Pile Load Research Articles

Safety Assessment of Kentledge Construction for Pile Foundation

Insufficient strength and stiffness of the kentledge system in the static pile load test will lead to test failures and even accidents. However, the codes and standards do not offer definite guidelines in this regard. This article carried out static load tests on the piles of a road bridge in Bhubaneswar, India, to highlight the importance of the kentledge strength and stiffness for the successful conduct of such tests. Based on the results of this study, the article proposed a methodology for the structural design of the kentledge system, which can be adopted to standardize the procedures of static pile load tests available in the existing codes. The findings of this study will be useful to practitioners working in pile construction.

Design of Axially Loaded Piles in Consolidating Soils

The present design method in various codes for axially loaded piles embedded in consolidating soil is not satisfactory. It is too conservative in calculating the maximum pile force. Furthermore, the additional pile settlement due to the consolidation is neglected in ascertaining whether the requirements of allowable settlement have been met. This is because the behavior of such piles is not well understood. A new step-by-step design method based on the combination of results of extensive parametric studies of an elastoplastic load transfer model incorporating pile–soil slip reported previously is presented. In contrast to the iterative procedure required by some existing methods to determine the neutral plane location, these design charts can be used to determine the pile top settlement, neutral plane location, and maximum pile load directly. Further saving in the design of pile foundation is obtained with the concept of a compensating-pile foundation.

A case study experimental pile load testing (PLT) for evaluation of driven pile behaviors

A case study experimental pile load testing (PLT) for evaluation of driven pile behaviors

Determination of optimal designs for geothermal energy piles in the soil supporting a multi-storey building

The article presents the optimal design of geothermal energy piles supporting a multi-story building at different pile spacing. The optimization model OPTPILE, based on the construction cost of the single pile, was used for this purpose. It was provided with geotechnical and structural design constraints that satisfy the requirements of building codes. The optimal design of a geothermal energy pile was studied for a 10-storey building with different pile spacing. So far, only a single energy pile has been optimized and therefore the spacing between the piles has not yet been considered in the design. However, in this work, pile spacing is taken into account by considering the entire load distribution of the multi-story building. A 3D beam-slab frame was created to determine the pile loads. The recommendation for the optimal design of geothermal energy pile spacing for a 10-storey building was developed. The results show that the optimal pile spacing (square distribution) for a 10-storey building is about 7 m. The construction cost for all thermal pile foundations and concrete structural components for a 10-storey building is estimated to be 101.1 €/m2. The optimal architecturally reasonable spacing of piles with a square distribution for a 10-storey building is 8.5 m. In this case, the cost of the concrete structural elements of the building and the piles increases by 1% to 102.1 €/m2. The cost of installing the heating pipes in the pile is about 1 €/m2.

Analysis of Negative Skin Friction on a Single Pile Based on the Effective Stress Method and the Finite Element Method

Negative skin friction (NSF) of piles in recent filling or soft area is an important effect factor of pile bearing capacity. Since field experiments on NSF are time consuming and it is difficult to large surcharge loads in experimental research, a unified calculation method of pile positive/negative skin friction was established based on the effective stress method for investigation. The closed-form analytical solutions for calculating the pile skin friction corresponding to the plastic and elastic state were derived respectively. Meanwhile, the axial load of a single pile under different distribution forms of the pile skin friction was deduced. The calculation method was verified by comparing with an in-situ test. Furthermore, a computer model, which was established by the finite element method, was used to study the effect of the friction coefficient, consolidation time, consolidation pressure, drainage condition, and pressure ratio on the distribution of NSF and the location of neutral point. The results show that the effect of the friction coefficient, consolidation time, and pressure ratio on the NSF were significant. The friction coefficient increased from 0.05 to 0.4, the position of the neutral point rose by 22%, and the drag load of pile shaft was obviously increased. The effect of consolidation pressure and drainage conditions on the neutral point were relatively less, but they had a great influence on the distribution and magnitude of NSF. Furthermore, under different consolidation pressures, the normalized maximum axial load, Fmax/p, of the pile shaft had a good linear relationship with the pressure ratio, n, and the slopes were the same.

