The original drainage design and what is most commonly installed on construction projects is precast concrete rings, with pipes cut into the side, the base formed with mortar/grano and surrounded in concrete. This is a slow process and often the drainage has defects, hard to get well detailed and needs regular maintenance, there is also construction related risks with the trench being open for considerable time, the weight of the concrete and the need to work inside the manhole in confined spaces.
This contractor have therefore worked with polypipe civils to design preformed large diameter manholes, usually used for storm drains. This solution is becoming more common on off-grid and large developments, but the solution works perfectly well for smaller developments. The manholes are fully formed in 100% recycled plastic, include for plastic formed benching and plastic welded fittings, are full tested in 10 times the maximum pressure and guaranteed to far exceed the lifespan of the concrete counterpart.
They are also very quick to install, typically the manhole can be installed within 3 days compared to 8 days for the concrete product, to further advance this they have developed permanent formwork to surround the plastic manholes, this allows them to accurately form the 150mm concrete casting that surrounds the manhole and also means that the manhole can be excavated, installed and backfilled in one day.
This reduces time, the risk associated with open trenches and the amount of concrete used to surround the manhole.