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By Hector Simchas

"1. BENTONITE: THE CRUCIAL CONSTITUENT OF SLURRYSuspensions of bentonite and water are used in a variety of applications in underground engineering. For the construction of underground elements like slurry walls or piles, bentonite slurries offer support to the excavation of loose soils and counter pressure against hydrostatic pressure of ground water, especially where soil permeability is high. In addition, for the construction of tunnels by the slurry-shield method or when hydromills are used for excavation, bentonite suspensions transfer the loosened soil to the surface. In applications like pipe jacking and microtunneling, or where high revolution drilling is required, bentonite also provides lubrication and cooling.To fulfill these functions, the properties of a bentonite slurry need to remain stable, or at least predictable, during the course of construction. Unfortunately, when a suspension mixes with earth, ground water and/or impurities, its properties may be compromised resulting to reduced performance, which would in turn lead to increased construction costs and the risk of the excavation collapsing. Our experience in the lab and onsite is presented herewith.2. MOST USUAL FACTORS OF PERFORMANCE FAILUREWater and soil quality are important factors defining the behavior of suspensions. In an extensive program of measurements in our technical laboratory, the effect of frequently encountered harmful substances on bentonite suspensions has been examined and the results are summarised in Table 1.Some tests show that the conductivity of water has a direct relationship with Marsh Viscosity. For example, we have seen that if the quantity of bentonite required to achieve a 40s Marsh Time ranges between 50-52 kg/m3 at water conductivity below 100 µS/cm; when conductivity is increased to 1,400 µS/cm, we need 65-68 kg/m3 in order to achieve the same property."

Jan 1, 2015

By H. (Sam) Salem

A site investigation for a wide and tall hotel building, in the San Juan Bay area, Puerto Rico, indicated a soil profile of silty clay on sand, soft and loose enough to require piled foundations. The apparent uniformity of the soil profile across the site indicated that a single pile driving and termination criterion could be applied to the installation of the piles ? driven precast concrete piles. Because of the size of the site and importance of the project, the project also included a static and dynamic testing programme. The dynamic monitoring using the Pile Driving Analyzer (PDA) verified a consistent hammer operation. However, the results of the static loading tests showed significant and inconsistent variation in pile capacity between locations and little correlation between end-of-driving and restrike penetration resistances (blow-counts) and pile capacity. Therefore, it was not possible to rely on a simple depth and blow-count termination criterion for the site. In contrast, pile driving response in terms of measured reflected force and mobilized resistance coupled with CAPWAP analysis gave a reliable correlation to the results of the static loading tests. As presented in the paper, the dynamic testing programme was enlarged and used to develop and verify a complex set of termination criteria tailored for the multitude of conditions encountered across the site to achieve and ensure economical and safe pile installation.

Jan 1, 2008

By Jeffery L. Ottesen

Early construction delays can jeopardize timely completion of subsequent work. As an early construction activity, and due to many unforeseen issues, deep foundation work inherently bears great potential for impacting the critical path of a planned construction schedule. This article describes two construction projects where delays related to deep foundation work forced the Contractor to consider various schedule recovery alternatives to mitigate those delays. Specifically, deep foundations on Vancouver BC's Millennium SkyTrain light rail extension and on a Mill Facility in the United States are discussed. This article cites examples of permitting delays, alleged design changes, differing subsurface conditions and changed construction methodology, the effect each problem had on the project, the mitigation means implemented by the Contractor to minimize adverse impacts of the problem, and Lessons Learned for each scenario.

