Roy E. Olson

Mechanisms controlling the permeability of clays

Coefficients of permeability, calculated using Terzaghi’s theory of one-dimensional consolidation, are reported for smectite, illite, and kaolinite, in water, methyl and ethyl alcohol, benzene, and carbontetrachloride. When the pore fluid was water the clays were homoionized to either the sodium or calcium form and the pore water electrolyte concentration was varied. The coefficients of permeability are evaluated in terms of both mechanical and physico-chemical variables. It appears that the coefficients of permeability are mainly influenced by mechanical effects, particularly the distribution of void sizes and the tortuosity of the channels. The coefficient of permeability is maximized if the flow channels consist of many small channels and a relatively few large ones, through which the main flow occurs. Physico-chemical variables exert great influence on the coefficient of permeability through their influence on dispersion or aggregation of the clay particles.RésuméLes coefficients de perméabilité calculés à l’aide de la théorie de la consolidation unidimensionelle de Terzaghi sont donnés pour une smectite, une illite et une kaolinite en présence d’eau, d’alcool méthylique, d’alcool éthylique, de benzène et de tétrachlorure de carbone. Lorsque le fluide remplissant les pores est l’eau, les argiles ont été rendues homoioniques, soit sous forme sodium, soit sous forme calcium et l’on a fait varier les concentrations en electrolyte de la solution des pores. Les coefficients de perméabilité ont été évalués à la fois en terme de variables mécaniques et physicochimiques. Il apparaît que les coefficients de perméabilité sont essentiellement influencés parles effets mécaniques, en particulier, la distribution des dimensions des vides et la tortuosité des pores. Le coefficient de perméabilité passe par un maximum lorsque les pores assurant l’écoulement sont constitués par de nombreux petits canaux et relativement peu de grands, à travers lesquels la plus grande part du débit s’établit. Les variables physico-chimiques exercent une grande influence sur le coefficient de perméabilité par le biais du rôle qu’elles jouent dans la dispersion et l’agrégation des particules d’argile.KurzreferatEs wird über Permeabilitätskoeffizienten, berechnet unter Verwendung der Theorie von Terzaghi über eindimensionale Verdichtung, für Smectit, Illit und Kaolinit in Wasser, Methylund Äthylalkohol, Benzol und Tetrachlorkohlenstoff berichtet. Wenn die Porenflüssigkeit Wasser war wurden die Tone entweder in die Natrium-oder die Calciumform homoionisiert und die Elektrolytkonzentration des Porenwassers wurde variiert. Die Permeabilitätskoeffizienten wurden mit Hilfe mechanischer sowie physikalisch-chemischer Variabler eingeschätzt. Es scheint, dass die Permeabilitätskoeffizienten in erster Linie durch mechanische Wirkungen beeinflusst werden, besonders die Verteilung von Hohlraumgrössen und die Gewundenheit der Kanäle. Der Permeabilitätskoeffizient wird maximiert wenn die Strömungskanäle aus vielen kleinen Kanälen und verhältnismässig wenigen weiten bestehen, durch welche die Hauptströmung stattfindet. Physikalisch-chemische Variable üben infolge ihrer Wirkung auf die Dispersion oder Zusammenballung der Tonteilchen einen beträchtlichen Einfluss auf den Permeabilitätskoeffizienten aus.РезюмеПриведены коэффициенты проницаемости для смектита, иллита и каолинита (по отношению к воде, метиловому и этиловому спиртам, бензолу и четыреххлористому углероду), подсчитанные в соответствии с теорией одномерной консолидации Терцаги. В тех случаях, когда наполнителем пор служила вода, глины гомоионизировались до натриевой или каль-циевой форм, и концентрация водного электролита пор изменялась. Коэффициент прони-цаемости оценивался как в отношении механических, так и в отношении физико-химических переменных. Как оказалось, на коэффициент проницаемости влияют, главным образом, механические эффекты, и в особенности — характер распределения пор по размерам и степень извилистости каналов. Коэффициент проницаемости достигает максимума в тех случаях, когда каналы, по которым проходит поток жидкости, состоят из множества мелких каналов и сравни-тельно небольшого числа крупных. Физико-химические переменные оказывают влияние на коэффициент проницаемости лишь в той степени, в которой они влияют на дисперсию или агрегацию глинистых частиц.

