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This paper presents a newly observed phenomenon of upscaling of rocks’ properties using big data nanoindentation and analytics involving Gaussian mixture modeling (GMM), leading to characterizing the cross-scale mechanical properties of four shales and one sandstone. A large number (i.e., ~ 500) of statistical indentation measurements to depths of 6–8 μm were performed on each rock, resulting in continuous depth-dependent hardness and Young’s modulus data from unknown phases, which were then segmented at various depths to extract an array of discretized subdatasets. Two-dimensional GMM of each subdataset yields the number, fraction, and properties of mechanically distinct phases, and re-assembly of these results leads to clearly discernible property-depth curves. Such improved data analytics consisting of data segmentation, GMM deconvolution, and re-assembly enables the transformation of a massive number of chaotic curves from unknown phases into a few discernible lines corresponding to identified phases, from which the mechanical properties of individual phases are accurately determined at relatively small depths. With increasing depth, initially unique mechanical properties of individual phases undergo multistage merging at the intermediate mesoscale and progressively homogenize into a unified value at large depths or macroscale (e.g., > ~ 5 μm), which is regarded as the bulk rock’s properties. More importantly, such depth-dependent transition and progressive merging and homogenization actually manifest the micromechanics of nanoindentation on a heterogeneous composite, including the indentation surround effect and rock’s microstructure (e.g., sizes and spacings of different solid particles and their properties). Compared to different micromechanical upscaling models, this newly developed big data indentation technique and pertinent data analytics enable more accurate, multi-parameter, and cross-scale characterization of highly heterogeneous materials and explicitly uncover the multi-staged, progressively-homogenized, depth-dependent upscaling of elasticity from individual constituents at the nanoscale to merged virtual interface phases at the mesoscale and to bulk material at the macroscale.

The objective of a geotechnical site-characterization program is to determine soil and rock stratigraphy, in-situ pore water pressure conditions, and soil and rock properties for analysis and design of geotechnical engineering infrastructure. It is best conducted using an integrated approach that combines various geo-disciplines to describe, evaluate, and determine expected site characteristics. The extensive advancement of tools and procedures in recent decades provides an opportunity to execute effective and thorough site-characterization programs routinely in practice. Yet, this is often not the case, and some may argue that today’s state-of-practice has regressed in recent decades. While contractual structures and budget restrictions may contribute to this lower level and quality of characterization, the technical knowledge and pragmatic strategies available are not always implemented.

Multiscale experiments were conducted to investigate the thixotropic behavior of a naturally occurring illite-rich marine clay with a moderate salinity and of a manufactured, highly purifie...

One of many barriers to the deployment of floating offshore wind turbines is the high cost of vessel time needed for soil investigations and anchor installation. A multiline anchor system is proposed in which multiple floating offshore wind turbines (FOWTs) are connected to a single caisson. The connection of multiple FOWTs to a single anchor introduces interconnectedness throughout the wind farm. Previous work by the authors has shown that this interconnectedness reduces the reliability of the FOWT below an acceptable level when exposed to survival loading conditions. To combat the reduction in system reliability an overstrength factor (OSF) is applied to the anchors functioning as an additional safety factor. For a 100 turbine wind farm, single-line system reliabilities can be achieved using the multiline system with an OSF of 1.10, a 10% increase in multiline anchor safety factors for all anchors in a farm.

This paper presents a summary of the geotechnical engineering properties of low to medium overconsolidation ratio offshore inorganic clays derived from a high quality database. These properties, such as preconsolidation stress and undrained shear strength, are required for design of most offshore infrastructure and for assessment of offshore geohazards. The database was developed through a series of Joint Industry Projects using results from offshore site investigations performed worldwide. The key feature of the database is that it only contains results obtained using good to excellent quality samples that were tested using advanced laboratory procedures such as constant rate of strain consolidation and consolidated undrained triaxial and direct simple shear. A secondary objective of the paper was to examine common empirical correlations between index tests (e.g., water content, Atterberg limits) and soil design parameters using the new database. Such empirical correlations between simple and inexpensive index tests and more costly advanced laboratory tests can serve a valuable purpose in offshore infrastructure design. This is particularly the case for preliminary design at early stages of projects where little information is known about soil properties, for small projects with limited site characterization budgets, and international projects at locations where advanced laboratory tests performed to international standards are not available. The paper describes development of the database and presents summary results and plots for undrained shear strength, in situ stress state, and consolidation and flow parameters. Results from the empirical correlations investigated are presented and the paper concludes with recommendations on use of the data and correlations in practice. The recommendations are limited to clays of low to medium overconsolidation ratio and are not applicable to highly overconsolidated and desiccated clays. While the database primarily consists of offshore clays, the correlations presented should also be applicable to terrestrial clays.

A shared multiline anchor system may reduce material and installation costs for floating offshore wind farms, but the concept also expands the physical space over which the analysis of the system must be considered. The multiline anchor force is a combination of forces that originate from different floating offshore wind turbine (FOWT) platforms, and this interconnectivity mandates investigation of spatial coherence of waves over the area of the connected turbines. The goal of this work is to determine if anchor force characteristics are sensitive to spatial coherence of the wave field, or if an assumption of independent wave fields at different FOWT locations provides sufficiently accurate anchor load characterizations. Spatially coherent irregular wave fields are generated and applied to FOWT systems in 3-line and 6-line anchor systems, revealing negligible sensitivity of multiline anchor force to wave spatial coherence. These results are continued with a parametric study showing how wave characteristics affect correlation lengths of spatially coherent waves. A review of installed offshore wind turbine spacings is presented as a context for these results. In each section, regular waves are first used to examine the dynamics in a simple context, then irregular waves are used to more realistically simulate ocean conditions.

