Water Wedge Research Articles

Energy evolution and water immersion-induced weakening in sandstone roof of coal mines

The instability of underground spaces in abandoned coal mines with water-immersed rocks is one of the main hazards hindering the geothermal energy use and ecological restoration of post-mining areas. This study conducted graded cyclic loading–unloading tests of five groups of sandstone samples with different water contents. The evolution of input, elastic, dissipated, damping, and plastic energies were explored, considering the damping effect. The normalized plastic energy serves to characterize the damage evolution of sandstone samples, whose failure characteristics were analyzed from both the macroscopic and microscopic perspectives. X-ray diffraction technique and scanning electron microscopy were used to reveal the softening mechanism of sandstone. The results show that under graded cyclic loading, input energy, elastic energy, and dissipated energy all increase gradually, and the fraction of elastic energy increases gradually at first and then tends to stabilize. The variation in the fraction of dissipated energy is opposite to that of elastic energy. In each cycle, the input energy is stored primarily in the form of elastic energy, whereas the dissipated energy is used primarily to overcome the damping of sandstone. When the normalized number of cycles approached unity, the plastic energy fraction sharply increases, while that of the dampening energy drops abruptly. With increasing water content, the effect of pore water on the lubrication, the water wedge, and dissolution of mineral particles becomes more obvious, reducing the elastic-storage limit of sandstone, meanwhile the sandstone damage factor increases significantly under the same cycle and the failure mode changes from brittle to ductile.

Mantle Wedge Water Contents Estimated From Ultrasonic Laboratory Measurements of Olivine‐Antigorite Aggregates

AbstractWhile it is known that serpentinized peridotite acts as a water reservoir in the mantle wedge of a subduction zone, the spatial distribution and quantity of the water stored in these reservoirs, as well as the acoustic velocity of the olivine‐antigorite aggregates, are not well constrained. Here, we report the propagation of seismic waves through synthetic olivine–antigorite aggregates, which are used as proxies for various mantle wedge lithologies, by varying the amount of antigorite at pressures up to 8 GPa. Our results indicate that the acoustic velocity is strongly dependent on the proportion of antigorite in the sample and somewhat dependent on pressure. We empirically explore the relationship between the acoustic velocity and the degree of serpentinization as well as pressure to map the water content in the mantle wedge. Our estimations show that the water content among the subducting slabs around the Pacific Ocean is between 0.5 and 5.0 wt%.

Fracture Characteristics and Failure Modes of Coal, Sandstone, and Shale Impacted by Water Jet under True Triaxial Conditions

In recent years, the water jet technology has become an important means for processing unconventional oil and gas resources. With the exploitation of resources to the deep development, the study of the fracture characteristics and failure modes of true triaxial water jet rock breaking is of major importance for the application of the water jet technology in deeper crustal levels. We selected three typical unconventional gas reservoirs, coal, sandstone, and shale, as samples for our rock-breaking experiments of water jet under true triaxial conditions. On the basis of the rock failure criterion considering triaxial stress, we establish the rock-breaking energy criterion of water jet under true triaxial conditions and study the rock-breaking mode of water jet under true triaxial conditions. Experimental results document that the true triaxial water jet rock-breaking energy criterion can predict the rock-breaking threshold pressure well. With the increase of triaxial stress, the breaking threshold pressure of coal, sandstone, and shale increased by 92, 38, and 37%, respectively. Under true triaxial conditions, the failure characteristics and failure modes of different rocks impacted by water jet differ significantly. The water wedge action of coal is weakened, the volume of the crushing pit was reduced by 90%, and the failure is mainly caused by the shear failure that is induced by jet pressure. Sandstone is still dominated by the denudation failure that is caused by jet, but the degree of destruction is weakened, and the volume of the crushing pit was reduced by 38%. The shale has changed from tensile failure that is dominated by stress waves to erosion pit failure that is dominated by shear action. The results of the study provide a reference for the application of the water jet technology for the exploitation of unconventional oil and gas resources in deeper crust levels.

