The boreholes filled with concrete (and reinforcement) are part of a 'Contiguous Bored Pile Wall'. All these bores will be in contact with each other and will be the outside wall of the station. A reinforced concrete beam will then be built on top of the piles tieing them all together. A couple of struts may be included. You can then dig out the soil and there is your station. The back wall to the terminal building was constructed this way. The 'waterproof membrane' is probably a geotextile material used to increase the strength of the sub base. The heaviest loading this area will probably have is the piling rig. I am assuming the mscp will be piled.
IN my opinion this project is one of the most complicated and difficult projects to design and to construct that I have seen. Again in my simple opinion the finished system may be very difficult to maintain.