There is increasing interest in using micropiles as a foundation type for floating offshore wind farms in deep water. Contrary to onshore projects, proof load testing of micropiles in the offshore environment is extremely difficult if even feasible, and as a result, better capacity prediction approaches are required. A key improvement would be incorporation of constant normal stiffness boundary conditions in the evaluation of shaft resistance of small-diameter grouted micropiles. The objective of this study is to present the results of a newly developed, active control system for performing constant normal stiffness tests on sand. A laboratory testing program of monotonic CNS tests on Monterey sand was performed in which relative density, soil spring stiffness, and initial normal effective stress were varied. The ability of the control system to maintain constant normal stiffness during shear was found to be excellent, and test results on both dilative and contractive samples demonstrated consistent trends of shear strength and changes in both shear band thickness and normal effective stress.

There is an increased interest in the use of drilled and grouted micropiles as a foundation for floating offshore wind farms in deep water. Unlike onshore projects, conducting proof load tests for micropiles in offshore settings is challenging, if not impossible, necessitating improved capacity prediction methods. The objective of this study is to assess whether constant normal stiffness (CNS) testing in the laboratory can more accurately model the axial capacity of small-diameter grouted micropiles. This was accomplished by performing a series of monotonic CNS tests on samples of Monterey sand at different values of relative density, soil spring stiffness, and initial normal effective stress. The results suggest that there is a unique relationship between the amount of shear band dilation and stress-corrected relative density and that an increase in soil spring stiffness suppresses dilation. Most importantly, a conceptual framework is presented that may improve our understanding of the static capacity of drilled piles, especially micropiles that includes non-linear normal stiffness changes around the pile. Field testing including pile load testing can be used to better verify this framework.

This paper presents an assessment of foundation damping in piled offshore wind jacket structures through a case study of the Block Island Wind Farm (BIWF). Foundation damping is one of several sources of energy dissipation which can improve fatigue performance in offshore wind structures. Damping was quantified through operational model analysis (i.e. system identification) using structural health monitoring data combined with foundation damping modeling. The results showed that for the 1st bending mode the hysteretic damping ratio of the pile under axial cyclic loading was estimated to range from 0.2% to 1.5%. This range was comparable in magnitude to the foundation damping ratios documented for operational offshore wind monopiles under lateral loading.

Offshore wind-turbine (OWT) support structures are subjected to cyclic dynamic loads with variations in loadings from wind and waves as well as the rotation of blades throughout their lifetime. The magnitude and extent of the cyclic loading can create a fatigue limit state controlling the design of support structures. In this paper, the remaining fatigue life of the support structure for a GE Haliade 6 MW fixed-bottom jacket offshore wind turbine within the Block Island Wind Farm (BIWF) is assessed. The fatigue damage to the tower and the jacket support structure using stress time histories at instrumented and non-instrumented locations are processed. Two validated finite-element models are utilized for assessing the stress cycles. The modal expansion method and a simplified approach using static calculations of the responses are employed to estimate the stress at the non-instrumented locations—known as virtual sensors. It is found that the hotspots at the base of the tower have longer service lives than the jacket. The fatigue damage to the jacket leg joints is less than 20% and 40% of its fatigue capacity during the 25-year design lifetime of the BIWF OWT, using the modal expansion method and the simplified static approach, respectively.

This paper describes a simple approach to modify a direct shear test device to perform interface shear tests under constant normal stiffness (CNS) conditions. There is continued interest in the use of piles and pile anchors for both fixed and floating offshore wind structures, particularly in the sandy soils along the East Coast of the United States. Design analyses and modeling may require CNS testing, which closely represents the boundary conditions near the interface of the pile during axial monotonic and cyclic loading. The simple and economical modifications allow for the testing of any pile material-sand interface by mechanically maintaining constant normal stiffness conditions on the sample during shear.

