Pile Cap Research Articles

Influence of sloping ground on lateral load capacity of single piles in clayey soil

In many practical situations, structures subject to lateral loading are located near slopes. The presence of a slope on deep foundations loaded in a downslope direction can decrease the overall lateral capacity of the system. In this paper, the effect of soil slope, undrained cohesion, pile–soil interface adhesion, pile diameter and pile cap on the lateral load carrying capacity of pile located at the crest of clay slope is studied using PLAXIS-3D. Clay is modelled as linearly elastic perfectly plastic Mohr–Coulomb material, whereas pile is modelled as a linear elastic material. Formation of gap on the extension side of pile–soil interface is also considered. Lateral load capacity of pile for a corresponding prescribed displacement of 5 mm is estimated. An equation to determine the value of lateral pile capacity in terms of undrained cohesion, pile diameter and pile–soil interface adhesion has been formulated from the results.

Dependence of ultimate bearing capacity and failure behavior of T-shaped deep cement mixing piles on enlarged cap shape and pile strength

A numerical investigation of the ultimate pile capacity (Qult) and failure behavior of T-shape deep cement mixing (TDM) piles is conducted under equivalent volume. Physical model tests are conducted to verify the numerical findings. The results reveal that both the shape of the enlarged pile cap and pile strength play key roles. Sensitivity analyses indicate that the effects of cap shape and pile strength on the complex load carrying behavior of TDM piles are attributable to changes in failure mode, which depend on the mobilized skin friction and bearing of both the cap and pile body.

Micropiles below groundwater at the south auditorium block site, Buffalo, New York

The CANALSIDE development in Buffalo, New York serves to revitalise the former site of the Buffalo Memorial Auditorium. The Auditorium was constructed in 1940 and founded on steel H-piles. It was demolished in 2009. The only portion of the Auditorium left intact was a subbasement equipment room with its floor 10 feet below groundwater. A four-story building was proposed to be constructed directly above the subbasement. The loads imparted by the new building would exceed the capacity of the existing piles, so micropiles were drilled through the subbasement floor to support the new building. Drilling through the existing slab and waterproofing system was a challenge due to water control. The concept for the micropiles included drilling from the subbasement roof through a standpipe bolted to the subbasement floor which was used to control water during drilling. The project included other foundation design and construction challenges, including asymmetrical pile cap geometry, water control and obstructions.

An Analysis of the Impact Exerted on Bearing Capacity of Pier and Pile after Increasing Pile Cap Height

An analysis was carried out in this paper on the bearing capacity of pier pile and seismic performance rule when the low‐pile cap is increased by 1 meter, 2 meters, and 3 meters. The bottom of the pile cap of pier no. 11 of Minjiang River bridge faces three “lows”: 7.6 meters lower than island, 4.6 meters lower than natural river bed, and 6.5 meters lower than low water level. The numerical simulation method is adopted to input three seismic waves of Wolong, Bajiao, and EL to evaluate the bearing capacity of pier and pile under strong earthquakes. Using the standard formula and numerical simulation method, it is observed that the bending moment and axial force of bridge pier show an insignificant change under different seismic waves when the pile cap is increased by 0–3 meters. With peak ground acceleration increased to 0.35 g, the vertical bearing capacity and flexural capacity of pier and pile gratify the requirements; however, the pile foundation will be subject to compression and bending damage.

A hybrid MC-HS model for 3D analysis of tunnelling under piled structures

In this paper, a comparative study of the effects of soil modelling on the interaction between tunnelling in soft soil and adjacent piled structure is presented. Several three-dimensional finite element analyses are performed to study the deformation of pile caps and piles as well as tunnel internal forces during the construction of an underground tunnel. The soil is modelled by two material models: the simple, yet approximate Mohr Coulomb (MC) yield criterion; and the complex, but reasonable hardening soil (HS) model with hyperbolic relation between stress and strain. For the former model, two different values of the soil stiffness modulus (E50 or Eur) as well as two profiles of stiffness variation with depth (constant and linearly increasing) were used in attempts to improve its prediction. As these four attempts did not succeed, a hybrid representation in which the hardening soil is used for soil located at the highly-strained zones while the Mohr Coulomb model is utilized elsewhere was investigated. This hybrid representation, which is a compromise between rigorous and simple solutions yielded results that compare well with those of the hardening soil model. The compared results include pile cap movements, pile deformation, and tunnel internal forces. Problem symmetry is utilized and, therefore, one symmetric half of the soil medium, the tunnel boring machine, the face pressure, the final tunnel lining, the pile caps, and the piles are modelled in several construction phases.

