Pile Load Research Articles

Prediction of axial load bearing capacity of PHC nodular pile using Bayesian regularization artificial neural network

Pre-stressed precast high strength concrete (PHC) nodular piles with hyper-MEGA construction method are favorably used in medium to high-rise building foundations. In this study, a feed-forward neural network (FFNN) was adopted to investigate the ultimate axial load bearing capacity of the PHC nodular pile. The network receives the composite pile and geotechnical conditions with eight input neurons and outputs the nodular pile's ultimate axial load bearing capacity. Among numerous possible FFNN network architectures, the most accurate one is determined by optimizing the hidden layer. Network training is conducted with Bayesian regularization backpropagation (BRB); the training datasets consist of static pile load test and standard penetration test index of soil profile collected from various projects in Vietnam. The significance of each input parameter is quantified with importance-based sensitivity analysis. An explicit function has been constructed from weights and bias values at each neuron in the FFNN to estimate the axial load bearing capacity. The excellent agreement of all output values by the proposed FFNN with the measured values proved the model’s robustness and reliability. The predictive capacity of the proposed FFNN model has significantly outperformed all current empirical formulas. The outcome of this study can be directly put into engineering practice to furnish an economically optimal design of the composite nodular pile.

Integral bridge abutments in response to seasonal temperature changes: State of knowledge and recent advances

Expansion and contraction of integral abutment bridges due to temperature changes force integral bridge abutments (IBAs) to move toward and away from the backfill, thus increasing horizontal earth pressures behind the abutments and inducing bending moments on pile foundations. This paper presents the state of knowledge and recent advances in understanding the behavior of IBAs in response to temperature changes including abutment movement, pile response, and horizontal earth pressure behind the abutment, examines the effect of bridge skew on the behavior, and discusses possible measures to mitigate temperature change-induced problems for IBAs. Field data show that both bending moments of piles near the bottom of abutments and axial loads of piles fluctuated with temperature. Redistribution of dead loads among bridge components due to planar temperature gradients and earth pressure changes behind the abutment contributed to axial load fluctuations in piles. Magnitude and distribution of horizontal earth pressures behind the abutment depend on factors such as abutment movement and abutment movement mode. Most of the current design methods overestimated the horizontal earth pressures at the bottom of the abutment during bridge expansion. Compressible inclusions placed behind the abutment, geosynthetic-reinforced backfill, and lightweight backfill in place of typical aggregate backfill are helpful to reduce horizontal earth pressures behind the abutment at high temperatures and temperature change-induced backfill settlements.

Behavior of a vertical pile in loose sand under the effect of an inclined load

The paper investigates the behavior of single vertical steel pipe pile embedded in sand subjected to compressive inclined load through MIDAS GTS/NX 2019 FEM package. The effect of the loading inclination angle and pile length and diameter on the performance of the pile were investigated. Inclined load carrying capacity and pile stiffness were presented. The pile head displacement and pile stiffness are significantly affected by load inclination angle. It was observed that, p-y curves of the pile-soil system are independent of loading inclination angle. In addition, the pile length and diameter are markedly affecting the behavior of the pile.

