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By Avi Shonberg

With the advancement of offshore wind farm projects towards deeper waters and larger wind turbine generators, founda- tion solutions other than the monopile have received increasing attention over the past 5 years. Monopiles are the most commonly used foundation solution for offshore wind turbines, with 82% in European waters founded on monopile foundations (EWEA, 2019). However, 2018 saw a record number of suction bucket jacket (SBJ) structures, which consist of a three-legged jacket sup- ported by a suction bucket at each leg (Figure 1), installed for offshore wind. applications. SBJs have now been installed successfully at the Borkum Riffgrund 1, Borkum Riffgrund 2 and Aberdeen Bay offshore windfarms. Suction-installed foundations, referred to in this paper as suction buckets, suction caissons, suction piles or suction anchors, have been widely used in the offshore industry since the early 1980s for a range of offshore applications predominantly as anchors for floating offshore structures - where they are "the most widely used anchor types for deep-water mooring applications" (McCarron, 2011). Suction buckets, installed using pumps that generate suction forces by creating a pressure difference between the inside and outside of the bucket, allow for the installation to be undertaken with minimal noise and without the use of mechanical force. Therefore, a key difference between suction-installed foundations and other foundation types is that the installation design, which must consider the soil type, soil strength and installation specific risks (for example, soil stratification with significant differences in permeability) may have a direct influence on the dimensions of the foundation. While the number of SBJS installed for offshore wind applications has increased significantly in recent years, the installation process for SBJ struc- tures is yet to become standard practice and is considerably more complicated than the installation process for mon- opiles. This paper provides a brief

Jul 1, 2022

By Tony Suckling

The commercially available finite element program Plaxis has a key benefit over other finite element analysis programs in that it has a relatively simple user interface to input and output data. This benefit though may also be it?s weakness in that anyone, regardless of their grounding in geotechnical engineering, may use the program and produce results for design. It is essential, as for all engineering design, that the models are checked by competent engineers. This paper describes the key recurring problems found by the authors when checking Plaxis models, such as the generation of the initial in-situ ground stresses and the modelling of groundwater. Interestingly, the authors have not encountered similar problems when checking finite element models produced using other programs and conclude that this may be due to the higher calibre of modeller needed to use these other programs. The geotechnical industry is in a situation at the moment where senior managers who may not have been trained in finite element modelling are relying on less experienced staff who have had some training in modelling, either at university or post graduation. The quality of this training is variable and all organisations running easy to use programs need to be aware of the potential risks and dangers. Management procedures and engineering checks that are essential to validate the results of these models are described, assuming that those in charge are not experienced modellers themselves. The model checking process by competent persons is absolutely essential and it is hoped that this paper will help those organisations that do not have such procedures as part of their own internal Quality Assurance or design validation system. The procedures described are valid for all finite element programs.

Jan 1, 2010

By Ahmed H. Bukhary, Naser A. Al-Shayea

The objective is to assess the overconservatism in the parameters used for designing offshore piles. Methodology includes analysis of shaft friction data obtained from more than five different locations in the Arabian Gulf, consisting of 40 piles to depths up to 86 m. Reports were collected for both the dynamic pile monitoring system (DMS) and their corresponding geotechnical reports based on the American Petroleum Institute (API). The values of shaft capacity for the sand layers were analysed by comparing those based on API to the corresponding DMS values. Results of the comparison of the data from these reports showed that the pile design parameters obtained using API guidelines is generally smaller than that measured by DMS. The difference is presented in terms of an overconservative factor (OCF) which is adjusted based on statistical nonparametric test performed on the two data sets. The adjusted OCF were found to be 1.79 and 2.00 for carbonate sand at (loose to medium dense) and (dense to very dense) conditions, respectively. The corresponding values for silica sand were only 1.2 and 1.06. In conclusion, based on the evaluation conducted for data from these reports, the API shaft friction is overconservative for carbonate sand. The API shaft friction for piles in sand can be increased by multiplying it by the adjusted OCF.

By Z. Q. Wang

The author is trying to clarify the existing problems in designing and laying out dynamic consolidation for soft ground improvement. Field testings and observations including vibrational parameters, pore pressures, stereoscopic photogrammetry etc. were run in order to trace the real behaviour of ground movement during tamping. It is believed that all the data got from the field work are rather informative and illustrative than that from theoretical modelling in the laboratory, thus some highlights relating effective thickness of compaction, maximum spacing between compaction points, number of blows for optimum tamping and seismic attenuation for environmental consideration are given.

Jan 1, 2010

By Masaki Kitazume

Five papers were presented orally to the topics of Jet Grouting and Deep Mixing. The session was started with a brief introduction by the moderators. Following the oral presentation, floor discussions were directed by the moderators. A brief introduction of each of the oral presentations is provided before each discussion.