Study and Application of Rock Breaking Mechanism of Concentrated Water Hydraulic Smooth Blasting in Broken Sand-Stone Geological Conditions

The use of polyenergy water pressure controlled blasting technology in tunnel construction is gradually being promoted, and the technology is often used in hard rock, and the mechanism of rock breaking in fractured sandstone strata is still lacking systematic research. The above mechanism was investigated using a combination of field experiments and ANSYS/LS-DYNA numerical simulation, and the results showed the following: (1) In the case of joint-hole blasting, the concentrating jet formed by the concentrating tube can effectively achieve controlled directional blasting of fractured sandstone. (2) The use of gun clay to seal the hole can effectively improve the stability of the blasting effect, reduce the waste of explosive gas, and effectively extend the duration of action. (3) The water bag enhances the blasting effect through the water wedge effect in the broken surrounding rock and also has the function of energy storage, which can effectively improve the blasting effect when combined with the gun clay. (4) The rock-breaking mechanism of polyenergy hydropressure smooth blasting in fractured sandstone geological conditions is the dual rock-breaking action of “polyenergy jet + water wedge action.” (5) In this article, based on the analysis of blasting mechanism, the deployment method of polyenergy hydropressure smooth blasting is designed and has been well applied in engineering practice.

Fracturing mechanism and pore size distributions of rock subjected to water jets under in-situ stress: Breakage characteristics investigation

Water jet drilling is considered a possible method used during the development of underground unconventional natural gas. Meanwhile, the fracture mechanisms of rock subjected to various in-situ stresses may differ significantly. Thus, laboratory experiments are conducted in this paper using the new jet testing system for the deep reservoir to simulate the drilling process of a water jet in the deep reservoir. The breakage mechanisms of rock are examined using the three-dimensional (3D) reconstruction visualization models of damage distributions, surface morphology, and micro-structural analysis on the influenced zone. The results revealed the dependence of two typical breakage characteristics on the stress state of the tested rock. When the samples were subjected to stress in the triaxial cell, the range of the hole was considerably reduced. Besides, as the horizontal stress difference was increased by 6 MPa, the diameter and depth of the erosion holes increase by 60% and 38.6% respectively. Moreover, the results of the scanning electron microscopy (SEM) showed that the fracturing of the hole wall was mostly caused by tensile failure generated by a water wedge that was easily controlled by high in-situ stress. The in-situ stress state of the reservoir significantly affected the pore size distribution and porosity. The increase of stress inhibited the increase of porosity around the hole. The porosity reaches 6.1% when the stress difference is 6 MPa, which increases by 135%. These results were anticipated to be used as a guide for the utilization of unconventional natural gas in deep reservoirs with complex stress.

Marine redox evolution and organic accumulation in an intrashelf basin, NE Sichuan Basin during the Late Permian

The Late Permian oceanic redox conditions are suggested to have had a causal relationship with the latest Permian mass extinction (LPME); however, the tempo-spatial variations of marine redox conditions which could have controlled environmental context of the LPME and organic accumulation remain loosely constrained. Here, we selected an organic-rich Lopingian succession deposited in an intrashelf basin, NE Sichuan Basin, SW China. To document the coeval oceanic changes, we present multiple geochemical proxies, including iron speciation, (major and trace) element contents, mercury (Hg) contents, total organic carbon contents (TOC) and carbonate carbon isotopic composition. Four intervals (I-IV) of discrete redox conditions were identified based on Fe–Mo–U–V datasets, revealing the evolutions from oxic to euxinic, and further to ferruginous conditions. Meanwhile, the primary productivity increased, then decreased in these intervals. The euxinic water wedge appeared in parallel with the high primary productivity and enrichment of organic matter, and advanced upslope and retreated downslope dynamically in the pace of sea-level rise and fall. In this case, marine redox variations were related to interactions of eustatic changes, organic decomposition, paleogeographic setting, upwelling currents, terrigenous input and volcanic activities. Compared with previous studies from other continents, it seems that the Paleo-Tethys was more anoxic and stagnant than Neo-Tethys and Panthalassa during the Late Permian, due to paleogeographic contexts and the more restricted oceanic circulation. In general, the prominent marine anoxia prevailed in the moderate water depth, and predated the major pulse of the LPME in several sections, which implies that anoxia may have not acted as the direct “killing mechanism” of this event.

