechanical behaviors of grouted rock masses.National Natural Science Foundation of China [41672258, 41102162]; Postgraduate Research & Practice Innovation Program of Jiangsu Province [KYCX18_0622]; Fundamental Research Funds for the Central Universities [2018B695X14]; Chinese Scholarship CouncilOpen access journalThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Predictions of Overbreak Blocks in Tunnels Based on the Wavelet Neural Network Method and the Geological Statistics Theory

Predicting overbreak blocks is a valid way to protect constructors, safeties in the process of tunnel excavation. In this paper, a prediction method of the overbreak blocks in tunnels is developed in the frame of the wavelet neural network of geological statistics models. Geometrical parameters of structural plane are first obtained by field survey. Then, a statistical model can be deduced from the measured geometrical parameters on the basis of the geological statistics theory. Furthermore, the volumes and distribution of the overbreak blocks are calculated by the theory of wavelet neural network. Finally, the valid support measurements can be designed according to the prediction results for all overbreak blocks appeared in tunnel excavation, and the amount of overbreak blocks can also be predicted. The code with respect to the method has been developed by the fortran language. The method proposed in this paper has been used in a tunnel construction. The results show that there exists an approximate 10%~30% difference between the prediction and the real volume of overbreak blocks. Therefore, the method can be well used to predict the volumes distribution and the overbreak blocks, and the accordingly support measurements can be also given according to the prediction results

Hydrogenated TiO2 nanoparticles loaded with Au nanoclusters demonstrating largely enhanced performance for electrochemical reduction of nitrogen to ammonia

Pristine TiO2/Au (P-TiO2/Au) is modified by hydrogen plasma (H-TiO2/Au) or hydrogen and oxygen plasma (H-O-TiO2/Au) treatment, and then used as electrochemical catalysts for nitrogen reduction reaction (NRR). H-TiO2/Au shows enhanced performance for the NRR process compared with both P-TiO2/Au and H-O-TiO2/Au. After hydrogenation treatment, some disordered regions on the surface of TiO2 nanoparticles are formed, and a large number of oxygen vacancies are incorporated into the TiO2 crystalline structures. When the samples are used as catalysts for electrochemical NRR, the yield of NH3 of H-TiO2/Au is about ten times compared to that of P-TiO2/Au and about three times that of H-O-TiO2/Au, while the highest Faradaic efficiency of 2.7% is also obtained at the potential of -0.1 V for the H-TiO2/Au catalyst. The density functional theory (DFT) calculation results confirm that H-TiO2/Au with oxygen vacancies and the disordered surface layer is much preferred energetically for the NRR process. It proves that enhanced adsorption of N2 molecules on the catalyst and reduced reaction barriers due to the presence of defects play an important role in improving catalysts’ performances. The results show that the plasma hydrogenation technique can be used as an efficient method to modify catalysts for electrochemical NRR processes

Experimental Investigation on Strength and Crack Mechanism of Rock-Like Samples with Open-Closed Cross-Flaws under Uniaxial Compression

AbstractRock masses with open-closed cross-flaws are common in nature. The open-closed cross-flaws usually control the strength of rock masses. However, studies about the influence of open-closed cross-flaws on cracking behaviors and mechanical properties of rock masses are rare. In this study, rock-like samples containing open-closed cross-flaws with different geometries were fabricated to be conducted uniaxial compressive tests. The cracks observed in the tests were classified to nine types, and two new crack modes were described and identified. Two failure modes, failure caused by tensile cracks and failure caused by the combined effect of tensile and shear cracks, were observed. The failure caused by the penetration of the rock bridge is not observed, indicating that the rock bridge is not a potential penetration path for the samples with cross-flaws. Experimental results show that, when α=0°, the peak stress decreases from 32.2 MPa to 17.0 MPa as β increases from 0° to 90°. When α=90°, the peak stress increases from 22.5 MPa to 40.0 MPa as β increases from 0° to 90°. The inclination angle of the open flaw has an obvious effect on the strength of samples. When the inclination angle of the open flaw is 0°, the peak stress is the lowest (17.0 MPa). When the inclination angle of the open flaw is 90°, the peak stress is the largest (40.0 MPa). The samples with an open flaw of large inclination angle tend to have great compressive strength. For samples with open-closed cross-flaws, the open flaw has a greater influence on the strength and failure mode than the closed flaw

