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By Ilhan Chang, Ernest Nsabimana, Kiseok Kwak, Juhyung Lee, Young-Hoon Jung

"Numerical analyses were performed to analyze the behavior of two different type of suction piles (mono type and group type) under various soil layer conditions (uniform silty clay layer, uniform silty sand layer, and two-layer deposit consisting of clay and sand layers) and lateral loading locations (top, middle, and bottom of the suction pile). According to the results, mono suction pile shows maximum resistance when load is applied on its middle, regardless of the soil layer conditions, while group suction piles varies significantly according to the allowance on head rotation. When head rotation is allowed, the behavior of group type piles become similar to the behavior of mono suction pile. Whereas, when rotation is prevented, resistance is maximized when load is applied on the top head. Moreover, group suction piles show higher efficiency regardless of the ground condition and geological stratum. For further advances, concrete block on the top of group suction piles are suggested as an effective alternative method to prevent partial rotation and maximize ground resistance for group suction piles.IntroductionWith the development of offshore technology, applications and real site installations of suction piles are increasing significantly nowadays. They are generally used as mooring anchors in various floating structures, marine platforms, and offshore wind turbines. According to its convenience in installation and removal, suction type foundations are becoming good alternatives for deep ocean support systems. The bearing capacity is similar to the bearing behavior of ordinary offshore structures (piles or drilled shafts). The most common use of suction caissons is anchors for catenary mooring lines, where the chain angle at the mudline is close to zero (Randolph, 2002; Sharma, 2004).Recently, it is reported that a huge isolated single suction pile can be replaced by a group of moderatesized suction piles (Randolph et al. 2004). A single monopile is easy to be produced and installed in site. It is expected that monopile foundation is not applicable for deep depths because it has a limitation on penetration according to its huge side skin area (i.e. friction). Moreover, stiffness requirements sometimes render thicker pile wall conditions which are impractical to be produced."

Jan 1, 2017

By Alexander B. Reeb, Richard J. Varuso, George M. Filz, Jehu B. Johnson

"T-walls, which are concrete floodwalls in an inverted “T” shape, are an integral component of the Greater New Orleans Hurricane and Storm Damage Risk Reduction System (HSDRRS). In order to resist large lateral flood loads, T-walls are typically supported on long batter piles that extend through the weak and compressible clays and peats commonly encountered in southern Louisiana. Since the piles are battered, settlement of the compressible foundation soils can result in loads acting normal to the piles and induce pile bending moments. Therefore, the design of pile-supported T-walls is a complex soil-structure interaction problem that requires detailed and careful numerical analysis to accurately estimate the stresses and bending moments in the piles. For this paper, numerical analyses were performed for three cross sections that each included a two-pile T wall system that was installed within a 15-ft tall new levee embankment. The cross sections were identical except that the elevation of the T-wall base was varied. This paper discusses the analyses, and it compares the influence of settlements and flood loading on the pile stresses and bending moments. In addition, this paper includes general recommendations for the analysis and design of pile-supported T-walls in practice.INTRODUCTION AND BACKGROUNDThe recently completed Greater New Orleans Hurricane and Storm Damage Risk Reduction System (HSDRRS) includes 350 miles of levees and floodwalls and is designed to defend against a 100-year storm surge event. The floodwalls predominantly consist of I-walls and T-walls. I-walls are comprised of a sheet pile wall curtain capped with a monolithic concrete wall above grade. T-walls are similar to I-walls, but they include a wide concrete base at grade, which forms an inverted “T” shape, and they are generally supported by long batter piles that provide additional lateral and rotational stability for resisting flood loads.During Hurricane Katrina, several I-walls failed, resulting in large breaches and devastating flooding (Duncan et al. 2008, IPET 2009). T-walls on the other hand performed quite well, including T-walls that were overtopped and eroded on the protected side, yet still did not collapse. As part of the HSDRSS, more conservative designs and height restrictions were required for I-walls (USACE 2011), and a number of I-wall sections were replaced with T-walls. However, the design of pile-supported T-walls is complex and requires careful consideration of both flood loading and settlements."