Rock breaking characteristics of cyclic electrohydraulic shockwaves

In recent years, to further increase the rate of penetration (ROP), cyclic electrohydraulic shockwaves drilling (EHSD) has been proposed. It is of great significance to study the rock breaking characteristics of this technology. Firstly, a series of experiments were carried out using three different types of sandstone rock samples. The results showed that all the rock samples were fractured after 15 to 40 impacts. Before fracture, the damage of rock samples can be divided into internal damage and external damage, including surface pits, orthogonal central tensile cracks developed from the bottom face, and other tensile cracks. Secondly, based on stress wave theory, a theoretical model for calculating the P-wave peak stress in the rock sample was established, and the calculation was carried out by MATLAB. The simulation results for S2-1 showed that the maximum transmitted compressive stress near the top face reaches 163.5 MPa. The P-wave reflected from the lateral faces formed a superposition area of tensile stress, and the maximum tensile stress reaches 5.44 MPa. With the increase of impact times, the maximum tensile stress gradually decreases and approaches the top face, which explains the formation of the orthogonal central cracks. In addition, it was found that rock samples are subject to the alternating changes of compressive and tensile stress under a single impact. Finally, based on the analysis and discussion of the above results, the rock breaking mechanism of EHSD was analyzed. The results showed that the EHSD mainly damages the rock through the water wedge effect, the tensile stress near the crack boundary, and alternating stress. The research can improve our understanding of how EHSD breaks rocks, which can promote the application of this technology in field drilling.

Rock fragmentation mechanism and engineering application by shaped water pressure smooth blasting

In recent years, various regions are vigorously promoting road infrastructure construction, and the tunnel is one of the essential ways of road infrastructure in mountainous areas, but the traditional smooth blasting has problems such as large disturbance of surrounding rock, easy to exceed and underdog, high dust concentration, etc., which delays the construction process of tunnel drilling, time-consuming and laborious. To solve these problems, this paper, relying on the newly built Guantian tunnel project of the ZJHZQ-9 section of Zhangjiajie to Jishou-Huaihua railway Project, studied the stress propagation law of rock blasting, vibration and displacement changes generated by seismic waves and analyzed them through theoretical analysis and numerical simulation, and drew the following conclusions: (1) Based on the basic theory of rock blasting, the principle of shaped charge action and forming mechanism of shaped charge jet are introduced. The effect of water medium and mortar on rock breaking in the blasting process and the movement law of mortar in the hole are analyzed; (2) ANSYS/LS-DYNA software was used for numerical simulation, and the blasting stress propagation law and surrounding rock damage were analyzed. The results showed that the stress propagation of the shaped water pressure smooth blasting was outstanding, and there was an obvious stress concentration phenomenon at the water bag, which verified the shaped energy jet effect of the shaped energy tank; (3) ANSYS/LS-DYNA software was used for numerical simulation, and the changes of vibration velocity and displacement of blasting simulation were analyzed respectively. The results showed that the vibration velocity of shaped charge hydraulic smooth blasting was the smallest, indicating that the water medium had certain energy storage and buffering effect, while the displacement change was on the contrary. Under the joint action of water bag and mortar, the water wedge enlarges the surrounding rock fissures so that the displacement variation of the shaped water pressure smooth blasting is the largest; (4) Through the field engineering application, the direction and width of blasting cracks correspond to the simulation results, which verifies the accuracy of the simulation.

An experimental study of ultra-high pressure water jet-induced fracture mechanisms and pore size evolution in reservoir rocks

