Search

Rock crack propagation is an important direction in the analysis of rock mechanical properties. However, due to the opacity of rock mass, crack evolution process cannot be directly observed. In this study, a heterogeneous anisotropic transparent rock made by mixture randomly distributed different sizes molten quartz sand and pure epoxy resin. This study aims to provide an intuitive and useful method of observing the characteristics of crack evolution, also crack evolution process is recorded by a high-speed camera based on Split-Hopkinson pressure bar (SHPB) tests. The results show that: change of internal color is monitored during loading, which confirms the visualization of internal crack evolution. Failure occurs along the loading direction, and many cracks are distributed in the center of the sample. When the main crack passes through the broken glass sand, it directly passes through the glass sand, and when it passes through the unbroken glass sand, it extends along the edge of the glass sand. Particle flow code(PFC) is used to simulate crack propagation process of transparent rock sample in the SHPB test, and the process is divided into four stages: no crack, crack initiation, crack coalescence, and crack stability. When the final failure of the sample occurs during loading course, tensile cracks account for 78.3% of the total cracks and shear cracks account for 21.7%. Furthermore, fracture of the sample is dominated by tensile action. Stress—strain curve and failure mode of numerical simulation are in good agreement with laboratory test. The visualization of rock crack propagation is helpful to the follow-up study of hydraulic fracturing of roadway and debonding of bolt. [ABSTRACT FROM AUTHOR]

Lead (Pb) is a toxic heavy metal and is commonly used in industrial applications. Thus, Pb poisoning is a concerning public health issue worldwide. The amounts of lead in natural water, urine, and blood can serve as significant indicators for monitoring the exposure of Pb poisoning. Waste toner has the characteristics of both "waste" and "resource," as it is a "resource in the wrong place." Here, a low-cost carboxylate-functionalized magnetic adsorbent was first synthesized from waste toner by a simple thermal treatment and served as a novel adsorbent with a flexible multidentate O-donor for pre-concentration of trace Pb. The characterization, adsorption behavior, and various factors of adsorption and desorption were adequately optimized, and prior to graphite furnace atomic absorption spectrometry (GFAAS) detection, a new magnetic solid-phase extraction method was proposed for the analysis of Pb in real environmental water and biological samples. The developed method exhibited a low detection limit (0.003 μg L−1), high enrichment factor (88.6-fold), good linearity (0.01–0.3 μg L−1), satisfactory precision with relative standard deviations of 7.9% (n = 7, CPb = 0.02 μg L−1), fast adsorption kinetics (5 min), and strong ability to overcome matrix interference. Validation was also performed by analyzing a certified standard reference material, and the method was successfully applied to real tap water, lake water, human urine, and human blood serum with satisfactory recoveries of 92.6–109%. [ABSTRACT FROM AUTHOR]

Drilling rate index (DRI) is an important index for evaluating the drillability of rock in mining, tunneling, and underground excavation. Various studies have been implemented to predict DRI based on the relationship between DRI and its influence factors. Meanwhile, many uncertainties are associated with the evaluation of DRI because of the complexity and nonlinearity of rock mechanical and physical properties. But the uncertainty has not been considered in previous studies. In this study, a novel method was proposed to evaluate DRI considering the uncertainty through combining the least square support vector machine (LSSVM) and Monte Carlo simulation (MCS). The LSSVM was adopted to map the relationship between DRI and rock strength index. Latin hypercube sampling (LHS) was used to produce the sample sets based on the uncertainty distribution of rock strength index. MCS was utilized to simulate the uncertainty of DRI. The proposed method was verified by three testing examples with the uncertainties. Interaction effects of DRI's influence factors were analyzed and discussed. The results show the proposed method can evaluate the DRI reasonably. Compared with the determinate method, the proposed method is more rational and scientific and conforms to the rock engineering practice. Interaction effects should be considered while predicting or evaluating the DRI. LSSVM can not only present well the nonlinear relationship between DRI and its influence factors, but also deal with the interaction effects of the DRI's influence factors. The proposed method provides a scientific tool to predict and evaluate the DRI and its uncertainty. [ABSTRACT FROM AUTHOR]

The performance and safety of a geotechnical engineering system are affected by uncertainties. The purpose of Reliability-Based Optimization (RBO) is to find a balanced design that is not only economical but also reliable in the presence of uncertainties. Numerous reliability optimization techniques have been proposed. In this study, the Artificial Bee Colony (ABC) algorithm is employed for reliable optimization of a geotechnical engineering system. The proposed ABC-RBO method combines ABC and First Order Reliability Methods (FORM). Optimization is performed with ABC, while the reliability analysis is performed with FORM, incorporating Excel solver. The proposed method is verified by two geotechnical engineering examples and compared with other methods, and shown to be robust, accurate, and feasible. [ABSTRACT FROM AUTHOR]