Chockfast Saves London

Chockfast Saves London
Project ID: Thames001
Project Type: Chockfast Orange
Project description

A very prestigious and demanding application for Chockfast was on the Thames Flood Barrier at Woolwich. Welding distortion of the gates prevented achievement of the designed for steel to steel fit on both the fixed and hinged connections to the gate arms. After extensive testing Rendall Palmer & Triton the engineering company responsible for the design and construction of the Barrier selected Chockfast Orange to fill the gaps between the mating steel surfaces.

The fixed ends were filled first and the gaps ranged between 2mm in the centre to 35mm at each end. The minimum 2mm gap was
determined by fitting 2mm thick stainless steel shims on the top face of the gate arms prior to landing the gates. The centre shims were trapped and supported the gate arm. These were left in place and encapsulated in Chockfast when the gap was filled by pouring through selected bolt holes. The shims not trapped by the gates were removed before pouring commenced.

The next phase was to grout the underside of the hinges which were set level on jack screws. The gate arms were not in place at this stage. The Chockfast was allowed to cure and then the bolts tightened.

Because of thermal growth and contraction of the gates the hinges had special sprung loaded steel pads fitted between the top of the
hinges and the underside of the gates to allow the gates to slide over them. The main support was provided by temporary jacks with low friction surfaces.

The special pads were then filled with Chockfast Orange and when the resin had cured the bolts were fitted and tightened. The hinges were then able to rotate and absorb the movement of the gate. The area remaining around the pads was then filled with Chockfast Orange by again pouring through bolt holes from inside the gate.

The work had to be carried out quickly during neap tides as these areas were submerged at high tide!

Another area where Chockfast overcame a serious problem was the support of the sub frames carrying the huge hydraulic rams and
crossheads that operate the gates. Initially these sub frames were to have been shimmed on to the finished concrete foundation. However the concrete was poured over datum height and had to be reduced in height with pneumatic chisels which left a surface impossible to shim. The sub frames had to be set level to very tight tolerances using Taylor Hobson instruments. Circular pads of Chockfast Grey were poured to provide level surfaces on which to stand the leveling jacks. Once level the frames were grouted by forming discreet pads of Chockfast Grey mixed with aggregate around each of the foundation bolts to make up the bulk of the pour thickness. A gap of approximately 10mm was left for a final pour with Chockfast Orange. The sub frame foundation bolts were then tightened after the Chockfast had cured.

Where fitters had failed to achieve level tolerances after weeks of shimming one frame, each sub frame was chocked in three days using Chockfast!

The design specification demanded the clamping bolts must not lose anymore than 5% of their pre stress over 50 years. Selected bolts are monitored and as far as we know tension has been maintained for the past 33 years.