Causes of Foundation damage and Retrofitting
In one of my previous articles, we discussed various steps in which the survey of the foundation has to be done in order to be considered for retrofitting.
In this article, we will discuss various reasons or causes for the damage of the foundations.
Types of foundation damage can be classified as follows:
Erosion
Settlement in the ground
- Groundwater lowering
- Limited bearing capacity of the ground (land)
- Uneven bedrock depth
- Excavations performed below the foundations and poor quality of backfill
- Increased load on the ground leading to failure
- Damage to the neighbouring houses
- Horizontal movement occurring in the ground
Frost heave/adfreezing
Alum shale
Now we will move on with the discussion in detail on the types of foundation damage occurring due to Settlement in the ground.
Lowering in the Groundwater level
When the buildings are built on compressible soils, the resulting stress on the soil causes the soil to compress. Raft foundations are used in these kind of soils.
Since the soil undergoes compression the upper portion of wooden piles rot when groundwater level sinks.
There are various conditions which can cause the changes in the groundwater level or pore water pressure. They are as follows:
- Ice Static Rebound
- Dewatering (seen in cities)
- Ditches and pipes below the groundwater level
- Deep Foundations and Basements (causing further drainage of the ground
- Tunnelling
- By the removal of foundation sills
- Construction of non-permeable surfaces such as roads, pathways causing the least amount of natural precipitation
- Use of deciduous trees should be avoided in areas with low groundwater. They require a lot of water for their growth. They pull all the water that is available around them causing the lowering of groundwater.
Limited Bearing Capacity of the Ground
Earlier, when the science of engineering and surveying wasn’t much developed, people failed to understand that it was important to analyze the nature and bearing capacity of soil. In case the soil was weak in nature and underwent compression, it would lead to settling problem.
This has been observed in some of the old buildings. In some cases, the foundation wall developed cracks which ultimately resulted in the failure of the structure.
Uneven Bedrock Depth (varying bearing capacities in the same patch of land where the construction is to be initiated.)
Analyzing the nature of the soil is important which most importantly deals with its bearing capacity. It is to be remembered that if the building is constructed on two different types of soils having different bearing capacities, it could lead to dislocation of the structural components.
For example:
If a building is constructed partially on bedrock and partially on fill mass. Since they have poor bearing capacity, there will be a difference in the settling of the structure.
The first consequence that will be seen will be the occurrence of cracks on the walls of various floors. It might also result into instability of the structure.
Foundations under which excavation is done and poor backfill
If in case excavation is to be performed under a foundation, it is important to note that the ground conditions are favourable and will not result into settling.
If the loads are loads and ground stability is not checked before performing excavation below the foundation, it could result into settling.
Increase in the Load
Buildings are designed with giving full considering to the maximum load that will be imposed on the structure. If these buildings last for years without undergoing damage, that is because the load on the structure is maintained and is not in excess which would result in the instability of the structure.
If in case changes are made in the loading conditions of the same building. It result into settlement of the structure causing excessive damage to the foundation.
Damage caused to the neighbouring houses
In cities, the buildings are constructed close to each other. If one of the building is demolished for reconstruction of a structure serving a different purpose, it might lead to the occurrence of a slide having severe consequences on the stability of the surrounding buildings in its vicinity.
Also check out:
Repair and Maintenance of Old buildings guide