Silverado Contractors, which is apparently doing the demo work, ran an ad in this week's edition of the SF Business Times showing deep into the excavation. Unfortunately, I can't find a better version of the phot by Sam Burbank other than to show a screen grab of the ad but even that I think is an image of what's going on we haven't seen before:
PS: This shot couldn't have been taken in 2016 I'm sure.