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By Remco Offenberg, Marcel Bielefeld, Martijn van Delft

The question of the continued suitability of existing foundations arises when the function of the superstructure changes. This can occur when the superstructure is replaced or when the existing structure is expanded, leading to higher loads on the existing foundation. Quite often it is a challenge to define the suitability (with respect to integrity, bearing capacity or both). The lack of information on the existing foundation (such as pile dimensions, installation records, original soil investigation, design calculations, etc.) makes it frequently seemingly impossible to assess whether the foundation or foundation elements can be re-used. The paper outlines the tools available to an engineer to evaluate existing foundation piles for potential re-use. The paper illustrates the application of these tools through a few case studies from The Netherlands, including the evaluation of a 400 years old bridge foundation to address increasing traffic loads.

May 1, 2022

By George W. Little, John Councilman

"The selection, evaluation, and modification of contractor mix designs for self-hardening seepage barriers, completed by the slurry trench excavation method, can be one of the most critical and challenging tasks to ensure the cutoff wall meets the design performance criteria. Contractor mix designs should incorporate all available geotechnical data, including subsurface soil characteristics, groundwater information, and potential site contaminates. However, the pre-construction mix design can have limitations if subsurface data is limited or shows variability from initial investigations. Placement of the seepage barrier material needs to be evaluated during construction to identify in-situ performance. In one particular case study, the self-hardening cutoff wall mix design was evaluated over a one year period followed by a year and a half installation period, in which, a number of adjustments were made to the laboratory mix design during construction due to performance in the field. Installation for the selected mix was monitored on a real-time basis, using quality control data, as well as early strength and permeability results to determine if adjustments to the self-hardening mix were necessary. Evaluation of early results and relationships between strength and permeability were used to make adjustments prior to achieving the final test results for 28-day strength and permeability. Test results of the installed mix illustrated a direct correlation between strength and permeability. Achieving a minimum unconfined compressive strength was necessary to meet the minimum permeability of the seepage barrier. Other determinations conclude that the thorough development of a pre-construction mix design can have limitations even when all geotechnical data and site conditions are taken into account. Understanding early indicators and key strength and permeability relationships are necessary to determine seepage barrier performance and limitations.IntroductionThe evaluation of contractor mix designs for self-hardening seepage barriers was reviewed for one particular case study where a mix was developed using available geotechnical background information, including considerations for impacted groundwater. Following development of the laboratory mix design, the seepage barrier wall was installed over a one and a half year period, where the contractor mix design was evaluated and modified to accommodate field conditions affecting performance. The objective of the project was to cutoff and collect impacted groundwater and prevent the migration of contaminants to the creek running adjacent to the project. The self-hardening seepage barrier wall was installed using the slurry trench excavation method along 4700 ft of alignment and extended to depths ranging from 20 to 85 ft below ground surface, where it tied in with a low permeability stratum or competent bedrock."

Jan 1, 2016

By Burt G. Look, David W. Lacey

"Certification of foundation capacity during the construction phase is often assessed by strength or weathering state descriptors based on visual observations. This case study used the Point Load Index (PLI) test as a quantitative tool in the construction certification of a pile’s design capacity. Construction phase tests were completed on irregular sized rock samples whilst comparable design phase testing was completed on intact rock core samples. Statistical comparisons were made to assess the repeatability between the PLI tests, with best-fit Probability Distribution Functions (PDFs) determined for both datasets. Pronounced differences were observed based on the PDF adopted to characterize the PLI dataset, the consequence of which would be a significant change to the pile’s design capacity. The adoption of the lower quartile value is shown to satisfy both design conservatism and construction simplicity requirements. The commonly held belief that rock samples produced during socket excavation may be biased towards the higher strength portion of the rock mass, is shown to be invalid for this site. As the central bridge piers were certified using Plate Load Tests (PLTs), the resultant load-settlement relationships were compared with the PLI strength assessments made for similar materials recovered from the adjacent abutment piles.INTRODUCTIONThe upgrade of the Foxwell Road Overpass across the Pacific Motorway in South East Queensland required the duplication of an existing four span bridge structure. The foundations of the new bridge included the installation of 1.2m diameter cast in place (bored) piles at the bridge abutments and 900mm diameter cast in place (bored) piles below a retaining wall to be constructed adjacent to the existing abutment.The site geology was dominated by the Palaeozoic Neranleigh–Fernvale Beds, predominantly comprised of argillite, sandstone and greywacke. Limited soil materials existed at the site, with Extremely Weathered (EW) rock typically encountered within metres of the existing ground surface. The exception to the existence of shallow rock were locations where existing filling of the site had occurred – i.e. approach embankments to existing bridge structure.Capacity of pile sockets is typically assessed onsite by descriptive rock strength or weathering assessment. Such descriptors encompass a wide range of values and lack precision. Due to the subjectivity of such assessment techniques – a factor of 3 is often observed in terms of strength assessment based on one’s interpretation of rock strength descriptors alone – uncertainty on site often occurs regardless of whether a lower bound, average or other characteristic design parameter applies."

