Side Resistances Research Articles

Evaluation of side and tip resistances for barrette piles using CYCU/Barrette/Side&Tip/64

This study focuses on evaluating the side and tip resistances for barrette piles under compression loading. An extensive dataset from field load tests, designated as CYCU/Barrette/Side&Tip/64, was utilized for analysis. These data were categorized into drained and undrained soils, based on the predominant soil conditions along the pile shaft. In contrast, tip resistance depended on the soil (drained or undrained) or rock condition at the pile tip. Eight interpretation methods were employed to evaluate the measured side and tip resistances of each load test. The predicted side resistance was calculated using the classical α and β methods developed for more common piles such as drilled shafts. For the prediction of tip resistance, end-bearing capacity models for a drilled shaft resting on soil or socketed in rock are considered. Subsequently, a comparison was made between the measured and predicted capacities. Based on these analyses, it was observed that the measured side resistance is the main contributor to the overall capacity of barrette piles. The percentage of measured side resistance ranges from around 80% to 90%. In addition, the predicted side resistance calculated using the α and β methods is smaller than the measured side resistance interpreted using the L2 criterion. To reduce this prediction bias, the adhesion factor (α) and stress factors (K/Ko) for barrette piles were adjusted. For the tip resistance, the trend is opposite – predicted values are larger than the measured values for barrette piles resting on soil or socketed in rock. Another approach to correct for prediction bias called the generalized model factor is presented.

Assessment of Axial Resistance of Piles Considering Consolidation Setup and Aging Setup Using Direct Pile Cone Penetration Test Methods

This paper focuses on evaluating the increase in axial pile resistance subjected to both consolidation and aging setups. Consolidation and aging setup models were first developed to estimate the setup parameters based on databases collected from literature, which include 10 instrumented piles for consolidation setup and 26 test piles for long-term aging. The eight top-performing pile cone penetration test (CPT) methods that were evaluated in a previous study were used to estimate the side resistance of soil layers at 14 days after pile driving. The developed consolidation and aging setup models were then used to extrapolate the results to evaluate the side resistance of each soil layer at the end of consolidation and for long-term aging. The estimated side and total resistances were compared with the measurements from pile load tests considering both consolidation and aging setups. The resistances estimated before and after completion of excess pore water pressure dissipation indicates that significant aging takes place after consolidation setup. The value of consolidation setup parameter ( Ac) was 0.53, and, for aging, the setup parameter ( Ag) was 0.23 in clay and 0.16 in sand. The results show that all pile CPT methods with/without using a consolidation setup model tend to underestimate the unit side resistance of clay soil layers. The use of pile CPT methods in combination with an aging model improved the accuracy of pile CPT methods, and this was verified using load test results for five piles subjected to aging. The Philipponnat and University of Florida (UF) methods showed the best performance on estimating the total resistance of piles subjected to aging.

Experimental study on the behavior of single pile foundation under vertical cyclic load in coral sand

The bearing behaviors of piles in coral sand are critical for project safety due to the unique physical and mechanical properties of coral sand, such as high void ratio, high compressibility, high friction angle and easy to break. A series of model experiments were carried out in this study to evaluate the vertical behavior of single pile in coral sand foundation under cyclic dynamic load with the consideration of the influence of the amplitude of cyclic load, the static biased load and the number of cyclic. Load-settlement relationships, settlement-cyclic number relationships, pile tip and pile side resistances have been thoroughly investigated. Results showed that the load in coral sand foundation will transfer to the pile tip more obviously compared with the pile foundation in quartz sand. Therefore, the pile side resistance will be reduced while the corresponding pile tip resistance will be increased. Particularly, the weakening of side resistance mainly occurs in the first 500 cycles. The development of cyclic cumulative settlement is affected by the combination of the magnitude of static biased load and cyclic amplitude. The existence of static biased load is conducive to restrain the cyclic cumulative settlement when the amplitude of cyclic load is less than static load.