Jan 1, 2017

By Zhou Haizuo, Diao Yu, Zheng Gang

"The conventional design method for the embankment supported by DM columns usually assumes the simultaneous failure of all the columns. However, the progressive failure may occur in practice, especially considering that many researches have justified the critical load of DM columns is bending moment. In this study, a finite difference method was adopted to simulate the embankment on soft clay improved by DM columns. An increasing surcharge was applied on the embankment surface to investigate the mechanism of the progressive failure of columns beneath embankment. To capture the brittle bending failure of the DM columns, the model employed a cut-off method, in which the column was separated on failed section as long as the ultimate bending failure was reached. Furthermore, high-strength DM columns were used to enhance the global stability of embankment in this study. The numerical results showed that the ultimate bending failure was first reached at the column beneath embankment toe, and then a continuous collapse extended to the column beneath the embankment shoulder. It is found that the reinforcement could be obviously effective when the reinforced area of high-strength DM columns was extended to a certain area.INTRODUCTIONDeep mixed (DM) columns have been commonly used as a soil-improvement technique to increase stability and to reduce settlement of embankment. Research on failure modes of DM columns owing to embankment fill and surcharge has been the subject of interest for a number of investigators (Miyake 1991; Kitazume 2000; Han 2005; 2006).The potential failure modes of DM column include bending, inclination, shearing, rotating, soil flowing and a combination of these modes (Kitazume and Terashi 1991; Broms 1999). Many researchers have found that bending failure of DM columns was more critical than the shear failure. A centrifuge test was performed by Kitazume (2000) and the results showed that the columns failed in bending before shear failure. In addition, several numerical computations illustrated that design method using the shear strength overestimated the stability of embankment over DM columns (Han and Huang 2005; 2006; Navin 2006; Liu 2007; Wang 1996). In practice, an equivalent shear strength method based on bending failure could better reflect the stability of embankment (Zheng 2010; China Code JGJ79-2011)."

Jan 1, 2015

By Brunella Recinto

Pile loading tests are carried out with two main objectives: 1) evaluating the ultimate resistance; 2) checking the behaviour of the pile under live load. In the first case and particularly for large diameter bored piles the cost of a loading test may be very high. In the late '80s, a new method to perform static loading tests was proposed. It is based on the use of a sacrificial hydraulic jack placed at the pile toe. The device, internally pressurized, expanding applies an upward force on the pile shaft and an equal but opposite downward force on the soil beneath the pile toe. This device is well known as Osterberg's load cell, shortly O-cell. The obtained results are typically summarized in two separate load-movement curves: one for the shaft side shear resistance and another for the toe resistance. The two curves are used to build what is generally named the "equivalent head load-movement curve" relying upon two hypotheses: - the pile is rigid; - the load movement relationship for the shaft is not affected by the direction of movement. The former assumption can be easily removed, while it is not possible to remove the latter. On the validity of this latter hypothesis, comparisons between conventional head loading tests and toe loading tests could be very helpful. Unfortunately in the literature there are only a few case histories and most of them are also poorly documented. In order to explore limitations and potentialities of the new testing method, a finite element model has been set up. Results of simulations of conventional head loading tests and of O-cell tests are analyzed, discussed and compared.

Jan 1, 2003

By Trevor I. Addenbrooke

Stress reducing piles were used for the first time at the Queen Elizabeth II Conference Centre near the Palace of Westminster in London, UK. The inclusion of these piles directly beneath heavily loaded columns was to reduce the high anticipated bending stress in the foundation raft, and to eliminate local yield of the London Clay beneath the column locations. Load cells were placed in one of the stress reducing piles during construction. The data showed that the pile carried about 30% of the column load. This can be contrasted with conventional piled raft design where the pile carries upwards of 80% of the column load. The build up of load on the pile and pile displacement have been accurately reproduced using coupled finite element analysis. These numerical results demonstrate the value of geometrically simple axially symmetric analyses for modelling a pile-enhanced raft. On site, excavation preceded construction of the raft and subsequent pile loading. Failure to model this construction sequence caused the shear strength to mobilize at the base of the pile first, during loading, whereas following the construction sequence caused the shear strength to mobilize at the top of the pile first.

