Why railway tracks are embedded with stones?

Answer 1

You're referring to ballast, and its used for drainage.

Note that underground railways seldom use ballast and so drainage must be solved in other ways (drains and pumps are common).
Stone chips along railtrack known as ballast .

The purpose of those ballast is:

1. it is cheap soil improvement for wheel load distribution thus prevent sinking in he ground

2. Absorbs vibration / noise a great extent by damping effect and acts like a dashpot /spring thus reduce jerk to passengers .

3. disposes rainwater off track to side by drain running along the track , at lower level. and rail bottoms dry thus prevent corrosion /errosion .

4. To avoid growing of plants on the rail track .

During periodic track inspection and maintenance , dressing is done to keep solidarity of the ballast and to keep rail level / slope . Superelevation at bends are adjusted and maintained and is maintained