Ultimate Depth Research Articles

Solving the Ultimate Water Accumulation Depth of Artificial Dam in Coal Mine Underground Reservoir Based on The Galerkin Method

Solving the Ultimate Water Accumulation Depth of Artificial Dam in Coal Mine Underground Reservoir Based on The Galerkin Method

Discrete element contact model and parameter calibration of sticky particles and agglomerates

The soil in southwest China is a cohesive soil in which discrete cohesive particles and aggregates coexist. In view of the problem that there are many studies on discrete cohesive particles and a lack of research on aggregates, discrete element software DEM is used to conduct a study on cohesive particles and agglomerates parameter calibration. The angle of repose is selected as the target value to calibrate the simulation parameters of sticky particles. Then, the simulation parameters of the viscous particles are used as the basis for the calibration of the contact parameters of the agglomerates, and shear experiments are conducted on the agglomerates, with the ultimate shear depth and ultimate shear force as target values. The results show that the parameters of the agglomerate are: Normal Stiffness per unit area is 5.627 × 108 N/m3, Shear Stiffness per unit area is 4.359 × 108 N/m3, Critical Normal Stress is 3.5 × 106 Pa, Critical Shear Stress is 4.5 × 106 Pa and Bonded Disk Radius is 5.43 mm. Through the particle sliding friction angle test and the agglomerate compression test, it was verified that the errors of sticky particles were 0.30 % and 0.37 % respectively, and the error of agglomerates was 1.69 %.

Sequential Evolution of Residual Liquefaction in a Silty Seabed: Effect of Wave-Loading History

Multiple liquefaction events may occur if a seabed is subjected to repeated but intermittent wave loadings. This study aimed to investigate the influence of the wave-loading history on the evolution of residual liquefaction in a silty seabed through a series of wave flume tests. The flume observations reveal that the preceding wave-loading history results in the densification of the silt bed and a noticeable settlement of the mudline. Meanwhile, the ultimate liquefaction depth, maximum amplitude of interfacial waves, and mudline settlement decrease due to prior wave actions. Both the maximum residual pore pressure ratio and the amplification ratio of transient pore pressure exhibit a declining trend with an increasing number of wave exposures, indicating that the liquefaction resistance of the soil is obviously enhanced. Throughout the continuous liquefaction stage, the residual pore pressure in liquefied soil regions maintains its maximum value. In contrast, the pore pressure in the un-liquefied soil layer experiences slight dissipation after reaching its peak during wave activity. Moreover, the reshaped topography of the silt bed following liquefaction-densification cycles may serve as an indicator of prior liquefaction events, transforming from mud volcanoes into ripples as the liquefaction depth decreases.

Experimental study on silty seabed scour around the single pile induced by the current

In this study, the effects of the current velocity, water content, consolidation strength, and soil particle size on the silty seabed scour around the single pile are studied through flume tests. The liquid limit and plastic limit of the silt are determined through water content tests to calculate the plasticity index. The shear strength and density of the soil were determined through direct shear tests and ring knife methods, respectively. The experimental results indicate that the ultimate equilibrium scour depth of the single pile on silty seabed does not increase or decrease with the increase of water content, but as the water content increases to a certain value, it begins to decrease. The consolidated silty seabed has a substantially smaller scour depth than unconsolidated seabed, and the greater the consolidation strength, the smaller the scour depth, and the more time is needed to achieve scouring equilibrium. The water content and consolidation strength both have an impact on the shape and radius of the scour hole. At high flow rates, the time for the silty seabed to reach the ultimate equilibrium scour depth is greatly shortened. When the flow rate is high, the time history curves of different water contents become more similar. Based on the experimental results, a prediction formula for the scour depth of the silty seabed considering the characteristics of fluid and soil is established. The error of the new formula is less than 20%, which can provide reference for pile scour protection on the silty seabed.

