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By Derek Egbert, Kevin Baumgartner, Howard Perko

Foundation designs in a bid-build business environment can be challenging as so much depends on the capabilities of the selected contractor.  Owners and governing agencies must be open to value engineering (VE) alternatives.  This paper presents a case history where a foundation VE design was prepared for a county bridge replacement. The existing structure was a two-lane, simply-supported, truss bridge approximately 270 ft long and 30 ft wide.  The new bridge is a three-lane, two-span, continuous steel plate girder bridge approximately 250 ft long and 49 ft wide.  The new bridge was to be founded on two end abutments and one center pier by a total of 173 micropiles. Due to the number of micropiles and the time requirement to install a single micropile, an alternative design was proposed utilizing driven steel piles for support of the abutments and rock-socketed drilled shafts for the center pier. Replacing the micropiles with the proposed alternative was intended to reduce overall construction time and cost. Shallow bedrock and soil scour presented unique challenges for the bridge foundation and required an in-depth investigation to determine the required depth of foundation elements to achieve pile toe fixity. It was determined the sand layer thickness was not sufficient in some places to provide fixity to the VE driven piles and therefore the east abutment had to remain the original micropile design.  Substitution of driven pile and rock-socketed drilled shafts in the other areas still resulted in both time and cost savings.  This case history shows how engineers, contractors, owners, and governing officials can collaborate collectively to develop effective foundation solutions. Keywords: micropile, driven pile, drilled shaft, abutment, center pier        

Oct 7, 2024

By Steve Babcock, Howard Perko

Since the development of the ICC-ES AC358 acceptance criteria, the use of helical piles as deep foundation solutions has grown in popularity and expansion of desired applications. With this has come a desire to use larger diameter shafts to support larger loads. Helical piles employ a unique method to predict performance by correlating the final installation torque to the ultimate load carrying capacity for both tension and compressive loads. This capacity-to-torque factor is commonly denoted as the ‘Kt’ factor. Previous publications from multiple authors have estimated the capacity-to-torque relationship both empirically and theoretically for helical piles.  Most of these prior studies focused on smaller shaft diameters from 1.5-inch square to 3.5-inch round.  Current trends have motivated the helical pile industry to utilize larger diameter pile shafts than are not well represented by the prior publications, including AC358. This paper presents an expanded body of empirical data comprised of full-scale load test results of helical piles with diameters ranging from 1.5 inches up to 18 inches. The curve fitting methods used to develop the AC358 equation are re-examined and offers an alternative that better fits the test data. The current methodology uses a simple exponential curve with a limit of zero as pile shaft diameter increases. This implies that at some point a helical pile’s diameter would become so large that it would have zero capacity, which is illogical. Utilizing a horizontal asymptote, other than zero, in the curve fitting analysis provides a better fit to the data.  The better fit increases to the capacity-to-torque ratio for larger diameter piles on the order of 15% to 30%.  Also, presented are some key insights that the authors offer for consideration in further development of this critical relationship.

Oct 7, 2024

By Ian Vaz, Taylor Stevenson, Takefumi Takuma

Taylor Stevenson, Blue Iron Foundations & Shoring LLC, Newport Beach, CA, U.S.A. Phone: (949) 933-9043, Email: taylor@blueironllc.com Chris DellAringa, Blue Iron Foundations & Shoring LLC, Newport Beach, CA, U.S.A. Phone: (916) 340-5600, Email: chris@blueironllc.com Ian Vaz, Giken America Corp., Orlando, FL, U.S.A. Phone: (407) 666-8119, Email: ivaz@gikenamerica.com Takefumi Takuma, Giken America Corp., Orlando, FL, U.S.A. Phone: (407) 907-4680, Email: ttakuma@gikenamerica.com, The Fullerton Creek Channel Phase 2 project undertaken by the Orange County Flood Control District stood out as an exemplary blend of innovation and environmental sensitivity. Tasked with stabilizing the channel banks, the project demanded an approach that mitigated noise and vibration, prompting the incorporation of the press-in piling method right from its conceptualization. This non-vibratory, minimal noise method of pile driving has revolutionized traditional piling techniques by significantly reducing environmental impact, making it an ideal choice for environmentally sensitive areas. Central to this unique method's success was Blue Iron Foundations & Shoring, entrusted with the press-in installation of 3,459 linear feet of PZC26 sheet piles, ranging from 38 to 45 feet in length. Leveraging their extensive equipment arsenal, Blue Iron utilized two of its Giken ECO 1400S press-in machines to install the sheet piles just mere feet away from existing structures. The utilization of 2 press-in machines enabled the simultaneous installation of both channel walls between April 24th and July 24th in 2019 to complete the project ahead of schedule. Despite very limited working space within the channel banks which made the project a challenge logistically, installation efficiency was still optimized without compromising the delicate environmental balance of the site which traversed through both residential and business areas. In conclusion, the Fullerton Creek Channel Phase 2 project showcased the fusion of groundbreaking technology and environmental consciousness. The adept utilization of the press-in piling method and cutting-edge equipment underscored the contractor's leadership in adopting innovative solutions while prioritizing environmental preservation in complex geotechnical projects.