Jan 1, 2002

By KeerthiRaaj Subrmanian, Muthukkumaran Kasinathan

"A railway embankment is under construction between Nagapattinam to Thiruthuraipoondi covering 36.5 km. The sub-soil strata comprises of soft clay extending up to 10 m below existing ground level, which is subjected to stability and settlement problems. A trial stretch covering about 5 kilometer was improved using Prefabricated Vertical Drains (PVD) with surcharge was recommended to accelerate the consolidation settlement. The geotechnical characteristics of the subsoil are examined through laboratory tests on representative soil samples. Recent improvement in the finite element analysis has facilitated modeling of PVD in finite element software for computing the settlement magnitude and time rate of consolidation. In this study the theoretically predicted settlement magnitude and time rate of consolidation from Terzaghi.s vertical consolidation, Barron's radial consolidation are compared with the analyzed FEM results for both the cases with and without PVD improved embankment. The comparative analysis between FEM and predicted data hold good for stresses and the associated deformations. The excess pore water pressure was significantly lower and their dissipation was faster in case of embankment with vertical drains. Thus PLAXIS 2D tool shows fairly convincing results in comparison to the theoretical solutions.1. INTRODUCTIONFrom the earlier times civilization has been developed in a fashion either at the banks of river or near to the shore region, because of the easier availability of food and water. This over centuries made them as huge cities, consequently population rise made the increased necessity of highway, railways, port and even more ground for construction. As a stake researchers are pushed to make a low bearing ground into a massive carrier of skyscrapers, embankment, bridges etc. These low bearing ground suffers from total and differential settlement, slope instability. Hence, numerous ground improvement techniques were followed to eradicate these concerns which include preloading, piling, stone column, vertical drains and geosynthetic reinforcement. Among them Prefabricated vertical drain (PVD) are often used to accelerate consolidation of soft subsoil and has been the main soil improvement method used in improving the soft marine clay deposit (Chu et al.(2004); Chai (2001) and Arulrajah et al.(2003)). Literature review of embankment over soft clay deposit reveals that combination of PVD with preloading is widely considered as an economical and less time consuming ground improvement technique."

Jan 1, 2015

By Zhang Wengang, L. John Endicott

The properties of many geological materials are variable. This is especially true for variations in elevation of the top of rock profile, strength of weathered rock, and conductivity of rock masses. Often the site investigation stage is completed by site specific ground investigation utilizing boring, sampling, and testing. Statistically this is a sampling procedure, but the borings are often widely spaced, and ground conditions between borings are deduced by interpolation. Often budgets are a limiting restraint and the information that is obtained may be less than desired. Sampling and testing is often biased. If claims for unforeseen ground conditions are to be avoided, the properties of the ground should be adequately identified. This paper describes how data can be used to evaluate the subsurface top of rock profiles, and can give insight into representative, maximum, and minimum strengths, and variation in conductivity relating to inflow of water into excavations, that can assist in planning the works and also in resolution, or avoidance, of disputes about unforeseen ground conditions. INTRODUCTION The mechanical properties of the ground are naturally variable. The work of Geologists, Engineering Geologists and Geotechnical Engineers is fundamentally investigative. Frequently, budgets for ground investigation are squeezed, resulting in widely spaced boreholes, with conditions between them determined by interpolation. Profiling can be adopted but the measurement, such as seismic velocity, is used as an indirect means of computing in-situ profiles and mass properties. Often a lot of test data are generated on large projects or by many projects in the same vicinity. Published data enlarge the database for a given project, and databases can be interrogated to gain insight into different categories of ground. Integration with geological studies can then lead to more reliable characterization of the ground in terms of identifying the materials present, their extent and their range of properties. This paper focuses on properties of rocks that are generally required for ground engineering, namely the top of rock profile, the unconfined strength of rock materials, and the mass conductivity. Data are obtained from Granodiorite and Granite in Hong Kong, and from Granite and the Jurong Series of weakly metamorphosed sedimentary rocks in Singapore. All four rock types have been tropically weathered, resulting in widely varying top of rock profiles, material strengths and mass conductivity. With a wide range in values for these parameters, project specific ground investigation conducted within a limited budget may run the risk of falling short of obtaining sufficiently reliable data sets, resulting in risk that unforeseen ground conditions may be encountered.

