Holdfast Training Services Trial Blog

Second week back from summer hols and things are progressing nicely. The shaft construction is becoming a bit repetitive so I thought I would give the spraying a go for my self.

Some of the nozzlemen are the highest paid workers on site, which is quite interesting as the course to qualify is only 5 days long.

Anyway we are getting close to the base slab now and that means that we need to depressuirse the water, to ensure there is no up heave when constructing the slab. We contracted this phase out, essentially constructing 2 x 11m small boreholes in the bottom of the shaft. The photos below show the sub contractors digging the boreholes.

Its a very simple solution to potential up heave of the base slab. The two boreholes will allow the water (although there is no water as we are in the Lambeth clay layer which is more like mudstone) to release the pressure. Theoretically once the base slab has been cast and the slab has gone off, the boreholes will be closed off and the base slab will take the force. However as I said there is no water in sight any where).

I have just attended the Waterproof membrane trials at Bond Street. THis will be the next phase, due in about 1 week. Essentially it is a large roll of waterproof membrane. THis roll will be lowered to the bottom of the shaft and pulled to the top, where it will be nailed in place. Once the membrane is in place the secondary/in situ lining will be constructed. THis is the poured concrete. I have just completed the TW design brief for the shuttering. THe shuttering will need to be able to handle lifts of 2m. THe sub contractors have estimated a 28 day period to complete the in situ lining, I am extremely doubtful but I remain optimistic.

I am currently eyeball deep in a CE (Compensation Event) trying to calculate the time delays caused by out of spec concrete. However my next post will probably be about the CE procedure and the lessons (if any) that I have learnt.

Just managed to book myself on the ICE presentation about the Super Sewer construction in London. Looks like it will be a good talk on the 19th Sept followed shortly afterwards by the ‘Hidden Shafts’ talk on the 02 Oct. Let me know if anyone else is planning on going to either of these events.