- Topic Submission
- Discussion & Evaluation
- Development
- Project
Geotechnical
Materials
Is this related to or a continuation of a previous Iowa DOT research project?
No
Does this idea include matching funds?
Yes
Amount of Matching Funds
$ 250,000
Source of Matching Funds
Michigan State University
Anticipated Benefits
The results of this study are expected to improve the performance, economics, and service lifespans of both paved and granular roads in Iowa. This study will develop design charts that may help Iowa DOT and county engineers and planners predict the performance of paved and unpaved roads based on results that are more representative of the field conditions. The results and recommendations of this project will provide a foundation for further development of decisionmaking tools to evaluate the relative paved and unpaved road performances for Iowa.
Focus Area
Sustainability / Technology
Project Title
Advanced Testing and Characterization of Iowa Soils and Geomaterials
Project Number
TR-780
Contracted Agency
Michigan State University
Project Champion
Principal Investigator
Funding Program
Iowa Highway Research Board
Project Funding
$315,000
Project Funding Including External Sources
$360,000
Partner Agencies
Iowa State University
Project Start Date
11/01/2019
Current Project End Date
10/31/2022
Project Complete Date
12/12/2023
Final Report Abstract
Accurate modeling of stress-strain characteristics of geomaterials plays a significant role in determining the achievable design life of roadways (e.g., granular roads and paved roads). Currently, the geomechanical characteristics of these materials are obtained
from standard laboratory tests such as California Bearing Ratio (CBR) and standard resilient modulus (MR). However, standard MR tests commonly conducted in the laboratory do not always apply the most damaging field loading conditions for predicting
MR and permanent deformation (rutting) responses of granular roadways and pavement base/subbase/subgrade layers. This is the main problem that causes significant performance problems for roadways. The geomaterials used in granular road surfaces and pavement foundation layers exhibit cross-anisotropic behavior indicating that deformation characteristics of such materials depend on the direction of the applied loads. In the real field conditions, loads applied via moving wheels on the roadway systems are imposed to not only the vertical direction, but all three directions (both horizontal and vertical directions). Therefore, it is crucial for advanced material characterization test equipment to be built and used to determine the anisotropic (all directions) behavior of geomaterials. In addition, it's worth noting that the stiffness and plastic deformation of these geomaterials are also significantly affected by the freeze-thaw (F-T) cycles. This combination of directional dependency and sensitivity to F-T effects underscores the complex nature of their behavior under various conditions.
In this study, various geomaterials (granular aggregates and subgrade soils) collected from different regions of Iowa were tested in the laboratory through the advanced testing equipment (which was designed and built as part of this project) to determine and
quantify the cross-anisotropic behavior of these materials in addition to the effect of F-T on the deformation characteristics. The findings revealed that the tested geomaterials exhibited cross-anisotropy regardless of factors like gradation, material origin, and
applied stress levels. Notably, granular materials demonstrated higher cross-anisotropy, where the horizontal resilient modulus (MR) was only a fraction of the vertical MR, while fine-grained materials displayed the lowest cross-anisotropy; in certain cases,
their horizontal stiffness even surpassed the vertical stiffness, depending on applied stress history. Anisotropy ratios (the ratio of horizontal MR to vertical MR) were calculated for all cross-anisotropic tests. Moreover, the MR was observed to be influenced by stress history during simulated laboratory testing mimicking moving vehicle loads. For permanent deformation (PD), similar to stiffness behavior, all tested materials exhibited cross-anisotropy, with the highest deformations recorded horizontally for
aggregate materials subgrade soils. Nevertheless, the discrepancy in deformation levels between different directions for the subgrade soil was relatively lower than that of the granular aggregate materials. Furthermore, investigations into F-T effects
indicated that an increase in the fines content of granular materials, coupled with an escalation in applied F-T cycles, led to stiffness degradation and increased PDs
from standard laboratory tests such as California Bearing Ratio (CBR) and standard resilient modulus (MR). However, standard MR tests commonly conducted in the laboratory do not always apply the most damaging field loading conditions for predicting
MR and permanent deformation (rutting) responses of granular roadways and pavement base/subbase/subgrade layers. This is the main problem that causes significant performance problems for roadways. The geomaterials used in granular road surfaces and pavement foundation layers exhibit cross-anisotropic behavior indicating that deformation characteristics of such materials depend on the direction of the applied loads. In the real field conditions, loads applied via moving wheels on the roadway systems are imposed to not only the vertical direction, but all three directions (both horizontal and vertical directions). Therefore, it is crucial for advanced material characterization test equipment to be built and used to determine the anisotropic (all directions) behavior of geomaterials. In addition, it's worth noting that the stiffness and plastic deformation of these geomaterials are also significantly affected by the freeze-thaw (F-T) cycles. This combination of directional dependency and sensitivity to F-T effects underscores the complex nature of their behavior under various conditions.
In this study, various geomaterials (granular aggregates and subgrade soils) collected from different regions of Iowa were tested in the laboratory through the advanced testing equipment (which was designed and built as part of this project) to determine and
quantify the cross-anisotropic behavior of these materials in addition to the effect of F-T on the deformation characteristics. The findings revealed that the tested geomaterials exhibited cross-anisotropy regardless of factors like gradation, material origin, and
applied stress levels. Notably, granular materials demonstrated higher cross-anisotropy, where the horizontal resilient modulus (MR) was only a fraction of the vertical MR, while fine-grained materials displayed the lowest cross-anisotropy; in certain cases,
their horizontal stiffness even surpassed the vertical stiffness, depending on applied stress history. Anisotropy ratios (the ratio of horizontal MR to vertical MR) were calculated for all cross-anisotropic tests. Moreover, the MR was observed to be influenced by stress history during simulated laboratory testing mimicking moving vehicle loads. For permanent deformation (PD), similar to stiffness behavior, all tested materials exhibited cross-anisotropy, with the highest deformations recorded horizontally for
aggregate materials subgrade soils. Nevertheless, the discrepancy in deformation levels between different directions for the subgrade soil was relatively lower than that of the granular aggregate materials. Furthermore, investigations into F-T effects
indicated that an increase in the fines content of granular materials, coupled with an escalation in applied F-T cycles, led to stiffness degradation and increased PDs
Transportation Research Board - Transportation Research Information (TRID) Database Page
Project Champion
Technical Advisory Committee
Project Manager
Delivering targeted solutions for Iowa's transportation future.
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