Analysis of Load-Settlement Curve Based on Load Transfer at Pile-Soil Interface

A field pile loading test was carried out on the Peshawar–Karachi Motorway (PKM) project in Pakistan to show the settling mechanism of bored pile foundation in pulverized soil and the force characteristics of frictional resistance at the pile-soil interface. The changes in pile lateral frictional resistance and pile settlement during the loading-unloading process of test piles were measured and analyzed, as well as the load-settlement distribution characteristics of test piles in different soil layers, the distribution of test pile internal forces, and the changes in pile-soil relative displacement. It was established that there was considerable deterioration of pile lateral frictional resistance and residual deformation of pile tip displacement throughout the test pile load-settlement process, and the association between the pile-soil interface frictional resistance and pile-soil relative displacement was addressed. The results reveal that the frictional resistance at the pile-soil interface is directly connected to the nature of the soil layer, with a positive connection between the natural density, specific gravity, compression deformation, and the plastic index under immediate load, and a negative correlation between the natural moisture content, compression coefficient, and settlement variations after unloading. The load-settlement of the pile rose in a non-linear proportion during the loading-unloading operation, with a maximum settlement value at the pile top of 8.14 mm and a residual deformation at the pile bottom of 1.94 mm. The frictional resistance of the pile perimeter was distributed non-linearly throughout the pile depth, and the frictional resistance of the pile-soil interface was severely deteriorated at an embedded depth of 15 m, with the degradation degree of the silty soil layer being significantly smaller than that of the silty clay soil. The relative pile-soil displacement was positively linked with the lateral frictional resistance of the pile under the same load, and the correlation coefficient in silty soil was much greater than that in sandy soil.

Centrifuge model tests and settlement calculation of belled and multi-belled piles in loess area

Belled and multi-belled piles are cast-in-place piles with one or several bell-shaped enlargements. In this study, centrifuge model tests were conducted to explore the bearing mechanism of belled and multi-belled piles in loess area. It was found that both the bell shape forming and pile loading procedure lead to the compaction effect of soil adjacent to the pile which was shown intuitively as the mutation of axial force and side friction resistance at certain positions of pile shaft. The compaction effect due to the bell-shape enlargement transformed to the squeeze out behavior when the bell is oversize, with negative effects on the bearing capacity of piles. The compaction effect due to bell tip stress together with the bell tip resistance strengthens the attenuation rate of pile axial force. A stable relationship in the percentages of bell tip resistance, pile tip resistance and the upper load was also found at the later load stage of multi-belled piles. A settlement calculation formula for multi-belled piles was proposed based on Mindlin solution. Finally, the accuracy of the formula was verified by model test results. The method for predicting the ultimate bearing capacity of multi-belled piles was proposed, and it was verified by an in-situ worked-out example.

Study on the ground mechanics index of deep soft foundation sections in the Dongting Lake region

Due to its special geographical location, the Dongting Lake Plain has formed a unique Dongting Lake phase deep soft ground layer. In order to investigate its stratigraphic mechanical index, a research was carried out using pile foundation static load test and pile body stress test based on a trans-Dongting Lake high speed project. The results of the study show that the ultimate bearing capacity of the test piles in this project is greater than the ultimate bearing capacity of the piles proposed by the design, and the reasons for this deviation according to the pile stress test are mainly due to the clay layer, silty powder clay layer and the side friction resistance of the fine gravel layer at the end of the pile are significantly greater than the recommended value of the ground investigation data, while the side friction resistance of the fine sand layer, powder fine sand layer and gravel sand layer is basically the same as the recommended value of the ground investigation data, This can be used as a reference for similar projects in the future.

A solution to the problem of pile settlement caused by vertical static loading with consideration to plastic properties of the foundation soil

Introduction. The article addresses the problem of nonlinear analyses of structures having pile foundations. The purpose of the study is to develop a method for determining the nonlinear behaviour of a single pile. The tasks of the study are to use the analytical method to define and solve the settlement problem of a single pile, taking into account the plastic properties of soils along the lateral surface and under the tip, as well as to verify the obtained solutions using the field data obtained by testing the pile subjected to static loading.
 Materials and methods. The analytical model of the telescopic motion of coaxial cylindrical soil layers around the pile was applied to obtain the solution. Pile settlement due to the punching of the bottom layer was calculated using the available formula dealing with a circular rigid stamp located at a given depth from the surface. To verify the solution, the authors used the materials of static loading tests conducted in respect of three reinforced concrete prismatic piles of the base of a hospital building located in the city of Tver. A static method was used to drive the piles.
 Results. A comparison between the results of the analysis obtained using the proposed solution and the field test data is presented. The analysis of this comparison shows that the solution allows describing the load-settlement curve for the static loading of a single pile. A reasonable mismatch between the calculated and field data is identified; it is associated with the inability of the derived formula to take account of soil consolidation.
 Conclusions.The solution, obtained for single pile settlement, takes into account plastic properties of soil on the lateral surface and under the pile tip. This solution describes the regularity of single pile deformation under static loading. Further research will take soil consolidation into account. The assumed values of the ultimate resistance of a pile along a lateral surface and under the pile tip have a considerable influence on the results of the calculation according to the solution obtained by the authors. A relevant task, to be solved in the course of further research, is to find alternative methods of their determination.