Ultra-high pressure water jets (UHP-WJ) rock breaking is a promising technology for developing unconventional natural gas reserves . In this study, rock-breaking experiments were conducted using typical reservoir rock samples such as sandstone , shale, and coal. The failure patterns in rocks after impact by UHP-WJ were analyzed. Moreover, the 3D damage field model of the rock was reconstructed based on CT scanning, and the internal crack distribution was visualized and examined. Furthermore, the fracture mechanisms of three types of reservoir rocks under the UHP-WJ impingement were studied. The results indicate that intergranular fractures produced due to shear stress are the dominant type of fracture in sandstones, tensile failure due to stress wave was the main type of fracture observed in shale, and coal exhibited the double breaking characteristics of stress wave effect and water wedge effect. The fragments size distribution of samples shows the largest fragments in shale, followed by coal, and the smallest fragments are observed in sandstone. Finally, the evolution of rock pore structure before and after the impact of UHP-WJ was monitored by nuclear magnetic resonance (NMR) methods. The results reveal that the micropores transform into mesopores and macropores in the sandstone, where the total porosity increased by 14.3%–24.8%. As the jet pressure exceeds 100 MPa, the porosity of shale increases significantly, such that the total porosity of the shale sample increased by 7.6%–37.1%. The mesopores transform into macropores and fractures with the influence of the water wedge effect in coal samples, resulting in the reduction of mesopores and the increase of macropores, where the total porosity of the coal sample increased by 14.6%–40%. The complexity and heterogeneity of pores were reduced under UHP-WJ with the increasing jet pressure. The findings provide a theoretical reference for optimizing the recovery from unconventional natural gas reservoirs .

Fracture mechanism and damage characteristics of coal subjected to a water jet under different triaxial stress conditions

Coalbed methane (CBM) recovery using water jet drilling is regarded as a promising technology for high-efficiency, heat-free, and environmentally-friendly development of deep resources. An investigation of the fracture mechanism of coal subjected to a water jet under triaxial stress is essential for the future application of this technology in a deep environment. In this study, the fracture mechanism was discussed, and laboratory experiments were conducted on coal breaking with a water jet under triaxial stress conditions for the first time. The results indicate that there are distinct fracture patterns with/without triaxial stress. With the increase of triaxial stress, the main component of coal failure transitions from tensile failure due to the water wedge to shear failure due to water hammer pressure. The rock-breaking ability of the water jet was impaired significantly under triaxial stress conditions. The tensile fracture zone induced by the water jet was concentrated in the range of 60° of the maximum principal stress direction. Computed tomography (CT) scanning tests were used to document the fracture morphology inside the coal specimens. CT scanning showed that the cracks around the hole were deflected into the direction of maximum principal stress, and the area of the damage caused by the jet decreased with increasing triaxial stress. Three-dimensional (3D) reconstructions of the impacted coal were established based on slice images for visualization. The results revealed that the weak planes in the coal and the triaxial stress were the dominant factors affecting the damage characteristics. When the average stress increased 5 MPa, the radial damage range decreases approximately 58%, and the axial damage range decreases approximately 57%. The damage is concentrated in the jet impact area. These findings provide a reference for the application of water jet technology in deep CBM recovery.

Investigation of the breaking manifestations of bedded shale impacted by a high-pressure abrasive water jet

Experiments on high-pressure abrasive water jet (AWJ) crushing shale were conducted with major consideration of bedding planes. The dynamic strain of the shale sample was obtained, and the shale-breaking manifestations and their influencing factors were analyzed by means of both qualitative and quantitative methods. The results indicate that the angle between the jet direction and bedding plane plays a dominant role in the rock-breaking manifestation, with a larger angle leading to a deep perforation hole in the shale and a small angle causing split-shaped breakage. The dynamic strain evolutions combined with the SEM images imply that the shale breaking manifestation of deep perforation holes is caused by the combined actions of huge compressive pressure and the edge chipping effect of abrasives, while the shale breaking manifestation of split-shaped breakage is contributed by huge compressive pressure and the water wedge effect. Additionally, the intermediate jet pressure and abrasive mass flow rate are found to be suitable for the formation of an excellent hole shape. The findings infer that the combination of a large angle, a suitable jet pressure and abrasive mass flow rate is demanded in the application of hydraulic AWJ perforation in shale gas exploitation, while a small angle with large jet pressure is demanded in the application of hydraulic AWJ slotting.

