Oliver-Denzil S. Taylor

Partially saturated soil causing significant variability in near surface seismic signals

The behaviour of dry, moist, and saturated soils has been studied for over a century without adequately investigating the behaviour associated with transient saturation in the near surface, i.e. the upper 1 m of overburden, including the effects of rapid meteorological changes, dynamic fluid flow, and variability of saturation on shallow seismic sensors. This paper presents observational data wherein the geophysical instrumentation response was significantly influenced by near-surface post-precipitation saturation and additional laboratory experimentation on the effects of saturation on shear wave velocity. The lack of partially-saturated data is primarily because transient meteorological events have not been critically important to the types of long-term deployments performed in the past, where sensors were situated in hard-rock, collecting data under idealized conditions, as opposed to sedimentary settings. Shorter-duration deployments and smaller system architectures, e.g. persistent monitoring, now necessitate detailed a priori knowledge of meteorological impacts to system design and performance. The purpose of this persistent monitoring geophysical instrumentation is to continually monitor the near surface and relate small perturbations to a specific source type(s) and distance(s) from the receiver. As such, the received signal is compared to known sources within a predetermined geological/ meteorological condition. Presented herein is the calibration signal generated by a 3.63-kg (8-lb) sledgehammer prior to and post 36 hours of steady precipitation. The resulting subsurface seismic velocity time-histories show a significant increase in signal amplitude, change in frequency content and no change in duration. Thus, the amplification effects of near-surface moisture variability combined with dynamic pore fluid could be interpreted as false positives of a specific source signature and/or instrument failure.

Hazard and Risk Potential of Unconventional Hydrocarbon Development-Induced Seismicity within the Central United States

AbstractUnconventional hydrocarbon development-induced seismic hazard in historically aseismic regions is more frequent and concentrated than seismicity in established tectonic high-hazard zones, and the current standard of practice for risk assessment for infrastructure is not applicable for this highly variable, induced hazard. A substantial seismic increase has been observed in historically aseismic regions and in close proximity to federal infrastructure within Arkansas, Kentucky, Missouri, Oklahoma, Tennessee, Texas, and Virginia. Seismological events M2.0 and greater, spanning February 8, 1950 until October 20, 2013 were analyzed to identify and assess the hazard potential. Geospatial and temporal observations correlate the seismic increase to the rise of unconventional hydrocarbon development, wherein all production components contribute to weakening of the subsurface and induced seismicity. Unconventional hydrocarbon production hazard has become more analogous with deep ore mining in terms of ener...

Near Surface Laboratory Testing Protocol Development

Geotechnical laboratory testing focuses on the behavior of soils subjected to confining pressures in excess of those experienced within the near-surface environment (the upper 1 m of the soil profile). Such standardized protocols have set-up stresses, e.g., seating loads and stabilization vacuum pressures, in excess of the failure strength observed at low confinement. Therefore, effective stress principles are often used to infer low confinement behavior within a laboratory setting. Neither the standardized protocols nor the use of effective stress principles encapsulate the near-surface environment or the true behavior. The purpose of this technical report is to provide laboratorytesting protocols for physical experimentation within the near-surface environment. For standardized testing equipment, e.g., triaxial and simple shear devices, existing protocols have been modified. New testing protocols have been designed for experimental equipment, e.g., the Ultrasonic NearSurface Inundation Testing device (UNIT) or for unconfined drained selfsupporting testing (UD). The protocols presented herein are for commercial and prototype equipment used in the ERDC Geotechnical and Structures Laboratory (GSL) and are readily adaptable to other equipment manufacturers’ devices. DISCLAIMER: The contents of this report are not to be used for advertising, publication, or promotional purposes. Citation of trade names does not constitute an official endorsement or approval of the use of such commercial products. All product names and trademarks cited are the property of their respective owners. The findings of this report are not to be construed as an official Department of the Army position unless so designated by other authorized documents. DESTROY THIS REPORT WHEN NO LONGER NEEDED. DO NOT RETURN IT TO THE ORIGINATOR. ERDC/GSL TR-18-12 iii

Can Repetitive Small Magnitude-Induced Seismic Events Actually Cause Damage?

Geoengineering activities such as reservoir impoundment, mining, wastewater injection, geothermal systems, and CO2 capture have been linked directly to induced seismicity. With the industrial boom in natural shale gas production regions previously aseismic areas have seen an exponential growth in the frequency of small magnitude events, with multiple events observed in close proximity within a 24-hour time period. While the overwhelming majority of induced seismic research has focused on the causality, the potential risk posed to critical federal infrastructure has escaped scrutiny. This proposes the question, “Can repetitive small magnitude-induced seismic events actually cause damage?” A review of the potential risk is presented herein, concluding that a simplistic definitive statement of whether single or multiple small magnitude-induced seismic events do or do not cause damage to critical infrastructure cannot be justified, and warrants additional study. However, recent observations and research suggest the likelihood that these geoengineering-induced events can and do cause detrimental degradation of the subsurface (damaging the overlying structure) is not insignificant.

SCOUR DETECTION AND RIVERINE HEALTH ASSESSMENT USING INFRASOUND

Scour and river system health monitoring are serious problems for monitoring of civil infrastructure, bridge capacity and performing military route assessments in remote regions. Knowledge of how the overall system behaves over time is crucial for assessment of bridge foundations and barge navigation. This research focuses on the use of infrasound for remote scour detection and river system health monitoring. Previous research on a steel, through truss railroad bridge at Ft. Leonard Wood, MO proved the feasibility of acoustically detecting the fundamental modes of a bridge from tactical distances (> 20 km) using infrasound monitoring without on-site inspection of the structure. While bridges are periodically inspected as per requirement by law, these inspections only provide a discrete data point without addressing the cyclical nature of scour. Scour decreases the overall stiffness of the structure by weakening the foundation and changing the vibrational modes proportionally to the degree of scour. The scour portions of this research focuses on the same steel-truss bridge and analyzes 3D and 2D substructure models coupled with the superstructure reaction loads to assess the modal deformations within the infrasound bandwidth and the correlation to scour of embedment material. The 3D models indicate that due to the modal deformations 2D modeling can accurately determine the change in low infrasonic fundamental frequency passband of the coupled superstructure/substructure. Therefore 2D plain strain models of the Interstate 20 Bridge in Vicksburg, MS and Ft. Leonard Wood, MO, steel-truss were investigated, for two different subsurface soil types, as a representative deep foundation and shallow foundation cases, respectively. These results illustrate the degree of scour correlates well with changes in low fundamental frequencies and with measured field data indicating that remote scour detection using infrasound is viable for the dominant, lower-frequency bridge modes. In addition to the scour assessment, the research illustrates the use infrasound to investigate river system health during periods of record flooding. Events of the 2011 Mississippi River flood are presented herein in which the same infrasound arrays were able to not only detect and localize a barge collision with the Interstate 20 Bridge but also identify vortex eddies and changes to the river current not observed by seismic methods. Further, regions of increased force against the eastern bank related to changes in river flow were identified with direct impact to channel navigation and embankment erosion.