Search Results (81)

To ensure the safety and stability of single point mooring (SPM) systems operating in shallow waters, this paper investigates the influences of shallow-water effects on mooring systems under different water depth-to-draft ratios. For the pile-founded column single point mooring system in shallow sea areas, based on the numerical calculation method verified by model tests, frequency domain and time domain calculations are carried out to study the specific impact of shallow water effects on the hydrodynamic parameters of the hull, and the critical water depth-to-draft ratios applicable to the two second-order wave load calculation methods (Newman approximation and Pinkster approximation) are analyzed. At the same time, the specific impact of shallow water effects on the dynamic response of the mooring system under three different hull loading conditions at the same and different water depth-to-draft ratios is studied, and the critical water depth conditions for bottom contact in each loading condition are summarized. The results show that the shallow water effect has a significant impact on the hydrodynamic parameters such as RAO of the hull response, especially in the low-frequency response region. There are obvious differences between the Newman approximation and the Pinkster approximation methods. In shallow water conditions, the Pinkster approximation method has a more accurate calculation effect, and when the water depth-to-draft ratio reaches a certain critical value, the calculation results of the two approximation methods are basically consistent. For the same and different water depth-to-draft ratio conditions, the amplitude of the hull motion in the full-load draft state is greater than the other two loading conditions, but the response results of the cable tension are opposite. The research results reveal the specific influences of shallow-water effects on pile-supported single-point mooring (SPM) systems, which can provide references for the safety and stability design of mooring systems and bear great engineering significance for advancing the deployment of single-point mooring systems in shallow water regions. Full article

The vertical bearing capacity of stiffened deep cement mixing (SDCM) piles is strongly influenced by curing age, making the determination of appropriate loading timing an important issue in engineering practice. To investigate this effect, a series of axial compression tests was conducted on floating short-core SDCM piles cured for 14 d to 90 d using a specially developed multi-pile curing device and loading system. The curing-age-dependent load–displacement response and load-transfer behavior were analyzed. Unconfined compression tests were also performed on the cemented soil to assess strength development. The experimental results show that the ultimate bearing capacity increased rapidly within the first 28 d and gradually approached a stabilized value of 3024 N after about 60 d, following either an exponential or hyperbolic evolution trend. In addition, the strength and stiffness of the cemented soil exhibited continued growth, increasing by approximately 38% and 25%, respectively, from 28 d to 90 d. At the early curing stage, the increase in ultimate bearing capacity was mainly governed by the strength development of the cemented soil, whereas the stabilized value at later stages was jointly controlled by the strength of the surrounding soil and the characteristics of the cemented soil–soil interface. With increasing curing age, the progressive hardening of the cemented soil enhanced the load-transfer contribution of the DCM column and promoted more uniform mobilization of shaft resistance along the pile. These findings provide useful guidance for determining appropriate loading schedules and for the design and construction control of SDCM pile foundations. Full article

Ultra-deep excavations in soft soil pose major challenges for deformation control. Based on field monitoring of a 38.3 m deep five-story metro excavation in Tianjin, this study systematically investigates the spatiotemporal deformation of the diaphragm wall, columns, and surrounding environment. Key innovations include the proposal of an extended ground settlement influence model and the quantification of stage-wise deformation development ratios. The maximum lateral wall displacement is about 40 mm, ranging from 0.028% H_e to 0.184% H_e (average 0.087% H_e), outperforming comparable bottom-up excavations in Shanghai. Wall top vertical displacement varies from −0.23% H_emax to 0.04% H_emax, and column rebound averages 3.5 mm, is significantly lower than that of excavations using the bottom-up method. The extended settlement model shows that the maximum settlement occurs at H_e/3 from the wall, the primary influence zone extends to 3H_e, and the secondary zone reaches 5H_e. Building settlement strongly depends on distance and foundation type, with raft foundations settling much more than pile-raft foundations. Stage-by-stage analysis reveals that, immediately after the completion of diaphragm wall construction, the settlement already exceeded 60% of the final maximum ground settlement. Furthermore, the deformation on the long side developed at a faster rate than that on the short side. These findings provide quantitative benchmarks for designing ultra-deep excavations in soft soil. Full article