Study on Analog Theory of Rock Mass Simulation and Its Engineering Application

During construction of 3D geological models, it is difficult to determine the uniform between geological model and true model. As a comprehensive index, rock quality designation (RQD) is reliable to assess the rationality of geological models. Unfortunately, The RQD of rockmass is determined completely by the deterministic threshold value and directions of the scan lines presently. To avoid this drawback, the modified method of the RQD value based on the threshold value and 3D space is proposed in this paper. Simultaneously, the analogue-simulation method based on rupture mechanism and classification of discontinuities is proposed. The elliptical discontinuity is considered for general discontinuity, and the special discontinuities, such as bedding, fault, and interlayer are dealt with individually. The accuracy of the 3D model is verified by the modified RQD. The 3D model of the rockmass is analogue simulated through repetitively obtaining data from the interval confidence of geometrical parameters of discontinuities, which are determined by a mass of data derived from field investigation. Besides, the dam base of the Xiangjiaba hydropower station is taken as an example, and the 3D model of the dam base is analog-simulated; its stability is evaluated by DDA method. The safety coefficient of the dam base is obtained by utilizing the overload method

Perfluoroalkyl and polyfluoroalkyl substances in the lower atmosphere and surface waters of the Chinese Bohai Sea, Yellow Sea, and Yangtze River estuary

Polyfluoroalkyl and perfluoroalkyl substances (PFASs), in the forms of neutral polyfluoroalkyl substances in the gas phase of air and ionic perfluoroalkyl substances in the dissolved phase of surface water, were investigated during a sampling campaign in the Bohai Sea, Yellow Sea, and Yangtze River estuary in May 2012. In the gas phase, the concentrations of neutral Sigma PFASs were within the range of 76-551 pg/m(3). Higher concentrations were observed in the South Yellow Sea. 8:2 fluorotelomer alcohol (FTOH) was the predominant compound as it accounted for 92%-95% of neutral Sigma PFASs in all air samples. Air mass backward trajectory analysis indicated that neutral Sigma PFASs came mainly from the coast of the Yellow Sea, including the Shandong, Jiangsu, and Zhejiang provinces of China, and the coastal region of South Korea. The fluxes of gas phase dry deposition, were simulated for neutral PFASs, and neutral Sigma PFASs fluxes varied from 0.37 to 23 pg/m(2)/s. In the dissolved phase of the surface water, concentrations of ionic Sigma PFASs ranged from 1.6 to 118 ng/L, with the Bohai Sea exhibiting higher concentrations than both the Yellow Sea and the Yangtze River estuary. Perfluorooctanoic acid (PFOA) was the predominant compound accounting for 51%-90% of the ionic Sigma PFAS concentrations. Releases from industrial and domestic activities as well as the semiclosed geographical conditions increased the level of ionic Sigma PFASs in the Bohai Sea. The spatial distributions of perfluoroalkyl carboxylic acids (PFCAs) and perfluoroalkane sulfonic acids (PFSAs) were different significantly. The Laizhou Bay was the major source region of PFCAs and the Yangtze River estuary was the major source of PFSAs. (C) 2017 Elsevier B.V. All rights reserved

A Sub-Electron-Noise Multi-Channel Cryogenic Skipper-CCD Readout ASIC

The \emph{MIDNA} application specific integrated circuit (ASIC) is a skipper-CCD readout chip fabricated in a 65 nm LP-CMOS process that is capable of working at cryogenic temperatures. The chip integrates four front-end channels that process the skipper-CCD signal and performs differential averaging using a dual slope integration (DSI) circuit. Each readout channel contains a pre-amplifier, a DC restorer, and a dual-slope integrator with chopping capability. The integrator chopping is a key system design element in order to mitigate the effect of low-frequency noise produced by the integrator itself, and it is not often required with standard CCDs. Each channel consumes 4.5 mW of power, occupies 0.156 mm${^2}$ area and has an input referred noise of 2.7${\mu\nu}_{rms}$. It is demonstrated experimentally to achieve sub-electron noise when coupled with a skipper-CCD by means of averaging samples of each pixel. Sub-electron noise is shown in three different acquisition approaches. The signal range is 6000 electrons. The readout system achieves 0.2${e^{-}}$ RMS by averaging 1000 samples with MIDNA both at room temperature and at 180 Kelvin

