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By John D. Thornley

Alaskan villages typically store a one-year supply of fuel to reduce significant delivery costs. Alaska Village Electric Cooperative (AVEC), an electric utility cooperative providing power to 51 Alaska villages, has made a concerted effort to upgrade and improve their undersized and aging facilities. The Village of Stebbins, located south of Nome on Norton Sound is receiving upgrades to its AVEC bulk fuel facilities. Stebbins offered unique challenges from a foundations perspective due to the nature of the soil. The geotechnical investigation found the soil below roughly a third of the footprint of the bulk fuel facility to be thawed with seasonal freezing and the remainder was found to be warm permafrost with ground temperatures of between 30°F and 32°F. This is a unique and challenging arctic engineering design issue because foundations are designed differently for frozen ground conditions. Driven piles were selected because of site constraints, such as the design flood elevation and the change from thawed to frozen ground conditions. The pile design specified that the pile embedment depths would be selected based on the results of pile driving analyzer (PDA) testing during construction in the thawed ground and maintained within the frozen ground portion of the footprint. Difficulties during pile driving in the frozen ground resulted in several piles becoming severely damaged, requiring subsequent removal. This resulted in a reevaluation of the means and methods for pile installation. Additional fieldwork was performed to further characterize the subsurface soils and their frozen nature. Options for installation of piles in difficult areas were evaluated including ground thawing, predrilling, and reducing embedment depths. Presented within this paper are the findings from the initial and subsequent field explorations, discussion of the design methodology, and the decisions that led to successful installation of piles at this challenging remote village.

By Moritz Schleeh, Christian Moormann

Temporary working platforms are generally required in order to ensure that heavy construction machinery such as drilling and trench wall units, pile drivers, vehicle and crawler cranes can be set up safely at the site of operation. Considering all possible operating and loading conditions, especially on ground of low shear strength and stiffness, the design and construction of temporary mobile working platforms needs to be considered more as a serious engineering task than as a second order structure of minor relevance. Working platforms reinforced with one or several geosynthetic layers have proven to be especially effective with regard to stability, serviceability and durability but their design requests even more sophisticated approaches. Existing design models are often based on simplified assumptions and do not consider the complex interaction between construction machinery, working platform and subgrade. Non-monotonic loading as well as elastoplastic and time-variant deformation of cohesive subsoil can adversely affect the base layer system and the serviceability and stability of the construction machinery operating on it. In this context, there is a need for improvement of design approaches and their optimisation considering that there are no generally accepted design approaches or technical codes of practice available for the design of temporary working platforms. The present paper deals with the multifaceted and non-trivial interaction effects of working platforms investigated by model tests, field measurements and numerical simulations to develop a design approach that ensures a safe installation and operation of heavy plants on unstable ground.

May 1, 2022

By Donald T. Robertson, Kurt Hecht, Michael K. Muchard

"This paper presents case histories of driven concrete pile damage detected with dynamic testing methods utilizing strain gages and accelerometers embedded in the pile at the prestressing yard during pile construction. Data from the embedded instrumentation is compared with data taken with external bolt on instrumentation and other test methods such as low strain testing on the same pile. In the most severe cases, the piles were extracted revealing and corroborating the embedded data collector results.INTRODUCTIONDynamic testing of driven pile foundations was originally developed in the late 1960’s and commercialized in the early 1970’s. While the methods of analyzing dynamic test data have improved with the advancement of computer technology, the test method and the sensors used to acquire the data have changed little. In 1998, under a research grant provided by the Florida Department of Transportation, (McVay et al, 2002) an Embedded Data Collector system (EDC) was developed. The collector utilizes two sensor packs, each consisting of one strain gage and one accelerometer, embedded near the pile toe and pile top. Utilizing the toe sensor pack, the system provides reliable real time pile end bearing capacity measurements. This end bearing capacity is combined with a Case Method Solution augmented with an automatic damping calculation to provide the overall pile capacity, pile skin friction capacity and pile end bearing capacity. Also, since the gages are embedded, they have the ability to track all changes from the casting yard (i.e. prestress), driving, and subsequent setup (freeze, relaxation, etc) at both the top and bottom of the pile."

