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By Fred Tarquinio, Giovanni Bonita, Lars Wagner

"A new embassy for the Peoples Republic of China is under construction in Washington, DC. The 475,000 square feet (44,125 m2) structure has five levels below ground and four above, making it the largest embassy in Washington DC. A vertical soil nail wall was used as the primary support of excavation system for the project. The soil nail wall was irregularly shaped, benched in areas, and up to 98 feet (29.9 m) in height. The soil nail and shotcrete system consisted of approximately 1,600 soil nails and 50,000 square feet (4,645 m2) of exposed shotcrete wall surface. Design and construction challenges included soft soil conditions, inside wall corners, underground utilities, seismic impacts from blasting, and logistical and political factors. Overall, wall movements were lower than expected, with maximum horizontal movement less than 0.25% of the total height of the excavation. INTRODUCTIONThe proposed Embassy of the Peoples Republic of China in Washington, DC, will consist of about 475,000 ft2 (44,125 m2) of building space and contain up to four fl oor levels above ground and fi ve levels of basement (Figure 1). When completed, the building will be the largest embassy in Washington, DC. The architect for the project, Pei Partnership Architects, along with the world-renowned architect I.M. Pei, made effi cient use of the site by inserting the building into the existing slope. Consequently, excavations reach heights up to 98 feet (29.9 m) on the southern side of the property and 42 feet (12.8 m) on the northern side.The soil nail and shotcrete system consisted of approximately 1,600 soil nails and 50,000 square feet (4,645 m2) of exposed shotcrete wall surface. The location of the building relative to the property line called for tight excavation requirements, including precise wall positions and shotcrete tolerances. Design and construction challenges included soft soil conditions, inside wall corners, arched walls, underground utilities, seismic impacts from blasting, and logistical and political factors."

Jan 1, 2007

By Clinton O. Rex, Adam S. Hurley, W. Morgan NeSmith

"Hartsfield-Jackson Atlanta International Airport underwent a $1.2 billion dollar expansion project centered on the construction of the new Maynard H. Jackson International Terminal. Passenger access between the new International Terminal and the domestic airport facilities is primarily via underground Automated People Mover (APM) trains. Prior to this expansion, the APM tunnel terminated beneath Concourse E, which previously served all international flights. The new International Terminal is located approximately ½-mile from the previous terminus of the APM tunnel.A paper describing the general approach to excavation support for construction of the entire APM tunnel extension from under Concourse E to the new International Terminal was published by two of the authors (Hurley and NeSmith, 2014). One of the features of note of the approach involved the intersection of the proposed new alignment of the APM tunnel extension under Concourse E with the old terminus. Specifically, the new tunnel extension conflicted with the location of the existing Auger Pressure Grouted (APG) piles supporting four columns in Concourse E. This paper presents design and installation details of the micropile underpinning approach used to support the existing columns to allow for the proposed excavation including the cutting and removal of the existing APG piles, while allowing Concourse E to remain in service during construction.PROJECT DETAILSGeneralThe construction of the APM extension required an excavation support system for a 450-ft long, 55-ft deep excavation across Taxiway Dixie and a 900-ft long, 30-ft deep excavation beneath the basement of existing Concourse E. The excavation under Concourse E required both excavation support and support of the existing columns over the proposed excavation zone. A general overview of the work area is shown on Figure 1."

Jan 1, 2017

By Jon Huff, Jeffrey Donville, Hannah Iezzoni, Dan Stevenson

Occasionally, in the design of deep foundations for a structure, a single deep foundation element may be used to support a building column. The most common type of element used in such cases is a drilled shaft (also referred to as a drilled pier, caisson, or bored pile). However, as installation capabilities have improved, large diameter augercast piles are increasingly more common. While drilled shafts and augercast piles differ significantly in construction methods, in the eyes of the International Building Code (IBC), both are treated as cast-in-place deep foundations and must comply with many of the same code provisions. Deep foundations are required to be braced such that lateral stability is provided in all directions, however isolated, cast-in-place elements that have a diameter (D) of at least 2-feet and a length (L) not more than 12 times the diameter can be an exception. In response to the concerns raised by some member professionals, the Deep Foundations Institute’s (DFI) Augered Cast-in-Place Pile and Drilled Displacement Pile Committee took a closer look at the code and its applications, the historical development of the code language through the years and performed analytical modeling to evaluate the impact of this ratio on a pile’s stability. The question is whether the limiting ratio included in the IBC 2018 code provisions is justified, or whether different criteria should be used to determine when isolated deep foundation members are allowed.