Jan 1, 2002

By Kento Miyamoto, Kazuki Imamura, Takayuki Tanaka

"Global economic development has drastically increased energy consumption in various fields, and CO2 emissions, which are a prime cause of global warming, have continued to increase. Therefore, measures for reduction of the load on the environment have been taken in various areas. Energy improvements of various types of work vessels used for offshore construction might be expected to greatly reduce consumption of fossil fuel, because many of these vessels are larger than land construction machinery and consume large amounts of fuel, which will lead to effective use of resources and alleviation of the load on the environment. However, such efforts are unusual because renewal or newbuilding of work vessels is rare. We developed a work-vessel hybrid energy system based on fuel-saving technology and use of natural energy to promote reduction of CO2 emissions for a large deep mixing barge in 2010. We developed an Automated Generator Start-Stop System, which automatically controls the number of active generators according to power demand during ground-improving work of the deep mixing barge in 2012, thus further improving the work-vessel hybrid energy system. These systems are introduced here.INTRODUCTIONIn recent years, CO2 emission, which is one of the factors of the Global Warming has been increasing. According to the report by National Institute for the Environmental Studies in Japan (2014), CO2 emission in Japan has amounted to 1,276 million tons. The industrial sector in the total emission becomes 500 million tons that is equivalent to 39%. Meanwhile, the offshore Deep Mixing Method requires work vessels mounted with a large power plant (Fig. 1). In sea ground boring, very large load acts on the deep mixing machine, and the large power is required, which results in the increase in CO2 emission. To achieve eco-friendly marine construction, the work-vessel hybrid energy system was developed. Table 1 shows specifications of the deep mixing barge with the work-vessel hybrid energy system."

Jan 1, 2015

By Rajesh A. Vaidya

A large scale piling work is undertaken in India for an important fast track industrial project. Thousands of solid square precast concrete piles are driven to depths of around 50m. Soils encountered are of alluvial origin with very soft clays varying in thickness from 10 to 18m at the top followed by medium dense to dense and occasionally very dense sand, stiff clay and finally dense to very dense sand layer as the founding layer. Recent site grading with around 4 metres thick hydraulically filled river sand necessitated driving the piles to the bottom sand layer to avoid problems on account of negative skin friction and to achieve optimum pile capacity. A process approach suggested by Bell et al (2002) to promote better understanding of the pile behaviour, pile capacity, and parameters assumed at design stage for static capacity and for wave equation analysis is followed with an aim to bring in effective economy in terms of pile length and pile installation speed. Soil investigation work is also undertaken in stages to cut down pile wastage. A judicious combination of PDA and static pile load tests is followed. Pile Driving Analyser (PDA) tests at end of driving and also at various stages of recovery of pile capacity are carried out to understand the pore pressure dissipation phenomenon. The paper attempts to present some of the valuable experiences that would go to establish precast pile as a very effective alternative to driven cast-in-situ piles and bored piles which are very common in this part of the world despite their limitations in terms of economy, speed and certain geotechnical aspects.

Jan 1, 2007

By R. K. M. Bhandari

Geotechnical investigation for a LPG plant located in Assam state - an area of high seisimicty - revealed a layer of loose to medium silty sand susceptible to liquefaction at some depth below the finished ground surface. Liquefaction analyses were carried out using simplified Seed's approach as well as considering the progressive buildup of pore pressures with cyclic earthquake loading. Seismic settlements were computed for areas where the analysis indicated partial liquefaction. Pile foundations in areas where complete liquefaction was indicated, were treated with gravel drains to prevent buildup of pore pressures. The paper presents and discusses the liquefaction analyses, effect of non-liquefiable overburden soil on the liquefaction potential of the silty sand and the remedial measures that have been taken to ensure safety of the pile foundations in transmitting vertical and lateral loads.

Jan 1, 1996

By Wanchai Teparaksa

Pile deviation generally can happen after installation of driven pile particularly in soft soil layers. In this case study, all 242 diameter 0.8 m spun piles were deviated from 20 to 820 mm. The large deviation was caused by lateral soil movement in the top very soft clay layer of thickness about 23 m. This very soft marine clay is very sensitive and anisotropic having high water contents of over 120% and low undrained shear strength of 5-10 kN/m2. The remedial works were carried out based on theory of load transfer and soil-structure interaction. All deviated piles were rectified and used as the foundation piles with strictly controlled pile load tests. The construction of a nine-storey building was successfully completed founded on the rectified piles and it has been opened for the service for over two years.

