The physical and mechanical properties of wet-milling ultra-fine grouting cement were studied,and its microstructure was observed through modern instrumentation analysis such as scanning electronic microscopy(SEM),X-r...The physical and mechanical properties of wet-milling ultra-fine grouting cement were studied,and its microstructure was observed through modern instrumentation analysis such as scanning electronic microscopy(SEM),X-ray diffraction and Hg-intrusion micromeritics.The experimental results indicate that wet-milling ultra-fine cement possesses high rheological properties and groutability.It can be filled densely in cracks of rock and hydrate fully,which may endow hydrated cement with high mechanical strength.Main hydration products of wet-milling ultra-fine cement are poorly crystalline C-S-H(Ⅰ),acicular AFt and plank-shape Ca(OH)_2.The dense crystal-network structure can be formed in the rock gaps filled with cement paste,but some weak regions exist owing to Ca(OH)_2.The features of micro-pore structure of hydrated wet-milling ultra-fine cement are few big harmful pores,abundant harmless micro pores and little most possible pore radius.展开更多
The structure and the hydraulicity of C2F formed by the rapid burning have been studied with the help of XRD,IR, Mossbauer spectra ,the combined water and other analytical means. The technique of the rapid burning can...The structure and the hydraulicity of C2F formed by the rapid burning have been studied with the help of XRD,IR, Mossbauer spectra ,the combined water and other analytical means. The technique of the rapid burning can change the crystal structure of C2F. There exist more octahe-dra (Fe3+), less covalent bonding and more crystal defects in the structure of C2F. It is important that the hydraulicity of C2F can be enhanced by means of the technique of the rapid burning.展开更多
Difference in properties of water-quenched granulated slag is mainly caused by the difference in BF slag granulating process, which, in turn, causes the difference in slag＇ s glassy structure. Changes in quick self-h...Difference in properties of water-quenched granulated slag is mainly caused by the difference in BF slag granulating process, which, in turn, causes the difference in slag＇ s glassy structure. Changes in quick self-hydraulicity of Baosteel different BF slag, changes in strength of different slag at different maintenance temperatures and changes in strength of different BF slag stimulated by clinker are tested in various ways. Effect of external factors on slag＇ s activity is analyzed. The results indicate that the slag from Baosteel has higher hydraulicity, and it increases with time.展开更多
To analyze the differences in the transport and distribution of different types of proppants and to address issues such as the short effective support of proppant and poor placement in hydraulically intersecting fract...To analyze the differences in the transport and distribution of different types of proppants and to address issues such as the short effective support of proppant and poor placement in hydraulically intersecting fractures,this study considered the combined impact of geological-engineering factors on conductivity.Using reservoir production parameters and the discrete elementmethod,multispherical proppants were constructed.Additionally,a 3D fracture model,based on the specified conditions of the L block,employed coupled(Computational Fluid Dynamics)CFD-DEM(Discrete ElementMethod)for joint simulations to quantitatively analyze the transport and placement patterns of multispherical proppants in intersecting fractures.Results indicate that turbulent kinetic energy is an intrinsic factor affecting proppant transport.Moreover,the efficiency of placement and migration distance of low-sphericity quartz sand constructed by the DEM in the main fracture are significantly reduced compared to spherical ceramic proppants,with a 27.7%decrease in the volume fraction of the fracture surface,subsequently affecting the placement concentration and damaging fracture conductivity.Compared to small-angle fractures,controlling artificial and natural fractures to expand at angles of 45°to 60°increases the effective support length by approximately 20.6%.During hydraulic fracturing of gas wells,ensuring the fracture support area and post-closure conductivity can be achieved by controlling the sphericity of proppants and adjusting the perforation direction to control the direction of artificial fractures.展开更多
Particle-fluid two-phase flows in rock fractures and fracture networks play a pivotal role in determining the efficiency and effectiveness of hydraulic fracturing operations,a vital component in unconventional oil and...Particle-fluid two-phase flows in rock fractures and fracture networks play a pivotal role in determining the efficiency and effectiveness of hydraulic fracturing operations,a vital component in unconventional oil and gas extraction.Central to this phenomenon is the transport of proppants,tiny solid particles injected into the fractures to prevent them from closing once the injection is stopped.However,effective transport and deposition of proppant is critical in keeping fracture pathways open,especially in lowpermeability reservoirs.This review explores,then quantifies,the important role of fluid inertia and turbulent flows in governing proppant transport.While traditional models predominantly assume and then characterise flow as laminar,this may not accurately capture the complexities inherent in realworld hydraulic fracturing and proppant emplacement.Recent investigations highlight the paramount importance of fluid inertia,especially at the high Reynolds numbers typically associated with fracturing operations.Fluid inertia,often overlooked,introduces crucial forces that influence particle settling velocities,particle-particle interactions,and the eventual deposition of proppants within fractures.With their inherent eddies and transient and chaotic nature,turbulent flows introduce additional complexities to proppant transport,crucially altering proppant settling velocities and dispersion patterns.The following comprehensive survey of experimental,numerical,and analytical studies elucidates controls on the intricate dynamics of proppant transport under fluid inertia and turbulence-towards providing a holistic understanding of the current state-of-the-art,guiding future research directions,and optimising hydraulic fracturing practices.展开更多
To enhance the operational capacity and space utilization of baffle-drop shafts,this study improved the traditional baffle-drop shaft by expanding the wet-side space,incorporating large rotation-angle baffles,and inst...To enhance the operational capacity and space utilization of baffle-drop shafts,this study improved the traditional baffle-drop shaft by expanding the wet-side space,incorporating large rotation-angle baffles,and installing overflow holes in the dividing wall.A three-dimensional turbulent model was developed using ANSYS Fluent to simulate the hydraulic characteristics of both traditional and new baffle-drop shafts across various flow rates.The simulation results demonstrated that the new shaft design allowed for discharge from both the wet and dry sides,significantly improving operational capacity,with the dry side capable of handling 40%of the inlet flow.Compared to the traditional shaft,the new design reduced shaft wall pressures and decreased the mean and standard deviation of pressure on typical baffles by 21%and 63%,respectively,therefore enhancing structural safety.Additionally,the new shaft achieved a 2%-12%higher energy dissipation rate than the traditional shaft across different flow rates.This study offers valuable insights for the design and optimization of drop shafts in deep tunnel drainage systems.展开更多
