Monolithic columns in high-performance liquid chromatography.

Substantial advances in the measurement of water content and bulk soil electrical conductivity (EC) using time domain reflectometry (TDR) have been made in the last two decades. The key to TDR's success is its ability to accurately measure the permittivity of a material and the fact that there is a good relationship between the permittivity of a material and its water content. A further advantage is the ability to estimate water content and measure bulk soil EC simultaneously using TDR. The aim of this review is to summarize and examine advances that have been made in terms of measuring permittivity and bulk EC. The review examines issues such as the effective frequency of the TDR measurement and waveform analysis in dispersive dielectrics. The growing importance of both waveform simulation and inverse analysis of waveforms is highlighted. Such methods hold great potential for obtaining far more information from TDR waveform analysis. Probe design is considered in some detail and practical guidance is given for probe construction. The importance of TDR measurement sampling volume is considered and the relative energy storage density is modeled for a range of probe designs. Tables are provided that compare some of the different aspects of commercial TDR equipment, and the units are discussed in terms of their performance and their advantages and disadvantages. It is hoped that the review will provide an informative guide to the more technical aspects of permittivity and EC measurement using TDR for the novice and expert alike.

A Review of Advances in Dielectric and Electrical Conductivity Measurement in Soils Using Time Domain Reflectometry

Specimens prepared from eight natural clayey soils used for clay liners and covers were subjected to cycles of wetting and drying. Volumetric shrinkage strains were recorded during drying. Specimens in which cracks formed during drying were subjected to hydraulic conductivity testing. Results of the study indicate that volumetric shrinkage strains are influenced by soil properties and compaction conditions. Volumetric shrinkage strain increased with increasing plasticity index and clay content, and as the compaction water content increased or decreased relative to optimum water content. Volumetric shrinkage strain decreased with increasing compactive effort. Specimens with the largest volumetric shrinkage strains typically contained the largest number of cracks. Hydraulic conductivity testing indicated that cracking of the specimens resulted in an increase in hydraulic conductivity, sometimes as large as three orders of magnitude.

Effect of Desiccation on Compacted Natural Clays

Fast, comprehensive two-dimensional liquid chromatography.

Preparative liquid chromatography.

A new device for cyclic testing of large size interfaces between structural and geologic materials and rock joints is described. Test results are reported for a sand‐concrete interface, and are used to express shear stress as function of normal stress, relative displacement, number of loading cycles and initial density. Constitutive behavior of the interface is expressed as nonlinear elastic and simulates loading‐unloading‐reloading response by using a modified Ramberg‐Osgood model. The parameters for the models are found from a series of cyclic displacement controlled tests. Predictions of the constitutive model and a finite element analysis are compared with observed test behavior.

Cyclic Testing and Modeling of Interfaces

Mechanistic design methods for flexible pavement require the specification of the resilient modulus Mr for each soil subgrade encountered in the pavement project. The resilient modulus is usually m...

Subgrade Resilient Modulus Correction for Saturation Effects

Mechanistic pavement design procedures based on elastic layer theory require the specification of elastic moduli for each material in the pavement section. Repeated load tests yielding a resilient modulus are frequently used to characterize the soil subgrade. Due to difficulties associated with cyclic testing, approximate methods are often used for design estimates of resilient modulus. These approximations are often based only on shear strength measures and do not account for the dependence on the magnitude of cyclic deviator stress. A procedure is described to relate the soil-index properties and the moduli obtained from unconfined compression tests, to resilient modulus. Two statistical models are described and demonstrated for 11 soils from throughout the state of Tennessee. One model provides an estimation of the breakpoint resilient modulus, or the modulus at a deviator stress of 6 psi (41 kPa). The second model provides a general nonlinear relationship for the modulus of fine-grained soils as a function of deviator stress. Both models are demonstrated for a range of soils and are shown to provide a good characterization of the response for the soils investigated. Similar relationships can be developed for other subgrade soils, and may prove useful to agencies that use deterministic pavement design procedures, but lack the capability for high-production repeated-load testing.

Estimation of subgrade resilient modulus from standard tests

A simple thinlayer element is developed and used in a finite element procedure for simulation of various modes of deformanon in dynamic soilstructure interaction. The constitutive behavior of the i...

Eric C. Drumm

Papers

Cyclic Testing and Modeling of Interfaces

Subgrade Resilient Modulus Correction for Saturation Effects

Estimation of subgrade resilient modulus from standard tests

Interface Model for Dynamic Soil‐Structure Interaction

Coupled discrete element and finite volume solution of two classical soil mechanics problems