Search Results (5,255)

To address the delayed strength development and uncertain rock-backfill interfacial stability of total-tailings paste backfill under low-temperature underground conditions, this study aims to quantify the coupled effects of slurry mass concentration, cement/tailing (C/T) ratio, curing temperature, and curing age on uniaxial compressive strength, and to clarify how interface roughness and curing age govern interfacial shear behavior and field strength. A silver–lead–zinc mine in Inner Mongolia was selected as the engineering background, and uniaxial compression, double-sided shear, SEM, and in situ strength tests were conducted. Results show that UCS increased with curing temperature, curing age, slurry mass concentration, and C/T ratio within the investigated ranges, with the comparative influence following the order: C/T ratio > curing age > curing temperature ≈ slurry mass concentration. With age, hydration products increased, pores and microcracks decreased, and structure densified. When joint roughness coefficient (JRC) increased from 0 to 26.76, cohesion rose from 93.31 to 965.57 kPa, and the failure mode shifted from interface slip to backfill shear. Increasing age from 3 to 7 d raised cohesion from 611.02 to 965.57 kPa and the internal friction angle from 29.09 ° to 33.98 °. Optimal conditions were 66 % concentration and 15 ℃, with C/T ratios of 1:4 (adhesive layer) and 1:8 (ordinary layer). Test results under various ratios and ages all indicate that the underground backfill has attained early self-standing and bearing capacity. Full article

The tunnel portal section is one of the most seismically vulnerable parts of a tunnel, where strong earthquakes may trigger slope instability and induce plastic damage in the tunnel lining. Based on viscous-spring artificial boundary theory, a seismic oblique-incidence method applicable to tunnel portal sections is developed by incorporating the effects of slope topography. A three-dimensional finite element model is then established to investigate the seismic response and damage mechanisms of the tunnel portal section subjected to obliquely incident SV waves. The numerical calculation results in this study indicate that fully connected plastic deformation zones eventually develop in both the original slope site and the slope site with a tunnel structure, leading to slope instability characterized by downward sliding of the rock mass along a slip surface. However, in the presence of a tunnel structure, plastic deformation initiates simultaneously at the slope toe and near the tunnel portal. The maximum plastic strain is concentrated near the tunnel portal. Both topographic amplification and the accumulation of sliding debris markedly aggravate lining damage. The seismic-wave incidence angle, ground conditions and seismic-wave spectral characteristics all have pronounced effects on plastic deformation in both the slope site and tunnel lining at the tunnel portal section. In addition, tensile damage is more pronounced and extends over a wider area than compressive damage. At shear-wave velocities of 450–550 m/s in the upper soft-rock site, the damage zone is approximately two to three times the horizontal projection length of the slope, which is identified as the primary damage zone and should be regarded as a key seismic fortification area in tunnel design. Full article

In high-water-cut inclined gathering pipelines, shutdown may lead to blockage due to the flotation and wall slip of gelled crude oil. This study investigates the slip behavior and critical conditions of gelled crude oil particles on an inclined pipe wall through visualization experiments, mechanical analysis, and the Extended Derjaguin–Landau–Verwey–Overbeek (XDLVO) theory and develops a method for calculating pipeline restart pressure. Experiments conducted using four crude oil samples identified three post-floating behaviors: adhesion, adhesion–slip, and bulk floating aggregation. The measured critical slip temperatures of samples 1#–4# were 33, 29, 36, and 37 °C, respectively, corresponding to 1–2 °C below their gel points. Adhesion represents a safe shutdown condition, whereas adhesion–slip and bulk floating aggregation indicate a risk of oil accumulation and blockage. When the temperature falls below the critical slip temperature, the gelled oil remains stably adhered to the pipe wall. A critical slip temperature prediction model was established using the gel point, oil–water density difference, and wax content as input parameters. The model produced absolute errors of 0.1–0.6 °C, with a mean absolute error of 0.4 °C. By coupling the Sukhov temperature-drop equation with the mechanical equilibrium equation, a restart-pressure calculation tool was developed. For two field restart cases, the predicted pressures showed relative errors of 6.45% and 7.70%, with a maximum absolute error of 0.06 MPa. The proposed method provides a preliminary quantitative tool for shutdown risk assessment, low-temperature transportation boundary determination, and restart-pressure estimation in high-water-cut inclined gathering pipelines. Full article

