Sustainable urban drainage design.
In today's world where cities become denser, to accomodate the increasing number of inhabitants the necessity to assign multiple functions to any single urban area increases continuously.
Solution
Solutions for subbase replacement
In the past a car park could just be a car park, however nowadays its design has to incorporate stormwater management, protect water quality and facilitate urban cooling by supporting surrounding green infrastructure.
The growing demand for a multifunctional layered city in urban planning creates new levels of complexity in civil engineering. For over twenty years Permavoid has been on the forefront of innovating, developing, testing and building solutions in civil engineering. By incorporating multifunctiple functions in reliable subbase solutions, any paved area can be put to work for the city.
By reintegrating on-site water management in urban planning cities become more resilient and are able to absorb the effects of changing weather patterns, preventing economic and ecological damage while protecting human health and well-being.
Process
How does it work?
The core behind Permavoid as subbase replacement is to create a shallow, but widely usable void high in the profile, as close to the surface as structurally possible. Permavoid's high compressive strength allows for placement close to the surface, creating the advantage of shallow excavation and minimal subgrade disruptions like rocky subgrades, groundwater, utilities and tree roots. In addition, minimal material transportation during construction. A typical detail for car parking starts with a 130mm buildup of pavement and bedding on top of Permavoid, up to a total buildup of 400mm for HGV accessible roads.
System functionality
In a situation where trees are expected to grow in an urban and paved environment, compaction of the soil, superficial tree roots damaging the pavement and greatly reduced soil-gas exchange are known growth-limiting factors. The Permavoid Sandwich Construction eliminates these by creating a shallow, stable and open subbase for the hardscape to ensure optimum load distribution and high load bearing capacity, preventing compaction of the rootable soil volume underneath. The system is used in parking lots, residential areas, malls and bicycle paths, with a free choice of pavement systems like block pavers, concrete or asphalt.
Benefits
Strong benefits within civil.
Even though engineered infrastructure remains hidden in trafficked and paved designs to most users, structural integrity and reliability are essential for all Permavoid solutions.
Permavoid provides a volumetric water storage capacity of 92% by replacing the traditional subbase layer with a structural void. This equates to a standard Permavoid module of 150mm deep, holding 138mm of water over the entire area: equivalent to a massive 1.38 million litres per hectare. Water can be retained and made available as a useful resource to recharge groundwater, maintain moisture content of soils, washdowns, cool the environment through evaporation or even generate potable water.
Water retention for reuse not only saves drinking water, it doubles in functionality by keeping rainwater out of the often overloaded sewer systems.
Unique patented systems
Permavoid's fully tested, reliable high strength subbase replacement systems can be integrated with Sustainable urban Drainage Designs - SuDS. In combination with a water permeable geotextile, on-site water attenuation for infiltration is created under the hardscape. With our waterproof membrane a combined water retention system is created and in combination with the Permavoid treatment textiles oils and other hydrocarbons can be separated.
Design base
The core behind Permavoid as subbase replacement is to create a shallow-but-wide usable void high in the profile, as close to the surface as structurally possible. Permavoid's high compressive strength allows for placement close to the surface. In addition, creating a void over the entire surface enables the system to act as a catchment for the entire paved surface with ample attenuation volume. Retaining water high in the profile also maintains the gravity fed water conveyance potential.
Full water management
Creating an actual water level in the Permavoid units in the subbase allows for full water management. The actual amount of water storage can be measured, incoming and outgoing flows can be controlled, water can be redirected to other systems for reuse and water can be added from other sources, for example to keep the Permavoid capillary irrigation system operational.
Permavoid cascading philosophy
Sloping areas can be split up into smaller flat areas, each passively cascading into the lower next level in a controlled manner. These individual small water managed areas are known as micro-catchments. The Permavoid system can attenuate water on almost any given gradient by implementing this cascading philosophy.
Managing water quality and water quantity with fundamentals of sustainable urban drainage.
Systems
Solutions for engineering.
