Search Results (114)

Circular deep excavations, characterized by their symmetrical geometry, are commonly employed in constructing foundations for large-span suspension bridges and as launching shafts for shield tunneling. However, the mechanical behavior of such excavations under asymmetric surface surcharge remains inadequately understood due to a paucity of relevant investigations. This study addresses this knowledge gap by establishing a three-dimensional finite element model (3D-FEA) based on the anchor deep excavation project of a specific bridge. The model is utilized to investigate the influence of asymmetric surcharge on the forces and deformations within the supporting structure. The results show that both the internal force and displacement cloud diagrams of the support structure exhibit asymmetric characteristics. The distribution of displacement and internal forces has spatial effects, and the maximum values all occur in the areas where asymmetric loads are applied. The maximum values of the displacement, axial force, and shear force of underground continuous walls increase with the increase in the excavation depth. The total displacement curves all show the feature of a “bulging belly”. The maximum displacement is 13.3 mm. The axial force is mainly compression, with a maximum value of −9514 kN/m. The maximum positive and negative values of the shear force are 333 kN/m and −705 kN/m, respectively. The bending moment diagram of different monitoring points shows the characteristics of “bow knot”. The maximum values of the positive bending moment and negative bending moment are 1509.4 kN·m/m and −2394.3 kN·m/m, respectively. The axial force of the ring beam is mainly compression, with a maximum value of −5360 kN, which occurs in ring beams 3, 4, and 5. The displacement cloud diagram of the support structure under symmetrical loads shows symmetrical characteristics. Under different load conditions, the displacement curve of the diaphragm wall shows the characteristics of “bulge belly”. The forms of loads with displacements from largest to smallest at the same position are as follows: asymmetric loads, symmetrical loads, and no loads. These findings provide valuable insights for optimizing the structural design of similar deep excavation projects and contribute to promoting sustainable urban underground development. Full article

In this study, we examined the microclimates at eight entrances to a karst system distributed between an elevation of 812 and 906 m in Southern Spain. The karst system, characterised by subvertical open tectonic joints that form narrow shafts, developed on the slope of a mountainous area with a Mediterranean climate and strong chimney effect, resulting in an intense airflow throughout the year. The airflows modify the entrance temperatures, creating a distinctive pattern in each opening that changes with the seasons. The objective of this work is to characterise the outflows and find simple temperature-based parameters that provide information about the karst interior. The entrances were monitored for five years (2017–2022) with temperature–humidity dataloggers at different depths. Other data collected include discrete wind measurements and outside weather data. The most significant parameters identified were the characteristic temperature (T_y), recorded at the end of the outflow season, and the rate of cooling/warming, which ranges between 0.1 and 0.9 °C/month. These parameters allowed the entrances to be grouped based on the efficiency of heat exchange between the outside air and the cave walls, which depends on the rock-boundary geometry. This research demonstrates that simple temperature studies with data recorded at selected positions will allow us to understand geometric aspects of inaccessible karst systems. Dynamic high-airflow cave systems could become a natural source of evidence for climate change and its effects on the underground world. Full article

Double-suction centrifugal pumps are extensively employed in industrial applications owing to their high efficiency, low vibration, superior cavitation resistance, and operational durability. This study analyzes how impeller oblique cutting angles (0°, 6°, 9°, 12°) affect a double-suction pump at a fixed 4% trimming ratio and constant average post-trim diameter. Numerical simulations and tests reveal that under low-flow (0.7Q_d) and design-flow conditions, the flat-cut (0°) minimizes reflux ratio and maximizes efficiency by aligning blade outlet flow with the mainstream. Increasing oblique cutting angles disrupts this alignment, elevating reflux and reducing efficiency. Conversely, at high flow (1.3Q_d), the 12° bevel optimizes outlet flow, achieving peak efficiency. Pressure pulsation at the volute tongue (P11) peaks at the blade-passing frequency, with amplitudes significantly higher for 9°/12° bevels than for 0°/6°. The flat-cut suppresses wake vortices and static–rotor interaction, but oblique cutting angle choice critically influences shaft-frequency pulsation. Entropy analysis identifies the volute as the primary loss source. Larger oblique cutting angles intensify wall effects, increasing total entropy; pump chamber losses rise most sharply due to worsened outlet velocity non-uniformity and turbulent dissipation. The flat-cut yields minimal entropy at Q_d. These findings provide a basis for tailoring impeller trimming to specific operational requirements. Furthermore, the systematic analysis provides critical guidance for impeller trimming strategies in other double-suction pumps and pumps as turbines in micro hydropower plants. Full article