Jan 1, 1900

By John Vickers, William H. Hover, Paul C. Schmall

"Any sudden subsurface issue that threatens the stability of existing buildings or infrastructure is cause for immediate investigation and prompt remedial action. Nowhere is this more true than the nation’s dams and levees. A breach of any kind, no matter how small initially, has the potential to be catastrophic and impact a wide downstream area. Addressing the problem quickly and effectively is therefore critical. When a turbid water discharge developed from a rock drainage embankment at the toe of the earthen dam impounding Cannonsville Reservoir, near Deposit, NY, the source of the problem was quickly identified as resulting from an artesian water release from an underlying permeable silty sand and gravel formation during drilling of three exploratory boreholes in preparation for construction of a hydroelectric plant at the downstream toe area of the dam facility. Work was halted, intense 24-hour monitoring was implemented, and as a risk reduction measure NYCDEP began to draw down the reservoir’s total storage at a rate of a billion gallons per day. Input sought from contractors within the geotechnical community helped result in the design and development of a deep well system to control the artesian pressure. Once this primary objective was accomplished, modified compaction grouting was performed at the borehole locations to densify loosened soils, fill any voids created by the discharge activity, and seal off the permeable aquifer. This paper discusses the dewatering program, specialized drilling techniques required, monitoring and verification of pressures within the dam, and the grouting program.BackgroundCannonsville Dam, owned and operated by the New York City Department of Environmental Protection (NYCDEP), is located in Deposit, New York on the West Branch of the Delaware River and impounds the Cannonsville Reservoir. Built between 1959 and 1964, the dam has an impervious central and upstream core zone keyed into the glacial till foundation, a semi-pervious downstream embankment zone, and a rockfill toe and is approximately 2,800 ft (853.4 m) long and 175 ft (53.3 m) high. The dam is formed by two embankment sections. The left section forms the main embankment blocking the main river channel, while the right section is constructed over a topographic saddle or low ridge. Reservoir level is actively influenced by withdrawals through the West Delaware Tunnel, based on water supply need. Under normal circumstances, water is continuously discharged downstream to the Delaware River."

Jan 1, 2016

By Jason Herron, Joseph Brown

The common couplings for joining sections of helical piles with an outside diameter of 6.625 inches and 8.625 inches are square on square, flange to flange, external pipe sleeve, internal pipe sleeve, and welded joint. Each coupling type has advantages and disadvantages in efficiency, capacity, installation, and economics of the installed pile. All these coupling types have been used in the helical pile market in North America for various applications and designs. Many of these applications require on-site testing, but test records are not typically shared with the helical pile industry. Due to the lack of information available for square on square and flange to flange couplings, testing was done to compare the efficiency of installation, load to deflection response, and torque to capacity ratios of external pipe sleeve, square on square, and flange to flange couplings. Field installations and tension tests were performed in non-cohesive (sand type) soil near Caseyville, IL and in cohesive (clay type) soil in Centralia, MO. The data collected during these tests included rotations per foot during installation, installation torque, applied pressure, and deflection. The results of this testing are analyzed and discussed within this paper. The results indicate that the square to square coupling is the most efficient of the designs tested, but this conclusion cannot be fully justified without further testing due to the variability in the data gathered and the small number of piles tested. INTRODUCTION A helical pile is typically assumed to be a medium-displacement pile when its outside diameter is between 4.5 inches and 8 inches and a high-displacement pile when its outside diameter is greater than 8 inches. A helical pile designer has multiple options when selecting a coupling type for medium- to high-displacement helical piles. Each type of coupling has advantages and disadvantages and must be analyzed on the bases of efficiency, capacity, installation, and economics of a project. Typical couplings that are chosen by designers include square on square, flange to flange, external pipe sleeve, internal pipe sleeve, and welded joint. A helical pile must transfer axial, lateral, bending moment, and torsional loads, and the coupling must be designed to effectively and efficiently transfer each type of load. During the installation of a helical pile, the rate of penetration and the disturbance of soil layers play a critical role in the efficiency and torque to capacity ratio (Kt) of the pile. It is common for a coupling to protrude beyond the outside diameter of the pipe section being used. This is necessary for the function of certain coupling types and can facilitate the connection of couplings. However, it causes increased soil disturbance and reduce the rate of penetration due to soil bearing against the protruding portion of the coupling. A helical pile designer typically will work to minimize the coupling protrusion and create a pile with optimal installation efficiency but may choose a design with lower installation efficiency if it offers sufficient economic advantage.

