Donald H. Gray

Resonant Column Tests on Partially Saturated Sands

This paper describes the measurement of the influence of capillary effects on the dynamic shear modulus of partially saturated sands. A Hall-type resonant column apparatus was used to perform the experiments. The materials tested included natural angular and subrounded sands, angular and subrounded sands with specified artificial gradations, and uniform angular and subrounded sands with various minus No. 400 sieve size fractions. Capillary stresses can significantly increase the shear modulus of unsaturated sands. Void ratio, confining pressure, degree of saturation, grain shape, and grain-size distribution are the primary factors affecting the shear modulus of partially saturated sands.

Soil Reinforcement with Recycled Carpet Wastes

A root or fibre-reinforced soil behaves as a composite material in which fibres of relatively high tensile strength are embedded in a matrix of relatively plastic soil. Shear stresses in the soil mobilize tensile resistance in the fibres, which in turn impart greater strength to the soil. A research project has been undertaken to study the influence of synthetic fibrous materials for improving the strength characteristics of a fine sandy soil. One of the main objectives of the project is to explore the conversion of fibrous carpet waste into a valueadded product for soil reinforcement. Drained triaxial tests were conducted on specimens, which were prepared in a cylindrical mould and compacted at their optimum water contents. The main test variables included the aspect ratio and the weight percentage of the fibrous strips. The results clearly show that fibrous inclusions derived from carpet wastes improve the shear strength of silty sands. A model developed to simulate the effect of the fibrous inclusions accurately predicts the influence of strip content, aspect ratio and confining pressure on the shear strength of reinforced sand.

