Pile Cap Research Articles

Verification of the secondary reinforcement influence on the strap beams design

The present work aims to expose a methodology for the design of strap beams between pile caps, and to investigate the effect of secondary reinforcement on the behavior of the pile cap located on the property line. For the study, it was selected the deep foundation geometry of a borderline pillar from the infrastructure design of a building. A design methodology was then presented for the foundations' reinforcement. In ABAQUS [1] software, based on the Finite Element Method, a non-linear analysis of four models related to the case study was performed, with the variation of the secondary reinforcement arrangement. It was found that the combined horizontal and vertical secondary reinforcements were efficient to ensure a more ductile failure for the concrete strut. However, the model with the secondary reinforcement inclined at 45º showed the highest resistance.

Wavelet Analysis for Evaluating the Length of Precast Spliced Piles Using Low Strain Integrity Testing

The difficulties with the application of low strain integrity testing for evaluating the length of driven precast piles of two sections justify the need for new data acquisition and analysis techniques. The standard time domain analysis of the recorded signals may not allow for distinguishing the desired responses from a pile toe and a splice. In this paper, we propose the use of a set of hammers of different weights and tip materials that will provide various sensitivities of the test to a pile splice. To further analyze the collected data, we study the distributions of phase angles obtained using complex continuous wavelet transform. The characteristic phase shifts that distribute from higher to lower frequencies can be interpreted as responses from a pile toe and a splice. To verify the proposed approaches, a series of numerical simulations were performed using the finite element method for the driven pile models with the different properties of a splice zone. Numerical simulation results show that the pile splices are clearly identified when using the shorter input pulses which can be generated by light hammers with a hard head material. The total length of a simulated pile with a 1 mm air gap between sections was undetectable by standard data analysis approaches and was evaluated when analyzing the wavelet phase angle distributions. Numerically validated data acquisition and analysis techniques were applied to field data analysis and allowed us to confidently identify the length of two-section piles grouped with a pile cap.

Flexible support of a pile embedded in unsaturated soil under Rayleigh waves

AbstractUnder the action of Rayleigh waves, pile head is easy to rotate with a concrete pile cap, and pure fixed‐head condition is rarely achieved, which is a common phenomenon for it usually occurs on the precast piles with insufficient anchorage. In addition, the propagation characteristics of Rayleigh wave have been changed significantly due to the existence of capillary pressure and the coupling between phases in unsaturated soil, which significantly affects the pile‐soil interaction. In order to study the above problems, a coupled vibration model of unsaturated soil–pile system subjected to Rayleigh waves is established on the basis that the pile cap is equivalent to a rigid mass block. Meanwhile, the soil constitution is simplified to linear‐elastic and small deformations are assumed to occur during the vibration phase of soil–pile system. Then, the horizontal dynamic response of a homogeneous free‐field unsaturated soil caused by propagating Rayleigh waves is obtained by using operator decomposition theory and variable separation method. The dynamic equilibrium equation of a pile is established by using the dynamic Winkler model and the Timoshenko beam theory, and the analytical solutions of the horizontal displacement, rotation angle, bending moment and shear force of pile body are derived according to the boundary conditions of flexible constraint of pile top. Based on the present solutions, the rationality of the proposed model is verified by comparing with the previous research results. Through parametric study, the influence of rotational stiffness and yield bending moment of pile top on the horizontal dynamic characteristics of Rayleigh waves induced pile is investigated in detailed. The analysis results can be utilized for the seismic design of pile foundation under Rayleigh waves.

Membrane Effect of Geogrid Reinforcement for Low Highway Piled Embankment under Moving Vehicle Loads

In this paper, the membrane effect of geogrid reinforcement was investigated based on numerical simulation to understand the serviceability and deformation of highway piled embankments under moving vehicle loads. The membrane effect of geogrid reinforcement in low embankments (i.e., the ratio of embankment height to pile spacing is less than 1.5) was clearly emphasized. It has been found that the maximum settlement of geogrid occurs in the central area between the piles, and the maximum tension was concentrated at the corner of the pile cap. Due to the attenuation of the soil arching effect under moving dynamic loads and the punching mechanism, the settlement and tension of the geogrid increased considerably by approximately 35% and 23% compared to those under static loads. A parametric study was also achieved, and the results presented that the geogrid reinforcement tension increased by increasing the pile spacing, embankment height and geogrid stiffness, vehicle wheel load and vehicle velocity. It was also found that the reinforcement tension was most sensitive to the pile spacing among all the parameters considered in this paper, whose magnitude increased by approximately 104% as the pile spacing increased from 2.0 m to 2.5 m under dynamic loads.