Jan 1, 2019

By Carlandrea Albonico, Salvatore Miranda

After a brief introduction of the whole Project, the paper describes two special geotechnical engineering solutions provided within the scope of the Galataport Project, in Istanbul, Turkey. The first refers to the new quay of Salıpazarı, which is a combination of retaining structure and ground improvement, formed by a combiwall, a reinforced concrete diaphragm wall and a soil improvement by deep soil mixing (Turbojet). The second, refers to the soil improvement works executed underneath three existing buildings. Single-fluid jet grouting columns had the scope of improving the mechanical properties of the bearing soil and reducing the associated risk of liquefaction. A set of underpinning micropiles was installed in order to allow the excavation of a partial basement inside two of these three buildings. All activities were conducted from inside the existing buildings, with reduced headroom. The paper highlights the importance of employing cutting-edge technologies within the foundation engineering field and state-of-the-art electronic control devices, in parallel with the essential human expertise, in order to obtain the desired results in this high-profile Project.

Nov 1, 2022

By Stuart Coutts

"This paper presents an overview of the author’s experience related to the assessment of the base capacity of straight shafted and enlarged-base bored piles in sand. A design approach based on CPT qc is described which has been calibrated using a database of load tests. The importance of correct installation techniques with instrumentation are illustrated and a discussion is presented on the current use of high strain dynamic testing to validate compliance with design. An example of a recent project with high quality instrumented load test data illustrates the close match to the proposed best practice approach and also highlights the importance for consideration of the effects of stress relief for deep foundations installed in deep excavations.1 INTRODUCTIONContinuous Flight Auger (CFA) piles are the bored foundation pile of choice for sand deposits across Australia. The evolution of the determination of the base resistance of CFA piles has been shaped by available investigative techniques, calculation methods, and calibration of designs with laboratory and field testing. The Cone Penetration Test (CPT) has been widely used in Western Australia (WA) where the test has been commercially available via multiple contractors for more than 25 years. On the East coast, the adoption of CPT testing has been slower with a transition from traditional Standard Penetration Testing (SPT) still occurring. Dynamic pile load tests are often used to derive parameters. The influence of pile installation on performance is commonly misunderstood and is an important element on any discussion of pile capacity for CFA pile types. The interface between the base of the constructed pile and the in-situ soil has an influence on capacity such that a poorly constructed pile base will have limited (if any) contribution to pile performance within the normal working range, generally within a 10 mm movement. The research presented in this paper pertains to CFA piles (no drilling fluids) and enlarged base piles constructed using CFA techniques under drilling fluids such that clean pile/base interface is targeted. Developments in modern piling equipment and instrumentation allow the pressure and volume of delivered concrete/grout to piles to be accurately monitored at various stages of installation such that repeatable ‘best practice’ can be achieved. The changes in soil conditions that occur due to the disturbance of the install technique are also important.Although the results of this research are likely applicable to bored piles, the interface between the pile and in-situ soil (shaft and base) need to be considered for various installation techniques. The effects of stress relaxation (due to removal of soil above pile base and adjacent shaft), time to concreting, and the zone of disturbed soil around the pile shaft are paramount.2 INSTALLATION CONSIDERATIONS The pile mix (concrete/grout) and interface with the in-situ soil are also an important consideration. For example, coarse grained, poorly graded, dry, clean sand will be partially permeated by most pile mixes; such that the influenced soil will be enhanced and in instances the overall effective pile dimensions increased. Permeation of the disturbed zone of a pile or anchor shaft along with scale effects (Lehane 2009) can have significant effect on shaft capacity and shaft frictions significantly exceeding expected are not uncommon based on ‘theoretical’ dimensions. Advancements in mix technology and mix techniques also have a large influence on the pile/soil interface. The ability of the piling rig and augers to excavate a plumb and gauge hole can also have a large influence on the zone of soil disturbed adjacent the constructed pile with a resulting influence on capacity."