Measurement of hydraulic conductivity of partially saturated soils

Increased interest in protection of the environment has led to a need to be able to predict long-term movement of moisture, and contaminants, in the vicinity of shallow land disposal sites for various toxic and radioactive wastes. The advantages of locating potential sites in arid regions has led to a need to develop means for predicting moisture movements in fairly dry, partially saturated soils and for measurements of the hydraulic conductivities of such soils. A technique was developed in which thermocouple psychrometers and the instantaneous profile method were used to measure conductivities of soils with suctions as high as 80 atm. For one clay of low plasticity, the conductivity dropped from about 10 - 7 cm/s when saturated to almost 10 - 1 2 cm/s for degrees of saturation of the order of 30 percent. Measured conductivities were used in a finite element solution to Darcys equation to predict final water content profiles. The predicted and measured profiles compared well, which suggests that the measured conductivities were tolerably accurate. Based on data presented, the proposed technique seems promising for conductivity measurements in clays with degrees of saturation between about 30 and 90 percent and in sands with 5 to 50 percent saturation.

SHEAR AND INTERFACE STRENGTH OF CLAY AT VERY LOW EFFECTIVE STRESS

Thin-specimen direct shear (TSDS) tests were conducted to measure the shearing strength of kaolinite, and interface strengths between kaolinite and acrylic plastic and anodized aluminum, at normal effective stresses from 1 to 2400 Pa (0.02 to 50 lb/ft2). At the lowest effective normal stresses, curved strength envelopes fitted through the data exhibited no cohesion and high secant friction angles. Accurate information on the behavior of soil in this low-pressure range is needed to properly interpret the behavior of prototype foundations in laboratory-scale model tests.

Estimation of Consolidation Properties of Clay from Field Observations

Analyses to obtain theoretical time-settlement cuves for embankments typically make use of soil properties measured in the laboratory on small disturbed samples subject to strain rates and hydraulic gradients that are several orders of magntiude greater than those encountered in the field. Only analyses of well-documented case histories can demonstrate the validity of such extrapolations. Refined analyses based on detailed field observations of settlements and pore water pressures at various depths beneath the main I-295 highway embankment adjacent to the Fore River in Portland, Me., have demonstrated that: (1) the field e versus log sigma curves are typically above the laboratory curves and have a sharper break at sigma max+ (2) c sub v is higher in the field than in the laboratory; (3) at this site c sub r /c sub v ranged from 1 to 2; and (4) there was a generally good correlation between field properties and reconstructed laboatory properties. At this site the large differences between strain rates and hydraulic gradients in the laboratory and the field apparently did not introduce important errors. (Author)

Axial Load Capacity of Piles in California in Cohesionless Soils

The literature abounds with methods to estimate the axial tensile or compressive load capacity of driven piles. Most of these methods have disadvantages associated with undue complexity, non-linear relationships, lack of sufficient support load test data, use of out-of-date technology, or simply lack of desired accuracy. The California Department of Transportation performed a series of load tests on driven piles for bridges, over a period of years, but lacked the kinds of soil information needed to extend their experience to new sites, and did not have the data in easily accessible forms. A project was initiated to make new soil borings and cone soundings at a number of sites and to incorporate data into an electronic database for ready access. There was a further interest in examining the accuracy of existing methods for predicting capacity and of developing estimation procedures that were fitted to experience in California. This paper is concerned with pile tests in cohesionless soils, ranging from silts through clean sands, but excluding sites with soils classified as gravelly sands or coarser. Experience indicates that the margin of error for predictions in cohesionless soils is substantially in excess of that for cohesive soils. The considered pile types are one-end and closed-end steel pipe piles and precast concrete piles. H piles were included in the investigation but they all encountered gravels and are thus excluded from this paper.

Behavior of Suction Caissons Measured in Laboratory Pullout Tests

Laboratory experiments are being conducted to study the behavior of suction casissons used for deep offshore moorings. Tests with a 100-mm diameter by 910-mm long caisson prototype, which is installed using dead weight or suction, are performed in a 1.1-m thick deposit of normally consolidated kaolinite. Instrumentation is used to record displacements, axial forces, and pore water pressures (at five locations along the interior and exterior surfaces of the caisson) during extraction of the caisson. Axial pullout tests have been conducted on caissons inserted using dead weight only or dead weight plus suction pressure, on caissons pulled with a vented or sealed top cap, and with rapid (undrained) versus slow (drained) pullout. Measured pullout capacities are interpreted in terms of the weight of extracted soil, side resistance on the caisson walls, and the reverse end bearing capacity at the tip.Copyright