Sep 8, 2021

By Richard D. Luark, Fernanda S. Madrona

Deep foundation construction in highly developed urban settings pose unique challenges of working with deep excavations in a relatively confined area while preserving the integrity of nearby structures. For construction of the below grade parking for two, 40-story residential high-rise towers, shoring walls were required to support the maximum 70-foot-deep vertical excavation in downtown Seattle, Washington. The design of the excavation support system consisted of soil nails combined with closely spaced vertical elements to allow the top row of soil nails to be installed up to 10 feet below the ground surface avoiding conflicts with adjacent underground utilities. To limit deflections next to a seven-story building, the upper rows of soil nails were post tensioned. An instrumentation program was implemented to monitor the deflections in the shoring walls by means of vertical inclinometers and optical survey monitoring. The shoring wall performance, designed to limit deflection to less than 1-inch to meet the City of Seattle requirements, was validated by the instrumentation program. This paper provides a discussion of the design and construction of the shoring walls as well as the monitoring data collected from the instrumentation system. PROJECT INFORMATION The project consisted of two residential high-rise towers, with five levels of below grade parking, located at 707 Terry Avenue Seattle, Washington. The project site covers a half city block, approximately 120 feet by 240 feet, and is bounded by Terry Avenue to the east, Columbia Street to the north, Cherry Street to the south, and an alley to the West. Prior to the development, site was occupied by surface parking. A 7-story concrete building with two stories of below grade parking, owned by the Archdiocese of Seattle is located just west of the 16-foot-wide alley. Numerous below grade utilities consisting of electrical, telecommunications, gas, water, sanitary sewer, steam, and storm drains, surround the project. The perimeter below grade parking walls extended within inches of the property boundaries. Topographic relief across the site was on the order of 8 feet. Figure 1 illustrates the site plan view.

Jan 1, 2019

By Alice Arana, David M. Cacoilo, Joel L. Volterra

"To make space for the new South Ferry Station in lower Manhattan, engineers and contractors carved out a new tunnel beneath three operating subway tunnels and tangentially to yet another tunnel. Creating the space required the design and construction of complex temporary excavation support and underpinning systems and the design and installation of real-time monitoring systems. Construction for the new station and tunnel was mainly cut-and cover in a mixed-face area of soil and rock approximately 2,000 linear ft long, 60 ft wide and up to 70 ft deep. Close coordination between the design/build team and the project owner, the Metropolitan Transportation Authority (MTA), was critical.With the construction of this $400 million project, the MTA and New York City Transit (NYCT) are correcting the numerous physical and operational deficiencies of the existing station and improving the lives of millions of commuters. Built in 1905, the original South Ferry Station is on the IRT Broadway–Seventh Avenue Line of the New York City Subway and is the southern terminal of the #1 subway service, which forms a loop to return uptown. The station has a sharply curved single platform on the outside of the outer track of a two track loop. This platform is short and does not allow the rear five cars of a normal 10-car subway train to load or unload. In addition, once the train stops at the station, commuters wait while retractable floor grates bridge the gap created between the platform and the subway car doors, and then they have only one exit from the station. Spray nozzles keep the tracks lubricated to reduce the train wheels’ friction caused by the tight curve. The sharp curvature of the loop and the inability to use half of the subway car doors slow train operation. With the new ADA-accessible station, 10-car trains will be able to open all doors, and additional entrances, escalators and elevators will greatly reduce travel times."