Prediction of driven pile resistances in shales considering weathering and time effects

The difficulty with shale sampling and testing and the lack of pile load tests in shales have created challenges with shale classification, pile resistance prediction, and understanding time-dependent pile responses. Treating shale as soil can yield a conservative pile design. Shales were classified into soil-based and rock-based depending on their weathering conditions, mechanical properties, and measured pile resistances. Failure behaviors of soil- and rock-based shales are discussed. Prediction equations were developed to account for predicting shale properties. Properties of rock-based shales decrease with the increase in weathering. New static analysis (SA) methods were proposed to predict unit shaft resistance ( qs) and unit end bearing ( qb) of piles in shales and validated. Our study yields higher resistance and efficiency factors for the proposed SA methods and piles in shales than existing SA methods developed for piles in soils. The qs in the soil-based shale exhibits pile setup, while the qs in rock-based shales experience both setup and relaxation. The qb in both soil-based and highly weathered shales is likely to experience pile setup. However, the qb in the moderately and slightly weathered shales experience both setup and relaxation.

Response of vertically-loaded pile in spatially-variable cement-treated soil.

Despite the extensive application prospects of piles in cement-treated soil, few studies have explored the ultimate bearing capacity especially in consideration of the spatial variability of cement-treated soil. This study examines the performance of driven piles which were installed inside the cement-treated ground, considering the inherent spatial variability of the cemented soil and the positioning error during piles installation through finite element analyses. The deterministic and random finite element analysis results have shown that the shaft resistance mainly provided the ultimate bearing resistance of piles in cement-treated soil. The spatial variability reduced the global performance of pile installed through a cement-treated soil. The ultimate bearing resistance of the pile inserted in cement-treated soil was controlled by drained condition. Drained ultimate bearing resistance should be used to determine the design working compression load of pile in cement-treated soil.

A variable parameter control method for charging pile load aggregator to participate in the fast frequency market

Abstract With the access of large-scale new energy sources, fast frequency regulation resources of the power system are scarce. A variable parameter control method for charging pile load aggregator to participate in the fast frequency market is proposed in this paper. It is that charging pile load aggregator actively adjusts the active power according to the frequency of the local power system, and the response speed is within 0-2 seconds. In addition, the variable parameter control method proposed in this paper specifically controls the power of charging pile according to the speed and amplitude of frequency drop, which has strong pertinence and simple control scheme, and further improves the frequency stability of the power grid.

Time-dependent evolution of bearing capacity of driven piles in clays

Analysis of the time-dependent variation in the axial capacity of driven piles is difficult yet critical for geotechnical engineers. In this work, to investigate the short-term evolution of the bearing capacity of driven piles, a two-dimensional finite-element (FE) model was developed using the Abaqus program. Pile installation, soil consolidation and loading were incorporated in an integrated FE model. Changes in the excess pore pressure and the void ratio of the surrounding soil were investigated to evaluate the consolidation mechanism. The findings revealed that excess pore water pressure dissipation was the primary cause of the short-term evolution of the pile's bearing capacity. The dissipation of excess pore water pressure lowered the void ratio and increased the strength and stiffness of the surrounding soil. The effect of the permeability coefficient was also assessed. The permeability coefficient was found to affect the rate of evolution but not its magnitude. A centrifuge model test was used to verify the numerical results. The findings of this study may serve as a guide for improved design and construction of driven piles.

Developing random forest hybridization models for estimating the axial bearing capacity of pile.