ELECTROCHEMICAL ALTERATION OF CLAY SOILS

The composition and physical properties of three clay soils were altered by introducing aluminum under an electro-chemical gradient in order to evaluate the role of pH in controlling changes in soil composition and the feasibility of pH buffering during electrochemical treatment.Both X-ray diffraction and selective chemical extraction methods were used to determine the distribution and mode of occurrence of aluminum in the treated samples. Aluminum was detected in the treated samples in both exchangeable form and as a hydroxy-aluminum interlayer. Aluminum oxide minerals such as gibbsite were not detected in any of the treated samples. Mineralization by aluminum ions was speeded and intensified in bentonite soils by buffering the catholyte with carbon dioxide.Plasticity of bentonite soil samples from South Dakota was reduced markedly by electrochemical treatment, whereas the plasticity of an illite soil from Illinois and an illite-montmorillonite soil from Mississippi were relatively unaffected. Nearly all treated samples exhibited some degree of electrochemical induration or mineralization. Induration was most pronounced in bentonite soil samples with high water contents and alkaline pH largely because of hydroxy-aluminum interlayering in the ciay. On the other hand interlayering was negligible in illite soil samples with low pH; the main effect of electrochemical treatment in this case was the addition of aluminum in exchange sites.RésuméLa composition et les propriétés physiques de trois sols argileux ont été modifiées par l’introduction d’aluminium sous un gradient électrochimique afin de définir le rôle du pH dans le contrôle des changements affectant la composition des sols et la possibilité d’amortir le pH au cours du traitement électrochimique. Les méthodes de diffraction des rayons X et d’extraction chimique sélective ont été utilisées pour déterminer la distribution et le mode d’intervention de l’aluminium dans les prélèvements traités. L’aluminium a été détecté dans les prélèvements traités à la fois sous la forme échangeable et en tant que couche intermédiaire d’hydroxy-aluminium. Les minéraux d’oxyde d’aluminium tel que le gibbsite n’ont été détectés dans aucun des échantillons traités. La minéralisation par les ions d’aluminium a été activée et intensifiée dans les sols de bentonite en amortissant le catholyte avec de l’oxyde de carbone. La plasticité des échantillons de sols de bentonite du Dakota du Sud a été réduite notablement par le traitement électrochimique, tandis que la plasticité d’un sol illite de l’Illinois et un sol illite-montmorillonite du Mississippi n’était pratiquement pas affectée. Presque tous les échantillons traités ont montré quelque degré d’induration électrochimique ou de minéralisation. L’induration était plus prononcée dans les échantillons de sols bentonite avec des teneurs en eau élevées et un pH alcalin surtout à cause des couches intermédiaires d’hydroxy-aluminium dans l’argile. D’autre part la couche intermédiaire était négligeable dans les échantillons de sols illites avec pH faible: le principal effet du traitement électrochimique dans ce cas était l’apport d’aluminium dans les zones d’échange.Kurzreferat Die Zusammensetzung und die physikalischen Eigenschaften von drei Ton-Erden wurden durch Einführung von Aluminium unter Steuerung der elektrochemischen Merkmale eingeführt, um die Rolle des pH-Wertes bei der Regelung von Änderungen in der Bodenzusammensetzung und die Möglichkeit einer pH-Pufferung während elektrochemischer Behandlung zu untersuchen.Sowohl Röntgendiffraktions-als auch selektive chemische Extraktionsmethoden wurden angewandt, um die Verteilung und Erscheinungsform des Aluminiums in den behandelten Proben zu bestimmen. Das Aluminium wurde in den behandelten Proben in sowohl austauschbarer Form als auch als Hydroxy-Aluminium-Zwischenschicht gefunden. Aluminiumoxydminerale wie Gibbsit wurden in keiner der behandelten Proben festgestellt. Die Mineralisierung durch Aluminium-Ionen wurde in Bentonit-Erden durch Pufferung des Kafholyten mit Kohlendioxyd beschleunigt und verstärkt.Die Plastizität der Bentonit-Erdproben von Süd-Dakota wurde merklich durch elektrochemische Behandlung reduziert, während die Plastizität einer Illit-Erde aus Illinois und einer Illit-Montmoril-lonit-Erde aus Mississippi verhältnismäßig unberührt blieb. Fast alle der behandelten Proben wiesen eine gewisse elektrochemische Verhärtung oder Mineralisierung auf. Die Verhärtung war in Bentonit-Erdproben mit hohem Wassergehalt und alkalischem pH besonders beachtlich, vor allem wegen der Hydroxy-Aluminiumschichtung im Ton. Andererseits war die Schichtung in Illitboden-proben mit niedrigem pH-Wert vernachlässigbar gering. Die Hauptwirkung der elektrochemischen Behandlung bestand in diesem Fall in der Bereicherung der Austauschpunkte mit Aluminium.РезюмеСостав и физические свойства трех глинистых грунтов оыли изменены добавлением алюминия при электрохимическом градиенте для определения роли рН в контролируемых изменениях состава почвы и возможности буфферного действия на рН электрохимической обработки. Для определения распределения и формы нахождения алюминия в обработанных образцах использованы как дифракция рентгеновских лучей, так и селективные химические вытяжки. Алюминий в обработанных образцах обнаружен как в обменной форме, так и в виде гидроксиалюминиевых межслоевых выделений. Минералы свободной окиси алюминия например гиббсит, ни в одном из обработанных образцов обнаружены не были. Минерали¬зация при участии иона алюминия была ускорена и усилена в бентонитовых грунтах при использовании углекислоты в качестве буфера католита.Пластичность образцов бентонитового грунта из Южной Дакоты заметно уменьшалась после электрохимической обработки, тогда как пластичность иллитового грунта из Иллинойса и иллито-монтмориллонитового грунта из Миссисипи практически не изменилась.Почти все обработанные образцы обнаружили некоторую степень химического затверде¬вания или минерализации. Затвердевание было наиболее отчетливым в образцах бентонито¬вого грунта с высоким содержанием воды и щелочной реакцией, в основном благодаря наличию гидрооксиалюминиевых межслоевых выделений в глинистом минерале.В образцах, иллитового грунта с низкими рН межслоевые выделения были весьма незначительными, главным эффектом электрохимической обработки в этом случае было увеличение содержания обменного алюминия.

Soil temperature and electric potential during diurnal and seasonal freeze-thaw

Abstract Combined measurements of soil temperature and electric potential in the upper 15 cm of a glacial sandy-loam soil were made during the winters of 1986–1987 and 19871988 at the University of Michigan Botanical Gardens using an electronic data acquisition system at frequencies varying from 10 min to daily (midnight). Most of the data was collected at hourly intervals. Analysis of temperature-potential time series at two locations with probes at (0, 3, 6, 9) and (0, 5, 10, 15) cm depths indicated that the variation of electric potential relative to the potential of a 1.5 m ground spike could be interpreted as the response of an electrolytic concentration cell without transference formed by a probe and the ground spike. As the electrolyte concentration is much greater at the ground spike, and electric potential varies inversely with concentration, the potentials at the soil probes varied over the range of approximately 300–700 mV in a manner consistent with the behavior of a concentration cell. The rapid and systematic pattern of potential variation during freeze-thaw events demonstrates that the effects of electrolyte concentration and dilution are products of evaporation-distillation, the melting of frost-purified ice, soil water advection to the freezing-evaporating region, concentrated electrolyte expulsion from the freezing region and the infiltration of rain and snow melt waters.