Jan 1, 2017

By Soorkty Elarabi

The aim of this paper is to discuss the impact of end bearing plate on the capacity of micropile. Preliminary studies have been made in Sudan in specific area of cohesive soil. Experimental works were carried on a number of micropiles with and without end bearing plate. Same diameters, lengths and techniques of placing cement grout are considered, there after the axial load test applied to find out the capacities of micropiles in both cases. Deduced results in each case show that the end bearing plate has no positive impact on micropile capacity.

Oct 1, 2022

By Andrew Z. Boeckelmann, David S. Graham, Paul J. Axtell

In the last fifteen years, several research studies have evaluated the ability to detect various types of deep foundation concrete integrity flaws with crosshole sonic logging (CSL) and thermal integrity profiling (TIP). This paper synthesizes the findings from the research, focusing on two studies that included CSL and TIP testing of drilled shafts with various types of flaws. The first, a 2016 research study of test shafts for the Wisconsin DOT, included inclusions inside and outside the reinforcing cage, intentional tremie withdrawal during concreting, and soft bottom flaws. The second, a 2021 study of production shafts for the Missouri DOT, included one shaft with and another without soft bottom conditions. After synthesizing the ability of each test method to detect each type of flaw, the paper presents recommendations for improving how CSL and TIP results are evaluated in practice. The recommendations highlight DFI‟s CSL interpretation protocol as well as the importance of evaluating TIP data versus time, not just depth. The paper includes example temperature-versus-time plots for various types of flaws and emphasizes how temperature-versus-time evaluation can be used to distinguish soft bottom conditions from standard bottom-of-shaft temperature roll off.

Oct 1, 2022

By Sylvia S. Eskander, Sherif S. AbdelSalam, Mona B. Anwar

Expanded Polystyrene (EPS) geofoam has long been used in numerous geotechnical applications due to its lightweight and durability. Among these applications is the use of EPS as an alternative fill material to conventional roadway soil embankments. This study investigates the benefits of using EPS roadway embankments to reduce the induced stresses and strains on the underlying peat and soft clay. Firstly, mechanical and interface properties of the EPS were acquired from a companion study that also considered the cyclic loading and creep effects. In order to determine the actual stress-strain distribution within the EPS blocks, a physical prototype was developed in this study with overall dimensions of 1.2 x 1.0 x 0.5 m, with a density of 35 kg/m3. The prototype EPS blocks were subjected to cyclic loading with intensities ranging from 10 to 50 kN. Then, a numerical model was developed to simulate the behavior of EPS roadway embankments. The numerical model outcomes were verified against the prototype measurements. A parametric design study was also conducted to develop a correlation between EPS embankment height and the stress-strain that occur in the underlying strata. Results showed that EPS embankments could reduce stress and settlement in the underlying soil by about 40% and 54%, respectively. EPS APPLICATIONS AND BACKGROUND Expanded Polystyrene (EPS) geofoam blocks have been effectively used during the past several decades in numerous geotechnical applications. EPS static and dynamic properties as well as interface behavior were extensively characterized in various published studies such as that conducted by Horvath, 1994; Stark et al., 2004; Zarnani and Bathurst, 2008; Trandafir et al., 2010; Athanasopoulos et al., 2012; AbdelSalam and Azzam, 2016; and others. However, to be able to use locally produced EPS blocks, its physical and mechanical properties must be thoroughly determined. The lightweight and compressible material of EPS geofoam makes it suitable both as a backfill and for absorbing pressure in both the vertical and horizontal directions. Kim et al. (2010) adopted EPS as an alternative for soil backfill around buried pipes; their model showed a reduction in the vertical stress acting on the pipes by up to 36%. Oshati et al. (2012) presented a case study of a field-instrumented box culvert with EPS blocks on top, which reduced vertical stress by 58%. Meguid et al. (2017) used an EPS inclusion to surround culverts and achieved up to 72% stress reduction, depending on the EPS density and the culvert depth to width ratio. AbdelSalam et al. (2017) used a relatively thin EPS inclusion behind flexible cantilever retaining walls, verifying that the lateral pressure can be significantly reduced by 25%; they also developed a design chart for this application. Moreover, AbdelSalam et al. (2019) investigated the use of EPS as a lightweight alternative for soil backfill above shallow tunnels. It was found that EPS had created a differential movement between the wedge located above the tunnel and the neighboring soils, which accordingly reduced the vertical stress acting on the tunnel by 85%, due to the use of lightweight EPS material and positive soil arching.