Through a case analysis,this study examines the spatiotemporal evolution of microseismic(MS)events,energy characteristics,volumetric features,and fracture network development in surface well hydraulic fracturing.A tot...Through a case analysis,this study examines the spatiotemporal evolution of microseismic(MS)events,energy characteristics,volumetric features,and fracture network development in surface well hydraulic fracturing.A total of 349 MS events were analyzed across different fracturing sections,revealing significant heterogeneity in fracture propagation.Energy scanning results showed that cumulative energy values ranged from 240 to 1060 J across the sections,indicating notable differences.Stimulated reservoir volume(SRV)analysis demonstrated well-developed fracture networks in certain sections,with a total SRV exceeding 1540000 m^(3).The hydraulic fracture network analysis revealed that during the midfracturing stage,the density and spatial extent of MS events significantly increased,indicating rapid fracture propagation and the formation of complex networks.In the later stage,the number of secondary fractures near fracture edges decreased,and the fracture network stabilized.By comparing the branching index,fracture length,width,height,and SRV values across different fracturing sections,Sections No.1 and No.8 showed the best performance,with high MS event densities,extensive fracture networks,and significant energy release.However,Sections No.4 and No.5 exhibited sparse MS activity and poor fracture connectivity,indicating suboptimal stimulation effectiveness.展开更多
Natural gas hydrates(hereinafter referred to as hydrates)are a promising clean energy source.However,their current development is far from reaching commercial exploitation.Reservoir stimulation tech-nology provides ne...Natural gas hydrates(hereinafter referred to as hydrates)are a promising clean energy source.However,their current development is far from reaching commercial exploitation.Reservoir stimulation tech-nology provides new approaches to enhance hydrate development effectiveness.Addressing the current lack of quantitative and objective methods for evaluating the fracability of hydrate reservoirs,this study clarifies the relationship between geological and engineering fracability and proposes a comprehensive evaluation model for hydrate reservoir fracability based on grey relational analysis and the criteria importance through intercriteria correlation method.By integrating results from hydraulic fracturing experiments on hydrate sediments,the fracability of hydrate reservoirs is assessed.The concept of critical construction parameter curves for hydrate reservoirs is introduced for the first time.Additionally,two-dimensional fracability index evaluation charts and three-dimensional fracability construction condition discrimination charts are established.The results indicate that as the comprehensive fracability index increases,the feasibility of forming fractures in hydrate reservoirs improves,and the required normalized fracturing construction parameters gradually decrease.The accuracy rate of the charts in judging experimental results reached 89.74%,enabling quick evaluations of whether hydrate reservoirs are worth fracturing,easy to fracture,and capable of being fractured.This has significant engineering implications forthehydraulicfracturingof hydratereservoirs.展开更多
Waterproof performance of gaskets between segments is the focus of shield tunnels.This paper proposed an analytical method for determining seepage characteristics at tunnel-gasketed joints based on the hydraulic fract...Waterproof performance of gaskets between segments is the focus of shield tunnels.This paper proposed an analytical method for determining seepage characteristics at tunnel-gasketed joints based on the hydraulic fracturing theories.First,the mathematical model was established,and the seepage governing equation and boundary conditions were obtained.Second,three dimensionless parameters were introduced for simplifying the expressions,and the seepage governing equations were normalized.Third,analytical expressions were derived for the interface opening and liquid pressure.Moreover,the influencing factors of seepage process at the gasketed interface were analyzed.Parametric analyses revealed that,in the normalized criterion of liquid viscosity,the liquid tip coordinate was influenced by the degree of negative pressure in the liquid lag region,which was related to the initial contact stress.The coordinate of the liquid tip affected the liquid pressure distribution and the interface opening,which were analyzed under different liquid tip coordinate conditions.Finally,under two limit states,comparative analysis showed that the results of the variation trend of the proposed method agree well with those of previous research.Overall,the proposed analytical method provides a novel solution for the design of the waterproof in shield tunnels.展开更多
This study proposed a repeated adjustable mixture injection strategy(RAM)based microbial induced carbonate precipitation(MICP)for efficient mitigation of rock fracture leakage.Granite fractures with small apertures we...This study proposed a repeated adjustable mixture injection strategy(RAM)based microbial induced carbonate precipitation(MICP)for efficient mitigation of rock fracture leakage.Granite fractures with small apertures were investigated,and bio-sealing experiments were conducted using five different cementation solution(CS)concentrations(0.25−2 M).The results showed that the RAM-based bio-sealing method can seal and bond the small aperture rock fractures with high efficiency and uniform precipitation by adjusting the CS concentration.The RAM-based bio-sealing mechanism is attributed to the following four stages:(1)fixation of bacterial flocs onto the fracture surfaces,(2)precipitation of CaCO3 onto the fracture surfaces,(3)growth of pre-precipitated CaCO3 and adhesion of new-suspended CaCO3,and(4)bridging and clogging processes.The optimal CS concentration of 1 M resulted in a fracture filling rate up to 85%,a transmissivity reduction of 4 orders of magnitude,and a shear strength ranging from 512 kPa to 688 kPa.The bio-sealing effect was found to be influenced by the CS concentration on bacterial attachment,calcium carbonate yield and calcium carbonate bulk density.The CS concentration of 1 M promoted bacterial attachment,and increased calcium carbonate yield as well as calcium carbonate bulk density,while concentrations above 1 M had the opposite effect.The bulk density of calcium carbonate played a crucial role in the sealing and bonding performance of bio-sealed fractures,particularly at comparable filling ratios and bridging areas.The bulk density was regulated by the size of calcium carbonate crystals and was determined by Ca2+concentration in the CS.This study provides valuable insights into the RAM-based bio-sealing method,highlighting its potential for efficient rock fracture leakage mitigation through precise control of CS concentration and understanding the underlying mechanisms.展开更多
Source properties and stress fields are critical to understand fundamental mechanisms for fluid-induced earthquakes.In this study,we identify the focal mechanism solutions(FMSs)of 360 earthquakes with local magnitude ...Source properties and stress fields are critical to understand fundamental mechanisms for fluid-induced earthquakes.In this study,we identify the focal mechanism solutions(FMSs)of 360 earthquakes with local magnitude M_(L)≥1.5 in the Changning shale gas field from January 2016 to May 2017 by fitting three-component waveforms.We then constrain the directions of the maximum horizontal stress(σ_(H_(max)))for four dense earthquake clusters using the stress tensor inversion method.The stress drops of 121 earthquakes with M_(L)≥1.5 are calculated using the spectral ratio method.We examine the spatiotemporal heterogeneity of stress field,and discuss the cause of non-double-couple(non-DC)components in seismicity clusters.Following the Mohr-Coulomb criterion,we estimate the fluid overpressure thresholds from FMS for different seismic clusters,providing insights into potential physical mechanisms for induced seismicity.The FMS results indicate that shallow reverse earthquakes,with steep dip angles,characterize most events.The source mechanisms of earthquakes with M_(L)≥1.5 are dominated by DC components(>70%),but several earthquakes with M_(L)>3.0 and the microseismic events nearby during injection period display significant non-DC components(>30%).Stress inversion results reveal that the σ_(H_(max)) direction ranges from 120°to 128°.Stress drops of earthquakes range between 0.10 and 64.49 MPa,with high values occurring on reverse faults situated at a greater distance from the shale layer,accompanied by a moderate rotation(≤25°)in the trend of σ_(H_(max)).The seismic clusters close to the shale layer exhibit low fluid overpressure thresholds,prone to being triggered by high pore-pressure fluid.The integrated results suggest that the diffusion of high pore pressures is likely to be the primary factor for observed earthquakes.The present results are expected to offer valuable insights into the origin of anomalous seismicity near the shale gas sites.展开更多