The Long-Baseline Neutrino Experiment: Exploring Fundamental Symmetries of the Universe

The preponderance of matter over antimatter in the early Universe, the dynamics of the supernova bursts that produced the heavy elements necessary for life and whether protons eventually decay --- these mysteries at the forefront of particle physics and astrophysics are key to understanding the early evolution of our Universe, its current state and its eventual fate. The Long-Baseline Neutrino Experiment (LBNE) represents an extensively developed plan for a world-class experiment dedicated to addressing these questions. LBNE is conceived around three central components: (1) a new, high-intensity neutrino source generated from a megawatt-class proton accelerator at Fermi National Accelerator Laboratory, (2) a near neutrino detector just downstream of the source, and (3) a massive liquid argon time-projection chamber deployed as a far detector deep underground at the Sanford Underground Research Facility. This facility, located at the site of the former Homestake Mine in Lead, South Dakota, is approximately 1,300 km from the neutrino source at Fermilab -- a distance (baseline) that delivers optimal sensitivity to neutrino charge-parity symmetry violation and mass ordering effects. This ambitious yet cost-effective design incorporates scalability and flexibility and can accommodate a variety of upgrades and contributions. With its exceptional combination of experimental configuration, technical capabilities, and potential for transformative discoveries, LBNE promises to be a vital facility for the field of particle physics worldwide, providing physicists from around the globe with opportunities to collaborate in a twenty to thirty year program of exciting science. In this document we provide a comprehensive overview of LBNE's scientific objectives, its place in the landscape of neutrino physics worldwide, the technologies it will incorporate and the capabilities it will possess.Comment: Major update of previous version. This is the reference document for LBNE science program and current status. Chapters 1, 3, and 9 provide a comprehensive overview of LBNE's scientific objectives, its place in the landscape of neutrino physics worldwide, the technologies it will incorporate and the capabilities it will possess. 288 pages, 116 figure

Model Test Study of Rainfall Factors on Failure Process of Xiashu Loess Slope with Gravel Layer

Rainfall is an important factor affecting the stability of Xiashu loess slope, so it is particularly important to understand the infiltration law and induction process of rainfall in Xiashu loess slope. In this paper, a Xiashu loess slope model with a slope ratio of 1 : 1.2 is constructed in the model box. The rainfall infiltration law, vertical stress characteristics, pore-water pressure characteristics, and deformation failure mode of the slope under two different rainfall types and four different rainfall degrees are analyzed. The instability and failure mechanism of Xiashu loess slope with gravel layer under different rainfall conditions is studied. The test results show that the influence of rainfall intensity factors on the gravel soil slope is mainly reflected in the degree of erosion of the slope. With the increase in rainfall frequency and intensity, the rainfall infiltration rate gradually increased, reached the highest value after standing, and then decreased with the increase of rainfall intensity. Rainfall has a great influence on the pore-water pressure in the gravel soil slope, and the pore-water pressure at the monitoring point of the slope toe changes the most. The vertical stress curve will change abruptly in the later stage of intermittent rainfall and during continuous rainfall

A precise theoretical method for high- throughput screening of novel organic electrode materials for Li-ion batteries

Organic electrode materials have gained significant attention due to their flexibility, lightweight characteristics, abundant resources in nature, and low CO2 emission. It's urgently needed for setting up an accurate high-throughput screening theoretical scheme that could find out possible candidates of electrode materials. Currently, the error between the theoretical potentials calculated by the PBE-D2 (DFT-D2, dispersion-corrected density functional theory) method and the experimental values is larger than 12%. Thus, it's essential to finding a more accurate method. In the present work, hybrid functionals and vdW correction methods are applied to investigate six reported organic electrode materials for Li-ion batteries. The results show that the hybrid functional combined with the D2 dispersion corrected method, i.e., HSE06-D2 (Heyd, Scuseria, and Ernzerhof, dispersion-corrected), is able to predict the potential of the organic material precisely with an average error of approximately 5%. This method occupies much hardware resources and being very time consuming, but it could be applied as the final ultrafine step in the high-throughput screening program