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By Frank Rausche

Why testing What tests can be done Dynamic load testing Loading device Measurements Analysis Examples

Jan 1, 2001

By Ambarish Ghosh, Rituparna Dey, Indrajit Chowdhury

"In port and harbor facilities, jetties and cargo berth terminals are usually installed on piles that remain partially embedded in soil, while a part of it behaves as columns supporting top deck. Technology in vogue adapts a pseudo static analysis in computer where the top deck including piles are analyzed as an integrated system based on finite element method when the piles are modeled as beam elements, while the soil in which it is embedded is modeled as linear or nonlinear springs. Typical berthing force of the ship is considered as a pseudo static force where the dynamic characteristics of the force is taken into consideration by an equivalent impact factor and little study exists on the actual behavior of these type of piles under the transient shock due to berthing impact. Present paper proposes an analytical solution based on which one can compute the dynamic response of such jetty piles considering shear modulus of soil constant with depth. Considering the solution is analytical in nature no special software is needed and can well be adapted fordesign office practice using generic utility software like MATHCAD, MATLAB etc. that makes theproposed model computationally very efficient.INTRODUCTIONResponse of piles under dynamic load has been an important study in the realms of civil engineering, where significant research has been carried out on its dynamic behavior under harmonic loads like one experienced in a machine foundation or under seismic force.A number of researchers have given solution to this problem like Parmelee et al (1964), Tajimi (1966), Penzien (1970), Novak et al (1974, 1983), Banerjee and Sen (1987), Dobry and Gazetas (1988),Chowdhury and Dasgupta (2008).However, most of these theories are based on piles loaded under harmonic load and valid for long piles where structural failure precedes the soil failure considering the piles are long and flexible."

Jan 1, 2015

By Johannes Labenski, Christian Moormann, Johannes Aschrafi

"Open steel pipe piles are used for various applications in costal engineering, port structures and increasingly important for offshore structures. During the installation of open steel pipe piles the formation of a plug has an influence on the installation process of the pile and also on the final bearing capacity. The formation of the plug depends on different factors, e.g. the pile diameter and the installation method. This paper starts with a structured overview about analytical methods (API, EAP-EAU, UWA-05, HKU-12, Modified API) to calculate the axial bearing capacity of open steel pipe piles. The numerical simulation of the installation process of open steel pipe piles has to fulfill high demands, i.e. to accurately represent the penetration of the pile inside the soil, the formation of the plug and also the stresses and strains during the installation. A numerical back analysis of a comprehensive field test, using the Coupled Eulerian-Lagrangian (CEL) method and a hypoplastic constitutive model for sand, reveals the stresses and displacements of the soil and of the piles. The analysis provides a comprehensive understanding of soilpile interaction.INTRODRUCTIONThe particular difficulty in the numerical simulation of plug formation, is that the effect of plugging inside open ended steel pipe piles has not been fully investigated. In scientific papers different approaches are documented to explain this phenomenon. Some are based on in-situ tests and others are based on numerical simulations. One of the challenges is to determine the end bearing capacity and shaft friction of the steel pipe pile. Different approaches have been developed over the years to determine them e.g. from Randolph et. al. (1991, 1994) and Paik et. al. (2003). Recent approaches are the ICP-05 Method (Jardine 2005), the UWA-05 Method (Lehane 2005) and the HKU-12 Method (Yu & Yang 2012a). A comparison of some methods can be found in Schneider et al. (2010). A plug inside an open steel pipe pile can be visualized as a spatial bracing of soil between the inner surfaces of the pile, cf. Lüking (2010).. However according to Lüking & Kempfert (2012) this bracing only exists for the height in the end of the pile equal to twice its diameter.To identify a plug inside a pile, there are different measurable parameters. One parameter is the development of stresses around the pile during and after its installation. Henke (2013) measured the inand outside horizontal stresses at the pile tip during the installation. The results showed higher stresses on the inside compared to the outside. To validate his measurements he performed a numerical back-analysis of the measured installation process and got matching results."

Jan 1, 2017

By Rajasekar Subbian, Jessica Oudhof

In the Netherlands pile foundation design is done using CPTs in accordance with EC7 national annexure. The capacity per tip level is calculated for every CPT followed by zonation to find the tip level per zone. The correlation factors are used to take into account the variability in ground across the zone and they depend upon the number CPTs within the zone. The CPTs and pile tip levels selection for zoning is an iterative process that can demand significant manual effort to produce an economical pile plan. This often leads to the use of conservative correlation factors in order to accelerate the design process. Thus, it has been automated in a tool with CPTs, pile location and loads, and capacities as input. The tool has also been employed in two case studies and the results are compared to the current design practise.