Jan 1, 2008

By James R. Gingery, Byron Foster, Bret Lingwall

While microzonation and setbacks are the typical mitigation for structures exposed to surface fault rupture hazards, lifelines and lifeline facilities are not easily relocated to avoid faulting. In these cases, other remedial measures including ground improvement may be warranted. Deep soil mixing ground improvement was used in this case to mitigate surface fault rupture and liquefaction hazards for a pump station at a wastewater treatment plant with wet wells up to 36-feet (11-m) deep. Paleoseismic field investigations were performed to characterize the site, then deterministic and probabilistic fault rupture displacement estimates were made and used to develop design scenarios. The fault rupture mitigation design consisted of a solid block of DSM encompassing and protecting the pump station and its wet wells. Three dimensional soil-structure interaction numerical modeling of the fault rupture scenarios was performed as part of the design. The analyses showed the fault rupture displacements could be diverted by the DSM and that satisfactory structure performance could be achieved. The design required construction of a large 100 percent replacement ratio block of DSM with a compressive strength of 500 psi. Aspects of construction of this DSM block are discussed.

Sep 8, 2021

By Min Sunn Ye, Wei Wang, Huawen Xiao, Kai Yao, Fook Hou Lee, Siang Huat Goh

"Previous research have shown that introducing fibers to cement soil mixture is effective in improving the ductility as well as maintaining the strength of cement-treated soil. A good knowledge of stiffness of the improved soil at small strain is essential for realistic predictions of ground movements that may affect adjacent buildings or underlying infrastructure. This paper presents a triaxial system with local strain measurement developed for studying shear modulus degradation of cement treated clay with fibers. Cylinder specimens (70mm diameter by 140mm height) with 50% cement, 100% water, 0% to 1% polypropylene fibers by mass, and 7 days of curing period were used. A local strain measurement system with floating type miniature submersible LVDT is introduced in this paper. Configuration of the mounts including the pin size, length and distance are presented and discussed. Based on the experimental results, a reasonable configuration of the mounts is recommended for fiber reinforced cement treated clay. Results showed that the proposed local strain measurement system is effective for testing the shear modulus degradation of cement treated clay with fibers under both unconfined and confined condition. Comparisons with results from resonant column and bender element tests served to verify the reliability of the local strain measurements using the proposed method.INTRODUCTIONIn many geotechnical engineering problems, the operational strain domain ranges from 10-3% to 10- 1%. A good knowledge of stiffness at small strains is essential for realistic predictions of the ground movements that may affect adjacent buildings or underlying infrastructure. As such, during the last 3 to 4 decades, the importance of using the small strain stiffness of soils for the design of foundation and underground structures has widely been accepted. Triaxial testing has been widely used to study the stress-strain behavior of soil in the laboratory. However, the stiffness obtained from the conventional triaxial apparatus is usually far smaller than those back-calculated from field measurements. This is mainly attributed to the overestimation of axial strains from the external strain measurements, which usually includes compliance effects of the loading and load measuring system as well as sitting, bedding and alignment errors between sample and system (Baldi et al., 1988). The poor resolution of the external strain measurements is another important contribution. Therefore, conventional procedures are inappropriate for small-strain stiffness evaluation due to low accuracy and resolution."

Jan 1, 1900

By Craig M. Shillaber

On any given day, a simple check of the news will turn up stories related to sustainability, resiliency, climate, or human or natural disaster. In recent years, the winter power grid failure in Texas, the Surfside Condo collapse, unsafe drinking water in Flint, Michi- gan, the Oroville Dam spillway failure, wildfires and flooding (to name a few) have appeared in the U.S. news cycle. As a result, young people are aware of the problems and challenges facing the nation and the world and want to be part of creating sustainable solutions for society. Many choose to major in civil engineering because of a desire to make a difference, address climate change, and develop sustainable and resilient infrastructure for the future. Sustainability is at the core of modern civil engineering practice. In its Policy Statement 418, the American Society of Civil Engineers (ASCE) explains sustainability is a set of conditions where human society can indefinitely keep and enhance quality of life without deteriorating economic, environmental and social resources. Sustainability is an integral part of the technical outcomes identified in the ASCE Body of Knowledge and features prominently in the ethical responsi- bilities of engineers based on the latest version of the ASCE Code of Ethics. Thus, to prepare graduates for successful and ethical engineering practice, civil engineering programs must provide instruction in how to account for social, environmental and economic con- straints in design. Since the deep foundations industry is integral to the broader civil engineering and construc- tion fields and is responsible for supporting critical infrastructure on which human society depends, sustainability should be a key con- sideration in foundations projects. Given the importance of sustainability within civil, geotechnical and foundation engineering, it is worthwhile for the deep foundations industry to consider where and how engineers are trained in sustainability topics through higher education at the undergraduate and graduate level, and what is driving sustainability content in civil and geotechnical engineering curricula.