Jan 1, 2002

By Kam Ng

For bridges or buildings that may be subjected to large vertical and lateral loads, drilled shafts offer an economic foundation solution. While the current drilled shaft design practice is considered adequate, introducing a performance-based approach to designing the drilled shafts will make their design more cost-effective and produce more dependable response. This concept was examined using analysis of 41 drilled shaft load test data from several states. This process identified the challenge with the lack of information from the Osterberg (O-cell) load test method to characterize the full top load-displacement response. When a typical single O-cell is utilized in a drilled shaft test, depending on the location of the O-cell and the geomaterials present along and beneath the shaft, the load test result typically quantifies either the side resistance or end bearing reaching the ultimate load-displacement curve but not both components. This limitation hinders the determination of a suitable shaft resistance as a function of a target top displacement. To overcome this challenge, an improved procedure is proposed for establishing the full load-displacement curve based on data gathered from one O-cell. The method will be presented in the paper for three different cases (i.e., side resistance reaches the ultimate during the test, end bearing reaches the ultimate during the test, and neither components reach the ultimate values). Because it allows the characterization of the full load-displacement curve, the proposed procedure will allow performance-based design of drilled shafts with due consideration to settlement while satisfying the Load and Resistance Factor Design.

Jan 1, 2013

By John A. Egan, Nathaniel Wagner, Micaela Largent, Jonathan P. Stewart, Debra Murphy, Jeremy Butkovich

The Millennium Tower is a 58-story reinforced concrete building that was constructed in San Francisco, California between 2005 and 2009. The Tower is founded on an embedded pile supported mat with pile tips bearing in dense marine deposits that overlie an over-consolidated marine clay layer known locally as Old Bay Clay. This clay layer experienced stress increases from Tower self-weight and from multiple episodes of de-watering between 2006 and 2018 at the Tower site and neighboring sites. Settlements of the Tower foundation have been measured since 2006 and lateral deflections of the Tower have been inferred and measured since 2009. Available information on this case history include geotechnical site conditions and data from a monitoring program that tracked foundation settlements, Tower tilt, groundwater levels at the Tower site, and ground inclinations over time. This presentation will discuss the ground deformation mechanisms that caused the observed movements, the degree to which the movements can be predicted, and lessons from this case history for the design of deep foundations for tall buildings in San Francisco and geologically similar regions.

Sep 8, 2021

By H. Cheng

The Bohai Oil Company has applied all together 11 jack-up oil drilling rigs (movable platforms) (1) which can be classified in terms of their forms of foundations into two types: the integ­ral mat and the column legged, as demonstrated in figure 1. Figure 1 a) indicates the entire structure of the sunk cushion type, i.e. the one with a box-like sunk cushion serving as its foundation by directly sitting on the sea bed. The length, width and height of the outer sides for the sunk cushion stand at 45.8 x 38.0 x 3.3m ( for Rig Bohai No.2 ) and 50.6 x 33.2 x 4.88m ( for Rig Bohai No.6 ), the relative areas of theirs being 1475m2 and 2008m2 respectively and both bigger than the plane areas of the rigs. With a view to realize a convenient drainage of mud while sinking, two holes of 14 x 14m and 32 x 18m in size are constructed in the center part of the sunk cushion. When work sets off, the underside of the sunk cushion operates as a foundation, the sunk cushion being connected to the platform by hull columns which transmit the load of the platform down­wards to the sunk cushion that passes it further onto the subgrade. [ ] Column legs for rigs may also be grouped into two categories considering their features: columns with and without boots. The bodies of boot columns are made up of trusses, whose bottoms, are boot-shaped with a big diameter. The diameter of boot columns of the rigs applied by the Bohai Oil Company shows bigger and it may reach 12 or 18m. In the boot columns, the transmission of the platform's weight into soil is done by the underside areas of boots. While in the case of the vertical columns, which are of cylinder columns of steel with sealed bottom ends shaped inverted arch, the entire drilling platform is supported by the carrying force delivered by the bottoms of these steel cylinders and the frictional force rendered by their outside walls. Such a type of columns is featured by a small diameter, 3m in general. Figure 2 exhibits the schematic diagram of sections regarding the two types of column legs.

Jan 1, 2010

By Michal Topolnicki

Deep Mixing Series: This article is the second keynote highlighted from DFI's virtual Deep Mixing Conference in 2021, for which Topolnicki served as a committeee co-chair Polish applications of deep soil mixing (DSM) technology occupy a leading position in Europe. That includes use for road and railway embankments, bridges, residential and industrial build- ings, silos, commercial centers, slabs, car parks and storage yards, excavation supports and cut-off walls. In fact, more than 350 road and railway viaducts and 200 wind turbines have been founded nationally on DSM columns, which are firsts on an international scale. This represents more than 1,200 imple- mentations by the Polish geotechnical industry. Considering the need to update DSM design recommendations, this article will attempt to summarize the best practices of wet DSM design and implementation, in particular. It draws on 20 years of experience and will high- light the properties and principles of the design of stabilized soil and lessons learned. Case studies are included to fur- ther understanding of the careful con- siderations needed with this technology.

