Removal of props
A 700 mm CHS being removed. Note the remaining props being built over.
A few weeks ago I promised to keep you updated on how the removal of the props was going. You can see by the photo the infill around the stairs has been filled and that I followed the advice of cutting 100 mm holes in the props to de-stress them. The removal of the props occurred pretty smoothly.
The only problem I encountered was that my boss had misinterpreted a consultants advice which caused me to check the capacity of the steel left and the concrete slab. After determining that it was ok, and after the said consultant went dark and refused to answer his calls we proceeded with the demolition as planned.
Anyway all went well but a tense moment and that was a floor ago.
What the site now looks like now – We are back at ground level and currently building the transfer slab with PT concrete.
However – I am still dealing with what we have left behind. More to follow…
![IMG_5145[1].JPG](https://pewpetblog.com/wp-content/uploads/2016/10/img_51451.jpg?w=595)
In foreground a 900 mm CHS and Double 1200 WB left behind.
Holdfast Training Services Trial Blog 
Have you a view on the bottom up design used ? You mention that you are completing a transfer slab now – So could the design have put that in early and gone up as well as down?
John, I have some pretty strong opinions on the design used. The first mistake is splitting the wall design into constituent parts that made coordination highly difficult (not impossible just has aged me by 10 years). For a saving of $50,000 this has cost $250,000 AUD already in variations.
Given the proximity of neighbouring structures and the tight programme a top down constructruction with a simultaneous build-up is the logical choice. However, I do not believe this competency exists in Queensland. Multiplex have doing it in the UK but, not here. I don’t believe the inexperienced project team, consultants or contractors could have pulled it off.
The basement is very tight on space and variations in columns could have interfered with car parking spaces which would be a major issue for the client. The capacity of the slabs would need to have been increased from 2.5 KN. Not a problem except height clearance is very tight. Consequently, while a simultaneous top down is the most logical solution it has its own challenges.
I believe there is a alternate propping system the could have used with an additional layer of anchors in the N/S and 4 props running East West at 7.5 m c/c (I will draw when I get the opportunity). A proprietary system would have been easy to install and remove but, digging under them could have been difficult. I would have placed the props slightly higher up so that B1 P1 could be completed without building over.
Easy fix – Stairs – It would have made the job considerably easier if the stairs were around the core at not by the retaining walls. Prefab stair masters could have been used and they would have been easier to incorporate in the build sequence. Instead. I have had to grind back out of tolerance piles and stick build every flight. This is all very costly and time consuming.
Doug, we have employed a methodology that allows us to build up and dig down at the same time. It sounds like a nice idea but it presents considerable project management challenges. Conceptually it would save programme time (It was suppoed to save us about 3 months) but once the issues are added its benefit is not as clear as you’d expect.
The main issues are based around the idea that you have multiple large packages being completed in the same footprint at the same time. Deconflicting the requirments of a concrete package, steel package and excavation package is unbelievably challenging. I therefore look at the relative simplicity of a tradtional bottom up approach as a major benefit in its own right.
Tom, great insight thank you. We can barely keep pace with going in one direction here, let alone up and down. I think it is beyond the capabilities of Multiplex in Qld.