Nov 1, 2022

By Abhirami B., V. Balakumar

Piled raft foundation system is an intelligent geotechnical concept, developed towards reducing the settlement of the raft and the footings by providing pile elements below the raft or footings, as the case maybe. Although a large volume of works has been done on the behaviour of piled rafts by observational studies, the effect of construction methodologies such as deep excavations, the installation methodologies used for piling etc appear to have not been covered adequately. This paper discusses the effect of deep excavations, pile installation techniques and the effect of adding structural elements, based on the data available from published literatures. Based on this study, the performance of the piled raft monitored by the author has been revisited and the results of such a study are discussed.

Nov 1, 2022

By Damir Dedic, Wörle. Patrick

"Soil properties within a construction project area are analyzed during the planning phase. However, it is only possible to achieve selective soil exploration, even in the case of very extensive investigatory programs, which results in a certain soil risk and uncertainties for planning and execution.Therefore, the application of monitoring systems is becoming increasingly important in the field of geotechnics. The application of suitable monitoring systems for these particular purposes provides considerable knowledge relating to the load bearing behavior of the soil and the ground anchor. Applications that present major challenges to measuring anchor forces include back-anchorages of long-lasting and very deep construction pits, construction pits in urban areas, slope and embankment supports for track and vehicular routes, port and lock structures, and uplift control. Apart from overseeing individual construction stages, monitoring systems analyze the interaction between the soil and structure throughout the latter’s entire life cycle and safeguard the functional capability of the applied system components. Geotechnical construction projects can be adapted, optimized and carried out with enhanced safety from the information obtained.Conventional Monitoring SystemsThere are numerous approaches for determining anchor forces of bar or strand anchors. Lift-off tests and measurements with load cells are the most common methods.Lift-off Test: Lift-off tests provide a possibility to monitor the prevailing force in strand or bar anchors. The entire anchor head structure is lifted using the appropriate equipment. The steel tendon is prolonged, or in the case of strand anchors, a screw-on cap holds the wedge carrier so that a tensioning jack can be mounted above it. Then, the tendon is prestressed until the lower anchor nut (bar) or wedge carrier (strand) is lifted off from the anchor plate. The intersection of the two straight lines in the figure represents the force at which the anchor nut or the wedge carrier lifts off from the anchor plate. Thus, the intersection displays the actual load of the anchor. This form of anchor force control gives conclusive results, but at the same time requires extensive accessories and extra personnel to execute the test. For this test, a sufficient bar overhang must be available, the wedge plate must possess an external thread, or there must be a strand overhang of at least 24 in (60 cm). Furthermore, the anchor head must be freely accessible and in a position to be reached with the necessary equipment."