Oct 7, 2024

By Spencer Waganaar, Katherine Winters, John Murphy

Hundreds of miles levees cutoffs have been placed in USACE levees in the Sacramento CA, Houston TX, and Southern Florida regions in the past 40 years, with smaller projects in additional regions. Many of these cutoff walls are designed for infrequent loading as they that are critical infrastructure for extreme flood events. With this infrequent loading, there are no widely accepted ways to monitor and quantify the condition and functionality of seepage cutoff walls for levees over multiple decades. The potential for deterioration is not well known. Lack of data on the longevity/design life of cutoff walls adds uncertainty to levee risk assessments, operational and maintenance costs, and community risk. USACE-ERDC is conducting a comprehensive review of existing research regarding cutoff wall longevity and deterioration to address these uncertainties. The potential mechanisms of deterioration are cracking, chemical reactions, vegetation growth, or animal burrows. This paper includes documenting experiences from USACE levee safety experts, pertinent failure mechanisms identified from engineering literature, whether and how these considerations for cutoff walls are currently incorporated into risk assessments, and assessing the need for need for further research to reduce uncertainty. The findings presented in this paper will include uncertainties and potential risks to levee performance due to levee cutoff wall deterioration and suggest areas for further field investigation. Findings could contribute to improving recommended potential post-construction QC practices, operations and maintenance practices, identifying early warnings of reduced functionality, reducing costly invasive/destructive testing, and informing risk assessment methodology.

Oct 7, 2024

By John McKinnon, Tony Barila, Ahmad Khatib

The 161 First Street project is an existing 4-story brick building, located in Cambridge, MA that underwent a complete renovation to allow for it to be utilized as an office building. The new addition will be supported by existing and new reinforced concrete columns supported by drilled micropiles (DMPs) at basement level. Alexandria Real Estate Equities, Inc. is the owner; Consigli was the construction manager; W. L. French was the site contractor; McNamara Salvia was the structural engineer and Haley & Aldrich was the geotechnical engineer. The existing and new reinforced column foundations will be supported by DMPs drilled from the basement, approximately 8’ below existing grade. A total of 163 DMPs, 87 with a compression design load of 160 kips and 76 with a compression design load of 40 kips, were installed. A pile load test was performed in tension to a maximum test load of 561.2 kips (3.5 x Design Load) to confirm the embedment length of the DMPs in the marine deposit and glacial till. Consgli invited Hub to participate with the project design team to evaluate the initial foundation design relative to the soil profile, logistics and construction schedule. The initial foundation support was a maze of helical piles. We evaluated several other piling options which were more cost-effective with less impact on concurrent construction activities and faster schedule. Ultimately, we recommended a micropile solution which was accepted by the project design team. The main challenges on this project were the low headroom, tight working space between the existing columns, the access to the work area via a single ramp and contaminated soils. The upper soils at this site were heavily contaminated. A novel drilling approach was utilized to ensure that the drill spoils in the upper 12ft were segregated from the soil below that depth. In addition, Hub utilized its Soil Separation System (SSS) to separate the water and soil from the wet drill spoils. This system allowed for the most efficient way to manage, collect, and dispose of the drill spoils within a low headroom application. The entire DMP scope was completed in four months. This duration was less than required by Consigli’s schedule. The DMPs were drilled with the Davey-Kent 515 and the Comacchio MC-4D drill rigs.