This paper describes the geology and geotechnical engineering properties of the Halden silt; a 10–12 m thick deposit of fjord-marine, low plasticity clayey silt. Over the last six years, the test site has been well characterized by combining the results from a number of geophysical and in situ tools, including; electrical resistivity tomography, multi-channel analysis of surface wave surveys, cone penetration testing, dissipation testing, in situ pore pressure measurements, seismic flat dilatometer testing, field vane testing, self-boring pressure meter testing, screw plate load testing and hydraulic fracture testing. The results from these investigations assist the interpretation of layering and in situ soil properties. Soil sampling and advanced laboratory testing have provided data for interpretation of geological setting and depositional history, soil fabric, strength, stiffness and hydraulic properties. However, interpretation of the stress history, based on oedometer tests and clay-based correlations to the cone penetration test, are unreliable. They contradict the depositional history, which suggests that the soil units at the site are near normally consolidated, except for some surface weathering and desiccation. Further, undrained shear strength interpretations are complex as the in situ tests are potentially influenced by partial drainage, and conventional undrained triaxial tests do not provide a unique (peak) undrained shear strength. Despite certain interpretation challenges the paper presents important reference data to assist in the interpretation and assessment of similar silts, and provide some guidance on important geotechnical properties for projects where limited design parameters are available. Halden research site: geotechnical characterization of a post glacial silt

This paper describes the geology and geotechnical engineering properties of a sensitive marine clay deposit at a research site located in Newbury, Massachusetts (MA) in the northeast USA. Results from in situ testing, soil sampling, and laboratory testing are presented. The clay is locally known as Boston Blue Clay (BBC) which is a glacial marine clay that was deposited approximately 14,000 years ago in the greater Boston, MA area during retreat of the Laurentide Ice Sheet. The thickness, stress history, and soil properties of BBC can vary significantly depending on location. At the Newbury research site, the BBC deposit consists of a shallow thin desiccated crust underlain by a 12-meter thick low plasticity clay with an overconsolidation ratio ranging from 2 to 3. Sensitivity of the clay ranges from approximately 10 to 30, based on field vane and fall cone measurements. In situ testing performed at the site included seismic piezocone and field vane. Soil sampling was performed using a variety of samplers including Sherbrooke block, fixed piston thin-walled Shelby tube, and a thick-walled drive sampler. A full suite of advanced laboratory tests was performed on the various quality samples collected, which ranged from very poor (thick-walled drive sampler) to excellent (Sherbrooke block), including constant rate of strain consolidation, consolidated undrained triaxial and direct simple shear. The efficacy of the Recompression and SHANSEP procedures to mitigate sample disturbance was evaluated using results from the advanced laboratory test program. The paper presents data from these advanced tests as well as other soil classification, index, and engineering properties based on in situ measurements and laboratory test results. A synopsis of constructed facilities built on and in BBC within the greater Boston area is also presented.

This paper presents a laboratory investigation of undrained triaxial shear behavior of a natural low-plasticity silt from Halden, Norway in the intact, disturbed, and reconstituted states. Sherbrooke block sample and reconstituted specimens were subjected to simulated tube sampling in a triaxial stress path cell system prior to reconsolidation and undrained shear to assess the effects of disturbance on undrained shear behavior, undrained shear strength, and effective stress friction angle. Shear stress and pore-pressure development were evaluated relative to that measured for the undisturbed reference state, i.e., that measured on specimens from the intact block sample. Specimens trimmed from fixed-piston tube samples collected from the field site were tested for comparative purposes. Collectively, the results demonstrated that neither the volumetric method of evaluating sample quality for clays nor shear wave velocity tracked sample disturbance well for this low-plasticity silt. Relative to the reference intact block sample tests, simulated tube sampling resulted in an increasingly pronounced dilative-type behavior during postdisturbance undrained shear and a general increase in undrained shear strength. Specimens from the block sample that were subjected to simulated tube sample disturbance had similar stress–strain behavior as that from conventional anisotropically consolidated triaxial compression tests conducted on specimens from the tube samples, suggesting that significant alteration of the intact soil state occurred during tube sampling. Practical suggestions for selection of undrained shear strength for intact low-plasticity silts that exhibit dilative behavior such as the Halden silt are proposed.

This paper presents the first effort to investigate the effects of uniform and nonuniform prestraining on the mechanical properties of nanostructured multilayers. Thin muscovite sheets were first subjected to a loading–unloading cycle under unidirectional compression and cantilever bending modes that induce uniform and nonuniform prestraining, respectively, and then probed by nanoindentation to characterize their Young’s modulus and hardness. Optical and electron microscopy and X-ray diffraction were also used to uncover prestraining-induced microstructure alterations. Precompression in the c* direction to a stress of 45 MPa induces elastic uniform straining and causes negligible alteration to the microstructure. Such a prestrained specimen possesses unaltered Young’s modulus and hardness. However, the nonuniformly prestrained specimens that were subjected to cantilever bending, even though bending is macroscopically purely elastic, exhibit decreased Young’s modulus and hardness, and such reduction depends on the magnitude of bending strains. The Young’s modulus decreases by up to 41.0%, from 69.5 to 41.0 GPa at 0 to ~ 6% bending strains, respectively, while the maximum hardness reduction is 40.4%. Such distinction induced by different prestraining modes stems from the bending-induced nonuniform straining as well as the muscovite’s unique nanoscale layered structure. Owing to the relatively weaker and reversible electrostatic interlayer bonding, bending-induced strain gradient along the c* direction causes relative interlayer slip and hence bonding switch and, upon unloading, leads to the formation of basal plane corrugation and subsurface blisters. Such structural incoherence and imperfections induced by even elastic bending reduce the Young’s modulus and hardness. These findings shed light on the processing–structure–property relationships for other nanostructured multilayers as well as the origin of variability of elastic modulus of muscovites reported in the literature.

