Recent research at the Norwegian geotechnical institute concerning the influence of chemical additions on quick clay

Abstract

This is an english version of a lecture presented in Norwegian at the Swedish Society for Clay Research meeting which was held in Oslo May 1967.

To a natural Norwegian illitic-chloritic quick clay salts of different cations were added. Atterberg limits and remoulded shear strength were determined before and after storage. After final storage chemical analyses were made.

The determinations showed that both the Atterberg limits and the shear strength increased, and that the effect depended on the added cation. For instance the liquid limit after 17 hours storage increased in the following order: NaCl < Fe(OH)₃ = FeCl₂ = MgCl₂ = CaCl₂ < FeCl₃ < AlCl₃ = KCl < Al(OH)₃. The remoulded shear strength after the same storage time increased in the order: Fe(OH)₃ < NaCl ≤ FeCl₂ ≤ MgCl₂ < CaCl₂ < Al(OH)₃ < FeCl₃ < KCl < AlCl₃. The chemical analyses included determinations in pore water, NH₄-acetate (pH = 5) extract and cations in Na-dithionite-citrate extract. From these analyses it was possible to study the relative exchanging power of the added cations. The ability to displace adsorbed cations followed the sequence: Na⁺ < K⁺ < Mg²⁺ < Ca²⁺ ≤ Fe²⁺ ≤ Fe³⁺ ≤ Al³⁺, and to displace adsorbed Mg²⁺ the sequence: Na⁺ < K⁺ < Ca²⁺ = Al³⁺ < Fe³⁺ < Fe²⁺. Electron micrographs were made on clay samples free of adsorbed iron and on the same samples after addition of Fe(OH)₃. The micrographs revealed that the added Fe(OH)₃ was present as dark “clusters” of 30–50 Å diameter on the mineral surfaces. In addition, the chemical analyses revealed that the Fe(OH)₃ and Al(OH)₃ (added as gels) had an exchanging power, and that the gels replaced Na⁺ more readily than K⁺ and Mg²⁺. The possible importance of cations released by chemical weathering on geotechnical properties and behaviour is discussed in the light of the experimental results.