Three-dimensional analysis for piled raft machine foundation embedded in sand

Three-dimensional analysis for the dynamic response of a piled raft foundation subjected to vertical vibration is presented in this study. The analysis considers several factors affecting the amplitude of displacement for deep foundation such as pile cap embedment, pile cap thickness, relative density of the sand and the boundary effect. A validation for an experimental piled raft model depending on a scale factor of (20) using at (Plaxis 3D) computer program was performed. The sand is simulated using Mohr-Coloumb model while the concrete is simulated as linear elastic material. It has been found that embedding the pile cap in the soil and increasing its thickness lead to decrease the maximum amplitude of displacement. Furthermore, the predictions showed that increasing the distance between the foundation and the boundaries and increasing the relative density of the sand can significantly minimize the dynamic response of the foundation.

Analysis of the Generating and Influencing Factors of Vertical Cracking in Abutments during Construction

In order to analyze the causes of cracking in abutments subject to concrete shrinkage and temperature variation during the construction process and to determine factors affecting the mechanical properties of the abutment, nonlinear calculations capturing abutment behavior are conducted with Midas/FEA software. Using these calculations, the cracking mechanism is identified, and the influence of the evaluated factors is analyzed. It is concluded that the deformation between the pile cap and abutment backwall as constrained by a pile foundation when subjected to concrete shrinkage and temperature changes is the basic cause of abutment cracks during construction; these cracks form over the piles and develop upward. For a given reinforcement ratio, the distribution of horizontal crack‐control steel using small, closely spaced bars is more beneficial. When pile‐bearing capacity meets the standard, the width of the generated cracks tends to decrease with the decrease in the diameter of the piles. The existence of a postcast strip in the abutment backwall also contributes to the decrease in the depth of the crack. Finally, the impact of age difference between the pile cap concrete and abutment backwall concrete on cracking is inconsequential.

Structural Repair to Conserve Langkawi’s Main Tourist Attraction: Practical Approach

Direct exposure to marine environment causes accelerated corrosion process of all reinforced concrete structures, consequently, causes cracks, deterioration and overall reduction in the sstructural integrity. The aim of this paper is to study the deterioration and technique of repair work at Eagle Square as a landmark of Langkawi Island. Most of the structural problems which occurred at the splash zone were spalling and delamination on beam, slab and pile cap. Material testing was carried out at selected locations to ob tain detailed information relating to the extent and causes of deterioration of the structure. The result showed that the carbonation depth was smaller than concrete cover and the amount of chloride ions was 0.23% by mass of cement and 50% of the splash zone was having 90% probability of corrosion. After obtaining the necessary data, the study directed towards deciding the remedial work. The Eagle Square structure members were successfully repaired in eight (8) months with proper works planning and repair technique appropriate to the damages.

A Study on the Mechanisms of Interaction between Deep Foundation Pits and the Pile Foundations of Adjacent Skewed Arches as well as Methods for Deformation Control

The construction of deep foundation pits is characterized by heavy loads on pile foundations, complex interactions between the foundation pit and pile foundations, and stringent requirements for deformation control. In this work, FLAC3D was used to perform computational analyses on the displacement responses of pile caps and the retaining walls of foundation pits in a variety of cases and reinforcement schemes. The computational results indicate that the piles of skewed arches interact with the retaining walls of the foundation pits through soil masses. We also revealed the mechanism by which deep foundation pits interacted with the pile foundations of adjacent skewed arches. Based on the mechanisms of interaction between foundation pit excavations and the piles of skewed arches, we proposed three reinforcement schemes for controlling the deformations associated with these interactions. The arched wall reinforcement scheme could provide a satisfactory result in terms of the control of horizontal displacements in the pile foundations and project costs.