This research assesses the reliability of floating offshore windfarms utilizing two different anchor configurations: a conventional single-line system in which each anchor is loaded by a single mooring line and a multiline system in which each anchor is loaded by three mooring lines. While there are advantages to adopting a multiline system for floating offshore wind farms, the interconnectedness of this concept introduces disadvantages, such as reduction of system reliability and the potential for cascading failures among multiple structures. The reduction in system reliability is investigated here by running Monte-Carlo simulations in which mooring line and anchor demands and capacities are sampled from probability distributions. Demand distributions are generated through dynamic simulations with environmental conditions corresponding to the 500-year storm. Failure of mooring lines or anchors are initiated when their capacity is exceeded by their demand. The results of this research show that the reliability of the multiline system degrades significantly when progressive failures are taken into consideration. This research also shows that design considerations, such as the sizing of mooring lines and anchors and designing for single-line or multiline loads, significantly influence the system reliability of a floating offshore wind farm.

Thixotropy-governed temporal microfabric evolution, in a naturally occurring illitic marine clay and a manufactured kaolinitic clay at their respective liquid limits, was probed quantitatively by both one-dimensional X-ray diffraction (1DXRD) and 2DXRD via orientation index (OI) and texture index (TI) respectively. Results showed that the two fabric indexes, OI and TI, continuously evolved nonmonotonically but consistently during the thixotropic hardening periods of up to 125 days. Due to the initial remolding-induced large-strain shearing, both clays started with a fabric consisting of highly parallel-oriented clay particles. With increasing time, the OI varied from 23.1 to 36.6 and from 3.8 to 4.5, while their TI ranged from1.004 to 1.008 and 1.010 to 1.029 for the kaolinitic and illitic clays, respectively. Moreover, the same trend of changes between the OI and TI for both clays indicated that the two XRD-based techniques are applicable to characterizing the temporal microfabric changes in soft clays undergoing thixotropic hardening. The fabric evolution may result from various microscale particle rearrangements, likely including clay particle reorientation, aggregation, and flocculation, which in turn are controlled by interparticle forces. The two XRD-based techniques are also discussed in terms of their advantages and can expectedly shed light on similar studies of time-dependent behavior of soft clays.

A comprehensive study is presented of the characteristics of calcareous concretions in the Connecticut Valley varved clay (CVVC), a glacial lake sediment, probed by an array of investigations, including compositional analyses via X-ray powder diffraction and energy-dispersive X-ray spectroscopy, mechanical property mapping by nanoindentation, selective dissolution, microstructure examination by optical and electron microscopy, and stable isotope analyses, with an objective to resolve some long-standing questions on their origin and growth mechanisms. Results show that these concretions are of a biogenic origin and consist of ~40 wt% primary host sediments and ~ 60 wt% secondary calcite post-depositionally precipitated as pore infills and inter-particle cement. The highly consistent layering and dry density between the carbonate-free host sediments in the concretions and in-situ varved sediments manifest that the precipitated calcite causes no disturbance to the original stratification and structure of the varved sediments. Moreover, both the mechanical properties (i.e., Young's modulus and hardness) and calcite concentration in concretions exhibit a radially decreasing pattern slightly disturbed by the sediments' layered textures. Further supported by the radial distribution patterns of stable carbon and oxygen isotopes, the CVVC concretions grow in a concentric pattern. A conceptual ion transport model is proposed to further interpret the growth mechanisms. These concretions grow radially in a nearly closed sediment system with diffusion-controlled transport of HCO3− from decaying organic matter and Ca2+ from porewater at direction-dependent rates dominated by the pore characteristics of the local host sediments. The diverse concretion morphologies are attributed to the different growth rates in different directions affected by the heterogeneous layering and pore sizes of the host sediments.

While the offshore wind industry has shown a steady trend towards floating turbines, costs of these systems remain high. A multiline anchor concept may significantly reduce the high cost of floating wind, in which floating turbines share anchors. This work investigates the potential cost benefit of implementing a multiline anchor system relative to the conventional single-line anchor system over a range of spatial parameters. The OC4 DeepCwind semisubmersible platform is used to design catenary mooring systems for different water depths and turbine spacings. In all cases, the maximum anchor force in the 3-line anchor system is less than or equal to that of the single-line anchor system. Cost models for the mooring lines, anchors, installation and geotechnical site investigation are presented and discussed. In a 100-turbine farm, the multiline anchor system results in a 9–19% reduction in stationkeeping costs, with high and low estimates for the cost models additionally included. Larger reductions in the combined line and anchor cost result from mooring system configurations with smaller ratios of water depth to turbine spacing. Due to perimeter effects in the multiline configuration, larger cost reductions can be achieved for larger farm sizes.

This paper presents a laboratory investigation of the influence of simulated tube-sampling disturbance on lightly overconsolidated intermediate soils by varying their plasticity and degree ...