Jan 1, 2017

By Dzianis Proshchanka, Yoshi Izumi, Koji Mitani, Ayuna Kitaura

"A new pile driving and drilling navigation system has been developed. It utilizes the commonly used surveying total station, combined with an innovative reticle. Conventional crosshairs have been replaced by a concentrically circular reticle called Baum. It allows for easily performed measurements of central axes of cylindrical objects such as piles, chimneys, electricity poles, etc. This provides several significant advantages compared to other existing systems. It is cost-effective as only one operator is required to control deviations in positioning and inclination. Furthermore, repetitive reinstallation of the instrument is not required for every pile driven or hole drilled. It is also a safer method, as workers have no need to be near a pile driver or drilling machine to perform the measurements. With Baum Station, necessary measurements can be performed away from the actual work area. Moreover, it is highly accurate with real-time solutions, as three-dimensional orientation information for the pile/drill is obtained simultaneously with the pile being driven or the hole being drilled. This allows for the highest levels of precision-control and correction to minimize eccentricity of the intended center positioning.INTRODUCTIONBackgroundIn foundation construction for structures, pile foundations are widely used for deep bearing strata. There are two patterns to driving piles: vertically or obliquely to the ground. The shapes of the piles are normally cylindrical. Vertical pile foundations are employed as the foundations of many structures due to their high workability. There is a problem however, which is that this method does not bear measurement data as construction accuracy is visually checked. On the other hand, tilted pile foundations are rarely employed because it is too difficult to ensure construction accuracy. In addition, commonly used percussion methods create noise and vibrations when the piles are hit, while there are advantages that thinner piles are available, ensuring earthquake-resistance, as tilted piles curb horizontal displacements of structures, which may be caused by earthquake ground motion. However, current requirements of cost reduction bring professional attention to tilted pile foundations, which can be driven reasonably and economically with much research of tilted piles having been carried out to improve their capacity. Also, a method of screwing piling has been developed, which produces small amounts of noise and vibrations. This method has solved tasks of workability and environmental burdens, and is becoming more and more common. However, there is a necessity to develop a method to accurately measure angles of piles’ axes in order to drive piles into the ground with appropriate angles. It is also expected to find out a way to control construction information, such as correction amount and driving record."

Jan 1, 2017

By Safwan Labanieh

An experimental set-up is specially designed to study the behavior of a friction pile of 3 cm diameter in contact with the soft clay of Mexico City in a small calibration chamber (CC) of 30 cm diameter and 50 cm height. The consolidation of this compressible clay is accomplished using a special system adapted to the CC itself to insure a good knowledge of the initial state. Loading results of the pile under a consolidation pressure of 50 kPa indicate an elastic mobilization of shear stresses at the shaft of the pile (?3 kPa for 1mm displacement) followed by a hardening plastic type behavior. Unloading-reloading results indicate a mobilization of shear stresses of the same type and of the same order of values obtained from the virgin loading stress path. Cyclic loading (?40 cycles) between 0 and 1 kPa (1/3 of the failure value) give similar results to those obtained from virgin loading.

Jan 1, 2002

By Mohammad Ali Rowshanzamir, Mehdi Aghayarzadeh

"This article is an effort to improve our understanding of the performance of geogrid retaining structures (GRS) through numerical analyses. The numerical modeling utilized a commercially available finite difference program, FLAC3D. In this context an extensive parametric study has been carried out on two different GRS walls (vertical reinforced block and inclined reinforced block) to investigate the influence of internal design factors such as soil strength properties and reinforcement stiffness on the performance of these walls. The main purposes of the parametric study were to (1) investigate the sensitivity of the modeling results to the input material properties, (2) examine the influence of the internal design factors on the performance of GRS retaining structures, and (3) improve the internal design of GRS walls on the basis of the working stress information obtained from the parametric study. Based on the analyses results, it was revealed that GRS walls with oblique reinforcement and reinforced block (rotated against natural backfill) have much better performance in terms of reduction in the stresses and strains of reinforcing elements as well as decrease in the wall lateral and vertical displacements in comparison with vertical reinforced block (conventional wall). For example, with 12° inclination of the wall reinforced block there was 50% reduction in the backfill settlement. Also increasing the reinforcement stiffness amount from 10MPa to 50MPa decreases the wall face displacement more than 50% in both GRS walls.INTRODUCTIONOver the past few decades, Geosynthetic- Reinforced Soil (GRS), a soil mass reinforced by geosynthetic layers to restrain the soil lateral deformations, has been employed in the construction of many types of earth structures, including retaining walls, embankments, slopes and bridge abutments. In fact GRS structures are typically more flexible (hence more tolerant to differential settlement), more adaptable to low quality backfill, easier to construct, require less over-excavation, and more economical. Nevertheless, there is a need for an accurate design tool that can predict the performance of GRS structures under working stress conditions and can predict their failure loads as well.Many studies have been published on the performance of the soil reinforced walls such as Isabel et al., 1996; Bathurst et al., 2000; Kazimierowicz-Frankowska, 2005; Nernheim and Bathurst, 2008; Chen and Chiu, 2008 Correia et al., 2012; Erlich et al. 2012. Several numerical studies have also been made throgh finite elements and finite difference techniques on reinforced soil retaining walls to analyze the wall deformations (e.g. Hatami et al. 2001& 2006, Liu and Won 2009, and Abdelouhab et al. 2011). A limited laboratory research has been reported indicating of improving effect of tilting face on GRW performance (Chen and Chiu, 2008). However no major numerical study was found on the effects of face or reinforcement tilting."