May 1, 2022

By Lance Rasband, Richard Hanke

"Seattle Tunnel Partners (STP) started mining on Seattle’s SR99 tunnel on July 30, 2013, working slowly through a 15 ft (4.6 m) thick fiber-reinforced concrete headwall. Once through the headwall, the machine would move through roughly 400 lineal ft (122 m) of jet grout-improved soil at a rate slightly over 6 ft (1.8 m) per day. It was anticipated that once through the improved area, Bertha—the world’s largest tunnel boring machine—would move at a rate of 35 ft (10.7 m) per day. By the end of October 2013, Bertha had mined roughly 430 ft (131 m), averaging 4.73 ft (1.4 m) per day, and had begun mining within native soils. By the start of December 2013, tunneling reached the 800 ft (244 m) mark and Bertha averaged 12 ft (3.7 m) per day, achieving as much as 42 ft (12.8 m) of progress on some days. However, on December 6, 2013, Bertha began to stumble and all progress quickly came to a halt. Preliminary InvestigationInitial reports stated that an obstruction had stopped the machine in its tracks. Malcolm Drilling received an early morning call on Sunday, December 8, 2013, from STP to rapidly mobilize a Bauer BG-50 drill rig with crews to investigate what was hindering Bertha’s progress. Malcolm’s equipment and crews flew into action and were completely mobilized and operational by mid-week. The preliminary investigation involved installation of 10 deep dewatering wells to reduce the hydrostatic head within the ground around the machine and allow STP personnel to inspect the cutter head from within the shaft for presence of obstructions. By the close of December 2013, the wells were installed and the dewatering system was fully commissioned. STP crews were then able to inspect the cutter head and found small fragments of a steel pipe wrapped around the outside of the shield. The steel was apparently from an abandoned 10 in (0.25 m) diameter monitoring well casing previously installed by WSDOT (Washington State Department of Transportation) to monitor groundwater conditions for the design and planning of this very project. After the steel was cut out of the head and cleared from Bertha’s path, she attempted to move forward but was only able to manage a slow crawl"

Jan 1, 2015

By Gihan E. Abdelraham, Youssef G. Youssef, Mohamed M. Kamel

"Previous studies defined Narrow Mechanically Stabilized Earth, NMSE, walls as a retaining wall with aspect ratio (wall width to its height, L/H) less than 0.70 as in traditional walls. Some studies investigated its behavior and its failure planes compared to those of traditional walls. In this paper, parametric study using finite element analysis PLAXIS, 8.2 has been introduced to discuss global factor of safety, FS, maximum horizontal displacement, Ds, maximum tension force of reinforcement element, Tmax, and active earth pressure coefficient, ka, as a function of different aspect ratio of NMSE wall, L/H, reinforcing elements spacing, S, elastic axial stiffness of reinforcement element, EA, wall batter, 1/m, soil friction angle, f, and wall height, H. The results indicated that increasing aspect ratio increases the factor of safety, maximum horizontal displacement, maximum tensile force and active earth pressure. Increasing elastic axial stiffness increases factor of safety, maximum tension force of reinforcement element while decreasing the maximum horizontal displacement.IntroductionReinforced earth is a composite geoconstruction material, which embodies two basic components; namely engineering fill and reinforcing elements. The latter one is responsible for improving the tensile and shear resistance of the soil. The soil-reinforcement technique has been in use for many geotechnical applications especially MSE walls.A narrow wall system is referred to as a MSE wall with an aspect ratio, L/H, below 0.70 that is placed in front of a stabilized wall. An example of a narrow wall system with its dimensions is illustrated in Fig. 1."

