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Greetings, I thank God for life. Thanks to all of you for reading, upvoting and commenting on my previous posts. Have you heard of a very tall sinking tower in San Francisco ? Well, it's a millennium tower of 58-storey building.
<br>The 58-storey San Francisco's Millennium Tower, designed by Handel architects LLP, led by partner Gary Handel, have been a subject of circumstances since its opening in 2009. Findings have shown that, as at last year, this high structure has sunk almost 17 inches since its inception. This settlement was brought out of darkness into light, when residents noticed staggering movement of objects across their floors, and posted videos online.
<br>_as_seen_from_the_south,_SF,_March_2008.JPG)<center><sub>The Millennium Tower (301 Mission Street) as seen from the south, SF, March 2008.
[Image source - <a href= https://commons.m.wikimedia.org/wiki/File:The_Millennium_Tower_(301_Mission_Street)_as_seen_from_the_south,_SF,_March_2008.JPG#mw-jump-to-license>public domain by its author, Hydrogen Iodide at English Wikipedia]</a></sub></center><br>
The multi-storey structure constructed on a friction pile of concrete, driven to a depth between 18.29 meters and 27.43 meters into soft soil that do not position itself on the solid rock that exist at some depth beneath the ground surface, was found sinking in an haphazard manner. The building gradually became slanted, as the Sandy and muddy soil underneath relinquish control over it.
The unfortunate occurrence on the San Francisco's Millennium Tower is a crucial example of the usual challenges or problems that may be encountered in the design and construction of the supporting part of big structures (i.e substructure or foundation).
The gradual sinking of the tower has been questioned and criticized by many. The question now is, why would a multi billion dollars structure, as such, sink 17 inches within 7years of opening it? Was it because the Geotechnical Engineer gave wrong report about the soil properties?
Maybe it was because the structural engineer built a foundation that could not withstand the heavy load of the large structure acting on it. Well, It's quite hard for anybody to give answers to such questions.
Notwithstanding, In conjunction with geotechnical engineers, there was an investigation incepted by the Millennium homeowners association with the aim to ascertain definitely, the cause. A big situation, as such, intentionally attracting attention is worth given answers to.
>The ultimate search for this answers is what brought about these attractive conspicuous questions; what is geotechnical engineering, and why is it a subject of importance for substructure ?
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<center>**Allow me to formally introduce you to geotechnical engineering and what a typical geotechnical engineering project entails**</center>
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https://cdn.steemitimages.com/DQmXYffSKTqXkaztRrtW1jeK22xVVB26X7VMxdTLWXaXAVy/Boston_CAT_Project-construction_view_from_air.jpeg
<center> <sub>View of Boston's Big Dig from the air. This view is looking from Boston over the Charles river. The A-frame bridge just being started here has since been completed, and the green highway structure has been removed
[Image source - <a href= https://en.m.wikipedia.org/wiki/File:Boston_CAT_Project-construction_view_from_air.jpeg> public domain in the United States]</a></sub></center></div>
The International Society for Soil Mechanics and Geotechnical Engineering stated that, anything that do not move in a fluid manner, travel through the air, or fall down are supported by rock or soil. An over budget of one-third of the construction project, reported by the National Economic Development Council, was ascertained to be due, at a large extent, to unforeseen geotechnical conditions.
<br>Geotechnical engineers, can however, provide solutions to major issues of construction, applying their knowledge of soil mechanics and rock mechanics. Therefore, Geotechnical Engineering is an important branch of civil engineering concerned with how naturally occurring materials found on earth behaves, using the understanding and working principles of forces acting on soil and rocks.
The importance of geotechnics in constructions, in any engineering discipline cannot be underestimated, particularly, the ones constructed on the surface of the earth or underground.
>Understanding the working principles of forces acting on rocks and soil as a geotechnical engineer, makes it possible and easier to carry out material and subsurface investigation. The basic features of the materials (such as the physical, chemical and mechanical) can also be determined. The successful endurance and physical motion of soil covered slope can be evaluated.
The underlying principles of geotechnical engineering are also important for risk assessment, that maybe caused by deferring conditions of the site; and efficient design and monitoring of any structure made from the earth and their foundations at large.
Before an investigation is carried out on any site, so as to determine the engineering properties of rocks and soil; the distribution of fracture in the rock formation; and the impervious rocks that exist underground; and their effects on the forthput construction, there is need for the material features to be determined by evaluating the project needs.
A total understanding of a proposed construction site is important, and that, justify the need for proper investigation of the site. The positive and negative effects, that the proposed construction site may have on us, our properties and environment from natural hazards (such as sink holes, landslides, earthquakes and rockfall) can also be taken into consideration.
After necessary site investigation, the foundation is designed, and subsequent design of earthwork is carried out. There's need for a foundation to be designed for the construction of different engineering structures such as bridges, commercial and residential buildings, high-rise buildings etc.