Oct 7, 2024

By Thomas Pullen, Gregory Spicer, Joe Welna, Lola Moussey

During the past several decades, a segment of Interstate 35W (I-35W) at 42nd Street, located in Minneapolis, Minnesota, has experienced flooding during intense storm events. Flooding is caused by a combination of runoff from the upstream watershed and backflow through the downstream stormwater tunnel system. The Minnesota Department of Transportation (MnDOT) evaluated several stormwater storage facility (SSF) concepts to mitigate flooding. The sub-grade storage tanks are located adjacent to I-35 WB, between the highway shoulder and 2nd Avenue, which is elevated approximately 25’ above the highway. Prior to construction, there was an embankment covering the footprint of the new storage tanks, which supported earth loads and provided base reactions for a soundwall running parallel to 2nd Avenue. Therefore, an earth retention system would need to be installed to permit removal of the embankment. The project team elected to build a soil nail wall, which was constructed in lifts as the embankment removal progressed. Notable challenges related to design and construction of the soil nail wall were as follows: (1) elevations and angles of the soil nails to avoid conflict with existing utilities on the backside of the wall, and (2) sound wall base reactions including separate load cases for wind load acting in each direction to determine the governing scenario for the retaining wall. Design and construction consisted of six underground storage cells approximately 80 feet deep and 42 feet in diameter. The cells were constructed using slurry diaphragm walls and depressurization which allows for handling a high groundwater table (approximately 10-15 feet below highway grade) and highly variable glacial outwash soils in a congested construction area. This paper will discuss the design and construction considerations for the soil nail wall and underground storage tanks.

Oct 7, 2024

By Bernardo Jimenez

Earthquake-induced deformation of bridge piers underlain by liquefied soil may impose significant demands on the foundation system due to lateral spread. A relatively simple equivalent-static analysis (ESA) procedure can adequately predict the response of bridge foundations to lateral spreading. Typical procedures for ESA analysis assume a 'infinite-length' lateral spread feature, implying that further increases in size would not increase the demand placed on foundations within the spread. Recent studies have indicated that if the areal extent of the spread feature is smaller than the zone of influence, the displacement demand must be reduced to account for pinning effects. This case can be considered a finite-length spread. Additionally, a reduction in demand imposed on one foundation component may occur during a finite-length spread due to the shielding effect from an adjacent foundation. This document reviews and applies a method to evaluate finite-length spread while considering pinning and shielding effects. The selected bridge system is the Taras overpass in Costa Rica. By using two-dimensional finite element analyses (FEA) interaction with ESA results, pinning and shielding effects are accounted for and compared to ESA analysis for 'infinite-length' spread. The results indicate that for bridge piers accounting for a finite-length lateral spread can significantly decrease demands on the foundations during design phases.

Oct 7, 2024

By Mohammad Moontakim Shoaib, Murad Abu-Farsakh, Hani Titi

The evaluation of load-settlement behavior of piles is very crucial in meeting the serviceability criteria for pile analysis and design. The most reliable approach for estimating this behavior can be achieved by conducting pile load tests. However, due to the considerable expense and time requirement of such in-situ testing, the load-transfer methods have been used routinely in practice. In this paper, an alternative tree-based machine learning (ML) modeling is explored to predict the load-settlement behavior of axially loaded single piles from cone penetration test (CPT) data. Two variants of tree-based ML models, the random forest (RF) and gradient boosted tree (GBT), are developed in this study to estimate the load-settlement behavior of piles from CPT data (corrected cone tip resistance, qt, and sleeve friction, fs). A database of load-settlement curves of 64 static pile load tests and the corresponding CPT test data were compiled and used for the development of these ML models. The developed RF and GBT models are evaluated based on several statistical criteria. The load-settlement curves for six PLTs predicted using the developed RF and GBT models were compared with the measured data and the load-settlement curves predicted using the conventional load-transfer methods. The results demonstrated the great potential of tree-based ML (RF, GBT) models for predicting the load-settlement behavior of axially loaded piles from CPT data. The comparison clearly shows that the ML models outperformed the conventional load-transfer methods. Amongst the two ML models, the results show that the GBT model outperformed the RF model.

