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By Matthias Pulsfort, Hanna Nissen, Markus Herten

An insufficient integrity of cast in-situ bored piles can lead to a reduction of the load bearing capacity and may require cost intensive repairs. Reasons for an insufficient pile integrity are linked to the construction process, mainly to poor concrete quality leading to bleeding and segregation of the fresh concrete. Moreover, the entrapment of soil and an insufficient concrete cover can pose a problem. Knowledge about the time-dependent development of the fresh concrete pressure during the construction process of bored piles is needed for a better understanding of the underlying processes causing these defects. Therefore, pressure measurements were carried out on different construction sites with pressure cells being installed at different depths along the reinforcement cage. The measurements revealed the maximum pressure acting on the surrounding soil. The achievement is a better understanding of the effects of the concrete placement specifically and the construction process in general on the surrounding soil to reduce the risk of pile imperfections.

Sep 8, 2021

By Matt Fenwick, Douglas R. Schwarm

Stringent underwater noise limits at the Fairview Ave. N. bridge replacement on Seattle's Lake Union required an innovative approach to supporting the 470-ft long drill trestle. Screw-in foundations would reliably mitigate noise, but the required 500-kip bearing resistance were an order of magnitude higher than typical helical piles. This paper describes the process of designing, installing, monitoring, and testing 22-inch dia. helical piles 80 feet long with 36- and 42-inch dia. helices. A static load test confirmed that the conventional k-factor design method can be extended to capacities of up to 800 kips. A 375 ft-kip drive mechanism had to be fabricated because no North American equipment could supply the necessary installation torque. Real time installation monitoring and later "re-torque" tests confirm that helical piles gain capacity with time, analogous to driven piles under restrike. Underwater and on-land measurements confirmed very low noise, suggesting the possibility of widespread adoption where similar limits are imposed. Overall, this case history illuminates the need for innovative deep foundation types in response to ever-increasing regulatory constraints.

Sep 8, 2021

By Rick Deschamps, Amanda Blank, Matthew W. Drewek, Michael P. Walker

The Prairie du Sac Dam, located on the Wisconsin River, northwest of Madison, Wisconsin, was constructed 1912-1914. The spillway is an Ambursen-type, consisting of a series timber pile supported pier and buttress walls and rollway slab. The timber piles supporting the spillway, numbering approximately 5,000, have deteriorated, and the spillway structure was underpinned with over 700 micropiles as part of a design-build construction project. The underpinning micropiles needed to be arranged to avoid interferences with the existing timber piles, requiring the micropiles to be installed in the open spaces between the piers and buttresses. Inevitably, the installation of the new micropiles encountered obstructions, including existing timber piles out of alignment, as well as timber piles used to support the original construction activities and sheet pile used to control water during the original construction. This paper discusses using finite element analysis to model the spillway structure to estimate the vertical and horizontal stiffness with an extensive sensitivity analysis was performed during the design phase to account for anticipated construction challenges and potential variations in the underpinning performance. The inherent rigidity of the spillway structure allowed for load distribution to the underpinning system even when new micropiles needed to be re-located and aligned to avoid interferences with existing timber piles and other abandoned foundation elements dating back to original construction.

Sep 8, 2021

By Vijaya Bhushan Rao, Jason Redgers

A substantial lifestyle destination in the United Arab Emirates, in the Emirate of Abu Dhabi comprising of 1315 villas, town houses and non-residential leisure facilities is built over an area of 280 hectares of former mangrove areas, natural sands and reclaimed lands. Large-scale subsoil investigations including field and laboratory testing carried out dividing the entire site in to 7 clusters. This investigation revealed alternating layers of loose sands and silty clays within the load influence zone of planned foundations, showing susceptibility to excessive settlements. Therefore, ground improvement works were undertaken using a combination of stone columns, Rapid Impact Compaction (RIC) and excavation and replacement of soils plus a 0.4m thick load transfer platform. This was necessary to limit the settlements, increase-bearing capacity and prevent long-term settlements. 30 no’s of full-scale Zone Load Tests, ZLT were carried out each for a duration of 30 days in order to ascertain the anticipated long-term settlements in the clay layers. In addition, further testing of electrical cone penetration tests, CPT, and Plate Load Tests, PLT. The use of Priebe and Asaoka’s observational procedure were applied to predict the final settlements and the use of back-analysis from the 30 days Zone Load Tests, ZLT results to establish the site-specific consolidation parameters in clay layers to optimize the design and ground improvement works.

