What is a geotechnical investigation?
A geotechnical investigation is conducted by a geotechnical engineer for the purpose of determining the subsurface soil and groundwater conditions at a particular site.
Why a geotechnical investigation should always be conducted before building any structure.
A geotechnical investigation helps to understand the foundation requirements for the construction of any new building structures, underground utilities, roadways, parking lots, etc. These investigations are essential for design and structural engineers to recommend design criteria for the construction and design approach for each project.
Risks in not completing a geotechnical investigation
If a geotechnical investigation is not completed, then the subsurface conditions are undetermined. Although someone may assume that the ground is suitable by visual appearance at the surface, this may not be the case. For example, a layer of peat (organic) material could be present several meters below the surface, which would be undetected without an investigation. In this case, the ground would be very soft and could lead to settlement over time, resulting in cracks in the foundation / floor slab, which may be structurally unsound. This may result in a far more expensive repair bill than the cost of completing the geotechnical investigation in the beginning.
A more extreme scenario may involve the ground completing giving away if the pressure exerted by the structure is greater than the bearing capacity of the ground. In this case, the structure could collapse, presenting serious danger to any occupants.
An Example of the importance of geotechnical investigations- Sampoong Department Store Disaster.
The Sampoong Department Store was built in 1990 on a site that was originally a landfill. The building was designed to have four floors, but the owner of the building wanted to add a fifth floor without consulting with a geotechnical engineer. As a result, the additional weight of the fifth floor was not properly supported by the foundation, which caused the collapse of the building on June 29, 1995.
The collapse resulted in the deaths of 502 people and injured 937 others, making it one of the deadliest building collapses in history. The investigation found that the lack of geotechnical investigation and the unauthorized addition of the fifth floor were major contributing factors to the collapse. The tragedy led to changes in building codes in South Korea and highlighted the importance of proper geotechnical investigations in building design and construction.
What tasks are involved with a geotechnical investigation?
In any geotechnical investigation, the general tasks are as follows:
1) Field Investigation
A field investigation can be conducted by either advancing test pits using an excavator or advancing boreholes using a geotechnical drill rig. The most suitable method is project specific and depends on a variety of factors, including the depth required (excavators are limited to their reach), whether bedrock samples are required (diamond coring required to obtain bedrock samples using drill rig), site constraints, availability of equipment, costs, etc.
Prior to excavating or drilling, the existing public and private underground utilities are located and marked. Next, the test pits / boreholes are advanced, while soil samples are collected by either grabbing a sample from the test pits or collecting them off the split-spoon sampler from drill rig.
Groundwater conditions are monitored either by visual observation or installing monitoring wells (piezometers), which remain installed for a period of time and checked once water levels have stabilized.
2) Laboratory Testing
Following completion of the field investigation, selected samples are tested for grain size analysis (sieve method), moisture content, and other tests as applicable. The test results are used to classify the soil, which will assist the geotechnical engineers with providing appropriate design recommendations for the project.
3) Reporting
Following completion of the field work and laboratory testing of the soil samples, a geotechnical report is prepared. The report summarizes the findings and typically includes the following:
Test pit / borehole logs including subsurface soil conditions, groundwater conditions, depth to bedrock, etc.
Laboratory testing results
Soil classification in accordance with the Unified Soil Classification System (UCS)
Recommendations regarding site preparation, groundwater management, bearing capacity, foundation design, pavement design, frost protection, etc.
Photos of field investigation
Are geotechnical investigations only needed for large-scale projects?
Absolutely not! AllRock has conducted geotechnical investigations for wide range of projects, from a new single home development to an investigation for the new Corner Brook Healthcare Facilities and even the new Trans-Canada Highway Exit 41 Interchange located just outside St. John’s. A geotechnical investigation is imperative for projects of all sizes to ensure that structures on the site will have a strong and stable foundation for many years to come.
Contact us today if you’re looking to get a geotechnical investigation done in Toronto, Ottawa, London, or throughout Newfoundland and Labrador. Geotechnical Engineering | AllRock Consulting | Canada
