Undrained monotonic simple shear response of clayey sands and silts

The paper describes the behavior of clayey sands under undrained monotonic shearing. The clayey sands comprised fine sand with varying proportions of kaolin clay (5%, 10% and 25% by dry weight) and are normally consolidated and sheared in the Berkeley type simple shear apparatus. The test results show how a relatively small proportion of clay can lead to a contractant response. With quantities of clay lower than about 10%, a strongly dilatant response follows the initial contraction. Dilation was not observed in the 25% kaolin mixture up to the maximum shear strain applied of 20%. A steady state is not reached for the dilative materials. The undrained strength defined as the shear stress at 20% shear strain is discussed and compared with undrained strength ratios shown by intact samples of siliceous silty clays and (offshore) calcareous silt. The normally consolidated undrained strength ratios of the intact soils are higher than those of the reconstituted clayey sands. Highest undrained strength ratios are shown by the angular carbonate silts despite their much higher in-situ void ratios.