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 presents an evaluation of inundation, erosion, and wave damage for a coastal community in Rhode Island, USA. A methodology called the Coastal Environmental Risk Index (CERI) was used that incorporates levels of inundation including sea level rise, wave heights using STWAVE, and detailed information about individual structures from an E911 database. This information was input into damage functions developed by the U.S. Army Corps of Engineers following Hurricane Sandy. Damage from erosion was evaluated separately from local published erosion rates. Using CERI, two different adaptation strategies were evaluated that included a combination of dune restoration, protective berms, and a tide gate. A total of 151 out of 708 structures were estimated to be protected from inundation and wave action by the combined measures. More importantly, the use of CERI allowed for the assessment of the impact of different adaptation strategies on both individual structures and an entire community in a Geographical Information Systems (GIS) environment. This tool shows promise for use by coastal managers to assess damage and mitigate risk to coastal communities.

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 presentation describes the shear wave velocity measurement techniques that have been utilized over that past decade at the Marine Geomechanics Laboratory (MGL) at the University of Rhode Island (URI). The shear wave velocity of marine sediments is of interest to both the underwater acoustics and marine geotechnical engineering communities. In underwater acoustics, sediment shear wave velocity plays an important role in understanding compressional wave attenuation. Geotechnical engineers utilize shear wave velocity, for example, for the analysis of seismic site response and evaluation of soil liquefaction potential. The shear wave measurement techniques that will be covered include laboratory bender element tests made within the triaxial apparatus that allows for the application of situ stress states on the test specimen. Bender elements have also been used in the lab to make shear wave velocity measurements in reconstituted sand fills at very low stress levels, as well as on intact clay sediments directly within a piston core. More recently, field measurements of shear wave velocity have been made using a system developed by colleagues at URI that involves the measurement and inversion of Scholte waves. The presentation aims to stimulate dialog between the fields of underwater acoustics and marine geomechanics on the topic of shear wave velocity.

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%.