House foundation construction is very important to have a safe structure. Failure of the foundation could lead to many serviceability issues.
In addition, foundation failure could lead to structural failures too.
Foundation failure can be classified in different means.
- Excessive settlement of the whole foundation
- Differential settlement
- Consolidation settlement
- Structural failure of footing
One of combination of above types of failures could occur. Therefore, construction of the foundation shall be done such manner that it minimizes the impact on the structure.
And also, it not all about the construction. The design of the foundations shall also be done in correct manner. Designer shall look into the all the possible aspect of failures of the foundation.
During the design of foundation, the following procedure could be followed.
Carrying out soil investigation
This is also called geotechnical investigation. It reveals the condition of the ground. We can get the cross-section of the soil layers under the foundation.
Boreholes can be drill up to the rock and in the rock to adequate geotechnical data to finalize the foundation type.
If we do the design and construction without adequate information, it could lead to the issue.
When we have to the geotechnical investigation data, type of foundation can be determined. Further, geotechnical capacity of the soil can be obtained.
The designer shall not always relay of the recommendations given in the geotechnical investigation report. It is his responsibility to make sure the design is correct and to interpret the result correctly.
If it is required to carrying of ground improvement, it shall be done with much care. In house construction, we are not in position to spend loads of money on the ground improvement.
Therefore, the correct and cost-effective method shall be selected.
How to Improve the Ground for House Foundation Construction
Soil investigation report generally provide outline for the ground improvement. We could follow the same. However, we need to select cost-effective methods.
There are many methods for improving the ground, but we have to be precise on our method of improvement. The common types of ground improvement for house foundation construction are as follows.
Refilling is one of the easiest methods.
In the method, we have to excavate up to the soil layer that having the adequate bearing capacity and the do the filling up to the level we do the construction of the foundation.
Soil, sand, quarry dust, ABC, etc. can be used.
When the water table is not close by, soil filling can be done. Otherwise, we have use other filling materials.
The filling shall be competed adequately, and it shall be done in layers. Generally, we do it in 300mm layer.
When there are compressible soils or clay soils, we use the preloading method for ground improvement. It is a very easy method, but it need time to complete the process.
In this method, we calculate the probable settlement of the foundation due to the applied loads from the superstructure.
We let the soil under the foundation to settle before construction of the foundation. It will minimize the foundation settlement as it already happened.
The settlement of the soil layers depends on the magnitude of load applied and the duration of loading. If we need to constructed foundation early or reduce the time for the expected settlement, load applied can be increased.
Generally, the solid filling is done in the land area where the foundation is constructed. Height of the soil fill is determined by the calculated settlement and expected time it will be there to reach the calculated settlement.
After preloading is started, we monitor the settlement of the soil to make sure it reaches the expected value. A time vs settlement curve is plotted, and it will indicate the rate of settlement and the way it reduces with the time.
Base on the reduction of the settlement values and decision on removing the preloaded soil will be taken. Thereafter construction of the foundation can be done.