Jan 1, 2017

By K. Madhusudan Reddy

Pile response under combined uplift and lateral load is very important and it is imperative to evaluate the effect of combined loading and only few studies were reported on pile behavior under combined uplift and lateral loads. Model pile made-up of aluminum having an outer and inner diameter of 25.4 mm and 19.4 mm respectively is used. Dimensions of the model steel tank are fixed as 1.0 m x1.0 m x 1.2 m (depth) to avoid the boundary effects under combined lateral and uplift loads. Experiments were carried out on single piles at isolated uplift, isolated lateral loading and combined lateral and uplift loading, embedded in sandy soil. Results indicate that load?deflection behavior is nonlinear for isolated uplift and lateral load tests as well as in case of combined loadings. It is also observed that the behavior of piles under isolated loadings is substantially different when compared to combined loading.

By Sitotaw Y. Fantaye

"The first segment of the Second Avenue Subway extension is approaching construction completion. The new extension will operate along Second Avenue from 96th Street to 63rd Street, where it will divert west along the existing 63rd Street line, stopping at the Lexington Avenue/63rd Street Station. The new line will have stateof-the-art stations at 96th, 86th, 72nd and 63rd streets.Most of the two-track, twin-tunnel subway was constructed using bored tunnel methods (Figure 1), with a tunnel boring machine (TBM). The launch and retrieving box of the TBM was strategically located at the south end of the 96th Street Station where bedrock exists approximately 70 ft (21.3 m) below street level. The TBM launch box and the 96th Street Station (Figure 2), including the ancillary facilities adjacent to the station, were constructed by the cut-and-cover method. The cut-and-cover work required the contractor to design and implement a stiff, tightlybraced retaining wall, approximately 100 ft (30.5 m) long, to tie the existing tunnel constructed in the 1970s to the new station, temporary street decking over the entire excavation, and a wide range of excavation support systems at various locations.The cut-and-cover construction posed significant challenges including: installation of street decking on busy Second Avenue, relocation and suspension of the myriad utilities beneath the streets, and configuration of a lateral support system that would minimize movement of adjacent structures but not slow down excavation activities. This article describes the innovative solutions developed to manage and facilitate safe and efficient construction without disrupting Second Avenue, a major southbound one-way thoroughfare.The work was performed in several phases involving: (1) preconstruction condition survey of existing buildings, (2) installation of instrumentation and monitoring, (3) major utility relocation efforts to move vital utilities from within the alignment of the slurry wall on both the east and west sides of the avenue, (4) implementation of maintenance and protection of traffic plans, (5) installation of temporary street decking across the entire avenue and over the excavation to allow an orderly movement of traffic and pedestrians, (6) staged excavation and installation of an intricate temporary bracing system beneath the decking (7) step-by-step construction of the new subway station’s structure and (8) staged removal of the bracing as the structure gained sufficient strength to resist the lateral loads. The main focus in this article is the design and construction of the temporary street decking and lateral bracing systems; the utility suspension system and the north tie-in that allowed the daunting task of excavation and construction of a new subway station in bustling New York City, with minimal disruption to the community, businesses and everyday traffic."