Analysis of the Cinapel Bridge’s Construction Operations using Simulation

Simulation has been well known as an effective technique that enables planning and analysis of a construction operation to be performed in advance anticipating problems of efficiencies that would occur in the implementation phase. Therefore, simulation technique could be used to design resources associated with a construction operation to be optimal and to analyze an ongoing operation to be evaluated and refined. This paper discusses the use of simulation to analyze several construction operations, i.e., bored piles, pile caps, piers, and girders, that will be used in building the Cinapel’s Bridge at the Cisumdawu Toll Road Project. The simulation using WebCYCLONE was utilized to determine the most optimal resources needed in each construction operation; resources needed to gain the highest productivity and the lowest wastes. Data of each operation for simulation were gathered from the field, as well as opinions from the practitioners related to the project. The results of the simulation are presented and recommendations are made for the contractor to refine the on-going construction operations as well as to design construction operations before the implementation in the fields.

Prediction of current-induced local scour around complex piers: Review, revisit, and integration

Complex piers (CPs), consisting of a column, pile cap and pile group, are commonly built as foundations for hydraulic and marine structures. Scour-hole development around CPs is studied in this paper. A total of 52 tests is carried out on 4 CP models, with experiments durations ranging from 24 to 120 h. All of the available experimental data for clear-water scour around CPs including the collected data of the present study and those previously published are reviewed and combined into a database. A special case of bridge piers with deep foundation or caisson instead of pile caps is also considered, which is herein called compound piers. The database contains 367 experiments for CPs and 162 experiments for compound piers. The predictive equations of the maximum scour-hole depth at complex piers including HEC-18 and FDOT equations are revisited and a new equation is proposed. Comparisons of the prediction equations shows that for CP data, the absolute error is 28%, 79% and 108% for the proposed, HEC-18 and FDOT equations, respectively. Underestimation below −20% error line occurs for 11%, 15%, and 7% of the cases in the proposed, HEC-18, and FDOT equations, respectively. For compound piers, the proposed equation has 41% absolute error while HEC-18 equation has 93% absolute error.

Parametric Study on How the Lateral Forces Acting on a Deep Foundation Influences the Axial Forces Developing in the Piles

Abstract A missing piece in the design of bridge substructure is that the equation given in structural mechanics that assesses the axial forces in the piles of a deep foundation does not take into account the effect of lateral forces acting on the pile cap. In practice, pile forces are determined using a FEA software. This method, however, can not be easily incorporated into an automated program that performs local and global optimizations of a structure. One of the reasons is that this method is particularly demanding on the computational resources. Since a bridge can have a number of deep foundations, which must be verified for various combinations of actions, which need to be optimized, recalculated in various scenarios and then the entire process reiterated for all structural solutions, computational cost can become prohibitive. Another reason is that due to the lack of a relation between all the parameters and dimensions that influence the behaviour of a deep foundation, their optimization is difficult. For this purpose, a parametric study has been carried out to investigate what parameters influence the relation between the lateral forces applied to the foundation and the axial forces that develop in the piles, and ultimately propose an equation that takes into account the lateral forces. The study is carried out using experimental data obtained on models using the finite element analysis method using SAP 2000 (v.15) software.

Numerical Simulation of Piles Subjected To Lateral Spreading and Comparison with Shaking Table Results

Pile foundations are relatively vulnerable to lateral loads. During liquefaction-induced lateral spreading, this vulnerability is particularly conspicuous due to a loss of strength and stiffness in the liquefied soil. A nonlinear effective stress analysis incorporating an elastoplastic constitutive model based on Finite Difference Method (FLAC2D program) was used to numerically simulate shake table experiment on piles in laterally spreading soils. The soil-pile interaction has been properly considered by using interface elements. The main objective of this paper is to assess the accuracy of a 2D numerical simulation of physical models in predicting the dynamic response of pile foundations and to identify the capability of 2D numerical simulation for 3D effects such as shadow and neighboring effects in pile groups without a pile cap. Results are presented and discussed, in which the obtained response from the simulation is compared to that measured in the test. For the single pile, a fairly good agreement was observed between computed and measured results. It was also found that the shadow and neighboring effects reduced lateral load on the piles by few percent of difference compared with experimental results.