РОБОТА БУРОНАБИВНИХ ПАЛЬ З РОЗШИРЕНОЮ ПЯТОЮ В НАБУХАЮЧИХ ГРУНТАХ ЗА ЧИСЛОВИМ МЕТОДОМ ГРАНИЧНИХ ЕЛЕМЕНТІВ

The topic is devoted to the topical problem of foundation construction and soil mechanics - elastic-plastic modeling of joint work of the system "soil base - brown pile" in order to determine the bearing capacity of the foundation to ensure stability and low subsidence of the structure, thus avoiding its possible uneven subsidence or destruction. To do this, it is necessary to provide forecasting and numerical implementation of calculations of the pile foundation structure.
 From the standpoint of the mechanics of a dispersed elastic-plastic medium, the idea of the peculiarities of the behavior under the load of a brown pile with an extended heel in clay swellable soils is presented.
 The calculations take into account the main content of the theory of elastic-plastic processes - the dependence of the stress- deformed state on the load history.
 The main computational equation of the soil model is the integral equation received K. Brebbia [1].
 Depending on the properties of the soil and the applied stresses, the sediment of the building is carried out as a result of compaction or extrusion of the soil from under the foundation.
 In both cases, the phenomenon of subsidence is due to soil flow, so it is natural that to the forefront of solving static problems of foundation construction is a condition or equation that determines the boundary between solid and fluid state of the soil depending on stresses.
 The application of numerical MGE to the solution of the nonlinear problem of geomechanics is substantiated by theoretical calculations, supported and illustrated by data of numerical calculation

Creep settlement analysis of pile foundations using viscoelastic model by incorporating nonlinear soil behaviour

ABSTRACT This study utilizes a nonlinear three-parameter viscoelastic model (a nonlinear spring in series with a Kelvin-Voigt element) to study the time-dependent creep behaviour in a single pile and group of piles. The method is based on modified Mindlin’s approach; and Laplace transforms have been utilized to simplify the viscoelastic problem into an equivalent elastic problem. The soil nonlinearity has been modelled by using a hyperbolic stress-strain relationship. The effects of parameters such as pile spacing, slenderness ratio and pile load factor on shear stress distribution, displacement of pile elements relative to the pile head, effects of enlargement of the pile base and interaction factors have been evaluated. The ratio of interaction factor for immediate and creep settlement is in the range of 0.4−0.9 for various pile groups. Since this study incorporates soil nonlinearity, the interaction factors increase by about 6%−10% when the pile load factor increases from 0.5 to 1.

Experimental and Numerical Investigation of the Load-Bearing Mechanisms of Piles Socketed in Soft Rocks