Discrete fracture network(DFN)commonly existing in natural rock masses plays an important role in geological complexity which can influence rock fracturing behaviour during fluid injection.This paper simulated the hyd...Discrete fracture network(DFN)commonly existing in natural rock masses plays an important role in geological complexity which can influence rock fracturing behaviour during fluid injection.This paper simulated the hydraulic fracturing process in lab-scale coal samples with DFNs and the induced seismic activities by the discrete element method(DEM).The effects of DFNs on hydraulic fracturing,induced seismicity and elastic property changes have been concluded.Denser DFNs can comprehensively decrease the peak injection pressure and injection duration.The proportion of strong seismic events increases first and then decreases with increasing DFN density.In addition,the relative modulus of the rock mass is derived innovatively from breakdown pressure,breakdown fracture length and the related initiation time.Increasing DFN densities among large(35–60 degrees)and small(0–30 degrees)fracture dip angles show opposite evolution trends in relative modulus.The transitional point(dip angle)for the opposite trends is also proportionally affected by the friction angle of the rock mass.The modelling results have much practical meaning to infer the density and geometry of pre-existing fractures and the elastic property of rock mass in the field,simply based on the hydraulic fracturing and induced seismicity monitoring data.展开更多
The hydraulic fractures induced in soft coal composite reservoirs have complex extension and energy evolution characteristics.In this study,the mechanism whereby gas outbursts can be eliminated by hydraulic fracturing...The hydraulic fractures induced in soft coal composite reservoirs have complex extension and energy evolution characteristics.In this study,the mechanism whereby gas outbursts can be eliminated by hydraulic fracturing was revealed.The combined fracturing process of a coal seam and its roof under different in situ stress and fracture spacing conditions was analysed through true triaxial physical tests and numerical simulations.The results showed that the pre-fracturing of the roof had a pressure relief effect on the coal seam,and the secondary pressure relief of the coal seam could be completed at a lower fracture initiation pressure.To ensure the continued presence of the stress shadow effect in actual projects,the fracture spacing should be maintained within the critical range influencing the fracture extension.If the vertical stress is high,a call on increasing the fracture spacing can be taken;otherwise,it must be reduced.In the early phase of fracturing,energy is mostly concentrated at the tip and surface of the fracture;however,the proportion of surface energy for subsequent fracturing is gradually reduced,and the energy is mostly used to open the formation and work on the surrounding matrix.Hydraulic fracturing creates new fractures to interconnect originally heterogeneously distributed gas zones,enabling the entire coal seam to first establish interconnected pressure equilibration,then undergo gradientcontrolled depressurization.Hydraulic fracturing can homogenize the stress field and gas pressure field in the original coal seam via communication pressure equalization and reduction decompression,reduce the elastic and extension energies,increase the minimum failure energy required for instability;and realize the elimination of gas outbursts.Our findings provide some theoretical support for the efficient development of coalbed methane and the prevention and control of dynamic gas disasters in coal mines.展开更多
Prepulse combined hydraulic fracturing facilitates the development of fracture networks by integrating prepulse hydraulic loading with conventional hydraulic fracturing.The formation mechanisms of fracture networks be...Prepulse combined hydraulic fracturing facilitates the development of fracture networks by integrating prepulse hydraulic loading with conventional hydraulic fracturing.The formation mechanisms of fracture networks between hydraulic and pre-existing fractures under different prepulse loading parameters remain unclear.This research investigates the impact of prepulse loading parameters,including the prepulse loading number ratio(C),prepulse loading stress ratio(S),and prepulse loading frequency(f),on the formation of fracture networks between hydraulic and pre-existing fractures,using both experimental and numerical methods.The results suggest that low prepulse loading stress ratios and high prepulse loading number ratios are advantageous loading modes.Multiple hydraulic fractures are generated in the specimen under the advantageous loading modes,facilitating the development of a complex fracture network.Fatigue damage occurs in the specimen at the prepulse loading stage.The high water pressure at the secondary conventional hydraulic fracturing promotes the growth of hydraulic fractures along the damage zones.This allows the hydraulic fractures to propagate deeply and interact with pre-existing fractures.Under advantageous loading conditions,multiple hydraulic fractures can extend to pre-existing fractures,and these hydraulic fractures penetrate or propagate along pre-existing fractures.Especially when the approach angle is large,the damage range in the specimen during the prepulse loading stage increases,resulting in the formation of more hydraulic fractures.展开更多
The recently developed SCCDS composite tube,a novel variant of the pipe-in-pipe(PIP)structure,demonstrates strong potential for subsea pipeline applications.However,theoretical research regarding its structural behavi...The recently developed SCCDS composite tube,a novel variant of the pipe-in-pipe(PIP)structure,demonstrates strong potential for subsea pipeline applications.However,theoretical research regarding its structural behavior under compression-torsion loading and bearing capacity calculations remains limited,particularly concerning the influence of dual hydraulic pressures during operation.This study examines the impact of dual hydraulic pressures on the compressive-torsional behavior of SCCDS composite tubes.A finite element(FE)model was developed and validated against experimental results,comparing failure modes,full-range loading curves,and bearing capacity to elucidate the working mechanism under dual pressures.A parametric study was then conducted to examine the effects of geometric-physical parameters.Results demonstrate that dual pressures substantially enhance the bearing capacity of sandwich concrete by increasing the normal contact stress at the interface.Increasing concrete strength(f_(c))provides minimal enhancement to torsional resistance compared to the yielding strengths of outer tube(f_(yo))and inner tube(f_(yi)).Higher diameter-to-thickness ratios of outer tube(D_(o)/t_(o))and inner tube(D_(i)/t_(i))significantly reduce torsional capacity.At 1000 m water depth,increasing the D_(o)/t_(o)ratio from 27.5 to 36.67,55,and 110 reduces bearing capacity by 11.17%,23.08%,and 36.14%respectively.Strict measures should be implemented to prevent substantial reductions in strength and ductility for SCCDS composite tubes with large hollow ratios(e.g.,χ=0.849)or high axial compression ratios(e.g.,n=0.8).The study proposes a modified calculation method for determining N-T curves that incorporates dual hydraulic pressure effects,providing guidance for performance evaluation of novel SCCDS composite tubes in deep-sea engineering.展开更多
