You may have heard at some point that a soil report is needed before a building can be constructed. You must have wondered what a soil report is and why it is necessary. Well, you’re not alone. Seeing as it may cost up to $1000 to carry out a soil report, it is normal to want to know where all that money is going into.
A soil report summarizes the result of a geotechnical examination of soil – this is the analysis of the soil condition at a proposed building site. The primary goal of a soil report is safety, which is achieved by looking for dangerous situations in the soil and recommending the design criteria that address them.
Apart from safety, soil report also helps to save some money on the construction cost because the structural engineers can design the proper foundation that fits the soil based on the criteria from the soil report. This is much better than over-designing or building too cautiously.
Who Prepares a Soil Report?
In many places, civil engineers are the only authorized peope to carry out soil examinations and prepare soil reports. Their task is determining the investigative scope, the required equipment, and everything needed for additional studies. The engineer and qualified representatives have to be on-site while exploration activities are ongoing.
Apart from overseeing the exploration activities and reporting the condition of the site’s soil, they also have to recommend strategies to rectify unsafe conditions up to the point that the structure isn’t at risk.
Ordinarily, construction activities can have adverse effects on soils, which is why its impact has to be considered carefully during the development process. In addition, in some places, the local authorities may request soil reports during the application process. This is another reason why a soil report is significant.
With a soil report, the engineers can determine if the land is ideal for the proposed building construction. It will tell if the geological and the soil conditions can give the stability and support required for the building to stand. Important to note is the possibility of settlement and allowable pressure that the soil can bear.
Details of a Soil Report
Here are some of the details in a typical soil report:
- Classification of the different soil types and a brief description of their characteristics.
- Potential or possibility to re-use the soil on site.
- Map of the soil locations on site
- Recommendations to handle and store the soils
- The area’s geological history
- Sampling details (such as depth, borehole location, soils encountered at different levels)
- Soil bearing capacity
- Groundwater conditions
- The soil’s chemical composition
- Prevalent seismic condition in the area (where appropriate).
- Foundation design recommendation
How soil report affects the foundation design?
After the engineer has carried out the site testing and has determined site classification, they can create an engineering design suitable for the foundation. They often attach it to the designer/architectural drawings.
Some of the variations in foundation design may include:
- The traditional stiffened raft concrete slab (which is stiff enough and capable of resisting soil movement).
- Waffle raft concrete slab (which is capable of limiting deflection caused by soil movement).
- Use of piers and piles in addition to the designs above.
- Elevated floor system with isolated footing support (mostly steel or timber floor systems)
- Strip footings to support in-fill slabs.
When you need a soil report
In many places, there is a code that sets the minimum requirement for local authorities to follow when they request geotechnical investigations and preliminary soil reports. For example, the building code in some countries and cities makes soil reports mandatory for subdivisions creating up to 5 parcels, condominiums, and community apartment projects with up to 5 parcels. If the preliminary report shows issues with the soil that may lead to some structural damages to the building, then a complete geotechnical examination is mandatory.
Depending on the site condition, the soil report may identify high water tables, expansive soils, a shift in structures of subsurface rocks, and the response of the soil to earthquakes. This could serve as a guide to the design team to plan for deep foundations. The soil engineer’s findings must be noted in the building design before they can issue a building permit.
Site classification and soil testing are legislative requirements of the government for all new constructions, especially residential buildings, to ensure that the foundation design is fit for purpose.
- The foundation of every proposed structure is the soil on which the whole building depends to continue to perform for as long as the building will exist.
- The soil type on the construction site will determine what design is appropriate to build on and the variety of materials to use.
- Site classification helps to dictate the cost, complexity, and method of the foundation.
Do you need more than a soil test on one block?
There are cases where soil requires further tests and possibly a re-classification of that site. Some of these cases include:
- There is already significant cutting and filling of that block after testing the soil. The fill soil may be compact already, but it still needs to be tested.
- Suppose you have changed the location of your proposed building within the same site. This works for large areas.
- When important structures like houses are removed.
- When abnormal features are identified during the construction process.
Who carries out site classification and foundations design?
Although there are a few exceptions to the people that can determine foundation designs and site classification, the best way to get excellent results for your building project is to engage one team to undertake this service from the beginning to the end. A professional and certified Chartered Engineer should supervise all these services.
A soil report is an essential part of the construction process. It’s one of those things that you must put in place before you start designing your constructions. It determines how you build your structure, what you can build, the type of foundation to use, the material you can use, etc.