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3 Introduction 1.1 Background Unstable slopes pose a potential threat to public safety and mobility and increase the cost of maintaining the nationâs highway system. Unstable slopes include embankments and cut slopes and beyond-the-right-of-way hazard sites that have exhibited movement or present a threat of movement. Unstable slopes consist of soil, rock, or mixtures of these materials and can exist in both natural slopes and constructed slopes. Unstable slopes are ubiquitous throughout the United States (U.S.) and internationally and across physiographic terrain types and infrastruc- ture systems, resulting in unfortunate safety incidents, travel disruption, damages to public and private property, and continuous investment needs throughout the life cycle. For infrastructure owners with investment needs that are greater than the available funds, optimizing the manage- ment of unstable slopes is an important step toward preventing unplanned expenses that erode the limited investment capacity that exists. In the United States, the practice for prioritizing the hazard from rockfall sites, a type of unstable slope, began in the 1980s with the development of the rockfall hazard rating system (RHRS) by the Oregon Department of Transportation with support from FHWA and other states (Pierson, 1991). This work has since been modified by many state and federal transportation departments to include other types of unstable slopes (WTI, 2017) and to align with transpor- tation asset management (NAS, 2019). Unstable slope management programs are not limited to the U.S. transportation practice with many international examples such as those used for highway and railway systems in the United Kingdom (Power et al., 2012, 2016), natural slope hazards in Switzerland, Italy, and Norway (BrÃ¼ndl et al., 2009, Devoli et al., 2018), pipeline systems and reservoirs in Canada and the United States (Newton et al., 2019), and for infrastruc- ture and urban development in Hong Kong (Malone, 1997). Key to the management of risk from unstable slopes is having reliable knowledge about the extent and movement characteristics of slopes through time. The data from geotechnical instru- mentation and monitoring technologies can be a valuable knowledge enabler in the manage- ment process for unstable slopes. Thus, advancements in geotechnical instrumentation and monitoring technology provide new opportunities to better inform the decision-making process for those who own or manage the consequences of unstable slopes, such as state and federal DOTs and other infrastructure owners. The types of technologies used for instrumentation and monitoring range from systems installed on the ground surface or within the subsurface to systems that monitor remotely from ground, aerial, or space-based platforms. Depending on the technology, the instrumentation and monitoring systems can measure physical properties that include deformation in one or more dimensions, stress, temperature, moisture, and vibration; capture static or continuous images; and provide warning to technical and operational professionals about potentially unsafe C H A P T E R 1
4 Advances in Unstable Slope Instrumentation and Monitoring or sudden changes in conditions. Instrumentation and monitoring technologies also often incorporate data management processes and technology for recording, storing, transmitting, and analyzing collected data over time. The benefits of using instruments include: â¢ Improving the precision and understanding of the extents of an unstable slope and changes with time; â¢ Providing information on the rate of movement and movement-influencing mechanisms; â¢ Reducing uncertainty in design or maintenance decisions; â¢ Supporting construction monitoring and quality control on projects with slopes; â¢ Acting as early warning systems and tracking conditions in near real time; â¢ Measuring the change in stability and hazard over time; and â¢ Optimizing operational decisions and timing of rehabilitation or maintenance actions. The use of instrumentation and monitoring in geotechnical engineering and for applications involving unstable slopes in the United States has existed for at least 50 years. Within the last 10 years, technology advancements in the practice of instrumentation and monitoring for unstable slopes include improved measurement precision and resolution over time; innova- tions in software, hardware, and communication and management of data; and expanding use of emerging technologies in remote sensing. 1.2 Synthesis Objectives The objective of this synthesis is to document the current state of practice for geotechnical instrumentation and monitoring of unstable slopes with a focus on the application of new technology or improvements to older technology implemented by DOTs in the last decade. Technology of interest includes those used for in situ instrumentation, remote sensing, warning systems, and data management including acquisition, storage, transmission, analysis presenta- tion, and visualization. 1.3 Synthesis Scope and Approach Information for this synthesis study was collected through a review of domestic and inter- national literature, a survey of geoprofessionals at state DOTs, and follow-up interviews with selected agencies for the development of case study examples. The literature review was performed concurrently to the survey process and was conducted with a focus on slope instrumentation and monitoring technology that have been developed or has advanced in about the last 10 years. The synthesis survey questionnaire was sent to U.S. DOTs, the District of Columbia, and Puerto Rico. Before distribution, a draft survey questionnaire was provided to the synthesis panel members for review and testing of functionality using a web-based application. The survey was sent out via email on January 24, 2019, after resolution of comments from the panel members. In total, 43 agency responses were received for a response rate of 84%. A list of the survey respondents is provided in Appendix B and compilations of each agency response are presented in Appendix C and Appendix D. The survey responses were reviewed and categorized to summarize the practice in the following topics: â¢ How unstable slopes are identified for monitoring with instrumentation â¢ Instrumentation and monitoring technologies in established or emerging use cases
Introduction 5 â¢ Data collection, analyzing, viewing, and communication technologies â¢ Innovative technologies developed by DOTs â¢ Sources of funding for unstable slope monitoring and procurement approaches â¢ Management of slope monitoring data â¢ The use of monitoring and instrumentation data following collection and analysis â¢ Advantages, disadvantages, and lessons learned of the technologies used. 1.4 Terminology Definitions for common terms and abbreviations used throughout the synthesis are in a glossary at the end of this report. 1.5 Report Organization This synthesis report contains five chapters including this introductory chapter. Chapter 2 presents the literature review summary. Chapters 3 and 4 summarize the findings from the DOT survey responses and the case study interviews, respectively. Chapter 5 provides recommenda- tions for future work.