8th February 2012
Twin-wall
Tresham College, Corby Campus
Twin Wall System (Retaining Wall)
Hannafin Contractors
Date: 23rd April 2010
Hannafin Contractors
Date: 23rd April 2010
Introduction
The building footprint has a retaining wall through the middle of it providing a split in levels between ground floor and 1st floor. Originally this was a traditional shuttered in-situ concrete wall, however, it was seen that a pre-cast alternative could reduce the programme and therefore bring the date forward for the steel frame to commence.
The wall used was a twin wall structure which consisted of units with the two outer 60mm already pre-cast. These are held together with reinforcement which also provides a gap of about 280mm. Once the units have been placed and stood over the starter bars out of the wall base, concrete is poured into the gap, with U-bars placed in the top ready for the 1st floor slab.
The wall used was a twin wall structure which consisted of units with the two outer 60mm already pre-cast. These are held together with reinforcement which also provides a gap of about 280mm. Once the units have been placed and stood over the starter bars out of the wall base, concrete is poured into the gap, with U-bars placed in the top ready for the 1st floor slab.
Quantities
Length of wall: 84m (1st run GL14-8)
80m (2nd run GL8-1 + external wall)
Width of wall: 400mm
Height of wall: 4.6 – 5.0m
Concrete infill: 112m3 (1st run GL14-8)
108m3 (2nd run GL8-1 + external wall)
80m (2nd run GL8-1 + external wall)
Width of wall: 400mm
Height of wall: 4.6 – 5.0m
Concrete infill: 112m3 (1st run GL14-8)
108m3 (2nd run GL8-1 + external wall)
Interface with other activities
Start of activity dependant on:
Forming base to retaining wall
Providing a suitable ground surface for a crane, concrete pump and access for concrete wagons
Follow on trades:
Pile caps and ground beams to areas used for crane
Waterproofing and backfill to wall
Steel frame
Insitu slabs to tie into top of retaining wall
Forming base to retaining wall
Providing a suitable ground surface for a crane, concrete pump and access for concrete wagons
Follow on trades:
Pile caps and ground beams to areas used for crane
Waterproofing and backfill to wall
Steel frame
Insitu slabs to tie into top of retaining wall
Resources employed
Labour
Crane driver
Banksman
Groundworkers x3
Plant/equipment
Crane
Access tower/cherry picker
Concrete Poker
Concrete Pump
Crane driver
Banksman
Groundworkers x3
Plant/equipment
Crane
Access tower/cherry picker
Concrete Poker
Concrete Pump
Access requirements
Crane movements
Delivery of module units
Access for tower scaffold or cherry pickers
Area for concrete pump
Access for concrete wagons to pump
Delivery of module units
Access for tower scaffold or cherry pickers
Area for concrete pump
Access for concrete wagons to pump
Material handling requirements
Delivery and off loading
Delivery of pre-cast units was on the back of open wagon. Off loaded directly with crane and placed on base in same movement.
Storage
At some points, it was not possible to place all of the units that had been delivered that day. This meant units needed to be off loaded and placed flat on the ground to allow the wagon to go and be installed the next day.
Vertical & Horizontal distribution
Crane for precast units
Concrete pump for concrete
For movement for labour to manoeuvre the concrete pump hose and poker, in the first run of wall a tower scaffold was used. This however meant that there was a lot of going up and down the scaffold and that it needed to be moved a lot. For the second run of wall, a cherry picker was used.
Delivery of pre-cast units was on the back of open wagon. Off loaded directly with crane and placed on base in same movement.
Storage
At some points, it was not possible to place all of the units that had been delivered that day. This meant units needed to be off loaded and placed flat on the ground to allow the wagon to go and be installed the next day.
Vertical & Horizontal distribution
Crane for precast units
Concrete pump for concrete
For movement for labour to manoeuvre the concrete pump hose and poker, in the first run of wall a tower scaffold was used. This however meant that there was a lot of going up and down the scaffold and that it needed to be moved a lot. For the second run of wall, a cherry picker was used.
Comparison to traditional formwork system
• Improvement in programme
• Efficient use of materials, minimal site wastage.
• Guaranteed face finish with pre-cast units
• Reduced handling i.e. with no formwork to be double handled
• Reduction in COSHH requirements with no chemical releasing agents
• Health & Safety improvement with less fixing and manual handling of rebar
• Efficient use of materials, minimal site wastage.
• Guaranteed face finish with pre-cast units
• Reduced handling i.e. with no formwork to be double handled
• Reduction in COSHH requirements with no chemical releasing agents
• Health & Safety improvement with less fixing and manual handling of rebar