Rock-socket pile design predominantly depends on the shaft resistance to support the load at the serviceability state. However, due to limited understanding of the pile–rock interactions, the pile capacity is normally calculated using empirical correlations. In this study, the load-bearing mechanisms of rock-socketed piles were investigated through a miniaturised pile–load test setup in a soft synthetic rock. X-ray CT imaging and numerical discrete element modelling were used to investigate the micro-mechanics influencing the load-bearing mechanisms at the pile–rock interface. The numerical pile model was established based on suitable constitutive models capable of simulating the soft rock behaviour. The analysis of X-ray CT images at various displacements revealed three different interface mechanisms, namely sliding, local shearing and progressive shearing. The numerical model validated this observed micro-mechanics in the rock asperities through the evolution of damage and micro-cracks. Insights from the experimental and numerical results indicated that the height of the rock asperities significantly dictates the failure mode. Results also illustrated that the shaft load–displacement response primarily depends on the forces acting on the leading edges of the pile asperity. In particular, it was observed that the bottom leading edge carried a predominant portion of the shaft loads due to its connectivity with the rock at the base of the pile. Though negligible, the forces on the trailing edges provided valuable information on the contribution of residual shaft resistance by the debris at the interface. Moreover, the numerical studies revealed the different failure modes at the pile–rock interface. The discussions presented in this study provide novel insights into the load-bearing mechanisms of piles socketed in soft rocks, which will help to improve design guidelines in the future.

Experimental Study on the Effect of Pile-End Soil on the Pile Load Transfer Law

This paper compares and analyzes the difference in the skin friction between pile-end soilless compressive pile and conventional compressive pile at various stages during loading by the in situ test method. The influence of pile-end soil on the load transfer law of compressive piles in clay-dominated stratified foundations is further investigated. The results show that the overall load–displacement curves of the pile-end soilless compressive pile and the conventional compressive pile both present a slow decline followed by a steep drop. The length of the linear section on the load–displacement curve of the pile-end soilless compressive pile is less than that of the linear stage of the conventional compressive pile. Under the vertical load, the distribution laws and distribution forms of the skin friction ratio of the pile sections of the two piles are more consistent. The pile-end soil of the conventional compressive pile restricts the skin friction of the pile’s middle-lower and lower pile segments when compared to the pile-end soilless compressive pile. This restriction manifests itself as a reduction in pile skin friction, and the weakening effect decreases from bottom to top.

A memory-enhanced p-y model for piles in sand accounting for cyclic ratcheting and gapping effects

The analysis of cyclically loaded piles is acquiring ever greater relevance in the field of geotechnical engineering, most recently in relation to the design of offshore monopiles. In this area, predicting the gradual accumulation of pile deflection under prolonged cycling is key to performing relevant serviceability assessments, for which simplified pile–soil interaction models that can be calibrated against common geotechnical data are strongly needed. This study proposes a new cyclic p−y model for piles in sand that takes a step further towards meeting the mentioned requirements. The model is formulated in the framework of memory-enhanced bounding surface plasticity, and extends to cyclic loading conditions the previous monotonic, CPT-based p−y formulation by Suryasentana and Lehane (2016); additionally, detailed modelling of pile–soil gapping is introduced to cope with the presence of unsaturated sand layers or, more generally, of cohesive soil behaviour. After detailed description of all model capabilities, field data from an onshore cyclic pile loading test are simulated using the proposed p−y model, with the most relevant parameters calibrated against available CPT data. Satisfactory agreement is shown between experimental and numerical results, which supports the practical applicability of the model and the need for further studies on a fully CPT-based calibration.

РОБОТА ПІРАМІДАЛЬНИХ ПАЛЬ В ЗАЛЕЖНОСТІ ВІД КУТА КОНУСНОСТІ

One of the effective methods to ensure reliable operation of the structure is the use of pyramidal piles, which in comparison with prismatic piles have an increased bearing capacity due to the increase of the compacted area around the pyramidal pile in its upper part. In this paper, based on the consideration of the theoretical foundations of the rheology of clay soils and the use of the numerical method of boundary elements, the results of numerical studies of the behavior under the load of pyramidal piles are presented. Intensive development of soil mechanics, which significantly affects the cost-effectiveness of decisions, and the widespread use of computers have significantly brought fundamental mathematical problems in applications, strengthened their interaction. The use of a numerical experiment has more closely linked the physical content of a problem, its mathematical formulation, numerical calculation methods, and computers than ever before. Growing demands of construction practice lead to the complexity of applied tasks. Numerical experiment allows to allocate a rational grain, to describe the most important types of behavior of a base design, to carry out the mathematical substantiation, to write down the mathematical model which is checked by means of experiments. Due to the geological conditions of Ukraine in industrial and civil construction, it is advisable to use pyramidal piles, and the features of their interaction with the bases and theoretical calculation methods are insufficiently studied. The lack of reliable methods for estimating the bearing capacity of pyramidal piles leads to an increase in stock ratios, making imperfect decisions, and makes it difficult to widely implement them in construction practice. Therefore, the topic of VAT research of rational pyramidal piles is relevant today.