The Impact of Groundwater Burial Depth on the Vegetation of the Dariyabui Oasis in the Central Desert

Vegetation and groundwater are important components of the ecological environment of oases in desert hinterlands and their relationship is crucial to ecosystem stability. In this study, Sentinel-2 data for 2016–2022 and measured groundwater burial depths were analysed for the Dariyabui Oasis in the hinterland of the Taklamakan Desert. The spatial and temporal changes in vegetation and groundwater burial depth from 2019 to 2022 were analysed based on the image–element dichotomous model of the normalised difference vegetation index, utilising the inverse distance weight interpolation method, cubic curve regression, image–element difference, slope trend analysis, and the Markov transfer matrix for determining the temporal and spatial response law between the two. Finally, the threshold value of groundwater burial depth for different vegetation cover types was clarified. The fractional vegetation cover of the Dariyabui Oasis showed a slight increase from 2016 to 2022. Vegetation in the northwest and southeast of the oasis increased, whereas vegetation decreased in the mid-north and northeast regions; 5.14% of the total area experienced increased coverage, whereas 3.35% experienced decreased coverage. The depth of groundwater in the oasis showed a pattern of gradual increase from the entrance to the end of the oasis, that is, south to north. The depth of groundwater in the oasis from 2019 to 2022 was stable, with a 4-year average depth of 4.1069 m and a maximum fluctuation of 0.4560 m. The interannual changes in the groundwater level showed an increasing trend in January–April, while groundwater levels showed a decreasing trend in May–July and August–October and remained constant in June–July and October–December. Oasis vegetation cover showed a negative correlation with groundwater depth, with a depth interval for the highest low-cover vegetation distribution of 3–6 m, and an ultimate depth threshold of 7 m. The depth interval with the highest medium-cover vegetation distribution was 3–4 m, that with the highest high-cover distribution was 2–4 m, and the ultimate depth threshold was 6 m. The depth of the oasis ranged from 3 to 6 m and the ultimate depth threshold was 7 m.

Analytical Study on Limiting Value of Shape Factor of Vertically Loaded Anchors in Saturated Soft Clay

The limiting values of shape factors are an important parameter for vertically loaded anchors (VLAs) at the deep-embedded depth, which influence the ultimate embedded depth and the maximum load-bearing capacity. The limiting values of load-bearing coefficients of VLAs which have different aspect ratios and different areas of fluke are obtained using the finite-element method. Furthermore, based on the expression of shape factors, the limiting values of shape factors of VLAs with different aspect ratios and different areas of a fluke are calculated. The influence of the aspect ratios and areas of fluke of VLAs on the shape factors is investigated. In addition, the effect of the shape factors of VLAs on the ultimate embedded depth and the maximum load-bearing capacity at the ultimate embedded depth is also studied. The results show that when the area of a fluke of VLAs is the same, decreasing the aspect ratio of a fluke can decrease the limiting value of shape factors; when the length of the fluke is constant, the area of the fluke has little influence on the limiting values of shape factors of VLAs. When the area of the fluke of VLAs is the same, the normalized ultimate embedded depth increases almost linearly with increasing the limiting value of shape factors and the maximum load-bearing capacity increases with increasing the limiting value of shape factors. The results can contribute to the design of the shape of a fluke of VLAs in soft clay.

Case study of mountainous geothermal reservoirs (Kopaonik Mt., southwestern Serbia): Fault-controlled fluid compartmentalization within a late Paleogene-Neogene core-complex

A composite hydrogeothermal survey of the magmatic-metamorphic post-NeoTethyan late Paleogene - Neogene crustal core-complex of the Kopaonik Mt., southwestern Serbian highlands, provides new constraints on the subsurface hydraulic across- and along-fault flow fluid regimes and geothermal anomalies associated with the two shallow reservoirs. The study is involving synergistic approach by combining structural geology, exploratory drilling, temperature logging, hydrochemical and hydrodynamic constraints further illustrating a complex conduit–barrier fault-controlled spatial compartmentalization of the two thermal water reservoir(s). The thermal waters of the Kopaonik Mt. geothermal field are channeled by the major regional faults and associated fracture zones that are crosscutting the volcanics and the adjoining metamorphites. The results show that the subsurface compartmentalization of the active reservoirs, which are supplying the spa town of Jošanička banja, are controlled by a seismically active regional faults (including the fault that is crosscutting the Slanište locality, having N-S trending). Owing to the linear channeling of the fault-controlled reservoirs, in which the main quantitative water circulation takes place, it was possible to identify the thermal fluid flow paths and associated recharge zones (catchments). The Jošanička banja thermal waters reservoir is accommodated at ca. 400–500 m depth, whereas the Slanište aquifer maintains a shallower position. The new surface - subsurface constraints allowed the estimation of the subsurface reservoir elevations, pinpointing the origin of shallow crustal geothermal processes. Of particular importance is better understanding of the subsurface spatial distribution and the ultimate depth of the developing Kopaonik Mt. geothermal field. The new interpretation shows a qualitative agreement with the core-complex-related heat sourcing, as well as the fault-controlled reservoir compartments, impacting the efficient extraction of the thermal waters, in terms of quantity, quality and water temperature.

