What characterizes normally consolidated clay?

Normally consolidated clay is characterized by having experienced the maximum past vertical stress that it has been subjected to, which is equal to its current vertical stress condition. This means that the clay has not undergone any significant previous loading that would exceed the current stress it is under. In this state, the pore water pressure is still high, and the clay retains its original characteristics of strength and compressibility unaltered by over-stressing.

In contrast, the other options illustrate different aspects of clay behavior. Compacted clay under high stress refers to over-consolidated clay, which is subject to higher stresses than it has previously experienced. Over-consolidated clay itself is characterized by having been loaded beyond its normal state, which means it is not normally consolidated. While saturation is an aspect of clay that may affect its behavior, a clay being simply saturated with water does not necessarily define its consolidation state. Therefore, the defining feature of normally consolidated clay being optioned correctly is that it has not experienced any vertical stress greater than its current condition, confirming that it is in a natural and balanced state of consolidation.