Key technologies that make productivity increase are revealed through analyzing the best practices and production data in major shale basins of North America.Trends of the key technologies and optimization designs for...Key technologies that make productivity increase are revealed through analyzing the best practices and production data in major shale basins of North America.Trends of the key technologies and optimization designs for shale oil and gas development are summarized and analyzed based on drilling and completion operations and well data.These technologies mainly include:(1)Optimizing well design and hydraulic fracturing design,including reducing cluster spacing,increasing proppant and fracturing fluid volumes,optimizing horizontal well lateral length and fracture stage length.The most effective method is to reduce cluster spacing to an optimized length.The second most effective method is to optimally increase proppant volumes.(2)Placing horizontal wells in the sweet spots and drilling the wells parallel or close to the minimum horizontal stress direction.(3)Using cube development with optimized well spacing to maximize resource recovery and reduce well interferences.Plus,in-situ stress impacts on hydraulic fracture propagation and hydrocarbon production are addressed.Determination of formation breakdown pressure is studied by considering the impacts of in-situ stresses,drilling and perforation directions.Whether or not the hydraulic fracturing can generate orthogonal fracture networks is also discussed.The key technologies and optimization design parameters proposed in this paper can be applied to guide new well placement,drilling and completion designs,and hydraulic fracture operations to increase productivity.展开更多
The performance and efficiency of hydraulic excavators heavily depend on the design and optimization of their working devices.The working device,which consists of the boom,arm,and bucket,plays a crucial role in determ...The performance and efficiency of hydraulic excavators heavily depend on the design and optimization of their working devices.The working device,which consists of the boom,arm,and bucket,plays a crucial role in determining the machine's digging capacity,stability,and overall operational efficiency.This paper presents a comprehensive study on the dynamics simulation and optimization of hydraulic excavator working devices.The paper outlines the fundamental principles of dynamic modeling,incorporating multi-body dynamics and hydraulic system analysis.It further explores various simulation techniques to evaluate the performance of the working device under varying operational conditions,including load and hydraulic system effects.The study also addresses performance optimization,focusing on multi-objective optimization methods that balance multiple factors such as energy efficiency,speed,and load capacity.Additionally,the paper discusses key factors influencing performance,such as mechanical design,material properties,and operational conditions.The results of the dynamic simulations and optimization analyses demonstrate potential improvements in operational efficiency and system stability,providing a valuable framework for the design and enhancement of hydraulic excavator working devices.展开更多
Hydraulic fracturing technology has played an important role in the exploitation of unconventional oil and gas resources,however,its application to gas hydrate reservoirs has been rarely studied.Currently,there is sti...Hydraulic fracturing technology has played an important role in the exploitation of unconventional oil and gas resources,however,its application to gas hydrate reservoirs has been rarely studied.Currently,there is still limited understanding of the propagation and extension of fractures around the wellbore during the fracturing process of horizontal wells in hydrate reservoirs,as well as the stress interference patterns between fractures.This study simulates hydraulic fracturing processes in hydrate reservoirs using a fluidsolid coupling discrete element method(DEM),and analyzes the impacts of hydrate saturation and geological and engineering factors on fracture extension and stress disturbance.The results show that hydraulic fracturing is more effective when hydrate saturation exceeds 30%and that fracture pressure increases with saturation.The increase in horizontal stress differential enhances the directionality of fracture propagation and reduces stress disturbance.The distribution uniformity index(DUI)reveals that injection pressure is directly proportional to the number of main fractures and inversely proportional to fracturing time,with fracturing efficiency depending on the spacing between injection points and the distance between wells.This work may provide reference for the commercial exploitation of natural gas hydrates.展开更多
Experimental research into the hydraulic conductivity curve (HCC) of unsaturated soil is limited due to the inherent challenge associated with labor, cost, and time. Typically, the HCC is estimated using the soil wate...Experimental research into the hydraulic conductivity curve (HCC) of unsaturated soil is limited due to the inherent challenge associated with labor, cost, and time. Typically, the HCC is estimated using the soil water characteristic curve (SWCC) based models and saturated hydraulic conductivity (SHC). However, the efficiency of the SWCC-based model is rarely assessed, and the influence of soil density and pore structure on HCC remains incomplete due to limited experimental data. To address this gap, this study employs an innovative filter-paper-based column method, which can measure the HCC over a wide suction range (e.g. 0−105 kPa), to capture the HCCs of both intact and compacted specimens with varying dry densities. The efficiency of two typical SWCC-based models is assessed using the measured data. Meanwhile, the mercury intrusion porosity (MIP) technique is employed to obtain the pore characteristic (i.e. pore size distribution (PSD)) and a method of predicting the HCC using the PSD data is proposed, emphasizing the dominant role of the pore structure in shaping the HCC. The results reveal that the dry density's influence on the HCC is primarily observed within the low suction range, corresponding to variations in the dominant and large pores. In the high suction range, the HCCs align along a linear trajectory when plotted in a log-log format. A notable finding is the overestimation of the HCC obtained from the SWCC-based models using the measured SHC. When the SHC is regarded as a fitting parameter, good agreement is achieved. The adjusted SHC value is typically 0-1 order of magnitude lower than the measured value, and this discrepancy diminishes as dry density increases. On the other hand, the proposed PSD-based model performs well with the measured SHC data. Caution is exercised when using the SHC to estimate the HCC for modeling water movement in partially saturated soil.展开更多
Due to severe mass transfer limitations,the remediation efficiency of low-permeability contaminated sites often fails to meet expectations.Hydraulic fracturing technology has been utilized to enhance amendment deliver...Due to severe mass transfer limitations,the remediation efficiency of low-permeability contaminated sites often fails to meet expectations.Hydraulic fracturing technology has been utilized to enhance amendment delivery,but the influence of soil heterogeneity is commonly overlooked.To address this issue,this study develops a numerical model to simulate the enhanced transport of amendments,incorporating convection,diffusion,adsorption,and degradation processes.Within the model,random permeability fields are generated based on geostatistical methods to explore how soil heterogeneity affects amendment injection efficiency,distribution characteristics,and the underlying physical mechanisms.The results indicate that(1)soil heterogeneity significantly reduces the amendment injection efficiency,with stronger heterogeneity correlating to lower efficiency,(2)soil heterogeneity markedly alters the amendment distribution characteristics,leading to the formation of localized“nodes”,(3)the mechanism by which heterogeneity reduces injection efficiency involves decreasing the density of preferential flow paths in the soil,and(4)the adverse effects of heterogeneity can be mitigated by employing pressure compensation or adjusting well spacing.展开更多
文摘The physical and mechanical properties of wet-milling ultra-fine grouting cement were studied,and its microstructure was observed through modern instrumentation analysis such as scanning electronic microscopy(SEM),X-ray diffraction and Hg-intrusion micromeritics.The experimental results indicate that wet-milling ultra-fine cement possesses high rheological properties and groutability.It can be filled densely in cracks of rock and hydrate fully,which may endow hydrated cement with high mechanical strength.Main hydration products of wet-milling ultra-fine cement are poorly crystalline C-S-H(Ⅰ),acicular AFt and plank-shape Ca(OH)_2.The dense crystal-network structure can be formed in the rock gaps filled with cement paste,but some weak regions exist owing to Ca(OH)_2.The features of micro-pore structure of hydrated wet-milling ultra-fine cement are few big harmful pores,abundant harmless micro pores and little most possible pore radius.
