Geotechnical exploration works – introductory part
Geotechnical exploration works
Geotechnical exploration works present one of the most important part in the developing phase of a new investment and a geotechnical designer should be included in the earliest possible phase of design.
A large part of our business is connected to geotechnical exploration and investigation and their quality is a precondition for developing a new idea about a project.
Are geotechnical exploration works so important?
The answer is yes because when planning, in the schematic design phase, it is necessary to consider a foundation system of the structure, open pit protection and other earth and geotechnical works. If a halt occurs during the construction, unforeseen circumstances, and with that unscheduled costs, it will mostly be caused by geotechnical conditions in the soil. Most of risks and problems in construction are connected to the foundation soil.
If you are approaching an investment in a professional and responsible manner, it is in your interested to reduce potential risks to a minimum. If you are thinking in that direction you will not think twice about exploration works.
Content and extent of foundation soil exploration has to be based on expected type and the construction project, e.g. type of foundation structure (shallow or deep foundations), soil improvement method (soil replacement, stone columns, preloading, jet grouting columns etc.), retaining structure (reinforced concrete wall, gabion retaining structure, mechanically stabilized earth wall etc.) and the position and depth of construction. In other words, in the planning of exploration works it is necessary to predict the future design solution which requires experience in exploration as well as in designing. Therefore it is important that a geotechnical designer is included in determining a program of geotechnical explorations.
Geotechnical exploration works or geotechnical exploration and investigation, and frequently called geomechanics, is a group of all explorations and investigations that are conducted in order to determine conditions in soil, rock and underground water. Results are processed and synthesized in to a report – geotechnical report or report.
During the exploration, as soon as possible, it is necessary to determine conditions in the foundation soil which can influence the selection of the geotechnical category.
Depending on the phase of design or construction, Eurocode 7 differese three phases of geotechnical exploration works:
• Preliminary exploration as a basis for the schematic design,
• Exploration for the project design
• Control and behavior monitoring
Geotechnical exploration and investigation for a project phase (main design phase) have to collect all necessary information about the soil and underground water for a final design of the structure and for proving that the important demands of the building are satisfied.
This phase is planned according to results of the preliminary geotechnical exploration and investigation phase. Suitability of field exploration works according to EN 1997- 2:2006 is given in the following table.
The position of exploration and depths of exploration and investigation have to be based on already conducted preliminary explorations, geological conditions, depth and type of the foundation system etc.
We distinguish the following methods and types of geotechnical exploration and investigation:
• explorational drilling
• probe pits and excavations
• geological and engineering geological exploration
• geophysical investigation
• standard penetration testing
• dynamic penetration testing
• flexible dilatometer testing
• Mernard pressuremeter testing
• Vane shear testing
• static and dynamic load pressure plate testing
• laboratory testing
• supervision of geotechnical exploration works
Some of the listed methods will be presented through following blogs. And for the end a couple of recommendations:
• include a geotechnical designer in the earliest phase of the project
• the program of geotechnical exploration and investigation should be made by a geotechnical designer that will later design the foundation or open pit and will know how to plan needed exploration and investigation
• a geotechnical report has to be signed by a authorized designer (member of the HKIG) and a authorized geologist
• it is preferable that the laboratory tests are conducted by a authorized laboratory