Study on the vertical bearing performances of piles on karst cave

Caves affected the load transfer mechanism of bridge pile foundation, and then the safety of the bridge was threatened. This study was to investigate the effect of karst cave under bridge pile foundations on the vertical bearing characteristics of bridge pile foundations by static load test, finite element analysis and mechanical model. The settlement of the pile was measured by displacement meter, and the axial force were measured by stress gauges in the test. The load-settlement, the axial force, the unit skin friction and the ratios of side and tip resistances were compared with the result of the simulation. Then sixteen conditions were selected in finite element analysis, one of them was a conventional pile not on cave. The others were about five kinds of height, five kinds of span and six kinds roof’s thickness of the cave. The simply supported and fixed wide beam were established to calculate the allowance roof thickness. The results reveal that when the cave span is greater than 9 m × 9 m or the roof thickness is less than 2 D (pile diameter), the stress and deformation of piles are significantly affected.

Combined Side and Base Resistance in Rock-Socketed Drilled Shafts – A State of the Art Consensus

Both side and base resistance contribute to drilled shaft rock socket axial resistance in most cases. While there are geological settings in which mobilization of side and/or base resistance may not be reliable, those situations are the exception, not the rule. The advent of bi-directional axial load testing of rock-socketed drilled shafts has resulted in a significant body of evidence regarding the independent behavior of side and base resistance mechanisms. Accordingly, over the last two decades, a wealth of data from these full-scale load tests of rock-socketed drilled shafts demonstrate this behavior when good design, construction and quality assurance/quality control (QA/QC) procedures are followed. The authors actively attempted to identify bi-directional test results to the contrary, including a survey of the entire Deep Foundations Institute (DFI) membership, but concluded there is a notable lack of evidence that side and base resistance do not mobilize simultaneously when proper design, construction and QA/QC procedures are followed in most geologic settings. Despite this fact, there are agencies and individual engineers that continue to disregard either side or base resistance for reasons that contradict available evidence, often resulting in excessive rock socket lengths that increase costs and the risk of problems during construction. The purpose of this document is to present a summary of the recent evidence indicating mobilization of combined side and base resistances at small, compatible displacements that are within the settlement tolerance of most structures in well-designed, constructed and inspected rock sockets. The recommended best practice for design of rock-socketed drilled shafts is to account for both side and base resistance unless there is a valid documented reason to disregard one or the other on a project-specific basis.

Using a genetic algorithm to develop a pile design method

A genetic algorithm (GA) was used in this study to develop a standard penetration test (SPT)-based design method for the axial capacity of driven piles. A total of 72 pile load tests was collected from literature and divided into two groups based on their measurements. The first group had the load-transfer distribution measurements for extracting both the unit side and tip resistances. These unit resistances were correlated by the GA with soil measurements and pile properties to develop the design method. The second group, where only the total capacity measurements were available, were used to validate the new design method and compare its performance with three existing SPT-based design methods. The new GA-derived design method considers nonlinear relationships with the effective stress and pile length and provides an unbiased prediction with a low coefficient of variation (COV) of 40.0 %, while the three existing methods overestimate the capacity by a factor of 1.62 to 1.65 with a high COV of 40.3 % to 52.8 %, which could result in an under design of pile foundations. This study shows that the GA was able to obtain complex relationships with great accuracy and the new design method can be applied to new cases reasonably well.

On the Use and Interpretation of In Situ Load Tests in Weak Rock Masses

Sockets are often constructed into weak rock mass to improve their axial response to applied compressive or tensile loads. This paper first establishes two separate load test databases for the side and base resistances in in situ socket load tests in weak rocks. The databases include the rock socket geometry, rock socket load–displacement response and the rock mass properties. The paper then reviews the available models for the prediction of (i) the axial resistance (compression or uplift), and (ii) axial deformation. The databases are used to evaluate the existing predictive models for axial resistance and axial deformation, and to evaluate the behavior of drilled shafts in weak rock mass. The load test databases are also used to evaluate the effect of rock mass variability on the reliability of foundations in weak rock. Based on the results of the analysis presented, the applicability of the existing models and approaches to the study of socket behavior in weak rocks are discussed.