Jan 1, 2016

By Adam Zagorski, Rusty Lucido, Curt Scheyhing

"The current California Department of Transportation (Caltrans) practice based on AASHTO LRFD Bridge Design Specifications is to use the O’Neill and Reese method (FHWA, 1999) for calculating the side resistance and base resistance of Cast-in-Drilled-Hole (CIDH) piles / drilled shafts. In this calculation, end bearing is typically neglected for piles constructed using a wet method due to questionable reliability of end bearing resulting from soil disturbance and inadequate cleaning of the base. Pressure grouting below the tips of drilled shafts in cohesionless soils has long been used worldwide to provide reliable end bearing capacity, but for decades it was relatively unused in this country. It has been used increasingly in the United States over the last decade. Before this project tip grouting has not been utilized on or accepted by Caltrans to maximize piles end bearing capacity. This project proved that tip grouting to mobilize reliable base resistance can be successfully implemented on a full-scale bridge project requiring over 350 large diameter shafts.For the Gerald Desmond Bridge Replacement Project, Shimmick/FCC/Impregilo, JV utilized a temporary Oscillator casing to the full depth to install CIDH piles. Piles were constructed by the wet method and then pressure grouted below the pile tip. A tip grouting procedure for these large diameter shafts was developed and tested to specifically address the geology and constraints of the project. This procedure was then proven during the Load Testing of test piles during the Test Shaft construction phase of the project. Tests showed a minimum reliable base resistance of 150 ksf could be mobilized in very dense sand at a downward movement of 5% of the pile diameter for piles ranging from 4.9 to 8.2 feet in diameter. By tip grouting, the length and diameter of the piles were significantly reduced."

Jan 1, 2017

By Lorie M. Dilley

Alaska Village Electric Cooperative (AVEC), an electric utility cooperative providing power to 51 Alaska villages, has made a concerted effort to install wind turbines in the villages they serve in an effort to mitigate the growing costs of electrical power generation. The subsurface soils in several of these villages consist of sands and silts with ground temperatures of between 30°F and 32°F. The presence of warm, degrading permafrost in three of the villages has required innovative foundation designs, including the use of helical piers and piles to support steel and concrete wind turbine foundations. The design of the deep foundations had to account for the effects of degrading permafrost likely resulting from observed climate change patterns. Uplift forces imposed on the foundations were approximately 100 kips per pile. Uplift pile load testing was conducted on the installed piers and piles in order to determine the actual working load that each pier or pile could sustain. In addition, pile driving analyzer testing was conducted on several piles installed in the permafrost and compared to pile load tests. Results indicated that the installed piers and piles achieved the necessary capacity with sufficient factors of safety. Thermosyphons were installed near the foundations in order to limit the effects of climate change on the permafrost. The two to four wind turbines in each of the three villages are currently operational. Refinement of the design based on the pile testing from the first village to the third has decreased the cost of the tower foundations and improved our understanding of designing for warm, degrading permafrost.

Jan 1, 2010

By Kazunori Matsushita, Masaru Sakakibara, Kenji Harada, Naotoshi Shinkawa, Mitsuo Nozu

The Sand Compaction Pile (SCP) method has been widely used as a typical countermeasure against liquefaction in Japan, and its effectiveness has been confirmed in many case histories of damages caused by the past large-scale earthquakes. A series of studies were conducted to evaluate the effectiveness of the compaction method and other factors, if any, in sustaining a seismic force that is greater than the assumed one and caused no damage. Based on the results of these studies, the Architectural Institute of Japan (AIJ) has indicated in its “Recommendations for Design of Ground Improvement for Building Foundations” published in 2006 that the liquefaction resistance ratio (tl/sz) of the composite ground, which consists of sand piles and surrounding compacted ground, is higher than the RL calculated by using the SPT N-values of the ground in-between the sand piles. In this paper, statistical analysis of safety factor against liquefaction, FL, was performed by using the SPT N-values of ground in Port Island and Rokko Island which were both fully reclaimed islands in Kobe city during the 1995 Hyogo-ken Nambu Earthquake (classified as intense shaking) and, together with the consideration of relative settlement, resulted in tl/sz of the composite ground being 1.5~2.5 times of tl/sz of the soil in-between piles after improvement. Furthermore, the liquefaction resistance curve of SCP-improved sites obtained from the relationship between SPT N-values and cyclic shear stress ratio during the 2011 off the Pacific Coast of Tohoku Earthquake, which was regarded as long-duration earthquake, was plotted to the left side of the curve originally proposed by Japan Road Association. Thus, the liquefaction resistance of the improved ground was found to be higher than that of the natural ground, even for the same SPT N-values, verifying the validity of the AIJ recommendation.

