Geotechnical Engineering Online Library

This paper presents a description of post-flood reconnaissance and geotechnical investigation of four earthen dams that were breached or damaged following an extreme flooding event in South Carolina in 2015. As a result of unprecedented rainfall and flooding that occurred during a five-day period at the beginning of October in 2015, a total of 51 earthen dams failed and nearly 200 were damaged. Many of these dams failed due to overtopping that led to a breach of the dam. Among the four dams investigated, full breach was observed at three dams; two of which were overtopped, and one was not. The fourth dam was not breached but was severely damaged. For each of these dams, the paper documents background information, pre-flood conditions, post-flood field observations and measurements, and laboratory testing results of collected soil samples. Impacts of vegetation on the dams and the effects of dam failure on critical infrastructure are also presented. The detailed descriptions and geotechnical investigations of the dam failures presented herein serve as case histories that can be used for dam breach modeling and risk assessment of dam failure.

The application of the Structure-from-Motion (SfM) methodology, as enabled by the growth of Unmanned Aerial Vehicle (UAV) technology, is expected to have significant impact in geotechnical engineering research and practice. SfM outputs are presented using selected geotechnical projects as examples, and include orthophotos, 3D point clouds, and three dimensional digital surface or terrain models. Repeated surveys allow for monitoring of deformation patterns at a cm-level resolution. The lessons learned from the application of the methodology at twenty-six sites that cover the breadth of geotechnical engineering practice, located in four countries (USA, Greece, Nepal, and New Zealand) and variable geologic environments are presented. It is shown that the methodology leads to an unprecedented level of mapping that covers large areas at high resolution. In addition to the high resolution models, SfM models are shown to be comparable in accuracy to other surveying techniques and mapping technologies such as light detection and ranging (LiDAR). The advantages and disadvantages of the methodology are also presented with the intent to facilitate the greater incorporation of this methodology in geotechnical engineering. The use of UAVs makes the methodology especially appealing for immediate post-disaster response as it enables the collection of optical data in areas that are inaccessible or unsafe.

Since November 2013, numerous sinkholes have been forming in the Armala area of Pokhara Valley, Central Nepal, posing serious threat to local residents. In order to provide measures aimed at reducing sinkhole risk, investigations into the cause and features of the sinkholes are crucial. This paper presents early research results based on two damage surveys conducted in June 2014 and November 2014 in the Armala area. Comparison of photos, taken in the two surveys, clearly indicates not only the formation of new sinkholes, but also the re-activation of filled sinkholes. By means of dynamic cone penetration tests and surface wave method investigations, qualitative characterization of the soil profile was attained, and shallow weak soil layers which are believed to be the location for future sinkholes could be identified. On the basis of the field investigation results, possible sinkhole formation mechanisms are identified for the Armala area. Furthermore, results of a reconnaissance survey conducted in the Armala area in early May 2015 (following the 2015 Gorkha Nepal Earthquake, which occurred on April 25th) are also reported. Although the epicentral distance to Pokhara was closer than Kathmandu, which suffered from severe damage, no major apparent effects of the earthquake were observed in the sinkhole damaged area.