Jan 1, 2019

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

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 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 Noreen Tarac, Pablo Forgoso, Philipp Schober

A multiple use storage facility building is being developed in the Philippines on a peninsula that was reclaimed in the 1990s without any soil treatment. The subsoil now consists of loose to medium dense silty sand underlain by a soft to medium stiff clay. A liquefaction assessment by analytical methods have shown that the loose to medium dense silty sand yields a high potential for liquefaction and lateral spreading during pthe design level seismic event. To mitigate the risk of liquefaction and lateral spreading, as well as assure the slope stability of the shoreline, a solution utilizing a combination of ground improvement techniques by means of a Mixed-In-Place (MIPTM) Lattice Grid Wall and Stone Columns was developed and successfully executed. For the detailed seismic design, a Finite Element 3D analysis was undertaken to simulate static and dynamic actions on the buttress wall. The liquefaction assessment and settlement calculation were carried out based on analytical design approaches. For the execution of the Lattice Grid Wall, the Mixed-In-Place (MIPTM) method developed by BAUER Spezialtiefbau GmbH was applied. The stone columns were installed using the Wet Top Feed method.

Sep 8, 2021

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 Matthias Pulsfort, Jiarui Du, Torsten Wichtmann, Achim v. Blumenthal, Diethard König, Rowena Verst

The influence of the interaction between support fluid and soil, e.g., filter cake formation, on the shear stress transfer in the soil-concrete interface of diaphragm walls and bored piles is still controversially discussed. Actual research on the soil-concrete interface using bentonite suspensions indicates that shear stress transfer is underestimated by existing standards. Investigations on the soil-concrete interface using polymer solutions are rare. Therefore, complementary field investigations and systematic laboratory studies were conducted to analyse the soil-concrete interface using both bentonite suspensions and polymer solutions. Thickness and composition of real-scale filter cakes were investigated on several slurry wall construction sites, where bentonite suspensions were used. Direct shear tests (60 mm x 60 mm) were executed for soilbentonite mixtures with varying amounts of bentonite and different granular fines representing a realistic bandwidth of in-situ filter cake compositions. Larger direct shear tests (300 mm x 300 mm) with preceding horizontal penetration, subsequent vertical tremie concrete placement, and filter cake consolidation were performed using both bentonite suspensions and polymer solutions. The results support the view that shear stress transfer in the soil-concrete interface can be described by a wall friction angle in a range of 25° to 30° for bentonite suspensions and between 35° and 40° for polymer solutions in non-cohesive soils.

May 1, 2022

By Dan Yang

Pile foundation designs are performed routinely based on geotechnical information available at the time of design, often with due consideration of large uncertainties inherent to soils and site conditions. These uncertainties frequently are the causes of piles being installed not the same as those designed, especially by factors beyond quality assurance and quality control. With a variety of both satisfactory and unsatisfactory pile test results from these nonconforming piles, the design engineers are required to examine the foundation performance as a whole against the project design requirements before signing off on them or calling for potentially costly remediation. Over the years, as-built analysis has been a consistent way of dealing with pile non-conformity and damage in our practice, avoiding many construction delays and it is an integral part of our pile foundation design. In this paper, the key elements of an as-built analysis along with several major bridge projects are presented.