Offshore wind turbine (OWT) monopile foundations are subjected to cyclic loading from wind, waves, and operational loads from rotating blades. Lateral monopile capacity can be significantly affected by cyclic loading, causing failure at cyclic load amplitudes lower than the failure load under monotonic loading. For monopiles in clay, undrained clay behavior under short-term cyclic soil-pile loading (e.g. extreme storm conditions) typically includes plastic soil deformation resulting from reductions in soil modulus and undrained shear strength which occur as a function of pore pressure build-up. These impacts affect the assessment of the ultimate and serviceability limit states of OWTs via natural frequency degradation and accumulated permanent rotation at the mudline, respectively. This paper introduced novel combinations of existing p-y curve design methods and compared the impact of short-term cyclic loading on monopiles in soft, medium, and stiff clay. The results of this paper indicate that short-term cyclic loading from extreme storm conditions are unlikely to significantly affect natural frequency and permanent accumulated rotation for OWT monopiles in stiff clays, but monopiles in soft clay may experience significant degradation. Further consideration is required for medium clays, as load magnitude played a strong role in both natural frequency and permanent rotation estimation.

The prediction of ultimate and fatigue demands for the design of offshore wind turbines (OWTs) requires accurate simulation of the dynamic response of OWTs subject to time-varying wind and wave loads. The magnitude of damping in an OWT system significantly influences the dynamic response, however, some sources of damping, such as foundation damping, are not explicitly considered in design guidelines and may increase damping significantly compared to commonly assumed values in design. Experimental and analytical studies have estimated the magnitude of foundation damping to be between 0.17% and 1.5% of critical, and this paper investigates how increased damping within this range affects load maxima and fatigue damage for a hypothetical 5MW OWT subjected to a variety of wind, wave, and operational conditions. The paper shows that increased damping effects the greatest percentage reduction of ultimate moment demands and fatigue damage when the OWT rotor is parked and feathered. In such cases, the aerodynamic damping is relatively low, allowing for additional damping from the foundation to account for a relatively larger proportion of the total system damping. Incorporating foundation damping in design guidelines may lead to more efficient structures, which is a crucial factor in overcoming the high cost barrier associated with offshore wind development.

The paper presents hydrogeologic properties for a leaky till–mantled fractured bedrock aquifer system based on geophysical and hydraulic tests performed at a drumlin located in northeastern Massachusetts, USA. The site profile consists of a fractured bedrock aquifer overlain by a 30 m thick unweathered, coarse-grained till aquitard. Steady state, decadal scale, hydraulics varied little until seasonal irrigation pumping was initiated in recent years, causing a substantial annual drawdown in the aquifer and leakage from the overlying till. High frequency hydraulic head data sets collected in monitoring wells record the hydraulic response to the irrigation pumping. These data sets, together with results from small scale slug and purge tests performed in monitoring wells, are used to characterize the hydrogeologic behavior of this groundwater system. Geophysical logging performed in bedrock wells confirmed the presence of numerous flowing fractures. The large-scale continuum analysis of the fractured bedrock aquifer response to the irrigation pumping yields transmissivity values consistent with those determined from the small-scale, short-term purge test results. The low hydraulic conductivity till has a significant impact on the drawdown behavior of the fractured bedrock aquifer. Calibrated values from the collective data sets and analyses result in the following properties for the 30 m thick unweathered till: hydraulic conductivity K′ = 7.2 × 10−9m/s, transmissivity T′ = 2.3 × 10−8m2/s, and storativity S′ = 2.7 × 10−4, and for the underlying fractured bedrock aquifer: T = 6.5 × 10−6m2/s with an average fracture aperture of 46 μm and hydraulic conductivity Kf= 1.3 × 10−3m/s. These results should describe similar unweathered coarse-grained till–mantled fractured bedrock aquifer systems and provide useful data for preliminary analyses prior to any site-specific investigations.

Underwater cast and cured geopolymers with Si/Al ratios of 1.78 and 2.00, synthesized from Class C fly ash and metakaolin, were characterized by X-ray diffraction, X-ray fluorescence, scanning electron microscopy, and unconfined compression, to understand the interactions between the geopolymer slurry and curing saline solutions and pertinent effects on its strength development. Slurries of geopolymers and Class G oil well cement were cast into porous molds that were immediately submerged into 0, 15, and 35 ppt saline solutions for 28 days curing, during which the pH of curing solutions was monitored. While the oil well cement exhibits a decreased compressive strength in high-salinity solutions, the strength of the two geopolymers increases with the curing solution's salinity. The underlying mechanisms are the chemical exchanges between the curing solution and geopolymer slurry, particularly the leaching or ingress of alkali ions (e.g., Na+, OH−) via diffusion, which depends upon the curing solution's salinity.

