Site Onyejekwe

Effect of Fiber Inclusions on Flexural Strength of Soils Treated with Nontraditional Additives

AbstractThe effect of randomly oriented discrete synthetic fiber inclusions on the properties of soils treated with proprietary liquid chemical stabilization additives was evaluated in a laboratory-based investigation. Mercia mudstone, Oxford clay, and limestone quarry fines were stabilized with a proprietary polymer and reinforced with discrete fibers. The findings were compared with untreated and reinforced specimens, which served as the control. Test results showed that the inclusion of randomly oriented discrete synthetic fibers had no significant effect on the compaction characteristics of the soils examined. However, it did result in significant improvements in the toughness of all soils examined and load retention after peak strength for Mercia mudstone and Oxford clay. Polymer/sulphonated oil-stabilized and fiber-reinforced Mercia mudstone and Oxford clay specimens were found to be highly susceptible to moisture, while polymer-stabilized and reinforced limestone quarry fines specimens demonstrated...

Scale of Fluctuation of Geotechnical Parameters Estimated from CPTu and Laboratory Test Data

For a complete probabilistic characterization of a geotechnical parameter, its mean, variance, and the scale of fluctuation have to be known. While the mean and variance can be easily determined, determination of the scale of fluctuation is a little more complex. Knowledge of the scale of fluctuation is important in reliability-based design as it is used in implementing spatial averaging and computing the variance-reduction factor. Published values of scale of fluctuation of geotechnical parameters are based on widely sourced data and hence may not be most appropriate for local situations. Based on 11 CPTu soundings and laboratory test results of fine-grained soils from 15 boreholes at four different locations in Missouri, this paper uses the semivariogram function to determine the scale of fluctuation of geotechnical parameters. Owing to scale of fluctuation being dataset-dependent, differences between published values and the Missouri values determined in this study were observed. Spatial averaging effect, depending on magnitude of the reduction in variance of parameters, can potentially lead to a more optimal and cost-effective design.

Threshold Strain for Postcyclic Shear Strength Change of Mississippi River Valley Silt Due to Cyclic Triaxial Loading

Soil microstructure is affected by cyclic loading, leading to changes in postcyclic shear strength. It is generally observed that the postcyclic shear strength of a given soil increases substantially after reconsolidation above a threshold strain for that soil. In this study, we investigated the threshold strain for change in the postcyclic shear strength of reconsolidated soil by conducting cyclic triaxial tests on reconstituted Mississippi River Valley silt with a plasticity index (PI) of 5.8. To this end, the effects of the cyclic stress ratio, overconsolidation ratio, effective consolidation pressure, and PI on the threshold cyclic axial strain were assessed. The postcyclic shear strength decreased slightly when the cyclic axial strain (ea,c) was less than 0.4 %, but it increased substantially when the cyclic axial strain was greater than 0.4 %. The threshold cyclic axial strain was determined as 0.4 %, which was close to the yield cyclic axial strain, equal to the strain at the intersection of two envelopes in ea,c versus p′ space. The threshold strain did not vary substantially with either the cyclic stress ratio or the overconsolidation ratio, but it decreased with the effective consolidation pressure. Within the PI range of 5.8 to 9.4, there was no obvious change in threshold cyclic axial strain. When we combined data from other researchers, it was found that the threshold shear strain increases from 0.1 % to 3.0 % with an increase in PI. The average line for threshold shear strain (γth) for postcyclic shear strength change was found to be almost parallel to that for cyclic pore water pressure in PI–logγth space.

Spatial Variation and Correlation between Undrained Shear Strength and Plasticity Index

Ph.D. Student, Department of Civil, Architectural, and Environmental Engineering, Missouri University of Science and Technology, Rolla, MO 65409. Email: xkb4c@mst.edu Ph.D. Student, Department of Civil, Architectural, and Environmental Engineering, Missouri University of Science and Technology, Rolla, MO 65409. Email: sokbd@mst.edu Assistant Professor, Department of Civil, Architectural, and Environmental Engineering, Missouri University of Science and Technology, Rolla, MO 65409. Email: geyun@mst.edu Professor, Department of Civil, Architectural, and Environmental Engineering, Missouri University of Science and Technology, Rolla, MO 65409. Email: Stephens@mst.edu

Variability Analysis of Undrained Shear Strength for Reliability-Based Design

Description of the spatial variation of compositional and mechanical soil parameters is often paramount in site characterization of geotechnical design and analysis. The values of the parameters themselves largely depend on in-situ state factors which are related to spatial locations. Also, for large-scale engineering projects such as earth dams or highways, it is generally expected that heterogeneous site characteristics will be revealed by investigations at spatially distant locations. Currently, most Reliability-Based Design methods are based on the second-moment statistics (mean and variance). However, they are unable to adequately describe the spatial variation of soil properties. In this paper, spatial correlation analysis is developed to evaluate the undrained shear strength profile at a location in Warrensburg in Missouri, where undisturbed samples were taken from Shelby tubes and undrained shear strengths were determined through the unconsolidated undrained triaxial hear strength (UU)