Accurate determination of the axial load capacity of the pile is of utmost importance when designing the pile foundation. However, the methods of determining the axial load capacity of the pile in the field are often costly and time-consuming. Therefore, the purpose of this study is to develop a hybrid machine-learning to predict the axial load capacity of the pile. In particular, two powerful optimization algorithms named Herd Optimization (PSO) and Genetic Algorithm (GA) were used to evolve the Random Forest (RF) model architecture. For the research, the data set including 472 results of pile load tests in Ha Nam province-Vietnam was used to build and test the machine-learning models. The data set was divided into training and testing parts with ratio of 80% and 20%, respectively. Various performance indicators, namely absolute mean error (MAE), mean square root error (RMSE), and coefficient of determination (R2) are used to evaluate the performance of RF models. The results showed that, between the two optimization algorithms, GA gave superior performance compared to PSO in finding the best RF model architecture. In addition, the RF-GA model is also compared with the default RF model, the results show that the RF-GA model gives the best performance, with the balance on training and testing set, meaning avoiding the phenomenon of overfitting. The results of the study suggest a potential direction in the development of machine learning models in engineering in general and geotechnical engineering in particular.

Effect of loading eccentricity on the ultimate lateral resistance of twin-piles in clay

This paper studies the effect of loading eccentricity and pile spacing on the ultimate lateral soil resistance of twin-piles using finite element limit analysis and analytical upper bound plasticity methods. Two kinematic mechanisms corresponding to the failure modes produced by the advanced finite element simulations are postulated with different eccentricity and pile spacing cases. Comparisons have shown excellent agreements between the two approaches. A series of parametric studies are then subsequently performed. Numerical results have shown that loading eccentricity considerably affects ultimate lateral soil resistance, leading to a maximum reduction of 50%. In addition, the curve of normalised pile resistance versus pile spacing ratio is dissimilar to that without considering the effect of loading eccentricity. The proposed solutions and failure mechanisms in this study will provide a deepened insight on the performance of twin-pile group under eccentric loads.

EVALUATION OF PARTICLE CRUSHING IN SOILS USING X-RAY CT DATA

The objective of this paper is to evaluate particle crushing in the soil using the results of X-ray CT scanning without any destruction and sampling. First of all, the properties of X-ray CT data are discussed using its statistical consideration. Then, a method for evaluating particle crushing is proposed. This method is implemented by scanning simple granular materials using aluminum rods and soil. Then, a series of model pile loading tests are conducted for the materials of non-crushable and crushable soils. Based on the results of CT scanning for the model grounds, the effectiveness of the proposed method for evaluating particle crushing using X-ray CT data is confirmed. Finally, one of the effective usages of X-ray CT data in geotechnical engineering is convinced.

Laboratory Model Test of Fully Buried Portal Frame-Shaped Slope-Stabilizing Piles

Abstract Fully buried portal frame-shaped piles have been widely used to control and stabilize large-scale landslides or slopes. However, the working mechanism of portal frame piles, such as the soil–pile interaction and load transfer behavior, is still not fully understood, which has limited the development of effective pile designs and construction. In this study, a well-designed laboratory model test was conducted in a sandy soil slope with a man-made slip surface. Nine portal frame piles were installed, synthetically considering the pile spacing between the rear and front piles as well as the support condition of the pile ends. To make the test closer to reality, in addition to a small thrust due to the excavation of the slope, greater landslide thrusts were imposed on the rear side of the portal frame piles by gradually applying static loads on the top of the slope. It is found that in addition to a concentrated thrust transferred via the cap beam, a landslide thrust accounting for 30 to 60 % of the landslide thrust on the rear pile was transmitted to the front pile by the soil sandwiched between the rear and front piles, which should not be ignored in designs. Meanwhile, to evenly mobilize the bearing capacity of both the rear and front piles, the reasonable spacing between them should be 1.0 to 1.5 times the diameter of the pile. The study also shows that portal frame piles should be embedded in a stable soil layer rather than the bedrock if they can meet the requirements for bearing capacity.

Spatial-temporal Dynamic Forecasting of EVs Charging Load Based on DCC-2D

The charging load of electric vehicles (EVs) has a strong spatiotemporal randomness. Predicting the dynamic spatiotemporal distribution of the charging load of EVs is of great significance for the grid to cope with the access of large-scale EVs. Existing studies lack a prediction model that can accurately describe the dual dynamic changes of EVs charging the load time and space. Therefore, a spatial-temporal dynamic load forecasting model, dilated causal convolution-2D neural network (DCC-2D), is proposed. First, a hole factor is added to the time dimension of the three-dimensional convolutional convolution kernel to form a two-dimensional hole convolution layer so that the model can learn the spatial dimension information. The entire network is then formed by stacking the layers, ensuring that the network can accept long-term historical input, enabling the model to learn time dimension information. The model is simulated with the actual data of the charging pile load in a certain area and compared with the ConvLSTM model. The results prove the validity of the proposed prediction model.

