Search Results (226)

Benthic macroinvertebrates are widely used for river ecosystem health monitoring, yet challenges remain in non-wadable rivers, particularly regarding sampling effort. We evaluated hand-net sampling efficiency at three sites along the Danjiang River (a Yangtze River tributary) by analyzing taxa richness across taxonomic levels under varying replicate numbers. In total, 61 taxa (41 families) of benthic macroinvertebrates were identified. Non-metric multidimensional scaling analysis indicated no significant spatiotemporal variation in community composition. However, sampling effort increased, and the benthic macroinvertebrate taxa richness at both genus/species and family levels also increased. At eight sample replicates, the taxa accumulation curve at the genus/species level did not show an asymptote, with the observed richness reaching 67–80% of the predicted values calculated by Jackknife 1. In contrast, the family-level curve exhibited a clear asymptotic trend, with the observed richness reaching 82–100% of the predicted values. As sampling effort increased, bias decreased and accuracy improved, particularly for family-level taxa. Additionally, the BMWP scores also increased with the sampling effort. When the replicate number was no less than six, the BMWP reached stable assessment grades for all cases. From the perspective of bioassessment in non-wadable rivers, the hand net is suitable for collecting benthic macroinvertebrates. However, there is a risk of underestimating taxa richness due to insufficient sampling effort. Using family-level taxa can partially mitigate the impacts caused by insufficient sampling efforts to a certain extent, but further validation is needed for other non-wadable rivers (e.g., those with soft substrates). In conclusion, our research results indicate that six replicate hand-net samplings in non-wadable hard-bottom rivers can be regarded as a cost-effective and reliable sampling method for benthic macroinvertebrate BMWP assessment. This strategy provides a relatively practical reference for the monitoring of benthic macroinvertebrate in the same type of rivers in China. Full article

Studies of microbial degradation of historic woods are essential to help protect and preserve these important cultural properties. The USS Cairo is a historic Civil War gunboat and one of the first steam-powered and ironclad ships used in the American Civil War. Built in 1861, the ship sank in the Yazoo River of Mississippi in 1862 after a mine detonated and tore a hole in the port bow. The ship remained on the river bottom and was gradually buried with sediments for over 98 years. After recovery of the ship, it remained exposed to the environment before the first roofed structure was completed in 1980, and it has been displayed under a tensile fabric canopy with open sides at the Vicksburg National Military Park in Vicksburg, Mississippi. Concerns over the long-term preservation of the ship initiated this investigation to document the current condition of the wooden timbers, identify the fungi that may be present, and determine the elemental composition resulting from past wood-preservative treatments. Micromorphological characteristics observed using scanning electron microscopy showed that many of the timbers were in advanced stages of degradation. Eroded secondary cell walls leaving a weak framework of middle lamella were commonly observed. Soft rot attack was prevalent, and evidence of white and brown rot degradation was found in some wood. DNA extraction and sequencing of the ITS region led to the identification of a large group of diverse fungi that were isolated from ship timbers. Soft rot fungi, including Alternaria, Chaetomium, Cladosporium, Curvularia, Xylaria and others, and white rot fungi, including Bjerkandera, Odontoefibula, Phanerodontia, Phlebiopsis, Trametes and others, were found. No brown rot fungi were isolated. Elemental analyses using induced coupled plasma spectroscopy revealed elevated levels of all elements as compared to sound modern types of wood. High concentrations of boron, copper, iron, lead, zinc and other elements were found, and viable fungi were isolated from this wood. Biodegradation issues are discussed to help long-term conservation efforts to preserve the historic ship for future generations. Full article