Jan 1, 2017

By Janaka J. Kumara, Takashi Kurashina, Yoshiaki Kikuchi, Takahiro Yajima

"The inner frictional resistance of open-ended piles depend heavily on the degree of soil plugging. Many factors including pile diameter, relative density and end conditions of the piles influence the degree of soil plugging. In this paper, the effects of inner sleeves attached at the pile base on the inner frictional resistance are discussed. The experiments were conducted on a medium-dense sandy ground using smallscale model piles. The results suggest that the inner frictional resistance is influenced by sleeve height for 50 mm diameter piles although it is independent for 30 mm diameter piles. The results also indicate that soil plug height is influenced by the sleeve height. The results of the incremental filling ratio (IFR) showed that penetration of non-sleeved piles is closer to unplugged state than the sleeved piles. The results of the IFR also reveal that the degree of soil plugging is affected by the sleeve height for 50 mm diameter piles although the variation is very limited in 30 mm diameter piles. The results on the coefficient of lateral earth pressure suggested that it increases from 1.08 – 1.75 when the sleeve height is increased from 10 – 100 mm for 50 mm diameter piles.INTRODUCTIONPrevious studies have shown that the behaviour of open-ended piles is different from closed-ended piles (Szechy, 1961; Randolph et al., 1979; Paikowsky and Whitman, 1990). Open-ended driven piles are widely used for deep foundations, in particular in offshore deep foundations. Generally, it is accepted that a short open-ended pile produces a smaller bearing capacity than a similar closed-ended pile (Nauroy and Tirant, 1983). However, a long open-ended pile can produce a similar bearing capacity as a closed-ended pile due to a large inner frictional resistance mobilised between the inner pile shaft and inner soil (Lehane and Randolph, 2002). The ultimate bearing capacity of an open-ended pile, Qu consists of three components as given in Eq. 1."

Jan 1, 2017

By Sushant Upadhyaya, Deniz Karadeniz

As part of the widening of I-64 in Williamsburg, Virginia, an extensive subsurface exploration program consisting of Standard Penetration Tests (SPT), Cone Penetration Tests (CPT), Dilatometer Tests (DMT), and Vane Shear Test was performed. In addition to these in-situ tests, an extensive laboratory testing program was completed including Consolidated-Undrained Triaxial, Unconsolidated-Undrained Triaxial, Direct Shear, and consolidation tests. The strength and the compressibility properties are deemed conservative for Yorktown and St. Mary’s Formations when evaluated based on the current topography, the existing overburden pressure and SPT values. SPT exhibited low blow counts especially within Yorktown Formation due to the increased excess pore water pressures resulting in a localized liquefaction at the tip of the split spoon sampler corresponding to remolded or fully softened strength of the soil. Therefore, the applicability of the SPT correlated soil parameters somewhat leads to conservative designs with deeper piles to achieve a desired structural load demand. Generally, the in-situ estimated soil design parameters are found to be comparable with the laboratory test results corresponding to long-term resistance gain with time. It is of practical importance to employ realistic soil design parameters for design applications such as pile foundations to provide cost and schedule savings. This paper presents a discussion on the soil strength estimates and variability from in-situ and laboratory tests for realistic strength characterization of Coastal Plain deposits.

By Paul Summers, Kevin Richardson, Willem (Billy) Villet, Paul J. Sabatini, Attasit Korchaiyapruk, Edward C. Clukey

"A deep mixing method (DMM) foundation was selected by the Project Team for a very large LNG facility in West Africa. As described in a companion paper, this foundation consists of a large number of columns installed by mixing cement with in-situ soils. The foundations are arrayed as a variety of honeycombed type configurations which, if installed to desired specifications, can provide a robust foundation alternative. The foundation is capable of distributing loads and limiting settlements even if some of the soil in the columns is not fully mixed during installation. An important part of the overall quality assessment program, therefore, involved developing a testing program to verify the methodology. In addition the impact of potential defects in columns on the overall foundation integrity had to be assessed. This paper describes some of the preliminary work done to establish the requirements for the quality assurance program. A key component of this program involved the sampling frequency used to assess potential defects in the columns. To verify the column integrity 104- mm samples were taken continuously at a selected frequency through the 23 m long columns. The preliminary work described in this paper demonstrated that the appropriate sampling frequency depends on both the desired reliability level as well as the number of defective columns encountered during testing.Initial finite element analyses were performed to assess the extent that defects could occur in columns within the honeycombed structure without adversely affecting the overall foundation integrity. The results from this work demonstrated that the spatial location of the defects was critical to properly assessing the foundation integrity.In addition to column sampling a load test was performed as part of the foundation verification process. The methods used to apply appropriate loads so that loads at the bottom of the columns approached design values are discussed in the paper.The results obtained from this preliminary study were then used to help develop a more comprehensive assessment program, described in a companion paper, to determine the robustness of the DMM foundations for both the LNG processing facilities and a condensate tank.IntroductionFoundations constructed with the Deep Mixing Method (DMM) can be an attractive and cost efficient alternate to other deep foundation options. This foundation is constructed by mixing soil and cement with an auger type drill. The foundation is usually constructed with a dual auger system that simultaneously creates two contiguous columns called foundation elements. Many elements are then arranged in a honeycombed configuration to create the overall foundation (Figure 1). A desired column strength can be obtained by varying the volume of cement added to the columns, the mixing rate of the soil and stroking sequence."

