Hybrid silica aerogel (HSA) nanoparticles were synthesized by sol–gel method and drying at ambient pressure. Also, two magnetic nanocomposites of HSA with Fe3O4 nanoparticles and chitosan (CS) were prepared including HSA‐Fe3O4 and HSA‐Fe3O4‐CS. The morphology, structure, and magnetic properties of the HSA as well as its nanocomposites were analyzed by SEM, XRD, TGA, VSM, and ATR‐FTIR techniques. The saturation magnetization (Ms) values for the Fe3O4 NPs, HSA‐Fe3O4, and HSA‐Fe3O4‐CS nanocomposite film were 69.93, 19.04, and 5.77 emu/g, respectively. Furthermore, the abilities of the HSA, HSA‐Fe3O4, CS, and HSA‐Fe3O4‐CS adsorbents were assessed for removal of cadmium(II) heavy metal ions (100 ppm) from aqueous solution. All adsorbents removed/adsorbed the maximum Cd(II) ions in 120 min when adsorbent dosage = 20 mg and pH = 8. Moreover, the highest adsorption capacities were 58.5, 69.4, 65.8, and 71.9 mg/g for the HSA, CS, HSA‐Fe3O4, and HSA‐Fe3O4‐CS, respectively. Kinetic studies using all adsorbents verified that Cd(II) adsorption obeyed the second‐order model illustrating the analyte chemisorption was happened on the adsorbent surfaces. All adsorption data were well consistent with the Langmuir isotherms. The reusability experiment confirmed that all of adsorbents could preserve >95% of their initial adsorption capacities even after five series of adsorption/desorption tests. Practitioner points Hybrid silica aerogel (HSA), HSA‐Fe3O4, and HSA‐Fe3O4‐CS adsorbents were produced. Nanocomposites were characterized by XRD, TGA, SEM, VSM, and ATR‐FTIR analysis. Adsorption of cadmium(II) ions by adsorbents was examined in aqueous solution. The highest adsorption capacity was obtained for the HSA‐Fe3O4‐CS (71.9 mg/g). Cd(II) adsorption followed second‐order kinetics and Langmuir isotherm model.

The high boring capability of full-face tunnel boring machines, especially in urban tunnels, has led to their increased use in tunnel excavation in various and unfavourable geological conditions. Therefore, many efforts have been made to predict and improve the performance of these machines. In this regard, most of the previous studies have focused on the effect of geological and mechanical properties of rock or soil. However, delays due to the maintenance and repair of these machines, which contribute to a major share of unwanted and unpredicted stops at work, have not been considered. Reliability analysis is a practical method based on studying the behaviour of breakdowns and maintenance of machines and systems. This approach can be suggested as part of the appropriate planning for machine maintenance and consequently reducing downtime and costs. In this way, it is possible to identify weaknesses and critical points of a machine or system of the boring process. In the present study, the reliability of the full-face tunnelling machine was analysed with the Monte Carlo simulation method. The studied machine is divided into 5 subsystems including mechanical, electrical, hydraulic, water and compressed air subsystems. Using breakdown data of about 24 months of boring operation, the reliability of each subsystem was simulated and evaluated. Eventually, the reliability of the boring machine was simulated using the Kamat-Riley (K-R) method. The results showed that if no maintenance operation is performed on the subsystems, the overall reliability of the boring machine will decline to zero after about 38 hours of continuous boring operation. Finally, to improve the overall reliability of the boring machine, based on accomplished reliability analysis, we suggest an effective preventive maintenance and repair system for keeping the machine in optimal operating conditions for a longer period.

One of the most significant factors in the estimation of dimension stone quarry cost is the production rate of rock cutting machines. Evaluating the production rate of chain-saw machines is a very significant and practical issue. In this research, it has been attempted to evaluate and select the suitable working-face for a quarry by examining the maximum production rate in the Dehbid and Shayan marble quarries. For this purpose, fi eld studies were carried out which included measuring operational characteristics of the chain-saw cutting machine, the production rate and sampling for laboratory tests from seven active case studies. Subsequently, the physical and mechanical properties of rocks including: Uniaxial Compressive Strength (UCS), Brazilian Tensile Strength (BTS), Los Angeles abrasion, quartz content, water absorption percentage, porosity, Schmidt hardness and grain size for all sample measurements were studied after transferring the samples to a rock-mechanics laboratory. Finally, the sawability of the quarried working-faces was evaluated using the PROMETHEE multi-criteria decision-making (MCDM) model according to the physical and mechanical properties. The results of the study indicated that the number 1 and 5 working-faces from the Dehbid and Shayan quarries are the most suitable working-faces in terms of production rate with the maximum recorded production values (4.95 and 3.1 m2 /h), and with net fl ow rates (2.67 and -0.36) respectively.