With the continuous improvement of the prefabricated modular technology system, the prefabricated subway station structures are widely used in underground engineering projects. However, prefabricated subway stations in soft soil can suffer significant adverse effects under seismic action. In order to study the seismic performance of a prefabricated subway station, this work is based on an actual project of a subway station in soft soil. And the nonlinear static and dynamic coupling two-dimensional finite element models of cast-in-place structures (CIPs), assembly splicing structures (ASSs), and assembly monolithic structures (AMSs) are established, respectively. The soil-structure interaction is considered, and different peak ground accelerations (PGA) are selected for incremental dynamic analysis. The displacement response, internal force characteristics, and structural damage distribution for three structural forms are compared. The research results show that the inter-story displacement of the AMS is slightly greater than that of the CIP, while the inter-story displacement of the ASS is the largest. The CIP has the highest internal force in the middle column, the ASS has the lowest internal force in the middle column, and the AMS is between the two. The damage to the CIP is concentrated at the bottom of the middle column and sidewall. The AMS compression damage moves upward, but the tensile damage mode is similar to the CIP. The ASS can effectively reduce damage to the middle column and achieve redistribution of internal force. Further analysis shows that the joint splicing interface between cast-in-place and prefabricated components is the key to controlling the overall deformation and seismic performance of the structure. The research results can provide a theoretical basis for the seismic design optimization of subway stations in earthquake-prone areas. Full article

To investigate the longitudinal mechanical behavior of shield tunnels traversing soft and hard heterogeneous strata, a refined three-dimensional numerical model was developed using ABAQUS. The model includes tunnel segments, longitudinal bolts, reinforcement, longitudinal thrust, and additional loading conditions to simulate realistic mechanical responses during construction and operation. The results show that significant differential settlement occurs at the interface between soft and hard soils. Greater joint dislocation is observed on the soft soil side, while joint opening is more pronounced on the hard soil side. Compressive damage concentrates at the soil interface, whereas tensile damage is more severe in soft soil zones. The dislocation at the vault is distributed over a wider area but has a smaller magnitude than that at the arch bottom. Parametric analysis indicates that increasing longitudinal thrust enhances tunnel stiffness and reduces joint dislocation. However, it also leads to increased compressive and tensile damage due to greater trans-verse deformation. Optimizing bolt configuration, including diameter, inclination, and quantity, improves longitudinal stiffness and joint integrity, helping to reduce tensile damage and control deformation. These findings provide theoretical support for the structural design and performance optimization of shield tunnels in complex geological environments. Full article

Although ridge preservation procedures have been shown to prevent post-extraction bone loss, the effectiveness of using a flap or flapless surgical approach remains unclear. The aim of the study was to compare the mentioned above alveolar ridge preservation procedures in the esthetic region of maxilla. Twenty-nine patients were randomly assigned to receive flap (n = 14) or flapless (n = 15) alveolar ridge preservation procedure. Sockets were grafted with alloplastic biomaterial, then covered with a collagen membrane in both groups. Clinical examinations were performed over a 6-month observation period and radiological (CBCT) examination was conducted before and 6 months after treatment. For both after flap and flapless procedures, there was a reduction in interdental papillae height and keratinized tissue width, increase in buccal soft tissues thickness with a decrease in radiological buccal bone plate width, decrease in radiological buccal and lingual plate height (significantly for the flapless group) and radiological alveolar process width reduction (significantly in flapless group at the height of 5 mm and 7 mm from the bottom of the socket). A decrease in the radiological buccal bone plate width was observed, where the further measuring point was from the bottom of the alveolus. In the mucoperiosteal flap preparation, group buccal bone plate width reduction at the height 3 mm, 5 mm and 7 mm was significant and in the flapless group a significant decrease was observed from 5 to 9 mm from the bottom of the socket. Despite ridge preservation, there is soft tissue thickening and a decrease in bone height and width regardless of the flap/flapless method used. Full article

To address the critical challenge of ensuring bottom water-inrush stability during the excavation of ultra-deep foundation pits for riverside suspension-bridge anchorages under complex geological conditions involving high-pressure confined groundwater, we investigate the application of D-RJP high-pressure rotary jet grouting pile technology for ground improvement. Its effectiveness is systematically validated through a case study of the South Anchorage Foundation Pit for the North Channel Bridge of the Zhangjinggao Yangtze River Bridge. The D-RJP method led to the successful construction of a composite foundation within the soft soil that satisfies the permeability coefficient, interface friction coefficient, bearing capacity, and shear strength requirements, significantly improving the geotechnical performance of the anchorage foundation. A series of field experiments were conducted to optimize the critical construction parameters, including the lifting speed, water–cement ratio, and stroke spacing. Core sampling and laboratory testing revealed the grout columns to have good structural integrity. The unconfined compressive strength of the high-pressure jet grout columns reached 5.45 MPa in silty clay layers and 8.21 MPa in silty sand layers. The average permeability coefficient ranged from 1.67 × 10⁻⁷ to 2.52 × 10⁻⁷ cm/s. The average density of the columns was 1.66 g/cm³ in the silty clay layer and 2.08 g/cm³ in the silty sand layer. The cement content in the return slurry varied between 18% and 27%, with no significant soil squeezing effect observed. The foundation interface friction coefficient ranged from 0.44 to 0.52. After excavation, the composite foundation formed by D-RJP columns was subjected to static load and direct shear testing. The results showed a characteristic bearing capacity value of 1200 kPa, the internal friction angle exceeded 24.23°, and the cohesion exceeded 180 kPa. This study successfully verifies the feasibility of applying D-RJP technology to construct high-performance artificial composite foundations in complex strata characterized by deep soft soils and high-pressure confined groundwater, providing valuable technical references and practical insights for similar ultra-deep foundation pit projects involving suspension bridge anchorages. Full article

