Ernest S. Berney

Percolation Threshold of Sand-Clay Binary Mixtures

Many poorly graded granular materials of engineering importance can be characterized as gap-graded binary mixtures. Such mixtures display a volume-change response at a threshold value of the coarse fraction that is reminiscent of systems described by percolation theory. An experimental investigation on a sand-clay mixture is presented that clearly displays threshold behavior and sheds light on the role that each soil fraction plays in transferring loads through the medium. There are two key effects. First, an analysis of void ratio of the interpore clay fraction for varying compaction energies reveals an abrupt reduction in clay density at the threshold fraction of sand, whereby it is virtually impossible to impart compaction on the clay fraction at sand contents exceeding this threshold. Second, although force chains cannot be observed directly, analysis of the sand in terms of its component void ratio, computed based on treating the clay as part of the void space, shows that the sand carries a majority of the load at component void ratios that are too high to form stable force chains. The traditional interrelationship between mean stress and void ratio based on critical state theory breaks down when the sand content nears its threshold fraction. When the sand content is near the threshold limit, increasing mean stress results in a greater dilative tendency. Results are compared with findings on consolidation of sand-bentonite mixtures, and so-called reverse behavior of sand-silt mixtures.

Full-Scale Instrumented Testing and Three-Dimensional Modeling of Airfield Matting Systems

Matting systems are used for temporary applications on soft soils to reduce ground pressure exerted by aircraft, heavy equipment, vehicles, and construction material. They have been used for military airfields, construction platforms, and similar applications. Previous evaluation studies of matting systems have typically consisted of full-scale testing, with only a limited amount of numerical modeling found in the literature. This paper presents results of full-scale accelerated testing of 21 test sections encompassing five matting systems, five soil-support conditions, and two aircraft loadings. One of the soil-support conditions was instrumented and tested in conjunction with three matting systems and one aircraft loading. Three-dimensional finite-element modeling was performed on the instrumented sections using the measured test data for calibration. Good matches of measured soil stresses were obtained with the model for two of the mats, whereas the model underpredicted stresses in the third mat. Modeling of the type performed in this paper was capable of correctly ranking the performance of the matting systems modeled relative to the full-scale test results.

Evaluation of Nonnuclear Soil Moisture and Density Devices for Field Quality Control

When new transportation infrastructure is constructed or current infrastructure systems undergo maintenance, sufficient soil strength is critical to a successful construction effort. Currently, soil design specifications are given for a minimum soil density and a specified range of soil moisture content. Quality control is achieved by monitoring the soil density and moisture content throughout the construction process. The nuclear density gauge (NDG) is most commonly employed to determine soil density and moisture content because of its ease of use, speed of readings, and reliability of results. However, potential safety hazards and rigorous user certification requirements have led many agencies to seek alternative devices. This paper focuses on a portion of a much larger study that compared a wide range of compaction control devices; the paper also assesses the performance of devices that measure soil density and moisture content. Several new, commercially available alternatives for the measurement of soil density were tested on various soil types and conditions to determine which device performed best and most consistently. For the same soil types and conditions, several devices and techniques for the determination of soil moisture content were also tested. The combination of the TransTech soil density gauge and the heated frying pan–open flame field moisture content techniques represented the best alternative to the NDG.

Rapid Soils Analysis Kit for Low-Volume Roads and Contingency Airfields

The ability to determine the construction requirements for soil without the need to conduct laboratory testing is essential in performing an expedient airfield or highway design. Until now, only subjective field analysis techniques satisfied this requirement, but their results failed to provide tangible numeric data that could be used to determine moisture–density and California bearing ratio (CBR) design criteria. This paper introduces a rapid soils classification kit with instruments that are compact and easily transported to provide an immediate measure of soil moisture, grain-size distribution, and plastic limit. An accompanying software program incorporates the numeric data generated from the soils kit, classifies the soil, and performs multiple regression routines based on a statistical analysis of a large database of soil properties to predict optimum water content and maximum dry density for the soil of interest. Built-in, higher-order regression equations allow the user to visualize complete moisture–density curves for varying compaction energies as well as soaked and unsoaked CBR as functions of water content for the constructed condition of the soil. The moisture–density curve and CBR strength represent the critical data necessary to enable contingency design and construction of highways and airfields.

Effect of near-surface hydrology on soil strength and mobility

Abstract History has repeatedly demonstrated the potentially negative influence of near-surface hydrology on military mobility. Increased moisture and saturation in soil results in a transition from solid to somewhat liquid states. As soil approaches the liquid state, the shear strength available for supporting traffic of ground vehicles or aircraft diminishes. Historical engagements elucidate the importance for armies to recognize soil conditions that could compromise manoeuvre. Since World War II, the US Army has pursued research aimed at equipping soldiers with the tools and knowledge needed to account for the impact of near-surface hydrology on mobility. Significant portions of the research have been focused on characterizing soil trafficability as a controlling factor in ground vehicle mobility and on developing methods for rapidly assessing soil conditions to ensure adequate bearing capacity for expediently constructed roads and airfields. In contrast, hydrological conditions can also produce extremely dry soil with potential for surface layers to break down under ground vehicle and aircraft traffic loadings, resulting in a propensity for extreme dust generation, an entirely different problem for military mobility that the research has also been addressing. Mobility problems associated with these adverse soil conditions have not been eliminated, but the research has produced significant advancements.