Construction of geofoam block embankments atop existing transportation infrastructure

Expanded polystyrene (EPS) block (geofoam block) is a mature geotechnology for constructing highway embankments. In addition to preventing bearing capacity and settlement related stability problems for the embankments constructed on soft soil sites, geofoam blocks are also used to construct embankments atop existing infrastructure. Selecting geofoam technology for these applications not only prevents possible structural problems due to the lightweight nature of geofoam blocks but also eliminates costly remediation alternatives. The details of three well-documented and monitored different geofoam embankments constructed atop different existing infrastructures (buried pipeline, buried culvert and pile cap of drilled shafts for a deep excavation) are presented. The backgrounds of these projects, design considerations, construction and instrumentation details are discussed. The monitoring results were presented, and long-term performance predictions were evaluated. Numerical modeling effort was utilized to model the both short- and long-term behavior of geofoam embankments. Time-dependent behavior of the embankments under service loads was compared with numerical simulations. Constitutive modeling and related mechanical properties of geofoam blocks, which mimicked the long-term field behavior, as a function of geofoam density were proposed for future numerical modeling efforts.

Shear behavior of RC pile cap beams strengthened using ultra-high performance concrete reinforced with steel mesh fabric

Although pile cap bases of structures are the most significant element in the construction and one of the most difficult parts in strengthening applications, previous studies on this element, particularly strengthening, are quite limited. The most extensively utilized, highly efficient, and simple to implement solution is ultra-high performance concrete (UHPC). In this study, six-half scaled pile cap beams were prepared and experimentally tested. Three of them were strengthened with UHPC (one in shear with connectors only, one in shear with connectors and steel mesh fabric (SMF), and one in shear and punching with connectors and SMF), while the other three were not strengthened to explore the influence of side bars. The bottom bars of the all six beams were identical, consisting of main longitudinal tensile and secondary lateral reinforcement. The load-displacement response, ultimate carrying load, failure mechanisms, energy dissipation capacity, and shear ductility of pile cap beams were all thoroughly investigated. The results revealed that using side bar reinforcement and UHPC with various techniques significantly enhanced the shear strength and ductility of pile cap beams. Except for the specimen including additional internal side bars, there were no appreciable differences in the peak load of un-strengthened reinforced concrete (RC) pile cap beams. The gain in peak load was 59% due to use of side bars. The RC pile cap beam strengthened in shear and punching with connectors and SMF exhibited the highest peak load and the highest energy dissipation capacity among all tested specimens.

Mechanical model for predicting wave loads on complex pile group foundations under linear wave action

Pile group foundations of offshore bridges have complex geometries and are subjected to enormous wave loads for a long time. Therefore, the accurate and efficient prediction of wave forces on pile group foundations is related to the economic design and safe operation of sea-crossing bridges. In this study, a mechanical model for predicting wave loads on complex pile group foundations under linear wave action is developed. At first, a three-dimensional hybrid technique combining the eigenfunction expansion method and the boundary element method is proposed for analyzing the wave diffraction problem from the large-scale pile cap. Based on this, the modified Morrison equation is utilized to solve the wave forces on piles. Meanwhile, the wave loads on the pile group are obtained by considering the pile group effect. The presented model is then employed to calculate the wave forces on cylindrical caps and piles below a square cap, and the calculation results match well with the published results, which illustrates the validity of the presented model. Finally, this model is extended to practical engineering applications. That is, the wave load characteristics on a pile group foundation with a quasi-elliptic cap and 13 tilted piles are systematically analyzed under different wave conditions. This study exhibits that the presented mechanical model can effectively calculate and output the wave loads on each component of the pile group foundation, and the calculation results can provide the data support for the design and optimization of complex pile group foundations.

INCREASING THE RELIABILITY OF THE LOW STRAIN INTEGRITY TESTING OF PILES UNDER EXISTING STRUCTURES

Inspection of piles located under the pile cap or an existing building is a common task in the practice of capital construction. The low strain impact testing allows us to estimate the pile length and the presence of defects in its body. This provides designers and builders with information on structures, which can be considered when planning the further operation of the foundation. Improving the reliability of test results for examining piles under cap is the issue of interest. On the example of field test results, the application of the multifrequency signal excitation during data collection and the wavelet analysis of signals during data processing are shown.

