You can refer below recommended books for your preparation

Engineering Mathematics

-Discrete Mathematics and Its Applications by Kenneth Rosen

-Higher Engineering mathematics by B.S. Grewal

-Advanced Engineering Mathematics by Erwin Kreyszig

Structural Engineering

-Theory of Structure by CK Wang, S. Rammamrutham, L.S. Negi & Jangit

-Theory of Elasticity by Timoshenko & Gere -Theory of Structure by Wilbur & Norris

-Strength of Materials/Mechanics of Structure by Gare & Timoshenko

-E. Popove, L. Singer -B.C. Punamia, Rammamrutham

Geotechnical Engineering

-Soil Mechanics by Gopal Ranjan & Rao,Venkat Ramaiha,S. K. Garg,

-B.C. Punamia, V N S Murthy

Water Resources Engineering

-Water Resources by S K Garg

-Water and Waste Water by SK Garg 1 and 2

-Fluid Mechanics- RK Bansal and Fox and Richard

Transportation Engineering

-Transportation by Justo Khanna

Environmental engineering

-Environmental Engineering by S. K. Garg Part I & Part

-Waste Water Engineering by B. C. Punamia Part I & Part II

Geomatics Engineering

Surveying (vol. 1,2,3)  by B.C.Punia, Ashok Jain, Arun Jain

Good Luck