Soil Testing in Building Construction
It can be quite dreadful if your newly constructed house starts slowly sinking on one side, like The Leaning Tower of Pisa! The worse, if it develop cracks and finally collapse in due course of time. All your effort, time and money spent on erecting a building go in vain if it happens. The thumb rule to avoid this is to start construction only after testing the quality of soil in the plot!
What is Soil Testing in Building Construction?
Basically, Soil Testing in Building construction refers to investigating the characteristics of soil in a plot. Geo-technical engineers or engineering geologists perform the soil tests. Soil testing gives necessary information to start working on design considerations (for foundations and earthworks) for that particular building construction.
The output of soil testing, for example, the character of the soil with respect to water content, mineral and chemical composition, decides the quality of material to be used for construction. For example, high sulphur content in soil requires usage of sulphur resistant cement for construction.
Soil testing reveals the physical and engineering properties of soil like moisture content, mineral presence, density, permeability and bearing capacity. These parameters determine the type of foundation to be used for construction. Essentially, the foundation has to be strong enough to effectively transfer the building weight to the soil underneath!
What is the relevance of Soil Testing on foundation?
Foundation is the first step of construction and a defect in foundation can result in failure or collapse of the building. Basically, foundation sustains and transmits the loads from the building to the ground without impairing damage to the building or surrounding buildings.
Also, foundation has to safeguard the building against damage by physical forces generated in the subsoil. Moreover a strong foundation has to resist the chemical compounds present in the soil to prevent corrosion of iron bars used as reinforcement.
Additional Reading: What is Reinforcement in Concreting?
The properties of soil has major influence on the design, stability and sustainability of the foundations to make it perform its functions.
The water content in soil is a vital factor that determines the type of foundation. This is because removing water from the soil results in soil particles to move closer together. On the other hand, absorption of water by soil makes the soil swell. The way soil reacts to presence or absence of water is based on the soil type. (Movement is higher in clayey soil than sandy soils)
Additional Reading: Types of foundations
Similarly, presence of vegetation or remains of old cut trees can cause soil movement in the plot. Proximity to mining areas can result in soil movement in large scale! Likewise, if the plot is a developed land by soil filling, it will have shrinkable soil. Such soil take more time to settle and become compact, to bear the loads from building foundation.
Any such soil movement affects the foundation settlement. The change in soil type may then result in excessive settlement or differential settlement posing threat to the structure itself.
Different soil testing methods are used to determine the appropriate type of foundation for the building.
What are the Types of Soil Testing in Building Construction?
In general, the following tests help to determine the quality of soil:
- Moisture Content Test – This test gives all information about moisture or water content of the soil. The know how of water table provides detailed impact of humidity on the foundation.
- Atterberg Limits Test – This test gives the critical water content of the soil at different conditions like liquid limit, plastic limit and shrinkage limit.
- Specific Gravity of Soil – This test gives the information about void ratio and degree of saturation of soil. Specific gravity value ranges from 2.65 to 2.85 for soil ideal for construction. A lower value like less than 2 denotes presence of organic and porous matter. Likewise, value above 3 indicates presence of heavy substances in the soil. An ideal soil for construction should have low amounts of organic content, porous matter and heavy materials.
- Dry Density of Soil – This test gives the weight of soil in a given volume of sample, enabling to categorise the soil into loose, medium dense and dense classifications. The less dense the soil is, the stronger the foundation should be.
- Compaction Test – This test gives the compaction characteristics of soil by reducing air voids in the soil by densification. The results of compaction test reveals maximum dry density and optimum water content of compacted soil.
Soil Types and Foundation Considerations:
Additionally, soil testing gives information about bearing capacity of the soil that determines the load sustenance capability of the soil. Also, the rate of settlement reveals the rate at which any structure placed on the soil settles. Moreover, soil testing methods helps to determine if the land may be subjected to subsidence, causing sinking of building in the future.
All these parameters helps to come up with the most suitable construction technique for the proposed building. It also gives a clear signal to the type and depth of the foundation to be used. Moreover soil testing also provides further insights to predict and resolve probable foundation problems.
From this, it is evident that the chosen foundation type has to strengthen the weak characteristics of soil. To strengthen the foundation even more, work on enhancing the soil features. Following section presents the solutions for common foundation problems for clay and sand soils.
Challenging features & Solutions:
- The bearing capacity in saturated clay is low. This results in weak foundations. Using compaction techniques to remove air from the soil pores can address this issue to a certain extent. Deep foundations is recommended in this type of soil.
- The shear strength (the stress that the soil can sustain) is low when wet. This results in a high possibility of soil consolidation in soft clays. Lowering the water table, pre-loading and driving piles to rock are the possible solutions.
- Swelling may occur that may alter the formation of clay. This can result in expansion or swelling of the foundations. The solutions to these are to maintain constant water table, to treat or stabilize the soil and to include swell pressure in design. You can also attempt to mechanically change the nature of the soil, but it might be an expensive option.
- A commonly observed problem is the excessive settlement in wet and loose deposits. This causes differential settlement in the foundations. The compaction of loose sands can help resolve this problem to a certain extent. You can also lower the water table to result in sand densification.
- The confining pressure of sand is usually low, affecting the bearing capacity of the foundation. Use deep foundations in such cases. Compaction of sand can also be used as this increases cohesion and friction leading to improved bearing capacity
To ensure a strong and solid foundation, carry out the following soil testing methods for each type of foundation.
What are the actions to be taken after getting a soil test report?
All the outputs from the various soil testing methods serve as inputs to suggest the type of foundation for the building. This also provides clear dimension of recommended sizes of foundation components. For example, the value of bearing capacity (typically some amount of load per square foot) is directly related to all the critical foundation components. Finally, all these recommendations are passed on to a foundation engineer who can design the best building foundation for the plot.
Well, it is evident that soil testing in building construction is a lengthy process. But not doing soil testing can result in failure of the building structure. The safety of your building structure is much more important than the time, effort and money spent on soil testing. And it is always advisable to go for an experienced soil testing service like that of Viya Constructions for the best results. Call us with your plot details to initiate the soil testing process and we would be happy to help!