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Shaft-surface friction pairs in marine equipment endure considerable wear and corrosion in seawater, particularly under cyclic loading. A friction and wear test bench was employed to replicate the conditions faced by ship stern shafts and bearings in seawater. The study aimed to assess the tribological performance of three types of polyphenylene sulfide (PPS) materials: pure PPS, PPS reinforced with 30% glass fiber (30% GF in PPS matrix), and PPS reinforced with 30% carbon fiber (30% CF in PPS matrix), against 316L stainless steel under varied lubrication conditions. Results demonstrate that all PPS variants exhibit minimal friction force and wear loss in seawater, with 30% CF in the PPS matrix displaying the least friction and wear characteristics. Friction force fluctuates within a 2.5 ~ 5 N range, and wear loss is 0.027 g. However, due to the uneven bonding of glass fiber (GF) within the PPS matrix, the addition of GF did not significantly enhance the materials’ anti-friction properties and wear resistance. The predominant wear mechanism involves severe three-body abrasive wear caused by GF detachment from the friction pairs surface. Additionally, the study explores carbon fiber’s resilience to cyclic loading, the lubricating effect of seawater mixed with carbon fiber debris, and the transfer mechanism of polymer films. These findings highlight synergistic anti-friction and wear-resisting effects between carbon fiber, seawater, and polymer transfer films, offering valuable insights for selecting effective shaft friction pairs materials in challenging seawater conditions.

The present experimental study investigates the influence of cyclic displacement amplitude and effective consolidation stress on the evolution of mobilized local shaft friction along piles submitted to large number of cycles (up to 10 5 cycles). Two-way cyclic displacement-controlled tests were performed on an instrumented pile-probe installed and loaded in a calibration chamber. Tests were performed on reconstituted specimens of saturated clay to examine the shaft friction evolution in the soil-pile interface during cyclic loading. Displacement-controlled static tests were also performed before and after the cyclic loading in order to quantify the influence of cyclic parameters on post-cyclic static response. It was found that the amplitude of cyclic displacement and the initial state of stress have an influence on the evolution of local friction during cyclic loading. The degradation rate of local friction increased for larger cyclic displacement amplitudes whereas with increasing the effective consolidation stress, the degradation rate decreased. The application of displacement- controlled cycles resulted in a modification in the behaviour of the interface. A significant peak of static friction followed by strain softening was observed during post cyclic static tests, which was not the case for pre-cyclic static tests. The peak value of friction obtained upon post-cyclic static loadings found to be more important for higher values of applied displacement amplitude during cyclic loading. Finally, a brief synthesis of the results is given.

Energy piles are an effective and economic means of using geothermal energy resources for heating and cooling buildings, contributing to legislative requirements for renewable energy in new construction. While such piles have been used for around 25 years with no apparent detrimental effect, there is limited understanding of their thermo-mechanical behaviour. This paper synthesises the results from three published field studies and illustrates some of the engineering behaviour of such piles during heating and cooling. Simplified load transfer mechanisms for a single pile subjected to pure thermal loadings (i.e. without mechanical load) and combined thermo-mechanical loadings have been developed and are used to interpret the field data with regard to change in axial stress and shaft friction during heating and cooling. The effect of end restraint and ground conditions on the thermo-mechanical response of energy piles is discussed. Values of change in axial stress and mobilised shaft friction due to thermal effects that may be useful in the design of energy piles are presented.

This study introduces a novel method for evaluating pile–soil interaction based solely on Dilatometer Test (DMT) results, enhancing and extending the established approach originally developed using Menard Pressuremeter Test (PMT) data. Currently, transfer functions utilizing DMT sounding results are in the early stages of development. Presented research fills the gap in DMT-based methods for pile design by introducing transfer functions for reversal loadings to calculate the unit shaft friction of screw displacement piles in Controlled Modulus Columns (CMC) technology. The proposed method utilizes DMT-derived soil parameters, offering a practical and accurate alternative to PMT-based models. Testing research fields were located in the Vistula Marshlands, Northern Poland. Site characterization consisted of piezocone (CPTU) and DMT soundings to characterize the soil profile and estimate soil parameters relevant for pile design. CMCs were installed and statically load tested under various loading schemes. Laboratory direct shear tests on smooth and rough soil-concrete interfaces were performed in both forward and backward directions (reversal loading) to simulate pile loading conditions. Results demonstrate improved adaptability of DMT-based transfer curves to local soil conditions and provide a reliable framework for predicting pile performance in soft soils. Proposed DMT-model returns similar ultimate bearing capacities of the pile to CPT 2012 method for first loading, simultaneously offering better agreement for reversal loading, a situation not accounted for in CPTU 2012 or most other CPT-based methods.