Sep 8, 2021

By Francisco A. Flores, Rigoberto Torres

The Complementary Technical Standards of Mexico’s City Building Code do not mention the criteria to compute the bearing capacity of Steel H-piles. It is necessary to increase knowledge in using steel H-piles as foundation elements in very soft soils of Mexico City. Considering their applicability to reinforce structures as well as new foundations in confined spaces, this research is proposed to obtain the axial load capacity of piles at scale in laboratory. This paper describes the construction and testing of scale models in laboratory of steel H-piles to measure their axial compression and tension load capacity in the soft soils of Mexico City. Three types of piles were fabricated at scale. Tests were performed on individual piles and pile groups. Based on the axial load tests, the load-displacement curves are presented both in compression and tension. The analysis of the results is shown, and comments are given regarding the ultimate bearing capacity of piles. Recommendations are presented regarding the determination of the bearing capacity of these piles in the very soft soils of Mexico City.

Sep 8, 2021

By Abolfazl Eslami, Sara Heidarie Golafzani

CPT-based methods considered as complementary tools for static analyses outperform other axial pile bearing capacity predictive methods. Considering soil spatial variability and minor errors associated with procedure and operator, CPT-base methods mitigate the effect of latent uncertainties in pile design. These methods were developed based on different databases and purposes. Hence, several statistical and probabilistic attributes were defined and implemented to assess the predictive CPT-based methods’ performance via CPT and pile databases in terms of the model parameter. These features make a comparison among methods in terms of precision, accuracy, and efficiency. Furthermore, CPT-based methods can be subjected to scrutiny over their backgrounds and how they were developed via reliability analysis. In this regard, a database of sixty-two driven piles and their adjacent CPT soundings were gathered, and six commonly applied CPT-based methods were examined according to criteria other than prevailing statistical and probabilistic ones, including; (a) input variables, (b) soil behavior classification (SBC) (c) model assumption (d) Influence zone, and (e) axial loading direction. According to these introduced criteria, CPTbased methods were classified and appraised via efficiency ratio. Eventually, these reliability-based, statistical, and probabilistic criteria evaluate the understudied methods performance for the investigated compiled database and help designers select consciously appropriate predictive methods according to the site conditions.

Sep 8, 2021

By David S. Graham, Benjamin Turner, Paul J. Axtell

Seismic challenges were at the forefront of design for two parallel replacement bridge structures over the Arkansas River as part of the I-30 Crossing Project in Little Rock, Arkansas. Although not an area of the country typically associated with high seismicity, proximity to the New Madrid Fault Zone resulted in design ground motions sufficient to trigger liquefaction in alluvial channel and point bar deposits. A detailed post-award subsurface investigation program utilized CPT with complimentary borings to obtain samples for laboratory testing to assess the continuity of potentially liquefiable layers, from which we concluded that continuous zones of liquefaction across the extent of the north approach could lead to lateral spreading towards the river. An overview of the foundation and superstructure design to resist lateral spreading forces in accordance with the latest published design guidelines and research is presented. Other seismic aspects of the design are covered including timber pile ground improvement to mitigate liquefaction at the north approach embankment and foundation input motions that differ from code-based ground surface motions due to foundation stiffness, strength, and geometry. The project showcases an example of successful collaboration between geotechnical and structural designers with contractor input to address seismic challenges in the South Central US. Furthermore, the importance of considering kinematic demands on columns and other superstructure components – not just foundations – is highlighted.

