Analysis using surface wave methods to detect shallow manmade tunnels

Multi-method seismic surface wave approach was used to locate and estimate the dimensions of shallow horizontally-oriented cylindrical voids or manmade tunnels. The primary analytical methods employed were Attenuation Analysis of Rayleigh Waves (AARW), Surface Wave Common Offset (SWCO), and Spiking Filter (SF). Surface wave data were acquired at six study sites using a towed 24-channel land streamer and elastic-band accelerated weight-drop seismic source. Each site was underlain by one tunnel, nominally 1 meter in diameter and depth. The acquired surface wave data were analyzed automatically. Then interpretations compared to the field measurements to ascertain the degree of accuracy. The purpose of this research is to analyze the field response of Rayleigh waves to the presence of shallow tunnels. The SF technique used the variation of seismic signal response along a geophone array to determine void presence in the subsurface. The AARW technique was expanded for practical application, as suggested by Nasseri (2006), in order to indirectly estimate void location using a Normalized Energy Distance (NED) parameter for vertical tunnel dimension measurements and normalized Cumulative Logarithmic Decrement (CALD) values for horizontal tunnel dimension measurements. Confidence in tunnel detects is presented as a measure of NED signal strength. Conversely, false positives are reduced by AARW through analysis of sub-array data. The development of such estimations is a promising tool for engineers that require quantitative measurements of manmade tunnels in the shallow subsurface --Abstract, page iii

Detection of cavities by a continuous-wave seismic method

Imperial Users onl

Vision-Based Control of Unmanned Aerial Vehicles for Automated Structural Monitoring and Geo-Structural Analysis of Civil Infrastructure Systems

The emergence of wireless sensors capable of sensing, embedded computing, and wireless communication has provided an affordable means of monitoring large-scale civil infrastructure systems with ease. To date, the majority of the existing monitoring systems, including those based on wireless sensors, are stationary with measurement nodes installed without an intention for relocation later. Many monitoring applications involving structural and geotechnical systems require a high density of sensors to provide sufficient spatial resolution to their assessment of system performance. While wireless sensors have made high density monitoring systems possible, an alternative approach would be to empower the mobility of the sensors themselves to transform wireless sensor networks (WSNs) into mobile sensor networks (MSNs). In doing so, many benefits would be derived including reducing the total number of sensors needed while introducing the ability to learn from the data obtained to improve the location of sensors installed. One approach to achieving MSNs is to integrate the use of unmanned aerial vehicles (UAVs) into the monitoring application. UAV-based MSNs have the potential to transform current monitoring practices by improving the speed and quality of data collected while reducing overall system costs. The efforts of this study have been chiefly focused upon using autonomous UAVs to deploy, operate, and reconfigure MSNs in a fully autonomous manner for field monitoring of civil infrastructure systems. This study aims to overcome two main challenges pertaining to UAV-enabled wireless monitoring: the need for high-precision localization methods for outdoor UAV navigation and facilitating modes of direct interaction between UAVs and their built or natural environments. A vision-aided UAV positioning algorithm is first introduced to augment traditional inertial sensing techniques to enhance the ability of UAVs to accurately localize themselves in a civil infrastructure system for placement of wireless sensors. Multi-resolution fiducial markers indicating sensor placement locations are applied to the surface of a structure, serving as navigation guides and precision landing targets for a UAV carrying a wireless sensor. Visual-inertial fusion is implemented via a discrete-time Kalman filter to further increase the robustness of the relative position estimation algorithm resulting in localization accuracies of 10 cm or smaller. The precision landing of UAVs that allows the MSN topology change is validated on a simple beam with the UAV-based MSN collecting ambient response data for extraction of global mode shapes of the structure. The work also explores the integration of a magnetic gripper with a UAV to drop defined weights from an elevation to provide a high energy seismic source for MSNs engaged in seismic monitoring applications. Leveraging tailored visual detection and precise position control techniques for UAVs, the work illustrates the ability of UAVs to—in a repeated and autonomous fashion—deploy wireless geophones and to introduce an impulsive seismic source for in situ shear wave velocity profiling using the spectral analysis of surface waves (SASW) method. The dispersion curve of the shear wave profile of the geotechnical system is shown nearly equal between the autonomous UAV-based MSN architecture and that taken by a traditional wired and manually operated SASW data collection system. The developments and proof-of-concept systems advanced in this study will extend the body of knowledge of robot-deployed MSN with the hope of extending the capabilities of monitoring systems while eradicating the need for human interventions in their design and use.PHDCivil EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/169980/1/zhh_1.pd

Elastic wave measurement in rock engineering

Imperial Users onl

Geophysical and lithological characterization of the Ellerbek Valley aquifer system