Background/Objectives: Indirect decompression through restoration of disc and foraminal height with a large lateral interbody cage has been advocated for selected patients, but its efficacy in a large series remains unproven. In this retrospective study, we evaluated the clinical and radiographic results of indirect decompression achieved by posterior longitudinal ligament (PLL) ligamentotaxis in minimally invasive oblique lateral interbody fusion (MIS-OLIF) performed without posterior decompression. Methods: We retrospectively reviewed 236 consecutive patients treated for single- or two-level degenerative lumbar disease (November 2019–May 2025); clinical follow-up of at least 24 months was available in 181 patients. Visual analogue scale (VAS) scores and radiographic parameters—disc height, foraminal height, foraminal area, spinal canal diameter and cross-sectional area (CSA) of the thecal sac—were compared before and after surgery, and extension ratios were correlated with preoperative values. Results: Clinical scores improved significantly. All radiographic parameters increased substantially: disc height +49.1%, foraminal height +33.7%, foraminal area +44.5%, canal diameter +37.4% and CSA +36.2%. Extension ratios were inversely correlated with preoperative values. Six patients (2.5%) required additional posterior decompression. The slippage subgroup showed greater radiographic gains than the stenosis subgroup. Conclusions: MIS-OLIF without posterior decompression significantly enlarged the foramen and spinal canal; reduction in disc bulging and PLL ligamentotaxis may contribute to this effect, with greater improvement in more severely degenerated, overtly slipped segments. Careful patient selection remains essential, and prospective comparative studies with longer follow-up are needed. Full article

Monolithic precast reinforced concrete (RC) frames with cast-in-place joint cores and grouted-sleeve splices are increasingly adopted in seismic regions, yet connection degradation is not carried through to system-level fragility: existing studies take hinge properties from code tables or one test, or stop at the joint. This study closes that gap with a reproducible transfer route in which the degrading, pinched M–θ hysteresis identified from a refined joint model becomes structure-level hinge parameters, with every intermediate quantity reported so that the route can be reproduced elsewhere. The joint model is an explicit finite-element interface-spring/contact strategy with Mohr–Coulomb interface behavior, tension cut-off, local spring failure, and sleeve–grout–rebar bond slip. Incremental dynamic analysis and fragility assessment of a six-story monolithic precast frame and a comparable cast-in-place frame show larger inter-story drift demands in the precast frame. At PGA = 0.40 g, its collapse exceedance probabilities are higher by 0.73 and 0.44 percentage points in X and Y, respectively. Global performance is broadly comparable, but the precast frame shows a consistent, modest unfavorable tendency caused by connection pinching and reduced ultimate rotation. Interface treatment, sleeve grouting quality, and connection-level ductility should therefore be explicitly considered in seismic performance assessment and design. Full article

Autonomous drifting requires coordinated steering and driving actuation near the tire friction limit, where strong tire nonlinearity and rapidly changing constraints challenge control accuracy and real-time solvability. This article proposes an equilibrium-free successive convexification (SCvx) nonlinear model predictive control framework for drift tracking under constant and varying curvature conditions. The front steering angle and rear-axle longitudinal force are optimized jointly subject to actuator, state, and tire-force constraints. A physics-guided MLP residual tire model is introduced to improve rear-tire-force prediction. Online reference generation determines the heading error, yaw rate, and rear longitudinal force targets from path curvature, lateral error, sideslip variation, and rear slip ratio error, eliminating the need for precomputed drift equilibria. SCvx converts the nonlinear predictive control problem into convex subproblems using virtual control, slack variables, and trust regions. Hardware-in-the-loop experiments confirm stable actuator coordination under both test conditions. Under varying curvature drifting, the proposed method reduces lateral error, velocity error, and yaw rate error by 39.2%, 53.7%, and 24.9%, respectively, compared with the Fiala tire model using the same solver. The results demonstrate improved tracking accuracy and numerical robustness for constrained autonomous drift control. Full article