Considerable effort has been made to link submarine slope failures to changes in local and global-scale environmental conditions, in order to assess landslide hazard probability. Here we provide the first radiocarbon dates of hemipelagic sediment overlying mass transport deposits and inferred failure surfaces of the Currituck Slide Complex (CSC), a prominent landslide scar on the U.S. mid-Atlantic continental slope. The dates, taken from both the upper and lower scars of the complex, constrain the age of the last major failure event to 13,835 and 16,020 years BP. Time correlation of the hemipelagic sediments across the landslide scar and proximal deposit suggests a single failure of both the upper and lower parts of this 160 km3 volume. A higher rate of sediment supply from the periglacial Appalachian Mountains and from glacial melt-water pulses, with an exposed continental shelf at that time, may have enlarged a shelf-edge delta at the site of the CSC, which may have facilitated or triggered failure. A smaller landslide at the southern edge of the complex with a less well-defined geomorphologic footprint is dated at 5500 BP and possibly represents the reshaping of the seafloor around the CSC triggered by lowfrequency earthquakes on the nearby continental margin.

This work presents the design and installation of a continuous monitoring system for one of the offshore wind turbines in the Block Island Wind Farm, which is located 6.1 km off the coast of Block Island in Rhode Island, USA. The instrumentation plan includes wired and wireless accelerometers, strain gauges, and inclinometers. Considerations for the instrumentation design are discussed, including the type, number and location of sensors, as well as some of the challenges in the installation of sensors. The process of transferring data, samples of collected data, automated system identification and some preliminary results are presented.

Encroachment of infrastructure on the natural beach system constrains dune volumes and necessitates construction of structural and nonstructural mitigation measures to improve coastal resilience. Nature-based solutions, such as dunes reinforced with geosynthetic sand containers (GSCs), are increasingly being used to stabilize coastlines and protect communities from smaller storm events (e.g. 50-year storms) while at the same time providing flexibility in design considering the uncertainty regarding rates of sea level rise and the increasing destructive power of storm events. Using risk-based hazard assessments, such as fragility curves, it is possible to quantify the resiliency of reinforced coastal systems to address these dynamic conditions. A fragility curve represents the conditional probability of failure of a coastal structure (e.g. natural dune, reinforced dune, seawall, etc.) as a function of a certain stress acting on the structure (typically water level, wave height/period; Gruhn et al. 2012). The main advantage of a fragility curve, compared to a damage function that quantifies a deterministic degree of damage directly to a stress, is that it can account for uncertainties in both the structural resistance (i.e. capacity) and the environmental stress (i.e. demand) of the system. The objective of this research is to present a fragility analysis of a U.S. Federally funded GSC-reinforced dune in Montauk, NY. This dune was constructed in 2016 and experienced significant erosion of the protective berm and sand covering the GSCs during a 1-year storm event that same year.

Distributed Acoustic Sensing (DAS) is a fiber optic sensing system that is used for vibration monitoring. At a minimum, DAS is composed of a fiber optic cable and an optic analyzer called an interrogator. The oil and gas industry has used DAS for over a decade to monitor infrastructure such as pipelines for leaks, and in recent years changes in DAS performance over time have been observed for DAS arrays that are buried in the ground. This dissertation investigates the effect that soil type, soil temperature, soil moisture, time in-situ, and vehicle loading have on DAS performance for fiber optic cables buried in soil. This was accomplished through a field testing program involving two newly installed DAS arrays. For the first installation, a new portion of DAS array was added to an existing DAS array installed a decade prior. The new portion of the DAS array was installed in four different soil types: native fill, sand, gravel, and an excavatable flowable fill. Soil moisture and temperature sensors were buried adjacent to the fiber optic cable to monitor seasonal environmental changes over time. Periodic impact testing was performed at set locations along the DAS array for over one year. A second, temporary DAS array was installed to test the effect of vehicle loading on DAS performance. Signal to Noise Ratio (SNR) of the DAS response was used for all the tests to evaluate the system performance. The results of the impact testing program indicated that the portions of the array in gravel performed more consistently over time. Changes in soil moisture or soil temperature did not appear to affect DAS performance. The results also indicated that time DAS performance does change somewhat over time. Performance variance increased in new portions of array in all material types through time. The SNR in portions of the DAS array in native silty sand material dropped slightly, while the SNR in portions of the array in sand fill and flowable fill material decreased significantly over time. This significant change in performance occurred while testing halted from March 2020 to August 2020 due to the Covid-19 pandemic. These significant changes in performance were observed in the new portion of test bed, while the performance of the prior installation remained consistent. It may be that, after some time in-situ, SNR in a DAS array will reach a steady state. Though it is unfortunate that testing was on pause while changes in DAS performance developed, the observed changes emphasize the potential of DAS to be used for infrastructure change-detection monitoring. In the temporary test bed, increasing vehicle loads were observed to increase DAS performance, although there was considerable variability in the measured SNR. The significant variation in DAS response is likely due to various industrial activities on-site and some disturbance to the array while on-boarding and off-boarding vehicles. The results of this experiment indicated that the presence of load on less than 10% of an array channel length may improve DAS performance. Overall, this dissertation provides guidance that can help inform the civil engineering community with respect to installation design recommendations related to DAS used for infrastructure monitoring.