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<center>**The relationship between geotechnical engineering and other engineering disciplines outside the civil engineering field**</center>
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https://cdn.steemitimages.com/DQmTqNADw4ppfYhuGsgQNgd7gAAtyTKJQmrrfTZJW5GDmsA/800px-Big_wave_cheney.JPG
<center> <sub>Big wave on Cheyne beach
[Image source - <a href= https://commons.m.wikimedia.org/wiki/File:Big_wave_cheney.JPG#mw-jump-to-license>public domain by its author, FrankPearson at English Wikipedia]</a></sub></center>
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The connection between the geotechnics of engineering to ocean and coastal engineering cannot be underestimated. This is because, ocean engineering may involve the lowest supporting layer and the systems that hold the facilities and structures in an environment that pertains to the sea. While, the planning, design and creation of a sheltered expanse of water (harbors); a landing place made by man for ships (quays); and marinas, which serves as an harbor for small boats is what we refer to as coastal engineering.
The closeness of the field of engineering geology and the geotechnics of engineering is like that of a five and six in the game of soccer. One of the significant difference between these two fields is that; A student studying engineering geology would get a degree in geology, but a geotechnical engineering student would be a degree holder in the field of engineering.
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<center>**Let me take you as far back as 2000 BCE to discuss history of the geotechnics of engineering**</center>
<br>The use of soil for the control of disastrous overflow of water, building of sites for burial, construction of the lowest supporting structures known as foundation, the operation of causing water to flow on land, and as construction materials for various engineering structures have been in place since time past.
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https://cdn.steemitimages.com/DQmd4hHHJ5nhGYQDoq8HRzh6oeWGaBd2k62tJvNViCSkjoy/1100px-EGY_orthographic.svg.png
<center> <sub>Orthographic map of Egypt centered at 26° N, 30º E.
[image source - <a href= https://commons.m.wikimedia.org/wiki/File:EGY_orthographic.svg#mw-jump-to-license>Creative CommonsAttribution-Share Alike 3.0 Unported]</a></sub></center>
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The ancient Egyptians, ancient Mesopotamians and the fertile crescent, made a demonstration of a typical flood control and irrigation structure, which was the first geotechnical work which was done. The signs found on the presence of canals, dykes and dams as far back as 2000 BCE in those ancient places, was what brought about the existence of the basic geotechnical demonstrations.
<br>The Construction of strip foundation, raft foundation and pad footings for various structures came into existence through the ancient Greeks. The use of soil as a material for design and construction depend solely on past experiences, not until the 18th century, when theoretical guides came into place.
<div class="pull-left">https://cdn.steemitimages.com/DQmZS5HTVZUeZFbpF4BuWGmWwVDnx1wJb2hB5fYzdx7BWZp/The_Leaning_Tower_of_Pisa_SB.jpeg.jpeg
<center> <sub>The Leaning Tower of Pisa.
[Image source - <a href= https://commons.m.wikimedia.org/wiki/File:The_Leaning_Tower_of_Pisa_SB.jpeg#mw-jump-to-license
>ublic domain by its author, Hydrogen Iodide at English Wikipedia]</a></sub></center></div>
The use of scientific method to critically inspect subsurface in constructions was initiated due to the engineering problems encountered in the foundation of some structures, such as Leaning Tower of Pisa. In 1773, A French military engineer, Charles Coulomb, who was also a physicist recorded how best the principles of mechanics are applied to soils, after which the determination of earth pressure methods have been improved upon, as against the military defensive structure.
<br>Coulomb made a suggestion for the aim of designing, he suggested that the sum of soil cohesion, c, and friction dtan(Φ), is equal to the maximum shear stress on the slip plane, immediately after he had carefully noticed the creation of a slip plane, right behind a retaining wall that are capable of sliding at failure.
maximum shear stress on the slip plane = c + dtan(Φ)
Where:
**c** is the soil cohesion
**d** is the normal stress
**Φ** is the soil friction angle
Fluids have been known to flow through media that are porous in the law of Darcy, stated by Henry Darcy in the 19th century. The estimation of stresses in the ground at some depth, is made possible, using the theory developed by Joseph Boussinesq for the distribution of stresses in solids with an elastic manner. The indices of clay consistency which was created by Albert Atterberg a long time ago, is what we use for the classification of soils nowadays.
In 1925, A well known geologist and civil engineer, Karl Terzaghi, who is considerred by many to be the father of modern geotechnical engineering and soil mechanics, used one of his published material titled "Erdbaumechanik" to instigate the engineering of modern geotechnics. He also made It known that effective stress of soil is controlled by the soil shear strength in a fundamental assumption of effective stress, which he came up with during the time.
The basic conceptual structure for the principles upon which the settlement rate of clay layers depends as a consequence of consolidation, and the principle of bearing capacity of foundations was also developed by Terzaghi. The scale models of various challenges arising in geotechnical engineering can be put to the proof by a method referred to as Geotechnical centrifuge modelling.
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<center> ***In Summary...*** </center>
There is need for us to give the design of foundation utmost attention in the world of constructions, because, foundation is the part that carry all the loads of the structures that act upon it, and this is why, the geotechnics of engineering is very crucial for substructures.
<center><sub>***Thank You All***</sub></center>
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<sub> **REFERENCES**<hr>
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* <a href= https://www.ngi.no/eng/Careers/What-is-Geotechnical-engineering>What is geotechnical engineering</a>
* <a href= https://www.autodesk.com/redshift/what-is-geotechnical-engineering>What Is Geotechnical Engineering, and Why Is It So Crucial for Infrastructure?</a>
* <a href= https://en.m.wikipedia.org/wiki/Geotechnical_engineering>Geotechnical Engineering</a></sub>
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