Maritime transport is a major component of global supply chains, but reducing its atmospheric emissions remains essential to improving the environmental sustainability of shipping. This study analyzes onboard emission data reported for the MV Ilshin Green Iris under real-world operating conditions to assess how fuel selection affects the direct-emission performance of a dual-fuel marine propulsion system. The vessel is equipped with a MAN B&W 6G50ME-C9.5-GI engine employing high-pressure dual-fuel (HPDF) technology. A quantitative comparison between heavy fuel oil (HFO) and liquefied natural gas (LNG) was performed at 50% of the maximum continuous rating (MCR). At 50% MCR, LNG reduced CO₂ emissions by 27.0%, NOx emissions by 20.7%, and CO emissions by 18.2% relative to HFO, while PM showed an indicative reduction of approximately 69%; its precise magnitude remains uncertain because a complete PM uncertainty budget was unavailable. Over the 900 s measurement period, the estimated reduction in CO₂ mass was 154 kg. During LNG operation, the specific CH₄ emission at 50% MCR was approximately 0.6 g/kWh. Using a 100-year global warming potential of 29.8 for fossil CH₄, this corresponds to approximately 17.9 g CO₂-eq/kWh, equivalent to about 10.5% of the direct CO₂ reduction between HFO and LNG at this operating point. The results are representative of the analyzed stabilized operating point rather than of the vessel’s complete operational profile. The main contribution of this study is a structured matched-load analysis of HFO and LNG emissions from the same HPDF marine engine. The analysis combines measurement-derived specific emissions with energy-based mass estimates, methane-related limitations, data-quality considerations, and regulatory and sustainability implications. Because both fuels were evaluated in the same engine at the same 50% MCR operating point, the study provides a consistent basis for assessing fuel-related differences within the limits of the available dataset. Full article

To evaluate the influence of fiber content, temperature, and loading rate on the dynamic compression performance of ultra-high performance concrete (UHPC), orthogonal Split Hopkinson Pressure Bar (SHPB) tests were performed on 120 MPa UHPC specimens. Range analysis of the test data reveals that the steel fiber content exerts the largest range on dynamic compressive strength, with loading rate ranking second and temperature having the least effect. A three-dimensional mesoscopic finite element model that accounts for temperature-dependent behavior was developed using a modified Karagozian & Case (K&C) constitutive model together with high-temperature bond–slip degradation curves. The simulated peak stresses are generally higher than the experimental values, with a Root Mean Square Error of 9.02 MPa, a Normalized Root Mean Square Error of 4.65%, and a maximum discrepancy of 10.07%, while the major experimental failure characteristics are reasonably reproduced. Additional numerical simulations indicate that the influence of steel-fiber content becomes increasingly temperature-dependent. Within the experimentally investigated range up to 300 °C, higher fiber content generally improves dynamic response and specimen integrity. At 600~800 °C, the numerical extrapolations suggest that the reinforcing efficiency of steel fibers may be substantially reduced under the assumed temperature-dependent degradation conditions. These high-temperature trends require further experimental validation. Full article

Steel–concrete composite beams offer significant advantages in long-span, heavy-load, and prefabricated construction; however, the concrete slabs are prone to tensile cracking under negative bending moments. To enhance cracking resistance, uplift-restricted and slip-permitted (URSP) perfobond rib (PBL) connectors were adopted with a cast-in-place high-performance concrete (HPC) topping. Five composite beam-steel column joint specimens were tested under quasi-static cyclic loading. The test variables included connector type, cast-in-place concrete type, and reinforcement grade. In addition, refined numerical simulations were conducted on the test specimens. Both test and numerical results show that: (1) The combined application of URSP-PBL connectors and HPC enhanced the cracking resistance of the composite beam, with the initial cracking load and corresponding cracking displacement increased by approximately 50% compared with the control specimen. (2) The ultimate flexural capacity of the composite beams under negative moments showed limited sensitivity to the type of cast-in-place concrete topping and the reinforcement grade within the tested range. (3) The use of URSP-PBL connectors improved the flexural stiffness of the composite beams. (4) The URSP-PBL specimens showed good energy dissipation capacity under cyclic loading, which was further improved with the addition of HPC in the topping. Within the tested range, the reinforcement grade showed limited influence on this performance. This study provides a scientific basis for the crack control design and engineering application of long-span composite beams. Full article