Indirect closed loop control of quasi-Z-source inverter for standalone solar PV-based energy conversion system

Nowadays impedance source inverter (ZSI) offers an attractive solution to renewable energy sources with low output, can buck/boost the output voltage by utilising shoot-through pulses. The presence of right half plane zero in control transfer function makes the closed loop control complex, an undershoot is visible in the capacitor voltage. This paper presents an indirect control method of peak dc link voltage for a quasi-Z-source (qZS) inverter connected system. Small signal model for dc and ac sides are elaborated, optimum parameters for impedance network and controller are designed by analysing various frequency and time responses. The control methodology uses a single loop PI controller at dc side, decoupled feed forward control at ac side and parasitic resistances are considered for dynamic analysis. Results depicts a fast reference tracking, without compromising stability, harmonic attenuation, and transient response. A stable controller response validates the presented design and control methodology.

Indirect closed loop control of quasi-Z-source inverter for standalone solar PV-based energy conversion system

Nowadays impedance source inverter (ZSI) offers an attractive solution to renewable energy sources with low output, can buck/boost the output voltage by utilising shoot-through pulses. The presence of right half plane zero in control transfer function makes the closed loop control complex, an undershoot is visible in the capacitor voltage. This paper presents an indirect control method of peak dc link voltage for a quasi-Z-source (qZS) inverter connected system. Small signal model for dc and ac sides are elaborated, optimum parameters for impedance network and controller are designed by analysing various frequency and time responses. The control methodology uses a single loop PI controller at dc side, decoupled feed forward control at ac side and parasitic resistances are considered for dynamic analysis. Results depicts a fast reference tracking, without compromising stability, harmonic attenuation, and transient response. A stable controller response validates the presented design and control methodology.

Performance of X-Section Concrete Pile Group in Coral Sand Under Vertical Loading

To reveal the bearing capacity of the X-section pile group in coral sand, a series of model load tests are conducted. The testing results are presented as load-settlement curves, pile-soil stress ratios, distributions of side friction and axial force, and load-sharing ratio between side and tip resistances. The reliability and accuracy of the numerical simulation model are verified by comparing the results of the model test. Comparative analysis between X-section and circular section piles with the same cross-sectional area indicates that the bearing capacity of the X-section pile group is much larger than that of the circular pile group. The axial force of X-section piles is smaller while the peak skin friction is larger than that of circular piles at the same depth. The skin friction of the core pile is the largest, followed by the side pile and the corner pile is the smallest when the load is relatively small; however, it is converse when the load is larger than 10 kN. Compared with piles in silica sand, the pile in coral sand has a lower bearing capacity, and the sand breakage leads to the steep drop failure of pile foundation. Moreover, pile positions under the raft have less effect on the load-share differences among corner, side and core piles in coral sand. This study provides a reference for the construction of pile foundations in coral sand.

Fouling modeling and prediction approach for heat exchangers using deep learning

In this article, we develop a generalized and scalable statistical model for accurate prediction of fouling resistance using commonly measured parameters of industrial heat exchangers. This prediction model is based on deep learning where a scalable algorithmic architecture learns non-linear functional relationships between a set of target and predictor variables from large number of training samples. The efficacy of this modeling approach is demonstrated for predicting fouling in an analytically modeled cross-flow heat exchanger, designed for waste heat recovery from flue-gas using room temperature water. The performance results of the trained models demonstrate that the mean absolute prediction errors are under 10−4KW−1 for flue-gas side, water side and overall fouling resistances. The coefficients of determination (R2), which characterize the goodness of fit between the predictions and observed data, are over 99%. Even under varying levels of measurement noise in the inputs, we demonstrate that predictions over an ensemble of multiple neural networks achieves better accuracy and robustness to noise. We find that the proposed deep-learning fouling prediction framework learns to follow heat exchanger flow and heat transfer physics, which we confirm using locally interpretable model agnostic explanations around randomly selected operating points. Overall, we provide a robust algorithmic framework for fouling prediction that can be generalized and scaled to various types of industrial heat exchangers.