Influence of parameters on the ultimate penetration depth of a double-plate vertically loaded anchor in soft clay

To make a new type of double-plate vertically loaded anchor (DPVLA) penetrate into clay deeper, the influence of parameters on the ultimate penetration depth of DPVLAs in soft clay should be investigated. The expression of the ultimate penetration depth applicable to DPVLAs in clay was determined in terms of the formula of the ultimate penetration depth of anchors with a wedge-shaped section. Based on the drag penetration tests, the movement direction of the bottom fluke of DPVLAs with different lengths of the bottom fluke and different included angles was obtained. By the finite-element method, the upper bound solutions of bearing capacity factors of DPVLAs with different included angles and different lengths of the bottom flukes were also obtained, which correspond to the maximum penetration depth induced by the initial orientation of the anchor. According to the determined expression of the ultimate penetration depth of DPVLAs, the ultimate penetration depth of DPVLAs with different included angles and different lengths of the bottom fluke in clay can be calculated. The results showed that increasing the length of the bottom fluke can increase the ultimate penetration depth when the included angles were the same for DPVLAs not only in the clay with zero strength at the seabed but also in the clay with uniform strength. However, when the length of the bottom fluke is the same, increasing the included angle of DPVLAs in clay can significantly reduce the ultimate penetration depth.

Deep drawing formability of AZ31 magnesium alloy based on magnetorheological elastomer support

AbstractIn this paper, the flexible support mould is designed by using magnetorheological elastomer (MRE) to assist in the deep‐drawing of magnesium alloys. Based on the magnesium alloy mechanical tensile test and magnetorheological elastomer regular force experiments, the deep‐drawing process of AZ31 magnesium alloy supported by support mould was numerically simulated by finite‐element analysis software ABAQUS. By varying the current input to the excitation coil to change the magnetic induction intensity and thus adjust the magnetic normal force of the magnetorheological elastomer, then using magnetic normal force to complete the auxiliary sheet metal deep‐drawing. The results show that, compared with the unsupported mould, the supported mould can effectively reduce the maximum thinning rate of magnesium alloy on the original basis, thus effectively increasing the ultimate depth of magnesium alloy deep‐drawing. It can replace the original buffer device, effectively solution the problem of pulling and cracking at the bottom of magnesium alloy caused by the original excessive damping force, and improve the yield rate of workpiece.

Experimental research on the erosion characteristics of organ-pipe cavitating jet for hydrate-bearing sediments

Cavitating jet is regarded as a promising breaking rate improvement technology in both the marine natural gas hydrate (NGH) fluidization exploitation method and the integrated radial jet drilling and completion method. Experimental studies on the influences of standoff distance, erosion time, inlet flow rate and hydrate saturation on hydrate-bearing sediments (HBS) breakage by organ-pipe cavitating jet (OPCJ) were conducted. The methane HBS synthesized in laboratory were employed as the experimental samples. The breaking effect were evaluated by four quantifiable indicators: erosion pit volume and maximum depth, and jet specific energy and specific cutting energy. Results show that under the same inlet flow rate, the standoff distance and erosion time have significant influences on the erosion pit shape. For the erosion pit volume and depth, the optimal standoff distances are respectively 4 mm and 5 mm (the diameter of nozzle is 1 mm), in which condition the OPCJ efficiencies of erosion and penetration on HBS are greatly improved. The ultimate erosion depth is 215 mm at an inlet flow rate of 0.085 L/s. The critical breaking velocities of OPCJ and conical jet (CJ) on HBS with hydrate saturation of 50% are respectively estimated to be 17.8 m/s and 24.2 m/s. Increasing hydrate saturation significantly decreases the erosion efficiency of OPCJ on HBS. The inlet flow rate is the most significant factor for the erosion pit volume and depth. This study provides a reference on the potential field applications for the NGH fluidization exploitation method and the integrated radial jet drilling and completion method.