Shales are a class of multiscale, multiphase, hybrid inorganic-organic composite materials exhibiting both frictional and cohesive behavior, and it is very challenging to characterize and interpret their complex mechanical properties. A statistical nanoindentation approach with pertinent viable data analytics was developed to probe the mechanical properties of shales across different length scales. Grid nanoindentation experiments with continuous stiffness measurement performed on shales to relatively large depths of 6–8 µm obtained massive data, which were processed by the new data analytics: segmentation at selected depths of a great number (e.g., >500) of continuous Young's modulus versus indentation depth curves obtained from unknown constituent phases yielded multiple discretized sub-datasets that were processed to extract individual phases’ elastic moduli at respective segmentation depths via probability density function (PDF)-based deconvolution; these depth-dependent Young's moduli of each phase were then fitted by a newly proposed surround effect model, leading to determination of the properties of both individual phases at the nano/micro-scales (i.e., virtually infinitesimal depths) and the bulk rock at the macroscale (i.e., ~10–100 µm depths). A significant advantage of this massive data-based indentation approach is that the mechanical properties of composite materials such as shales can be probed across different scales by a single measurement technique. In addition, a new criterion, termed Bin Size Index, was formulated for selecting depth-dependent, rational, optimized bin sizes for PDF construction. For the studied shales, results show that five mechanically-distinct phases are discerned, including a virtual interface phase between hard and soft constituents accounting for a majority of indents. Coincidently, the Young's modulus of the bulk rock is nearly the same as that of the interface phase, suggesting that the macroscopic properties of similar composites may be estimated from measurements on the interface of two phases with contrasting mechanical properties. Finally, this approach can guide the selection of appropriate indentation depths to probe the mechanical properties of both highly heterogeneous bulk materials at the macroscale and their individual constituent phases at the nano/micro-scale.

Unlike most onshore geotechnical projects, conducting offshore site investigations is often difficult and technically challenging due to the harsh ocean environment. Hence, an important cost consideration is minimizing the number of soundings for an offshore project while ensuring reliable and safe designs. This study examines the possibility of reducing the number of soundings at site by using practical numerical tools to predict cone tip resistance (qt ) at unsampled locations. Prediction errors were quantified within a probabilistic framework. Two prediction approaches, i.e. 2D linear regression and Kriging, were adopted. Site investigation data from an existing offshore wind farm with homogeneous stiff clay deposit were collected and analyzed. Result shows that in a homogeneous soil deposit, it is possible to use as little as 20% of the available data to predict the remaining 80% qt profiles with small error. Monopile deformation under typical design load was also calculated using shear strength derived from the qt profile at each wind turbine location. The small spatial variation of monopile deformation suggests that a reduction in the number of geotechnical soundings for sites with uniform soil conditions would not significantly impact the foundation design.

Offshore wind energy has become a promising source of renewable energy in recent years with many installed farms around the world successfully producing energy. As preliminary wind resource studies reveal, in the US much of the potential could be tapped in deeper water where floating solutions become favorable. The efficiency of floating offshore platforms is being studied and demonstrated in pilot projects such as Hywind in Scotland. In order to reduce the substructure cost in offshore wind projects, which is usually 25-30%, a novel shared anchor concept has been studied with spar supported turbines. Simulations are carried out with National Renewable Energy Laboratory’s (NREL) OC3 Hywind floating system and 5MW wind turbine. A similar study has been carried out with semisubmersible platforms earlier. Comparing the statistics of the net anchor forces from both the types of platforms reveals decreased anchor forces in case of spar due to large force cancellation and decreased response to wave action. Given the shared anchor concept in-principle reduces the material cost with reduced number of anchors than the conventional anchor types; further reduction in anchor forces in case of spar supported platform would be more cost-beneficial with more material savings.

Sampling and laboratory testing of soils is often necessary to evaluate site-specific soil properties. Prior research has been primarily performed for clays, producing accepted practices th...

Current and future climate-related coastal impacts such as catastrophic and repetitive flooding, hurricane intensity, and sea level rise necessitate a new approach to developing and managing coastal infrastructure. Traditional &ldquo, hard&rdquo, or &ldquo, grey&rdquo, engineering solutions are proving both expensive and inflexible in the face of a rapidly changing coastal environment. Hybrid solutions that incorporate natural, nature-based, structural, and non-structural features may better achieve a broad set of goals such as ecological enhancement, long-term adaptation, and social benefits, but broad consideration and uptake of these approaches has been slow. One barrier to the widespread implementation of hybrid solutions is the lack of a relatively quick but holistic evaluation framework that places these broader environmental and societal goals on equal footing with the more traditional goal of exposure reduction. To respond to this need, the Adaptive Gradients Framework was developed and pilot-tested as a qualitative, flexible, and collaborative process guide for organizations to understand, evaluate, and potentially select more diverse kinds of infrastructural responses. These responses would ideally include natural, nature-based, and regulatory/cultural approaches, as well as hybrid designs combining multiple approaches. It enables rapid expert review of project designs based on eight metrics called &ldquo, gradients&rdquo, which include exposure reduction, cost efficiency, institutional capacity, ecological enhancement, adaptation over time, greenhouse gas reduction, participatory process, and social benefits. The framework was conceptualized and developed in three phases: relevant factors and barriers were collected from practitioners and experts by survey, these factors were ranked by importance and used to develop the initial framework, several case studies were iteratively evaluated using this technique, and the framework was finalized for implementation. The article presents the framework and a pilot test of its application, along with resources that would enable wider application of the framework by practitioners and theorists.

The contribution of foundation damping to offshore wind turbines (OWTs) is not well known, though researchers have back-calculated foundation damping from “rotor-stop” tests after estimating aerodynamic, hydrodynamic, and structural damping with numerical models. Because design guidelines do not currently recommend methods for determining foundation damping, it is typically neglected. This paper investigates the significance of foundation damping on monopile-supported OWTs subjected to extreme storm loading using a linear elastic two-dimensional finite element model. The effect of foundation damping primarily on the first natural frequency of the OWT was considered as OWT behavior is dominated by the first mode under storm loading. A simplified foundation model based on the soil-pile mudline stiffness matrix was used to represent the monopile, hydrodynamic effects were modeled via added hydrodynamic mass, and 1.00% Rayleigh structural damping was assumed. Hysteretic energy loss in the foundation was converted into a viscous, rotational dashpot at the mudline to represent foundation damping. Using the logarithmic decrement method on a finite element free vibration time history, 0.17%-0.28% of critical damping was attributed to foundation damping. Stochastic time history analysis of extreme storm conditions indicated that mudline OWT foundation damping decreases the maximum and standard deviation of mudline moment by 7–9%.

