Structure degradation and changes in the mechanical behaviour of a stiff clay due to weathering

The paper discusses the results of research into the causes of weathering o f stiff Pleistocene clays located in the Montemesola Basin (TA, Italy), and on the effects of weathering on the flay's mechanical behaviour, The weath ered clays are yellow-brown and overlie the original grey clays in the whol e basin. The liquidity indexes of both the yellow and the grey clays, their fabric, as observed by means of scanning electron microscopy, as well as t he yellow clay oxidation features suggest that drying has been the main wea thering process in the basin. This is confirmed by the results of drying-we tting cycle tests carried out in the laboratory on undisturbed clay samples , which show the drying-wetting cycles to produce changes in the grey clay similar to those present irt situ due to weathering. Results of oedometer, stress path and triaxial tests show that weathering has caused a degradatio n of the clay bonding and an associated reduction in the size of the clay s tate boundary surface. Both one-dimensional and isotropic compression data and the shear data indicate that the effects of weathering on the mechanics of the clay may be established according to the decrease in the clay stres s sensitivity. Weathering also causes a decrease in the normalised shear st iffness, as observed by means of bender element tests, which is also relate d to a decrease in the stress sensitivity.