文摘The structure and the hydraulicity of C2F formed by the rapid burning have been studied with the help of XRD,IR, Mossbauer spectra ,the combined water and other analytical means. The technique of the rapid burning can change the crystal structure of C2F. There exist more octahe-dra (Fe3+), less covalent bonding and more crystal defects in the structure of C2F. It is important that the hydraulicity of C2F can be enhanced by means of the technique of the rapid burning.
文摘Difference in properties of water-quenched granulated slag is mainly caused by the difference in BF slag granulating process, which, in turn, causes the difference in slag＇ s glassy structure. Changes in quick self-hydraulicity of Baosteel different BF slag, changes in strength of different slag at different maintenance temperatures and changes in strength of different BF slag stimulated by clinker are tested in various ways. Effect of external factors on slag＇ s activity is analyzed. The results indicate that the slag from Baosteel has higher hydraulicity, and it increases with time.
基金funded by the project of the Major Scientific and Technological Projects of CNOOC in the 14th Five-Year Plan(No.KJGG2022-0701)the CNOOC Research Institute(No.2020PFS-03).
文摘To analyze the differences in the transport and distribution of different types of proppants and to address issues such as the short effective support of proppant and poor placement in hydraulically intersecting fractures,this study considered the combined impact of geological-engineering factors on conductivity.Using reservoir production parameters and the discrete elementmethod,multispherical proppants were constructed.Additionally,a 3D fracture model,based on the specified conditions of the L block,employed coupled(Computational Fluid Dynamics)CFD-DEM(Discrete ElementMethod)for joint simulations to quantitatively analyze the transport and placement patterns of multispherical proppants in intersecting fractures.Results indicate that turbulent kinetic energy is an intrinsic factor affecting proppant transport.Moreover,the efficiency of placement and migration distance of low-sphericity quartz sand constructed by the DEM in the main fracture are significantly reduced compared to spherical ceramic proppants,with a 27.7%decrease in the volume fraction of the fracture surface,subsequently affecting the placement concentration and damaging fracture conductivity.Compared to small-angle fractures,controlling artificial and natural fractures to expand at angles of 45°to 60°increases the effective support length by approximately 20.6%.During hydraulic fracturing of gas wells,ensuring the fracture support area and post-closure conductivity can be achieved by controlling the sphericity of proppants and adjusting the perforation direction to control the direction of artificial fractures.
基金the Australian Research Council Discovery Project(ARC DP 220100851)scheme and would acknowledge that.
文摘Particle-fluid two-phase flows in rock fractures and fracture networks play a pivotal role in determining the efficiency and effectiveness of hydraulic fracturing operations,a vital component in unconventional oil and gas extraction.Central to this phenomenon is the transport of proppants,tiny solid particles injected into the fractures to prevent them from closing once the injection is stopped.However,effective transport and deposition of proppant is critical in keeping fracture pathways open,especially in lowpermeability reservoirs.This review explores,then quantifies,the important role of fluid inertia and turbulent flows in governing proppant transport.While traditional models predominantly assume and then characterise flow as laminar,this may not accurately capture the complexities inherent in realworld hydraulic fracturing and proppant emplacement.Recent investigations highlight the paramount importance of fluid inertia,especially at the high Reynolds numbers typically associated with fracturing operations.Fluid inertia,often overlooked,introduces crucial forces that influence particle settling velocities,particle-particle interactions,and the eventual deposition of proppants within fractures.With their inherent eddies and transient and chaotic nature,turbulent flows introduce additional complexities to proppant transport,crucially altering proppant settling velocities and dispersion patterns.The following comprehensive survey of experimental,numerical,and analytical studies elucidates controls on the intricate dynamics of proppant transport under fluid inertia and turbulence-towards providing a holistic understanding of the current state-of-the-art,guiding future research directions,and optimising hydraulic fracturing practices.
基金supported by the National Key Research and Development Program of China(Grant No.2021YFD1700802).
文摘To enhance the operational capacity and space utilization of baffle-drop shafts,this study improved the traditional baffle-drop shaft by expanding the wet-side space,incorporating large rotation-angle baffles,and installing overflow holes in the dividing wall.A three-dimensional turbulent model was developed using ANSYS Fluent to simulate the hydraulic characteristics of both traditional and new baffle-drop shafts across various flow rates.The simulation results demonstrated that the new shaft design allowed for discharge from both the wet and dry sides,significantly improving operational capacity,with the dry side capable of handling 40%of the inlet flow.Compared to the traditional shaft,the new design reduced shaft wall pressures and decreased the mean and standard deviation of pressure on typical baffles by 21%and 63%,respectively,therefore enhancing structural safety.Additionally,the new shaft achieved a 2%-12%higher energy dissipation rate than the traditional shaft across different flow rates.This study offers valuable insights for the design and optimization of drop shafts in deep tunnel drainage systems.
基金supported by Yunlong Lake Laboratory of Deep Underground Science and Engineering Project(No.104024008)the National Natural Science Foundation of China(Nos.52274241 and 52474261)the Natural Science Foundation of Jiangsu Province(No.BK20240207).