Soil and groundwater from the Neponset River floodplain deposit that receive high concentrations of deicing agents from nearby highways were investigated. The silty sand floodplain is separated by a silty aquitard from the underlying aquifer that serves as a public water supply. We made a transport-based assessment of the capacity of the aquitard to protect the underlying aquifer. One hundred seventeen soil samples and 469 groundwater samples collected during a period of 4 yr from boreholes and 10 wells grouped in two well clusters were analyzed for dissolved Cl concentration. The soil characterization and groundwater monitoring results agreed, showing a very slow change in subsurface Cl contamination with time. These data also calibrated a vertical one-dimensional advective-dispersive transport model across the deposits. Advective transport dominated only in the top 3.37 m of the floodplain deposit, with dispersion being the main transport mechanism below this depth. Due to the silty nature of the aquitard, dispersion rather than diffusion was the main transport mechanism into the floodplain-aquitard system. Soil and groundwater quality data confirmed a Cl concentration at the floodplain surface near the highway runoff drainage outlets of 2450 mg L. The model estimated a vertical dispersivity at the site of 8 mm and a vertical hydrodynamic dispersion coefficient of 3.71 × 10 m s. These data confirmed the aquitard's capacity to contain deicing agents, protecting the underlying aquifer from contamination.

A new permeameter is proposed for performing laboratory hydraulic conductivity tests on gravels with hydraulic conductivity values ranging from 0.1 to 1 m/s. A small diameter riser is connected to a large diameter cylinder, which holds the coarse-grained specimen saturated in a water bath. The release of pneumatic pressure, applied to the free surface in the riser, induces an underdamped oscillatory response of the water level in the riser, similar to an underdamped in situ slug test response in monitoring wells. A closed-form model is used to analyze the measured oscillatory hydraulic head data to calibrate the minor losses in the permeameter and the hydraulic conductivity of the specimen by performing tests without and with a specimen. The average model error of calibrated pressure head values in the riser for the tests considered are about 5% of the initial displacement of about 2 cm. The hydraulic conductivity values are calibrated considering the replicate tests, the tests of different speci...

An overview of offshore wind turbine (OWT) foundations is presented, focusing primarily on the monopile foundation. The uncertainty in offshore soil conditions as well as random wind and wave loading is currently treated with a deterministic design procedure, though some standards allow engineers to use a probability-based approach. Laterally loaded monopile foundations are typically designed using the American Petroleum Institute p-y method, which is problematic for large OWT pile diameters. Probabilistic methods are used to examine the reliability of OWT pile foundations under serviceability limit states using Euler‐Bernoulli beam elements in a two-dimensional pile‐spring model, non-linear with respect to the soil springs. The effects of soil property variation, pile design parameters, loading and large diameters on OWT pile reliability are presented. Copyright © 2014 John Wiley & Sons, Ltd.

A repeatable preparation method is useful for investigating systematic variations in behavior across a range of soil types (e.g., gradation, plasticity) and test conditions (e.g., stress level, stress history). Existing methods for preparation of laboratory specimens can be generally categorized into those for cohesionless and cohesive soils, thereby focusing on a narrow range of soils and test conditions. The applicability of these conventional preparation techniques for soils with intermediate (or transitional) properties and behaviors are relatively unknown. In this study, a range of intermediate soils that are not amenable to traditional sand-like or claylike characterization are prepared using a slurry deposition technique and evaluated in oedemetric consolidation, undrained monotonic triaxial shear, and both undrained monotonic and undrained cyclic direct simple shear by three researchers at two separate universities. Results indicate that the slurry technique developed herein can produce uniform mixtures of nonplastic, low-plasticity, and high-plasticity soils, with repeatable behaviors obtained from singular mixtures for all test methods. Evaluation of specimen response across this range of soils exhibits systematic trends of increasing compressibility with increasing plasticity and a transition from dilative to contractive tendencies with increasing soil plasticity. Collectively, these results for synthetic mixtures of silica silt and kaolin clay suggest that the slurry deposition technique is applicable to fine-grained, intermediate soils across a range of plasticity from nonplastic to high-plasticity soils.

Results from microcompression testing of micron-sized saltwater individual kaolinite flocs with different ageing times of up to 152 days show that the rearrangement of flaws or weak links towards a more uniform distribution contributes to the thixotropic increase in floc mechanical properties. Evidence of this newly identified thixotropism of clay flocs is provided by the Weibull moduli of floc stiffness and yield shear strength, which are well fitted using the stretched exponential thixotropy model. The Weibull modulus is a good quantitative descriptor of the thixotropic evolution of clay floc microstructure.