Feb 10, 2003

By Patrick T, David K. Miller

Driven piles are an effective and cost-efficient deep foundation method; however, when piles are driven near existing buildings and improvements, vibrations must be controlled to non-damaging levels. Monitoring of adjacent structures is important for loss prevention, specification compliance, and public relations. The fundamentals of ground vibrations, including particle velocity, acceleration, displacement and frequency will be discussed. Types of pile driving and the ground vibrations that result will be summarized. Industry standards for safe vibration levels for various structures (residential, commercial, industrial, historic, utilities) will be reviewed. The paper/presentation will include a discussion of soil settlement from pile driving vibrations and case histories of observed settlements. Methods for calculating vibration amplitudes and frequencies will be presented. Best practices for monitoring and controlling ground vibrations, including available state-of-the art equipment, will be outlined. The paper/presentation will conclude with steps for designing and implementing a monitoring and control program.

By Willie M. NeSmith

The use of drilled (screwed) displacement piles is an emerging sector of the United States deep foundation industry. During installation of these systems, a Ko to Kp environment is created in the materials surrounding the pile immediately prior to casting, and this condition results in increased shaft and toe resistance in soils where displacement leads to densification. Current continuous flight auger and drilled shaft design methodologies in the United States assume a Ko to Ka condition in the vicinity of the pile, and are thus an inappropriate starting point for static capacity analysis of drilled displacement piles. This paper examines constructability issues, and the sensitivity of performance to installation, and offers an empirical design methodology for drilled displacement piles. The proposed design process has been based on evaluation of 40 load tests, primarily in granular materials, and in a variety of geologic settings, and includes modification for soil types within the coarse-grained range.

Jan 1, 2002

By Charles R. Conlon, Matthew J. Niermann

This paper presents the underpinning and excavation support systems used for construction at 2100 L Street in Washington, DC. The excavation for the proposed building extended below bedrock, which presented significant challenges for underpinning the historic Stevens School, constructed in the late 1800’s. The Stevens School was underpinned using several techniques consisting of soil mixing below an unreinforced foundation, traditional hand-dug pits to rock, micropiles below rock, and bracket piles. The excavation support system for the remainder of the project consisted of soldier piles and lagging supported laterally by tiebacks and braces. Shotcrete and rock bolts supported the exposed bedrock. This paper will discuss the design, construction and monitoring results.

By Gary M. Weinstein

Micropiles have seen increasing use for foundation support and slope stabilization applications over the past half century. Most often designed and installed in groups of vertical or battered elements or combinations thereof, continued applied research conducted through partnerships established between academia, government and industry has led to the recent development of practical engineering and design guidelines for such micropile systems. In contrast to a group of directly loaded micropiles, the micropile network relies on a three-dimensional array of reticulated elements to encompass and internally reinforce the soil, resulting in a network or "knot" effect. The potential for enhanced engineering behaviour of reticulated micropile network systems compared to that of a group of micropiles has been continually revealed by numerous researchers in the past. The concept is elementary - the roots of a tree interact with the soil to form a composite foundation capable of performance superior to that of the individual parts. However, given the large number of parameters which must be modelled and studied, experimental assessment and rational analysis of the soil-structure system has been difficult and therefore, in contrast to above, reliable design methods have not yet been forthcoming.

Jan 1, 2003

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 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 Lin Li

A reliability based analysis method for a drilled shaft stabilized slope system is presented in this paper. In the past effort, a deterministic method using the limiting equilibrium method of slices for determining the global factor of safety of a slope reinforced by a row of drilled shafts was developed using the soil arching concept. The drilled shaft stabilization mechanisms for the slope were treated as the drilled shaft induced soil arching, which reduces the driving forces on the down slope side of the drilled shaft. The effect of drilled shafts induced soil arching on the reduction of the driving stresses in the limiting equilibrium slope stability analysis was quantified by the load transfer factor through extensive finite element simulation studies. A semi-empirical equation was also developed for expressing the load transfer factor as a function of the soil properties, including strength parameters and unit weight as well as the slope geometry and soil profile, the location and spacing of the drilled shaft, and the dimension of the drilled shaft. However, due to the inherent uncertainties of the soil properties and the model error of the semi-empirical load transfer equation, a modification of the deterministic method into a probabilistic method is developed in this paper. The Monte Carlo statistical method is used to generate random variables for the soil strength parameters based on the prescribed probability characteristics, including mean, COV, and the probability distribution function. In addition, the modeling error of the load transfer factor is also treated as a random variable in the Monte Carlo simulation method, in which the mean, COV, and probability distribution function for the bias of the semi-empirical equation are used. The developed theories were coded into a computer program for analyzing complex slope geometry and slope profile conditions. Two examples are shown in the paper to illustrate the analysis results of the developed probability approach for determining the reliability of a drilled shaft stabilized slope system.