Apr 1, 2022

By Jesús E. Gómez

A recent bridge underpinning project provided a unique opportunity to obtain information on the load-deflection response of 260 hollow-core bar micropiles. All production micropiles were proof-tested to a maximum load of 125 percent of the design load. In addition, four verification tests were performed on sacrificial micropiles to at least two and a half times the design loads. This paper presents the results of the verification and proof tests performed for this project, and provides recommended values for design of hollow core bar micropiles in soils similar to those encountered. This work shows that hollow core bar micropiles provide a significant unit bond capacity in both granular and fine soils, which may be greater than that typically expected in pressure-grouted (Type B) micropiles. The hollow core bar system allows faster installation rates in the soil types encountered than other traditional micropile techniques, and can be installed with relatively simple quality control procedures.

Jan 1, 2007

By Paul W. Mayne

The axial load-displacement-capacity and load-transfer response of deep foundations can be conveniently assessed by geophysical piezocone tests that provide four independent readings with depth, including tip stress (qt), sleeve friction (fs), porewater pressures (ub), and shear wave velocity (Vs). The penetration data (qt, fs, and ub) of the CPT are utilized to obtain the pile side friction (fp) and end bearing capacity (qb) while the shear wave measurements provide the initial stiffness. Within an elastic continuum framework, the axial pile deflections are calculated and an approximate nonlinear response is obtained by modulus degradation from small-strain response (G0) to intermediate- and large-strains (G). The continuum solution permits separation of load transfer along the sides and proportion to the base. Applications are shown for case studies involving an end-bearing drilled shaft, two friction-type drilled shafts in Alabama and Georgia, and a "Class A" prediction involving driven pipe piles in residuum of the Atlantic Piedmont geology. Load-transfer data were available for the drilled shaft foundations.

Jan 1, 2002

By Piotr D. Moncarz

As major urban areas begin to run out of "good-terrain" for their expansion, they begin to claim high water-table areas within or adjacent to water fronts or swamps. Similarly, major infrastructure projects encroach on or cross high organic content areas. The associated major structures often require deep foundations located in soils investigated through core samples removed at a discrete number of locations. The investigation is nearly always preoccupied with soil mechanical properties, sometimes with soil non-organic chemistry for concrete and metal corrosion, seldom, if ever, for organic-chemistry and bio-conditions as related to concrete longevity. Not surprisingly so, bio-corrosion of concrete is one of the least understood phenomena by practicing civil engineers. This paper shows how low-iron, organic-rich sediments may trigger sulfate degradation of concrete, even when standard pre-construction chemical analyses indicate only a moderate sulfate level. The discussion is illustrated with a case of a pile foundation in the United States driven into marine channel sediments and sediment-derived fill material. The concrete piles lost their structural integrity due to secondary ettringite formation and depletion of iron in the cement paste. Disintegration of concrete occurred only where it contacted superficial marine sediments and sediment-derived fill material. Concrete in direct contact with seawater or native sand and silt materials appeared to be sound. Sediments in contact with the degraded concrete were highly anoxic and had a history of sewage contamination, contained low concentrations of total iron (<2%), Fe(III) (<0.3%) and moderate levels of sulfate (1500ppm), and exhibited high bacterial activity. This environment resulted in the microbial dissolution of Fe(lll)-rich ferrite in hardened cement paste. Iron depletion in the cement paste had made the concrete vulnerable to degradation by sulfate, even at moderate levels of sulfate concentrations in the sediments.