Global labour shortages in the agricultural sector, combined with diminishing arable land and a growing population, are driving investment in autonomous agricultural machinery. Autonomous systems that can navigate crop environments and perform planting, treatment, and harvesting alongside humans are required, but the gap between published research and commercially deployed systems remains wide across most operational scenarios. Why are agricultural robots still not widely deployed in real farms despite decades of research in autonomous navigation and path planning, and what is preventing full farm autonomy? This paper reviews the principal enabling technologies for autonomous agricultural integration, with a specific focus on path planning as the differentiator between research-stage and deployed systems. Current research in human–robot integration, open-field navigation, row identification and following, crop sensing, and power efficiency is synthesised and evaluated against a deployability criterion. A Deployability Assessment Framework is introduced, comprising structured tables that assign Technology Readiness Levels to twelve path-planning families and benchmark eleven commercial and research platforms against field-validated accuracy data. The analysis shows that point-to-point GNSS navigation has reached TRL 9 with over one million commercial units deployed, vision-based crop row following is at TRL 5–7 depending on crop and season, and whole-farm autonomy with dynamic re-planning is at TRL 3–5. The primary barriers are the absence of standardised evaluation benchmarks, the failure of perception models to generalise across seasons and crop types, and the decoupling of terrain and slip feedback from global path planners. Our review reveals that open-field GNSS navigation is commercially mature, but true whole-farm agricultural autonomy remains unsolved because current systems are not robust enough across seasons, terrain, sensing conditions, and operational transitions. Full article

Coal-fired power plants equipped with selective catalytic reduction (SCR) and wet flue-gas desulfurization (WFGD) can co-control mercury, but performance is limited by incomplete upstream Hg⁰ oxidation and downstream re-emission. This study evaluated a 660 MW unit using gas-, liquid-, and solid-phase measurements and coordinated single-factor and coupled operating tests. Under baseline conditions, SCR Hg⁰ oxidation was 31.66%, WFGD Hg²⁺ capture was 73.79%, and net mercury removal was 31.08%, with a stack Hg^T concentration of 4.70 µg/Nm³. Coupled optimization increased SCR Hg⁰ oxidation to 69.76% and WFGD Hg²⁺ capture to 96.05%, reduced the re-emission index from 0.596 to 0.250, and raised net removal to 70.83%. SCR inlet temperature, equivalent space velocity, and catalyst health were the dominant upstream factors, while S(IV), oxidation–reduction potential (ORP), slurry pH, and oxidation air supply governed downstream stabilization. A practical operating window was identified near 340 °C, with a normalized stoichiometric ratio (NSR) of approximately 1.0, high ammonia injection uniformity, pH of 5.5–6.0, ORP of approximately 200 mV, and S(IV) of approximately 2 mmol/L. The results show that coordinated operation of existing SCR–WFGD equipment can substantially reduce stack mercury without dedicated mercury-control hardware, provided that NH₃ slip, SO₃-related risk, catalyst condition, and absorber stability are simultaneously constrained. Full article

Under out-of-plane loading, composite sandwich wall panels may develop relative slip between the wythes and end slip at the intermediate-layer interface, weakening composite action and flexural stiffness. Previous studies have mainly focused on bearing capacity and connector performance, while the complete slip-development process, parameter effects, and quantitative slip-warning indicators remain insufficiently investigated. To investigate the flexural slip mechanism and design control method, three one-way composite sandwich wall panels with different wythe thicknesses, reinforcements, and stiffness ratios were tested under four-point bending. The load–deflection response, crack development, relative slip, and end slip were recorded. The measured slip values were normalized by the midspan yield deflection to obtain the absolute slip ratio, relative slip ratio, and end slip ratio. The results show that both the relative slip between the inner and outer wythes and the end slip exhibit a three-stage evolution with increasing load: almost no slip before cracking, approximately linear development after cracking, and rapid increase after yielding. The stiffness matching of the inner and outer wythes and the thickness of the intermediate layer are important factors affecting slip development. Based on the test results and comparison with existing experimental data, the yielding stage is recommended as the slip-warning control point, with warning values of 0.03 for the relative slip ratio and 0.06 for the end slip ratio. Finally, a simplified model based on partial composite action theory was established using binary linear regression and the least-squares method. The model achieved a centered $R^2$ of 0.937, while the slip influence coefficient increased from 2.4–8.8% at yielding to 30.3–66.0% at the peak stage, quantitatively supporting yielding-stage warning control. Full article