Oct 7, 2024

By Benjamin Giacometti, Adam Hacker, Enrique Farfan, Tom Pace

The Louisville Metro Levee System reduces flood risk to the City of Louisville, Kentucky. The levee system was constructed by the U.S. Army Corps of Engineers and is now operated and maintained by the local sponsor, the Louisville and Jefferson County Metropolitan Sewer District (MSD). The levee system has a total length of 26.1 miles, consisting of concrete floodwalls and an earthen levee with sixteen flood pump stations for flood protection.   MSD determined the need to upgrade the existing Paddy’s Run Flood Pump Station’s capacity to reduce the risk of interior flooding. Due to the age and complications associated with upgrading the existing pump station, a new flood pump station will be constructed within the existing levee prism and portions of the existing station will be selectively demolished. MSD initiated a Progressive Design-Build project for a new Paddy’s Run Flood Pump Station. The project proposed a diaphragm wall construction to serve as the temporary support of excavation for the new flood pump station, permanent foundation for the new flood pump station, levee under seepage cutoff, and embankment stability. The lateral soil pressures on the diaphragm walls result from the staged construction sequence, including the effects of bracing to provide lateral support to each wall, and soil-structure interaction. To properly account for these effects, Plaxis 2D models were created for different sections of the structures. The lateral soil pressures for the diaphragm wall design were obtained from the output of these Plaxis models. This paper and presentation summarizes the geotechnical aspects of the diaphragm wall design and how it was used to inform the structural design.

Oct 7, 2024

By Kenny Younger, John R. Morris, Scott Stonecheck

For the University of Pittsburgh's new Athletic Sports Performance Center project, a unique, technical design assist/build approach was employed to overcome both the dense urban environment and challenging subsurface conditions.  The new sports arena will house multiple venues for the university in the years to come.  With no braced floors obstructing sight lines and heavy roof loads through 65-ft tall external walls, Amelie designed an online hybrid temporary/permanent tied back soldier beam wall system over 45,000-sf of exposed face as a vertical slabs, supported on 14" wide strip footings to these 65-ft heights, thereby minimizing the cast in place outer wall thicknesses with depth.   The design also addressed surcharge effects from buildings in close proximity to the shoring system.  During construction, a significant coal mine interval was addressed as to not negatively impact the integrity of the shoring system and existing dormitory buildings.  The case history represents a one of a kind technical approach to a hybrid shoring system while sharing subsurface risk and contingency techniques to avoid potential negative outcomes.      

Oct 7, 2024

By Kellie E. Gagnon, Aidan Hodge, John Vaught, Kelli Gagnon

The USACE geologists at the Bluestone Dam Phase 5 Dam Safety Assurance (DSA) Megaproject in Hinton, WV have employed the use of Terrestrial LiDAR scanning and photogrammetry for the purpose of mapping and documentation of stilling basin foundation conditions. Following the excavation and cleaning of a 60-foot by 60-foot monolith foundation, a Trimble SX-10 scanning total station is used to capture high density 3D scans, imagery, and survey measurements of the monolith floor and adjacent side walls. This data is used to generate high density point clouds of the entire foundation and sidewalls, which in turn facilitate the creation of numerous products that aid in the documentation and future assessment of the project foundation. These products include high resolution true color orthophotos, detailed topographic maps, excavation reports, and 3D models. Quarter scale orthophotos of the foundation and sidewalls are printed out and used as base maps for geological field mapping, allowing for greater accuracy and faster execution time when compared to traditional field mapping methods. Topographic maps, orthophotos, and data obtained from excavation reports contribute to the generation of detailed and accurate Foundation, Completion, and Geotechnical Reports, and will help inform the project Post Implementation Evaluation (PIE). Annotated 3D models, with the future incorporation of virtual/augmented reality technology, will allow design personnel, project delivery teams, and risk assessment teams to virtually inspect bedrock conditions and better identify any underlying geological conditions that impact post-construction performance of the project. This innovative approach has allowed project geologists to exceed the requirements for foundation mapping and documentation as outlined in ER 1110-2-1156. The quality and volume of spatial and geological data collected using this method has allowed for a faster and more efficient foundation approval process, reducing the time during which the foundation is exposed during construction and lowering risk at the project.

