Soil Investigation or Geotechnical Investigation is a procedure that determines the stratigraphy (study of rocks) and relevant physical properties of the soil underlying the site. This is done to ensure that the substructure, which is eventually going to hold up structures, is safe and enduring . The results of soil investigations are presented in a Soil Report also known as a Geotechnical Report.
Often, a construction project requires a soil report. This report is the summary of a Geotech investigation. The primary aim of this report is safety. It’s also conducted to identify dangerous soil conditions and recommend design criteria to address the issues in the soil. This report can also help a business save construction costs by allowing the structural engineers to design a foundation based on the criteria of the report.
It’s important to note that Geotech investigations can be expensive since digging is required. Preparing the soil report could cost around $3,000 to $5,000. You will be paying for these expenses out of your pocket. Therefore, before starting a construction project, always keep a separate budget for a soil report. Keep in mind that the information that the report reveals is truly beneficial for the project design and construction.
A team of licensed geo-tech engineers or civil engineers experienced in soil engineering are the designated people who can perform soil surveys. The engineer comes to the property and drills a hole in the ground, where the construction is to begin.
This allows the engineer to test the soil’s structural integrity, determining how weak or strong it is. The engineer might as well have to examine the soil sample in a tab to gain insight into its strength and composition. The surveyors also analyze the boundaries of the property, soil types, groundwater level, and more. If you plan to build a home in a soil area of low strength, you must obtain a soil report before the construction. The same approach applies to planning to construct buildings with ill supported foundations or construction on steep slopes.
Section 1803.6 of IBC  deals with Reporting. Where geotechnical investigations are
required, a written report of the investigations shall be submitted.
A detailed Soil Report even contains various recommendations that can be made in light of the investigation results. The report maker recommends the number of stories built at max, the weight that can be supported by the land, and the foundation design recommendations that should be followed.
The report also clearly explains the various measures & precautions that should be taken into consideration while laying the project’s foundation. For instance, most soil reports these days clearly mention the measures & precautions which must be taken while laying the sewer systems & drainage systems. This helps prevent future water leaks that can ultimately damage the building’s foundation.
These days, most local authorities also require the Geotech engineer to add a detailed site plan in the report. Notably, a detailed site plan is an adequately designed sketch of the site showing all relevant physical features around the building site like existing buildings, roads, open spaces, drains, etc. If any boreholes have been dug, they too must be mentioned clearly in the site plan.
Next comes the requirements of the clients. In this part of the report, all client requirements are clearly mentioned. Here, all the information required by the client from this particular investigation is also described, along with the names of the tests that will be needed to collect the listed information.
Arguably, one of the most essential parts of the soil report is the Analysis of its various tests. This section of the soil report discusses fundamental aspects of the soil. This section contains various aspects like the soil’s consistency, the nature of the soil, the bearing capacity of the soil, plasticity, specific gravity, etc. Besides this, various other soil characteristics related to safety are also mentioned in this part of the soil report.
Another vital part of the report is where all the laboratory reports & test details are mentioned. This part is responsible for mentioning all the necessary tests which are done & their results. Along with that, this section must also contain information on what other tests may be required in the future for the smooth-ongoing of construction.
Now that we know what these reports are, many of you must be thinking about the need to require a soil report. Let’s see under what circumstances a construction project needs a soil report.
According to IBC Section 1803.2 , except for some conditions, geotechnical investigations shall be conducted as indicated in Sections 1803.5.1 through 1803.5.12 of code. Here are some of conditions which a project could possibly require a soil report:
As indicated in Section 1803.5.2 , where the classification, strength or compressibility of the soil is in doubt or where a load-bearing value superior to that specified in the IBC code is claimed, a geotechnical investigation should be conducted.
According to Section 1803.5.3 of IBC , starting a project on an expansive soil area requires the authorities to prepare a detailed soil report before permitting any construction on such land. That’s because expansive soils tend to swell when saturated with water and contract again as soon as they’re dry.
These changes in the soil’s behavior can lead to cracks in the building’s foundation while also damaging its other structures. Not only this, but expansive soil can even cause the building on it to lift & settle, again and again, thus leading to cracks and damages in the building’s foundation.
