Evaluation of Critical Shear Strength of Soils in Nebraska Based on Revised CPT

Multiple NDOT researches confirmed that the back-calculated strength of soils at failed slopes in Nebraska was often much lower than the measured one in the design stage (Song et al. 2017, 2020). In some cases, the strength of soils at failure slopes was only 10% to 30% of the initial strength. Further study showed that this behavior was associated with the geological/geotechnical history of the region. And it is shared by the US, Canada and several EU(European Union) countries. This shear strength is called "wet-drained-fully softened" shear strength by researchers. The laboratory testing techniques to obtain this critical strength, however, are not standardized. Furthermore, an easily applicable field testing technique does not exist to the knowledge of this researcher. This research proposes an innovative CPT based testing technique that can obtain this critical strength of soils in the field conveniently. The following figure shows that the CPT equipment with the capability of water injection can penetrate into the ground, inject water so that surrounding soils may be wet, then conduct the CPT test. Then the wet condition is obtained, the drained condition is obtained by incorporating the piezometer readings, and, the fully softened condition is obtained by taking strength parameters from the skin friction of CPT. Consequently, the "wet-undrained-fully softened" strength is obtained. This technique is much quicker for testing than the currently available laboratory technique, and therefore, the cost is more economic. This research is an innovative research, however, the UNL team has years of accumulated experience in exploring soil properties with this CPT. HPT is a recently developed device that can inject water into field soils and obtain hydraulic parameters of saturated and unsaturated soils. The team has full access to these devices so that this research can progress smoothly. HPT was developed by the CPT manufacturer, and it is a system that can be easily fitted to the existing CPT system. Additionally, the CPT platform of UNL and NDOT are the same, therefore, technology transfer for findings in this research will be unquestionably smooth.

Language

• English

Project

• Status: Programmed
• Funding: $158,705.00
• Sponsor Organizations:

  Nebraska Department of Transportation

  1500 Nebraska 2
  Lincoln, NE  United States  68502
• Project Managers:

  Halsey, Lieska

• Principal Investigators:

  Song, Chung

  Eun, Jongwan

  Kim, Seunghee

• Start Date: 20230701
• Expected Completion Date: 20250531
• Actual Completion Date: 0

Subject/Index Terms

• TRT Terms: Shear strength; Soil aggregates; Test procedures
• Identifier Terms: Nebraska Department of Transportation
• Subject Areas: Geotechnology; I30: Materials; I51: Earthworks and Soil Drainage;

Filing Info

• Accession Number: 01881243
• Record Type: Research project
• Source Agency: Nebraska Department of Transportation
• Files: RIP, STATEDOT
• Created Date: Apr 25 2023 3:26PM