it is time for me to do my duty as a fellow SGForumer. shots
from Saturday.
the new platform from the outside. you can see the supporting
concrete beams for the roof is now ready. I have managed to see it
from the concourse level and it looks a lot like the current
ones.
notice the workers working on the "room" on the right hand side
of the photo at platform level. it should be the structure for the
washrooms and various utilities.
the southbound viaducts are more or less completed, with only
two more segments left. one in the next photo and the other along
Jurong East Central.
the northbound viaduct supports are fully up, as for the
segments, this is as far as it went on the side nearer to the
station. segments on the other end (where existing northbound
tracks will connect to the new ones) have been lifted to Toh Guan
Road or so.

one of the two final southbound viaduct segments left.

most likely even that segment above would have been filled up as
well. saw the workers preparing this segment for lifting on
saturday.
Have to correct your description. The structure being shown
on your photo is a precast beam, not a precast segment.
Segments are smaller than a beam, and they are joined together,
several of them in a span.
From your second last photo, the beam waiting on the ground is
going to sit onto the crosshead directly.