Jan 1, 2017

By Lin Li

A reliability based analysis method for a drilled shaft stabilized slope system is presented in this paper. In the past effort, a deterministic method using the limiting equilibrium method of slices for determining the global factor of safety of a slope reinforced by a row of drilled shafts was developed using the soil arching concept. The drilled shaft stabilization mechanisms for the slope were treated as the drilled shaft induced soil arching, which reduces the driving forces on the down slope side of the drilled shaft. The effect of drilled shafts induced soil arching on the reduction of the driving stresses in the limiting equilibrium slope stability analysis was quantified by the load transfer factor through extensive finite element simulation studies. A semi-empirical equation was also developed for expressing the load transfer factor as a function of the soil properties, including strength parameters and unit weight as well as the slope geometry and soil profile, the location and spacing of the drilled shaft, and the dimension of the drilled shaft. However, due to the inherent uncertainties of the soil properties and the model error of the semi-empirical load transfer equation, a modification of the deterministic method into a probabilistic method is developed in this paper. The Monte Carlo statistical method is used to generate random variables for the soil strength parameters based on the prescribed probability characteristics, including mean, COV, and the probability distribution function. In addition, the modeling error of the load transfer factor is also treated as a random variable in the Monte Carlo simulation method, in which the mean, COV, and probability distribution function for the bias of the semi-empirical equation are used. The developed theories were coded into a computer program for analyzing complex slope geometry and slope profile conditions. Two examples are shown in the paper to illustrate the analysis results of the developed probability approach for determining the reliability of a drilled shaft stabilized slope system.

Pier, well cap and steining junction is a complicated 3-d re-ion. The prevalent design procedure for the pier, well cap and steining in isolated manner is not rational. In absence of an integrated approach for design of the junction structure, the well cap is designed uneconomical and at the same time pier and steining are left relatively unsafe. Strut-and-Tie Model based design is a simple solution to this problem. An example illustrating design of the junction structure using STM is presented. On comparison of the outcomes of the STM based design with the prevalent design, the following anomalies are found: i) For smooth flow of forces, length of pier at its base should preferably be made equal to the outer well diameter, ii) STM based design for the pier is more rational, economical and safe. iii) Due to presence of hoop stress, as indicated by the STM, the steining concrete in a depth of p times outer diameter of the well from the well cap level should be limited to M15 grade, iv) STM based design for the steining is more rational, economical and safe.

Jan 1, 1996

By Marcus Daubner

This paper explains how BAUER Spezialtiefbau GmbH uses digital methods on projects - starting from work preparation to completion of works. More precisely, the advantages of BIM-based planning during work preparation and the automated and structured data management - both machine production data and the manually recorded quality-relevant reports - during execution phase are displayed. In this context, the benefit of the digital twin to optimize processes, to reduce defect costs, for a more effective reporting sys-tem, and the further usage of as-built information in the BIM or GIS process is described.

Sep 1, 2022

By Peter Deming

"PART 1 OF 2INTRODUCTIONSlurry trenches are the least cost hydraulic barrier available, if the excavated spoils can be recycled into backfill. As such, slurry trenches are constructed where possible, sometimes at high risk. Slurry trenches are also used to install biopolymer drainage trenches, which have a low safety factor because the biopolymer slurry weight is marginally greater than the weight of water. In marginal ground the construction risk falls to both the Owner who designs and asks for the construction, and the Contractor who manages the work and promises to complete the project successfully. This paper discusses design and construction of slurry trench barriers in marginally stable ground and where groundwater chemistry invokes the need for slurry management details to obtain proper backfill placement.As a designer, Mueser Rutledge Consulting Engineers works for both Owners and Contractors. We are usually able to convince Owners of their responsibility for design detailing in order to obtain a working final product and to obtain reasonable bids from Contractors by disclosing construction needs and designing to reduce the contractor’s exposure. We often work for Contractors to produce designs which result in successful construction in projects where the Owner’s engineer places the responsibility of design and construction on the Contractor.This paper is intended to inform both Owner and Contractor audiences of resources which are available to reduce the risks of trench collapse in difficult ground conditions. We hope it serves this purpose.DESIGNSubsurface InvestigationsSubsurface conditions should be defined by borings focused on definition of the soil profile and soil design parameters. After general subsurface conditions are defined, barrier borings should be drilled along the final alignment.Definition of Soil Strength and CompactnessCompactness of sand and gravel strata should be defined with Standard Penetration Test N-values. The shear strength of cohesive materials should be defined by laboratory testing. Silt and fine sand strata with little cohesion should be investigated using mud rotary techniques to prevent disturbance. General strength characterization by soil layer should be used for analysis of trench wall stability."

