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Hi In general carbonates are beneficial and marly soils are more competent than purely clayey ones. France is a country well endowed with marls and this idea is well reflected in french codes of practice (e.g. piles, Bustamante & Frank, Ground Engineering, 32,3). The causes of this behaviour are not clear as yet, but is very tempting to see carbonates as structuring agents and some data is available supporting this position (e.g. channel tunnel chalk Biarez et al. at "Hard soils -soft rocks" 1998) I was talking about saturated soils. If we consider now the saturation process then again I can't see why carbonates would be worst than clays. Carbonates won't swell as clays do. Admittedly, thay can be solved by water, but their solution rate is too slow for this to be of engineering concern. If the soils were to be saline or gypsiferous then solution will be indeed a problem (the reference here is James "Soluble materials in civil engineering" Ellis Horwood 1992). It is true, however, that carbonates might mask the presence of active clays by lowering the plasticity values. (This is, at least, what I inferred from work published by [log in to unmask], but it may be worth asking him). It may be then that what seems to be a problem caused by carbonates its really a problem hidden by carbonates (e.g. active clays). Yours Marcos Arroyo [log in to unmask] phone:0117 9288 286 Room 0.37A Queen's Building Department of Civil Engineering University of Bristol University Walk Bristol BS8 On Tue, 23 Jan 2001 11:12:10 +0000 Siavash Ghabezloo <[log in to unmask]> wrote: > Hi > Marls are types of calcareous soils that include high > calcite(Caco3) content, they are fine grained and have good strength > parameters(qu,CBR,..) in the dry condition , but when they are in > touch with water their strength parameters are greately reduced.They > are classified as ML,CL or CH according to unified classification > system ( there are coarse grained marls in some places in the world > such as Saudi Arabia) , the major difference between these soils and > other type of clays are their calsium carbonate content , thus I > think the cause of strength reduction must be some reaction between > water and calcite or another reason that depends on calcite, > but I couldn't find any clear reason or reaction for this problem in > the litrature.I would appreciate if anyone could give any kind of > information about these kind of soils and especially the problem > mentioned above and it's causes. > > Sincerely > Siavash Ghabezloo > ----------------------