Jan 1, 1900

By Ihab Allam PE, Meeok Kim. PE. Ph. D

The wet weather equalization basin (EB) planned for Pacifica, CA is a 45 feet deep rectangular shaped underground water tank containing over 2.1 million gallons of water, and located only 500 feet away from the Pacific Ocean. The location and size of the water tank, and the geotechnical characteristics of the selected site presented many engineering and construction challenges. The engineering had to consider a structural system which can fit into the limited area of the site and yet need to meet the storage volume requirement. In addition, the system construction should meet the city’s tight budget and schedule.

By Marc Raithel, Sven Schröer, Lilma Schimmel, Dimiter Alexiew

"The Geotextile Encased Columns (GEC) deep foundation system for embankments and dikes on soft soils was introduced some 20 years ago and is now considered State-of-the-art in Germany, Europe and, step by step, worldwide. The GECs consist of compacted non-cohesive granular fill similar e.g. to common gravel columns with one decisive difference: they are confined in a high-strength, high-modulus, flexible geotextile “cylinder” (encasement). This engineered element with parameters being adaptable in a wide range provides a decisive tool to control and optimize the behavior of the GEC foundation system. Consequently, the GECs work properly even in extremely soft soils, and a wide range of fills inclusive of sands can be used. In the meantime vast design and technological experience is available and codified design methods exist. Initially the paper briefly describes the general idea, the basics and specifics of design, construction technology, materials, restrictions and optimal application areas. Then it focuses on three informative case studies. They are briefly presented focusing for brevity only on the most important facts and experience inclusive of the most meaningful data of short- and long-term measurement programs.INTRODUCTIONWhen considering embankments on soft soils, generally two groups of solutions exist:Unsupported embankments; there are four main options:a) build up embankment extremely slowly waiting for sufficient consolidation after every stage;b) replace the soft soil partially or totally;c) install a high-strength basal reinforcement providing overall and local stability and allowing much faster embankment construction;d) combine c) with strip drains to accelerate consolidation and thus the construction process additionally (Fig. 1, left).Today, practically only option ""d"" is of practical relevance. Despite all the pros and cons, the common attribute of all non-supported options is that local and overall stability (Ultimate Limit State-ULS) can be achieved and controlled, but not the short- and long-term settlements (Serviceability Limit State-SLS). The latter can be significant, e.g. up to 30% of the nominal planned embankment height. Supported embankments (Fig. 1, right): the main common idea is to over-bridge the soft soil layers by supporting vertical elements of different types: rigid piles, trench walls etc. or by ""softer"" solutions of different column types (compacted, cemented, mixed-in-place etc.). Herein the borderlines between “piles”, ""pile-similar elements"" and ""soil improvement” are fluent and depend on country, traditions, codes etc. The common attribute of the “supported” schemes is a minimized settlement. Twenty years ago a new specific solution was launched: the Geotextile Encased Columns (GEC), which is discussed in more detail below."