Jan 1, 2019

By Tu Bao

HP-Pile foundations are the most favorable type of foundations for bridges because of their constructability, versatility with regard to subsoil conditions, and settlement controllability. For many years, bridge engineers have puzzled over the most economical way to orient HP-Piles: Should the strong axis be oriented in the longitudinal direction or in the transverse direction? The accurate design of foundations may considerably reduce construction costs. In order to answer this question, 3-D finite element models will be set up to analyze the effects of pile orientation on bridge behavior. Because seismic loading usually controls the structural design in seismic zones, it is important to investigate the effects of pile orientation under such loading. HP-Piles are designed conservatively due to the uncertainty of the dynamic soil-structure interaction during earthquakes. For the bridge substructure, the soil?s stiffness plays an important role in load distribution as the soil and piles act as a combined system to resist the seismic loading. The dynamic soil-structure interaction mechanisms of bridges in both the longitudinal and the transverse directions will be investigated through the use of 3-D finite element models. The numerical models will realistically simulate the soil-pile-abutment-wingwall-superstructure system subjected to seismic loads. Nonlinear soil springs will be employed to model the non-elastic soil behavior. The analysis will provide theoretical support to the design practice. KEYWORDS: HP driven piles, finite element, pile orientation, soil-structure interaction

By Andrew Rietz, Yu Bao, Steven Halewski

"HP-Pile foundations are the most favorable type of foundations for bridges because of their constructability, versatility with regard to subsoil conditions, and settlement controllability. For many years, bridge engineers have puzzled over the most economical way to orient HP-Piles: Should the strong axis be oriented in the longitudinal direction or in the transverse direction? The accurate design of foundations may considerably reduce construction costs. In order to answer this question, 3-D finite element models will be set up to analyze the effects of pile orientation on bridge behavior. Because seismic loading usually controls the structural design in seismic zones, it is important to investigate the effects of pile orientation under such loading. HP-Piles are designed conservatively due to the uncertainty of the dynamic soil-structure interaction during earthquakes. For the bridge substructure, the soil’s stiffness plays an important role in load distribution as the soil and piles act as a combined system to resist the seismic loading. The dynamic soil-structure interaction mechanisms of bridges in both the longitudinal and the transverse directions will be investigated through the use of 3-D finite element models. The numerical models will realistically simulate the soil-pileabutment- wingwall-superstructure system subjected to seismic loads. Nonlinear soil springs will be employed to model the non-elastic soil behavior. The analysis will provide theoretical support to the design practice.IntroductionAs sustainability has asserted itself in the public’s eye, bridge professionals have rushed to develop criteria for sustainable bridges. The three main categories that define and distinguish sustainable bridges are: lower energy input, increased durability, and simplified deconstruction. By optimizing the structural members, the engineer is able to reduce the material quantities for the bridge, effectively reducing the energy input for the bridge (Hunt; Whittemore). A deeper understanding of soilfoundation- structure mechanism will facilitate sustainable bridge design by lowering energy input and increasing the service life of bridges (Rietz et al.)."

Jan 1, 2017

By Amalia Giannakou

When designing structures in seismically active areas, foundations of critical structures are typically located away from known faults. Indeed many seismic codes prohibit construction in the immediate vicinity of seismically active faults establishing minimum setbacks from the faults. However, for long structures such as bridges, tunnels and pipelines, a fault maybe unavoidable, and fault rupture risk impossible to preclude. This paper presents a case study of a bridge foundation design that incorporates the consequences of fault deformations passing through the foundation. A series of site surveys were conducted to characterize the fault environment, and fault displacement hazard analyses were conducted to develop design displacement demands. Subsequently, numerical analyses were performed to evaluate the fault rupture-induced demands on a pier foundation in terms of displacements and rotations. Initially, analyses were performed that model the free field fault rupture propagation to the ground surface of the fault to ensure that the basic site characteristics are captured. Subsequently, the foundation elements were introduced in the model and the fault rupture is simulated again. The interaction and influence of the foundation on the fault rupture propagation is calculated, and the consequent demands and distortions of the foundation block provide a basis for structural engineers to design the bridge.