Jan 1, 2010

By Brian Koch

Michels installed 242 drilled shafts to support the piers for a new basket-handle, true-arch twin bridge across the Mississippi River from Moline, IL to Bettendorf, IA. The installation of the drilled shafts was completed with the simultaneous use of two Liebherr LB36 and one IMT 300 drill rigs. Utilizing barges, 233 drilled shafts were installed in the river. Michels crews also installed 7-ft to 10-ft permanent steel casing into the bedrock, and drilled to depths of 60 feet for each shaft. Despite working in strong currents, freezing temperatures and on rocking barges, Michels crews placed the shafts within 3 inches of plan position. Since the drilled shafts are the key piece in supporting the bridge structure, Michels provided cross-hole sonic logging to verify the integrity and strength of the concrete within the shafts and to add another level of quality control for the owner/customer. Extensive planning took place each day to ensure that tugboats, the linchpin of the project, were being efficiently utilized to shift the barges and materials daily. On any given day, Michels transported five concrete trucks by barge from shore to shaft sites to pour between 40 and 240 cubic yards of concrete. The Michels environmental team was diligent with preparing, discussing and implementing a water treatment plan that was accepted by all state and federal agencies and adhered to strict environmental regulations. Grain hopper barges were rented to control and treat the water that was used in the drilling operations. Another challenge crews ran into was the discovery of caverns when drilling into some parts of the bedrock. Michels worked with the engineer to develop a plan to construct the drilled shafts that encountered the caverns.

Jan 1, 2019

By Stefano Pirrello

"Sydney’s booming real estate market has pushed property developers to invest in historically “no-go” areas, which were previously too expensive to develop. These areas are usually near rivers where the sites are underlain by deep alluvial and estuarine sediments. In these ground conditions conventional bored pile techniques are often not competitive. Contiguous Flight Auger (CFA) and Drilled Displacement Piles (DD) techniques are on the other hand suitable for these ground conditions. This paper deals with the design and construction challenges encountered with these piling techniques for a series of high-rise towers in Sydney’s West. The advantages of DD over CFA piles such as reduced overall spoil with substantial cost savings and achievable rock sockets in medium strength bedrock are discussed. Design validation through interpretation of real-time data from the piling rigs’ on-board computer data, and low and high strain pile dynamic testing (PDA) is discussed. Testing data is presented as CAPWAP (Case Pile Wave Analysis Program) analyses for different concrete grades.INTRODUCTIONThe booming real estate market in Sydney has pushed property developers in investing in historically “no-go” areas, which were previously too expensive to develop. These areas are usually near rivers where the sites are underlain by deep alluvial and estuarine sediments. In these ground conditions conventional bored pile techniques are often not competitive. Contiguous Flight Auger (CFA) and Drilled Displacement (DD) Pile techniques are on the other hand suitable for these ground conditions and were utilised using concrete injection methods. This paper deals with the design and construction challenges encountered with these piling techniques for a series of high-rise towers in Sydney’s West.GEOLOGY & GEOTECHNICAL CHARACTERIZATION OF THE SITEThe Sydney 1:100 000 Geological Series Sheet shows that the site is underlain by man-placed filling and alluvial/estuarine sediment. The sediment comprises silty to peaty sand, silt and clay. Shell layers are also expected to be present within the soil profile. The Prospect/Parramatta River 1:2500 Acid Sulphate Soil Risk Map shows the site as ‘Disturbed Terrain’ in which soil investigations are required to assess acid sulphate soil potential. Several Cone Penetration Tests and Boreholes were carried out during the geotechnical investigation. All boreholes were extended to bedrock and NMLC-sized diamond core drilling was used to obtain 50mm continuous core of the rock, enabling unconfined compression strength testing to be carried out on selected samples. A summary of the ground conditions encountered on this site and inferred from the CPTs can be described as follows:"

