National Academies Press: OpenBook

Advances in Unstable Slope Instrumentation and Monitoring (2020)

Chapter: Chapter 4 - Case Examples

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Suggested Citation:"Chapter 4 - Case Examples." National Academies of Sciences, Engineering, and Medicine. 2020. Advances in Unstable Slope Instrumentation and Monitoring. Washington, DC: The National Academies Press. doi: 10.17226/25897.
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Suggested Citation:"Chapter 4 - Case Examples." National Academies of Sciences, Engineering, and Medicine. 2020. Advances in Unstable Slope Instrumentation and Monitoring. Washington, DC: The National Academies Press. doi: 10.17226/25897.
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Page 29
Suggested Citation:"Chapter 4 - Case Examples." National Academies of Sciences, Engineering, and Medicine. 2020. Advances in Unstable Slope Instrumentation and Monitoring. Washington, DC: The National Academies Press. doi: 10.17226/25897.
×
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Page 30
Suggested Citation:"Chapter 4 - Case Examples." National Academies of Sciences, Engineering, and Medicine. 2020. Advances in Unstable Slope Instrumentation and Monitoring. Washington, DC: The National Academies Press. doi: 10.17226/25897.
×
Page 30
Page 31
Suggested Citation:"Chapter 4 - Case Examples." National Academies of Sciences, Engineering, and Medicine. 2020. Advances in Unstable Slope Instrumentation and Monitoring. Washington, DC: The National Academies Press. doi: 10.17226/25897.
×
Page 31
Page 32
Suggested Citation:"Chapter 4 - Case Examples." National Academies of Sciences, Engineering, and Medicine. 2020. Advances in Unstable Slope Instrumentation and Monitoring. Washington, DC: The National Academies Press. doi: 10.17226/25897.
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Page 32

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27 Case Examples The following case study discussions present a synthesis of information obtained through follow-up interviews with the Vermont, Minnesota, Maryland, and Oregon DOTs (Table 4.1). States were selected based on geographical and geological distribution throughout the country (Figure 4.1) and comments provided in the survey indicating various problems being addressed through instrumentation and monitoring. The interviews were conducted to gain understanding of the advantages and disadvantages, and lessons learned from the implementation of new instrumentation and monitoring technologies in their DOT. 4.1 Vermont Agency of Transportation: Recurring LiDAR Surveys for Slope Monitoring In 2018, the Vermont Agency of Transportation (VTrans) completed a project to repair an unstable slope that failed during the Hurricane Irene storm event in 2011. The slope repair consisted of two different improvement areas: an anchored mesh section and a stone fill section. A photo of the stone fill section is provided in Figure 4.2. Following construction, a portion of the stone fill section exhibited movement. In response to the movement, the VTrans Survey Unit conducted a baseline LiDAR survey of the slope in fall of 2018 and a second survey was conducted in spring of 2019. The surveys were completed by VTrans personnel and with VTrans in-house ground-based LiDAR survey equipment. The data from the two surveys were quantitatively compared to develop a heat map of the entire slope illustrating areas of movement by changes in surface geometry between the fall 2018 and spring 2019 surveys (Figure 4.3). To produce change-detection heat maps of the slope, the VTrans Survey Unit personnel completed the data-reduction process, and a consultant also was engaged for a similar data- reduction task. The purpose of the parallel data-reduction tasks was to confirm the results between two different analysis teams. Additionally, this was the first time the VTrans Survey Unit had performed change detection on an unstable slope. The outcomes from the change-detection survey work have been favorable for both the VTrans Geotechnical and Survey Units. At the subject slope repair site, VTrans is able to understand the relative distribution of ground movement across the entire slope, including magnitude of movement, which has contributed to improved knowledge and decision-making confidence on future actions and needs for investment. Because of the confidence gained through the LiDAR survey work, VTrans will continue performing surveys approximately 3 to 4 times per year as a long-term monitoring program at the subject site, versus initiating a second repair project or more expensive exploration and instrumentation programs. The use of ground-based C H A P T E R 4

28 Advances in Unstable Slope Instrumentation and Monitoring State Case Example Vermont Recurring LiDAR Surveys for Slope Monitoring Minnesota Cost-Benefit of Instrumentation and Monitoring Maryland Implementing UAVs and New Software Oregon Evidence-Based Long-Term Planning Table 4.1. Case examples. Figure 4.1. Geographical distribution of case studies. Figure 4.2. Photograph of stone fill slope repair (VTrans Photograph).

