Richard W. Stephenson

A Slurry Consolidation Approach to Reconstitute Low-Plasticity Silt Specimens for Laboratory Triaxial Testing

Silt specimen reconstitution using a slurry consolidation approach is commonly used for laboratory testing. This paper presents a new slurry consolidation approach to reconstitute silt specimens for use in triaxial testing. Silt specimens were reconstituted in a split vacuum mold mounted on a special experimental setup. The uniformity of the reconstituted specimens was verified by measuring the water content and grain size distribution throughout the specimens. The testing program was expedited using a special sample handling technique to move the specimen from the special experimental setup to the triaxial chamber base platen. The handling process did not disturb the specimens to a measurable degree. Further, the replicas of the reconstituted specimens were verified by submitting them to basic volumetric measurements followed by static and cyclic triaxial tests. The triaxial test results reported very small differences.

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

Ultrasonic pulse velocity tests on compacted soil.

In this paper, results of a series of ultrasonic pulse velocity tests on compacted soil were presented and discussed. Ultrasonic pulse velocity tests provide compression and shear wave velocity information that can be used in calculating dynamic elastic moduli such as Young’s modulus and shear modulus. From the test results, calculated Poisson’s ratio shows a linear relation with the water content in compacted soil, which leads to a linear trend in both P and S wave velocity against water content. Furthermore, presenting plots in bulk density versus wave velocity gives a clearer trend than dry density versus wave velocity.

Liquefaction Behavior of Mississippi River Silts

Civil infrastructure built on alluviums and recent deposits, such as dams, contain significant amount of silts. The static and dynamic behavior of these fine-grained soils has been investigated less than the clay-like or sand-like soils. Low plasticity silts (PI = 6) obtained east of St. Louis in Illinois are known as loess that has been re-deposited by water in the floodplains of the Mississippi River. These silts were reconstituted in the laboratory by slurry at water content above the liquid limit and then consolidated to an initial effective stress. The initial laboratory characterization under monotonic loading included a series of consolidated undrained triaxial compression tests at different effective confinement to determine the critical state parameters. A series of stress-controlled cyclic triaxial compression tests were run under normally and overconsolidated conditions. The liquefaction behavior of the silt at different over consolidation ratios and its relationship to the monotonic behavior is presented and discussed.

Evaluation of Pre-consolidation Stress Determination Methods

Pre-consolidation pressure provides valuable information about soil behavior and, specifically, settlement under an induced load. Soil is expected to have less settlement before its pre-consolidation pressure and much more settlement after that point. The pre-consolidation pressure and the compressibility of the soil can be determined from the results of a one dimensional consolidation test. Different methods have been developed to obtain the accurate pre-consolidation pressure from one dimensional consolidation test data. This paper presents and discusses the results of the one-dimensional consolidation test data from an extensive testing program. The test specimens used were obtained from multiple borehole locations and were extracted using Shelby tube samplers. The focus of this paper is the comparison of three pre-consolidation stress determination techniques, which were performed on each specimen of the large sample pool. The methods used were the Casagrande method, strain-energy method, and intersecting tangent method. The implementation of these methods will be evaluated. In addition, the subjectivity of each method will be addressed. The final results of the techniques will then be compared and contrasted.

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)

Transverse-Earthquake Induced Deformations of a Bridge Approach Embankment in the New Madrid Seismic Zone

It is predicted that strong earthquakes, larger than M 7.0, may occur within next 50 years in the New Madrid Seismic Zone (NMSZ), the location of three of the most powerful earthquakes in United States history. Large displacements may occur during strong earthquakes that can cause an embankment to fail or lose its function. The hyperbolic stress-strain model with Masing rules was modified to account for strength and stiffness reduction due to change in the effective confining pressure. The Byrne model was combined with a hyperbolic model to calculate the pore water pressure caused by seismic shaking. This modified hyperbolic model was implemented into the computer code, FLAC, and calibrated against the 1971 Upper San Fernando Dam failure. It appears that the modified model is superior to the built-in Finn model in FLAC to predict the earthquake-induced deformation of the embankments. Then it was applied to study the seismically induced deformation of an approach embankment to Bridge A1466 in the NMSZ near Hayti, Missouri.