Evaluation of nasal airflow resistance of operated unilateral cleft lip and palate surgery patients compared with skeletal class III individuals

ObjectiveThe purpose of this study was to measure the nasal airflow resistance of operated unilateral cleft lip and palate (UCLP) patients using the anterior rhinomanometry method compared with non-cleft skeletal class III individuals with isolated maxillary hypoplasia serving as the control group. Material&methodsSixteen UCLP patients who have undergone lip and palate reconstructions and alveolar cleft grafting but not advanced surgeries as the study group and 16 non-cleft skeletal class III participants as the control group (corresponded for age and sex to the study group) were included in this prospective study. All of the patients had class III occlusion due to isolated maxillary hypoplasia. Nasal airflow was measured with anterior rhinomanometry (in ml/sec) for each nostril separately. For evaluation of nasal side subgroups of the UCLP group for nasal resistance, the cleft sides and non-cleft sides of individuals were examined in two separate groups. The nasal side resistance of the control group was evaluated as the average of both nasal side resistances. The nasal resistances for nasal sides and total nasal resistance were measured in Pa/L/sec. The observed data were analyzed using Kolmogorov-Smirnov test used for normality, and the Student t-test and Mann Whitney U test used to determine the differences between the groups. P values of <0.05 were considered statistically significant. ResultsAs the primary outcome of this study, it was found that both the cleft sides and non-cleft sides of the UCLP individuals had statistically significantly higher nasal resistance than the healthy skeletal class III control group (p < 0.05). It was revealed that the cleft side had more nasal resistance than the non-cleft side for both inspiration and expiration, but the results were not statistically significant (p = 0.41/p = 0.28). ConclusionThe results showed that operated UCLP patients have nasal resistance and breathing problems, even when lip, palate, and alveolar cleft operations have been performed.

Load‐Bearing Characteristics of Large‐Diameter Rock‐Socketed Piles Based on Ultimate Load Tests

As part of a large converter project in Shandong Province, vertical static load tests and internal force tests were conducted on three large‐diameter rock‐socketed piles, their load transfer mechanism was clarified, and the ultimate side resistance and ultimate resistance performance characteristics of the rock‐socketed sections were analyzed. The test results showed that the three test piles were damaged under maximum loading, the Q‐s curve exhibited a steep drop, the pile compression was around 1.2 times the pile diameter, and the bearing capacity of a single pile did not meet the design requirements. The side and end resistances of the three test piles all reached their ultimate values, but the ultimate side resistance was lower than the lower limit of the recommended value in the current technical code for building pile foundations. The end resistance under maximum loading accounted for 38.4–53.8% of the peak load, which was relatively high. By comparing it with other studies, there was no significant correlation between the coefficient of rock ultimate side resistance of the rock‐socketed segment and the pile diameter of the rock‐socketed segment. However, the coefficient of ultimate resistance increased gradually with the pile diameter. However, the latter correlation was not significant when the pile diameter was less than 1000 mm.

Narciclasine inhibits angiogenic processes by activation of Rho kinase and by downregulation of the VEGF receptor 2

The process of angiogenesis is involved in several pathological conditions, such as tumor growth or age-related macular degeneration. Although the available anti-angiogenic drugs have improved the therapy of these diseases, major drawbacks, such as unwanted side effects and resistances, still exist. Consequently, the search for new anti-angiogenic substances is still ongoing. Narciclasine, a plant alkaloid from different members of the Amaryllidaceae family, has extensively been characterized as anti-tumor compound. Beyond the field of cancer, the compound has recently been shown to possess anti-inflammatory properties. Surprisingly, potential actions of narciclasine on endothelial cells in the context of angiogenesis have been neglected so far. Thus, we aimed to analyze the effects of narciclasine on angiogenic processes in vitro and in vivo and to elucidate the underlying mechanism. Narciclasine (100–300 nM) effectively inhibited the proliferation, undirected and directed migration, network formation and angiogenic sprouting of human primary endothelial cells. Moreover, narciclasine (1 mg/kg/day) strongly reduced the VEGF-triggered angiogenesis in vivo (Matrigel plug assay in mice). Narciclasine mediated its anti-angiogenic effects in part by a RhoA-independent activation of the Rho kinase ROCK. Most importantly, however, the compound reduced the de novo protein synthesis in endothelial cells by approx. 50% without exhibiting considerable cytotoxic effects. As a consequence, narciclasine diminished the presence of proteins with a short half-life, such as the VEGF receptor 2, which is the basis for its anti-angiogenic effects. Taken together, our study highlights narciclasine as an interesting anti-angiogenic compound that is worth to be further evaluated in preclinical studies.