By Orestis Zarzouras, Amalia Giannakou, Jacob Chacko

"When designing structures in seismically active areas, foundations of critical structures are typically located away from known faults. Indeed many seismic codes prohibit construction in the immediate vicinity of seismically active faults establishing minimum setbacks from the faults. However, for long structures such as bridges, tunnels and pipelines, a fault maybe unavoidable, and fault rupture risk impossible to preclude. This paper presents a case study of a bridge foundation design that incorporates the consequences of fault deformations passing through the foundation. A series of site surveys were conducted to characterize the fault environment, and fault displacement hazard analyses were conducted to develop design displacement demands. Subsequently, numerical analyses were performed to evaluate the fault rupture-induced demands on a pier foundation in terms of displacements and rotations. Initially, analyses were performed that model the free field fault rupture propagation to the ground surface of the fault to ensure that the basic site characteristics are captured. Subsequently, the foundation elements were introduced in the model and the fault rupture is simulated again. The interaction and influence of the foundation on the fault rupture propagation is calculated, and the consequent demands and distortions of the foundation block provide a basis for structural engineers to design the bridge.IntroductionThe Izmit Bay bridge, a 3-km-long suspension bridge that crosses Izmit Bay in Turkey, is planned to be constructed in one of the most seismically active places in the world. The south approach structures for the Izmit Bay Bridge along the western side of the Hersek peninsula bring the bridge down from on the order of El. 60 meters at the South Anchorage to an elevated embankment approximately 1.3 km farther south (Figure 1). The south approach structures are located within a zone of secondary deformation around the primary trace of the North Anatolian Fault. The concept design team has developed a concept design for a “viaduct” structure that consists of 10 spans with lengths varying between 136 m and 100 m and two back spans one of 125 m, attached to the main bridge and the other of 74 m attached to the south embankment."

Jan 1, 2017

By Lok M. Sharma, Deep K. Khatri, Bradfield. Brett

"A shored enclosure was required to access a control structure upstream below the dam of a deep lake. The shoring involves the interaction of the structure, soil, and water and the loads imposed include the hydrostatic forces of the water, soil pressures as well as dynamic forces due to currents and waves. Deep excavation support systems have traditionally been designed using classical methods that involve direct computations of earth pressures. However, traditional analysis does not take into account soil-structure interaction. Numerical modelling offers better means to analyze soil-structure interaction. This paper presents a 2D finite element (2D-FE) analysis of a deep excavation support structure that was required to remove and replace a control structure at the upstream toe of a dam. The sheet-piling shoring was designed to withstand the lateral pressures from 14 m deep free water and 5.5 m deep excavation below the free water to reach the required excavation level to replace the gate structure. Elastic-plastic analyses were performed to predict the stresses and deformations of the complicated shoring structure and excavation bottom. The soil parameters, procedures used to develop the 2D-FE model, and the results are discussed in this paper. The shoring system is currently under construction.INTRODUCTIONA deep shoring system enclosure is required to keep out water and soil and to provide a support for unbalanced loadings due to dewatering and/or, excavation in order to permit construction of the permanent structures in the dry. A braced shoring system consists of a single wall sheet piling which is driven into the ground to form a “box” around the excavation site and is braced on the inside. After bracing the sheet piling, seal concrete is placed into the bottom to prevent water from seeping into the open excavation from underneath the sheet piling, and the water is pumped out to provide the dry work area. The braced shoring involves the interaction of the structure, soil, and water and the loads imposed include the hydrostatic forces of the water, soil pressures as well as dynamic forces due to currents and waves. Deep excavation support systems have traditionally been designed using classical methods that involve direct computations of earth pressures, (active, passive, or apparent pressures). There have been some uncertainties regarding the actual distribution of earth pressures due to influence of the support wall flexibility, as these traditional methods do not take into account soil-structure interaction. Numerical modelling offers better means to analyze soilstructure interaction."

Jan 1, 2017

By S. P. Lin

The numerical models of nonlinear piles for deep foundations are studied in this paper. The purpose of these is to clarify the mechanical behaviour of deep foundation nonlinear piles subjected to axial and lateral loadings. Based on the site data of p-y curve as well as t-z curve of foundation soils, it is possible to evaluate pile performance under above mentioned loads by means of combined FEM/FDM models. Numerical examples are presented in tall building and offshore jacket for illustrating the technique, it show high efficiency of these models. Some information to be interested by design engineers are given, especially for those who pay very concerns on the interaction behaviours of structure and its pile foundation.