Metal-plate-connected (MPC) joints govern the stiffness and load-bearing performance of many prefabricated timber roof trusses, yet their response to repeated moisture changes remains critical for serviceability and durability. This study evaluated five continuous C24 Norway spruce reference specimens and fifteen specimens joined with GNA20-MIT nail plates using sequential four-point-bending stiffness measurements and wetting–drying conditioning. Test I was used as the initial stiffness stage, whereas Tests II and III followed successive 24 h water-immersion and 6-day natural-drying intervals; the specimens were subsequently tested to failure. The mean apparent modulus of elasticity of the MPC specimens decreased from 1.39 to 1.22 GPa (approximately 12%), but a Friedman repeated-measures test did not show a statistically significant stage effect (χ²(2) = 4.13, p = 0.127). Because the same specimens were repeatedly loaded, and no unexposed MPC control group was included, this change cannot be attributed exclusively to moisture cycling. In the primary analysis retaining all 15 MPC specimens, the mean apparent bending strength of the connected elements was 16.92 MPa, compared with 34.14 MPa for the structurally different continuous reference specimens; excluding M7 yielded 17.87 MPa only as a sensitivity analysis. Failure of the connected specimens was progressive and dominated by plate slip and partial spike withdrawal, whereas solid specimens failed more abruptly in bending. The results therefore support attention to connection flexibility and serviceability under variable environmental and loading histories, while further controlled testing is required to isolate the specific contribution of moisture cycling. Full article

Four full-scale exterior beam-to-column connections comprising H-section beams and square hollow-section (SHS) columns were tested under low-cycle reversed loading to investigate two engineering-oriented T-stub section configurations and the effects of the presence or absence of triangular stiffeners. Failure modes, moment–rotation response, stiffness degradation, energy dissipation, and cumulative damage were evaluated, together with nonlinear finite element simulations and a modified Park–Ang damage assessment. All specimens progressed from bolt-hole slip through plastic deformation to localized fracture. In the unstiffened connections, damage concentrated near the T-stub flange-to-web junction; stiffeners redistributed critical demand toward the stiffener welds, adjacent T-stub webs, and SHS column walls. The maximum differences in initial rotational stiffness relative to J1A were 15.69% and 15.07% in the positive and negative loading directions, indicating that the elastic-stage response reflected the combined deformability of the T-stub, blind-bolt assembly, and column wall. The maximum increases in yield moment, peak-resistance moment, and ductility coefficient were 20.59%, 43.71%, and 45.91%, respectively. Complete-history energy dissipation varied non-monotonically across the tested configurations. The finite element model reproduced the global and local responses, while the damage-index results showed overall correspondence with the observed failure progression. The findings emphasize stiffness compatibility and rational distribution of plastic demand rather than maximum local stiffness. Full article

Concrete-faced rockfill dams (CFRDs) constructed in narrow and steep valleys are strongly influenced by the mechanical interaction between the dam body and abutment bedrock. Under long-term construction and reservoir impoundment, time-dependent frictional slip along the dam–abutment interface may alter deformation transfer within the dam system. This study investigated the Dashixia extra-high CFRD through large-scale contact rheological tests and three-dimensional finite element analysis. A contact rheological model was established from interface tests and incorporated into a full-scale numerical model considering valley topography, staged construction, and reservoir impoundment. The influence of contact rheology on dam deformation, face-slab response, and peripheral-joint behavior was evaluated. The results show that contact rheology has little effect on global dam settlement but significantly increases horizontal displacement and redistributes local deformation near the abutments. Under the normal reservoir water level, the maximum upstream displacement, downstream displacement, and settlement increase by 0.7, 3.4, and 1.5 cm, respectively. Meanwhile, the maximum peripheral-joint settlement increases from 43.7 to 69.8 mm, and the maximum tensile opening increases from 8.7 to 12.8 mm. For the Dashixia CFRD, inclusion of dam–abutment contact rheology increases the predicted maximum peripheral-joint settlement and tensile opening by 59.7% and 47.1%, respectively, highlighting the greater sensitivity of local joint deformation compared with global dam settlement. Full article