Study on the Mechanism of a Hanging Roof at a Difficult Caving End in a Fully-Mechanized Top Coal Caving Face

During the mining process of fully-mechanized caving faces, the roof of the roadway behind the working face easily forms an arched-shape hanging roof structure with the working face pushed forward, which results in potential hazards such as gas accumulation and large-scale roof collapse. Based on the actual situation of a hanging roof at a difficult caving end in fully-mechanized top coal caving faces, through borehole exploration, surrounding rock displacement observation, bolt stress monitoring, theoretical formula calculation, and numerical simulation methods, the structure characteristics of the hanging roof at the end of the fully-mechanized caving face are studied. The ultimate failure depth and ultimate break distance of the hanging roof structure at the end of the working face are obtained, and its formation mechanism is analyzed. It is concluded that the hanging structure is formed by the following reasons: the lithology of sandy mudstone and fine sandstone above the top coal of the roadway is strong; the hanging roof structure is less affected by working-face mining; there is a result of insufficient rotary pressure of the upper mudstone while working together with the protective coal pillar and end support the caving step distance of the curved hanging roof structure is 10~13.55 m.

Bringing ultimate depth to scanning tunnelling microscopy: deep subsurface vision of buried nano-objects in metals.

A method for subsurface visualization and characterization of hidden subsurface nano-structures based on scanning tunelling microscopy/spectroscopy (STM/STS) has been developed. Nano-objects buried under a metal surface up to several tens of nanometers can be visualized through the metal surface and characterized with STM without destroying the sample. This non-destructive method exploits quantum well (QW) states formed by partial electron confinement between the surface and buried nano-objects. The specificity of STM allows for nano-objects to be singled out and easily accessed. Their burial depth can be determined by analysing the oscillatory behaviour of the electron density at the surface of the sample, while the spatial distribution of electron density can give additional information about their size and shape. The proof of concept was demonstrated with different materials such as Cu, Fe, and W in which the nanoclusters of Ar, H, Fe and Co were buried. For each material, the maximal depth of subsurface visualisation is determined by the material parameters and ranges from several nanometers to several tens of nanometers. To demonstrate the ultimate depth of subsurface STM-vision as the principal limit of our approach, the system of Ar nanoclusters embedded into a single-crystalline Cu(110) matrix has been chosen since it represents the best combination of the mean free path, smooth interface and inner electron focusing. With this system we experimentally demonstrated that Ar nanoclusters of several nanometers large buried as deep as 80 nm can still be detected, characterized and imaged. The ultimate depth of this ability is estimated to be 110 nm. This approach using QW states paves the way for enhanced 3D characterization of nanostructures hidden well below a metallic surface.

Prediction and quantification of bioclogging depth limit and rate based on numerical simulation and experimental validation in managed aquifer recharge

AbstractMany microorganisms are naturally occurring in both recharging water and porous media, and microorganisms will grow and clog the pores of porous media. Porous media show different clogging depth and rate, which depends on the carbon source concentration. The bioclogging depth limit and rate under the effect of the nutrient concentration can be disentangled through column experiments and numerical simulation approaches. We use the TOUGHREACT method‐based on the monod equation of microbial growth to explore the process of microbial growth and permeability change, and correct with experimental results. The experimental results show the influence of nutrient concentration (glucose) on microbial growth and clogging of porous medium, and leads to clogging of porous medium. The clogging rate was defined as the rate of change of hydraulic conductivity with time for quantitative study of bioclogging in our study. Simulated results found that the clogging rate increases 0.035 and 0.00673 (m/d/min) respectively in the glucose concentration range of 0.045–0.6 and 0.6–5 mmol/L, simultaneously, the ultimate clogging depth decreases 18.2 and 1.7 mm respectively in the glucose concentration range of 0.045–0.6 and 0.6–5 mmol/L. The aim of this study was to evaluate the effects of nutrient concentrations on bioclogging and shed light on the establishment of nutrient concentration standards for recharge water during groundwater artificial recharge.

