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Current calculation methods for the vertical bearing capacity of steel pipe piles are predominantly designed for smaller diameters and do not account for the soil inside the pile. This necessitates an evaluation of their applicability to piles with diameters exceeding 2.0 m. This study aims to refine the existing formula for calculating vertical bearing capacity, as outlined in the Port Engineering Foundation Code of China, by investigating the vertical bearing capacity of large-diameter steel pipe piles through numerical simulations. By analyzing the relationship between the internal friction resistance of the soil core within the pipe and the bearing capacity for diameters ranging from 2 m to 10 m, this paper proposes a revised formula specifically tailored for steel pipe piles with diameters greater than 2 m, incorporating the effect of the soil core. The validity of the proposed formula is then confirmed through comparison with field data from four large-diameter steel pipe piles. The results demonstrate that the modified method proposed in this study performs better than the original formula when compared with the measured data.

The development of underground spaces in mega-cities necessitates understanding the interaction among various underground structures. Soil acts as the fundamental medium in bearing and transmitting forces during the construction of these structures. In shield tunnels, the deformation of adjacent soil is a primary concern. or underground structures with piled raft foundations, this deformation directly impacts the foundation’s bearing capacity and causes differential deformation. This consideration becomes especially crucial for large-diameter shield tunnels when intersecting with piled raft foundations. To address this issue, the study examines a case of a mega-diameter shield tunnel intersects a piled raft foundation, which is the built for an underground railway station. The research focuses on soil deformation between the tunnel and the structure during construction, analyzing the variation of pile neutral points across the foundation based on soil deformation. A method is proposed to rapidly predict incremental negative frictional resistance of piles due to tunnel excavation, guided by soil deformation. The study clarifies the specific range of tunnel excavation’s influence on pile-bearing capacity, offering practical insights and potential theoretical guidance for similar future projects.

This paper presents an analytical approach for estimating frictional resistance to pipe movement at soil and external pipe surface of buried coated pressurized steel pipes relative to the internal thrust force. The proposed analytical method was developed based on 36 experiments, which involved three coating types (cement mortar (CM), polyurethane type-I (PT-I), prefabricated plastic tape (PPT)) on pipes' surfaces, three different soils (pea-gravel (PG), sand (S), silty-clay (SC)), and four simulated over burden depths above the pipe's crown. Investigation showed frictional resistance decreased with increasing over burden depth above the pipe's crown. The degree of frictional resistance at the pipe-soil interface was found to be in the order of PG > SC > S for all coating variations and overburden depths. CM coated pipe buried in all three types of soil produced significantly higher frictional resistance as compared to other coating types. Based on experimental data, the developed analytical introduced a dimensionless factor \" Z\", which included effects of types of coatings, soil, and overburden depths for simplified rapid calculation. Analysis showed that the method provided a better prediction of frictional resistance forces, in comparison to previous analytical methods, which were barely close in predicting friction resistance for different coating variations, soil types, and overburden depths. Friction resistance force values reported herein could be considered conservative.

Compacted cement stabilized gravel pile can effectively control secondary disasters of subgrade, while the bearing mechanism of semi-rigid pile composite foundation is not clear. The load–settlement ( Q – S ) curves, pile mechanical features and pile–soil stress characteristics of the composite foundation were analyzed by field tests and numerical simulation. Moreover, the characteristic value and calculating equation of the bearing capacity were discussed. Results show that the axial force of the group pile in composite foundation increases first and then decreases with the depth, the negative friction resistance is in the upper part, the neutral point is located at one-fifth of the length below the top. The lateral friction of the lower part of the pile plays a role before the upper lateral friction, and more than 90% of the pile load is supported by lateral friction. The curve of pile–soil stress ratio is hump-shaped, the stress ratio of pile to adjacent pile center soil is 6.08–6.65, and the stress ratio of pile to diagonal pile center soil is 7.5–9.45. Q – S curve of the single pile is characterized as a sharp decline, the characteristic value of the bearing capacity can be obtained by the equation of rigid pile, and the reduction coefficient of the pile strength is 0.25. Q – S curve of the composite foundation performs a slow downward tendency, the characteristic value of the bearing capacity can be obtained by the equation of compacted cement–soil piles, it is suggested that the correction coefficient of the vertical compressive bearing capacity is 1.0, and the bearing capacity correction coefficient of soil between piles is 1.05–1.15.

More and more rigid frame bridges with high piers and large spans are built in the high and steep slope areas of deep valleys in southwest China. The slow deformation of the slope in the geological sense often causes the problems of piles, which in turn causes damage of the upper bridges. The vertical bearing characteristics of bridge piles in slope still need to be conducted because of the peculiarity of slope topography. The vertical deformation and bearing characteristics of piles in the slope area were experimentally studied by considering different influencing factors and the fitting formula for the ultimate bearing capacity of the piles under vertical load is obtained. The results show that the vertical deformation and ultimate bearing capacity (defined by vertical limit settlement deformation of 0.013 times the pile diameter) of the pile are closely related to its position in the slope. The pile in the middle of the slope has the lowest vertical ultimate bearing capacity. Moreover, the side frictional resistance transfer depth of the pile in continuous slope is greater than that of the pile in unilateral slope. Additionally, the slope angle has a significant influence on the vertical bearing performance of piles. The delayed settlement of the pile top decreases approximately 40% at most and the vertical ultimate bearing capacity of the pile increases 48.6% at most as the slope angle decreases by 15°. Meanwhile, the side friction resistance of the pile increases with the decrease of slope angle. The bending moment applied to the pile top reduces the vertical ultimate bearing capacity of the pile and increases the axial force of the pile body. The results can provide data support for pile design and instability judgment with similar geological conditions.