The Filtering Effect of Pile Foundations in Clay

This paper reports the results of a series of centrifuge experiments exploring the dynamic response of pile foundations. The model tested in a centrifuge at 50g consisted of an isolated pile and two pile groups embedded in a kaolin clay, subjected to a sequence of quasi-sinusoidal waves with different amplitudes and frequencies. The results are back-analyzed through a two-step procedure. First, a one-dimensional ground response analysis is performed, in which the small-strain shear modulus is evaluated using data from air hammer tests, while a literature model is used to account for nonlinearity of soil behavior. Second, a three-dimensional finite-element analysis of the model foundations is carried out using the mobilized soil damping ratio and shear modulus determined from the previous step. The aforementioned procedure allowed to reproduce satisfactorily the response of the model foundations tested in the centrifuge, showing that the response of these models is strongly affected by the inertial oscillation of the cap connecting piles necessary to accommodate the measurement devices and to rigidly connect the piles’ heads of the groups. The same numerical model was then adopted to evaluate the change of seismic motion due to pure kinematic interaction effects by setting the pile cap mass equal to zero. This allowed to check the prediction capability of simplified methods of analysis for the evaluation of the base excitation of pile-supported structures. In addition, a number of issues related to the execution of centrifuge tests aimed at investigating the kinematic interaction between pile and soil are highlighted and discussed.

Seismic evaluation of frictional FRP piles in saturated sands using shaking table tests

This manuscript presents results of two shaking table tests that were used to characterize seismic performance of Fibre-Reinforced Polymers (FRP) pile groups in saturated sand. A laminar shear box with a dimension of 1.0 m × 1.0 m and a depth of 1.0 m was employed to contain the soil medium and allow the soil to respond in the same fashion as the free field. Two types of composite group piles (2 × 2) made of Carbon FRP (CFRP) and Glass FRP (GFRP) along with a series of Aluminum model piles were manufactured and embedded as frictional piles within the soil. The pile-soil models were subjected to acceleration time histories adopted from the 2010 Val-des-Bois Earthquake in Canada and the 1995 Kobe Earthquake. The foundation motions recorded along the model piles showed significantly higher levels of excitation compared to the accelerations recorded within the soil at the same level. This was attributed to strong interaction between the soil and the foundation, and higher flexural stiffness of the model piles. Pile material was also found to influence the seismic response of pile caps and its superstructure through kinematic soil-pile interaction and possible rocking motion. The aluminum pile cap experienced significantly higher acceleration response compared to the FRP piles. Among the FRP piles, GFRP piles were shown to provide slightly better performance and could be an appropriate alternative piling material for frictional traditional piles especially in liquefiable soils.

Research on Bearing Capacity of Secant Piled-Bucket Foundation in Saturated Clay

The secant piled-bucket foundation (SPBF) is innovatively proposed to suit the large-capacity mainstream, which is optimized from a traditional foundation and consists of an upper pile cap and a lower bucket skirt. Compared with the pile foundation, the SPBF has great advantages and deserves further study. In this research, the bearing mode, bearing capacity and failure mode under various loads of SPBF in saturated clay have been fully studied. First, the small-scale model test in saturated clay is carried out to verify the finite element (FE) method; the deviation between the FE results and the test results under vertical load and horizontal–moment load is 10.65% and 10.25%, respectively. Next, the bearing mode of SPBF in engineering scales is investigated via FE method, the results indicating that the bearing mode of SPBF is similar to that of a prestressed tubular foundation. Finally, the bearing capacity and failure mode of SPBF are studied and the findings show that the vertical bearing capacity and horizontal–moment bearing capacity of SPBF is 96.53 MN and 1.62 MN, and the weak parts of SPBF are concrete of the pile cap and the anchor bolts, respectively. This paper provides support for design and further optimization in the future.