Sep 8, 2021

By Babak Mamaqani, Pirooz Barar

The Heights project was located at Fashion Valley North, San Diego, CA. The scope of the project was to replace two existing commercial buildings with a large 7-story multi-family residential building. There was an existing 1:1 slope on the north side of the site. A permanent soil nail wall, 1,000 linear ft long, with a maximum height of 100 ft, was needed to replace the 1:1 slope at the north side of the project to accommodate the development. Previously there was a design for the permanent soil nail wall which required up to 115 ft long soil nails with large diameter rebars and 13 in. thick permanent facing. PB&A was engaged by the owner to conduct soil nail design optimization and value engineering to reduce construction costs and improve scheduling. First, the SnailPlus program was used to check the stability under static and seismic conditions and to design soil nail lengths and sizes. Then, soil nail head forces were calculated to design the permanent facing using FHWA recommended procedure. Another challenge of the project was to evaluate the interaction between a future San Diego Gas and Electric (SDG&E) tower and the soil nail wall. Finite element analyses were conducted with the PLAXIS program to ensure the deflection of the future tower would be within the acceptable range. The soil nail design optimization helped the owner to save approximately $800,000 in construction cost and improved construction scheduling.

Sep 8, 2021

By Reda Mikhail, M. Birkan Bayrak

The Washington State Department of Transportation (WSDOT) State Route (SR) 167/70th Avenue East Vicinity Bridge Replacement Design-Build project is located in Fife, Washington. This $40 million project consists of replacing the existing 70th Avenue Bridge over Interstate 5 (I-5) with a single-span bridge of about 220 feet long with approach embankments. The subsurface conditions along the new bridge alignment generally consists of alluvial deposits with high potential of liquefaction overlying glacially overridden deposits. In the early stages of the project, drilled shafts were considered as the deep foundation system; however, after an additional subsurface investigation is completed at the site, driven pipe piles were selected as the deep foundation system. Bridge abutments are supported by 24-inch diameter, 80-foot-long open-end driven steel pipe piles. The pile length was determined to bypass a relatively thick liquefiable zone and to tip the piles above what could be compressible soils. The use of advanced seismic analysis was instrumental in optimizing the pile length. The dynamic testing performed on numerous piles indicated what could be unique soil setup factors compared to those measured in local projects as well as those reported in national design manuals. Detailed discussions of the pile foundations design and construction is presented in this paper.

Sep 8, 2021

By WenJun Dong

This paper presents the stability assessment of the steel pipe piles that are used to support a deadman beam to anchor an adjacent bulkhead wall. Finite element analyses are performed to assess the stability of the bulkhead wall and determine the required tie-back force to the pile. The piles are relatively close to the bulkhead wall such that their soil resistance wedge zones are not fully developed but truncated by the bulkhead wall. The reduced lateral resistance capacity of the anchor piles is determined by applying the Coulomb wedge method on the truncated soil passive zones between the pile and wall. Both the conventional soldier pile stability (in terms of force and moment equilibrium) and Winkler soil spring (for soil-pile-interaction) analyses are used to assess the stability of the anchor piles.

Sep 8, 2021

By Haoran Zhang, Chu Ho

A recent design-build project in New York involved various degrees of additions and improvements to four existing transit stations. Reuse of the existing foundations was considered a more sustainable alternative than constructing new foundations for the project. This approach mitigated the extent of demolition work and limited the amount of downtime for track operations. A key challenge for reusing the existing foundations was the lack of as-built drawings. In order to obtain some measure of confidence for the proposed foundation reuse, non-destructive investigation technology was adopted to evaluate the structural integrity of the piers and foundations. A total of 47 piers for the existing passenger platform were investigated for possible reuse. Several test pits, excavated to verify the foundation type and configuration, indicated the piers were founded on a combination of shallow footings and drilled shafts. Pile integrity tests were performed to verify the length of the drilled shafts. Geotechnical capacity of drilled shafts was evaluated for side friction and end bearing resistance, and confirmed using a proof load test conducted from the existing platform structure. This paper presents the investigation methodology and discusses the approach adopted for geotechnical design of the existing foundations for reuse.

