The engineering geology of clay minerals: swelling, shrinking and mudrock breakdown

Abstract

Swelling, shrinking and physical breakdown processes are reviewed with reference to well-known mudrock and overconsolidated clay formations in the UK and USA. Swelling results from two processes: the equilibration of depressed porewater pressures following stress relief, and the physico-chemical (osmotic) response of component clay minerals. Expansion in Na-smectite, and to a lesser extent Ca-smectite, clays is governed by double-layer swelling, whereas in kaolinites it is purely a mechanical unloading phenomenon; illites show an intermediate response. Intraparticle swelling in mudrocks older than the Silurian in the UK, or Upper Mississippian in the USA, can be expected to be reduced because of the removal of expandable layers by burial diagenesis. Shrinkage, like mudrock breakdown, is restricted to the partly saturated zone. Suction pressure-moisture content curves of indurated mudrocks are shown to be different from mudrocks and clays with high proportions of expandable clay minerals. Classification of expansion potential based on activity ratio poses problems with indurated types, but with some modification of method reasonable predictions can be made. Controls on physical disintegration are identified as: (i) incidence of sedimentary structures and discontinuities, (ii) slaking (air breakage), (iii) expandable clay mineral content, especially smectite, and (iv) clay mineral fabric orientation. Exceptionally high exchangeable sodium percentages have been measured in Coal Measures rocks susceptible to breakdown.

Physico-chemical effects on the behaviour of a coastal mudslide

“…Skempton (1953) used data for Weald Clay to compare the relationship between plasticity index and clay fraction which showed two groups of data, as follows: Group 1; clay fraction 15±40%, plasticity index < 20%; Group 2; clay fraction 50±70%, plasticity index 30±45%. Taylor & Smith (1986) also show data that is consistent with this grouping. Although the discussants point out that the index properties are low, the range of values of clay fraction and plasticity fall between these sets of data.…”

The Impact of Secondary Phyllosilicate Minerals on the Engineering Properties of Various Igneous Aggregates from Greece

“…This may be due to the fact that even the low percentages of smectite and illite are capable of adsorbing water in their phyllosilicate structure (especially smectite) during the preparation of engineering constructions such as concretes. From these, the swelling clay minerals of smectite may swell up significantly [73] hence causing severe destruction to their host rocks. Another possible factor which may influence the physicomechanical performance of volcanic rocks may be the distribution of clay minerals.…”

The Impact of Secondary Phyllosilicate Minerals on the Engineering Properties of Various Igneous Aggregates from Greece

“…This may due to the fact that even the low percentage of smectite and illite is capable to adsorb water in their phyllosilicate structure during the preparation of engineering constructions. These swelling clay minerals may swell up to 700%-800% [63] hence causing severe destruction to their host rocks. …”