Jan 1, 2017

"TREVIICOS CorporationINTRODUCTIONThe Walter F. George lock and dam was constructed on the Chattahoochee River between 1955 and 1963 with the double function of improving navigation and generating power. Its 82 ft. by 450 ft. (25m x 137m) lock can accommodate large barge traffic and its four generating units with a plant capacity of 150 MW have an average energy output of 453,000 MWH. The dam consists of a 1,496 ft. (456m) long concrete structure housing the spillway, a non overflow portion, the power units and two earthen wing dams extending to the Georgia and Alabama sides, respectively 5,810 feet and 6,130 feet long (1770m and 1868m). As soon as the reservoir was impounded it became apparent that excessive seepage was occurring. From 1962 to 1985 a series of remedial works was performed using several techniques, but the problems continued under the dam, jeopardizing its generating potential and possibly undermining its stability.Finally, the decision was made to construct a deep cutoff primarily under the concrete portion of the dam to remedy the problem. PROCUREMENTOn July 5th, 2001 best and final offers were solicited by the Corps of Engineers (COE) for the construction of a deep cut-off to be built in front of the concrete portion of the dam from the bottom of the lake and tied into it. The cut-off had to cross an existing lock structure and an underwater retaining wall, as well as the remnants of a steel coffer cell left in place from the initial construction.The specifications required that the wall be built with a minimum thickness of 24” (600mm) and that it extended from the bottom of the lake to elevation -5 (1.52m) into the Providence formation, an impervious layer.While the land portions of the wall were on average 208 feet (63.4m) deep, the marine portion started from up to 90 feet (27m) of water and continued through different rock formations for another 100 feet (30m).Contractors were invited to propose their own method of constructing the cut-off and offers would be evaluated using several criteria, including technical, economical, organizational and experience.Three proposals were received and on August 14, 2001 an award was made to the Joint Venture (JV) of Treviicos and Rodio."

Jan 1, 2014

By Danny Winters, Wesley Schmutzler, Christopher Lewis, Matteo Bertoni

"SR 83/US 331 is a primary North/South roadway in Walton County that is a crucial link for tourism and commerce between the Walton County beaches and the heavily traveled I-10 corridor in the panhandle of Florida. The facility also serves as the primary hurricane evacuation route from southern Walton County. This 3.4 mile project involves expanding the current two-lane crossing of Choctawhatchee Bay to a fourlane facility to increase capacity and dramatically improve mobility within the corridor. One of the major goals of the project is to perform ground stabilization using Deep and Shallow Soil Mixing (DMM & SMM) along existing causeways. Ground stabilization is required due to the existence of moderately deep very loose soils that have settled considerably over the years. As a result, the Florida Department of Transportation (FDOT) incurred significant maintenance expenses and was unable to maintain an acceptable ride quality. FDOT considered soil mixing as one option to control this settlement. Quality Control for soil mixing relies heavily on the monitoring system used to control mixing parameters. This paper will examine in detail, the reporting of the Drilling Mate System (DMS) used to ensure the quality of each soil mixed element.INTRODUCTIONThe Florida Department of Transportation (FDOT) issued a Design-Build Maximum Price Request for Proposal (RFP) for the Choctawhatchee Bay Bridge expansion. The design-build (D/B) team of Skanska/Parsons Brinckerhoff was awarded the contract. The D/B team, in order to meet the unique deep ground improvement challenges of the Choctawhatchee Bay Bridge Project, selected Foundation & Geotechnical Engineering (FGE) as the engineer to design the ground improvement and TREVIICOS South (TIS) to execute the works.The FDOT in their RFP states that “either bridge or utilize a deep ground improvement method to stabilize the three segments of the existing earthen causeway” and “one possible method of deep ground improvement which is considered viable is deep soil mixing”. FGE developed a proposal to provide a unique rigid transfer platform to effectively stabilize the existing causeways. This platform (Fig. 1) consists of an upper 10 ft thick stabilized soil layer which transfers axial load to a series of deep columns. This robust system guarantees superior durability, ride quality and pavement condition and will exceed all required design and performance criteria including, “Less than 2 inches of settlement within a 1,000-foot section”."

Jan 1, 2017

By Akhila Manne, Prasad P. V S R

Storage tanks are heavily loaded thin-shelled structures that exert large loads on and require large foundations to support them. They are generally very sensitive to foundation settlements as it may hinder the performance of tanks resulting in significant commercial or social impacts. Selection of their foundation is dependent on availability of suitable ground and limitations imposed by design specifications. Design of the tank foundations is generally based on theoretical methods and validation by representative field tests. This paper reviews settlement criteria for storage tanks as per national and international standards, case studies of large to medium diameter tanks supported on deep foundation i.e., bored cast-in-situ piles and shallow foundations on improved ground and their performance during load tests & hydro-tests is discussed. Paper concludes that storage tanks can also be supported on shallow foundations resting on improved ground reducing the settlement, time and cost significantly depending on the sub-soil.