Soil is the habitat for soil organisms and associated soil physical and chemical processes. The subsoil is a large reserve of water and nutrients. Soil and subsoil are thus significantly involved in the yield capacity of a site and its resilience in the case of unfavorable weather conditions. Subsoil can also retain water in drought phases and stores carbon. In times of climate change and scarcity of resources, many scientific activities involve subsoil and require sensors to assess subsoil conditions and properties. An electrically driven penetrometer with an integrated soil water content sensor could be an appropriate tool for such applications; however, such a subsoil measurement tool does not exist. One major reason for this is that, when penetrating compacted subsoil, high penetration forces (including friction) act on the penetrating thin rod (diameter 1 cm). The development of a tractor-mounted subsoil penetrometer for depths up to 2 m is described in this study. An ASABE standard cone is implemented, which can access heavy compacted layers. The rod, which includes wires for embedding an FDI moisture sensor in the cone tip, is covered by a protection tube. The penetration resistance measurement can be performed without being influenced by shaft friction. The rod, along with the sensor, is implemented in a tower that can be shifted laterally and can take probes in a single line without moving the tractor. To confirm the quality of the developed subsoil penetrometer, a suitable evaluation method is presented. Typical arable soil (loamy silt) was filled in boxes and compacted homogeneously using a hydraulic stamp so that different setups of the penetrometer could be compared and evaluated. The evaluation concludes that the distance between the free cone tip and the protection shaft should be at least 10 cm to measure the penetration resistance of soil without being influenced by the protection tube. Furthermore, the developed penetrometer has sufficient stability and precision for accessing subsoil. In field trials, the subsoil penetrometer was compared with a standard penetrometer and has proved its suitability.

This paper examines the stiffness degradation and interface failure load on soft soil–concrete interface. The friction behavior and its variability is investigated. The direct shear tests under constant normal load were used to establish parameters to hyperbolic interface model which provided a good approximation of the data from instrumented piles. Four instrumented piles were used to obtain reference soil–concrete interface behavior. It was found that the variability of the friction characteristics is the highest for organic clays and the lowest for organic silts. The intact samples exhibit lower shear strength than reconstituted ones. The adhesion varies significantly depending on interface and soil type, which can result in high scatter of the skin friction prediction. The analysis of parameters variability can be used to determine the upper and lower bound of friction behavior on the interface at constant normal load condition. The backward shearing results in decrease in shear strength up to 40% of the precedent forward phase but higher initial stiffness by a factor of between 2 and 3. Presented research provides basic shear and stiffness parameters for four soft soils (organic clay, organic silt, peat, and silty loam) and gives information about variability of interface characteristics.

Helical pile is an invention of pile foundation that has many advantages. Helical pile produced bearing capacity greater than other pile foundations. It because The Bearing capacity of helical pile is contributed by end bearing capacity (Qb), shaft friction bearing capacity (Qs) and bearing capacity of helix or cylindrical (Qcyc) along pile. On of the Several factors that influence bearing capacity of helical pile was the configuration of helix diameter arrangement. This research was a laboratory experiment using a box, sand as the medium and a miniature of steel pile. The diameter pile test was 1,5 cm and length was 63 cm. Each pile has three helix along the pile with a configuration of diameter from top to bottom was 10 cm – 8 cm – 6 cm and from top to bottom 6 cm – 8 cm – 10 cm. The kind of Loading test was used in this research was Quick Maintain Load (QML). From the research, It was found that the variation wich gave the most significant influence in remained the greatest bearing capacity was the pile with diameter configuration of helix from top to bottom 6 cm – 8 cm – 10 cm or pile D6810.

The displacement behavior of soil inside open-ended piles during driving is associated with soil plugging performance. This study analyzed the ultimate equilibrium of the pile-soil during pile installation and then established the ultimate balance equation. A pile-soil contact dynamic resistance factor (DRF) was incorporated by the kinematic method to develop the equation under dynamic loading. The inertial force and DRF were both integrated into the displacement analytical model, and the ultimate equilibrium differential equations of the soil inside the open-ended pile subjected to hammering loads were developed to derive the analytical solution of plug displacement under drained and undrained conditions respectively. For the same average acceleration and pile diameter, the higher the magnitude of the shaft friction factor (β) was, the more significant the compression of the soil inside the pile was. Smaller pile diameter resulted in more dramatic compaction of the soil within the pile, although this effect was weak. Furthermore, the internal soil was exponentially compressed with the increase in acceleration. The results were compared with numerical results. The analytical solutions could predict the soil displacement of open-ended piles during driving and provide useful insights into the actual situation of soil plug.

A new technique for finishing the surfaces of friction pairs has been proposed, which, in combination with the original test method, has shown a significant influence of the initial roughness configuration (surface texture) on friction and wear. Two types of finishing processing of the shaft friction surfaces were compared, and it was found that the friction and wear coefficients differ by more than 2–5 and 2–4 times, respectively. Based on a new methodology for analyzing standard roughness parameters, the tribological efficiency criteria (in the sense of reducing friction and wear) are proposed for the initial state of the friction surface of a radial plane sliding bearing shaft relative to the friction direction, which is consistent with its frictional characteristics. Comparison of the laboratory test results with the surface tribological efficiency criteria showed that these criteria are very promising for controlling existing technologies and optimizing new technologies for friction surface finishing in various friction systems.

Soft rock is extensively distributed worldwide, and the piles in the soft rock are widely used in high- rise buildings and bridge engineering with high loads and high settlement requirements. The soft rock- socketed pile differs from the hard rock and soil pile in terms of failure mode and interface characteristics. The pile-rock interface of piles in soft rock features an expansion slip and normal constant stiffness. Direct simple shear is more consistent with the actual case than direct shear in stress and deformation. Based on this, a new type of DSS apparatus with constant stiffness is developed to study the interface of pile-soft rock. The shear test of soft rock and pile-soft rock interface with different roughness is carried out, and the rationality of the test method is demonstrated. Combined with the reasonable generalization of the roughness of the interface, an indoor test method for obtaining the shaft friction of a pile in soft rock can be proposed.