Water table is the plane under which water saturates the ground. Water table level rises during heavy rainfall and falls in drought. If the water table is above the basement of the home or crawl space, it could exert hydrostatic pressure, resulting in flooding and leaks.
Soil report helps find a rise or low in the water table levels. If the level is high, the engineer addresses potential leaks and flooding in the floors below the grade level. Damp proofing can be done to create a moisture barrier. A groundwater control system must be designed, and waterproofing can be done to mitigate the high water table’s effects.
Section 1803.5.4 of IBC says, a subsurface soil investigation shall be performed to determine whether the existing ground-water table is above or within 5 feet below the elevation of the lowest floor level where such floor is located below the finished ground level adjacent to the foundation .
Deep foundations transfer the building load beneath the subsurface layer to the bedrock or a layer with adequate strength. This type of foundation is used when the bearing capacity of surface soil fails to support the building’s design loads. This usually happens when the quality of the surface soil is poor, or the building is heavy.
Per Section 1803.5.5 of IBC, a geotechnical investigation shall be conducted where deep foundations will be used .
Rock layers are also called strata. According to Section 1803.5.6 of IBC , Where subsurface explorations at the project site indicate variations in the structure of rock on which foundations are to be constructed, a sufficient number of borings shall be drilled to sufficient depths to assess the competency of the rock and its load-bearing capacity.
Soil placed as engineering fill is compacted to a dense state to obtain satisfactory engineering properties such as, shear strength, compressibility, or permeability. In addition, foundation soils are often compacted to improve their engineering properties. Section 1803.5.8 of IBC  states that where shallow foundations will bear on compacted fill material more than 12 inches in depth, a geotechnical investigation shall be conducted.
A controlled low-strength material (CLSM) is a self-consolidating, cementing material used primarily as a backfill as an alternative to compacted fill. Other terms have been used to describe this material, including flowable fill, unshrinkable fill, controlled density fill, flowable mortar, plastic soil-cement, and soil-cement slurry . Section 1803.5.9 of IBC indicates where shallow foundations will bear on controlled low-strength material (CLSM), a geotechnical investigation shall be conducted .
According to Section 1803.5.11 of IBC , for structures assigned to Seismic Design Category C, D, E or F, a geotechnical investigation shall be conducted, and shall include an evaluation of potential geologic and seismic hazards such as slope instability, liquefaction, total and differential settlement and surface displacement due to faulting or seismically induced lateral spreading or lateral flow.
The geotechnical investigation required by Section 1803.5.11, for structures assigned to Seismic Design Category D, E or F, shall include requirements of Section 1803.5.12  too.
Per Section 1803.7 soil report is not required for one-story wood-frame and light-steel-frame buildings of Type V construction with a floor area of 4,000 sq.ft or less not located within Earthquake Fault Zones or Seismic Hazard Zones.
In summary a soil report is required these days before the commencement of any new project. Without a proper soil report, a construction could end in danger. A soil report dramatically reduces the risk chances of a construction project and is thus, one of the most important things required these days in construction.
Our engineers can help you figure out the soil report requirements for your project and will efficiently design the foundation and the building per the information provided in the soil report to make sure your building is safe. Further, with so many years of experience we offer the most optimum foundation design tailored specifically for your project to minimize the construction cost.
As a principal engineer at Artin, Ellie oversees business development and financial projections, securing objectives and funding, as well as maintaining project budgets. Her background and experience in engineering, 12+ years of project management experience, and being certified as a Project Management Professional (PMP) allows her to manage and support each project to be delivered to clients on time and within budget. Ellie is a diligent senior project manager engineer offering a proven record of success at leading all stages of a project.
As a Principal Engineer at Artin, Ardy is licensed Professional Engineer (PE) in 11 states and licensed Structural Engineer (SE) in California and Nevada. Ardy earned his PhD in structural engineering in 2012. He has 15 years of experience in structural design of new construction, retrofit and rehabilitation projects for different types of buildings. Having hands on experience in industrial, commercial and residential buildings, Ardy has served as the design lead for more than 100 projects across the US (mostly in California)