Study on the process damping in milling of thin-walled Ti-6Al-4V workpiece: Modeling, analysis, and prediction

Due to limited stiffness and wall thickness, chatter usually occurs in the milling of thin-walled components, which reduces the surface quality and machining productivity. It is well acknowledged that process damping, which results from the interference between the flank face and the machined surface, can improve the chatter stability. This paper analyzes the influence of process damping on the milling system of thin-walled Ti-6Al-4V alloy based on the Nyquist criterion and the Routh criterion. Meanwhile, a detailed and improved calculation model of the interference area is presented to promote the prediction accuracy of process damping. The comparison of computational results and experimental findings verifies the accuracy of the proposed model. The decrease of spindle speed increases the interference area as well as the total damping of the milling system. When the spindle speed is 1000 rpm, the ultimate stable axial depth of cut increases from 1.2 mm to 2.7 mm by utilizing the special designed end mills based on the presented model.

Coupled Eulerian-Lagrangian finite element analysis of penetration processes in silty clay for bucket foundation

ABSTRACT Bucket foundations, as an innovative type of offshore wind turbine foundation, have been widely adopted for their cost competitiveness and time effectiveness in construction and installation. For a successful installation, the penetration process prediction is crucial. This paper investigates the penetration process of both thin-walled and thick-walled bucket foundations in silty clay through small-scale experiments. Based on the experimental results, empirical formulas of penetration resistance are modified. Next, a Coupled Eulerian-Lagrangian (CEL) numerical method is validated and used to simulate the sinking process of engineering prototypes. The penetration resistance obtained by the calculated and numerical methods is in good agreement. Additionally, through the 3D CEL analysis, the disturbance of bulkheads and skirts on soil plugs is gained. The Eulerian volume fraction shows that the soil surface within the outer compartments is prone to rise to form a soil plug, which will bring out a sudden sharp increase in the penetration resistance due to the contact of lid and soil, and consequently affect the ultimate installation depth.

Experimental study of grouting protection against local scouring of monopile foundations for offshore wind turbines

Local scouring is a severe threat to the safety of offshore wind turbines, and it cannot be eliminated completely by traditional protection methods. In this paper, to improve seabed scouring resistance, a new local scouring countermeasure—grouting protection—is proposed, and flume scouring tests are reported. It is found that after grouting, the micro-morphological characteristics of the soil are changed, with the internal friction angle and cohesion of the seabed soil being improved significantly. The grouted seabed has different modes during the development of scouring, i.e., cracking, peeling off, incipient motion, and abrasion. Further analysis shows that the critical shear stress of grouted seabed particles is much greater than that of ungrouted ones, and the ultimate scouring depth of grouted seabed is much lower than that of ungrouted seabed. The protective effect of grouting on local scouring is fully verified: compared with collar protection, grouting protection is more reliable under weak hydrodynamic action, and compared with riprap protection, grouting protection is more efficient under extreme hydrodynamic action.

Enhanced photoacoustic imaging in tissue-mimicking phantoms using polydopamine-shelled perfluorocarbon emulsion droplets

The current work features process parameters for the ultrasound (25 kHz)-assisted fabrication of polydopamine-shelled perfluorocarbon (PDA/PFC) emulsion droplets with bimodal (modes at 100–600 nm and 1–6 µm) and unimodal (200–600 nm) size distributions. Initial screening of these materials revealed that only PDA/PFC emulsion droplets with bimodal distributions showed photoacoustic signal enhancement due to large size of their optically absorbing PDA shells. Performance of this particular type of emulsion droplets as photoacoustic agents were evaluated in Intralipid®–India ink media, mimicking the optical scattering and absorbanceof various tissuetypes. From these measurements, it was observed that PDA/PFC droplets with bimodal size distributions can enhance the photoacoustic signal of blood-mimicking phantom by up to five folds in various tissue-mimicking phantoms with absorption coefficients from 0.1 to 1.0 cm−1. Furthermore, using the information from enhanced photoacoustic images at 750 nm, the ultimate imaging depth was explored for polydopamine-shelled, perfluorohexane (PDA/PFH) emulsion droplets by photon trajectory simulations in 3D using a Monte Carlo approach. Based on these simulations, maximal tissue imaging depths for PDA/PFH emulsion droplets range from 10 to 40 mm, depending on the tissue type. These results demonstrate for the first time that ultrasonically fabricated PDA/PFC emulsion droplets have great potential as photoacoustic imaging agents that can be complemented with other reported characteristics of PDA/PFC emulsion droplets for extended applications in theranostics and other imaging modalities.