Train-induced ground vibrations can propagate into pile foundations, potentially causing undesirable vibration in nearby buildings, laboratories housing vibration-sensitive equipment, and manufacturing facilities for high-precision processes. This paper presents an innovative method for predicting building vibration from free-field ground vibration measurements at locations away from the tracks during train pass-bys. The proposed method accounts for site-specific soil profiles and train-soil-pile-structure interactions and is implemented in four steps. In Step 1, train-induced vibration transmission into the ground is estimated using an axisymmetric finite element model that simulates wave propagation through layered soils from the tracks to free-field ground locations. Step 2 estimates free pile head vibration using a three-dimensional finite-element model that captures the ground-borne transmission of track inputs through soil layers to the pile. Step 3 estimates vibration at the junction of the pile head and depot column base using a finite-element model to estimate the pile head impedance and an analytical impedance model for the depot structures supported by the pile. In Step 4, estimates of column-base vibration that transmits into over-track buildings are compared to measured column-base vibration levels obtained during train pass-bys. The method was applied at a metro depot in China, where tracks were in close proximity to columns supporting over-track buildings. Ground and column base vibration levels were measured during multiple train pass-bys. The estimated vibration levels at the base of depot columns closely agreed with the measured vibration levels at the columns during six-car train pass-bys. It demonstrated the potential effectiveness of this hybrid method for assessing vibration transmission into structures atop existing railway tracks. By integrating field measurements, finite element simulations, and analytical impedance models, the proposed hybrid method provides a framework for evaluating the transmission of the train-induced vibration to nearby building structures. Full article

Ground failure during major seismic events associated with soil liquefaction can lead to major structural damage to both the columns and the bridge upper deck due to large seismic-induced displacements in the support foundation. Liquefaction-driven ground motion incoherence during the dynamic event and permanent soil deformations are key variables in the observed damage. This paper summarizes a numerical study of an alternative bridge foundation design proposed to reduce support displacements and bearing capacity failure during and after an earthquake, as well as relative settlement associated with partial loss of bearing capacity when the bridge column is founded on a potential liquefiable layer. Three-dimensional numerical models were developed using FLAC^3D. The seismic environment was characterized by a uniform hazard spectrum, UHS, for intraplate and interplate earthquakes, as presented in the current construction Mexico City regulations. Initially, a one-dimensional analysis was performed using SHAKE to evaluate liquefaction susceptibility. Results show that the structured cell foundation reduces excess pore-pressure generation by up to 42% compared to shallow foundations and 25% compared to pile systems. This improvement is associated with (i) restriction of cyclic shear strain, (ii) modification of deformation patterns, (iii) partial confinement of pore-pressure development within the enclosed soil mass, and (iv) preservation of effective stresses during shaking. Additionally, the system reduces shear strain localization and decreases acceleration transmitted to the superstructure by up to 14–33%. The findings demonstrate that structured confinement systems can significantly influence the mechanisms governing liquefaction, offering a promising alternative for bridge foundations in seismic regions. Full article

To investigate the structural dynamic response of pile-column bridge piers in mountainous regions under rockfall impact, this study takes the No. 4 double-column pier of Changba Bridge in Nanchuan, Chongqing, as a prototype. Based on similarity theory and differential equation analysis, a scaled model test was designed and conducted. By considering different rockfall impact angles (30°, 45°, 60°) and different impact positions on the pier (top, middle, bottom), the strain response characteristics of the pier concrete and reinforcing steel were systematically analyzed. The results indicate that the peak strain at the impacted location increases significantly with the increase in the rockfall impact angle; when the impact angle increases from 30° to 60°, the peak strain increases by approximately 22.8%. The peak strain decreases as the impact position approaches the bottom of the pier, with the most pronounced strain response observed at the middle position. The strain response of the reinforcing steel follows the same pattern as that of the concrete, albeit with a brief delay. Furthermore, the stirrups exhibit predominantly transverse orthogonal strain, while the longitudinal reinforcing bars exhibit predominantly longitudinal orthogonal strain. It is concluded that the impact angle is a key parameter affecting local damage to the pier, and the middle section of the pier should be regarded as a priority protection zone. This study provides a theoretical basis for the design of bridge piers in mountainous regions against rockfall impact. Full article

Targeting the “Fishtailing Effect” associated with shallow-water, pile-founded column single point mooring (SPM) systems, this study investigates the vessel’s motion characteristics under multiple operational scenarios using a numerical calculation method validated by model tests. A refined classification of combined wind, wave, and current conditions was conducted. The study examines the vessel’s sway and mooring line tension response under both collinear and non-collinear combinations of these environmental forces. Furthermore, methods for suppressing vessel motion were explored. The results indicate that vessel motion leading to the “Fishtailing Effect” is more prone to occur under collinear wind, wave, and current conditions. Wave and wind energy can, to some extent, mitigate the vessel motion. When the current speed exceeds a certain critical threshold, the extreme values of the mooring forces on the swaying vessel undergo an abrupt change. Applying a stern tug force and reducing the mooring line length are both effective in decreasing the vessel motion range and the tension in the mooring lines. The findings shed light on the fishtailing-effect characteristics of tankers moored at pile-founded column SPM systems, providing a valuable reference for the safety and stability design of such mooring systems. Full article