Cylindrical retaining structures are widely adopted in intercity railway tunnel engineering due to their exceptional load-bearing performance, no need for internal support, and efficient utilization of concrete compressive strength. Measured deformation data not only comprehensively reflect the influence of construction and hydrogeological conditions but also directly and clearly indicate the safety and stability status of structure. Therefore, based on two geometrically similar cylindrical shield tunnel shafts in Shenzhen, the surface deformation, structure deformation, and changes in groundwater outside the shafts during excavation were analyzed, and the deformation characteristics under the soil–rock composite stratum were summarized. Results indicate that the uneven distribution of surface surcharge and groundwater level are key factors causing differential deformations. The maximum horizontal deformation of the shafts wall is less than 0.05% of the current excavation depth (H), occurring primarily in two zones: from H − 20 m to H + 20 m and in the shallow 0–10 m range. Vertical deformations at the wall top are mostly within ±0.2% H. Localized groundwater leakage in joints may lead to groundwater redistribution and seepage-induced fine particle migration, exacerbating uneven deformations. Timely grouting when leakage occurs and selecting joints with superior waterproof sealing performance are essential measures to ensure effective sealing. Compared with general polygonal foundation pits, cylindrical retaining structures can achieve low environmental disturbances while possessing high structural stability. Full article

A localized freezing technique was proposed as an auxiliary method for retrofitting the lining of a vertical shaft. The influence of the freezing temperature, lining thickness, slot height, and slot duration on the evolution of the freezing wall in the clay layer was analyzed using a hydro-thermal numerical model. Under the baseline conditions (stratum temperature of 24 °C, shaft lining thickness of 2 m, and freezing temperature of −30 °C), the freezing wall behind the slotting zone was 0.74 m at 90 d, 1.89 m at 180 d, 2.78 m at 270 d, and 3.48 m at 360 d. The average growth rate of the freezing wall during one year was negatively linearly correlated with the freezing temperature and the shaft lining thickness, with change rates of −0.00033 m/(d∙°C) and −0.00262 m/(d∙m), respectively. Using the thickness of the freezing wall behind the slotting zone to reach 1.2 m as the slotting criterion, a freezing duration of 123 days is required under typical operational parameters. The evolution of the freezing wall was simulated for a slotting duration of 15 d with a slot height of 0.5–2.0 m and for a slot height of 1.5 m with a slotting duration of 5–20 d. The freezing walls did not melt in both schemes and expanded outward. The research findings are significant for improving freezing methods for shaft linings. Full article

To address the frequent failure of anti-falling devices in inclined shaft tunnel boring machines caused by cyclic loading and fatigue during construction, this study proposes an optimized self-responsive anti-falling device design. Based on the operational conditions of the “Tianyue” tunnel boring machine, a three-dimensional model was constructed using SolidWorks. Finite element static analysis was employed to validate structural integrity, revealing a maximum stress of 461.19 MPa with a safety factor of 1.71. Explicit dynamic simulations further demonstrated the dynamic penetration process of propellant-driven telescopic columns through concrete lining walls, achieving a penetration depth exceeding 500 mm. The results demonstrate that the device can respond to falling signals within 12 ms and activate mechanical locking. The Q690D steel structure exhibits a deformation of 5.543 mm with favorable stress distribution, meeting engineering safety requirements. The energy release characteristics of trinitrotoluene propellant and material compatibility were systematically verified. Compared to conventional hydraulic support systems, this design offers significant improvements in response speed, maintenance cost reduction, and environmental adaptability, providing an innovative solution for fall protection in complex geological environments. Full article