Jan 1, 2006

By Emad Farouz, Roger Failmezger

"The proposed reconstruction of I-75 downtown consists of widening an approximately 2.46 Km section of IR-75 through the northern section of downtown Dayton, OH, USA. Bridge B-13 is a 9-span continuos prestressed concrete I-beam, 319.0-meter (1,048-foot) long bridge with a stub abutment on MSE walls for the rear abutment, and a stub abutment with spill-through slopes for the forward abutment. The piers in the river were located parallel to the Great Miami River, and are full-height reinforced concrete walls. PRESSUREMETER TEST PROCEDUREThe driller advanced either casing or augers approximately 1 meter above the pressuremeter test. Steel casing was used to advance borings performed in the river, and augers were used for borings on land. Mud rotary drilling with a large diameter roller bit was used to remove all of the gravel and cobble fragments inside the casing or augers.At the pressuremeter test elevation the driller used a 63.5-mm (2.5-inch) carbide button bi-cone bit, using a rotation rate of about 60 rpm, a mud fl ow rate of about 10 gallons per minute (40 liters per minute), and an advance rate of 6 to 10 minutes per meter (2 to 3 minutes per foot). To minimize vibrations, advance rates were slower where excessive cobbles were encountered. The 63.5-mm (2.5-inch) O.D. slotted casing pressuremeter was lowered to the test elevation, often requiring either pushing or hammering into the test zone. We believe that the test zone was not perfectly straight, or that gravel or cobble fragments jutted into the test zone and had to be displaced to advance the pressuremeter into the test zone. The slotted casing prevented membrane damage during insertion. A photograph of the slotted casing being lowered into the borehole is shown below.The pressuremeter was calibrated for system compressibility and membrane resistance. At full expansion of 800 cm3, the membrane resistance of the slotted casing was about 2.5 bars.Strain-controlled tests were performed using a Texam control unit with a monocell probe. Volume increments of 20 cm3 were injected into the probe and corresponding pressures were measured. Near the end of the elastic portion of the test, an unload-reload cycle was done. A creep test was performed for 10 minutes at the next volume increment. The test continued until either 800 cm3 were injected or the membrane burst."

Jan 1, 2007

By Mark Koelling

This paper presents a case history of a ground improvement program conducted in a soft soil environment and seismically active region in the northwest corner of Washington State near the Canadian border. The program was performed over several years, and provided adequate soil bearing conditions for the construction of several structures. Completed development includes separate construction of four adjacent structures, each with unique total and differential settlement requirements and built at approximate two year intervals. Site soils consist of 45 feet of loose saturated sand and silt overlying 70 feet of very soft to stiff (N60 = 0 to 7) normally consolidated clay. Adding to the complexity of the site is the owner?s requirement that all existing structures remain open and in service during construction of each subsequent structure. The paper presents the site geotechnical information and the foundation design issues. Details of a combination of ground improvement methods is presented, including stone columns, wick drains, a preload surcharge, and staged construction to provide soil support for shallow foundation construction of all structures at this site. The soil test results and settlement observations are presented along with QA/QC measures. Lastly, a brief method sustainability comment will be made.

Jan 1, 2010

By Arturo Ressi di Cervia

"The Construction of the Thrust Pits for Jacking of the I-90 Tunnel for the Central Artery/Tunnel Project (Part of Contract No. C09A4) in Boston MA was nominated for DFI’s 2002 Outstanding Project Award. In the judging, the project and the specialty subcontractor, Treviicos Corporation, was chosen for a Special Recognition Award. INTRODUCTIONBoston’s Big Dig, as the construction of the underground artery became known, is undoubtedly the largest urban construction project of this century.The Central Artery/Tunnel Project, or CA/T, to call it by its proper name, runs approximately eight miles through the heart of Boston, five miles of which are built underground while maintaining traffic on the elevated existing structure, while at its southern end I-90 is extended to Logan airport under active rail lines, Fort Point Channel and Boston Inner Harbor.Since the alignment of the road closely parallels the shoreline as it existed in colonial times, the cut and cover construction had to contend with substantial portions of filled ground, not to mention existing subway lines, live utilities, building foundations and, last but not least, the irritable Boston drivers and litigious adjacent property and business owners.Consequently, while it is impossible to single out the most difficult or challenging contract, the jacking of the tunnels of I-90 under the live rails of Amtrak certainly will rank high on the list.Never before, anywhere in the world, was an attempt made to jack tunnels of this size: the South Bay Interchange consists of three 78 feet (24 m) wide by 38 feet (11.6 m) high tunnels, the shortest of which is 167 feet (51 m) long. TECHNOLOGYIn order to achieve this engineering feat it was necessary to consolidate the soil under the track to prevent it from moving or settling during the jacking process. After a detailed analysis of the geological profile to be traversed it was decided that freezing was the most suitable method, since it could be applied to the full range of soils present on the proposed alignment."

Jan 3, 2003