The undrained response of sands with additions of particles of various shapes and sizes

As a natural deposit, sand is rarely found clean—that is, without fractions of silt or clay. The engineering behaviour of two different host sand gradations mixed with additions of particles of various shapes and sizes is compared with that of clean sand. Anisotropically consolidated specimens are sheared in triaxial compression and extension at their ‘loosest’ initial state resulting from the same depositional method, namely air pluviation. Additive materials at contents less than 2·5% by weight can dramatically change the undrained behaviour of the host sand. The addition of rotund particles (e.g. silt) should be distinguished from that of flat or platy particles of different size (e.g. kaolin, silt or sand-size mica). The importance of shape and location of additives in modifying the sand structure is not reflected in measures such as void ratio. Mixtures of both sands with silt-size mica exhibit the most unstable response, although these had the lowest values of void or granular void ratio. The undrai...