Sep 8, 2021

By Benjamin B. Buensuceso III

Crosshole sonic logging (CSL) is a popular quality assurance and quality control method used to examine the concrete quality of cast-in place deep foundations, though the evaluation of the results is subject to certain limitations. One such limitation explored in this paper is the occurrence of false positives, where signal anomalies indicated by CSL test results are not necessarily indicative of imperfections in the foundation that could affect its performance. A case study of false positives evaluated in CSL records in a major infrastructure project in Metro Manila is presented in this paper. A detailed desktop evaluation and results from complementary high-strain dynamic load testing and low-strain pile integrity testing were used to evaluate the significance of the suspected false positive signal anomalies from the CSL test results. Recommendations for the proper interpretation and evaluation of CSL test results in Philippine practice, given the method’s limitations and examples presented, are also shared.

Sep 8, 2021

By Amanda R. Parry, Chris R. Pray

Predicting and modeling the soil structure interaction of laterally loaded piles with significant unbraced lengths is one of the challenges faced in designing many waterfront structures. Designers often rely on pile specific design software to calculate forces in an embedded pile and then couple that with either a structural design software to capture the behavior of the rest of the structure or use potentially overly conservative assumptions to omit modelling the piles entirely. Given that some projects have hundreds of piles coupled with hundreds of loading conditions, the shuttling of results from the structural analysis software into the pile analysis software can become cumbersome, difficult to track and manage, and prone to user input errors. An alternative approach recently used on two large marine infrastructure projects consisted of calibrating a structural analysis software to replicate the resultant outputs from a software developed specifically for pile analysis. This calibration was done using thoughtfully placed springs along a pile modeled in the structural analysis software to replicate the soil-structure interaction of the piles. The focus of this paper will be on the methodology used to calibrate the two software programs and an evaluation of the results which showed close agreement. Based on the two case studies, calibrating a generic finite element analysis software via this method should be considered as a reasonable and time saving design approach for pile-supported structures.

Sep 8, 2021

By Bernardo J. Jiménez Vega, Edy L. T. Montalvan

Rammed stone columns and similar reinforcement systems are used worldwide more frequently as a cost-effective method for improvement of foundations on soft soils. The effectiveness of the treatment method is evidenced by the increase in bearing capacity and reduction of compressibility of the treated ground. In this study, two job sites with over 500 stone columns were studied. On both jobs sites, shallow soft silty soils were found and stone columns were designed to support the foundations of MSE walls, which serve as abutments for viaducts. In order to verify the soil improvement efficiency CPT tests were performed before and after the construction of stone columns, also plate load tests were performed on both job sites to verify the deformation modulus of the stone columns. From CPT data it was observed an increase up to 30% of sleeve friction and 20% of tip resistance, which demonstrated a higher deformation modulus maintaining the same strength in the soil after stone columns construction. The plate load tests yield load-deformation curves which indicated that the original assumed modulus was conservative. As a result of these findings, optimization of the settlement reduction ratios was conducted using the modified values of deformation modulus for the soil and stone column, obtaining a reduction up to 30% of stone columns for further job sites with similar soil conditions.

Sep 8, 2021

By Oladayo O. Komolafe and Majid Ghayoomi

p-y curves have been used over the years to determine the lateral resistance of piles. This method is popular among practicing engineers due to its simplicity and its ability to determine the slope, displacement, shear force, and bending moment for various depths along the pile. The ultimate lateral load resistance is a key component of p-y curve formulation. The p-y curve formulation by Reese et al. (1974) does not consider the effects of soil’s degree of saturation on theoretical ultimate lateral resistance of the failure wedge. This limits an accurate assessment of the lateral soil resistance near the ground surface and the consequent p-y curves. This paper extends the existing approach for determining the failure wedge in unsaturated cohesionless soils with suction dependency, especially for the depths that are above the water table within the wedge. The modification to the failure wedge analysis was made by considering the variation of the degree of saturation which affects effective stress and lateral earth pressure. Through a set of parametric analyses, the impact of incorporating principles of unsaturated soil mechanics in the estimation of theoretical ultimate lateral resistance is examined, and its implications on lateral pile response are discussed.