To accurately investigate the stress and deformation behavior of support structures during mechanical shaft construction, this study proposes an analytical method for active earth pressure calculation based on limit equilibrium theory, incorporating both the radial variation of the circumferential stress coefficient and the spatial arching effect. Considering the entire sliding soil mass behind the shaft wall as the analytical object, the inclination angle of the sliding surface under active limit conditions is derived. Subsequently, by incorporating interlayer shear forces, a horizontal layer analysis is employed to establish the vertical and radial force equilibrium equations, leading to the formulation of an active earth pressure model for circular shafts. Furthermore, based on elastic mechanics theory, a corresponding method is developed to calculate the internal forces of the shaft structure. The theoretical predictions show good agreement with existing model test results and field monitoring data, demonstrating the accuracy and reliability of the proposed approach. The findings provide a theoretical basis for optimizing the design of circular shafts and assessing the structural stability of shaft walls. Full article

The use of the vertical shaft sinking machine (VSM) for shaft construction can effectively improve construction safety and efficiency. This study focused on analyzing the internal forces and deformation characteristics of a 50.3 m deep shaft constructed by the VSM method. Findings reveal that the external pressure of the shaft is positively correlated with the excavation depth, increasing as the depth grows. Pumping water inside the shaft disrupts the balance of the soil behind it, leading to a reduction in the external pressure of the shaft wall. During the excavation and sinking stage, the bottom connecting beam mainly endures compression. After water pumping, the coupling and restrictive effect between the bottom connecting beam and the shaft wall strengthens, significantly boosting the internal compressive stress. The stress states of the segments above and below the shaft vary: the upper segments are under pure compression, while the lower ones may experience uneven deformation due to multiple factors. Moreover, the cast-in-place piles and surrounding stratum show a “bulging” deformation pattern during sinking, greatly influenced by the shaft’s attitude deviation, whereas grouting at the shaft bottom and internal water pumping have minimal impact on the surrounding stratum. Full article

The rapid advancement of modern megapolises has led to a dearth of surface space, and, in response, engineers have begun to trial substitutes below ground level. Shafts are generally used to provide temporary access and permanent work to the subsurface for tunnelling, as well as for lifts or ventilation purposes. In urban areas, one important design issue is the prediction of the excavation-induced displacements by open caisson shaft construction. Settlements and ground movements associated with open caisson shafts are influenced by the choice of construction method, soil composition, and excavation geometry. Compared with other geotechnical construction events, for instance, tunnelling, the literature relating to the ground deformations induced from open caisson shafts are comparatively limited. This review offers an evaluation of several case studies that utilize experimental and computational modeling techniques to provide clearer insights into earth pressure distribution and induced surface and subsurface soil displacements, as well as the associated ground deformations during open caisson shaft construction. The modeling test results are compared to the state of the practice ground deformation prediction theories and measured results from field monitoring data. Findings indicate that the lateral earth pressure distribution aligns closely with the theoretical predictions based on Terzaghi’s and Berezantzev’s models, and lateral earth pressure diminishes gradually until the onset of active wall displacement. Current modeling techniques generally fail to properly represent in situ stress states and large-scale complexities, emphasizing the need for hybrid approaches that combine physical and numerical methodologies. In future studies, modern approaches, including artificial intelligence (AI) monitoring (e.g., PINNs, ACPP), multi-field coupling models (e.g., THMC), and transparent soil testing, hold profound potential for real-time prediction, optimization, and visualization of soil deformation. Numerical–physical coupling tests will integrate theory and practice. Improving prediction reliability in complicated soil conditions such as composite and heterogenous strata using different modeling techniques is still unclear, and further investigation is therefore needed. Full article