Jan 1, 2017

By George Filz, Morales, Carlos, Bertero, Filippo Maria, Alessandro, Leoni

"The Deep Mixing Method (DMM) represents a viable solution to improve adverse geotechnical properties of foundation soils for many practical applications. A pre-construction soil investigation campaign is necessary to assess soil properties and to retrieve samples of different soil layers for a laboratory Bench Scale Testing program (BST). The BST has to be designed using various binder types, binder contents, and water/cement ratios in each of the soil types. Following the laboratory program, a full scale Field Test (FT) is typically necessary to verify the results of the BST. This paper will highlight the differences and the importance of performing both pre-construction laboratory tests and field tests to ascertain the proper mixing parameters in the different soil layers. Comparative analyses and interpretations between the lab and field stages, along with accumulated information about soil properties and quality control (QC) results, allow fine-tuning the production parameters throughout a project. Three Deep Mixing Method projects, where both laboratory and field tests were executed, are illustrated: (1) The LPV 111 Project (New Orleans, LA, USA): DMM was used for ground improvement/foundation strengthening to stabilize and support the burden of a new levee raise; (2) The Rio Puerto Nuevo Project (San Juan, PR, USA): DMM was applied to improve the soils adjacent to a 90"" forced sewer main relocation and to improve the soils for the base of a new drainage channel; and (3) State Road 83 (US 331) over Choctawhatchee Bay project (Walton County, FL, USA): DMM was applied to stabilize the causeway sections of the bridge enhancement project. Data recorded during laboratory and field tests for these projects were analyzed and interpreted to select the most appropriate construction parameters to provide a final high-quality product.INTRODUCTIONThe Deep Mixing Method (DMM) represents a viable solution to improve adverse geotechnical properties of foundation soils in many situations. The effectiveness of working parameters depends largely on the physical and mechanical properties of the soil to be treated. Therefore, well designed laboratory and field test programs, aimed to disclose the interaction between the site-specific soils and the mixing parameters, are essential to achieve the desired end product.Generally a pre-construction soil investigation campaign has to be performed to assess soil properties and to retrieve samples of different soil layers for the laboratory Bench Scale Testing programme (BST). The BST has to be designed using various binder types, binder contents (or cement factors - CF), and grout water/cement ratios (W/C) in each of the soil types; the selection of the different combinations and dosages for the BST is based on past extensive experiences on similar materials. Following the laboratory programme results, a full scale Field Test (FT) has to be designed and executed, installing several DMM elements to verify the results of the BST and fine tune the construction parameters, with the appropriate binder type and dosage and the most effective equipment and tool configuration."

Jan 1, 2015

By Paul Doherty

It is known that the axial capacity of a displacement piles installed in clay varies with time. Consolidation theory suggests that dissipation of porewater pressure set-up during pile installation would lead to increased effective stress and hence higher pile resistance. In recent years a number of case histories have reported time dependent capacity increases for piles installed in sand. Although there is some debate regarding the physical mechanisms controlling this phenomenon, known as ageing, it is unrelated to pore pressure dissipation as piles in sand are installed in primarily drained conditions. A series of field tests designed to investigate ageing effects in soft clay are presented in this paper. Full-scale load tests on 6m long 250 mm square concrete piles, which were driven into soft clay are described. The piles were first tested approximately 100 days after installation, at which stage full equalization of the excess pore pressures had occurred. Static load tests were then performed up to 10 years after pile installation. The piles exhibited significant ageing, with their shaft resistance increasing by up to 66% over a 10 year period. Possible mechanisms for such aging characteristics are explored.

Jan 1, 2011