文摘Through a case analysis,this study examines the spatiotemporal evolution of microseismic(MS)events,energy characteristics,volumetric features,and fracture network development in surface well hydraulic fracturing.A total of 349 MS events were analyzed across different fracturing sections,revealing significant heterogeneity in fracture propagation.Energy scanning results showed that cumulative energy values ranged from 240 to 1060 J across the sections,indicating notable differences.Stimulated reservoir volume(SRV)analysis demonstrated well-developed fracture networks in certain sections,with a total SRV exceeding 1540000 m^(3).The hydraulic fracture network analysis revealed that during the midfracturing stage,the density and spatial extent of MS events significantly increased,indicating rapid fracture propagation and the formation of complex networks.In the later stage,the number of secondary fractures near fracture edges decreased,and the fracture network stabilized.By comparing the branching index,fracture length,width,height,and SRV values across different fracturing sections,Sections No.1 and No.8 showed the best performance,with high MS event densities,extensive fracture networks,and significant energy release.However,Sections No.4 and No.5 exhibited sparse MS activity and poor fracture connectivity,indicating suboptimal stimulation effectiveness.
基金support of the National Natural Science Foundation of China(Grant No.52074332).
文摘Natural gas hydrates(hereinafter referred to as hydrates)are a promising clean energy source.However,their current development is far from reaching commercial exploitation.Reservoir stimulation tech-nology provides new approaches to enhance hydrate development effectiveness.Addressing the current lack of quantitative and objective methods for evaluating the fracability of hydrate reservoirs,this study clarifies the relationship between geological and engineering fracability and proposes a comprehensive evaluation model for hydrate reservoir fracability based on grey relational analysis and the criteria importance through intercriteria correlation method.By integrating results from hydraulic fracturing experiments on hydrate sediments,the fracability of hydrate reservoirs is assessed.The concept of critical construction parameter curves for hydrate reservoirs is introduced for the first time.Additionally,two-dimensional fracability index evaluation charts and three-dimensional fracability construction condition discrimination charts are established.The results indicate that as the comprehensive fracability index increases,the feasibility of forming fractures in hydrate reservoirs improves,and the required normalized fracturing construction parameters gradually decrease.The accuracy rate of the charts in judging experimental results reached 89.74%,enabling quick evaluations of whether hydrate reservoirs are worth fracturing,easy to fracture,and capable of being fractured.This has significant engineering implications forthehydraulicfracturingof hydratereservoirs.
基金Project(52278421)supported by the National Natural Science Foundation of ChinaProject(2024ZZTS0754)supported by the Fundamental Research Funds for the Central Universities of Central South University,China+2 种基金Project(2023CXQD067)supported by the Central South University Innovation-Driven Research Programme,ChinaProject(2022QNRC001)supported by Young Elite Scientists Sponsorship Program by CASTProject(2023TJ-N24)supported by the Youth Talent Program by China Railway Society and the Hunan Provincial Science and Technology Promotion Talent Project。
文摘Waterproof performance of gaskets between segments is the focus of shield tunnels.This paper proposed an analytical method for determining seepage characteristics at tunnel-gasketed joints based on the hydraulic fracturing theories.First,the mathematical model was established,and the seepage governing equation and boundary conditions were obtained.Second,three dimensionless parameters were introduced for simplifying the expressions,and the seepage governing equations were normalized.Third,analytical expressions were derived for the interface opening and liquid pressure.Moreover,the influencing factors of seepage process at the gasketed interface were analyzed.Parametric analyses revealed that,in the normalized criterion of liquid viscosity,the liquid tip coordinate was influenced by the degree of negative pressure in the liquid lag region,which was related to the initial contact stress.The coordinate of the liquid tip affected the liquid pressure distribution and the interface opening,which were analyzed under different liquid tip coordinate conditions.Finally,under two limit states,comparative analysis showed that the results of the variation trend of the proposed method agree well with those of previous research.Overall,the proposed analytical method provides a novel solution for the design of the waterproof in shield tunnels.
基金supported by the National Natural Science Foundation of China(Grant No.41925012)Key task project for joint research and development of the Yangtze River Delta Science and Technology Innovation Community(Grant No.2022CSJGG1200)State Key Laboratory for GeoMechanics and Deep Underground Engineering(Grant No.SKLGDUEK2214).
文摘This study proposed a repeated adjustable mixture injection strategy(RAM)based microbial induced carbonate precipitation(MICP)for efficient mitigation of rock fracture leakage.Granite fractures with small apertures were investigated,and bio-sealing experiments were conducted using five different cementation solution(CS)concentrations(0.25−2 M).The results showed that the RAM-based bio-sealing method can seal and bond the small aperture rock fractures with high efficiency and uniform precipitation by adjusting the CS concentration.The RAM-based bio-sealing mechanism is attributed to the following four stages:(1)fixation of bacterial flocs onto the fracture surfaces,(2)precipitation of CaCO3 onto the fracture surfaces,(3)growth of pre-precipitated CaCO3 and adhesion of new-suspended CaCO3,and(4)bridging and clogging processes.The optimal CS concentration of 1 M resulted in a fracture filling rate up to 85%,a transmissivity reduction of 4 orders of magnitude,and a shear strength ranging from 512 kPa to 688 kPa.The bio-sealing effect was found to be influenced by the CS concentration on bacterial attachment,calcium carbonate yield and calcium carbonate bulk density.The CS concentration of 1 M promoted bacterial attachment,and increased calcium carbonate yield as well as calcium carbonate bulk density,while concentrations above 1 M had the opposite effect.The bulk density of calcium carbonate played a crucial role in the sealing and bonding performance of bio-sealed fractures,particularly at comparable filling ratios and bridging areas.The bulk density was regulated by the size of calcium carbonate crystals and was determined by Ca2+concentration in the CS.This study provides valuable insights into the RAM-based bio-sealing method,highlighting its potential for efficient rock fracture leakage mitigation through precise control of CS concentration and understanding the underlying mechanisms.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.U20A20266 and 12302503)Scientific and technological research projects in Sichuan province(Grant No.2024NSFSC0973).
文摘Source properties and stress fields are critical to understand fundamental mechanisms for fluid-induced earthquakes.In this study,we identify the focal mechanism solutions(FMSs)of 360 earthquakes with local magnitude M_(L)≥1.5 in the Changning shale gas field from January 2016 to May 2017 by fitting three-component waveforms.We then constrain the directions of the maximum horizontal stress(σ_(H_(max)))for four dense earthquake clusters using the stress tensor inversion method.The stress drops of 121 earthquakes with M_(L)≥1.5 are calculated using the spectral ratio method.We examine the spatiotemporal heterogeneity of stress field,and discuss the cause of non-double-couple(non-DC)components in seismicity clusters.Following the Mohr-Coulomb criterion,we estimate the fluid overpressure thresholds from FMS for different seismic clusters,providing insights into potential physical mechanisms for induced seismicity.The FMS results indicate that shallow reverse earthquakes,with steep dip angles,characterize most events.The source mechanisms of earthquakes with M_(L)≥1.5 are dominated by DC components(>70%),but several earthquakes with M_(L)>3.0 and the microseismic events nearby during injection period display significant non-DC components(>30%).Stress inversion results reveal that the σ_(H_(max)) direction ranges from 120°to 128°.Stress drops of earthquakes range between 0.10 and 64.49 MPa,with high values occurring on reverse faults situated at a greater distance from the shale layer,accompanied by a moderate rotation(≤25°)in the trend of σ_(H_(max)).The seismic clusters close to the shale layer exhibit low fluid overpressure thresholds,prone to being triggered by high pore-pressure fluid.The integrated results suggest that the diffusion of high pore pressures is likely to be the primary factor for observed earthquakes.The present results are expected to offer valuable insights into the origin of anomalous seismicity near the shale gas sites.