Grains stored in silos and pellets for injection molding deteriorate in quality due to increased moisture in the particles when exposed to air for a long period of time, so it is necessary to reduce the moisture in the particles through the mixing process. However, few studies have conducted parallel experiments and simulations to understand the behavior of particles depending on their moisture content. In this study, mixing experiments were conducted using superabsorbent polymer (SAP) beads that expand depending on the moisture content, and the interparticle friction coefficient and interface friction coefficient required for simulation were derived. As a result, it was found that moisture generates an adhesive force that causes interparticle cohesion, and as the moisture content increases further, the particles adhere to the vessel wall due to the adhesive force. In addition, particles with high moisture content (e.g., 90%) showed faster mixing behavior similar to dry particles, as indicated by the Lacey Mixing Index (LMI), while low moisture particles (e.g., 60%) showed the slowest mixing. It is expected that the mixing characteristics of particles depending on the moisture content can be understood and will be useful for the design of horizontal shaft mixers. Full article

To address the issues of low shear strength, susceptibility to eccentricity, and alignment difficulties in post-inserted core piles, a new type of steel tube concrete integrated mixing composite pile has been independently developed. This pile type replaces the conventional mixing pile shaft with a larger diameter steel tube equipped with mixing blades. After forming the external annular cement mixing pile, the steel tube is retained, and the hollow core is filled with concrete. To thoroughly explore the vertical compressive bearing characteristics of the steel tube concrete mixing composite pile and clarify its vertical compressive behavior, static load field tests and PLAXIS 3D finite element numerical simulations were conducted on four test piles of different sizes to analyze the vertical bearing performance of the steel tube concrete mixing composite pile. The research results indicate that for a composite pile with a length of 40 m, an outer diameter of 1000 mm, and a steel tube diameter of 273 mm, the ultimate bearing capacity of a single pile is 7200 kN, with the steel tube concrete core contributing approximately 81% of the vertical bearing capacity, while the cement mixing pile contributes around 19%. Based on the characteristic that the maximum axial force is concentrated in the upper half of the pile length, an innovative variable-diameter design with a reduced wall thickness of the steel pipe in the lower part of the pile was proposed. Practical verification has shown that, despite the reduced material usage, the load-bearing capacity remains largely unchanged. This effectively validates the feasibility of the “strong upper part and weak lower part” design concept and provides an effective way to reduce construction costs. Full article

In this study, a novel ocean current energy converter is proposed. The energy converter is composed of two crossflow turbines. The two turbines rotate at the same speed but in opposite directions; therefore, the summation of the hydrodynamic torques applied to the two turbines is equal to zero, which can make the converter self-stabilizing. A channel is designed to guide a large amount of water flowing through the turbine, thereby increasing the incident velocity, power, and efficiency of the turbine. The guide vanes are positioned in front of the turbine to guide the ocean current, producing the optimal flow incident angle and thereby increasing the performance of the turbine. A novel empirical formula for determining the power and efficiency of the converter is derived. Moreover, a computational fluid dynamics (CFD) analysis of the energy converter is conducted using the commercial software Star CCM+ in the standard κ-ω turbulence model with wall functions. The accuracy of the empirical formula is verified by comparing the theoretical results with those obtained using the CFD method. Finally, the effects of several parameters on the performance of the energy converter are investigated. The optimal parameters are obtained as follows: (1) The optimal setting angles of vanes γ₁ = 78°, ${\gamma }_2={\gamma }_1+10°$, and ${\gamma }_3={\gamma }_1-5°$. (2) The optimal blade angle β = 44°. (3) The optimal rotating speed N = 2.6 (V_cur/1.6) rpm. (4) The optimal ratio of turbine center distance r_L4 ≥ 2.50. (5) The optimal ratio of turbine shaft length is approximately 5.5 < (r_shaft = W_shaft/D_tur)_opt < 5.7. (6) The performance of each turbine with N_blade = 31 blades is significantly better than that with N_blade = 23 blades. Full article

