Someone will be able to give a more detailed answer than me, but the points have been in at Bicester south junction for a while, probably more than a year, and the time since they were installed has been used to build the bank on which the new chord will sit. It's quite a drop from the main line to the Oxford branch (I'd heard seven metres) which means a hell of a lot of work has had to happen in order to get to the point where we are now.
There seems to have been a lot of drainage installed, there are tunnels and channels buried beneath the main mound to allow water to flow through and there are lots of cables and wires buried inside too which I presume are there to add strength to stop the hill from shearing under load when trains are running. Track has been laid on the mound but I don't think it's anywhere near ready for traffic yet. You can get a really good view of all of this as you go by on the train so it's worth just taking a ride from Bicester to Haddenham if you want to check it out.