Nov 1, 2022

By John P. Turner, Benjamin J. Turner

"Non-destructive testing and evaluation (NDT/NDE) methods have become standard tools as part of the post-construction quality assurance of drilled shaft foundations. In responding to anomalies, foundation designers, owners, and contractors face a number of choices, including: (i) acceptance of a shaft with known anomalies, (ii) further investigations of integrity (e.g., concrete coring), (iii) repair schemes, and (iv) reject and replace. To assist in selecting the best option, analyses are often performed that involve assessing the structural performance of reinforced concrete shafts that may include defective concrete or voids. Currently, the analytical tools for predicting the flexural strength and stiffness of drilled shafts with defective concrete located in discrete regions of the cross section are limited. This paper presents a robust moment-curvature analysis tool for drilled shafts based on the fiber-element discretization method. The tool allows for consideration of anomalous or defective concrete regions in the shape and location that they are believed to exist in the shaft while considering explicitly the nonlinear material behavior of the intact regions based on expected material properties. A case study is used to illustrate the practical application of the analysis to drilled shaft projects.INTRODUCTIONImperfections such as defective concrete or accidental eccentricity of reinforcing cages are an inherent part of the drilled shaft construction process that will occur occasionally even when construction best-practices are followed. Petek et al. (2002), O’Neill and Sarhan (2004), Poulos (2005), and others have described the effects that construction defects can have on the axial and lateral performance of drilled shafts. Our industry has seen rapid progress in recent years in the development and improvement of tools for detecting drilled shaft anomalies, such as gamma-gamma and crosshole-sonic logging, sonic-echo testing, thermal integrity profiling, and even visual inspection with invasive video cameras. Nonetheless, in most cases the wealth of data from these tests is used by foundation engineers to make a fairly “black or white” decision—should the defects be repaired, or should the shaft be rejected? A third option that is not typically considered is to directly analyze the section, including anomalies, and compare the reduced strength and/or ductility to the actual project demands. This option takes full advantage of the data collected during integrity testing, and may provide a justifiable means for avoiding further construction costs and delays, whether for repair or replacement."

Jan 1, 2016

By Terzis D. PhD, Katterbach M.

While awareness around the environmental impact of existing grout materials and chemical binders is increasing rapidly, biotechnologies are growing traction as sustainable alternatives in groundwork operations. Herein we present the principles and application methods of bio-grouting. The term is used to describe a system which is based on soil, groundwater or marine enzymes which are able to catalyze the production of calcite replicating a natural phenomenon. The system’s end result are mineral crystalline bridges which act as binders to improve the geotechnical properties of soils. This paper presents a comprehensive description of bio-grouts, their underlaying mechanisms contributing to mineralization as well as environmental considerations. With their water-like rheology, bio-grouts have a wide application range and are minimally invasive, requiring only very limited injection pressures. The equipment is the same as that used in conventional cement grouting, and the reactant components are worldwide available or easily suppliable, which explains why bio-grouting has nowadays become a valuable and sustainable alternative towards efficient soil treatment. Recent developments in the last years have allowed to further increase the applicability and efficiency of bio-grouts to ultimately bridge the gap between research and practice. A case study is illustrated in this paper showing the successful implementation of bio-grout for the stabilization of weakly cemented sandstone to safeguard an adjacent road segment in Switzerland

May 1, 2022

By Matthew Runion, Christopher Lawler

The Aeolus – Jim Bridger Transmission Line Project is located in southern Wyoming, home to some of the largest coal seams in the world. Coal seams present unique challenges to underground construction, as they are at high risk of coal-seam fires and do not provide a reliable bearing stratum. Accurate identification of these hazards was essential for reliable design and successful construction of foundations on this project; however, environmental restrictions and other protections created short time frames to access several sites. Coupled with a firm construction deadline, this meant that a comprehensive geotechnical investigation prior to construction would not be possible. This paper presents the project as a case study, and details how an Engineer-Procure-Construct (EPC) contracting format supported by a comprehensive Quality Assurance (QA) program provided a solution to the defined challenges. It describes the initial design process using incomplete geotechnical data and explains how the developed QA program verified design assumptions and reduced geotechnical risk through early identification of geologic conditions during construction. Specific examples will be given, and industry implications will be discussed.