Finite-Element Analysis on the Tensile Membrane Effect in Geogrid Reinforced Piled Embankment under Dynamic Loading

This study presented a numerical investigation of the tensile membrane effect in the geogrid reinforced piled embankment under dynamic loading. It has been found that the maximum sag of the geogrid was attained at the center of two adjacent piles, while localization of tensile force was observed at the corners of the pile caps. Under the dynamic loading, the sag and the strain of the geogrid increased when compared with the static loading, an increase of around 45.9% and 24% was, respectively, yielded for the sag and the strain of the geogrid. This increase of tension in the geogrid may mainly result from the degradation of the soil arching effect under dynamic loading. A parameter study was performed, and it showed that the tensile force in the geogrid increases with the rise of the embankment height, the clear pile spacing, and the tensile stiffness of the geogrid. However, the increase of the friction angle of the embankment fill led to a decrease in the tension in the geogrid, which may benefit from the improvement of the soil arching developed in the embankment fill. It was found that the tensile behavior of the geogrid was the most sensitive to the pile spacing. When pile spacing increased from 2.0 m to 3.0 m, the tensile force in the geogrid increased by about 248%.

Vertical Displacement of Pile Under Dynamic Machine Loading

The aim of this research is to calculate the vertical amplitude for pile foundations subjected to dynamic machine loading using a theoretical analysis based on some special formulus. The effect of each of machine frequency, pile length and diameter and embedded depth of pile cap on the vertical amplitude of the pile were studied. It was found that generally, by increasing the pile diameter, pile length, and embedment ratio of pile cap, the maximum vertical amplitude of group pile-cap system decreases. It can also be observed that the ratio of operating machine to natural frequencies (ω/ωn) corresponding to maximum amplitude decreases with increasing of pile diameter, and ratio of pile cap embedment. On the other hand, it can be seen that the damping ratio of the system was increased with increasing pile diameter and ratio of pile cap embedment, while the stiffness of the system increases with increasing pile length.

Compression Tests of Very Large Reinforced Concrete Pile Caps and Comparison with Predicted Strength

Compression Tests of Very Large Reinforced Concrete Pile Caps and Comparison with Predicted Strength

Identification of Different Shallow Foundations Using 3D Electrical Resistivity Modeling

The electrical resistivity method has been successfully used to detect shallow buried foundations, almost, by using 2D electrode arrays. Basic geometry foundations (e.g., buried walls) have been investigated, although, more complicated foundation designs (e.g., stepped footing, pile group with a pile cap) are widely used in the construction industry. Investigation of these complicated foundation types, and engaging 3D surveys, therefore, are required. Multiple 3D electrical resistivity forward modeling was used to simulate different foundations (isolated simple footing, isolated stepped footing, combined simple footings, and pile group with a pile cap). The generated data sets then inverted using a robust inversion algorithm where RES3DINVx64 was used to perform the inversion process for the 3D models. The results from the 3D inverse modeling, suggest the pole-dipole and dipole-dipole arrays for all the investigated foundations.

Calculation and Analysis of Nonlinear Algorithm for Stability of Nanosilica Powder Soft Soil Pile Foundation.

In order to reasonably evaluate the stability of the embankment supported by the rigid pile composite foundation, a nonlinear algorithm calculation and analysis method for the stability of the nanosilica powder soft soil pile foundation is proposed. First, the soft soil foundation reinforced by the composite structure of “piles (prestressed pipe piles, (cement fly-ash gravel, CFG) piles)—pile caps—geotextile pads” is analyzed through the soft soil embankment test section of the Wenfu high-speed railway. Second, the compressive modulus under one-dimensional confining compression is calculated using the layered summation method. Finally, the deep lateral deformation of the pile foundation soil is measured by an inclinometer to evaluate the actual displacement of the pile foundation soil. In the standard method, the empirical coefficient 1.1–1.7 is multiplied on the basis of the calculation result of this method to correct the calculation error. Combined with the test results, it is shown that nanosilica powder can give full play to its excellent characteristics: promoting hydration speed and hydration degree through the reaction of pozzolan refining and consuming Ca(OH)2 crystals produced by cement hydration. Soft soils and modified soft soils: a certain amount of nanosilica powder can significantly improve the strength of soft soil at different ages.

