A failing wastewater manhole with structural damage was identified. Damaged was a direct cause of elevated H2S gases present (within the localized WW network) accumulating and slowly attacking / eating the internal walls of the concrete manhole from the inside out.
The manhole replacement was a deemed as a high risk and high priority replacement as it processes and discharges up to 30l/s which is equivalent to approximately of 85% of Raglans wastewater.
With the manhole intended for replacement neighboring our beautiful Raglan harbour, significant methodological and contingency planning was undertaken to mitigate any general and/or environmental risks posed upon the project if the installation went ‘pear shaped’.
As a result of conducting a thorough assessment upon the existing asset, the process of modelling the failing, H2S deteriorated concrete manhole as a replica of the insitu manhole was undertaken to recreate / construct a replacement in the form of a Smartstream PE product.
The PE manhole was an excellent alternative in this situation with whole-of-life benefits of the PE product including;
- Polyethylene does not suffer from internal and external gas attacks (H2S protection)
- Ease of application upon an existing network which allowed for essential utilities to remain in service
- Elimination of root intrusion and ground water ingress through PE welded joints
- Value-for-money product with significant time and cost savings through installation techniques
- Durable and light weight, which reduces transport and handling costs.
- Along with hydraulic benefits the spherical base allows multiple inlets to be attached at any angle between 45 ̊ and 315 ̊, with allowance of varying and specific grades
- The Polyethylene manhole removes any delay in concrete related tasks as it removes ‘curing time’, manhole sectional builds and additional sealing or consumable products used during construction.
A 1st for the Waikato District Council
The replacement of this manhole was carried out as the first polyethylene (PE) manhole to be installed within the Waikato District network. The successful, effective and smooth installation of this PE manhole paves the way allowing alternative beneficial options for future activities upon existing and/or new infrastructure.