By Kevin Baumgartner, Steven Babcock

A landfill in Phoenix, AZ reached capacity and was graded over in the 1970s. The property was subdivided into lots in 2007 to create a business park. However, the challenging site conditions caused by the underlaying landfill put into question the feasibility of typical deep foundation systems. Several different foundation systems were evaluated to support the proposed development. The considered systems were: drilled concrete shaft, driven piles, drilled micropiles and helical piles. Soil stability, landfill decomposition, method of installation, flexibility of design, anticipated material, and equipment costs were considered. A system of helical piles with concrete pile caps and grade beams was selected. To mitigate unknown obstructions, holes were drilled through the landfill debris at pile locations and then backfilled with screened granular material. The helical piles were installed through these backfilled holes and advanced to bear in competent native material below the landfill. This method allowed for minimal disturbance of the landfill materials and provided a strong and adaptable foundation. Additional advantages of helical piles on this site include minimal installation vibration, no grout or concrete in the deep foundation, and capacity verification for each pile via torque correlation. Two load tests were performed to verify the design.

Sep 8, 2021

By Alex Ryberg, Matthew L. Becker

Several integrity testing methods exist which may be used to evaluate drilled shafts. Each test method has advantages and limitations. On occasion, the results from different test methods may lead to conflicting conclusions, making it difficult to conclusively know which results more accurately represent the quality and integrity of a drilled shaft. This case study focuses on the integrity testing evaluation for two drilled shafts which were constructed using permanent casings and installed through flowing river water. Integrity testing was performed using Thermal Integrity Profiling (TIP) and Crosshole Sonic Logging (CSL) on each shaft. During testing, the influence of flowing water and soil layering needed consideration in the collected TIP data. Similarly, concrete curing time influenced the CSL test results and required the CSL tests to be performed multiple times with additional wait times following concrete placement. To aid in the shaft integrity evaluations, Low Strain Integrity testing via the Pulse Echo Method (PEM) was performed on several shafts and concrete coring was also performed to help further assess the acceptance or rejection of the questionable shafts. This paper presents an overview of the testing methods that were applied, their basic methodology, as well as potential limitations that should be considered when evaluating their results.

Sep 8, 2021

By Eric S. Lindquist, Charles A. Luxford

The State of Texas recently adopted a master plan to expand the existing Capitol Complex in Austin. Phase 1 of this expansion will add two new State office buildings and five levels of underground parking to the existing Complex. Additionally, a landscaped pedestrian mall will be built atop a portion of the underground parking to enhance the area as a cultural destination. Capitol Complex website: https://www.tfc-ccp.org/ Brierley Associates was selected to provide detailed design of the entire Phase 1 earth retention system for an approximately 40-65 ft (12-20 m) deep, 500,000+ yd3 (380,000+ m3) excavation through overburden soils and limestone bedrock. To facilitate overall project coordination, all design packages were required to develop Revit models, including the retention system package. With the project located in an urban setting, this 3D model also facilitated coordination of the retention system with adjacent major structures and utilities. The retention system is a combination of soil nails, soldier piling with tiebacks and rock anchors with a shotcrete facing as a substrate for the below-grade blindside waterproofing system. Due to the substantial scope of excavation, a significant number of utilities had to be routed on a temporary span over the excavation. Brierley Associates designed this utility support structure, which required extensive coordination with the excavation support and existing utilities located directly underneath the structure’s foundations. Preconstruction geotechnical work identified a fault zone that might be encountered within the excavation; however, the fault feature was found to have a more adverse location and orientation than originally anticipated. This observation required that a portion of the temporary anchors be converted to higher-capacity, corrosion-protected permanent anchors.

