Stability Evaluation and Monitoring During Staged Construction of Fly Ash Closure Projects is the title of a technical paper presented at World of Coal Ash 2017 was based on several challenging projects being completed by CALM Initiative members. One of the difficulties being encountered by many CCR impoundment owners, design engineers and contractors is how to assess the stability of ash slopes and fill embankments during the completion of a closure project. As a typical CCR impoundment is drained and prepared for either excavation or close-in-place closure, the subsurface drainage conditions, effective stress and undrained shear strength of the fly ash materials frequently change. To address these challenges, experienced geotechnical engineers and contractors have developed innovative and practical methods for insitu testing, proof testing and construction monitoring of the partially saturated fly ash including:
- Utilizing the cone penetrometer (CPT), the Van Den Berg vane shear device, and hand held vane shear devices for obtaining strength measurements of the fly ash during the design and construction phase.
- Developing guidelines for staged construction and assessing the behavior of the fly ash during ash impoundment closure construction by using the Observational Method as explained by Terzaghi and Peck, 1969.
Field measurement and assessment of changing conditions, and increases in porewater pressure by using “real time” porewater pressure transducers