There is no one book for GATE.

Having said that there are several books of different subjects that cover the topics very well.

But, remember, in exams like gate, more important thing is to know what to study and what not to study.

Therefore, first of all take a print out of syllabus & identify the topics. Then you can go for books.

Transportation: khanna and justo

Building Material :Rangwala

FM : rk bansal or Modi & seth

Soil: Arora or gopal ranjan & rao

SOM: b.c. punmia

RCC : B. C. Punmia

TOS : ramamrutham

EE : s k garg

Irrigation & hydrology : sk garg

Survey : B C punmia vol. 1& 2.

Still I'd suggest you to go through handwritten class notes of any reputed coaching ( IES master or MADE EASY) or ACE engg academy).

If you're having difficulty in understanding any particular topic then you can study that particular topic, from book.

Also, enroll in any test series for GATE and give it like real GATE exam.

Don't be disheartened if you're unable to perform well in test series. It is designed to find out any mistake in your preparation, so after each test try to analyse your mistakes and rectify them.

Hope this helps.

Thank you.