What is a Soils Report and When is it Required?
If you intentionally clicked on this post, chances are, your construction or home project needs a soils report. It’s okay to be confused about the procedure, most people are. Usually, most people refer to engineering firms for more insight. However, this article aims to intimate you about the soils report and when you may require it.
Most permits would require soils report, and in California, soils report cost as high as $1000. Hence, it is no surprise that you want to know what you’re paying for.
A soils report is a summary of a geotechnical investigation, and it involves the analysis of the suitability of the soils for the proposed construction project. Taking into consideration, the present soil condition, soil strength, and much more.
But why is the soil condition so important? You might ask. The obvious answer is safety. It is important that dangerous soil conditions are noted and necessary measures are taken to address them. Additionally, soil reports can prove cost-effective in the immediate future. This way, your structural engineers will design a foundation according to the report, rather than the usual cautious over-designing.
In California, only soils reports from registered professionals are considered viable. Their jobs include:
- Determining the scope of the investigation
- Determining the equipment required, and
- Assessing the need for additional studies.
Another requirement for this procedure is the presence of a qualified representative engineer during all exploration activities.
In addition to supervising exploration and giving soil reports, the engineer’s task also includes recommending measures for correcting unsafe soil conditions, until the proposed project is no longer at risk of damage.
When Is a Soils Report Required?
According to the minimum requirement set by the California building code (CBC) concerning preliminary soil reports and geotechnical investigations. The preliminary soil reports are necessary for all subdivisions creating:
- 5 or more parcels
- 5 or more condominiums
- Community apartment projects with 5 or more parcels
- Conversions of dwellings to stock cooperatives with 5 or more units.
If the preliminary report indicates dangerous soil conditions that can result in structural damage to the building, a full geotechnical investigation is mandatory, per the CBC.
California being a seismic prone zone, the requirements for a soil report may differ, for each local government, from that of the CBC. However, most cases require soil reports for every new project.
A soil report can indicate different soil conditions, depending on the condition of the site. The report may include; the soil’s response to an earthquake, expansive soils, high water tables, shifts in subsurface rock structures.
Additionally, a soils report may include more than just the soil conditions, it may also provide guidelines for the design team in designing deep foundations. Notably, soil issues on the soil report must be effected on the design before the issuance of a building permit.
As the name implies, expansive soils expand when full of moisture and relax when dry. Obviously, this situation cannot be good for the building’s foundation. Buildings on this type of soil would lift and settle irregularly, causing the foundations to crack.
For expansive soil conditions, the reporting engineer must propose ways to keep the building safe against the expansion and contraction of the soil. Usual solutions include:
- Post-tensioned foundations
- Replacement of expansive soils with imported fill material
- Deep foundations
- Adequate drainage solutions.
Another name for the water table is the groundwater table, it is the plane underground upper level, beneath which the soil is permanently water-saturated. The water table can rise in the event of heavy rainfall and can also fall in a drought. If the water table is higher than the building’s basement, it can be very dangerous. In this case, the water exerts a high amount of hydrostatic pressure on the building, leading to cracks and leaks.
The soil report determines the level of the water table and how high it can rise. And in the case of a high water table, the engineer will have to propose measures to counter potential leaks. Some of which may include:
- Groundwater control systems and/or waterproofing
- Damp proofing may be an acceptable moisture barrier in the absence of hydrostatic pressure.
Low Bearing Capacity
If the soil’s report shows that the soil has a low bearing capacity, it means the soil cannot comfortably carry the design load of the building. This can lead to a sinking foundation. And in this case, the engineer can propose measures such as;
- Deep Foundations
- Compacted Fill Material
- Controlled Low-Strength Material
Seismic Design Categories (SDC) C Through
According to some local government’s adaptation of the CBC, If your potential building falls under the SDC C, D, E, and F. The geotechnical investigation of the following hazards is imperative.
- Slope instability
- Total and differential settlement
- Surface displacement due to faulting or seismically induced lateral spreading or lateral flow
For buildings under the SDC, S, D, E, and F, soil reports may include data you can find on this page. Please note, before you set your building’s design in motion, it is important that you confirm the need for a soils report.
So there you have it, whether you’re starting up a residential home or a commercial building, you might need the soils report. Soil report recommendations, if incorporated in the design phase, would guarantee the safety of your building.