Jan 1, 2017

By A. Flora, E. Bilotta, F. Foria, V. Nappa

"All the typical applications of deep mixing rely on the good mechanical properties of the improved columns to strengthen or stiffen the ground for a number of geotechnical applications.This paper focuses on a completely different kind of deep mixing, carried out in order to obtain columns much softer than the surrounding soil. This kind of deep mixing, named Soft Deep Mixing (SDM), is introduced as an original means to tackle seismic risk, and can be convenient when the existing structure to be protected has a historic relevance that cannot be altered with structural modifications. The idea is that properly assembled layers made of partially overlapped SDM columns, with dynamic impedance much smaller than that of the surrounding soil, will filter and reflect most of the seismic energy.The paper presents the results of some 2D parametric numerical analyses aimed to investigate the seismic performance of this innovative approach. Simplified dynamic inputs (Ricker wavelets, having only one largely predominant frequency) were adopted to better understand the effect of signal frequency. The analyses show that the effectiveness of the soft grouted isolating barrier depends on soil and SDM geometrical, physical and mechanical properties, as well as on the frequency content of the seismic input.INTRODUCTIONPassive structural systems installed at the foundation level of existing buildings are a common solution to protect them against earthquakes. However, installation procedures are expensive and not always feasible, as for instance in the case of valuable buildings. As an alternative, ground improvement techniques can be used to modify ground properties, in order to mitigate the intensity of shaking at ground level. The propagation of shear waves in the ground can be modified by introducing a layer of artificially modified material, having a dynamic impedance (defined as n =p VS, where p is the material density and VS the velocity of shear waves) very different from that of the natural soil. Both very high or very low values of the dynamic impedance of the grouted soil (nt) can be effective in reducing the overall transmitted energy, with the difference that – for a given reduction of the transmitted energy - stiff grouted layers tend to filter the low frequency components of the amplitude spectrum without modifying in a significant way the high frequency components, while soft grouted layers have the opposite effect. Then, ideally the choice of the best grouting technique should be made considering the effects of the different frequency components on the building to be protected. These effects are detrimental for the structure when they are close to its natural frequency: high frequency components result into large structural loads on massive squat structures (high natural frequency), and low frequency components may be critical for tall and flexible structures (low natural frequency). Therefore, the typical procedure of stiffening the uppermost soil layers regardless of the kind of building to be protected is not necessarily beneficial, and for the case of squat structures soft grouting should be preferred. However, this procedure has not been taken into account yet in the engineering practice, and may pose static problems at ground level (i.e. excessive static settlements)."

Jan 1, 2015

By Bradley J. Fleming

Although soil improvement and its application to deep foundations is gaining popularity in the engineering community, this technique is not widely used in high seismic regions due to lack of fundamental understanding of both the behavior of improved soils under high-strain cyclic loading and the interactions between the pile, improved soil, and unimproved soil. This paper describes part of an ongoing Network for Earthquake Engineering Simulation (NEES) project, where two identical full-scale steel pipe piles were driven at a soft clay site in Oklahoma. The soil surrounding one of these piles was improved using the cement deep soil mixing technique in order to enhance its lateral load behavior. Both piles were tested for seismic resistance using dynamic and quasi-static loading. The pile in unimproved soil provided larger displacements with limited lateral force resistance. This pile was subjected to lateral displacements of up to 400 mm, but experienced minimum inelastic actions. On the other hand, the pile in improved soil reached its lateral capacity at a displacement of 100 mm, at which point the critical region at the base of the pile just above the improved ground experienced buckling and fractured due to low cycle fatigue. Compared to the pile in unimproved soil, the improved ground increased the system strength by 42%. Although the soil was improved over 2900 mm, the effective improvement depth was approximately 1300 mm below the ground surface. In this paper, it is demonstrated that the effects of block type soil improvement of limited horizontal and vertical dimensions can be described using a simplified theoretical approach involving a modification to the well-known p-y representation of soil response. An example using this method is presented and shown to give adequate support to a standard 12-inch diameter steel pipe pile embedded in soft soil.