Laboratory Testing Apparatus for Slopes Stabilized by Anchored Geosynthetics

A laboratory testing apparatus is described for examining slopes subjected to seepage and stabilized by anchored geosynthetics (AGS). The AGS technique can increase the stability of cohesionless slopes such as coastal dunes against surficial erosion and shallow mass failure caused by wave action and seepage forces. In the AGS, a geosynthetic fabric is placed on the face of the slope and tensioned via anchorage to the ground. The required tension is achieved through frictional or pullout resistance of earth anchors that are fastened to the fabric and driven into the underlying soil mass. In the laboratory testing apparatus, however, AGS tensioning is provided by thin wires connected to rigid steel tubes that exert line loads on the fabric. The wires in turn are connected to dead weights “beneath” the slope that simulate anchor loads. The prototype slopes are failed by uniformly decreasing anchor loads while maintaining the seepage gradient and orientation constant. Very good agreement was observed between experimental results and theoretical predictions of the failure mode and the average AGS loads at failure.

TWO ELECTRIC POTENTIAL SIGNATURES OF SERIAL DIURNAL FROST

During a 96-hour period in mid-March 1987, a series of four serial frost-thaw events occurred in a research field at the University of Michigan Matthaei Botanical Gardens. Soil temperature and electric potential were recorded at two near surface probe arrays (0, 3, 6 & 9 cm) and (0, 5, 10 & 15 cm) with a horizontal separation of approximately 1 m beneath the organic-mineral soil interface at hourly intervals. These time series revealed strong repetitive serial patterns. When the electric potential measurements were converted to a surrogate measure of electrolyte concentration, the C-index, strong coupled flow effects appeared to be present in the time series owing to the effects of surface freeze-thaw, evaporation-distillation and soil water advection. The data set shows the low frequency effects of upward soil water advection increasing the soil temperature and modulating the electrolyte concentration. These observations also demonstrate that soil freezing processes have two distinct regimes dominated by...

Influence of Nearshore Till Lithology on Lateral Variations in Coastline Recession Rate Along Southeastern Lake Michigan

Abstract Retreat of coastal bluffs around margins of the Great Lakes is a continuing process. Despite the positive correlation which exists between lake level and recession rates, considerable lateral variation in rates is typical of many coastal areas, while causes of this spatial variation are not well understood. Detailed examination of a 10 km segment of Lake Michigan shore near the town of Glenn, Michigan, suggests that lateral variations in the lithology of Pleistocene drift are directly correlative with spatial variations in recession rates. High recession rates and concave shorelines occur along segments composed of either outwash sand or sandy till which contains gravel up to 2 cm in diameter as the coarest clast size. Conversely, low rates and the occurrence of convex shoreline segments are related to exposures of bouldery till. The exact nature of the relationship between bouldery till and the low recession rates is ambiguous. Features observed along this area suggest two non-mutally exclusive possibilities: 1) during erosion, bouldery till develops flat gently sloping wave-cut benches in the upper shore face; and 2) erosion of this coarse till results in the development of upper shoreface surfaces covered with large boulders. Both features may serve to attenuate wave energy in the nearshore zone. In either case, lateral varition in the recession rates near Glenn is greatly influenced by the lithology of glacial drift exposed in bluff faces and the nearshore areas.

Project #27: Walden Pond

GEOMORPHIC SETTING: Walden Pond is a 62-acre glacial kettle-hole pond in a Massachusetts state park and is a National Historic Landmark. Walden Pond was the setting of Henry David Thoreau’s classic, “Walden,” which has been read by thousands for over a century. Thoreau, a poet, philosopher, and naturalist, is considered to have begun the American environmental movement. The pond has attracted large crowds of bathers since Victorian times (Fig. 1).

Project #8: Toboggan Hill

GEOMORPHIC SETTING: Toboggan Hill is artificial mound (hill) consisting of industrial waste covered with a clay cap and top soil layer (Fig. 1). Toboggan runs were constructed on one side of the hill. The facility was incorporated into a county park running along Edward Hines Drive and paralleling the Rouge River.

Project #34: Walgreens Slope

GEOMORPHIC SETTING: The site is part of the landform creating Cape Cod. Area soils consist of glacial outwash and moraine deposits, many of which form steep noncohesive slopes. Area soils permit infiltration of even the highest rainfall volumes when they are covered with forest vegetation and leaf litter. However, if the forest cover is disturbed, many local soil types become highly susceptible to both surficial erosion and to deeper seated slope failures (Fig. 1)