[no abstract

Seismic detection of transient changes beneath Black Rapids Glacier, Alaska

Thesis (Ph.D.) University of Alaska Fairbanks, 1998To gain new insight into the mechanisms of basal motion, I have demonstrated the feasibility of an active seismic technique to measure temporal changes in basal conditions on sub-hourly time-scales. Using changes observed in the summer of 1993 on Black Rapids Glacier, I have determined part of the basal morphology and the mechanisms of seismic change there. One region of the glacier's bed was monitored daily using seismic reflections, for a period of 45 days. The majority of these reflections were nearly identical. However, the englacial drainage of two ice-marginal lakes and one supra-glacial pothole upglacier of the study site each caused significant anomalies in the daily reflections, as well as dramatic increases in basal motion. Two of these seismic anomalies were nearly identical despite the fact that their drainage events occurred at different locations. Further, these two seismic anomalies were followed by records identical to the non-anomalous state, showing that the changes were seismically reversible. In one of these events, two records taken 36 minutes apart revealed that the transition between the anomalous and normal states occurred completely within this short interval. Reflection arrival times during the anomalies require that a basal layer at least 5 m thick was either created or changed in situ. Reflection amplitudes indicate that such a layer could be either water or a basal till, but water layers of such thickness are not physically reasonable. Published values of wave speeds and densities of till are then compared to those constrained by the observed reflection coefficients. Only a decrease in till saturation can produce the observed changes in reflection amplitudes in the time required. Because the transition from anomalous to normal states can occur in as little as 36 minutes, any mechanisms involving the diffusion of water through a thick till layer are ruled out, such as a change in porosity or pore-water (or effective) pressure. We therefore interpret the cause of the seismic anomalies as due to a temporary decrease in saturation, and propose that such a change may occur quickly and reversibly following a lake drainage by a redistribution of the overburden pressure

geophysical characterizations of glacial aquifers and earth-fill dams

Geophysical investigations of groundwater aquifers and earth-fill dams have gained vast attention during the past few decades. Exploring new groundwater aquifers is always essential to meet the growing need for water resources by the growing population. Investigating dam safety is also crucial as dams store water in lakes and reservoirs and contribute directly to the water supply and flood control. Despite the recent advances in geophysical investigations, delineating complex aquifers and efficient inspection of earth-fill-dams is still challenging. In this study, I conducted and evaluated different geophysical surveys for delineating groundwater aquifers and investigating earth-fill dams. The land streamer shear (S)-wave reflection method was tested in this study as an alternative to traditional geophysical methods for delineating thin and shallow sand and gravel aquifers in northern Illinois. With the aid of available water wells alongside the seismic profiles, the S-wave surveys have successfully resolved multiple sand and gravel aquifers in the surveyed area. The study tested various geophysical methods to investigate the integrity of two earth-fill dams and their underlying rock foundation in central Oklahoma. Tested geophysical methods included seismic P-wave reflection, S-wave reflection, multi-channel analysis of surface wave (MASW), P-wave refraction, and electric resistivity tomography (ERT). The geophysical surveys characterized the different materials and conditions of the two dams and the underlying rock foundations and highlighted the advantages and limitations of the applied geophysical methods. This study introduced the S-wave reflection method as a reliable tool to delineate relatively thin glacial aquifers and evaluated the efficacy of various geophysical methods for investigating earth-fill dams

Seismic prediction and imaging of geological structures ahead of a tunnel using surface waves

To improve the performance and safety of tunnel constructions, we introduce a new seismic prediction method utilizing tunnel surface waves to detect relevant geological structures ahead of the tunnel face. On the basis of both synthetic and field data, we investigate the propagation characteristics of such surface waves propagating along the tunnel wall. We further introduce a simple but robust automatic prediction scheme that can estimate the distance to a reflector ahead of the tunnel

Ultra-Shallow Imaging Using 2D & 3D Seismic Reflection Methods

The research presented in this dissertation focuses on the survey design, acquisition, processing, and interpretation of ultra-shallow seismic reflection (USR) data in two and three dimensions. The application of 3D USR methods to image multiple reflectors less than 20 m deep, including the top of the saturated zone (TSZ), a paleo-channel, and bedrock, are presented using conventional acquisition methods and a new automated method of acquiring 3D data using hydraulically planted geophones. Processing techniques that focus on near-surface problems, such as intersecting reflection hyperbolae caused by large vertical velocity changes and processing pitfalls, are also discussed. The application of AVO analysis of 2D USR data collected during a pumping test yielded amplitude variations related to the thickness of the partially saturated zone that correlated spatially and with changes in pumping. USR methods were also used to image the TSZ less than one meter deep, the shallowest TSZ reflection to date

Investigating the dynamic response of rock mass to reservoir drainage at Grimsel test site, Switzerland, as an analogue for glacial retreat

