The term Brownfield land is used for a land that has been developed previously, i.e. buildings and associated infrastructures have been constructed on such land previously.
Building structures on Brownfield land is substantially significant since it reduces the amount of green land required to construct new structures in urban area. However, it should be known that such land would pose high degree hazards to structure.
Therefore, number of strategies have been established and recommended to be considered while structural foundations are intended to be built on Brownfield lands. This article will shed light on those strategies considered to overcome hazard posed by Brownfield land.
Fig.1: Redevelopment of Brownfield Land (Cleaning and Foundation Construction)
What are the Dangers Posed by Brownfield Lands?
- Brownfield load carrying capacity is poor
- Harmful interaction between building materials and chemically aggressive ground condition is another danger
- Underground fire related to combustible materials
- Gas generation due to biodegradation of organic materials in the ground
Strategies to Protect Buildings Constructed on Brownfield Land
1. Avoid Creating Hazard
Certain brownfield dangers may be prevented prior to the land reclamation, as shown in Figure 2, and cleaning the construction site.
For instance the prevention of mixing different fill materials at site may lead to avoid detrimental reactions and subsequent polluting leachate that could be greatly detrimental to the structure.
Fig.2: Brownfield Reclamation
It might be argued that, separation of different fill material increases total construction cost, but the advantages achieved will offset the additional cost.
This is because the building will likely to suffer from severe damages and considerable maintenance cost will be required if the hazard is not dealt with at the first place.
2. Relocate Building Development
In the case where significant dangers are found out at the site and the risk is too high, then it is possible to leave the site or part of the site as a hazard mitigation strategy.
If the area is large, then it is advised to avoid the utilization the most dangerous area for most sensitive applications. This measure is suitable for large development area which includes retail, commercial and residential buildings with various types of brownfield land. In contrary, there is no room for such maneuver if the area is small.
Fig.3: Sizable Brownfield Land
3. Isolate Buildings from Ground Hazard at the Site
Separation of structural foundation from compressible fill is another measure used to protect buildings on brownfield land.
Commonly, pile foundation, which extends through compressible soil and transfer superstructure loads to strong strata, is used to isolate building from the detrimental effect of the compressible soil. The pile foundation would not serve its purpose unless it adequately reaches strong and firm soil layer.
Finally, if expansive soil is present at the construction site, then it is recommended to introduce sleeve to the pile to accommodate ground heave. Figure 4 shows the installation of pile foundation to separate buildings from harmful influence of compressible soil.
Fig.4: Piles Installed to Isolate Buildings from Compressive Soil
4. Isolate Buildings from Ground Hazard Adjacent to the Site
It is required to differentiate the land next to the contaminated land that is being developed. Sometimes, the land adjacent to contaminated land will encounter problems after the completion of construction.
For example, there have been cases in which contamination is moved to the uncontaminated land that pose significant danger. In this case, it is needed to establish proper strategy to control the contaminant and avoid problems at unpolluted site.
It is demonstrated that, ground vertical barriers and engineered cover layers are considerably effective in controlling and blocking contaminant and isolation of contaminated land.
Figure 5 shows the installation of slurry trench cut off wall to prevent the migration polluted materials such as leachate to the adjacent land. If the movement of dangerous gas such as methane is required to be block, then geo-membrane liner is installed before the slurry is set.
Fig.5: Slurry Cut Off Wall are Installed to Contain Contamination
5. Remove the Poor Ground
Another strategy to tackle hazard to brownfield land is the removal of contaminated soil and place sound soil material fill if necessary.
However, the above approach may not be suitable especially in the case where the degree of contamination is considerably high that contaminated soil is not allowed to be deposited in landfills, or the quantity of soil required to be removed is large.
So, it is possible to sort the poor soil after excavation to ease the movement or treatment of contamination. Then, the remained acceptable material in combination with treated materials can be mixed and used as fill material. Finally, the remainder of contaminated soil is disposed.
Fig.6: Remove Poor Soil from Brownfield Land
Fig.7: Soil Treatment
6. Improve the Poor Ground
Another method of protecting buildings from the brownfield hazard is the treatment of physical and chemical properties of contaminated soil at the site. In this way, the ground related dangers can be mitigated.
Fig.8: In-Situ Soil Treatment at Brownfield Land