Penetration Model for Installation of Skirted Foundations in Layered Soils

During installation of a skirted foundation, resistance to penetration is a combination of side and tip resistances. When penetrating a permeable soil unit, tip resistance in particular can be high but if seepage water flow from the outside to the inside of the skirted foundation exists, the pore water gradient will reduce the effective stresses and therefore also penetration resistance. Recent installation data from the field and laboratory suggest that this effect can also occur during installation in layered profiles. This paper presents a model that accounts for seepage flow in unlimited permeable layers that are overlain by one or several impermeable layers. The model assumes that seepage flow in the underlying sand layer is induced by an incremental lift of the internal soil plug, which enables the transfer of some of the differential pressure applied under the foundation lid to the bottom of the lifted soil plug. A single equation is proposed to calculate the critical suction number for layered soil conditions that can be used with an empirical model to calculate the reduction in penetration resistance. A calibration of the proposed equation for the critical suction number is carried out using an axis symmetrical finite-element model that uses a linear elastic soil model and assumes steady-state flow conditions. The calibration of the proposed equation for calculating the critical suction number was first carried out for a homogenous permeable soil. This was done to benchmark the model against previously published data. In a second step, the calibration was done for a layered profile and different flow boundary conditions. The proposed penetration model is demonstrated by back-calculating full-scale installations. The paper closes with a discussion of the main assumption of plug lift, and a simple model to evaluate the degree of plug lift is proposed.

Advanced Method for Quantifying Socket Roughness and Empirical Correlations

Abstract This article describes an advanced method for quantifying socket profiles and proposes empirical relations to estimate the maximum side resistance at the soft rock socket. At three boreholes in Busan, South Korea, socket profiles with a continuous 500-mm length were recorded by the Kyungsung Sonar Roughness Profiling System that was developed by the authors, and full-scale bidirectional pile-loading tests (BDPLTs) were performed to evaluate the mobilized side resistances for the soft rock sockets. Based on the reports of previous research, the concept of self-affine fractals was adopted to idealize the measured profiles, and the roughness ratio, which is a nondimensional factor, was proposed to quantitatively describe the asperity of the idealized profiles. From the results of the BDPLTs, the unit-side-load transfer curves, f-w curves, for the soft rock socket were plotted to determine the maximum unit-side resistances in accordance with the new mobilized displacement criterion predicated upon the reviews of 17 f-w curves for the soft rock socket obtained from BDPLTs conducted at other sites in South Korea. Furthermore, using these data, including the socket diameter, the unconfined compressive strength of the soft rock, and the roughness ratio, advanced empirical correlations considering socket roughness were studied and proposed in this article.