Jan 1, 2002

By Georgette Hlepas

How often phrases like these have been made by project managers and project teams trying to explain why there has been cost growth, project delays and differing site conditions claims. But does it really take x-ray vision? Do we really approach geotechnical construction projects unprepared for the subsurface that may be encountered because we can't get the answer? Too often our industry seems to think the answer is, "yes." However, this is not because we can't understand the subsurface. All too frequently it is because a choice is made to save money or time by foregoing or shortchanging upfront subsurface investigations. This is accepting a risk at the beginning of the process and realizing it during construction. Case histories have proven time and time again that upfront investment in site exploration and constructing a ground model mitigates risk in design and construction. But how much do we prepare? What level of investigation (or investment) is appropriate? The answer of course, is it depends; how much risk are you willing to take for your project and what are the potential consequences?

May 1, 2022

By Todd Nottingham

Channel deepening of major ports is challenging designers to explore innovative solutions to ensure stability of bulkheads, such as for the Oakland Inner Harbor. This particular challenge was met with the use of the SPIN FIN® Tension Pile for restraint of an HZ combination wall along the Oakland Inner Harbor Shoreline in Oakland, California. A SPIN FIN pile is a pipe pile with welded plates at the pile tip that increase pile capacity. A brief history of the project will be provided as well as results of pile load tension tests, pile strain gauge, and wall deflection under construction loads. Tension pile load deflection results will be discussed with recommendations toward establishing deflection-based ultimate load criteria. A discussion of predicted wall loads and field observed wall loads will be provided.

Jan 1, 2008

By Jorj O. Osterberg

The practice of using side shear resistance in the design of drilled shafts socketed in rock is discussed. In the absence of field test data for the particular rock involved, the designer often neglects the side shear altogether or uses an extremely conservative value. The uncertainty of using strength data from compression tests on rock cores is discussed. Examples of full scale load tests are given which illustrate that even in the weakest of rocks, considerable side shear resistances are obtained, enabeling reductions in the depths of the sockets and consequent savings. Existing Practice. The existing design practice in using side friction/bond between a drilled shaft in rock or hard soil varies very considerably in different areas of the U.S., in different areas of the world, among different Geotechnical Engineers, and in the requirements of different building codes. In fact, the variation is so great that it is inconsistent and contradictory. For example, in Florida where fairly weak coral limestone and sandstone is prevalent, the general practice is to use side friction only and to allow no end bearing. In Chicago, Detroit, Boston and other areas where soft clay overlies stiffer clays, hardpan and limestone or other hard rock, the common practice is to allow for no friction and to use end bearing only, even though the lower portion of a shaft frequently penetrates stiff to hard clays and hardpan (glacial till) before bearing on hardpan or rock. In Hong Kong, if the hole is stabilized with drilling mud, no end bearing is allowed. In Boston (Thompson, Erikson, and Smith, 1989), two tests at two sites on 18 inch pipe piles penetrating 100 feet of soft clay and driven only inches into an argillite, tested 140 and 210 tons in ultimate side shear resistance. Certainly, with long drilled shafts, no matter how soft or weak the soil or rock is, some if not considerable side friction occurs, and where drilling mud is used, there must be considerable end bearing.

Jan 1, 1991

By Cornelis Van Der Veen

Foundation piles, partly passing through unconsolidated compressible layers, suffer a downward drag that is called negative skin friction. The negative skin friction depends on the movement of the surrounding unconsolidated soil relative to the pile and on the friction between pile and soil as a function of that movement. The negative skin friction adds to the load on the pile. However as it is a function of the pile movement relative to the soil, the amount of negative skin friction to be taken into account to determine the allowable bearing capacity depends on the allowable pile settlement. In this paper this property is indicated by the factor µ. As under the conditions of ultimate pile bearing capacity negative skin friction does not occur, a factor of safety is introduced, which is lower than normal. Eventually a formula for the bearing capacity is given in which µ and both figure. The exact values for given circumstances have to be determined empirically. A few examples are given.