To study and quantify the impact of water storage on lake slope stability after the closure of an open-pit mine, we targeted slope control measures by large-scale parallel computing methods and strength reduction theory. This was based on a three-dimensional refined numerical model to simulate the evolution of slope stability under different water storage levels and backfilling management conditions, and to quantitatively assess the risk of slope instability through the spatial distribution of stability coefficients. This study shows that during the impoundment process, the slope stability has a nonlinear decreasing trend due to the decrease in effective stress caused by the increase in pore water pressure. When the water storage was at 0 m, the instability range is the largest, and the surface range is nearly 200 m from the edge of the pit; when the water level continued to rise to 50 m, the hydrostatic pressure of the pit lake water on the slope support effect began to appear, and the stability was improved, but there is still a wide range of unstable areas at the bottom. In view of the unstable area of the steep slope with soft rock in the north slope during the process of water storage, the management scheme of backfilling the whole bottom to −150 m was proposed, and the slope protection and pressure footing were formed by discharging the soil to −40 m in steps to improve the anti-slip ability of the slope. Full article

Dense aggregations of species in the family Pinnidae give soft substrata a specific characterization. They may influence the biological and physical properties of the surrounding sediments. Bottom-trawl samplings performed in the Sea of Marmara revealed populations of a large pinnid species, particularly at depths of 40–45 m in soft substrata. Both morphological and DNA analyses confirmed the species’ taxonomic identity as Atrina fragilis. This species had a population density ranging from 31 to 469 ind.km⁻², and the shell lengths ranged from 21.3 to 31 cm. A total of 47 macrozoobenthic species belonging to eight taxonomic groups were found on the shells of ten live and nine dead A. fragilis individuals. Polychaeta accounted for 53% of the total number of species and 75% of the total number of individuals. Among these species, Protula tubularia and Serpula concharum comprised almost 30% of all epifaunal populations. Community parameters changed according to the shell length and width. Different faunal assemblages were encountered on the shells. Given the ecological significance of A. fragilis as both a habitat-forming and sensitive benthic species, conservation measures should prioritize the protection of known habitats and the regulation of activities that lead to seabed disturbance. Full article

This study conducts a numerical simulation of the working performance of a single horizontal shaft forced mixer using the Discrete Element Method (DEM). It systematically investigates the effects of blade installation angle, feeding method, mixing speed, and coarse aggregate particle size on the mixing uniformity. A 1:2 scale model was developed, incorporating Newton’s laws of motion and a soft-sphere contact model to simulate the particle trajectories and interactions during mixing. The results indicate that top–bottom feeding enhances mixing efficiency significantly by forming vertical convective circulation, achieving a mixing uniformity above 0.9. A moderate rotation speed of 30 rpm provides the best balance between energy consumption and mixing performance. As the coarse aggregate size increases (from 9 mm to 15 mm), the enhanced particle inertia leads to a decrease in mixing uniformity (from 0.9 to 0.6). Additionally, the discrepancy between simulation and experimental results is less than 0.1, validating the reliability of the model. This research offers theoretical guidance for the structural optimization and parameter selection of single-shaft mixers, contributing to improved mixing efficiency and concrete quality in engineering applications. Full article