We understand the importance of healthy city trees. Therefore, the goal of every Permavoid subbase installation combining pavement and trees is to create a multifunctional growing site, in a fully paved urban situation such as walkways, squares and car parking spaces. We protect the paved surface from root damage and maximise usable above ground space. The Permavoid systems can be used with new and existing trees. For existing trees where a previously open growing site is converted into hardscape the system makes sure the underlying root system is not affected. For new trees a complete growing site can be constructed, with the capillary system beneath the rootzone.
The Permavoid hollow subbase can be used for high quality bicycle paths, in a shallow construction, while at the same time preventing soil compaction of the subgrade and permanently facilitate soil gas exchange to prevent tree-root damage to the pavement on top. It can double as a system to detain and infiltrate rainwater harvested from the paved surface. This way the construction of bicycle paths through existing green landscapes does not change the functionality of soil, encouraging the continuation of existing tree growth.
The Permavoid hollow subbase can be used for high quality bicycle paths, in a shallow construction, while at the same time preventing soil compaction of the subgrade and permanently facilitate soil gas exchange to prevent tree-root damage to the pavement on top. It can double as a system to detain and infiltrate rainwater harvested from the paved surface. This way the construction of bicycle paths through existing green landscapes does not change the functionality of soil, encouraging the continuation of existing tree growth.
In dense urban developments on-site rainwater infiltration is often limited with the majority of surface being build or paved. Yet more cities impose requirements on real estate developers restricting the amount, and speed of stormwater management. Many podium decks are paved and used as car park, entrance way of for sports recreation. Permavoid subbase on podium decks fulfills both functions of drainage and attenuation between the building and hardscape. Stormwater in the subbase on multifunctional roofs or podium decks can be reused to feed the Permavoid Capillary Irrigation System, and allows harvesting of stored water for other purposes.
The concept of sustainable water management is a major driver in nowadays urban development with peak rain events becoming more frequent. With Permavoid beneath a car park water can be managed on-site, without the use of complex piping systems. With pervious pavement stormwater can be captured and attenuated beneath the paved surface and with impervious pavement types water can be fed into the geocellular units using the PermaChannel system. The PermaFilter treatment geotextile surrounding the Permavoid units can be added as an extra treatment step and acts as a hydrocarbon barrier. Keeping pollution out of the water management system.
The necessity to construct roads in unfavorable locations is not uncommon. Many types of soil are unsuitable for road conctruction when the load bearing capacity is taken into account. For these challenging conditions Permavoid offers various lightweight solutions. For example, in case of low load bearing soils like peat, contaminated locations where removing and treating soil from site is costly and in locations where the stormwater infiltration capacity can't be diminished by construction of an impermeable road surface. Rainwater from the paved surface can be fed into the hollow system for infiltration to maintain soil moisture as before.
The necessity to construct roads in unfavorable locations is not uncommon. Many types of soil are unsuitable for road conctruction when the load bearing capacity is taken into account. For these challenging conditions Permavoid offers various lightweight solutions. For example, in case of low load bearing soils like peat, contaminated locations where removing and treating soil from site is costly and in locations where the stormwater infiltration capacity can't be diminished by construction of an impermeable road surface. Rainwater from the paved surface can be fed into the hollow system for infiltration to maintain soil moisture as before.
Inspiring projects
Get inspired by these projects.
From large scale trafficed podium decks to bikepaths and protecting city trees; we are proud of the projects we have realized with our partners throughout the years.
Have a look at a selection of the Permavoid subbase replacement projects and learn more about the technology in our civil brochure.
Greenstreets | UK
Water permeable asphalt
Parking Bet 365 Offices Stoke | UK
Shallow water treatment and attenuation
Greenwich Wharf London | UK
Podium level attenuation and planter irrigation
Avenue du Dr Fichez Paris | France
Construction of a bicycle way along a tree line adjacent to a main road
TKI Project Kattenburgerstraat | Netherlands
Passive 3-Stage Design with detention, capillary irrigation, and infiltration
Greenwich Reach London | UK
Stormwater run-off, storage and attenuation
Find your local distributor nearby.
Permavoid source control ensures that no precious water goes to waste by catching, storing and reusing stormwater for irrigation, evaporation and infiltration. Find your local Permavoid distributor here to learn more about the technology and become part of the international movement.