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.

A novel direct SPT method to accurately estimate ultimate axial bearing capacity of bored PHC nodular piles with 81 case studies in Vietnam

Bored PHC nodular piles (BPNP) are an eco-friendly and advantageous option for pile foundations of medium-rise to high-rise buildings. As none of the current methods to estimate the ultimate axial load-bearing capacity is accurate enough for BPNP in engineering practice, this study aims to achieve that objective by developing a new direct SPT method. To that end, we use static pile load test and SPT data of 81 PHC nodular piles collected in Vietnam. The ultimate bearing capacity is interpreted from the load–displacement curve in pile static load tests by various methods to determine the most suitable method for the nodular piles. Furthermore, 8 methods to determine axial load pile capacity directly from the standard penetration test are examined. Each method’s effectiveness is evaluated by comparing its predicted values with the measured values. Finally, the genetic algorithm for function optimization is employed to develop a new direct SPT method that can accurately predict the ultimate axial load-bearing capacity of nodular piles. The reliability of the proposed formula is justified by comparing the proportion of end bearing capacity with other published works. It is verified that the developed directed SPT method outperforms all current methods and could be implemented directly in engineering practice.

A Soil-Pile Response under Coupled Static-Dynamic Loadings in Terms of Kinematic Interaction

Abstract Although the axial aptitude and pile load transfer under static loading have been extensively documented, the dynamic axial reaction, on the other hand, requires further investigation. During a seismic event, the pile load applied may increase, while the soil load carrying capacity may decrease due to the shaking, resulting in additional settlement. The researchers concentrated their efforts on determining the cause of extensive damage to the piles after the seismic event. Such failures were linked to discontinuities in the subsoil due to abrupt differences in soil stiffness, and so actions were called kinematic impact of the earthquake on piles depending on the outcomes of laboratory tests and other numerical analyses. In this research, numerical modeling is used to explore the kinematic forces created in a single pile erected in two sand layers under two different conditions (dry and saturated states). Based on the obtained results from the physical model, the maximum bending moment was observed at a depth around 200 mm below the ground surface in the loose sand layer, then these values gradually reduced until it becomes negative in the dense sand layer. It has been demonstrated that this modeling may be used to predict how a pile foundation would respond to “kinematic” loading generated by ground movements during a seismic event. Consequently, the current findings could be used in the design and construction of bored aluminum or steel piles in Al-Karbala soil.

Visual Rewards From Observation for Sequential Tasks: Autonomous Pile Loading.

One of the key challenges in implementing reinforcement learning methods for real-world robotic applications is the design of a suitable reward function. In field robotics, the absence of abundant datasets, limited training time, and high variation of environmental conditions complicate the task further. In this paper, we review reward learning techniques together with visual representations commonly used in current state-of-the-art works in robotics. We investigate a practical approach proposed in prior work to associate the reward with the stage of the progress in task completion based on visual observation. This approach was demonstrated in controlled laboratory conditions. We study its potential for a real-scale field application, autonomous pile loading, tested outdoors in three seasons: summer, autumn, and winter. In our framework, the cumulative reward combines the predictions about the process stage and the task completion (terminal stage). We use supervised classification methods to train prediction models and investigate the most common state-of-the-art visual representations. We use task-specific contrastive features for terminal stage prediction.