Public awareness of first aid treatment in acute burns

Background/Aim: Burn injury is a global public health concern. First aid in burns can reduce morbidity and mortality by stopping the burning process and reducing the size and ultimate depth of the burn injury. The aim of this study is to assess the knowledge about first aid for burns in an urban population in Malaysia. Methods: We conducted a cross-sectional study using questionnaires to assess the knowledge about first aid for acute burns in our single tertiary main national referral unit for burn injuries. A total of 100 respondents were interviewed. Respondents were voluntary outpatients in the surgical outpatient department. Results: Twenty-two percent of the respondents complied with World Health Organization (WHO) recommendations. Other methods used were toothpaste (5.6%), soy sauce (4.4%), traditional oils (3.3%), aloe vera gels (2.2%), and a variety of creams (3.3%). Twenty-five percent agreed that the best information in first aid is through a first aid course; 15% chose a phone application, 14% chose a website, and 12% chose a television advertisement. The recommended first aid treatment (running tap water for ≥ 20 minutes) has proven beneficial in reducing tissue temperature and severity of injury. Conclusion: In 2019, 91% of the Malaysia population had access to the internet, which offers fast and reliable information on first aid for acute burn injuries. The majority of our population still lacks knowledge about first aid treatment for acute burns. Implementation of education regarding burn first aid should target all populations in Malaysia through different community health campaigns, with collaboration between government and non-governmental agencies.

Conversion, Polymerization Shrinkage, Heat Generation, and Depth of Cure of Novel Dental Composites

This study aims to determine the conversion, polymerization shrinkage, heat generation, and depth of cure of novel dental composites, and compare with current commercial composites. Methods: A total of 24 different formulations were tested for their conversion, shrinkage, heat generation, and depth of cure. Conversion was determined by using FTIR. Polymerization shrinkage and heat generation were determined theoretically using conversion, monomer volume fraction, average molecular weight of monomers present in each formulation, and number of methacrylate groups present in each monomer. Depth of cure was determined using the ISO 4049 scraping test.Results: The values obtained in this study for shrinkage, and heat generation were comparable to commercial bulk filled composites Z250, and Gradia. The factors that reduced the shrinkage and heat generation to a greater extent were sample thickness, and CaP addition. The higher shrinkage and heat generation in thin samples can be explained by large number of photons on the top surface. The heat generation is affected by the same variables as that of conversion and shrinkage. The heat generation values for samples using conversions at a thickness of 4 mm were ~ 0.06 kJ/cc, while using 1 mm thickness values gave ~ 0.08 kJ/cc. The reduction in depth of cure with the addition of CaP was ~ 5 %.Conclusion: The relatively higher, or comparable degree of conversion for experimental composites than commercial materials, could indicate their greater suitability for clinical applications. Polymerisation shrinkage, and heat generation are directly related to conversion, and conversion is affected by depth (thickness) of composites More detailed analysis is needed to confirm the ultimate depth of cure of these materials.

Experimental Study and Performance Characterization of Semi-Flexible Pavements

Semi-flexible pavement (SFP) is made up of a porous skeleton of asphalt mixture and cement grout. This special structure granted SFP superior strength and durability and made it a promising solution for the paving of heavy trafficked area. This paper performed in-depth study on the mechanistic behavior of SFP. Firstly, the volumetric mix design of SFP was introduced, and followed with strength, moisture susceptibility, viscoelastic behavior, fatigue life as well as rutting resistance through a series of laboratory tests. Marshall stability tests and dynamic stability tests suggested that SFP gained fair strength and rutting resistance from the curing of cement grout. Meanwhile, SFP was found not sensitive to freeze–thaw cycles through indirect tensile tests. In dynamic modulus tests, SFP exhibited significant viscoelastic behaviors. In four-point beam fatigue tests, the average fatigue lives of SFP reached 85.4 k loading repetition under 400 µε level. In Hamburg wheel tracking tests, the ultimate rutting depth of SFP was smaller than 2.5 mm. The viscoelastic behavior and rutting propagation of SFP was characterized with master curve and power function by fitting the test results. SFP was also compared with traditional asphalt mixtures in MMLS3 accelerated tests and its performance turned out to be prevailing.