By Christopher J. Ramsey, Don W. Dotson

"An existing four lane section of US 27 was widened to eight lanes. The project lies in the rugged Valley and Ridge Province of the Appalachian mountains starting at the Tennessee River in Chattanooga, Tennessee and extending 2.6 km north to Signal Mountain Boulevard. This terrain presented many challenges to accommodate the road widening in the narrow, rugged topography. Multiple tiered wall systems consisting of large tieback walls, post-tensioned reaction blocks, and gravity MSE walls for a total of approximately 30 retaining walls were required. The retaining walls served to stabilize the thrust faulted geology while also minimizing right-of-way acquisitions. The cut walls consist mainly of a tiered system of tied-back soldier piles walls with cast-in-place concrete facing. Cast-in-place pile shear walls were required along the toe of existing MSE walls to maintain stability during construction. This paper discusses the design methodology, which includes a hybrid (rather than traditional) earth pressure diagram intended to reduce life-cycle maintenance and long-term performance. Further this paper addresses wall construction, slope stability analysis, landslide mitigation alternatives, soldier pile wall design features, site challenges, monitoring and performance (to date) of the wall systems.INTRODUCTIONThis project involves the proposed widening of US Highway 27 (State Route 29) from the north end of the Tennessee River Bridge at Manufacturer’s Road to State Route 8 (Signal Mountain Road), approximately 2.64 km of roadway (Fig. 1). The project site is located adjacent to the Tennessee River on the north side of downtown Chattanooga, Tennessee in Hamilton County. The existing, limited access highway is to be widened from four lanes (two northbound and two southbound) to a minimum of eight lanes. Some portions of the alignment will expand to as much as ten lanes where northbound and southbound ramp acceleration/deceleration lanes coincide.In addition to the number and heights of cuts and fills involved, a major factor in determining an economical design for the alignment is the complicated geologic conditions along the roadway alignment. The existing roadway is situated between several steep cut slopes, some of which are only marginally stable or currently exhibit signs of instability. Due to the proximity of the project to the downtown area, the steep slopes along the alignment, and the relatively dense population near the alignment, widening the pavement and constructing cut and fill slopes to a stable configuration would result in major land acquisition for slope right-of-way."

Jan 1, 2015

By Mark Zablocki, Dakarai McCoy

Ground vibrations are an unavoidable effect of driving piles and may pose a risk to nearby infrastructure and the comfort of adjacent occupants. Driven-pile-induced ground vibrations are known to vary widely based on ground conditions, pile material, and installation means and methods. A monitoring sensor to record ground vibrations during pile driving is necessary for understanding potential impacts to sensitive infrastructure and should be considered when implementing a monitoring program anticipating ground vibrations. The implementation of a vibration monitoring program historically relies on experiential-based decision-making, which may result in the costly vibration monitoring of low-risk infrastructure. Prior understanding of anticipated ground vibrations is necessary to create an appropriate monitoring program. A framework is proposed for organizing data from past monitoring programs and quantifying the anticipated risk of driven-pile-induced vibrations. An example of risk quantification from data imported to ]a cloud database is presented by comparing driven steel H-pile and prestressed precast concrete vibration monitoring measured and collected by Haley & Aldrich between 2010 and 2020. The methods presented within the example can be applied to quantify a first order approximation of risk for ground vibrations at proposed driven pile sites based on the measured performance of previous sites with similar ground characteristics and pile installation methods. The presented novel data managements tools allow for a quick aggregation of vibration data with similar site conditions.

