Comprehensive exploration approach of coal mine water-conducting channels in urban environment: a case study in Xintai, China.

In the process of coal mining, prevention and control of water hazard is essential. It is the precondition for water hazard control to detect and determine the distribution of underground water-conducting channels. In urban environments, traditional methods such as active source seismic exploration and transient electromagnetic exploration commonly used in the field are difficult to carry out effectively due to various factors. In this paper, the microtremor survey method (MSM) and the opposing coils transient electromagnetic method (OCTEM) are adapted to conduct the surface exploration of the coal mine water-conducting channels in the urban environment. Combined with the detection results of the low-velocity area and the low-resistivity area, the distribution of water-conducting channels is preliminarily analyzed and determined, which is basically consistent with the drilling and coring results. It verifies the feasibility and accuracy of the comprehensive exploration method used in this paper.

Intelligent decision method for stability assessment of shield tunnel based on multi-objective data mining.

Due to improper operation of the shield construction process and unknown geological surveys, shield construction faces many risks in passing through complex strata, among which the excavation face instability is the most serious, potentially leading to disastrous accidents. To address these issues, this research focuses on the limit support pressure and the excavation face stability in the soil when crossing the Yangtze River. First, an analytical formula for the limit support pressure of the excavation face is established through the wedge model. The support safety coefficient is used to assess the excavation face stability quantitatively. Then the rough set algorithm is used to analyse the sensitivity of each index to establish the reduced evaluation index system for the excavation face stability. The back propagation (BP) neural network is used to train the learning data, and a neural network evaluation model with a prediction error of 5.7675 × 10-4 is established. The prediction performance of BP is verified by comparison with the TOPSIS prediction model and the cloud model. The evaluation method proposed in this paper provides an essential reference for evaluating the underwater shield tunnel excavation face stability. This article is part of the theme issue 'Artificial intelligence in failure analysis of transportation infrastructure and materials'.

Stability classification probability model of loess deposits based on MCS-Cloud.

The stability classification of loess deposits around tunnels is a vital prerequisite for safe construction in underground environment. Due to the fuzziness and randomness of loess physical and mechanical parameters, the stability prediction of loess deposits shows uncertainty. Existing loess deposit stability classification models rarely consider the uncertainty of influencing factors. A novel classification probability model of loess deposits is proposed for the above problems based on Monte Carlo simulation and multi-dimensional normal cloud (MCS-Cloud). Specifically, five loess parameters, including water content, cohesion, internal friction angle, elastic modulus, and Poisson ratio, were selected as predictors for the stability level of loess deposits. The weights of the predictors were obtained through 50 test samples. After acquiring the numerical characteristics of the normal cloud, the stability level can be comprehensively evaluated with the weighted multi-dimensional normal cloud model. The classification model was applied to the loess tunnel in Yan'an, China. The prediction results are in good agreement with practical engineering, denoting the rationality of the weighted multi-dimensional normal cloud. Finally, the stability classification of loess deposits was discussed from the perspective of uncertainty analysis with the application of MCS. Results proved that the MCS-Cloud model is feasible for classifying the stability of loess deposits surrounding tunnels. The obtained classification probability can be used for quantitative risk assessment of loess tunnels.

Intelligent prediction of rockburst in tunnels based on back propagation neural network integrated beetle antennae search algorithm.

Rockburst is one of the major engineering geological disasters of underground engineering. Accurate rockburst intensity level prediction is vital for disaster control during underground tunnel construction. In this work, a hybrid model integrating the back propagation neural network (BPNN) with beetle antennae search algorithm (BAS) has been developed for rockburst prediction. Before model building, 173 groups of rockburst dataset were collected. Six geological parameters are selected as predictors for rockburst, including the maximum tangential stress of the surrounding rock σθ, the uniaxial compressive strength of rock σc, the tensile strength of rock σt, the stress ratio σθ/σc, the rock brittleness ratio σc/σt, and the elastic energy index Wet. After preprocessed by outlier detection and synthetic minority oversampling technique (SMOTE), the new dataset was divided into training and test parts. BAS could optimize the weights and biases of BPNN from the training process. Then the established hybrid model was applied to the test samples with predicted accuracy of 94.3%, proving that the hybrid model has practical value in researching rockburst prediction.

A new method for subsea tunnel site selection based on environmental bearing capacity.

Engineering site selection is an essential and systematic work in the early engineering construction stage. At present, the subsea tunnel site selection mainly depends on manual experience. There is still a lack of subsea tunnel site selection systems based on environmental impact. This study develops a comprehensive site selection evaluation system based on the analytic hierarchy process (AHP) and fuzzy evaluation method for the subsea tunnel site selection. It is a multi-indicator mathematical model evaluation system. On this basis, the ecological site selection method of the subsea tunnel is further studied, an indicator system for evaluating the environmental carrying capacity of the island is established, and the site selection results of the subsea tunnel based on the environmental indicators are obtained. We compared the site selection results of the two methods. The results show that the conventional method and the ecological site selection method based on environmental indicators can well carry out the site selection of subsea tunnels. The two methods take into account both the overall and local optimum of the subsea tunnel route and organically combine the overall and local objectives. This way provides a reference for the design and construction of the subsea tunnel in the future and points out the direction for the site selection of other large-scale projects with significant environmental impact.