Roughly 60% of potentially exploitable offshore wind power is located beyond the range of water depths suitable for fixed foundations, where floating offshore wind towers (FOWTs) moored to the seabed are required. Anchors comprise a critical component of the mooring system. A variety of anchor types are potentially suitable for this purpose, but all have limitations in regards to the types of seabed soils in which they may be deployed and the type of mooring systems (catenary, taut) for which they are suitable. Additionally, foundations for offshore wind make up a large portion of project cost; therefore, minimizing the costs of fabrication, transport and installation of anchors is a key aspect of overall project feasibility. In contrast to offshore oil-gas installations, offshore wind towers are deployed in arrays, which offer the possibility of reducing project costs by attaching more than one mooring line to a single anchor. In addition to direct cost savings, the multiline anchor concept permits a reduced scale of costly offshore geotechnical site investigations. This paper first examines different anchor types that are potentially suitable as anchors for FOWTs, largely within the context of their traditional usage in securing a single mooring line to the seabed. Then, the potential for adapting these anchors to multiline systems is assessed. Anchor types examined include: driven piles, dynamic piles, suction caissons, drag embedded anchors, vertically loaded anchors, pile driven plate anchors (PDPA), dynamically embedded plate anchors (DEPLA), and suction embedded plate anchors (SEPLA). Performance considerations for each anchor include: Soil profile constraints, vertical load capacity, horizontal load capacity, precision of positioning, installation cost, efficiency, performance under sustained loading, potential loss of embedment, as well as other anchor specific considerations.

A mooring and anchoring concept for floating offshore wind turbines is introduced in which each anchor moors multiple floating platforms. Several possible geometries are identified and it is shown that the number of anchors for a wind farm can be reduced by factors of at least 3. Dynamic simulation of turbine dynamics for one of the candidate geometries and for two directions of wind and wave loading allows estimation of multiline anchor forces the preview the types of loads that a multiline anchor will need to resist. Preliminary findings indicate that the peak demand on the anchor may be reduced by as much as 30% but that anchors used in such a system will need to be able to resist multi-directional loading.Copyright © 2016 by ASME

The Burswood clay is a lightly overconsolidated and sensitive silty clay of high to extremely high plasticity. In two extensive characterisation studies, a wide range of in situ tests were carried out at the Burswood site, including full-flow penetrometer tests (T-bar, ball and plate). In addition, thin-wall tube samples and high-quality Sherbrooke block samples were collected for laboratory testing. The stress–strain–strength, consolidation and compressibility characteristics of Burswood clay were investigated, and the performance of various penetrometers in characterising the soft Burswood clay was assessed. The paper compares values of stiffness and shear strength measured by different in situ and laboratory tests, quantifying the degree of non-linearity of the stress–strain response, the effect of sample disturbance on the measured mechanical properties, the degree of strength anisotropy, and the influence of strain rate on the measured shear strength. In addition, factors relating the net penetration resistance measured by cone, T-bar and ball penetrometers to yield stress, small-strain shear modulus and different measures of undrained shear strength are also provided.

Full-flow penetrometers (the T-bar and ball) are increasingly used on sites with thick deposits of soft clays, particularly prevalent offshore. Full-flow penetration tests were performed at five international well-characterized soft clay test sites to assess the use of full-flow penetrometers to estimate undrained shear strength. Field vane shear data were used as the reference undrained strength. Statistical analyses of strength factors indicates that full-flow penetrometers provide an estimate of undrained shear strength at a similar level of reliability compared to the piezocone. Relationships for estimating the strength factor and soil sensitivity using only full-flow penetrometer data obtained during initial penetration and extraction are developed. A strong dependence of the strength factor on sensitivity was identified and can be used for the estimation of undrained strength. The effectiveness and use of the developed correlations are demonstrated through their application at an additional test site.

ASTM D4186/D4186M-12, Standard Test Method for One-Dimensional Consolidation Properties of Saturated Cohesive Soils Using Controlled-Strain Loading, requires back pressure saturation for all specimens to accurately measure pore fluid pressure and flow behavior. Constant rate of strain (CRS) consolidation testing performed without back pressure saturation has the potential to provide significant time and cost savings, as the need for costly back pressure saturation equipment and the time required for specimen back pressure saturation would be eliminated. The results of one-dimensional CRS consolidation comparison tests performed with and without back pressure saturation on high quality Sherbrooke block and 76-mm diameter modified tube specimens and on reconstituted specimens of low overconsolidation ratio, soft, saturated clays are presented herein. Comparison of the compression curves from specimens tested with and without back pressure saturation, especially at stresses greater than the estimated in situ vertical effective stress, show good agreement. Flow behavior between the two types of specimens is more erratic at low stresses but becomes more comparable as the effective stress level increases. It can be concluded from the results that accurate CRS consolidation stress–strain behavior can be measured for saturated specimens tested without back pressure saturation for stresses greater than the in situ vertical effective stress.

Leaky aquifers provide protected drinking water since the aquifer is overlain by an aquitard, and this study develops a method to estimate hydraulic properties of the latter deposit. Steady pumping, supply well shutdowns, and slug tests generate data in adjacent monitoring well clusters that characterize the aquitard. An existing steady model estimates a site-averaged value of the aquitard permeability k if its thickness is known, and this site-averaged estimate may be compared with local k estimates from conventional and extended slug tests. A shutdown attenuation model estimates a local value of the consolidation coefficient CV, which combines with the local k value to specify the compressibility α of the aquitard. The method is illustrated for the Fowl Meadow Aquifer, a stratified drift deposit used as a drinking water supply in eastern Massachusetts (USA), with an overlying silt aquitard of 10 m thickness. Steady data and theory suggest a site-averaged k of 2.3 × 10–17 m2 for the aquitard, while the shutdown attenuation model generates local CV values that vary from 10–5 to 10–3 m2/s. The slug tests yield a local k variation (10–17–10–13 m2) that brackets the site-averaged value, and an α range of 10–9–10–7 Pa–1.