基金Australian Research Council Linkage Program(LP200301404)for sponsoring this researchthe financial support provided by the State Key Laboratory of Geohazard Prevention and Geoenvironment Protection(Chengdu University of Technology,SKLGP2021K002)National Natural Science Foundation of China(52374101,32111530138).
文摘Discrete fracture network(DFN)commonly existing in natural rock masses plays an important role in geological complexity which can influence rock fracturing behaviour during fluid injection.This paper simulated the hydraulic fracturing process in lab-scale coal samples with DFNs and the induced seismic activities by the discrete element method(DEM).The effects of DFNs on hydraulic fracturing,induced seismicity and elastic property changes have been concluded.Denser DFNs can comprehensively decrease the peak injection pressure and injection duration.The proportion of strong seismic events increases first and then decreases with increasing DFN density.In addition,the relative modulus of the rock mass is derived innovatively from breakdown pressure,breakdown fracture length and the related initiation time.Increasing DFN densities among large(35–60 degrees)and small(0–30 degrees)fracture dip angles show opposite evolution trends in relative modulus.The transitional point(dip angle)for the opposite trends is also proportionally affected by the friction angle of the rock mass.The modelling results have much practical meaning to infer the density and geometry of pre-existing fractures and the elastic property of rock mass in the field,simply based on the hydraulic fracturing and induced seismicity monitoring data.
基金financially supported by the National Key R&D Program(Nos.2023YFC3009000 and 2023YFC3006804)the National Natural Science Foundation of China(Nos.52130409,52121003,51874314,and 52274190).
文摘The hydraulic fractures induced in soft coal composite reservoirs have complex extension and energy evolution characteristics.In this study,the mechanism whereby gas outbursts can be eliminated by hydraulic fracturing was revealed.The combined fracturing process of a coal seam and its roof under different in situ stress and fracture spacing conditions was analysed through true triaxial physical tests and numerical simulations.The results showed that the pre-fracturing of the roof had a pressure relief effect on the coal seam,and the secondary pressure relief of the coal seam could be completed at a lower fracture initiation pressure.To ensure the continued presence of the stress shadow effect in actual projects,the fracture spacing should be maintained within the critical range influencing the fracture extension.If the vertical stress is high,a call on increasing the fracture spacing can be taken;otherwise,it must be reduced.In the early phase of fracturing,energy is mostly concentrated at the tip and surface of the fracture;however,the proportion of surface energy for subsequent fracturing is gradually reduced,and the energy is mostly used to open the formation and work on the surrounding matrix.Hydraulic fracturing creates new fractures to interconnect originally heterogeneously distributed gas zones,enabling the entire coal seam to first establish interconnected pressure equilibration,then undergo gradientcontrolled depressurization.Hydraulic fracturing can homogenize the stress field and gas pressure field in the original coal seam via communication pressure equalization and reduction decompression,reduce the elastic and extension energies,increase the minimum failure energy required for instability;and realize the elimination of gas outbursts.Our findings provide some theoretical support for the efficient development of coalbed methane and the prevention and control of dynamic gas disasters in coal mines.
基金financially supported by,the Fundamental Research Funds for the Central Universities(Grant No.2023QN1064)the China Postdoctoral Science Foundation(Grant No.2023M733772)Jiangsu Funding Program for Excellent Postdoctoral Talent(Grant No.2023ZB847)。
文摘Prepulse combined hydraulic fracturing facilitates the development of fracture networks by integrating prepulse hydraulic loading with conventional hydraulic fracturing.The formation mechanisms of fracture networks between hydraulic and pre-existing fractures under different prepulse loading parameters remain unclear.This research investigates the impact of prepulse loading parameters,including the prepulse loading number ratio(C),prepulse loading stress ratio(S),and prepulse loading frequency(f),on the formation of fracture networks between hydraulic and pre-existing fractures,using both experimental and numerical methods.The results suggest that low prepulse loading stress ratios and high prepulse loading number ratios are advantageous loading modes.Multiple hydraulic fractures are generated in the specimen under the advantageous loading modes,facilitating the development of a complex fracture network.Fatigue damage occurs in the specimen at the prepulse loading stage.The high water pressure at the secondary conventional hydraulic fracturing promotes the growth of hydraulic fractures along the damage zones.This allows the hydraulic fractures to propagate deeply and interact with pre-existing fractures.Under advantageous loading conditions,multiple hydraulic fractures can extend to pre-existing fractures,and these hydraulic fractures penetrate or propagate along pre-existing fractures.Especially when the approach angle is large,the damage range in the specimen during the prepulse loading stage increases,resulting in the formation of more hydraulic fractures.
基金supported by the High-level Talent Research Startup Fund(Grant No.1608722024)of Xi’an University of Archit-ectureTechnology and the Shaanxi Province High-level Youth Talents Program(Grant No.Z20240589).
文摘The recently developed SCCDS composite tube,a novel variant of the pipe-in-pipe(PIP)structure,demonstrates strong potential for subsea pipeline applications.However,theoretical research regarding its structural behavior under compression-torsion loading and bearing capacity calculations remains limited,particularly concerning the influence of dual hydraulic pressures during operation.This study examines the impact of dual hydraulic pressures on the compressive-torsional behavior of SCCDS composite tubes.A finite element(FE)model was developed and validated against experimental results,comparing failure modes,full-range loading curves,and bearing capacity to elucidate the working mechanism under dual pressures.A parametric study was then conducted to examine the effects of geometric-physical parameters.Results demonstrate that dual pressures substantially enhance the bearing capacity of sandwich concrete by increasing the normal contact stress at the interface.Increasing concrete strength(f_(c))provides minimal enhancement to torsional resistance compared to the yielding strengths of outer tube(f_(yo))and inner tube(f_(yi)).Higher diameter-to-thickness ratios of outer tube(D_(o)/t_(o))and inner tube(D_(i)/t_(i))significantly reduce torsional capacity.At 1000 m water depth,increasing the D_(o)/t_(o)ratio from 27.5 to 36.67,55,and 110 reduces bearing capacity by 11.17%,23.08%,and 36.14%respectively.Strict measures should be implemented to prevent substantial reductions in strength and ductility for SCCDS composite tubes with large hollow ratios(e.g.,χ=0.849)or high axial compression ratios(e.g.,n=0.8).The study proposes a modified calculation method for determining N-T curves that incorporates dual hydraulic pressure effects,providing guidance for performance evaluation of novel SCCDS composite tubes in deep-sea engineering.