Optimized Design of Piled Embankment Using a Multi-Effect Coupling Model on a Coastal Highway

This study presents a multi-effect coupling model to optimize the design of a geosynthetic-reinforced pile-supported embankment (GRPSE) considering the coupling effects of soil arching, membranes, and pile–soil interaction on a coastal highway. The developed model could optimize the design of the GRPSE to fulfill the design and construction requirements at a relatively low project cost. This was achieved by adjusting the critical factors that govern the settlement of GRPSEs, such as pile spacing, tensile stiffness of geosynthetic reinforcement (GR), arrangement of piles, pile cap size, and cushion thickness. The model predictions were validated by a series of field tests using a range of geotechnical sensors. The results show that model predictions agreed with experimental measurements reasonably well. In addition, the results indicate that in comparison to a square arrangement of piles, a triangle net arrangement can decrease the differential settlement of pile soil. Furthermore, this study demonstrates that a change in the GR’s tensile stiffness has little impact on the settlement of GRPSEs. This study can help to improve the stability of roadbeds of coastal highways.

Soil arching effect in reinforced piled embankment for motor-racing circuit: Field tests and numerical analysis

When constructing superstructures on soft soils, severe issues including excessive settlements, bearing failures, and large lateral displacements arise and cause challenges for geotechnical engineers. Reinforced piled embankments are being used increasingly for various types of engineering construction such as highway widening and roadway construction, thereby making it crucial to comprehend and evaluate systematically the effect of soil arching, which has a significant influence on the performance of such embankments. This study focuses on two large-scale field tests of the piled embankments for an international motor-racing circuit in China, and the effect of the load transfer platform formed by geosynthetic reinforcement and gravel layer is investigated. Field monitoring data of soil pressures and settlements of pile caps and soils are reported and analyzed, and the test results show that soil arching acts significantly to transfer the load to the pile caps with an increase in loading from the embankment. Geogrids within the gravel layer can not only improve soil arching (reflected by higher stress concentration ratio) but also diminish differential settlements between pile caps and the ground surface. A numerical test considering different influencing factors is also conducted, thereby enabling both studying the effects of varying the field parameters and comparing with the insitu measurements. A proposed numerical model of the reinforced piled embankment is also shown to work well when compared with the results of the field tests. This study enhances the comprehension of soil–pile–geogrid interactions and guides similar projects in the future.

Lateral Load Capacity and p-Multiplier of Group Piles with Asymmetrical Pile Cap under Seismic Load

Earthquakes are a high-risk natural phenomenon in Indonesia, which is between three tectonic plates: the Eurasian, Pacific, and Indo–Australian plates. This study examines the response of bored piles with asymmetrical pile cap in the Auditorium Building of Brawijaya University to seismic loads, which is still rare to conduct this research. This study assessed based on 3D finite element-numerical approach, where lateral resistance and p-multiplier values compared on the effects of combination lateral loads, pile stiffness, and soil stiffness. The behavior of lateral resistance and deflection group piles with asymmetrical pile cap and single pile with square pile cap gives a good agreement. The side slope of the pile cap can increase the shear zone, increase the lateral resistance, and the most considerable lateral resistance to the lowest occurs in the horizontal direction, opposite the loading direction. In addition, the pile configuration that is not symmetrical gives an increasing p-multiplier value followed by an increasing deflection and the p-multiplier from the 3D finite element method was within the recommended range.

Experimental Study on Wave Force on Large-Scale Pier Column Foundation of Sea-Crossing Bridge for Preserving the Marine Environment

Based on the project sea area where the large-scale sea-crossing bridge is located, the marine environment is facing the threat of severe marine environmental issues such as strong typhoons and big waves. In order to resist the impact of the super wave load, the research focuses on a new structure derived from soft computing techniques in a simulated environment. Since the conventional methods cannot be used for handling such an important problem, soft computing techniques can certainly help to provide simulated solutions. These solutions can be exploited in a real-time environment to test their viability. The overall physical model test of the wave with a scale of 1 : 40 is carried out in this research study by using the proposed methodology. By setting a series of groups such as different wave height, period, water level (pier foundation scouring depth), and wave-current coupling, it is studied that the wave height and period are in positive proportion to the wave force on the pier column structure. However, there is no obvious relationship with the water level change (scouring depth). The buoyancy of the pile cap structure is about 1.27 times greater than that of the pier structure. Compared with the combined wave force of the single wave and wave current, the sensitivity and the relationship have been studied. Using this study and several engineering results completed in the early stage and also verified by the measured data, the results show that the proposed soft computing technique has good accuracy and can provide a reference for the load estimation of large-scale foundation structures.