Case Examples 29 LiDAR remote sensing in this case study is better informing decisions through increased data coverage and confidence, and at a lower cost than traditional methods. As a result of this work, VTrans reported planning to scale up the program and implement ground-based LiDAR surveys at other locations such as future repair projects and existing rock slopes and retaining walls. VTrans also intends to continue developing in-house resources for this work, including training of survey staff, in order to complete the work without contractor or consultant support. 4.2 Minnesota DOT: Cost-Benefit of Instrumentation and Monitoring Through the demonstration of favorable cost and benefit relationships and the value instru- mentation and monitoring data can provide in decision making, the Minnesota Department of Transportation (MnDOT) has successfully funded and implemented project-specific programs on several occasions. As an example, the department undertook an interstate widening project that included new construction in an area with known landsliding and ground deformation. During the design phase, MnDOT geotechnical staff recommended an automated instrumentation and Figure 4.3. LiDAR change-detection results for stone fill shown in Figure 4.2.

30 Advances in Unstable Slope Instrumentation and Monitoring monitoring system consisting of crack meters, GNSS stations, and MEMS in-place inclinom- eters. The total system investment was $30,000. This cost was in addition to the expense of a typical geotechnical exploration program that would be for the widening project. By making the additional investment in an instrumentation and monitoring program for the unstable slope, the department benefited from a system that could provide reliable and more frequent data to inform MnDOT design and construction decisions; measure earthwork and structure performance during and following construction; and proactively monitor and mitigate risk in response to ground movement. In the opinion of MnDOT geotechnical staff, the instrumenta- tion and monitoring system expense for the project was preferable to carrying uncertainty about the performance of the unstable slope into construction and beyond. Carrying the uncertainty could have resulted in more costly work during construction and the greater likelihood of needing postconstruction remedial work. In another example, MnDOT geotechnical staff compared the cost for procurement and installation of an automated monitoring system with the direct costs for labor and travel to make recurring data collection visits to a geotechnical instrumentation site. The benefits of an automated system included providing continuous data from a remote location, which generated a greater quantity of data over the manual approach that required travel and up to a half day of personnel time for each in-person data collection event. By investing in the automated monitoring system, MnDOT realized the benefit of access to near-real-time geo- technical instrumentation data and enabled time savings for the staff that could be directed toward other valuable activities. Drawing from these and other similar examples, MnDOT geotechnical staff works to communicate the purpose of instrumentation and monitoring programs to project managers and other key staff in terms of cost and risk management opportunities. When combined with a series of successful implementation projects that show prior effective instrumen- tation investments, MnDOT geotechnical staff believes they have established a favorable reputation within the department that includes both defining the problems that instrumen- tation can solve and providing reasonable and practical solutions in areas of potentially unstable ground. Separately, MnDOT geotechnical staff also communicate the value of instrumentation and monitoring on earthwork projects through the comparison to well-established processes for construction quality and performance monitoring, such as inspection of foundation construc- tion and materials testing. The direct costs for these common construction quality practices can be approximately quantified relative to the total project cost. A similar process can be used for the cost of an instrumentation and monitoring program, which, when combined with commu- nication about the value and risk management opportunities, may enable support for additional investment. In some situations, instrumentation and monitoring during construction may provide additional benefit in terms of reducing the waiting period for settlement consolidation or accelerating the schedule. Quantifying the benefits has been a valuable process for MnDOT geotechnical professionals to gain stakeholder support and funds for instrumentation and monitoring projects. This approach is important for MnDOT because the department does not yet have a dedicated pool of funds that can be used for starting instrumentation and monitoring projects, and each installation is typically funded through a separate design, construction, or maintenance budget. In the future, MnDOT geotechnical staff would like to have a pool of funds that can be directed toward suitable projects without first having to prove the value to each specific project team. Additionally, such a pool could be used to invest in agency-wide instrumentation and monitoring needs such as contracting for cellular services and web-based viewing platforms and statewide remote-sensing technology.

