'soft clay' is correct and usable in written English.
You can use it to describe a type of clay that is easily molded or shaped. For example: "The pottery class used soft clay to create small figures."
Traces are engraved in soft clay.
His back seems to turn to soft clay, gouged, scored, and sculpted by her hands.
They are rough and unreliable, made of soft clay that flakes off in the rain.
Settling also refers to movement of structures located above deep beds of soft clay.
Children should be kept away from the soft clay or mud flap.
Think of me as soft clay, ready to be molded in your image.
Piles cannot be placed in soft clay, but they can be placed in medium-stiff clay.
The Jiangsu soft clay is a lightly overconsolidated and sensitive clay of high plasticity in nature.
The foundations of these high-rise buildings posed a major problem, given the soft clay soil of central Chicago.
In Class A prediction, the soft clay was modelled as a single homogeneous layer.
This paper presents the strength improvement of soft clay mixed with coal ash.
