Richard L. Handy

Loess distribution by variable winds

Systematic decreases in loess thickness with distance from the source, usually considered to reflect a prevailing wind direction, may relate to variable wind directions. If winds blowing transverse to a linear source carry their load to a farthest distance designated X m , winds blowing at an angle α to the source will distribute their load over a reduced distance, X m sin α, leading to a proportionate increase in thickness by a factor of 1/sin α. Thus where α is small, for winds nearly parallel to the source, deposition should be limited to a narrow corridor adjacent to the source, leading to greater accumulations in this area. Representation of random wind directions by integration of the thickness equation gives a linear relationship between thickness and the logarithm of distance, as observed empirically along loess traverses and in sampling near dusty roads. Addition of a moderate prevailing wind to the variable wind model preserves the semilogarithmic thickness relation on the downwind side of the source but reduces thicknesses on the upwind side and substitutes a nearly linear relationship between thickness and distance from the source. Loess thickness contours should be approximately parallel to the source regardless of the prevailing wind direction. The contours bulge outward adjacent to wider source areas, probably because of increased dust concentrations in the air. The variable wind hypothesis does not fully account for extraordinary thicknesses of loess within a few miles of the source. These extraordinary thicknesses appear to relate in part to a still-rising dust cloud and hence increased low-level dust concentrations in air close to the source.

Alluvial Cutoff Dating from Subsequent Growth of a Meander

A meander in the Des Moines River grew rapidly following a channel cutoff ca. 1880, after which the rate of growth slowed gradually as the channel approached the edge of the meander belt. A first-order rate equation of the form S/S 0 = e − Kt was found to describe the distance S of the river from the edge of the meander belt at any time t after cutoff.

Stick-slip of Lightly Loaded Limestone

Abstract The phenomenon of stick-slip of a limestone tested in d direct shear at constant rate of strain under normal loads of 0·75–20·00 kg/cm2 and temperatures from 30 to 200°C was investigated. Stick-slip was found to depend upon the temperature, normal load and previous frictional history of the rock. Stick-slip could always be induced from smooth slip by raising the temperature. Temperatures above that required to induce stick-slip result in larger slips, longer sticks and higher shear load relaxations. At normal loads above 3·00 kg/cm2, stick-slip began at 30°. Accumulation of debris has the same effect as lightening normal load, allowing smooth slip below 100°C. Smooth slip below this temperature is attributed to adsorbed water. The dependence of stick-slip upon temperature and reaction to the creation or introduction of debris led to the conclusion that stick-slip of limestone is a result of asperity to asperity bonding.

Borehole Shear Tests in a Shallow Marine Environment

A wireline adaptation of the borehole shear test (BST) with high-pressure shear plates was one of several in-situ test methods selected to measure strength of overconsolidated phosphatic clays and lime rock at proposed pier locations for the replacement of Sunshine Skyway Bridge, Tampa Bay, Florida. Although the sites soils ordinarily would be determined to be too hard for stage BSTs, an on-site decision was made to try it in lieu of single-point testing to save time. Of 18 stage tests attempted in very hard clay, 10 gave satisfactory failure envelopes, 5 gave envelopes indicative of residual shear strength, and 3 gave invalid envelopes attributed to progressive seating of the shear plates. Stage tests in the harder rocks and shell were less successful. Average cohesion from the 10 satisfactory stage tests in the overconsolidated clays was 91 kPa and the average friction angle Φ = 25.7°. The BST data proved useful for converting a large number of undrained penetration tests into the effective stress strength parameters needed for design. The additional use of special BSTs using smooth plates also permitted site-specific shear strength corrections for soil against steel piles and casings.

A Stress Path Model for Collapsible Loess

Stress paths were determined for loess in situ at two sites, from overburden pressures and from lateral stresses measured with the Ko Stepped Blade. Ko is as low as 0.1 to 0.3, compared with 0.4 to 0.5 for a normally consolidated silt soil. The Ko values are consistent with compression of a laterally confined solid having a low Poisson’s ratio.

Modification of CA-Montmorillonite by Low-Temperature Heat Treatment

The objectives of this investigation were to measure the effects of moderate heat treatments, below the dehydroxylation temperature, on physical and chemical properties of a calcium-montmorillonite clay. Previous workers have noted the reductions in cation exchange capacity and swelling property after heating in the range 200°–400°C, and have suggested several possible explanations, such as hysteresis effect, increased interlayer attractions owing to removal of interlayer water, or changes in the disposition of interlayer or layer-surface ions.

Liquefaction, Lateral Stress, Consolidation State, and Aging

AbstractIn 1986–1989, Jackson Lake Dam, Wyoming, was removed after standard penetration tests indicated that the foundation soil was subject to liquefaction. Part of a subsequent research program involved measuring lateral in situ stresses at various depths in the foundation soil by use of the Ko Stepped Blade, a device that introduces a stepwise lateral displacement of soil so contact pressures can be extrapolated to give the hypothetical pressure on a zero-thickness step. The foundation soil was cohesionless mix of alluvial and deltaic silts and sands with some sharp-edged gravel. The lateral stress measurements established relationships between the four topics in the title of this paper. A normal consolidation state, meaning that a soil is in equilibrium with its own weight, can be established when Ko is constant with depth and lateral effective stresses extrapolate to zero at the ground surface. On this basis, three stress zones were identified: (1) Based on limited data, an uppermost zone, to a depth...