Date of Award:

1965

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Civil and Environmental Engineering

Advisor/Chair:

A. Alvin Bishop

Abstract

A study was conducted to find out both the effect of different exchangeable cations and the concentration of ions in the soil pore fluid on strength and plastic properties of a sample of cohesive soil taken from the bank of an open drain ditch at the Utah State University Irrigation and Drainage Farm.

The experimental results of this study may be summarized by the following points:

  1. A general decrease of liquid limit and an increase in both shear strength and modulus of elasticity, with increasing salt concentration in the pore fluid, were observed for all samples, with the exception of HC1-treated samples for which shear strength was independent of HCI concentration in the pore water.
  2. An increase in both shear strength and modulus of elasticity with decreasing exchangeable sodium percentage was definite.
  3. The increase of soil shear strength caused by different exchangeable cations with distilled water in the soil pores was in the order Na + < Ca ++ < Mg ++ < K + < HCl-treated soil, whereas the modulus of elasticity increased in order Na + < K + < Ca ++< HCI-treated soll < ++ Mg
  4. A decrease in the liquid limit with decreasing exchangeable sodium was found.
  5. The influence of the different exchangeable cations used on soil liquid limit was in the order Na + > HCl-treated sample > Mg++ > Ca ++ > K+ .

From this study it could be concluded that:

  1. The strength and plastic properties of cohesive soils are affected greatly by the type and concentration of adsorbed ions as well as by the ions concentration in the pore fluid.
  2. The failure of the sloping sides of drain ditches may be attributed at least in part to increasing exchangeable sodium percentage.
  3. For satisfactory and economical design of earth structures, a knowledge of chemical as well as physical properties of cohesive soils is essential. The boundary conditions which may change the soil physico-chemical properties with time should be considered.
  4. Strength properties of HCl-treated soils are controlled by aluminum rather than hydrogen ions. Exchangeable aluminum was liberated as a result of the breakdown of the clay fraction in soils when treated with HC1.
  5. The experimental results are not completely explained in terms of the Gouy-Chapman theory of double layers. However, the Stern theory which considers the specific adsorption of ions on clay surfaces is a better alternative and does explain the results adequately.

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