Inversion of damage inducement of wharf pile foundation under heaped load based on parametric model

Uneven stowage of wharf is one of the main external loads during its service period. The main load-bearing structure of the overhead vertical wharf is the lower pile foundation. Under the action of the upper pile load, the pile foundation will be damaged to varying degrees, and the local damage may cause adverse effects on the overall structural safety of the wharf. In order to realize the inversion analysis of the adverse damage inducement of wharf stowage, the stress detection results of the lower pile foundation are taken as inversion data samples, and 10,000 sets of stress data are obtained by establishing a parameterized numerical calculation model. After normalization and dimension reduction, they are input into the established neural network model, and the action position and strength of stowage damage inducement are identified. The results show that the inversion analysis samples obtained by the parameterized model in this paper have higher accuracy and generalization in the calculation of neural network model.Article HighlightsThe difference of recognition indexes between training samples and test samples is small, and there is no lack of fitting ability, and the generalization ability is strong.The regression learner network has two hidden layers, and the number of nodes is 10 and 4, respectively. The parameter setting with the activation function as identity can meet the inversion needs of the heap damage inducement.Inversion calculation of wharf damage incentives needs to establish samples with large data space, while materialization model calculation takes up a lot of computer memory and takes time.

Monitoring of an instrumented geosynthetic-reinforced piled embankment with a triangular pile configuration

ABSTRACT A comprehensive monitoring programme was undertaken at a geosynthetic-reinforced piled embankment over soft ground to better understand its time-dependent performance. The programme involved continuous monitoring of earth pressure, axial force in piles, settlement of structural elements, lateral movement of subsoil, and geogrid tensile strain of the instrumented system. Earth pressure measurements evidenced the mobilization of soil arching; pile efficacies were derived from established analytical methods and assessed against observed data for piles with circular cap configuration arranged in a triangular pattern, with the Concentric Arches model giving the best predictions. The development of axial load in piles can be properly captured by a regression equation with analytical approach. Penetration and compression behaviours of structural elements were evaluated by settlement measurement on piles and soils at ground level relative to pile toe or substratum. The proposed approach in obtaining tensile force of geogrid was verified with the measured differential-settlement data.

Numerical investigation of the monotonic drained lateral behaviour of large-diameter rigid piles in medium-dense uniform sand

This paper presents a numerical investigation of the monotonic lateral response of large-diameter monopiles in drained sand with configurations typical of those employed to support offshore wind turbines. Results from new centrifuge tests using instrumented monopiles in uniform dry sand deposits are first presented and used to illustrate the suitability of an advanced hypoplastic constitutive model to represent the sand in finite-element analyses of the experiments. These analyses are then extended to examine the influence of pile diameter and loading eccentricity on the lateral response of rigid monopiles. The results show no dependency of suitably normalised lateral load transfer curves on the pile diameter and loading eccentricity. It is also shown that, in a given uniform sand, the profile with depth of net soil pressure at ultimate lateral capacity is independent of the pile diameter because of the insensitivity of the depth to the rotation centre for a rigid pile. A normalisation method is subsequently proposed which unifies the load–deflection responses of rigid piles with different diameters at a given load eccentricity.