On-Site Full-Scale Load Test and Reliability Evaluation of Prefabricated Bridge Substructure for “Pile–Column Integration”

The application of prefabricated bridge structures is of great significance to building industrialization, which can realize the green construction and maintenance process of low energy consumption and low emission as well as the normal operation of transportation in time, and effectively realize the green development requirements. However, the substructure of a conventional prefabricated bridge usually needs to cast a bearing platform between pier and column, and may not give full play to the advantages of prefabricated bridge construction. Given the engineering characteristics that most of the pile foundations in the bridge design of this engineering project are end-bearing piles, in which the pile foundation is not deep and the pile column is not high, the assembly process of “pile–column integration” has been proposed in this study. Aiming at the reconstruction and expansion project of the Qinzhou–Beihai section in the Lanzhou–Haikou expressway, the test site with representative geological conditions was firstly selected. The pile–column structure of the bridge can be completed by prefabricated pile foundation, pier, and cap beam based on the integral assembly installation method. The vertical compressive static load test, horizontal static load test, and reliability test of pile–column connection were introduced in detail to analyze whether the bearing capacity and connection effect of pile–column can meet the requirements. Test results showed that the limit value and corresponding characteristic value of the vertical compressive bearing capacity and horizontal critical load of a single pile could meet the design requirements. The displacement curve of single pile No. 5 at the flange connection position under various loads of the test pile does not have an obvious angle break, and there is no sudden change in the slope, indicating that the flange connection quality is good. Due to many interference factors and some abnormal strain measurement data, the strain data are suggested as auxiliary to the displacement results. The findings of static load testing and connection reliability in this study proved the feasibility of this prefabricated bridge substructure “pile–column integration”, which can provide a reference for the rapid construction of bridges.

Influence of Vertical Load on the Lateral Response of Piles in Normally Consolidated and Over-Consolidated Clay: Centrifuge and Numerical Modelling

Although pile foundations are usually subjected to both lateral and vertical loads, there have been few studies on the pile response under the combined loadings. Moreover, those few studies led to inconsistent conclusions concerning the influence of vertical load on the lateral pile response. This study aims to investigate the effect of vertical load on the monotonic and cyclic lateral response of piles in normally consolidated (NC) and over-consolidated (OC) clay through a series of centrifuge tests. Three-dimensional finite element analyses using an advanced hypoplastic clay model were also performed to gain deep insight into the mechanism. It is revealed that after applying the vertical load and allowing the dissipation of the induced excess pore pressure, the lateral initial stiffness and ultimate capacity of the pile in the NC clay increased by 10.0 and 49.4%, respectively. However, in the OC clay, the application of the vertical load resulted in a 12.6 and 32.4% reduction in the lateral pile initial stiffness and ultimate capacity, respectively, showing a distinct response from that in the NC clay. The above-mentioned distinct influence of vertical load for piles can be attributed to the different evolutions of stress ratio (q/p’) of the soil around the pile in the NC and OC clay, which determines the soil mobilisable shear strength and consequently the lateral pile responses.

A numerical study on the group effect for offshore piles in clay under lateral loading

Pile group foundations are widely used in the offshore industry to support large jacket structures, such as oil platforms and substations for offshore wind farms. The pile group foundations are commonly designed using methods developed for single piles but modified to account for the group interaction effect. The modification for pile group effect has been conventionally based on elasticity solutions or empirical observations from field/model pile load tests. In the past decade, considerable progress has been made with respect to modelling single pile response under lateral loading in clay. However, there appears to be limited progress for modelling pile groups in the offshore industry. The design practice has stayed unchanged for several decades. This paper presents a numerical study in an attempt to come up with design recommendations for typical pile group configurations used in the offshore industry. A comprehensive numerical investigation of the group effect for several typical pile group configurations are performed, examining the effect of pile spacing and the loading direction. From the parametric analyses, the so-called p and y modifiers which are to be applied to correct the single pile p-y curves for consideration of the group effect are proposed. An example is presented to demonstrate the application of the modifiers.