Oct 7, 2024

By Desi Dikova, Daniel Wagstaffe, Lori Simpson, Eric Lindquist

1621-1629 Market Street is a mixed-use development in the South of Market district of San Francisco, located directly above Bay Area Rapid Transit (BART) tunnels and alongside the San Francisco Municipal Railway (MUNI) tunnels that run below Market Street. The project included the construction of five new buildings up to nine stories tall, each with single-level basements, supported on improved ground. The project transformed a cluster of commercial buildings and surface parking lots into residential, retail and office buildings, and publicly accessible open spaces. Subsurface conditions at the site include uncontrolled fill, loose sand, and marsh deposits, with groundwater approximately 15 feet deep. Engineering challenges faced during design and construction included: protecting the tunnels beneath and adjacent to the site; the presence of uncontrolled fill, loose sand and potentially liquefiable soil; the phasing of multiple, non-concurrent basement excavations; and construction in a dense urban area, including protection of both on-site and neighboring buildings and other improvements. In addition to Building Code requirements, the project complied with BART’s stringent requirements on loading, settlement, vertical and horizontal movement control, groundwater control, and limiting tieback lengths to provide clearances to tunnels and utilities. This paper reviews these challenges, with a focus on the temporary support of excavation (SOE) systems and the ground improvement. The SOE systems consisted of deep soil mixing (DSM) cutoff walls for four of the buildings and soldier-pile-and-lagging for the other; all were restrained by tiebacks or internal bracing. The DSM walls were incorporated into SOE systems for neighboring buildings with each phase, resulting in efficient shoring utilization. The ground improvement consisted of an interconnected grid of DSM panels that mitigated liquefaction and extended building loads to a dense sand layer. Load testing of DSM elements was performed to confirm adequate bearing capacity.

Oct 7, 2024

By Valerie Vasquez, Howard Perko

Construction of large-scale battery energy storage systems (BESS) is becoming prevalent throughout the United States to meet demands of the electric grid and optimize effectiveness of alternative energy sources. Helical pile foundations are regularly used for support of battery containers and transformers.  This type of foundation system is reuseable and sustainable, and is advantageous because of its ability to carry high axial loads at relatively low cost. This paper presents multiple case histories of BESS supported on helical pile foundations and explores the design and implementation aspects of helical piles. Case histories include several sites in Texas, one in Mississippi, and one in Nevada. The quantity of individual BESS units at each site ranged from approximately fifty to two-hundred.  Each individual unit was supported on six or eight helical piles, resulting in thousands of helical piles utilized across all sites. For design, the feasibility of using helical pile foundations is first considered by review of the site-specific geotechnical report.  A boring analysis is constructed. If the project site is suitable for helical pile foundations, an initial helix sizing is performed. Given the dimensions and weight of the BESS units and environmental factors, the required helical pile loads and layout is developed. Helical pile capacity can be verified based on torque correlations. To confirm the helical pile design is acceptable, test installation programs are implemented at each site. The purpose of the test is to measure the depth at which the required installation torque is achieved. Based on the data collected, helical pile length is optimized across the subject site. If site grading has not been performed prior to the test installation, adjustments are made to account for expected cut/fill. This method of optimization through field testing results in an economic and speedy foundation system for rapid deployment of BESS.

Oct 7, 2024

By Liz Smith

The I-35 NEX project is a $1.6 billion design-build in northeast San Antonio in an area with known karst features. The project involves single-column, nonredundant, large diameter shafts that support an elevated highway. This case history describes the site reconnaissance, field investigation, design evaluations, and construction challenges. 