This work studies heat transport in the fluid–solid interface of a packed bed to demonstrate the feasibility of preheating lumpy manganese ores to 600 °C with air at 750 °C. Preheated manganese ores aim to reduce furnace energy consumption during smelting in submerged arc furnaces to produce manganese ferroalloys. The preheating process was experimentally studied in a pilot-scale shaft-type column. The air was heated to 750 °C and used as a heat transfer fluid to heat a packed bed of manganese ore from room temperature to 600 °C. A one-dimensional three-phase (manganese ore, air, and the column wall) numerical model was developed to simulate the preheating process. The energy balance of the three phases was carried across a finite volume using the volume averaging technique. Numerical schemes were applied, and non-dimensional parameters were introduced before applying numerical techniques to solve the systems of linear equations. Python NumPy and SciPy modules were used for the computation of the packed bed temperature fields. Temperature data from the preheating tests were used for model validation. The model prediction of the transfer process agreed with experimental results to least square errors of less than 25 °C. Data from experimental measurements confirmed the feasibility of using air as the transfer fluid in the preheating of manganese ore. Detailed temperature field data generated from the model can be used for the sizing of manganese ore preheating units and the implementation of control protocols for the preheating process. Full article

The geometry of the ladle bottom and the position of stirring paddles during hot metal stirring significantly influence hydrodynamic characteristics, thereby affecting desulfurization efficiency. Water model experiments and hydrodynamic simulations were conducted to investigate the effects of ladle structures and stirrer positions on the flow field and mixing characteristics in hot metal desulfurization. The results indicate that ladles with a spherical-bottom structure effectively reduced the “dead zone” volume in the hot metal flow. In the water model tests, the mixing time for the spherical-bottom ladle was reduced by 22.5% and 20% at different stirring paddle speeds compared to the flat-bottom ladle, facilitating the better dispersion of the desulfurization agents. The hot metal flow velocities in all directions were also superior in spherical-bottom ladles. Under identical conditions, eccentric stirring generated shallower and broader vortices, with the vortex center offset from the stirring shaft axis, thereby minimizing the risk of “air entrainment” associated with high-speed central stirring. During eccentric stirring, the flow-field distribution was uneven, and the polarization of the stirrer was observed in the water model, whereas central stirring revealed a more uniform and stable flow field, reducing the risk of paddle wear and ladle wall erosion. Central stirring exhibits distinct advantages in the desulfurization process, whereas eccentric stirring is exclusively applicable to metallurgical modes requiring a rapid enhancement of bottom flow and localized rapid dispersion of desulfurizing agents. Full article

In deep foundation pit engineering, the soil undergoes a complex stress path, encompassing both loading and unloading phases. The Shanghai model, an advanced constitutive model, effectively accounts for the soil’s deformation characteristics under these varied stress paths, which is essential for accurately predicting the horizontal displacement and surface settlement of the foundation pit’s enclosure structure. This model comprises eight material parameters, three initial state parameters, and one small-strain parameter. Despite its sophistication, there is a scarcity of numerical studies exploring the correlation between these parameters and the deformation patterns in foundation pit engineering. This paper initially establishes the superiority of the Shanghai model in ultra-deep circular vertical shaft foundation pit engineering by examining a case study of a nursery circular ultra-deep vertical shaft foundation pit, which is part of the Suzhou River section’s deep drainage and storage pipeline system pilot project in Shanghai. Subsequently, utilizing an idealized foundation pit engineering model, a comprehensive sensitivity analysis of the Shanghai model’s multi-parameter values across their full range was performed using orthogonal experiments. The findings revealed that the parameter most sensitive to the lateral displacement of the underground continuous wall was κ, with an increase in κ leading to a corresponding increase in displacement. Similarly, the parameter most sensitive to surface subsidence outside the pit was λ, with an increase in λ resulting in greater subsidence. Lastly, the parameter most sensitive to soil uplift at the bottom of the pit was also κ, with an increase in κ leading to more significant uplift. Full article