see the picture. BT tower in the background. they fastened the tower to the ground by screwing it in to a giant hole.

see the foreground. they are doing the same again. a giant drill bit prepares the hole. a giant rawl plug is added. they then bring the building and simply screw it in. Probably with an automatic screw driver type thing.

if you've ever seen the very top of BT tower you will see they opted for a Philips style crosshead rather than a straight slotted. you can learn about screwing here