As a key transportation infrastructure, it is of great significance to ensure the seismic safety of the high-speed railway hub station. Taking Changde high-speed railway hub station as background, a comprehensive 3D numerical model of the high-speed railway station structure is proposed to consider the engineering geological characteristics of the site, soil nonlinearity, and pile-soil interactions. The results show that the hub station structural system, considering pile-soil interaction, presents the ‘soft-upper-rigid-down’ characteristics as a whole, and the natural vibration is lower than that of the station structure with a rigid foundation assumption. Under the action of three strong seismic motions, the nonlinear site seismic effect is significant, the surface acceleration is significantly enlarged, and decreases with the buried depth. The interaction between pile and soil is related to the nonlinear seismic effect of the site, which deforms together to resist the foundation deformation caused by the strong earthquake motions, and the depth range affected by the interaction between the two increases with the increase of the intensity of earthquake motion. Among the three kinds of input earthquake motions, the predominant frequency of the Kobe earthquake is the closest to the natural vibration of the station structure system, followed by the El Centro earthquake. Moreover, the structures above the foundation of the high-speed railway hub station structural system are more sensitive to the spectral characteristics of Taft waves and El Centro waves compared to the site soil. This is also the main innovation point of this study. The existence of the roof leads to the gradual amplification of the seismic response of the station frame structure with height, and the seismic response amplification at the connection between the roof and the frame structure is the largest. The maximum story drift angle at the top floor of the station structure is also greater than that at the bottom floor. Full article

Mediterranean subtidal reefs host ecologically significant habitats, including forests of Cystoseira spp., which form complex benthic communities within the photic zone. These habitats are increasingly degraded due to climate change, invasive species, and anthropogenic pressures, particularly in the eastern Mediterranean. In support of habitat monitoring under the EU Natura 2000 directive and the Nature Restoration Regulation, this study investigates the utility of high-resolution satellite remote sensing for mapping subtidal brown algae and associated benthic classes. Using imagery from the SuperDove sensor (Planet Labs, San Francisco, CA, USA), we developed an integrated mapping workflow at the Natura 2000 site GR2420009. Aquatic reflectance was derived using ACOLITE v.20250114.0, and both supervised classification and spectral unmixing were implemented in the EnMAP Toolbox v.3.16.3 within QGIS. A Random Forest classifier (100 fully grown trees) achieved high thematic accuracy across all habitat types (F1 scores: 0.87–1.00), with perfect classification of shallow soft bottoms and strong performance for Cystoseira s.l. (F1 = 0.94) and Seagrass (F1 = 0.93). Spectral unmixing further enabled quantitative estimation of fractional cover, with high predictive accuracy for deep soft bottoms (R² = 0.99; RPD = 18.66), shallow soft bottoms (R² = 0.98; RPD = 8.72), Seagrass (R² = 0.88; RPD = 3.01) and Cystoseira s.l. (R² = 0.82; RPD = 2.37). The lower performance for rocky reefs with other cover (R² = 0.71) reflects spectral heterogeneity and shadowing effects. The results highlight the effectiveness of combining classification and unmixing approaches for benthic habitat mapping using CubeSat constellations, offering scalable tools for large-area monitoring and ecosystem assessment. Despite challenges in field data acquisition, the presented framework provides a robust foundation for remote sensing-based conservation planning in optically shallow marine environments. Full article

Collar monopile foundation is a new type of offshore wind power foundation. This paper explores the horizontal bearing performance of collar monopile foundation in saturated cohesive soil through a combination of physical experiments and numerical simulations. After analyzing the deformation characteristics of the pile–soil system under horizontal load through static load tests, horizontal cyclic loading tests were conducted at different cycles to study the cumulative deformation law of the collar monopile. Based on a stiffness degradation model for soft clay, a USDFLD subroutine was developed in Fortran and embedded in ABAQUS. Coupled with the Mohr–Coulomb criterion, it was used to simulate the deformation behavior of the collar monopile under horizontal cyclic loading. The numerical model employed the same geometric dimensions and boundary conditions as the physical test, and the simulated cumulative pile–head displacement under 4000 load cycles showed good agreement with the experimental results, thereby verifying the rationality and reliability of the proposed simulation method. Through numerical simulation, the distribution characteristics of bending moment and the shear force of collar monopile foundation were studied, and the influence of pile shaft and collar on the horizontal bearing capacity of collar monopile foundation at different loading stages was analyzed. The results show that as the horizontal load increases, cracks gradually appear at the bottom of the collar and in the surrounding soil. The soil disturbance caused by the sliding and rotation of the collar will gradually increase, leading to plastic failure of the surrounding soil and reducing the bearing capacity. The excess pore water pressure in shallow soil increases rapidly in the early cycle and then gradually decreases with the formation of drainage channels. Deep soil may experience negative pore pressure, indicating the presence of a suction effect. This paper can provide theoretical support for the design optimization and performance evaluation of collar monopile foundations in offshore wind power engineering applications. Full article