Currently, one of the major trends in the construction industry is the creation of structures with increased strength and durability. The solution is the use of nanomaterials as modifiers for cementitious composites. The aim of this study is to produce concretes with a variable structure modified with a combination of aluminum oxide (NA) and titanium oxide (NT) nanoparticles with improved properties. A variatropic structure is characterized by differences in properties across the cross-section of the material. Concretes were produced using vibration (V), centrifugation (C), and vibrocentrifugation (VC) technologies. Modification was carried out with NA particles from 0% to 4.0% in increments of 1.0% and NT from 0% to 2.0% in increments of 0.5% of the binder mass. Through experimental study, the impact of combined nanomodification on the compressive strength, water absorption, and frost resistance of concrete created with different technologies was investigated. The most effective modification dosages with NA and NT particles were determined to be 2% and 1%. The determination of concrete properties and the statistical processing of experimental results were carried out in accordance with the requirements of standardized methods. Compared to control samples, the maximum compressive strengths for V, C, and VC concretes were 12.4%, 17.5%, and 20.3% higher, reaching 48.9 MPa, 58.4 MPa, and 62.9 MPa, respectively. The lowest water absorptions for V, C, and VC concretes were 5.21%, 4.24%, and 3.76%, which are 18.5%, 24.4%, and 29.2% lower than those of the control samples. After a series of freeze–thaw cycles—6 for V, 8 for C, and 10 for VC—the losses in compressive strength and mass of the nanomodified composites were less than those of the control samples, indicating an increase in the frost resistance of concrete. The influence of concrete production technology on the effect of nanomodification with NA and NT particles was proven. Nanomodified C and VC concretes have improved physical and mechanical properties compared to V concretes. Nanomodified concretes with a variable structure have a more organized microstructure with a greater number of clusters of calcium silicate hydroxides. The resulting variable-structure concrete has improved properties and can be used to manufacture columns, piles, and transmission line supports. Full article

The Cairo Monorail System presents significant geotechnical challenges due to its integrated structural configuration and its alignment across heterogeneous soil conditions, including collapsible and swelling soils. This study investigates the foundation performance of the monorail through a combination of advanced site investigations, full-scale pile load testing under dry and wetted conditions, and finite-element modeling incorporating soil–structure interaction. Field load tests on large-diameter bored piles founded in collapsible soils demonstrated a pronounced increase in settlement and a reduction in stiffness following wetting, confirming the sensitivity of pile behavior to moisture variations. Three-dimensional numerical analyses of the integrated monorail system showed that differential settlements between adjacent columns are generally limited to less than 9 mm under serviceability loading conditions, satisfying passenger comfort requirements. Long-term coupled seepage–deformation analyses conducted using PLAXIS indicated that surface water infiltration into swelling soils may induce time-dependent monopile heave of approximately 10 mm over a 50-year design life, which remains within acceptable serviceability limits. The results demonstrate that detailed geotechnical characterization, combined with appropriate numerical modeling strategies, can effectively control differential deformation and long-term heave in continuous monorail systems, ensuring their operational safety and long-term performance. Full article

In order to investigate the effects of gravel particle size and geogrid aperture on the bearing performance of geosynthetic-encased stone columns, a discrete–continuum coupled numerical model was established based on laboratory test results, and a series of numerical simulations were conducted. The results indicate that, under the same loading level, the maximum lateral bulging of geosynthetic-encased stone columns increases with increasing geogrid aperture and decreases with increasing gravel particle size. The distance between the location of maximum lateral bulging and the pile-top decreases as the aperture increases, whereas it increases with increasing particle size. The bearing performance of geosynthetic-encased stone columns shows a positive correlation with gravel particle size and a negative correlation with geogrid aperture. The influence of particle size on bearing performance becomes insignificant when d₅₀ exceeds 40 mm. When the particle size is smaller than the geogrid aperture, contact between the gravel and the geogrid is established but remains insufficient, leading to separation as the load increases. In contrast, when the particle size is larger than the aperture, the effect of particle size on bearing performance is much more pronounced than that of aperture. Therefore, the use of gravel with a particle size slightly larger than the geogrid aperture is recommended in practical engineering applications. Full article

Timely adjustment of belt conveyor speed according to the conveyed load is a key approach to achieving energy-efficient operation. Line laser-assisted vision has been widely adopted for load measurement, in which image processing techniques are employed to extract and analyze the outer contour of material piles highlighted by laser stripes. To address issues such as laser stripe thinning and breakpoint handling, the point-by-point interpolation method (PPIM) was previously proposed, enabling column-wise extraction of laser stripe pixels by incorporating the geometric characteristics of material accumulation, thereby improving real-time performance. However, its adaptability remains limited under complex pile geometries and strong reflective interference. In this paper, the pixel traversal strategy is further optimized to achieve efficient and robust extraction of the laser stripe centerline. By performing a single, non-global image traversal, laser stripe thinning, breakpoint identification, interpolation, continuity reconstruction, and cross-sectional area calculation are integrated into a unified processing framework. Experimental results demonstrate that the improved method achieves a 0.3% increase in measurement accuracy compared with the original PPIM, while maintaining excellent real-time performance with a processing speed of up to 94 frames per second (FPS). The proposed approach provides a more reliable load perception basis for intelligent speed regulation of belt conveyors, contributing to energy-efficient and stable operation. Full article