Fibre-optic distributed acoustic Sensing (DAS) provide information on vibration response comparable with geophones and seismometers and may become widely used for infrastructure monitoring. DAS can be used to monitor earthquake activity, carbon dioxide sequestration, pipelines and roadway/railway subgrade integrity. Little is known about the effect of soil type and burial method on DAS response. The objective of this paper is to present the results of a field study in which DAS was installed in different soil types (silty sand, clean sand, gravel and a flowable fill) adjacent to an existing, decade-old DAS array. Impact tests were performed to evaluate DAS response in the different soil types and a portion of DAS array installed a decade prior. Signal-to-noise ratio (SNR) was used to compare performance of DAS response. Results of the monitoring programme indicate that portions of the array in sand, gravel and silty sand had a good response with comparable SNR. A newer portion of the array showed ∼5 dB better than the decade-old portion of DAS array, both in silty sand, with the old portion still performing well. These results may help build confidence with the geotechnical community regarding the longevity performance of DAS for infrastructure vibration monitoring.

This paper proposes a new approach for incorporating the positive attributes of the small-strain shear wave velocity (VS), stress-based simplified procedure and the cyclic strain procedure into penetration test, stress-based simplified liquefaction triggering models, with the objective of more fully accounting for the influence of intrinsic soil properties and soil state variables on liquefaction triggering. Current simplified liquefaction procedures are limited in their ability to capture the effects of intrinsic properties (grain size, mineralogy, grain shape, etc.) and the state properties (stress state, void ratio, fabric, etc.). To overcome these limitations, a new mechanistically based K-gamma factor is proposed that can be incorporated in penetration test, stress-based simplified liquefaction triggering models in place of the currently used K-sigma factor. However, K-gamma is conceptually very different from K-sigma. While most K-sigma relationships have largely been empirically based and relate to the soil's cyclic resistance to liquefaction, K-gamma is more mechanistically based and relates to the loading imposed on the soil. Specifically, K-gamma is based on equating the shear strain induced in a given soil at given initial stress state and subjected to a given shear stress to the induced shear strain when the soil is confined at a reference initial stress state, all else being equal. Analyses show that K gamma is able to capture the liquefaction triggering behavior in both lab and field data in a wide range of soils and stress states. Numerically, K-gamma and K-sigma are similar for young, normally consolidated sandy soils when the factor of safety (FS) against liquefaction triggering is close to one, but may differ significantly for other scenarios and/or conditions. This has important implications for probabilistic-based analyses which consider a range of shaking intensities imposed on the soil, not just the case where FS=1. (C) 2022 American Society of Civil Engineers.