Oct 7, 2024

By Michael Arnold, Oliver Kaden, Cyril Bou Sleiman

In the framework of the Herbert Hoover Dike Rehabilitation project, BAUER Foundation Corp. had been tasked with the installation of 17.5 miles (28 km) of seepage cutoff wall distributed over three task orders.  The cutoff wall is 50 to 65 feet (15 to 20 m) deep and minimum 24 inches (0.61 m) wide. Beside numerous connections to existing concrete structures and existing cutoff wall segments, the work included the connection of the cutoff wall to three utility pipes at pump station S-131: one 96-in (2.44 m) diameter corrugated metal pipe (CMP) and two 48-in (1.22 m) steel pipes. The cement deep soil mixing method of Cutter Soil Mixing (CSM) has been used to install the wall.  The contract documents stipulated the use of jet grouting for all pipe connections.  The large diameter and the deteriorated state of the CMP caused the contractor question whether it would be feasible to meet strict contract requirements for the interface utilizing jet grouting methods. The contractor prepared a value engineering cost proposal (VECP) to avoid jetting around the CMP. The proposal included an excavation shored using sheet piling and soldier piling, partial removal of the CMP, jet grouting below the CMP, reconnection of the CMP, backfilling with controlled low strength material (CLSM), jet grouting around the steel pipes and finally CSM tie-ins into the CSLM block and jet grout cutoff wall. The paper introduces the project, the existing conditions, the geotechnical site conditions and the requirements specified by USACE.  It describes the pursued approach, the equipment used, and auxiliary measures needed to facilitate the approach.  Strength and permeability results are presented. The paper also discusses challenges encountered and related lessons learned.

Oct 7, 2024

By Jonathan Ernst, John Regan, Leo Hart

Originally built in 1856, the existing bridge carries 5 railroad tracks servicing MNRR and AMTRAK and spanned over Atlantic Street in Stamford, CT providing two (2) lanes of traffic beneath the bridge.  Replacement of the bridge was driven by several factors including age, traffic improvements to widen the narrow underpass to service 5 lanes of traffic and increase headroom beneath the bridge to reduce restrictions on larger vehicular traffic.  The proposed pile supported bridge abutments were designed to be constructed while keeping all 5 railroad tracks in service, creating a need for individual jumpspan girder systems beneath each track.  A temporary excavation support system (SOE) design was included in the Contract  and consisted of drilled H-piles soldier piles and bracing with bolted connections.  GTR re-designed the SOE system to accommodate low headroom restrictions and constructability issues associated with track outages and site logistics.  Several key factors were to be considered for the SOE system: (1) headroom restrictions beneath catenary systems, (2) train axial, lateral, braking and traction forces, (3) headroom during pile cap construction, (4) integrating the SOE system to accept the “jump span” bridge components, and (5) Phased construction considerations.  To address these factors, GTR designed an SOE employing drilled micropile load bearing soldier piles with internal bracing to tunnel beneath the active railroad traffic.  This SOE scheme was successfully installed in low headroom conditions beneath existing  catenary lines in five (5) phases and included an innovative pre-fabricated bearing connection “top hat” to accept the jump span bridge.  Each phase of work was successfully installed and completed to support each active railroad track in five - 9-day outages. To achieve the required excavation support, a detailed phasing plan was required to support each adjacent track as subsequent jump span bridges were installed.  Although tedious excavation and bracing installation process was required, supporting the railroads required a robust system to ensure the safety of the workers and rail traffic alike.  After the SOE and jump span bridges were installed, the abutment foundations were constructed beneath the jump span bridges and between the SOE’s. Careful analysis and planning allowed for the creation of an accurate and precise system to support the axial and lateral train pressures while performing the required construction under the rail traffic.  This paper presents a unique case study of the “tunneling” beneath active railroad tracks utilizing a temporary support of excavation system to construct proposed pile supported abutments.

Oct 7, 2024

By Jerry Dimaggio, Ahmad A. Alhasan

With the increased vulnerability of transportation infrastructure to extreme events, resilience of transportation and infrastructure assets has become more critical. The term geotechnical asset applies to all infrastructure features constructed on, in, or of soil and rock. Depending on a specific application, a “geotechnical asset” may serve as a foundation of an asset, the asset itself, or both. This extent and variability of type (walls, slopes and structural foundations) makes them the most critical and challenging assets to manage and maintain. Moreover, geotechnical assets are vulnerable because of the number of internal asset variables and their susceptibility to accelerated moisture, erosion, and environment-related changes, which directly or indirectly impact the asset performance. This paper discusses the workflow and components of a recently developed resilience-based design framework of geotechnical assets. The core concept in Resilience-Based Design is to model the asset performance over time including possible repeated extreme events. These events result in accumulated progressive damage and accelerate the deterioration of the asset leading to progress serviceability or strength failure. The framework focuses on capturing the impacts of damage on the assets performance and incorporating preventive and corrective maintenance during the asset service life. The Resilience-Based Design (RBD) framework was then contrasted to the Allowable Stress Design (ASD) and Load and Resistance Factor Design (LRFD) frameworks in a significant case study of a soil slope stabilized using anchored drilled shafts. The slope was monitored over an extended period of time to capture the creep deformations of the stabilized slope. The design procedure will model multiple flood events using weather models developed for the area. Following the detailed case study example of the framework, the paper discusses the needs and procedures to implement the framework for a wide range of applications.