Sep 8, 2021

By Mary Ellen Bruce Large

"In partnership with California Department of Transportation (Caltrans), Federal Highway Administration (FHWA), and with support from International Association of Foundation Drilling (ADSC), Deep Foundations Institute (DFI) organized a workshop on quality assurance (QA) practices for acceptance of post-grouted drilled shafts in conjunction with DFI’s 40th Annual Conference on Deep Foundations. The 1½-day workshop was held on October 15-16, 2015 at the Oakland Marriott City Center in Oakland, CA.Post-grouting, in the context of this workshop and report, refers to the alternative design and construction of base-grouted drilled shafts wherein a grout distribution system is installed during construction and used to grout the base under pressure after the drilled shaft concrete has gained adequate strength, resulting in a stiffer axial-compression load-displacement relationship and additional possible ground improvement effects.The primary goals of the workshop were to•?Identify and summarize the state of the practice for design, construction, inspection, verification, acceptance criteria, reliability and performance of post-grouting.•?Identify gaps and needs in quality assurance that should be addressed for successful use of post-grouting.This report is structured to follow the workshop program: workshop presentations outlined the state of practice and views from owners, engineers and contractors on acceptance of post grouting methods for drilled shafts; and subsequent workshop discussions attended by a small invited group of participants focused on identifying areas of agreement and disagreement on post-grouting best practices, acceptance criteria, design and verification procedures, and inspection requirements. A partial list of attendees of the open and closed sessions is provided as Appendix A, and copies of presentations are included as Appendix B.FHWA and Caltrans are the primary audiences for this report, and its content will be used to develop a roadmap for deploying the findings into policy and practice. The secondary audience is the broader industry group, and the report content will be disseminated in a variety of formats."

Jan 1, 2016

By Mary Ellen Bruce Large

"INTRODUCTIONIn partnership with California Department of Transportation (Caltrans), Federal Highway Administration (FHWA), and with support from International Association of Foundation Drilling (ADSC), Deep Foundations Institute (DFI) organized a workshop on quality assurance (QA) practices for acceptance of post-grouted drilled shafts in conjunction with DFI’s 40th Annual Conference on Deep Foundations. The 1½-day workshop was held on October 15-16, 2015 at the Oakland Marriott City Center in Oakland, CA.Post-grouting, in the context of this workshop and report, refers to the alternative design and construction of base-grouted drilled shafts wherein a grout distribution system is installed during construction and used to grout the base under pressure after the drilled shaft concrete has gained adequate strength, resulting in a stiffer axial-compression load-displacement relationship and additional possible ground improvement effects. The primary goals of the workshop were to•?Identify and summarize the state of the practice for design, construction, inspection, verification, acceptance criteria, reliability and performance of post-grouting.•?Identify gaps and needs in quality assurance that should be addressed for successful use of post-grouting.This report is structured to follow the workshop program: workshop presentations outlined the state of practice and views from owners, engineers and contractors on acceptance of post grouting methods for drilled shafts; and subsequent workshop discussions attended by a small invited group of participants focused on identifying areas of agreement and disagreement on post-grouting best practices, acceptance criteria, design and verification procedures, and inspection requirements. A partial list of attendees of the open and closed sessions is provided as Appendix A, and copies of presentations are included as Appendix B.FHWA and Caltrans are the primary audiences for this report, and its content will be used to develop a roadmap for deploying the findings into policy and practice. The secondary audience is the broader industry group, and the report content will be disseminated in a variety of formats."

Jan 1, 2016

By Satyajit A. Vaidya

This paper presents a case-study in the design and construction of deep foundation element supported mats for two residential towers on an18,000-square-foot site in Brooklyn, New York. Based on site sub-surface conditions, conventional mat foundations bearing on medium dense sand, having an allowable bearing capacity of 3 tsf, were originally anticipated for the 16 and 25-story towers. However, when the tower shear walls were relocated to the edges of the mat foundations due to architectural revisions, the significantly increased mat edge contact stresses applied to the soil subgrade resulted in calculated settlements of a magnitude that would adversely impact the proposed structures and the neighboring/bordering lot-line building and rail transit subway structures. To address this issue, deep foundation element supported mats were designed for the towers. The design was performed as an iterative process involving structural SAFE and geotechnical Plaxis finite element computer analysis to develop a coordinated geo-structural model of the foundation system. Initial presumptive design values of 45 pci and 445 kips/inch were used for the modulus of subgrade reaction and minimum deep foundation element stiffness, respectively. The designed foundation system consisted of 40 and 60-inch-thick mat foundations for the 16 and 25 story towers, respectively. Initially, the deep foundation elements were designed as 50-foot-long, 14-inch-diameter elements installed to sustain a maximum individual compressive load of 250 tons. The final deep foundation element design was subsequently refined to consist of a 48-foot-long, drilled and grouted IBO Titan 103/51 element designed to sustain a maximum load of 167 tons. Subsequent field load tests on the deep foundation elements confirmed element stiffness ranging from 1,040 to 1,530 kips/inch, with measured mobilized side shear of about 29 psi. The mat foundation reinforcement was adjusted for the pile stiffness values determined in the field load tests, and the deep foundation supported mats were constructed. The two towers were subsequently constructed, and have performed successfully.