On the energy conversion characteristics of a top-mounted pitching absorber by using smoothed particle hydrodynamics

The top-mounted pitching point absorber is one of the most promising wave energy converters in that it can be easily attached to an existing offshore structure. However, it is difficult to predict accurately its energy conversion performance because of the strongly nonlinear hydrodynamic behaviour. Herein, smoothed particle hydrodynamics (SPH) is used to solve this wave-structure interaction problem. The SPH method is first validated against free surface deformation measurements obtained from a wedge water entry experiment. SPH simulations of regular wave interaction with fixed and freely pitching devices agree well with measured data, providing confidence in the prediction of power conversion performance. Absorbed power and capture width ratio exhibit uni-modal behaviour with wave period. The wave period of peak power within this distribution increases with PTO damping. According to the observed scaling behaviour with device scale, an optimally damped larger scale device is effective at absorbing energy from incident waves of longer wavelength. In finite deep water, the larger device achieves higher efficiency compared with the smaller ones, and its peak efficiency at 2πh/λ=1.1 provides reference for siting.

Underwater Sound Propagation Modeling in a Complex Shallow Water Environment

Three-dimensional (3D) effects can profoundly influence underwater sound propagation in shallow-water environments, hence, affecting the underwater soundscape. Various geological features and coastal oceanographic processes can cause horizontal reflection, refraction, and diffraction of underwater sound. In this work, the ability of a parabolic equation (PE) model to simulate sound propagation in the extremely complicated shallow water environment of Long Island Sound (United States east coast) is investigated. First, the 2D and 3D versions of the PE model are compared with state-of-the-art normal mode and beam tracing models for two idealized cases representing the local environment in the Sound: (i) a 2D 50-m flat bottom and (ii) a 3D shallow water wedge. After that, the PE model is utilized to model sound propagation in three realistic local scenarios in the Sound. Frequencies of 500 and 1500 Hz are considered in all the simulations. In general, transmission loss (TL) results provided by the PE, normal mode and beam tracing models tend to agree with each other. Differences found emerge with (1) increasing the bathymetry complexity, (2) expanding the propagation range, and (3) approaching the limits of model applicability. The TL results from 3D PE simulations indicate that sound propagating along sand bars can experience significant 3D effects. Indeed, for the complex shallow bathymetry found in some areas of Long Island Sound, it is challenging for the models to track the interference effects in the sound pattern. Results emphasize that when choosing an underwater sound propagation model for practical applications in a complex shallow-water environment, a compromise will be made between the numerical model accuracy, computational time, and validity.

Damage and fracture characteristics of rocks with different structures under high-velocity water jet impact

This paper aims to investigate the damage and fracture characteristics of rocks with different structures under water jet impact. Three types rocks including heterogeneous coal, homogeneous sandstone, and transversely isotropic shale, were selected as the impact target rock. Water-jet impingement experiments with jet velocities varying from 447 m/s to 774 m/s were conducted. The rock macro-breakage characteristics were obtained by describing the breakage patterns, measuring the erosion depth and area, and counting the cracks number. A 3D reconstruction method based on the computed tomography and digital image processing technology was proposed to visualize the internal breakage characteristics and quantitatively analyze the damage field distribution. Combined with fracture morphology from scanning electron microscope, the failure mechanisms of rocks with three structures under water jet impact were revealed. The results indicate that coal, sandstone and shale will experience different breakage patterns with the increasing jet velocity: layered transverse cracks → “十”-type crack network → splitting crack, only one spindle-shape erosion pit, surface debris spalling → layered transverse cracks → “T”-type crack network. The effects of jet velocity and rock structure on the evaluation indexes (such as erosion depth and damage area, the number and angle of transverse cracks) were investigated thoroughly. In addition, the relationships between total damage degree based on breakage volume and jet velocity, and between damage variable based on breakage area and erosion depth, were compared and discussed. The failure mechanisms of three rocks impacted by water jets are as follows: (i) the reflection and interference of stress wave combined with the pressured water wedge effect cause the layered breakage and longitudinal splitting breakage of heterogeneous coal; (ii) the grinding effect of back flow mainly accounts for the formation of spindle-shape erosion pit in homogeneous sandstone; (iii) the shock stress wave effect and bedding structure lead to the spalling of large shale block and layered breakage, and the reflected wave tensile accompanied with pressured water wedge effect cause the tensile splitting breakage.