Case Examples 31 4.3 Maryland DOT: Implementing UAVs and New Software The Maryland Department of Transportation reported the realization of inventory and monitoring benefits for unstable slope and embankment sites using new tools, such as UAVs, and implementation of software. The Geotechnical Division within Maryland DOT views these tools and software solutions as creating opportunities that have not previously existed before. Approximately a year and a half ago, the Geotechnical Division purchased a commercial drone (UAV) for about $1,000 and a separate software license for a proprietary program, which enables users to construct 3D terrain models from digital photographs. During the same period, a member of the department geotechnical team obtained their UAV pilots license. Since purchasing the UAV, the Geotechnical Division has performed about 70 to 80 flights for photogrammetric remote sensing of various locations, including approximately 15 flights to track change at one critical unstable slope location. The Division also now has two licensed UAV pilots. Separately, the Geotechnical Division has been using the Maryland statewide LiDAR data- base to begin inventory of embankments and slopes, including unstable slopes, within about 500 feet (150 m) of the highway centerlines. The process has been simplified with the purchase of a proprietary GIS program in the fall of 2018. The Geotechnical Division also is experimenting with an application within the GIS program which enables development of mobile application field forms that are currently used for devel- opment of an unstable rock slope inventory. The department intends to adapt these forms and continue using the application for inventory of unstable soil slopes. The Geotechnical Division indicated that peers in other technical disciplines within Maryland DOT are developing GIS content, and this is creating the opportunity to leverage data from others, such as hydraulic structures, maintenance activity, and traffic volume and incident data. Within the Geotechnical Division, the team has developed an Oracle database for storing geo referenced data related to geotechnical boring logs and other digital data. These data are then used to generate preliminary maps of soil conditions within the ROW. The Geotechnical Division also has a team member who is working with deep learning from the information in the database and developing routines for predictive models that provide preliminary geology interpretation to stakeholders. Through the combination of these data and tools, the Geotechnical Division is now able to view information about geology, rock slopes, and embankments in relation to other assets and department data. The Geotechnical Division has recently experienced a transition in staff with the retirement of several long-term staff members. Most of the current Geotechnical Division has about 1 to 2 years of experience with the Division and is not able to rely on institutional knowledge. The ability to view newly acquired georeferenced data through the processes discussed above is helping the Geotechnical Division close the gap created by departing institutional knowledge. In the future, the Geotechnical Division intends to begin transferring paper-based files and inventory into the electronic databases, which will close this gap further. These recent advancements in remote sensing, data management, and software use are occurring because of the interest and motivation of a few key team members in these topics. The implementation has occurred primarily through self-teaching and experimentation. The agency reported that the key to implementation has been the recognition by others in the department that slopes and embankments can be incorporated into asset management plans, thus enabling support and funding equipment and software to inventory and track performance of slopes and embankments.

32 Advances in Unstable Slope Instrumentation and Monitoring 4.4 Oregon DOT: Evidence-Based Long-Term Planning The Oregon Department of Transportation (ODOT) is using instrumentation and monitoring advancements to increase confidence in operational decisions through new sources of data. In the short-term, ODOT has installed seven MEMS in-place inclinometers with remote communication on five large landslides in their program. The MEMS in-place inclinometers installations can provide near-real-time monitoring at intervals as short as 30 minutes. Historically, ODOT geotechnical staff would have to make periodic visits to read conventional inclinometers. Following the installation of the MEMS in-place inclinometers, the department now has the benefit of more data on the five landslides and with a lower commitment of resources. These data, while limited to only one or two locations, are providing ODOT with more confidence in operational decisions related to the instability of large landslide complexes that impact their right-of-way. A separate long-term research collaboration with Oregon State University is tasked with developing LiDAR informed algorithms to predict slope deterioration. The research study is evaluating the temporal change measured through LiDAR for two conditions: rockfall slopes and coastal bluff retreat. The study was initiated using static and mobile ground-based LiDAR and is evaluating the incorporation of aerial LiDAR. Both projects are multi-year efforts that are nearing the midpoint of study. The change condition maps obtained through LiDAR surveys are useful for determining how much rockfall or slope retreating is occurring, in addition to creating improved resolution in mapping data. The LiDAR surveys also have a benefit for worker safety because personnel are not required to traverse hazardous slopes using rope access. The information from the surveys will be used to create evidence-based models that can be used to estimate future performance based on deterioration rates. When complete, ODOT intends to implement the work at a statewide and operational scale.

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Geotechnical instrumentation and monitoring technologies have been used to inform safety, operational, and treatment decisions for unstable slopes.

The TRB National Cooperative Highway Research Program's NCHRP Synthesis 554: Advances in Unstable Slope Instrumentation and Monitoring documents and synthesizes the state of practice for implementation and use of advancements in unstable slope instrumentation and monitoring by state departments of transportation over approximately the last decade.

The types of instrumentation and monitoring technologies range from devices installed on or in slopes to remote-sensing methods from ground, aerial, or satellite-based systems.

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