| Development of bored piling techniques
Bored pile
installation methods evolved initially from the construction of water
wells in which the brickwork lining was utilised as a bearing element.
When, in the middle of the last century, mechanised winches and grabs
came into use, it became possible to construct cased boreholes in unstable
ground, even below the groundwater level, at fairly low cost.
By the 1920's,
concrete technology had achieved a level of development, which made it
possible that large diameter boreholes could be utilised as foundation
piles. With the development during the 1950's and 60's of compact drilling
rigs, consisting of base carrier, winch and casing oscillator, the grab
excavation technique was advanced to a form, which is still in use today.
Another development
was the rotary drilling technique with flush circulation, which was used
primarily for relatively deep boreholes (e.g. oil wells) due to the complexity
of the site installation. In the USA, where flush circulation techniques
were of great importance early on in oil drilling technology, rotary drives
were developed and mounted on crawler cranes or trucks. A square shaped
kelly bar, suspended
on a cable winch and guided through the turntable, made it possible, to
drill into stable soils and rock with high production rates. After World
War II, the problem of "caving in of borehole walls" was solved by using
supporting fluids, such as bentonite slurry and chemical additives. This
technique became generally accepted in Europe during the 1960's.
Recently,
the rotary drilling method, particularly for the installation of large
diameter boreholes, was significantly im-proved by the invention of the
rotary drive, mounted on a sledge allowing movement along the stiff mast
of the drilling rig. Due to the latest developments in the field of hydraulic
and electronic systems, drilling rigs are now designed and manufactured,
which are capable of achieving a maximum of productivity with a minimum
of energy input as well as with a minimum use of human power.
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