Vertical Wedge Drop Experiments as a Model for Slamming

_ A deeper comprehension of hydrodynamic slamming can be achieved by revisiting the wedge water entry problem using flexible structures. In this work, two wedge models that are identical, with the exception of different bottom thicknesses, are vertically dropped into calm water. Pressure, full-field out-of-plane deflection, strain, vertical acceleration, and vertical position are measured. Full-field deflections and strains are measured using stereoscopic-digital image correlation (S-DIC) and strain gauges. A nondimensional number, R, quantifying the relative stiffness of the structure with respect to the fluid load is revisited. An experimental parametric study on the effect of R on the nondimensional hydrodynamic pressure and the maximum strain is presented. It was found there is a sharp change in the trend of pressure and strain when R passes through a critical value. It was also discovered that the structural deformation causes a delay in the peak pressure arrival time and a reduction in the peak pressure magnitude during the wedge water entry. Introduction When high-speed planing craft operating in waves becomes airborne and reenters the water surface, a substantial impact or “slam” between the vessel bottom and the water surface will occur (Faltinsen 2005; Lloyd 1989). The bottom slamming events occur frequently and may injure the passengers, compromise the equipment onboard, or even damage the structure. Slamming is a major cause of speed reduction in small craft where slamming loads are important. Current design criteria are primarily based on empirical measurements with little regard for the fluid–structure interaction (FSI) physics of the slamming phenomenon. This study offers a first step toward better understanding of FSI in slamming for optimal structural design in the future. Since the cross sections of most surface effect ships may be approximated by a V-shaped wedge, the slamming characteristics of these sections may be examined by dropping a wedge model into water (Faltinsen 2005; Lloyd 1989). Studying the wedge water entry problem is also helpful in shedding light on the wet deck slamming of catamaran, sloshing under the chamfered roof of a partially filled tank (Faltinsen 2000), seaplane landing (Wagner 1932), water landing of spacecraft and solid rocket boosters, water landing/ditching of aircraft (Abrate 2013), and animal diving behavior (Chang et al. 2016).

Development of a hydraulically controlled piston-pressurized pulsed water jet device and its application potential for hard rock breaking.

To improve the efficiency of hard rock breaking by a pulsed water jet (PWJ), a hydraulically controlled piston-pressurized PWJ (HCPPPWJ) device has been developed, by which the large amplitude pressurization of the jet could be realized through the motion coupling of the piston and the valve core inside the device without requiring additional control or ultra-high-pressure components. Under the continuous injection of low-pressure hydraulic oil, the device has a stable pressurization effect and controllable pulse pressure and pulse frequency. The jet pressure varies periodically with the alternation of high and low pressures; in the rising stage of the pulse pressure, the jet morphology presents an umbrella-like thin-layer structure, which ensures an effective initial impact force of the jet in contact with the target. With the addition of high-frequency stress waves and water wedge pressure, local flaky exfoliation was observed when the granite surface was eroded, and the maximum radius and volume of the erosion pit were greater than those in the case of employing a continuous water jet. Compared with the interrupted PWJ, the HCPPPWJ efficiently utilizes the jet energy during the erosion process, and the specific energy is lower. The results prove that the HCPPPWJ device is an advanced tool in the field of hard rock breaking.

Hydroelastic effects of slamming impact Loads During free-Fall water entry

ABSTRACT This paper examines the hydroelastic problems of a two-dimensional symmetric flexible wedge water entry through free-fall motion. Water entry is numerically investigated by coupled Finite Volume Method and Finite Element Method using a strong two-way coupling approach. The emphasis of this study is on numerical approach and the paper provides an accurate two-way FSI coupling method for the water entry of two-dimensional symmetric elastic wedge section in different conditions. The effect of freefall velocity is investigated by comparing the constant velocity and freefall impacts. It is shown that the bottom deflection is overestimated by using the constant velocity. In order to evaluate the accuracy of the numerical model, the numerical results are compared and validated against published experimental data and favourable agreement is reported. The vertical position, impact velocity, acceleration, pressure distribution, and deflection along the bottom plate of the elastic wedge are evaluated and compared to experimental data. For better understanding of the hydroelastic slamming, the results are presented for different deadrise angles and vertical velocities. The relation between the structural deflection and vertical velocity, deadrise angle, and pressure distribution is investigated. It is observed that the significance of hydroelasticity increases with decreasing deadrise angle and increasing impact velocity.