Jan 1, 2010

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 Arash Saeidi-Rashk-Olia, Dunja Peric

Energy piles are gaining increased popularity due to a growing demand for clean energy. To further advance the understanding of soil-structure interaction in energy piles, recently-derived analytical solutions have been implemented to investigate the impact of stratigraphy on the soil-structure interaction. This was accomplished by comparing the measured and predicted head displacements, axial strains and stresses in an energy pile embedded in the actual homogeneous and layered soil profiles, as well as into synthetic homogeneous soil profiles. The analytical solutions for homogeneous soil profile captured the smooth experimentally observed response versus depth very well. In the case of a layered soil profile, the corresponding analytical model was capable of capturing nuances in trends of axial stress and strain versus depth at the interface of different layers. The analytical predictions for the layered profile appear to be slightly less accurate than for the homogenous profile. The experimental data obtained from the layered profile appear to be a bit more scattered than those from the homogeneous profile. In the former case, the interplay of the individual soil layers with the pile occurs while maintaining the continuity of the pile stress and displacement at the interface of different layers. The response throughout each layer of the layered profile is quantitatively different than the corresponding homogeneous response. Nevertheless, qualitatively the response throughout each layer of the layered profile is similar to the response of the pile embedded in the corresponding homogeneous layer.

Sep 8, 2021

By David T. Farber

"Stabilization of an existing cellular tower foundation system without dismantling the tower or compromising the existing foundation system was accomplished by installation of a jet grouted pile system. The tower was originally designed to be placed on a steep hillside and to be supported by a mat foundation founded on existing bedrock. The as-built conditions of the tower foundation system showed it to be constructed on a combination of loose fill of varying thickness and native stiff silts and gravel material. To avoid the potential of differential settlement, a jet grouted pile foundation system was installed to the top of bedrock. The jet grouted pile system was rapidly installed over a two-day period so as to not delay operational permitting of the tower.INTRODUCTIONA tri-legged lattice cellular communication tower was constructed on the side of a steep hill located in a mature hard wood forest. Access to the site as well as available work area was limited to small track type drill rigs and equipment. The original tower design required the tower to be supported by a mat foundation bearing directly on bedrock. Based on a review of the foundation construction and results of a subsurface investigation, it was discovered that the foundation was built directly over a loose fill material that varied in thickness from 0 to 4.27 meters (0 to 14-ft). Because of the uncompacted nature and varying thickness of the loose fill materials, the tower would be susceptible to differential settlement which, could lead to tower instability.The objectives of this project included the following:• stabilize the mat foundation against differential settlement without removing the existing tower structure or foundation system• rapidly complete stabilization activities to allow operational permitting of the towerSOIL CONDITIONSThe subsurface soil conditions that the tower mat foundation rested on were evaluated by installing three borings in a row from the inward slope portion of the mat foundation (B-1) to the outward slope portion of the mat foundation (B-3). Figure 1 illustrates the subsurface soil stratigraphy. The three borings encountered the following subsurface conditions:"

Jan 1, 2005

By Robert Alperstein, Nidal AbiSaab, Joe Pastore

"This paper describes the design and construction aspects of the foundation support for a 57-story building currently under construction in lower Manhattan. The site is located near the East River with subsurface conditions consisting of about 40-ft [12.2-m] of unsuitable historic fill and soft plastic clay underlain by about 130-ft [39.6-m] of dense sand resting on bedrock. A mat foundation supported on unsuitable soils improved by jet grouting was selected for the project. Design concepts and selection of the engineering properties of the improved and natural foundation soils are discussed. The results of quality control testing and methods to verify design parameters during construction are presented.INTRODUCTIONNew York City (especially Manhattan) is known for its skyline of high rise structures. The geologic conditions in the New York Metropolitan Area influence the selection of foundations and feasibility of high rise construction as noted by Horvath (2013). These conditions include varying depth and quality of bedrock, multiple glacial events during the Pleistocene Epoch, and the effects of human modifications to the subsurface environment. Clusters of relatively taller buildings are generally located in Lower and Midtown Manhattan where sound crystalline bedrock is at relatively shallow depth beneath the ground surface and shallow foundations rest on the bedrock surface. In recent years the use of more costly high capacity driven piles or drilled caissons and deep basements has enabled the high skyline to spread to other areas."

Jan 1, 2016