New manhole, saddle connection, sewer diversion & void filling

Overview/scope of works

We were contacted by The O2 arena for subsidence, During the last few years, an extent of subsidence in the region of a rainwater collector adjacent to The O2 arena main entrance has been noticed and monitored. This has been flagged as a concern requiring urgent attention as the reduction in level of the rainwater collector has dropped between 400 to 600mm. Beyond the drop of the collector, the adjacent Peninsular square slab is being undermined presenting a risk of local failure of the slab with potential for significant disruption to The O2 arena main entrance. Overall, this was considered as requiring urgent intervention to stabilise the concrete slab and correct the underlying problem.

New pipe diverted out to the existing, to avoid the excavation works in front of the main O2 arena entrance, a new 450mm drain-pipe running away from The O2 arena from the existing collector to connect into the main drainage infrastructure which is approximately 20m distance. Whilst this diversion work is carried out temporary over pumping will be set up to divert all rainwater into the next collector.

Unfortunately for the client, the path of this new 3m deep drainage pipe would cross both the recently installed district-heating piping in addition to the high-voltage cables installed at the time of the Millennium Dome build. We opted to carry out this work via a timber heading.

Once all new drainage has been completed the process of the void fill takes place this void is found between the concrete slab and the ground beneath, the amount of material was estimated which covers approximately 440m2 with an allowance of 4500kgs of material. This allowance will be able to fill circa 115m3, which equates to an average of 260mm voiding throughout the assumed affected area.

Key Requirements & Challenges:

• Pedestrian Management:

  The O2 arena had many events on during our time on site (16 weeks) so good planning and communication with the client played a massive part in getting this work completed, other attractions like UP at the 02 also needed to stay open to honour all tickets purchased by the public. Temporary footpath put in place with extra signage to navigate the pedestrians in the right direction & destination.

• Depth of Excavation (3.5m):

  Excavated using a 5-tonne with safety and protection measures in place to ensure stability and protect the existing infrastructure, this machinery can only be operated by fully qualified plant operator experienced in deep drainage.

• Precise Connection Method:

  The existing 1200mmØ surface water sewer was stitched drilled carefully removing a section off the shoulder of pipe, once removed and new saddle was installed sealing it sand, cement & sika 4a water stop.

• Reinstatement to Specification:

  • Compacted as dug & MOT Type 1 was compacted in layers using a mechanical trench rammer/ forward reverse diesel wacker plate.
  • Cut edges, drill bar, A393 mesh poured C40 concrete.
  • Existing slabs replaced
  • Timber heading dry packed by hand
  • Finished with a final jet down.

At Premier Drainage Solutions, we do not rely on temporary reinstatements. We believe in completing work permanently and to the highest standard, preventing future disruption and repeat visits.

Outcome:

• Sewer diversion & connection completed to Thames Water standards
• Full reinstatement carried out to specification
• Project delivered safely with approved plan and programme for works
• Client received a permanent, long-term solution