Characteristic zones for initial state of sand under undrained shearing

A new line for characterising the initial state of sand in the e-lnp plane is firstly introduced in this note, which is defined as the normal compression line (NCL) for sand. Together with a series of existing characteristic state lines, four characteristic zones are subsequently established in the e-lnp plane, namely, liquefaction zone; strain softening zone; quasi-steady state zone and strain hardening zone. Under undrained shearing, saturated sands with the initial state located at the same zone can exhibit similar type of stress–strain relation denoted by the name of zone. A good agreement has been found between the proposed zones and existing experimental results, revealing the ability of proposed zones in characterising the initial state of sand. Finally, the significance of the proposed characteristic zones is demonstrated in the applications associated with sand.