Foundation Damage and Retrofitting

Causes of Foundation damage leading to 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

1. Natural rock
2. Brick

Rot

Insects

Moisture damage

1. Frost wedging
2. Salt bloom

Settlement in the ground

1. Groundwater lowering
2. Limited bearing capacity of the ground (land)
3. Uneven depth of the bedrock (varying bearing capacities of the soil in the same patch of land)
4. Excavations performed below the foundations and poor quality of backfill
5. Increased load on the ground leading to failure
6. Damage to the neighbouring houses
7. Increased load
8. 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 erosion.

Erosion due to Natural rock

The durability and strength of any natural rock depends on two major factors. They are as follows:

Amount of the smallest and weakest mineral present in the rock

Distribution of the smallest and weakest mineral deposit in the rock

Weaker minerals have weaker bond within their group itself as well as with the other mineral groups. Their amount and proper distribution within the rock determines the strength of the rock.

When these minerals get worn away, everything breaks down or dissolves. The rock starts crumbling into pieces. The connections between the other stronger mineral groups are lost.

This results into the degraded quality of the stone. It leaves the original stone – a conglomeration of loose particles.

There are also other reasons responsible for deterioration of the natural rock. Foundation surface damaged by:

1. Frost action
2. Salt
3. Washing or the like

This increases the rate of deterioration of the rock. The rate of erosion of natural rock is generally very slow. It takes a very long time for a natural rock to actually start getting eroded.

Natural rocks such as limestone, sandstone and shale are very much likely to get eroded.

Foundation damage due to erosion of bricks used in construction

Bricks are known as the most porous material which absorb moisture easily. They are commonly used for foundation and walls of the structure.

In colder regions where the temperature of the surroundings are low enough to convert moisture into frost, use of bricks in foundation is to be restricted because frost damage can lead to splitting of the surface of the brick parallel to the outside.

In case of large continuous cracks, the strength and durability of bricks is totally destroyed. Bricks have certain resistance capacity against frost damage.

It depends on material properties such as:

1. Pore distribution of the brick (percentage)
2. Water absorption capacity of the brick
3. Strength of the brick

There are also other factors which have to be considered. They are:

1. Moisture content in the atmosphere
2. Climate of the place
3. Freeze-thaw cycles
4. Freezing speed (the time taken for the water to freeze at the atmospheric temperature)

We will discuss “Damage to Foundation by Rot and Insects” in our succeeding articles…

 Also check out:

Guide to repair and Maintenance of Old Buildings