Polyelectrolyte brushes consist of charged polymer chains attached to a common backbone or surface. They provide excellent lubrication between two surfaces for both engineered and physiological materials. The packing of the brushes is sensitive to pH, temperature, or added salts. Yu et al. show that the presence of multivalent ions can cause brush collapse, similarly to monovalent ions (see the Perspective by Ballauff). Critically—and not observed with the addition of monovalent ions—very low concentrations of multivalent ions cause bridging between the brushes and increase friction between the surfaces to the extent that their value for biomedical devices is limited. Science , this issue p. 1434 ; see also p. 1399 Low concentrations of multivalent ions dramatically increase the friction between polymer brushes. Polyelectrolyte brushes provide wear protection and lubrication in many technical, medical, physiological, and biological applications. Wear resistance and low friction are attributed to counterion osmotic pressure and the hydration layer surrounding the charged polymer segments. However, the presence of multivalent counterions in solution can strongly affect the interchain interactions and structural properties of brush layers. We evaluated the lubrication properties of polystyrene sulfonate brush layers sliding against each other in aqueous solutions containing increasing concentrations of counterions. The presence of multivalent ions (Y 3+ , Ca 2+ , Ba 2+ ), even at minute concentrations, markedly increases the friction forces between brush layers owing to electrostatic bridging and brush collapse. Our results suggest that the lubricating properties of polyelectrolyte brushes in multivalent solution are hindered relative to those in monovalent solution.

Pile-soil interaction is considered to be one of the most important problems in the study of the mechanical behaviour of pile foundation. In this paper, the lateral friction resistance and pile-soil relative displacement of bridge piles in deep soft soils are monitored for an extended period by using concrete strain gauges that are embedded in the test pile. Field test results show that both the pile lateral frictional resistance and pile-soil relative displacement increase along with time, while the pile-soil interaction demonstrates a time effect. Therefore, an elastic-viscoplastic constitutive model must be established to better simulate the time-dependent mechanical behaviour of the pile-soil contact. Based on the Goodman model, we developed an elastic-viscoplastic interface constitutive model of the pile-soil interface into the FRIC subroutine through ABAQUS software, which is one of the most commonly used finite element analysis softwares in the world, to simulate a well-recorded pile test in deep soft soils. The calculated pile lateral frictional resistance and pile-soil relative displacement are close to the measured values, and the ability of the interface model to describe the changes in the shear stress-strain of the pile-soil interface along with time is validated.

The adhesion of soft connective tissues (tendons, ligaments, and cartilages) on bones in many animals can maintain high toughness (∽800 J m −2 ) over millions of cycles of mechanical loads. Such fatigue-resistant adhesion has not been achieved between synthetic hydrogels and engineering materials, but is highly desirable for diverse applications such as artificial cartilages and tendons, robust antifouling coatings, and hydrogel robots. Inspired by the nanostructured interfaces between tendons/ligaments/cartilages and bones, we report that bonding ordered nanocrystalline domains of synthetic hydrogels on engineering materials can give a fatigue-resistant adhesion with an interfacial fatigue threshold of 800 J m −2 , because the fatigue-crack propagation at the interface requires a higher energy to fracture the ordered nanostructures than amorphous polymer chains. Our method enables fatigue-resistant hydrogel coatings on diverse engineering materials with complex geometries. We further demonstrate that the fatigue-resistant hydrogel coatings exhibit low friction and low wear against natural cartilages. Fatigue-resistant adhesion is of interest for a range of applications, but has been limited in synthetic hydrogels. Here, the authors report on a synthetic hydrogel with ordered nanocrystalline domains resulting in high fatigue-resistant adhesion and demonstrate the coating of different surfaces.

Polymer nanocomposites with enhanced performances are becoming a trend in the current research field, overcoming the limitations of bulk polymer and meeting the demands of market and society in tribological applications. Polytetrafluoroethylene, poly(ether ether ketone) and ultrahigh molecular weight polyethylene are the most popular polymers in recent research on tribology. Current work comprehensively reviews recent advancements of polymer nanocomposites in tribology. The influence of different types of nanofiller, such as carbon-based nanofiller, silicon-based nanofiller, metal oxide nanofiller and hybrid nanofiller, on the tribological performance of thermoplastic and thermoset nanocomposites is discussed. Since the tribological properties of polymer nanocomposites are not intrinsic but are dependent on sliding conditions, direct comparison between different types of nanofiller or the same nanofiller of different morphologies and structures is not feasible. Friction and wear rate are normalized to indicate relative improvement by different fillers. Emphasis is given to the effect of nanofiller content and surface modification of nanofillers on friction, wear resistance, wear mechanism and transfer film formation of its nanocomposites. Limitations from the previous works are addressed and future research on tribology of polymer nanocomposites is proposed.

Fluorinated polymers constitute a unique class of materials that exhibit a combination of suitable properties for a wide range of applications, which mainly arise from their outstanding chemical resistance, thermal stability, low friction coefficients and electrical properties. Furthermore, those presenting stimuli-responsive properties have found widespread industrial and commercial applications, based on their ability to change in a controlled fashion one or more of their physicochemical properties, in response to single or multiple external stimuli such as light, temperature, electrical and magnetic fields, pH and/or biological signals. In particular, some fluorinated polymers have been intensively investigated and applied due to their piezoelectric, pyroelectric and ferroelectric properties in biomedical applications including controlled drug delivery systems, tissue engineering, microfluidic and artificial muscle actuators, among others. This review summarizes the main characteristics, microstructures and biomedical applications of electroactive fluorinated polymers.