Across the "third Bredalbane plain" just before the final climb to Cullerin and part of the way up the hill they have lifted the up main by about 300mm, maybe more. With the down main still in its original location, the contrast is obvious.
This is the same area where the slow lane of the Hume Highway (600 mm of reinforced concrete) has almost completely failed under normal truck traffic, so clearly the soil conditions aren't the best.
The lift will give a lot more rock for the water to run out of before mud forms.
There is a lot of potential in the Cullerin range to return to the original Pre 1915 alignments. These could be worked on without disturbing the current alignment, because that's how they built the deviation in 1915.
You would need to deepen cuttings and raise some bridges to get the grades down from the original 1 in 40 (but there's quite a lot of 1 in 40 left in the down direction anyway...)