FOUNDATION FAILURE

Introduction

Foundation failure can cause the building to collapse, foundation is the just element of a building where the construction starts, but when it fails, it can cause many defects in the building including failure or collapse of the building.

Repair of defects in foundations are mostly difficult and very costly, so it is most important to understand the types of foundation failure to avoid them by taking necessary steps before construction starts.

Remedy for foundation failure due to uneven soil bearing capacity of the soil

        When water present between soil particles is removed, the soil tent to move closer together. When water is absorbed by soil, the soil starts to swell. This movement of soil is based on the type of soil. Large movement is seen with clayey soils than sandy soils. This kind of movement of soil due to change in water content effect the foundation settlement. Foundation tends to settle to and executive settlement of foundation may lead to differential settlement and damage to the structure.

        Soil movement can occur due to:

i.     Presence of vegetation or remains of old cut trees.

ii.    Presence of mining areas.

iii.  Shrinkage soils.

Remedy

i)           Use of pile foundation where the soil is shrinkable, so that forces are transferred to the hand strata or rock.

ii)         Taking the foundation levels down to avoid foundation on shrinkable soils.

iii)       The vegetation is remove from the construction site and its roots are removed. Any cavity due to roots of vegetation shall be compacted and filled with concrete.

iv)        Presence of any mining area needs to be inspected and professional help shall be taken while constructing new building in such areas.

v)          Restrained the ground by using retraining wall.

2) Remedy for Drying Action of Tree Roots in Foundation

Sometimes, small trees, shrubs or ledges in grown very near to the wall. The roots of these shrubs absorb moisture from the foundation soil, resulting in reduction of their voids and even weathering, due to this, the ground near the wall depressed doom. If the roots penetrates below the level of footing, settlement may increase, resulting in foundation cracks.

If there is a tree behind any building constructed, the roots of tree affect the building there by creating a hole beneath the foundation of the building. As a result of this, settlement can take place within the areas.

(1)Remove the tree close to the building to reduce the possibility of changes in ground moisture content of the building and also to avoid more penetration to the building.

(2)Any leaking drains, water main or broken downpipes are the cause of the subsidence, simply repairing them will be all that is needed to stabilize the building.

(3)If there are cracks or holes in the foundation wall, it can be remedied by breaking the wall and replace it with new ones in other to avoid excessive cracks. In other ways, it can also be done by breaking the defected area, cut some reinforcement steel and place it horizontally inside the wall and put concrete on it for more stability.

Remedy for Drying Action of the Bearing Strata in Foundation (Climate Drying)

        This cause the floor or the ground of the building to swell up or shrink due to changes in its moisture content of the soil increasing due to broken drains, heavy rains, and freezing. Shrinkage can occur by the soil drying out during long period of dry weather and tree extracting moisture from the ground. This is because of the action of bearing strata.

1)   Restrained the ground by using retraining wall to prevent it gradually from settlement and shrinking of the floor.

2)   Strengthen weak or damage foundation by underpinning thereby digging to establish a new bearing capacity for the foundation to be stable on ground.

3)   Remove large trees that are too close to the building and tap root that has penetrated into the foundation of the building.

4) Remedy for Mining Subsidence in Foundation

This is a situation where settlement has taken place due to the mining work undertaken several years back and as a result of this any building erected on that place will definitely collapse.

If mining has taken place in certain areas and storey building is built on it without knowing that mining work had been taken place, as a result of these, the load of the building imposed on the place, there is a tendency that the building will collapse when settled. When such case happened, the ones to watch out for are small crack usually running diagonally, that appear quite suddenly in plaster and also on exterior brick work, around doors and windows in particular place. Cracks there indicate that there may be subsidence are usually thicker than a couple of millimeters and are wider at the top. Distortion of the building will also cause doors and windows to stick or fail to close. Another sign is rippled wallpaper, with no signs of damp to attribute this.

Remedy

     i.        Underpinning: Underpinning a house prevents further movement by increasing the dept and support of the existing foundations. The standard way of doing this is to dig out short sections underneath the existing foundations and fill them in with concrete. Underpinning is a slow process, with each section having to be inspected before work can continue. It is also an expensive process, costing around 500 per linear metre.

    ii.        Restrained the ground by using retaining wall to reduce the amount of settlement of the area where mining occurred.

5) Remedy for Foundation Failure due to Settlement of Soil Fill:

If the building is constructed on a newly developed land by soil filling, the foundation on such soil tends to settle more with time as long time is needed for such soil to settle and become compacted to resist the loads from the building foundation.

i)         It shall be ensure that such soils are adequately compacted before construction begins on them.

ii)       The foundation depth shall be increase to the hard strata or rock below the filled soil, or pile foundation shall be use to prevent subsidence of foundation.