Abstract "For highway structures in Nebraska and many Mid-Western states, the extreme precipitation brought the failure of slopes even though they were designed and constructed complying with relevant codes and practices. Back analyses of these failed slopes showed that the strength of soils at failure turned out to be substantially lower than the tested one at the design stage. Further studies showed that this kind of substantial strength reduction was due to the strength reduction of glacial tills during wet seasons. This reduced strength of soils is called “Wet-Drained-Fully-Softened-Strength(WDFSS)”, however, the method to evaluate this critical strength takes extremely long time (months if not years for one test) and high cost. This research team developed a new field-testing method to evaluate this critical strength by utilizing an innovative “self-wetting” CPT-based method that can evaluate this WDFSS in a rational time span, that is usually a day.
This research team, therefore, proposes to evaluate the WDFSS of various Nebraska soils with this innovative CPT method, so that WDFSS can be conveniently obtained and utilized for design work.
In addition, this study includes the Santee Reservation area – one of Native American Reservations in Nebraska as one of test sites. This area showed as high as 90% strength reduction for clayey glacial tills in the previous study (Song et al. 2019). Providing specific geotechnical information to the tribal government will greatly enhance the usage of their territory in more resilient and productive ways. "
Description "Global warming and extreme precipitation brought the failure of slopes for highway structures in Nebraska, even though they were designed and constructed according to relevant codes and practices. Back analyses of these failed slopes showed that the strength of soils at failure turned out to be substantially lower than the tested ones at the design stage. Further studies showed that this kind of substantial strength reduction was due to the strength degradation of glacial tills during wet seasons. This reduced strength of soils is called “Wet-Drained-Fully-Softened-Strength(WDFSS)”. This kind of strength is not popular, but they are known for soils in European countries. The method to evaluate this critical strength takes an extremely long time (months if not years for one test) and high cost. This research team developed a new field-testing method to evaluate this critical strength by utilizing an innovative “self-wetting” CPT-based method that can evaluate this WDFSS in a rational time span - a day.
This research team, therefore, proposes to evaluate the WDFSS of various Nebraska soils with this innovative CPT method so that WDFSS can be conveniently obtained and utilized for highway design work, and a safer and more resilient highway system can be obtained. In addition, this study includes the Santee Reservation area – one of Native American Reservations in Nebraska as one of test sites. This area showed as high as 90% strength reduction for clayey glacial tills in the previous study. Providing the specific strength reduction ratio to the tribal government will greatly enhance the usage of their territory in more resilient ways. "
Objective USDOT strategic goals include safety, economic strength and global
competitiveness, equity, climate and sustainability, transformation, and organizational excellence. Evaluating critical strength of soils through logical method are well aligned with all and each of these items.
Impacts/Benefits By introducing realistic but critical soil strength data and related testing methods, the project has the potential to revolutionize disaster prevention capability on a regional as well as national scale. The incorporation of advanced testing methods will foster innovation in transportation and construction sectors, setting a new standard for data-driven decision-making. Furthermore, the research's emphasis on resilience can instill a sense of confidence and security among communities, multipronged trust in both technological advancements and governance. Test sites of this research are in Nebraska this time, however, the methodology and results of this research will be creating a replicable model that can be adapted for DOT’s in other states and countries, promoting a future where communities are better respond to, and counteract natural disasters.