Sep 8, 2021

By Brian J. Olson, Kevin Haiar

Originally constructed between 1939 and 1941 as part of Franklin D. Roosevelt’s New Deal programs, the Bonneville to Hood River 115 kV Transmission Line required an infrastructure upgrade to remain reliable and in-service. The line traverses the rugged landscape of the Columbia River Gorge on the Oregon- Washington border, featuring steep, talus slopes; uneven, rocky terrain; and a variety of environmental sensitivities. This paper details the design and construction of 27 micropile foundations for new, fire- hardening steel poles through a particularly challenging stretch of the alignment. The difficult access and environmental constraints at these sites designated them as helicopter-accessible and precluded the collection of detailed geotechnical information prior to construction. Micropiles provided a viable foundation alternative due to their portability and flexibility during construction. Detail will be provided on the extensive preliminary desktop study performed, as well as the process of developing engineering designs to successfully accommodate for variability and unknowns in complex geological conditions. With an increasing number of electric power projects traversing challenging terrain and facing similar obstacles, this project stands to provide valuable lessons learned to the industry.

Sep 8, 2021

By Vijaya Bhushan Rao, Jason Redgers

A mixed-use development comprising of multistoried residential towers, retail and associated infrastructure covering an area of 500,000 m2 is under construction in Dubai. The subsoil conditions consist of calcareous sands with high carbonate and shell content with hard and competent strata encountered at varying depths. To achieve the design requirements of soil stiffness, friction angle, limit differential and total settlements and mitigate the liquefaction due to a seismic event then ground improvement were deemed necessary. In order to provide the most time and cost efficient solution numerous techniques were applied to meet the requirements for all depths such as Vibrocompaction, VC (depth >8m), Dynamic Compaction, DC (depth < 8m)] and Rapid Impact Compaction, RIC (depth <4m). The specified ground improvement requirements were translated into a target Cone Penetration Test, CPT line that served as the defacto performance requirements for the project. Suitable correction factors were applied to the CPT results to account for the high carbonate content following the works of Al-Homoud and Wehr 2006, Belotti and Jamiolkowski , 1991 and Vesic, 1965. Furthermore, the alpha factor, α, used to obtain stiffness from CPT results was applied following A.C. Meigh 1987 and Massarsch & Fellenius, 2005 where high over consolidation ratios (OCR) could be demonstrated.

Sep 8, 2021

By Yazen Khasawneh, Osvaldo P. M. Vitali, John E. Agee, Mohammad Nassim

A 3D FEM modeling of a ground improvement solution for an ice rink slab with stringent differential settlement limits is presented. Due to the complexity of the geotechnical conditions and strict deformation requirements, a structural slab supported by micropiles was initially proposed. However, this solution was costly and alternative solutions using ground improvement techniques were investigated. The proposed slab is supported directly on rock at one end and on approximately 45-ft deep cohesive soils on the other end. The numerical simulations show that differential settlement would be larger than allowable, if the ice rink slab is supported directly on the existing subgrade. The addition of the ground improvement scheme with compaction grouting demonstrated that the anticipated differential settlements are reduced significantly and would become less than the allowable magnitude. This study demonstrates that the use of numerical simulations to study complex loading and geological conditions will help to optimize designs and may result on significant cost savings.

Sep 8, 2021

By Sina Z. Yekta, Zhangwei Ning, Pierre Frappin

This paper describes a DC (direct current) electrical resistivity method, which uses the contrasts in resistivity measurements to estimate the diameter of jet grouted columns as soon as they have been completed, with varying depth and water table, and without excavation. The measurement procedure is illustrated by several examples of application sites, including the Grand Paris tunneling works during the last 3 years where the method was systematically recommended in quality control for jet grouting works.

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