Acoustic pressure and three components of particle velocity were measured on bottom mounted Ocean Bottom Recorders (OBX) during an experiment conducted in Narragansett Bay, Rhode Island, USA. Intensity based algorithms were implemented to estimate the direction of arrival (DOA) using data from a source of opportunity. Time-frequency representation of the azimuth angles were constructed to understand the temporal and frequency dependance of the azimuth estimates. This visualization offers a useful tool, especially when used in conjunction with the spectrogram, to identify multiple sources and their frequency content and time of occurrences. The ambient noise data collected on the OBX was used to estimate the bottom parameters using the H/V ratio method. This bottom model was then used to predict the waveguide invariant. The predicted value of the waveguide invariant provides a reasonable match to the value calculated using the striation pattern in the spectrogram of the data.

The STORMTOOLS Coastal Environmental Risk Index (CERI) has historically been used to assess the damage to residential and commercial structures from coastal flooding, including the effects of sea level rise (SLR) in RI. In the present study, CERI was extended to address the impact of flooding for 100 yr storm, including the effects of SLR, to the newly renovated Warren, RI wastewater treatment facilities (WWTF), located on the tidal Warren River, using FEMA HAZUS damage curves. The analysis shows that the average damage for 100 yr flooding, across all components of the facility, increases with sea level from 16% (0 ft SLR), 23% (2 ft SLR), 26% (3 ft SLR), to 28% (5 ft SLR). The primary settling and chlorination tanks are at most risk and the aeration and reaction tanks at least risk. In an effort to validate the FEMA HAZUS WWTF damage curves, CERI was applied to predict flood damage during the 3 day, March/April 2010 flooding event (500 yr) to the Cranston, Warwick, and West Warwick WWTF located on the Pawtuxet River, RI. The predictions of the damage to each WWTF from this event were compared to observations of the damage made by the plant operators. The percent damage was estimated by comparing the cost of the damage to the assessed value of the facility. Using the FEMA HAZUS damage curves for the observed level of inundation (7 to 8 ft) predicted that the Warwick and West Warwick facility damage ranged from 15 to 45% with an average value of about 30%. The Cranston WWTF damage was very low (<1%) because of the elevation of the facility. The observed damage for the 2010 flood event was approximately 21% for the Warwick facility and 18% for the West Warwick facility, between the FEMA HAZUS lower and average values. Damage to the Cranston facility was consistent between FEMA HAZUS and observed values at <1%.

Under the STORMTOOLS initiative, maps of the impact of sea level rise (SLR) (0 to 12 ft), nuisance flooding (1–10 yr), 25, 50, and 100 yr storms, and hindcasts of the four top ranked tropical storms have been developed for the coastal waters of Rhode Island (RI). Estimates of the design elevations, expressed in terms of the Base Flood Elevation (BFE) and thus incorporating surge and associated wave conditions, have also been developed, including the effects of SLR to facilitate structural design. Finally, Coastal Environmental Risk Index (CERI) maps have been developed to estimate the risk to individual structures and infrastructure. CERI employs the BFE maps in concert with damage curves for residential and commercial structures to make estimates of damage to individual structures. All maps are available via an ArcGIS Hub. The objective of this senior design capstone project was to develop STORMTOOLS Design Load maps (SDL) with a goal of estimating the hydrostatic, hydrodynamic, wave, and debris loading, based on ASCE/SEI 7–16 Minimum Design Standards methods, on residential structures in the RI coastal floodplain. The resulting maps display the unitized loads and thus can be scaled for any structure of interest. The goal of the maps is to provide environmental loads that support the design of structures, and reduce the time and cost required in performing the design and the permitting process, while also improving the accuracy and consistency of the designs. SDL maps were generated for all loads, including the effects of SLR for a test case: the Watch Hill/Misquamicut Beach, Westerly, along the southern RI coast. The Autodesk Professional Robot Structural Analysis software, along with SDL loading, was used to evaluate the designs for selected on-grade and pile-elevated residential structures. Damage curves were generated for each and shown to be consistent with the US Army Corps of Engineers empirical damage curves currently used in CERI.