Study on Bearing Capacity of Prestressed Pipe Pile Foundation Under Horizontal Load

Background and Objective:Prestressed high strength concrete pipe pile (PHC) shows brittle fracture when subjected to more than its own bearing capacity. Therefore, the non-prestressed steel bar is added to the PHC pipe pile, that is, the mixed reinforced pipe pile (PRC). The mechanical behavior of PRC group piles and PHC group piles under horizontal force is studied, and the bending moment diagram and displacement diagram of the pile body are compared so as to find the weak parts.Material and Method:In this paper, Φ600 pipe piles are chosen, and the PRC pipe piles are made of non prestressed steel bars of the same number as the prestressing steel bars, and the two steel bars are spaced apart. Referring to a specific project of Binhai New Area, the geological parameters are used, and the force analysis of group piles under horizontal force is carried out by using the ANSYS software.Results:ANSYS simulation results show that, under the horizontal loading, when the number of piles in group piles is different, the locations of maximum bending moments are different. Increasing the number of the PRC pipe pile with non prestressed reinforcement can effectively reduce the maximum bending moment of the pile body.Conclusion:Under horizontal load, with the increase of pile number and the pile cap aggrandizement, the position of maximum moment of pile body is shifted from 5-8 times diameter of pile to the top of pile. When the pile number reaches a certain amount, the maximum bending moment will appear at the joint between the pile cap and the pile body. At the same time, increasing the non prestressed steel bar does not influence the bending moment, and the reinforcement of the pile cap and the pile top should be strengthened.

SOIL-STRUCTURE INTERACTION ANALYSES OF PILE SUPPORTED BUILDING FRAME

The effect of the soil-structure interaction on the simple single storeyed and two bayed space frame resting on pile group of two piles with flexible cap is examined in this paper by resorting to more rational approach and realistic assumptions. Initially, 3-D FEA is carried out independently for the frame on the premised of fixed column bases. Later, pile foundation is worked out separately. The stiffness so obtained for foundation is used in the interactive analysis of frame to quantify the effect of soil- structure interaction on the response of the superstructure. For modeling the foundation system two approaches of finite element analysis are used. In the first approach complete three dimensional finite element analysis is resorted to wherein pile, pile cap along with the soil are discretized into 20 noded isoparametric continnum elements and interface between pile and soil is idealized as 6 noded isoparametric interface elements. In the second approach simplified finite element analysis procedure is used wherein beam element, plate element and spring elements are used to model pile, pile cap and soil respectively. The salient feature of the investigation is that the interaction between pile cap and soil underlying it is considered. In the parametric study presented here, effect of pile spacing and pile configuration is evaluated on the response of superstructure in the form top displacement in frame and bending moment at top as well as bottom of the superstructure columns. Results obtained by either analysis are compared.

Punching shear failure in three-pile caps: Influence of the shear span-depth ratio and secondary reinforcement

The strut-and-tie model (STM) is currently established as the best approach for pile cap design. This model leads to efficient estimations of the main reinforcement placed in strips between piles. However, good practices and some international Concrete Design Standards recommend some secondary distributed reinforcement, and even vertical stirrups that are not considered by the STM. An experimental campaign with nine three-pile caps tested by a centered load is presented to show the influence of both secondary reinforcement and the shear span-depth ratio on pile cap strength.The experimental results show a potential redistribution of internal forces in pile caps after yielding of main reinforcement, finally collapsed due to punching. Secondary reinforcement proves efficient to enhance pile cap strength since it takes part in complementary resistance mechanisms. As expected, the failure load increases with shear span-depth ratio reduction. The STM neither captures the effect of this ratio nor considers punching failure. Checking this failure mode is also required for pile caps.The punching formulation of Eurocode 2 allows considering the influence of this ratio, but some interpretation is required whether one deals with pile caps, regarding the effective width of the shear enhancement factor and the definition of the basic control perimeter. A proper definition would prevent unsafe or very conservative results. Therefore, some recommendations for the verification of deep pile caps following the Eurocode 2 are presented. The contribution of vertical stirrups as punching reinforcement is also investigated. The proposed approach is applied to the existing experimental database of three- and four-pile caps to check formulation validity, and conservative predictions with low coefficient of variation are reached.

Dynamic lateral response of under-reamed vertical and batter piles

Dynamic lateral response of three under-ream reinforced concrete piles constructed in silty sand {vertical, P1 (β = 0°); and batter piles P2 (β = 10°) and P3 (β = 20°)} having equal length of 2.5 m, shaft diameter 0.2 m and under-ream bulb of diameter 0.5 m were considered for this experimental study. Dynamic loads were generated using an oscillator motor assembly mounted on top of pile cap and the response of these piles were recorded in real time using three accelerometers placed along the depth of the pile cap. These piles were subjected to varying dynamic load by changing the eccentricity setting of the oscillator in the frequency range of 0–40 Hz. The test results show that the resonant frequency of the soil-pile system decreases; and peak lateral displacement increases with increase in the force level. The variation of rotational stiffness and the damping ratio of the soil-pile system with force level did not follow a clear trend. Thus the presence of an under-ream bulb in a batter pile does not have a significant influence on the lateral behaviour of batter piles.

