(a) Karl Terzaghi
(b) Fellenius
(c) Kray
(d) Henkel
Ans. (a) :  Karl Terzaghi

Explanation:-
According to Terzaghi (1948) soil mechanics is the application of laws of mechanics and hydraulics to engineering problems dealing with sediments and other unconsolidated accumulations of solid particles by mechanical and chemical disintegration of rock regardless of whether or not they contain any admixtures or organic constituents.