Investigating the seismic damage mechanism of large underground complexes is essential for the safe development of urban underground space. This paper examines a five-story and three-span underground complex situated in a soft soil site. Shaking table tests were designed and conducted on both the free field and the soil–underground complex interaction system. The time–frequency evolution of the free field under various seismic motions was investigated. A combined experimental and numerical simulation approach was employed to examine the seismic response of the soil–underground complex interaction system. The structural deformation evolution, stress distribution, and development process of plastic damage under different seismic motions were analyzed. The results reveal that soft soil exhibits a significant energy amplification effect under far-field long-period ground motions. Structural deformation is mainly governed by horizontal shear. Under strong seismic excitation, plastic damage first initiates at the end of the bottom-story columns and extends to column-to-slab and wall-to-slab connections, where abrupt stiffness changes occur. Under the far-field long-period ground motion, the structural deformation, stress distribution, and plastic damage are significantly greater than those under the Shanghai artificial wave. These findings provide valuable insights for the seismic design of large underground complexes in soft soil sites. Full article

Pile–raft foundations are widely used in soft soil engineering due to their good integrity and high stiffness. However, traditional design methods independently design pile–raft foundations and superstructures, ignoring their interaction. This leads to significant deviations from actual conditions when the superstructure height increases, resulting in excessive costs and adverse effects on building stability. This study experimentally investigates the interaction characteristics of pile–raft foundations and superstructures in soft soil under different working conditions using a 1:10 geometric similarity model. The superstructure is a cast-in-place frame structure (beams, columns, and slabs) with bamboo skeletons with the same cross-sectional area as the piles and rafts, cast with concrete. The piles in the foundation use rectangular bamboo strips (side length ~0.2 cm) instead of steel bars, with M1.5 mortar replacing C30 concrete. The raft is also made of similar materials. The results show that the soil settlement significantly increases under the combined action of the pile–raft and superstructure with increasing load. The superstructure stiffness constrains foundation deformation, enhances bearing capacity, and controls differential settlement. The pile top reaction force exhibits a logarithmic relationship with the number of floors, coordinating the pile bearing performance. Designers should consider the superstructure’s constraint of the foundation deformation and strengthen the flexural capacity of inner pile tops and bottom columns for safety and economy. Full article

The shallow, soft subsea formations, characterized by low strength and poor stability, lead to complex interactions between the screw motor drilling tool and the wellbore wall during directional drilling, complicating the accurate evaluation of the tool’s deflection capability. To address this issue, this paper proposes an integrated mechanical analysis method combining three-dimensional finite element analysis and transient dynamic analysis. By establishing a finite element model using 12-DOF (degree-of-freedom) spatial rigid-frame Euler–Bernoulli beam elements, coupled with well trajectory coordinate transformation and Rayleigh damping matrix, a precise description of drill string dynamic behavior is achieved. Furthermore, the introduction of pipe–soil dynamics and the p-y curve method improves the calculation of contact reaction forces between drilling tools and formation. Case studies demonstrate that increasing the tool face rotation angle intensifies lateral forces at the bit and stabilizer, with the predicted maximum dogleg severity within the first 10 m ahead of the bit progressively increasing. When the tool face rotation angle exceeds 2.5°, the maximum dogleg severity reaches 17.938°/30 m. With a gradual increase in the drilling pressure, the maximum bending stress on the drilling tool, maximum lateral cutting force, and stabilizer lateral forces progressively decrease, while vertical cutting forces and bit lateral forces gradually increase. However, the predicted maximum dogleg severity increases within the first 10 m ahead of the bit remain relatively moderate, suggesting the necessity for the multi-objective optimization of drilling pressure and related parameters prior to actual operations. Full article