IMPROVED SOIL-PILE INTERACTION OF FLOATING PILE IN SAND WITH SHAFT TREATMENT

The present study explored the efficacy of pile shaft surface treatment on the improvement of soil-pile frictional resistance for floating or friction piles. 4 surface conditions of model piles measuring 200 mm long and 20 mm in diameter were examined, namely smooth (control), roughened, fishbone and checked shafts. A pile cap made of plywood was fixed to the top of the pile with 10 mm embedment depth, leaving 190 mm clearance for installation in the sand bed. The test chamber was a see-through glass tank with a footprint of 100 mm x 200 mm and 300 mm height. Coarse sand of D50 = 1.5 mm were loosely placed in the chamber by layers up to 200 mm height before the piles were installed either in single or triple group formations. The incremental load test of conducted via application of dead load ranging between 0.01-0.08 kPa on the pile cap, and the corresponding settlement was recorded. The test results revealed settlement to be reduced by the piles in the order of roughened > fishbone > checked > smooth for the single pile configuration, with maximum reduction of 40 % recorded by the roughened pile. As for the pile group, settlement reduction of the piles with surface treatment clearly outperformed the control pile by almost 50 %, though differences between the former were marginal with seemingly overlapping stress-strain plots. All in all the surface treatment of pile shaft enhanced the shaft friction for the piles installed in sand, but field implementation would require further examination of the pile-driving efficiency as the improved piles could cause additional resistance during installation.

Total reference-free displacements for condition assessment of timber railroad bridges using tilt

The US railroad network carries 40% of the nation\'s total freight. Railroad bridges are the most critical part of the network infrastructure and, therefore, must be properly maintained for the operational safety. Railroad managers inspect bridges by measuring displacements under train crossing events to assess their structural condition and prioritize bridge management and safety decisions accordingly. The displacement of a railroad bridge under train crossings is one parameter of interest to railroad bridge owners, as it quantifies a bridge\'s ability to perform safely and addresses its serviceability. Railroad bridges with poor track conditions will have amplified displacements under heavy loads due to impacts between the wheels and rail joints. Under these circumstances, vehicle-track-bridge interactions could cause excessive bridge displacements, and hence, unsafe train crossings. If displacements during train crossings could be measured objectively, owners could repair or replace less safe bridges first. However, data on bridge displacements is difficult to collect in the field as a fixed point of reference is required for measurement. Accelerations can be used to estimate dynamic displacements, but to date, the pseudo-static displacements cannot be measured using reference-free sensors. This study proposes a method to estimate total transverse displacements of a railroad bridge under live train loads using acceleration and tilt data at the top of the exterior pile bent of a standard timber trestle, where train derailment due to excessive lateral movement is the main concern. Researchers used real bridge transverse displacement data under train traffic from varying bridge serviceability levels. This study explores the design of a new bridge deck-pier experimental model that simulates the vibrations of railroad bridges under traffic using a shake table for the input of train crossing data collected from the field into a laboratory model of a standard timber railroad pile bent. Reference-free sensors measured both the inclination angle and accelerations of the pile cap. Various readings are used to estimate the total displacements of the bridge using data filtering. The estimated displacements are then compared to the true responses of the model measured with displacement sensors. An average peak error of 10% and a root mean square error average of 5% resulted, concluding that this method can cost-effectively measure the total displacement of railroad bridges without a fixed reference.

Construction technology of high-rise pile cap foundation of offshore wind power in Taiwan Strait

Offshore wind farms promise to become an important source of energy in the near future. The high-rise pile cap foundation is one of the typical foundation types for offshore wind turbine. This paper introduces the structural characteristics and construction technology of high-rise pile cap foundation, aiming at the characteristics of the sea area of Taiwan Strait and combining with engineering examples. The construction technology of high-rise pile cap foundation is expounded emphatically from the manufacture and transportation of steel pipe piles, pile foundation construction and bearing platform construction. Compared with the traditional construction technology, the construction technologies used in this project are safer and more reliable. The construction period of piles cap foundation is shortened by 10 ∼ 48 days. The construction technology provides reference for offshore wind power foundation construction.