Jan 1, 2010

By Matthew D. Marks

"The Sacramento Area Flood Control Agency initiated the Natomas Levee Improvement Program in 2006 which would bring the entire 42 mile Natomas Basin perimeter levee system into compliance with applicable Federal and State standards for levee protecting urban areas. The soil-bentonite slurry cutoff has been utilized as the primary construction method for addressing the under seepage deficiencies. To date, a combined total of over 4,500,000 square feet of slurry cutoff wall have been constructed utilizing excavation methods to a maximum depth of 75 feet and deep soil mixing methods to a depth of 90 feet. The construction of these cutoff walls has required the use of newly designed and custom built long boom and stick attachments for large hydraulic excavators and additional resource will be required to complete future phases. Key components of the NLIP program have included advancements in the development of soil-bentonite backfill mix designs, specified ranges on the soil backfill gradation to address concerns of long term consolidation of the backfill material, evaluation of the trench slurry filtrate loss with regard to cutoff wall acceptance, maintenance high slurry densities to provide greater trench stability, and continued development of backfill mixing procedures.IntroductionThe Natomas Levee Improvement Program (NLIP) was initiated by the Sacramento Flood Control Agency (SAFCA) in 2006. The long term objective of the NLIP is to provide 200-year level flood protection to the basin. To date, approximately 21 of the 42 mile Natomas Basin perimeter levee system has been completed, totaling over $100,000,000 in construction contracts, of which slurry cutoff walls make up approximately $25,000,000. Other construction elements include excavation and removal of unsuitable levee materials, raising or widening existing levees, construction of landside seepage berms, drainage canals, and miscellaneous structures.Although each construction phase of the NLIP includes various construction elements of levee restoration program, the slurry cutoff wall is the primary construction element for addressing the under seepage deficiencies. To date, approximately 4,500,000 square feet of slurry cutoff walls have been installed using excavation and deep soil mixing (DSM) methods. This includes approximately 2,000,000 square feet of slurry cutoff wall along 5 miles of the NCC South Levee and 2,500,000 square feet of slurry cutoff wall along 16 miles of the Sacramento River East Levee (SREL). The work has been completed under 8 separate contracts, through SAFCA, and performed between September 2007 and December 2012. A summary of the contract phases and associated cutoff wall square footage is provided in Table 1. Most of the work has been performed within the seasonal dry weather period in the Sacramento valley, which occurs between April and October. This has required much of the work to be performed on an aggressive construction schedule, year after year."

Jan 1, 2017

By C. Guney Olgun, Fleur Loveridge, Tracy Brettmann, William Powrie

"Abstract Deep foundations are increasingly being used, not just to carry structural loads, but also to act as heat exchangers as part of a ground source heat pump system. Such foundations, often called energy piles, have the potential to make significant contributions towards meeting the heating and cooling demands of buildings, thus reducing the overall energy consumption and carbon dioxide emissions during their lifespan. To ensure that the available energy from these systems is maximized, it is important to determine the thermal conductivity of the surrounding soils, a key design input parameter. In situ thermal response tests are commonly used to carry out this task for small diameter borehole heat exchangers. However, there has been debate over the applicability of these tests to energy piles due to their larger diameter and the consequent increased influence of the pile thermal properties on the test outcome. This paper examines the results of three thermal response tests carried out on piles of different diameters and thermal properties installed at the same site in Texas. Transient analysis of the test results, combined with comparisons to laboratory testing of soil samples from the site, is used to given an indication of the applicability of the thermal response test over different timescales for the different piles. It is concluded that the test is most suited to smaller diameter piles constructed with lower thermal diffusivity materials. Recommendations are given for the conduction of pile thermal response tests and interpretation of test data.INTRODUCTIONAs issues of energy security and scarcity become more important, the use of ground source heat pumps to provide renewable and sustainable heating and cooling to buildings is set to increase. Traditionally such systems use special purpose ground heat exchangers to extract and/or inject heat from/into the ground. The heat exchangers comprise a series of plastic pipes cast into the ground and then connected to the heat pump via a series of header pipes. In the case of building space heating, the heat pump then steps up the temperature difference to deliver the extracted heat at a useable level. However, financial and carbon savings can result by utilizing the building foundations as heat exchangers as well as to carry the building structural loads.Piles, often termed “energy piles”, are the most common type of foundation heat exchanger, and their construction has been increasing in recent years (Amis et al, 2009). However, while energy piles have the potential to make significant contributions towards meeting building heating and cooling demands, there remains scope for improving their thermal efficiency through improved analysis approaches (e.g. Loveridge & Powrie, 2013). In fact the greater diameter of many energy piles means they have the potential to deliver increased short term thermal energy storage compared to more commonly installed borehole heat exchangers."

Jan 1, 2014