Response Characteristics and Experimental Study of Underground Magnetic Resonance Sounding Using a Small-Coil Sensor.

Due to its unique sensitivity to hydrogen protons, magnetic resonance sounding (MRS) is the only geophysical method that directly detects water and can provide nondestructive information on subsurface aquifer properties. The relationship between the surface MRS signal and the location and characteristics of aquifers using large-coil (typically 50-150 m) sensors has been discussed based on forward modelling and experiments. However, few researchers have studied underground MRS using a small-coil sensor. In this paper, a parametric study and a large-scale physical model test were conducted to shed light on the critical response characteristics of underground MRS using a small-coil sensor. The effects of the size and number of turns of the transmitter coil and receiver coil, the geomagnetic declination, the geomagnetic inclination, and the position, thickness, and water content of a water-bearing structure on the performance of the underground MRS were studied based on numerical simulations. Furthermore, we derived the kernel function and underground MRS signal curves for a water-bearing structure model based on the simulations. Finally, a large-scale physical model test on underground MRS using a small-coil sensor was performed using a physical test system for geological prediction of tunnels at Shandong University. The results show that the inversion results of the physical model test were in good agreement with the physical prototype results. Using both numerical modeling and physical model tests, this study showed that underground MRS using a small-coil sensor can be used to predict water-bearing structures in underground engineering.

Ionic Liquid as Reaction Medium for Synthesis of Hierarchically Structured One-Dimensional MoO2 for Efficient Hydrogen Evolution.

Hierarchically structured one-dimensional (1D) MoO2 is synthesized for the first time in ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([BMIM][Tf2N]). The synthesis system is very simple (single [BMIM][Tf2N] solvent plus MoO2(acac)2 reactant). [BMIM][Tf2N] itself works as both the reaction medium and the template for the formation of these interesting 1D MoO2 particles with ultrathin nanosheet subunits. The as-synthesized hierarchically 1D MoO2_40 particles exhibit remarkable electrocatalytic activity with good long-term cycle stability for the hydrogen evolution reaction (HER) in acidic media. The HER activity of present synthesized MoO2 is comparable to those of the most active Mo-based electrocatalysts in acid media reported up to now. Therefore, the ionic liquid route provides us with a newly powerful tool for the synthesis of interesting alternative to noble metal catalysts for efficient electrocatalytic production of hydrogen in acidic environment.

Splitting failure in side walls of a large-scale underground cavern group: a numerical modelling and a field study.

Vertical splitting cracks often appear in side walls of large-scale underground caverns during excavations owing to the brittle characteristics of surrounding rock mass, especially under the conditions of high in situ stress and great overburden depth. This phenomenon greatly affects the integral safety and stability of the underground caverns. In this paper, a transverse isotropic constitutive model and a splitting failure criterion are simultaneously proposed and secondly programmed in FLAC3D to numerically simulate the integral stability of the underground caverns during excavations in Dagangshan hydropower station in Sichuan province, China. Meanwhile, an in situ monitoring study on the displacement of the key points of the underground caverns has also been carried out, and the monitoring results are compared with the numerical results. From the comparative analysis, it can be concluded that the depths of splitting relaxation area obtained by numerical simulation are almost consistent with the actual in situ monitoring values, as well as the trend of the displacement curves, which shows that the transverse isotropic constitutive model combining with the splitting failure criterion is appropriate for investigating the splitting failure in side walls of large-scale underground caverns and it will be a helpful guidance of predicting the depths of splitting relaxation area in surrounding rock mass.

A Green Synthesis of Nanosheet-Constructed Pd Particles in an Ionic Liquid and Their Superior Electrocatalytic Performance.

The ionic liquid 1-ethyl-3-methylimidazolium acetate ([EMIM]Ac) is investigated as a solvent for the synthesis of Pd particles. Interestingly, nanosheet-constructed Pd particles could be successfully synthesized in [EMIM]Ac without any additional reducing agent and template under ionothermal conditions. [EMIM]Ac itself works as the solvent, the reducing agent, and the template for the formation of these interesting Pd particles, making this method complementary to the well-known ionic-liquid-precursor approach. Furthermore, [EMIM]Ac can be recycled with no loss of activity for the formation of nanosheet-constructed Pd particles within our studied cycles. Specifically, the nanosheet-constructed Pd particles exhibit superior electrocatalytic activity and stability towards ethanol oxidation and formic acid oxidation compared with commercially available Pd black catalyst, thus demonstrating their promising applications in fuel-cell area. The current approach, thus, presents a green approach towards the synthesis of Pd particles, using only a simple palladium salt and an ionic liquid.

Gold particle synthesis via reduction of gold salt in the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate aqueous solution.

The formation of gold particles via reduction of HAuCl4 x 4H2O by ascorbic acid in the presence of ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate and sodium alginate has been studied. The shape of the synthesized particles could be tuned by controlling the reaction conditions. Specifically, the flowerlike gold particles can be synthesized by the present synthetic route. It demonstrates that both the ionic liquid and the sodium alginate play an important role for the formation of the flowerlike particles. The synthesized flowerlike particles show enhanced electroactivity for H2O2.