Suppose you want to build your dream retirement home on the slopes of the beautiful Rift Valley. Your engineer tells you that a geotechnical investigation is a compulsory step—a very critical step in ensuring the safety and durability of your build—his words, but you have no idea what it is or how to carry out one.
Regardless of the type of construction being done, whether your house, pipeline, or a massive shopping mall, a geotechnical investigation must be carried out. This is to determine if the ground is suitable and sturdy enough to safely begin construction.
Figure 1: A Side-by-Side Comparison of a Well-Engineered Structure vs. One Built Without Proper Soil Investigation
Geotechnical investigation is the procedure of acquiring information on subsurface soil conditions and synthesizing them to determine geomaterial parameters required for design. It aims to understand and provide information on the site’s subsurface conditions. Ultimately, this investigation seeks to understand the soil conditions below the surface, identify potential geological hazards at the project site, and present geotechnical analyses. It also provides appropriate recommendations for the design of the foundation system and relevant earth structures, retaining walls, and other necessary facilities.
The information from this process can help businesses/clients save massive costs that would otherwise be incurred in the long run.
Geotechnical investigations are performed by a certified geologist or a professional civil engineer with experience.
Here’s a typical example of how the investigations are conducted:
A desk study involves examining all relevant documentation pertaining to your site. This includes mapping geology, hydrology, ground conditions, site usage (both present and past), geography, etc. The goal is to maximize available information and minimize unnecessary duplication.
A non-destructive method of examining subsurface conditions. It provides 3D information on site by measuring variations of selected physical properties of the ground such as wave velocity, resistivity, density, and magnetic susceptibility.
Method | Description | Image |
Seismic refraction | Measures seismic wave velocity | |
Seismic reflection | Identifies subsurface layers | |
Resistivity | Measures electrical resistance | |
Magnetometer | Detects magnetic anomalies | |
Electromagnetic | Measures conductivity |
INSERT IMAGES OR EVEN TABULATE THIS INFORMATION PLUS THE IMAGES OF EACH METHOD.
Trial Pits or Boreholes
Methods allow samples to be taken for description and laboratory testing. Trial pits allow the most thorough in-situ examination of soil or rock masses, while boreholes are useful for deeper explorations.
Figure 2: A sample trial pit |
In-Situ Tests
These tests measure different geotechnical parameters.
Test | Purpose | Image |
In-situ density | Determines soil density | |
CBR | Assesses subgrade strength | |
Plate Bearing Test | Measures Load bearing capacity of soil | |
Direct Shear Test | Evaluates shear strength | |
Standard Penetration Test | Determines soil resistance | |
Field Vane Test | Measures undrained shear strength |
Groundwater Investigations
Groundwater is one of the most frequent causes of geotechnical issues. Understanding the groundwater regime and pore pressure distribution is critical. Water quality measurements, such as pH value and sulphate and chloride contents, may also be necessary.
Ground Description and Classification
Soil and rock descriptions should be made from cores taken during investigations. These descriptions, along with in-situ and laboratory test results, form a lasting record of ground conditions.
Laboratory Tests
These are carried out to measure a wide range of soil and rock characteristics.
Test | Purpose |
Static cone penetrometer | Evaluates soil resistance |
Dynamic Probing Test | Determines soil stratification |
Flow through sampler | Assesses permeability |
Penetration Vane Test | Measures shear strength |
Self-Boring Pressure meter Test | Evaluates in-situ stress |
Factual Reports: Geotechnical Site Reports
The record of all investigations for a specific site.
Interpretation of Site Investigation: Geotechnical Design Report
Interpretive reports provide advice on:
Conclusion
Geotechnical investigations play a crucial role in ensuring the safety, stability, and cost-effectiveness of construction projects. From understanding subsurface conditions to mitigating potential risks, these investigations provide the foundation for resilient structural designs. By working with qualified professionals and utilizing the right investigation methods, project stakeholders can make informed decisions that lead to sustainable and durable structures.