The undrained remolded shear strength of soft clays is of importance in geosystem design, particularly for offshore structures. Common methods to estimate remolded shear strength, such as correlations with cone penetration data, direct measurement with an in situ field vane shear device, and laboratory measurements, produce varied results and can be particularly costly and time consuming. Full-flow penetrometers (T-bar and Ball) provide an alternative rapid method to estimate remolded shear strength and soil sensitivity through remolding soil by repeated cycling of the penetrometer up and down over a given depth interval. The cyclic penetration resistance degradation curve inherently contains information regarding remolded strength and sensitivity. The objective of this paper is to assess the ability of full-flow penetrometers to predict remolded strength and soil sensitivity, and to develop a suite of predictive correlations in which these properties can be estimated in the absence of complementary laboratory or in situ test data. To accomplish this, full-flow penetration profiles and cyclic tests were performed at five well characterized soft clay sites, which together represent the broad range of soils in which the penetrometers will be often used. A previously developed model for the reduction in penetration resistance with cycling is modified to predict the entire degradation curve, including the remolded penetration resistance using only measurements obtained during initial penetrometer penetration and extraction. Using field vane shear strength as the reference measurement, correlations are developed to predict soil sensitivity and remolded shear strength based solely on full-flow penetrometer data, which is particularly useful in site investigation programs where site specific data are not yet available or are sparse. Finally, the usefulness of these relationships is demonstrated by implementing them for two additional soft clay sites.

Summary We derive a closed form theory of water level fluctuations caused by slug tests in a well with an annulus that extends to the piezometric surface. This hydraulics can be created by small diameter slug test equipment in a large diameter well, with an annulus established by borehole casing and the riser pipe of the equipment. The conservation of mass equation couples aquifer hydraulics, core hydraulics inside the riser pipe (which include inertia), and annular hydraulics outside the riser pipe (which include inertia and linear friction). The linear friction is needed to attenuate oscillations between the core and annulus, which would otherwise persist indefinitely after damping of aquifer discharge. A characteristic velocity is adopted for the annular friction, so that aquifer permeability is the sole calibration parameter. We calibrate the theory with overdamped and underdamped experiments run in a limestone aquifer at the Hydrogeological Experimental Site of Poitiers in France by Audouin, O., Bodin, J. 2007. Analysis of slug tests with high frequency oscillations. Journal of Hydrology 334, 282–289. The data and analytical theory yield plausible, accurate permeability estimates of 4.1 × 10 −12 and 1.7 × 10 −11 m 2 . Portable, small diameter slug testing devices may accordingly be used in permanent, large diameter cased boreholes to estimate aquifer permeability, although the annular effects can obscure aquifer hydraulics. The annular effects may also occur in slug tests on wells with skins, bypasses, and packers, although different boundary and matching conditions would be needed to model this hydraulics.

Summary We measure and model the unsteady, axisymmetric response of an unconfined aquifer to delayed, arbitrary recharge. Water table drainage follows the initial elastic aquifer response, as modeled for uniform, instantaneous recharge by Zlotnik and Ledder [Zlotnik, V., Ledder, G., 1992. Groundwater flow in a compressible unconfined aquifer with uniform circular recharge. Water Resources Research 28(6), 1619–1630] and delayed drainage by Moench [Moench, A.F., 1995. Combining the Neuman and Boulton models for flow to a well in an unconfined aquifer. Ground Water 33(3), 378–384]. We extend their analyses with a convolution integral that models the delayed response of an aquifer to infiltration from a circular infiltration basin. The basin routes the hydrograph to the water table with a decay constant dependent on a Brooks and Corey [Brooks, R.H., Corey, A.T., 1966. Properties of porous media affecting fluid flow. Journal of the Irrigation and Drainage Division ASCE 92(2), 61–88] unsaturated permeability exponent. The resulting closed form model approaches Neuman’s [Neuman, S.P., 1972. Theory of flow in unconfined aquifers considering delayed response of the water table. Water Resources Research 8(4), 1031–1045] partially penetrating pump test equation for a small source radius, instantaneous, uniform drainage and a shallow screen section. Irrigation pump data at a well characterized part of the Plymouth-Carver Aquifer in southeastern Massachusetts calibrate the small source model, while infiltration data from the closed drainage system of State Route 25 calibrate the infiltration basin model. The calibrated permeability, elasticity, specific yield, and permeability exponent are plausible and consistent for the pump and infiltration data sets.

While improvements in equipment and sampling methods have enabled collection of better quality samples of soft clays for more reliable engineering design and performance prediction, current sample quality assessment methods typically require destructive laboratory testing performed long after samples are taken. This paper describes a nondestructive technique for sample quality assessment of soft clays using shear wave velocity. A portable bender element device was used to measure shear wave velocity ( Vvh ) in the field immediately following collection of Sherbrooke block, tube, and split spoon samples of Boston blue clay. Vvh values were compared to in situ values from seismic piezocone ( VSCPTU ) tests. The ratio Vvh ∕ VSCPTU was compared with results from a conventional, laboratory-based assessment method. Results indicate a consistent correlation between laboratory-based methods and the Vvh ∕ VSCPTU ratio, which ranges from Vvh ∕ VSCPTU =0.77 for the block samples to 0.28 for split spoon samples. The ...