By Alex Grenoble, Alex Reeb, George Filz, Farzad Abedzadeh

"This paper summarizes available information on the characteristics and properties of deep-mixed soilcement produced by the wet method. The topics covered in this paper include: unit weight, unconfined compressive strength, strength variability for field mixed materials, influence of curing time, influence of consolidation pressure, Young’s modulus, differences in strength and stiffness between small and large samples, creep deformations, Poisson’s ratio, and tensile strength. In addition, this paper discusses the development of design considerations and recommended property values for a project that uses soilcement to protect an existing dam penstock from loads applied by an overlying stability berm. Some of the key recommendations for the deep-mixed soil-cement to be used in this project are that (1) a curved strength envelope that includes tensile strength can be used in the analysis, (2) the stress-strain and strength properties can be characterized using Duncan and Chang's (1970) hyperbolic model, and (3) a specification based on the median unconfined compressive strength value is appropriate.INTRODUCTIONFor many projects, including foundation and embankment support, deep mixing can be designed based on simplified procedures and following standardized guidelines (e.g., FHWA 2013). However for unusually complex or critical projects, it is often necessary to perform numerical analyses, and in order to perform these numerical analyses well, a thorough understanding of the material properties is needed.This paper summarizes information on the characteristics and properties of deep-mixed soil-cement produced by the wet method, and it discusses the development of design considerations and recommended property values for a specific project, herein referred to as the penstock project, that requires numerical analyses. For the penstock project, a horseshoe-shaped enclosure of soil-cement is being considered beside and above an existing dam penstock to protect it from loads applied by an overlying stability berm that will be constructed for seismic remediation. The concept is to use soilcement created by the deep mixing method along the sides of the penstock and to use compacted soilcement above the deep mixing to create the crown of the protective soil-cement zone around the penstock. For this application, the soil-cement stiffness, rather than its strength, is the controlling design parameter. To achieve the necessary soil-cement stiffness, the strength will be high enough that the factor-of-safety values against instability along potential failure surfaces passing through the soil-cement are high. Following conventional practice, the soil-cement acceptance criteria will be based on the unconfined compressive strength, and the specified strength will be selected to produce the desired modulus value."

Jan 1, 2015

By Kevin P. Gleckler, Steven C. Highfill

"Escalators to access platforms for the Second Avenue Subway Station at 72nd Street in Manhattan are to be installed in the basement of an existing 19-Story residential building. The escalators, which extend below the existing building foundations, require excavation of an inclined rock cavern up to 80-feet deep. Underpinning of columns within the 19-story building as well as a stone masonry party wall and columns for an adjacent 5-story building was completed prior to excavation of the rock cavern to ensure structural stability.This paper will discuss the analysis and design of the underpinning system, the installation and load transfer procedures and the cavern excavation immediately below. The underpinning system was subject to very strict deformation limits and to electronic monitoring prior to and throughout the load transfer and construction process. Key details such as the load transfer mechanism between the reinforced concrete column and the temporary structural steel underpinning frame will be discussed. The challenging rock excavation process will be described which utilized conventional equipment and pattern drilling with Damite rock splitting mortar.INTRODUCTIONPhase 1 of the Second Avenue Subway is being built by MTA Capital Construction (MTACC) to improve subway service on the east side of Manhattan. Entrance 1 for the 72nd Street Station of the Second Avenue Subway is located on the east side of 2nd Avenue at the corner of E 69th Street in New York City. Access to the station mezzanine, approximately 80-feet below grade, is designed to be routed through the basement of an existing 19-story residential building. From the sidewalk, stairs and escalators within the width of sidewalk connect the riding public to a basement level mezzanine, which turns into the building at roughly 16 feet below grade (Fig. 1). Riders then connect to three long escalators to arrive at the station mezzanine. The escalators are to be installed within an inclined and arched cast-in-place (CIP) concrete lined rock cavern (Fig. 2). Construction of both the entrance into the basement and the escalator cavern require the transfer of columns within the 19-story building. Excavation of the escalator cavern also impacts the foundation support for columns and a load bearing party wall for the 5-story residential building immediately to the north. Two stages of load transfer were used at each location. The Stage 1 transfer used a temporary underpinning system to unload the current structure which allowed for construction of the permanent transfer girders. Stage 2 transferred the load from the temporary system to the permanent transfer girders."

Jan 1, 2016