文摘Key technologies that make productivity increase are revealed through analyzing the best practices and production data in major shale basins of North America.Trends of the key technologies and optimization designs for shale oil and gas development are summarized and analyzed based on drilling and completion operations and well data.These technologies mainly include:(1)Optimizing well design and hydraulic fracturing design,including reducing cluster spacing,increasing proppant and fracturing fluid volumes,optimizing horizontal well lateral length and fracture stage length.The most effective method is to reduce cluster spacing to an optimized length.The second most effective method is to optimally increase proppant volumes.(2)Placing horizontal wells in the sweet spots and drilling the wells parallel or close to the minimum horizontal stress direction.(3)Using cube development with optimized well spacing to maximize resource recovery and reduce well interferences.Plus,in-situ stress impacts on hydraulic fracture propagation and hydrocarbon production are addressed.Determination of formation breakdown pressure is studied by considering the impacts of in-situ stresses,drilling and perforation directions.Whether or not the hydraulic fracturing can generate orthogonal fracture networks is also discussed.The key technologies and optimization design parameters proposed in this paper can be applied to guide new well placement,drilling and completion designs,and hydraulic fracture operations to increase productivity.
文摘The performance and efficiency of hydraulic excavators heavily depend on the design and optimization of their working devices.The working device,which consists of the boom,arm,and bucket,plays a crucial role in determining the machine's digging capacity,stability,and overall operational efficiency.This paper presents a comprehensive study on the dynamics simulation and optimization of hydraulic excavator working devices.The paper outlines the fundamental principles of dynamic modeling,incorporating multi-body dynamics and hydraulic system analysis.It further explores various simulation techniques to evaluate the performance of the working device under varying operational conditions,including load and hydraulic system effects.The study also addresses performance optimization,focusing on multi-objective optimization methods that balance multiple factors such as energy efficiency,speed,and load capacity.Additionally,the paper discusses key factors influencing performance,such as mechanical design,material properties,and operational conditions.The results of the dynamic simulations and optimization analyses demonstrate potential improvements in operational efficiency and system stability,providing a valuable framework for the design and enhancement of hydraulic excavator working devices.
基金financially supported by the National Key Research and Development Plan(2023YFC2811001)the National Natural Science Foundation of China(42206233)the Taishan Scholars Program(tsqn202312280,tsqn202306297)。
文摘Hydraulic fracturing technology has played an important role in the exploitation of unconventional oil and gas resources,however,its application to gas hydrate reservoirs has been rarely studied.Currently,there is still limited understanding of the propagation and extension of fractures around the wellbore during the fracturing process of horizontal wells in hydrate reservoirs,as well as the stress interference patterns between fractures.This study simulates hydraulic fracturing processes in hydrate reservoirs using a fluidsolid coupling discrete element method(DEM),and analyzes the impacts of hydrate saturation and geological and engineering factors on fracture extension and stress disturbance.The results show that hydraulic fracturing is more effective when hydrate saturation exceeds 30%and that fracture pressure increases with saturation.The increase in horizontal stress differential enhances the directionality of fracture propagation and reduces stress disturbance.The distribution uniformity index(DUI)reveals that injection pressure is directly proportional to the number of main fractures and inversely proportional to fracturing time,with fracturing efficiency depending on the spacing between injection points and the distance between wells.This work may provide reference for the commercial exploitation of natural gas hydrates.
基金supported by the National Natural Science Foundation of China(Grant No.41825018)Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDA23090402)the National Natural Science Foundation of China(Grant No.42141009).
文摘Experimental research into the hydraulic conductivity curve (HCC) of unsaturated soil is limited due to the inherent challenge associated with labor, cost, and time. Typically, the HCC is estimated using the soil water characteristic curve (SWCC) based models and saturated hydraulic conductivity (SHC). However, the efficiency of the SWCC-based model is rarely assessed, and the influence of soil density and pore structure on HCC remains incomplete due to limited experimental data. To address this gap, this study employs an innovative filter-paper-based column method, which can measure the HCC over a wide suction range (e.g. 0−105 kPa), to capture the HCCs of both intact and compacted specimens with varying dry densities. The efficiency of two typical SWCC-based models is assessed using the measured data. Meanwhile, the mercury intrusion porosity (MIP) technique is employed to obtain the pore characteristic (i.e. pore size distribution (PSD)) and a method of predicting the HCC using the PSD data is proposed, emphasizing the dominant role of the pore structure in shaping the HCC. The results reveal that the dry density's influence on the HCC is primarily observed within the low suction range, corresponding to variations in the dominant and large pores. In the high suction range, the HCCs align along a linear trajectory when plotted in a log-log format. A notable finding is the overestimation of the HCC obtained from the SWCC-based models using the measured SHC. When the SHC is regarded as a fitting parameter, good agreement is achieved. The adjusted SHC value is typically 0-1 order of magnitude lower than the measured value, and this discrepancy diminishes as dry density increases. On the other hand, the proposed PSD-based model performs well with the measured SHC data. Caution is exercised when using the SHC to estimate the HCC for modeling water movement in partially saturated soil.
基金supported by the National Natural Science Foundation of China(Grant Nos.42227804 and 42402279)the Natural Science Foundation of Shanghai(Grant No.24ZR1467500).
文摘Due to severe mass transfer limitations,the remediation efficiency of low-permeability contaminated sites often fails to meet expectations.Hydraulic fracturing technology has been utilized to enhance amendment delivery,but the influence of soil heterogeneity is commonly overlooked.To address this issue,this study develops a numerical model to simulate the enhanced transport of amendments,incorporating convection,diffusion,adsorption,and degradation processes.Within the model,random permeability fields are generated based on geostatistical methods to explore how soil heterogeneity affects amendment injection efficiency,distribution characteristics,and the underlying physical mechanisms.The results indicate that(1)soil heterogeneity significantly reduces the amendment injection efficiency,with stronger heterogeneity correlating to lower efficiency,(2)soil heterogeneity markedly alters the amendment distribution characteristics,leading to the formation of localized“nodes”,(3)the mechanism by which heterogeneity reduces injection efficiency involves decreasing the density of preferential flow paths in the soil,and(4)the adverse effects of heterogeneity can be mitigated by employing pressure compensation or adjusting well spacing.