Jan 1, 1900

By John S. Civetta, Seth Martin, Marc J. Gallagher, Arthur J. Alzamora, Ronald Peralta

The Crown Building, built circa 1921, is a 26-story iconic building located at West 57th Street and Fifth Avenue in the heart of Manhattan. The paper highlights collaboration between the geotechnical engineer and foundation contractor to develop economical and practical solutions to foundation design and construction challenges associated with this complex redevelopment project. The project includes both below-grade and above-grade expansion of the occupied building, and required undermining the existing foundations, and essentially doubling the foundation loads. The below-grade expansion required surgical foundation work including drilling minicaissons, shoring columns, underpinning, and excavating 20 feet of rock.

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 Lucian Bogdan

On many occasions during construction and service life of the structure, it is crucial to know the load in post tensioning tendons and anchors. Although there are many methods to measure the tendon force, most of them are cumbersome, expensive and the accuracy differs depending on the method used Dyna Force sensor uses the Elasto-magnetic technology (EM) and non destructive testing (NDT) to direct measure stress level in prestressed strands or bars installed on ground anchors or post tensioning tendons. Dyna Force sensor can be used to rapidly read the change in load during proof and performance tests and compare with the pressure gauge and during the life on the anchor to monitor existing lock-off load. It can be used also to determine the load along the bonded length of the anchor allowing the contractor to increase or decrease this length. The paper presents Dyna Force operating principle and some applications. In conclusion, the Elasto magnetic technology applied through Dyna Force is a new and easy to use approach to monitor anchor load during proof test and service life of the structure.

Jan 1, 2009

By Andy Boeckmann

In early 2021, DFI formed a Foundation Reuse Task Force due to concurrent and coincidental discussions of this topic during meetings of the Subsurface Char- acterization for Deep Foundations and Testing and Evaluation committees. Interested members from both commit- tees, as well as of the Sustainability Com- mittee, joined forces to form the task force. The task force mission is to promote foundation reuse by leveraging experi- ence among DFI members and collabo- rating across pertinent committees. General goals of the task force are to identify, assess and reduce risks associated with reuse; to educate owners and decision-makers about reuse; and to improve the investigation, design, construction and testing practices associated with reuse. One of the first orders of business for the task force was to organize a roundtable discussion of foundation reuse for DFI's 46th Annual Conference on Deep Foundations in Las Vegas. Last fall's discussion was framed as a continuation of the successful "Horses for Courses" session of SuperPile '21, which also focused on foundation reuse. However, whereas the SuperPile session focused on technical content, the annual conference panel on October 13, 2021, was envisioned as a less technical conversation that emphasized audience participation while addressing approaches to decisions about foundation reuse issues. The roundtable consisted of five panelists: • • • Bryan Hartnagel, Ph.D., state bridge engineer, Missouri DOT (MODOT) Tom Bradley, project director, Stanhope, London Hilary Shields, senior geotechnical engineer, Arup, London Jim Mackey, vice president/chief marketing officer, McGee Group, London Susan White, attorney, Benesch, Cleveland The roundtable was moderated by Andy Boeckmann, Ph.D., P.E., a senior engineer who works in Dan Brown and Associates' Missouri and Illinois offices, and is an article co-author.

Feb 1, 2022

By David Sherwood

The paper has been prepared as the basis for the 2008 John Mitchell Memorial Lecture. It reviews major developments in ground engineering over the last 20 years, not from the point of view of technical processes, but from the drivers that have driven these developments and the needs that they have met. It concludes with a glimpse into the future and suggests to where current trends will probably lead us. By its nature such a review is closely aligned with personal experience and it relies heavily on case histories largely from within the writer?s own experience over that period.

Jan 1, 2008