A Load-Testing Program on Large-Diameter (66-Inch) Open-Ended and PSC-Instrumented Test Piles to Evaluate Design Parameters and Pile Setup

This paper presents the results from a pile load testing program for a bridge construction project at Chalmette, Louisiana. The load testing includes three 66-in. spun-cast post-tensioned open-ended cylinder piles and one 30-in. square prestressed concrete (PSC) pile driven at four different locations along the bridge site in clayey-dominant soil. Both cone penetration tests and soil borings/laboratory testing were used to characterize the subsurface soil conditions. All test piles (TP) were instrumented with strain gauges to measure the load distribution along the length of the TPs and to measure the side and tip resistances, separately. Dynamic load tests (DLT) were performed on all TPs at different waiting periods after pile installations to quantify the amount of setup (i.e., increase in pile resistance with time). Case Pile Wave Analysis Program (CAPWAP®) analyses were performed on the DLT data to calculate the resistance distributions along the TPs. A static load test was performed only on the PSC pile and statnamic load tests (SNLT) were conducted on both pile types. Design parameters such as the total stress adhesion factor, α, and the effective stress coefficient, β, were back-calculated. The α values ranged from 0.41 to 0.86, and the β values ranged from 0.13 to 0.29. The load test results showed that SNLT overestimated the tip resistance as compared with dynamic and static load tests. Moreover, the pile tip resistance was almost constant during the testing period, and setup was mainly attributed to increase in pile side resistance with time.

Semi-analytical solutions for vertically and laterally loaded piles in multilayered soil deposits

In geotechnical practice, it is of considerable importance to assess the behavior of vertical–lateral coupled loading piles in multilayered soil deposits. This study deals with a semi-analytical formulation for the performance of a pile suffering from combined vertical and lateral loads. The emphasis is on quantifying the mobilization of the subgrade reaction provided by the layered soil stratums. In the proposed method, subgrade reactions, correlated with both the accumulative axial load transfer and side resistances depending upon the pile–soil interaction, are abstracted as a series of nonlinear springs in both vertical and lateral directions. On account of this, an alternative transfer matrix method is applied to characterize the pile reaction along the depth under the identified boundary conditions atop the pile; meanwhile, the condition of static equilibrium, between two specific pile segments located at the border of soil layers, is also essential. On this basis, validation of the solution is conducted by comparing with observations from experiments and predictions obtained from other existing methods. In addition, the influence of properties in shallow soil layer and the vertical load on the lateral response of the pile is also discussed. The results indicate a reduction in the lateral displacement and the maximum bending moment within the pile with the increase in the shallow soil stiffness, but a growth with the increase in vertical load due to the “P-Δ effect.”

Marangoni condensation of steam-ethanol mixtures on a horizontal low-finned tube

Abstract Careful heat-transfer measurements have been conducted for condensation of steam-ethanol mixtures in vertical downflow over a horizontal, water-cooled, low-finned copper tube. Care was taken to avoid error due to the presence of air in the vapor. The tube had diameter at the fin root 12.7 mm and rectangular section fins with height 1.6 mm, thickness 0.5 mm and space between fins 1.0 mm. Tests were conducted at pressures of atmospheric, 55 kPa and 14 kPa. Concentrations of ethanol by mass in the boiler when cold prior to start up were 0.025%, 0.05%, 0.1%, 0.5% and 1.0%. The highest vapor velocity at approach to the tube was 7.5 m/s at atmospheric pressure and 15.0 m/s at vapor pressure 14 kPa. Effects of ethanol concentration on both retention angle and heat transfer were measured. The retention angle was strongly dependent on the vapor velocity and ethanol concentration which affected the condensation rate, composition and temperature of the condensate at the interface and consequently the surface tension of condensate. The results are compared with data for pure steam on the same finned tube and Marangoni condensation on a smooth tube under the same conditions. Similarly, results for condensate retention of water on finned tube are compared with earlier data and theoretical model. Vapor-side, heat-transfer coefficients were obtained by subtraction of coolant side and test tube wall thermal resistances from overall measurements.

On behavior of load transfer for drilled shafts embedded in weak rocks

This study deals with the formulation of an analytical solution for load transfer in drilled shaft and its application. The emphasis is on quantifying the mobilization of side resistances, which are closely related to shear behaviors of the concrete-rock interface. In this modelling, the side resistance is idealized by using elasticity-brittleness-plasticity, and a simple slip-line field is built to identify the critical shear displacement. The closed-form solution of load transfer is obtained by using the proposed shear model. Comparison between predictions and field observations is also made to validate performance of the proposed method.