Model studies on effect of pseudo-rock-socket strength on resistance of friction-only piles

1-g small scale model experimental investigations were carried out in the laboratory to study the behavior of piles, socketed in rock, under axial load. In this study, an attempt is made to investigate the mechanics of load distribution by friction on model piles made of Aluminum tubes, socketed in pseudo-rock samples. A series of rock socketed model pile load tests was carried out using the indigenously developed loading frame and set-up. Two Aluminum tube piles having outer diameter of 60 and 80 mm were used in the investigations. Different length-to-diameter ratios were considered by changing length of piles. Sponge was provided at the tip of the model pile to avoid the influence of end resistance and to create skin frictional resistance only. Different mixes of pseudo-rock specimens were prepared by varying the proportions of cement and plaster of Paris. Uniaxial compression strength tests were conducted on the pseudo-rock specimens to evaluate the effect of strength of pseudo-rock specimens on skin friction. Also, elastic constants (modulus of elasticity and Poisson ratio) and shear parameters (cohesion and angle of internal friction) of pseudo-rock specimens were determined. Experimental results show that the load-settlement curve is nonlinear for axial compression load tests. An empirical relationship is established between compressive strength of pseudo-rock and maximum skin friction mobilised in the socketed portion of pile. The experimental results and the results obtained by using empirical equations suggested by other investigators are compared and a good correlation is observed.

Experimental Investigation on the Vertical Bearing Characteristics of Jacked Piles in Saturated Silt Foundations under Excavation

A model test system for vertical bearing characteristics of the jacked piles in saturated soil foundations under excavation has been introduced. The system device comprises a soil pressure loading system, a model pile loading system, a soil vacuum saturation system, a model box, a model pile, and a control and data acquisition system. The soil vacuum saturation system designed for the model box of this test device can ensure that the saturated soil in the model box can reach a higher degree of saturation. Loading and unloading were conducted on the soil sample in the model box through the soil pressure loading system to simulate the soil excavation so that the soil sample and that in the field have the same stress state and history. The soil consolidation pressure, pile jacking pressure, pile tip force, soil consolidation settlement, and pile displacement at the top were collected and monitored in real time through the control and data acquisition system. This device is used to conduct an experimental study on the bearing characteristics of the jacked piles in saturated silt foundations under excavation. The results indicate that the static load test increases the residual pressure on the tip of the jacked pile while also increasing soil stiffness at pile tip and ultimate tip resistance, thereby increasing the pile top stiffness and ultimate load-carrying capacity. However, when the jacked pile is left undisturbed for the same time, the static load test on the jacked pile does not affect the pile skin friction resistance. There is a better linear relationship between the pile skin friction resistance and the undrained shear strength of the soil under the corresponding stress path during the static load test of the normally consolidated soil and the jacked pile after overburden pressure unloading. There is a good linear relationship between the ultimate resistance and the undrained shear strength of the soil under the corresponding stress path in pile sinking, normally consolidated soil, and during the static load test on jacked pile after unloading.

Evaluation of Static Pile Load Test Results of Ultimate Bearing Capacity by Interpreting Methods

in geotechnical engineering, foundation piles are ideal for deep foundations that cannot bear higher loads. This architectural expansion places a great deal of responsibility on the engineer to anticipate the appropriate load for the constructor. Unfortunately, calculations of the pile’s bearing capacity are not accessible. It has always been a source of concern for geotechnical engineers, as the structure’s safety depends on the pile’s bearing capacity and gives it a safe value. These research tests are previously known pile load test data from several locations in Nasiriyah to determine the ultimate load-carrying capacity using various interpreting methodologies. A database that was used to test the pile load for three different areas in Nasiriyah, southern Iraq: The Main Drain River Bridge Project, the Al-Eskan Interchange Project, and the Al-Hawra Hospital, as determined by analytical methods, as well as evaluating the final loading values resulting from the methods used, by ASTM D-1143, American and British Standard Code of Practice BS 800. The final capacity for the pile bearing is estimated using these approaches, which are depicted in the form of a graph-based on field data. Chin-Kondner and Brinch Hansen algorithms anticipate the highest failure load for all piles based on the comparison. On average, Chin–Kondner’s ultimate load is 22% higher than Hansen’s maximum load for the 22 pile load tests. Decourt and DeBeer, and Mazurkiewicz’s techniques yielded the closest average failure load. Buttler-Hoy approach yielded the smallest failure load.