Jan 1, 2010

By N. Q. Huy

This paper describes the application of finite element analysis to simulate the static and quasi-static pile load tests in different drainage conditions. The possible effect of excess pore water pressure will be studied from the simulations results. The results show that the drainage condition has effect on the bearing capacity of a pile derived from the quasi-static pile load test. The excess of pore pressure reduces the pile toe resistance while it increases the pile shaft resistance. The factors which influence the effect of excess pore pressure are also discussed.

Jan 1, 2006

By P. Seethalakshmi, Yatakuri Yaswanth Naidu

The use of a single pile, group of piles with pile cap, piled raft foundation system, etc., are prevalent in transferring the superstructure load from the soft soil layers to the firm underground layers to reduce the settlement and improve the bearing capacity. The recent development of disconnected piled raft foundation has gained greater importance in improving the load transfer mechanism among the pile, raft, and subsoil by reducing the vulnerability of the greatest axial force on the pile head which leads to pile failure. The present study aims at analyzing the performance of unreinforced and Geogrid reinforced disconnected piled raft foundations under vertical loading using the commercially available finite element software PLAXIS-3D. A parametric study was conducted on unreinforced and reinforced disconnected piled raft foundations to explore the effect of varying pile stiffness as well as the inclusion of Geogrid layer on the load vs settlement, the load sharing ratio of piles and raft, and the distribution of axial load and bending moment along the length of the pile. The Mohr-Coulomb model was used for the granular cushion layer while the Modified Cam Clay model was used for soft clay underlain the sand layer. Raft and piles were assumed to be rigid and linear elastic. The results showed that axial force taken by piles with higher stiffness was maximum while settlement at the bottom tip of the pile with higher stiffness was maximum in both reinforced as well as unreinforced disconnected piled raft systems.

Sep 1, 2022

By Sepideh Damavandinejad Monfared

In recognition of the practicality of using inclined micropiles as elements for foundation support to resist static and seismic loading conditions, specifically in retrofitting projects, this study presents an investigation into the beh avior of an inclined micropile subjected to simultaneous lateral load and bending moment. Three-dimensional numerical simulations are performed using the finite element method to assess the influence of micropile geometrical parameters such as angle of inclination, length, and diameter on the response of micropile-soil system. The Mohr-Coulomb failure criterion is used to define the behavior of soil and stabilized soil around micropile materials and the micropile, constructed of concrete and steel, is assumed to be elastic. The interaction between soil and micropile is taken into account by defining interaction elements covering both tangential and normal behavior. The study is carried out using nonlinear FEM analyses. The results of these simulations indicate that negative micropiles, in which slip surface deflects downward, have higher lateral load capacity than positive micropiles with slip surface deflecting upward. The conducted research also shows that increasing the diameter and the length of micropile increases the lateral load capacity. Increasing micropile diameter is more effective in increasing lateral load capacity. A relationship is developed from statistical regression analysis of the finite element modeling computations to estimate the lateral displacement of a micropile inclined at an angle of 30o in silty sands.

By Sepideh Damavandinejad Monfared

"In recognition of the practicality of using inclined micropiles as elements for foundation support to resist static and seismic loading conditions, specifically in retrofitting projects, this study presents an investigation into the behavior of an inclined micropile subjected to simultaneous lateral load and bending moment. Three-dimensional numerical simulations are performed using the finite element method to assess the influence of micropile geometrical parameters such as angle of inclination, length, and diameter on the response of micropile-soil system. The Mohr-Coulomb failure criterion is used to define the behavior of soil and stabilized soil around micropile materials and the micropile, constructed of concrete and steel, is assumed to be elastic. The interaction between soil and micropile is taken into account by defining interaction elements covering both tangential and normal behavior. The study is carried out using nonlinear FEM analyses. The results of these simulations indicate that negative micropiles, in which slip surface deflects downward, have higher lateral load capacity than positive micropiles with slip surface deflecting upward. The conducted research also shows that increasing the diameter and the length of micropile increases the lateral load capacity. Increasing micropile diameter is more effective in increasing lateral load capacity. A relationship is developed from statistical regression analysis of the finite element modeling computations to estimate the lateral displacement of a micropile inclined at an angle of 30o in silty sands. IntroductionMicropiles are small diameter (typically less than 300 mm), cast-in-place, drilled, and grouted replacement piles with steel pipes which after being conceived in Italy (Lizzi,1978), were originally developed for underpinning existing structures (Bruce et al.,1990) to arrest and prevent structural movement, upgrade loadbearing capacity of existing structures, repair or replace deteriorating or inadequate foundations or raise settled foundations to their original elevation."