Characteristics of the Exchange Flow of the Bay of Quinte and Its Sheltered Embayments with Lake Ontario

The nature of the exchange flow between the Bay of Quinte and Lake Ontario has been studied to illustrate the effects of the seasonal onset of stratification on the flushing and transport of material within the bay. Flushing is an important physical process in bays used as drinking water sources because it affects phosphorous loads and water quality. A 2-d analytical model and a 3-dimensional numerical coastal model (FVCOM) were used together with in situ observations of temperature and water speed to illustrate the two-layer nature of the late summer exchange flow between the Bay of Quinte and Lake Ontario. Observations and model simulations were performed for spring and summer of 2018 and showed a cool wedge of bottom water in late summer extending from Lake Ontario and moving into Hay Bay at approximately 3 cm/s. Observed and modelled water speeds were used to calculate monthly averaged fluxes out of the Bay of Quinte. After the thermocline developed, Lake Ontario water backflowed into the Bay of Quinte at a rate approximately equal to the surface outflow decreasing the flushing rate. Over approximately 18.5 days of July 2018, the winds were insufficiently strong to break down the stratification, indicating that deeper waters of the bay are not well mixed. Particle tracking was used to illustrate how Hay Bay provides a habitat for algae growth within the bay.

Changes in the structure and mechanical properties of a typical coal induced by water immersion

Understanding fundamental aspects of the effects of water on both the mesostructure and mechanical characteristics of coal and coal-water interactions is important for increasing the utilization of coal and has not been thoroughly addressed by researchers. To fill this gap, a series of laboratory tests were carried out systematically using coal from the Tashan Coal Mine in China; both untreated samples and samples soaked for 3 h, 6 h, 12 h, 24 h, 36 h, 2 d, 4 d, 10 d, and 20 d. The water absorption characteristics, pore structure, mineral composition, surface morphology and wave velocities of the coal samples that varied with water-soaking time were studied comprehensively by using nuclear magnetic resonance, X-ray diffraction, scanning electron microscopy and ultrasonic testing. In addition, the mechanical properties, i.e., uniaxial compressive strength σu and elastic modulus E, and the deformation and failure characteristics of the coal under different water-soaking periods were obtained by conducting uniaxial compression tests. The parameters of the water infusion techniques were also analyzed to address the hard coal roof of the Tashan coal mine. The results showed that as the water soaking time increased, the average pore sizes expanded and new pores developed; the pore types changed from micropores to mesopores to macropores. Longer water immersion led to not only greater pore connectivity and coal permeability but also changes in the mineral composition and structural characteristics. In addition, the velocity of the ultrasonic longitudinal wave first increased with seepage, enabling moisture to fill the macropores, and then decreased after 4 d due to the water wedge effect. Moreover, both σu and E decreased and could be expressed by exponential functions in terms of soaking time; after 20 d, σu and E decreased by 21.9% and 28.53%, respectively. The appropriate water infusion time and distance for advance were suggested to be 10–15 d and 60–90 m, respectively.

Fragmentation Pattern and Removal Mechanism of Concrete Subjected to Abrasive Water Jet Impact

Abrasive water jet (AWJ) breaking technology is suitable for the maintenance and repair of concrete structures, generating minimal dust, low tool wear, and no vibrations or selective destruction. The failure features and mechanisms of concrete subjected to AWJ impact are fundamental issues of AWJ breaking technology, which are also related to the safety and quality of engineering construction. Based on computed tomography (CT), scanning electron microscopy (SEM), and image processing technology, this paper studied the fragmentation pattern and removal mechanism of concrete under AWJ impact. The general failure characteristics and crack propagation law of concrete subjected to AWJ impact were described through AWJ impact concrete tests. The spatial distribution of damage in concrete subjected to AWJ impact can be divided into the intensive action zone, the transition zone, and the weak action zone. The removal mechanism of AWJ was discussed by comparing the impact performance of a pure water jet (PWJ) system. The results indicate that abrasive particles can cause cliff‐shaped fracture and lip‐shaped distortion in the aggregate part and flat fracture surface in the matrix part. There is no obvious crack in the interfacial transition zone (ITZ) due to the weakening of the water wedge effect.