Hurricane Sandy was the deadliest and most destructive event of the 2012 Atlantic hurricane season. It originated as a storm off the coast of West Africa that turned into a tropical wave in the southwestern Caribbean Sea, and then into a hurricane that moved slowly north along the United States East Coast. Numerous regional coastal communities and urban centers in New Jersey (NJ) and the New York City (NYC) metropolitan area experienced widespread flooding, extreme winds, and heavy damage that disrupted daily life and business in Lower Manhattan, the world’s financial capital. Consequences with great geotechnical engineering interest include: (i) modification of the regional coastal geomorphology due to storm surge, with the birth of new inlets, erosion, scour of soil at the shorelines; (ii) damage in coastal communities that revealed the vulnerability of residential building foundations not designed according to modern flood protection standards; and (iii) interruption of service of buried structures and below ground infrastructure due to flood damage to nonstructural components. This paper presents observations of characteristic damage to geotechnical infrastructure and alteration of the geologic setting collected and documented by the Geotechnical Extreme Events Reconnaissance Association (GEER; geerassociation.org) team that was activated while the hurricane reached NY-NJ. It was led by the first two coauthors with a core of ten GEER volunteers from academia and the industry, who were joined by a large team of local engineers with the support of public agencies, all working diligently to capture observations in a timely manner. A summary of the reconnaissance work, background research, main design impacts, and examples of improvement projects are provided. The importance of urban infrastructure resiliency and sustainability is discussed as a main lesson from this case history, and some actions needed to achieve those are proposed.

Increased coastal erosion rates have forced communities to rethink how to manage vulnerable coastlines. In many locations there is a trend towards implementing temporary engineering solutions, such as geotextile sand containers (GSCs) and geo-tubes, to stabilize erosion hot spots and assess the impact of these designs while long-term solutions are developed. GSCs and geo-tubes have the potential to increase the resilience of natural systems to protect coastlines from smaller storm events (e.g. 25-year storms) while providing flexibility in design considering the uncertainty regarding future rates of sea level rise and storm frequency. The objective of this paper is to summarize the performance of geotextile stabilized coastal sites and present results of on-going field studies to assess the performance of GSC reinforced dunes in Montauk, NY. The better-than-expected, resilient performance of GSCs and geo-tubes at most locations and recent reinforcement of dunes, bluffs, and shorelines in New York, Massachusetts, and Hawaii emphasizes the need for continued field research and in situ monitoring to collect high-quality performance data to better evaluate laboratory experiments and numerical models developed to predict the hydraulic stability of these systems.

This paper uses case studies of scour at bridges in Rhode Island to evaluate the current HEC-18 scour equations used to assess bridge safety and design. The study utilizes data from two major historical storm events—a 500-year flood and a 25-year hurricane (Sandy). Hydraulic analyses were performed using the HEC-RAS program at three bridge study sites, two in riverine environments and one in a tidal environment. Detailed bathymetry and topography of each site was obtained using a variety of methods. Flow boundary conditions were obtained from USGS gages and a numerical storm surge model. Sediment samples indicated that the bed materials were cohesionless ranging from silts to boulders. Scour predictions were compared to sounding data collected before and after the historical events. The results of the analyses indicated that the HEC-18 equations yielded conservative predictions of scour at all bridges analyzed in this study. The level of conservatism depended on the particular equation that was utilized. The results also suggested that the level of conservatism could be reduced by better characterization of the D50 of the bed materials and consideration of the transient nature of storm events.

Misquamicut is a coastal community located in Westerly, Rhode Island with a high density of structures that is at risk from inundation, wave, and wind damage from large storm events. The area has suffered significant damage from storms in the past such as the Hurricane of 1938, Hurricane Carol in 1954, and most recently, Superstorm Sandy in 2012. This area is also highly susceptible to sea level rise (SLR), which is predicted to be as high as 7 feet by the year 2100 (NOAA, 2017). A tool called the Coastal Environmental Risk Index (CERI) was used to estimate damage to structures located in Misquamicut due to a 100 year storm event with and without 7 feet of sea level rise. Using CERI, four mitigation strategies were evaluated to improve resiliency of the community: basement window plugs, dune restoration and reinforcement, a tide gate, and elevation of structures.