Jan 1, 2017

By Muttharam M, Karthick Kumar V

Helical piles foundation systems have been extensively used in engineering application. It is commonly adopted to resist the compression, uplift force, overturning moment and lateral forces. Helical pile system is extensively used in many structures such as Transmission towers, Wind farms and other offshore structure because it is easy and quick to install. Realizing the importance of helical pile, an attempt is made in the present investigation to bring out the effect of spacing between the helix, blade thickness, and shaft thickness through numerical analysis. To validate the finite element model experimental investigation was carried out. In this investigation model steel piles with dual helical plate embedded in clay bed with the consistency of 0.4 was tested to study the effect of uplift loading on the behaviour of piles in tensions. Model helical pile with 12.5 mm diameter circular shaft and helix diameter of 25 mm. The model pile embedded in clay bed for a depth of 400 mm. Parametric analysis of helical pile by varying blade thickness, shaft thickness, and the spacing of helix was carried out by using Finite Element tool Plaxis 3D. From this analysis, an increase in thickness from 4 mm to 10mm increase the uplift load. Similarly, an increase in spacing of helices from 0.5 m to 1.5m increase the uplift capacity beyond that it decreases the uplift capacity. By keeping the contact area of the helix as constant as the number of a helix and helical spacing was varied, the critical number of the helix was found as 2 and the critical spacing of helix was found as 1.5 m for this study.

Nov 1, 2022

By Christian L. Escalera

Over seven years ago, on October 29, 2012, Superstorm Sandy pummeled the Northeast of the United States inflicting heavy damage on New York City Transit’s (NYCT) system. Since then, NYCT has been methodically rehabilitating and hardening its assets to upgrade service and prevent future impacts caused by similar devasting storm surges. Part of these resiliency efforts, NYCT’s 207th St Yard Project is one of many projects that make up the Sandy Repair and Flood Mitigation Program. The work to be performed on the 207th Street Project includes building a perimeter Floodwall along the Harlem River, extending up 215th Street and 9th Avenue with the intent of having the ability to withstand a 500 Year Storm flooding event. The original 1,535 lineal feet of the marine side floodwall design consisted of 937 each W40x235 H-Piles continuously welded to PS 27.5 flat sheet to form an interlocked and composite steel seawall that would protect the NYCT 207th Yard from a storm surge of the Harlem River. However, after the Contract was awarded and a Notice to Proceed was issued, Walsh Construction Company II (WCCII) partnered with Mueser Rutledge Consulting Engineers (MRCE) to propose a redesign of the marine wall section as a Value Engineering Change Proposal (VECP). This VEP redesign is comprised of 279 each 54in Diameter Steel Pipe Piles that are interconnected with continuously welded PZ 35 sheet piles interlocks. The intent of the VEP was to provide a cost savings that could be shared by both parties as well as alleviate some constructability and alignment control concerns that WCCII had expressed to NYCT. The VEP allowed WCCII to substantially lower the total cost which was shared between NYCT and WCCII.

By John Wise

Significant movement to an existing slurry wall which serves as a retaining wall on 'O' Street in Southeast Washington, D.C. initiated the Department of Public Works for the District of Columbia to invite specialty contractors to propose a rehabilitation and stabilization for the failed slurry wall. Nicholson Construction Company proposed and was awarded a contract for the construction of an anchored precast lagging and soldier pile wall to be located approximately 4 feet in front of the existing structure with granular fill placed between the new and existing walls. Stabilization of the existing slurry wall also included drilling horizontal weep holes and demolishing the failed panels down to the existing ground surface. A new and improved drainage system was also constructed to increase the amount of water directed toward the existing storm sewer system running along 'O' Street. This paper provides a detailed account of these construction activities.

Jan 1, 2003