The Yellow River Floodplain region of Shandong Province is dominated by silty soils that challenge geotechnical construction. Drilling–Mixing–Jetting (DMJ) Deep Cement Mixing Pile groups have been adopted to improve the geotechnical properties of the soil. This study conducted field tests to evaluate column strength and numerically investigated the effects of area replacement ratio (7.10%, 10.66% and 14.21%) and column spacing. It is observed that the DMJ-integrated columns demonstrate enhanced soil–cement strength in the Yellow River Floodplain region, with sample strengths varying between 2 and 8 MPa. The electrical resistivity of soil–cement shows a strong linear correlation (Pearson’s R > 0.75) with unconfined compressive strength. Settlement reduction ratios range between 32.11% and 94.75% and increase with higher area replacement ratio (ARR) and applied stress but decrease with larger column spacing. Bearing capacity improvement factors are found to be increased with ARR, while column spacing has minimal effect, with values between 423.89 kPa and 431.61 kPa. Lateral displacement decreased with column installation and increasing area replacement ratio (ARR), while the effect of column spacing was confined to depths near the column head. Full article

Existing pile foundations in the Arctic face significant limitations regarding bearing capacity, environmental impact, and dismantling capabilities. This study proposes and geomechanically justifies a novel technology for constructing dismantlable modular pile foundations in permafrost using a pile with a dome-plug (PDP). Comparative numerical modeling was conducted to analyze the bearing capacity of the proposed PDP versus a conventional pile without a dome-plug (PWDP) across six types of frozen rocks (clays, loams, sandy loams), specifically accounting for salinity. The results indicate that the dome-plug effectively transforms the shell pile into a combined pile-column, providing a bearing capacity increase ranging from 35% to 63%. Notably, the highest relative improvement was observed in the weakest saline rocks. The proposed technology serves as a superior alternative to traditional piling methods, enabling the deployment of modular foundations as a cost-effective and eco-friendly substitute for artificial soil islands. Full article

The phenomena of capillarity, dipole–dipole attractions, and hydrogen bonding make the application of mass transfer models to predict the drying rate by air convection in wood chips imprecise. So, the modification of these models by tailoring their equations is required. This study aims to adapt theoretical mass transfer models to improve the prediction of drying time for Pinus spp. chips subjected to a known hot air stream with known velocity, temperature, and relative humidity. An experimental device was constructed to control the variables, where the air stream passes vertically through a cylinder filled with wood chips. The tested air velocities ranged between 7 and 10 m/s, with relative humidity between 10 and 30% and temperatures between 40 and 70 °C with 3 and 6 cm chip columns. It was demonstrated that the drying rate of chips in a convective process with air is not constant but rather decreases over time, and that the critical moisture content is above 42%. Factors such as the height of the chips pile influence the predictive equations for the drying rate. The average relative drying rate ranged between 0.063 and 0.040 g of water s⁻¹ kg of dry chip⁻¹ in both heights; meanwhile, the average absolute drying rate was between 0.0031 and 0.0032 g of water s⁻¹. Modifications of the models have been developed that adjust theoretical values with experimental values, resulting in an r² value of 0.80. Full article

This paper analyzes the seismic performance and damage characteristics of high-rise frame-core-tube structures on soft soil, explicitly incorporating dynamic soil–pile–structure interaction (SSI). A refined 3D finite element model of a 52-storey soil–pile–structure system was developed in ABAQUS, utilizing viscous-spring boundaries and the equivalent nodal force method for seismic input. Nonlinear analyses under six seismic waves were compared to a fixed-base model neglecting SSI. Key findings demonstrate that SSI significantly alters structural response; it amplifies lateral displacements and inter-storey drift ratios throughout the structure, particularly at the top level. While total base shear decreased, frame column base shear forces substantially increased. SSI also reduced peak top-storey accelerations, diminished short-period spectral components, and prolonged the predominant period of response spectra. Analysis of member damage revealed SSI generally reduced compressive and tensile damage in core walls, floor slabs, and frame beams. Principal compressive stresses at the base of frame columns increased under SSI. These results highlight the necessity of including dynamic SSI in seismic analysis for high-rises on soft soil, specifically due to its detrimental amplification of forces in frame columns. Full article