Oct 7, 2024

By Karla Myers, Howard Perko

Foundation designs utilizing helical pile groups are increasingly widespread in the electric power utility industry.  Yet the application of these systems lacks uniformity and knowledge gaps may exist. Recently, a body of codes and practice documents have been prepared by DFI and ASCE subcommittees regarding standard practice for electric power transmission structures design.  These codes and standards are discussed as they apply to helical pile groups.  With a better understanding of how the codes apply to these foundation types, engineers and designers can more confidently and adeptly specify and bid from a broader range of deep foundation options. Design of electric power transmission structures is most challenging at angles, water crossings, and dead ends.  These structures often are characterized by large overturning moments. This presentation will cover simple hand calculations for estimating the distribution of pile reactions from ground line tower moments.  Then, pile groups modeling using Ensoft® Group will also be covered in depth and with specific design examples from real case histories.  Design considerations for sizing of individual piles and key differences between pile design for building structures and pile design for power transmission towers and applicable codes and standards will be discussed.  Preliminary findings from field measurements performed on existing helical pile group supported structures, if available, may be included as they relate to validation of models.

Oct 7, 2024

By Seth Robertson

Instrumented static load testing is an effective means for assessing load-transfer characteristics of augered cast‑in‑place piles under static axial load. Strain gauges are typically instrumented on the steel reinforcement at specific locations along the pile’s embedded length for determining geotechnical resisting forces in side-shear and end-bearing. Conversion of strain to internal force at each gauge level can be complicated, requiring critical assessment of the pile properties and potential strain-dependent behavior. Current codes and standards provide recommendations for approximating these necessary pile properties, although these methods may not routinely yield realistic interpretation of measured strains. Non-linear rigidity may be exhibited over a static load test duration and there remains limited published methods for determining load-distribution characteristic under these conditions. Through measuring embedded strain and uniaxial stress simultaneously, the pile’s strain-dependent rigidity can be directly determined, thus minimizing uncertainty in the analytical process. While not commonly implemented in standard load test practices, stressmeters have been installed adjacent to strain gauges for this reason. A case study is presented where stressmeters were specially adapted for installation on augered cast-in-place piles on a bi‑directional static load test program. Based solely on the measured strains, it was realized that a non-linear rigidity would be required for properly converting strains to internal forces. The uniaxial stresses determined from the stressmeter measurements provided valuable insight in the pile material response to applied loads, ultimately reducing to a non-linear piecewise function of rigidity versus strain. Derivation of this non-linear piecewise function and methodology for computing internal forces are addressed. Comparisons of the non‑linear rigidity function to alternative rigidity (linear and non-linear) determination methods are presented. Recommendations for improving instrumented static load tests are summarized, primarily focusing on prospects and interpretation of embedded stressmeter measurements in top-down and bi‑directional static load tests.

Oct 7, 2024

By Melinda Hummel, Howard Perko

Colorado has a diverse geology including alluvial, colluvial, and eolian deposits overlying sedimentary, metamorphic, and igneous bedrock at varying depths and outcrops.  There is often concern for helical piles bearing on bedrock in these soil profiles, particularly if the bedrock is sloping or too hard to penetrate.  Though it has been accepted for a long time that helical pile axial capacity is correlated with installation torque, there are sometimes concerns regarding helical piles that refuse or “spin-out” on bedrock without meaningful torque readings.  This paper covers common practices in the industry for design of helical piles end bearing on bedrock.  Hardness of bedrock and penetrability of helical piles into bedrock are presented.  Design choices that can be used to help improve penetration are discussed.  Common approaches to estimate capacity of helical piles that “spin-out” and other concerns for helical piles end bearing on bedrock are described.  Keywords End Bearing, Helical Pile, Bedrock

Oct 7, 2024