An effective solution for the geologic disposal of nuclear waste, with no environmental risk (i.e. avoidance of harmful release of radioactive material), is a fundamental issue for the environment protection, and for the future continued reliance on nuclear power. Although geological disposal is considered as the best option, there are still elements of risk to be addressed, such as glacial retreat, which could impact the safety performance of a geological disposal facility. In this project two consecutive annual cycles of a reservoir in the Swiss Alps are used as a small scale analogue of the glacial retreat cycles, in order to investigate the response of granitic rock (as a host rock to a geologic disposal facility) to significant load changes. Assuming that the reservoir’s stress changes cause the fractured and weakened rock slopes to slip, I chose to use microseismic monitoring as a tool to monitor the reservoir induced seismicity. A seismic network was deployed in the tunnels adjacent to the reservoir and recorded continuously ground movement over a 3.5-year period (Nov 2014 – Aug 2018). In order to be able to detect microseismic slips in the acquired real field dataset I explore various algorithms from the literature and develop my own methodology. The two main problems my research focuses on are the length of the dataset (big data issues) and the signal to noise ratio of the events I want to detect (small magnitude events in a varying noisy background). My results show, albeit not all of the seismic signals were possible to locate or characterise, that the reservoir unloading increases the frequency of occurrence of microseismic events for a short time period in the region surrounding the reservoir. It is possible therefore that the construction of a geologic disposal facility will have a similar effect. However, the magnitudes of the induced events are very small and hence unlikely to have a significant effect as part of a safety case for a geologic disposal facility. The contributions of this thesis can be summarised to: (i) using a reservoir as a small-scale test site analogue for exploring the seismic hazard in radioactive deep geologic disposal facilities due to glacial retreat; (ii) sensor deployment design and sensor data cleaning with noise characterisation for microseismic monitoring over several years; (iii) proposal of a new algorithm (NpD) for detecting potential seismic signals under not well-constrained conditions and without requirement of a priori knowledge about the expected signal frequencies and amplitudes; (iv) the NpD detection algorithm and acquired 3.5 years dataset are made freely available; (v) detailed discussion of onset time picking and hypocentre localisation methodologies, where again novelty lies in using, comparing suitability and adjusting a number of well-known approaches for the purposes of my project; (vi) compilation of a seismic catalogue related to the dynamic response of the rock mass to reservoir drainage.An effective solution for the geologic disposal of nuclear waste, with no environmental risk (i.e. avoidance of harmful release of radioactive material), is a fundamental issue for the environment protection, and for the future continued reliance on nuclear power. Although geological disposal is considered as the best option, there are still elements of risk to be addressed, such as glacial retreat, which could impact the safety performance of a geological disposal facility. In this project two consecutive annual cycles of a reservoir in the Swiss Alps are used as a small scale analogue of the glacial retreat cycles, in order to investigate the response of granitic rock (as a host rock to a geologic disposal facility) to significant load changes. Assuming that the reservoir’s stress changes cause the fractured and weakened rock slopes to slip, I chose to use microseismic monitoring as a tool to monitor the reservoir induced seismicity. A seismic network was deployed in the tunnels adjacent to the reservoir and recorded continuously ground movement over a 3.5-year period (Nov 2014 – Aug 2018). In order to be able to detect microseismic slips in the acquired real field dataset I explore various algorithms from the literature and develop my own methodology. The two main problems my research focuses on are the length of the dataset (big data issues) and the signal to noise ratio of the events I want to detect (small magnitude events in a varying noisy background). My results show, albeit not all of the seismic signals were possible to locate or characterise, that the reservoir unloading increases the frequency of occurrence of microseismic events for a short time period in the region surrounding the reservoir. It is possible therefore that the construction of a geologic disposal facility will have a similar effect. However, the magnitudes of the induced events are very small and hence unlikely to have a significant effect as part of a safety case for a geologic disposal facility. The contributions of this thesis can be summarised to: (i) using a reservoir as a small-scale test site analogue for exploring the seismic hazard in radioactive deep geologic disposal facilities due to glacial retreat; (ii) sensor deployment design and sensor data cleaning with noise characterisation for microseismic monitoring over several years; (iii) proposal of a new algorithm (NpD) for detecting potential seismic signals under not well-constrained conditions and without requirement of a priori knowledge about the expected signal frequencies and amplitudes; (iv) the NpD detection algorithm and acquired 3.5 years dataset are made freely available; (v) detailed discussion of onset time picking and hypocentre localisation methodologies, where again novelty lies in using, comparing suitability and adjusting a number of well-known approaches for the purposes of my project; (vi) compilation of a seismic catalogue related to the dynamic response of the rock mass to reservoir drainage