Fractures are amongst the most important factors determining the behavior of rock masses. The lack of direct access to the real fractures' distribution leads to the use of indirect methods for their study. The generation of the discrete fracture network is one of the most common indirect methods. Fractures' shape is one of the most important properties that the simulation of which is of great help in studying the fracture network. A wide range of shapes which include from infinite plates to elliptical shape have been suggested for the simulation of fractures. The present paper makes use of the data collected from the pumped-storage power plant and dam project in Roudbar, Lorestan Province, to provide circular and elliptical network of discrete fractures; moreover, the parameters as density, intensity and the real mean value of the length of the fracture traces have been used to evaluate the effect and accuracy of the selected shapes. Following the implementation of the proposed method, it was made clear that the elliptical discrete fracture network, with a mean error value of 13.5 %, outperforms the circular disk discrete fracture network, with a mean error value of 27.5 %; hence, it was found providing more accurate results for the description of the fractures network in the aforementioned region.

The fractures geometrical characteristics can be calculated by various sampling methods in 1 dimension (1D) & 2 dimensions (2D). The Discrete Fracture Network (DFN) simulation results show some of the equations are suitable for calculation of mean trace length and the difference between actual value and their values is less than 15%. Apparent density is dependent on scale, but the Mauldon's estimators are independent of scale despite the variation in fracture length. For all joint sets, the difference of apparent areal intensity by samplings windows and circular estimator is less than 5% proportionate to actual value. A reduction of Fisher constant doesn't have much effect on mean trace length of the fractures with length less than 1.5 m, but it results in a 21% difference for fractures with length longer than 1.5 m. Variation of this parameter affects the density, too and the difference can be 5% to 10% depending on fracture length. But, variation in Fisher constant doesn't have any effect on areal intensity for fractures with length less than 2 m.

The hydrothermal synthesis and optical properties of Nb 5? -doped lithium metasilicate and lithium disilicate nanomaterials were investigated. The microstructures and morphologies of the synthesized Li 2-2x-Nb 2x SiO 31d and Li 2-2x Nb 2x Si 2 O 51d nanomaterials were studied with powder X-ray diffraction and scanning electron microscopy techniques, respectively. The synthesized niobium-doped lithium metasilicate and lithium disilicate nanomaterials, respectively, are isostructural with the standard bulk Li 2 SiO 3 (space group Cmc2 1 ) and Li 2 Si 2 O 5 (space group Ccc2) materials. Photoluminescence spectra of the synthesized materials are studied. The measured optical properties show dependence on the dopant amounts in the structure.

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One of the most crucial steps in producing dimension rocks is the rock cutting process, which incurs a high cost. The amperage draw of rock cutting machines is a major cost factor of this production process. Determining the effect of factors, such as the machine’s operating configurations, mechanical and physical characteristics of the rock, and type of cooling/lubricant fluid, on the cutting machine’s performance can significantly reduce operational costs. This study evaluates the electrical current consumption of a disc cutting machine during the cutting of hard rocks for producing dimension rocks under different operating conditions and using different fluids for cooling/lubrication. For this purpose, a number of cutting tests were performed under different operating conditions (cutting depths of 0.5, 0.7, 1, and 1.3 cm and feed rates of 45, 60, 75, and 90 cm/min) with five cooling/lubrication fluids, including tap water, soap water with a ratio of 1:40 and 1:20, and a commercial cutting power (Abtarash) with a ratio of 30:10 and 15:10. After examining the relationship between operating parameters and the amperage draw of the cutting machine in the presence of five fluids, several linear and nonlinear multivariate statistical models were developed to predict the amperage draw of the cutting machine. The developed models were evaluated using the t-test and F-test statistical methods. The results showed that using the developed models, the amperage draw of the cutting machine can be accurately predicted from the properties of the cooling/lubrication fluid, including viscosity and pH.