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Английский язык для студентов строительных специальностей
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UNIT 10. FOUNDATIONS OF BUILDINGS | 229
Deeper foundation walls can also be built by the slurry wall method, in which a linear series of closely spaced caisson-like holes are successively drilled, filled with concrete, and allowed to harden; the spaces between are excavated by special clamshell buckets and also filled with concrete. During the excavation and drilling operations the holes are filled with a high-density liquid slurry which braces the excavation against collapse but still permits extraction of excavated material. Finally, the basement is dug adjoining the wall, and the wall is braced against earth pressure.
Give a brief overview of the structure and contents of Text10B.
Relate each heading to the corresponding paragraph of Text 10B.
a) Caissons.
b) The slurry wall method.
c) Bearing piles.
d) Reinforced concrete foundation walls.
e) Some specific features of foundations.
f) Floating foundations.
22. Read Text IOC "Deep Foundations" and answer the questions. Discuss your answers with your groupmates.
a) What is the difference between a deep foundation and a shallow foundation?
b) Why is a deep foundation preferred over a shallow foundation?
c) What are the other names of a deep foundation?
d) What are driven foundations characterized by?
e) What is the structure of pile foundation systems?
f) How are boring techniques employed for drilled piles?
g) What do dry boring methods consist in?
h) What is specific of wet boring?
• TEXT IOC
Deep Foundations
A deep foundation is a type of foundation distinguished from shallow foundations by the depth they are embedded into the ground. There are many reasons a geotechnical engineer would recommend a deep foundation over a shallow foundation, but some of the common reasons are very large design loads, a poor soil at shallow depth, or site constraints (like property lines). There are different terms used to describe different types of deep foundations including piles, drilled shafts, caissons and piers. The naming conventions may vary between engineering disciplines and firms. Deep foundations can be made out of timber, steel, reinforced concrete and pre-tensioned concrete. Deep foundations can be installed by either driving them into the ground or drilling a shaft and filling it with concrete, mass or reinforced.
Prefabricated piles are driven into the ground using a pile driver. Driven piles are either wood, reinforced concrete, or steel. Wooden piles are made from trunks of tall trees. Concrete piles are available in square, octagonal, and round cross-sections. They are reinforced with rebar and are often prestressed. Steel piles are either pipe piles or some sort of beam section (like an H-pile). Historically, wood piles were spliced together when the design length was too large for a single pile; today splicing is common with steel piles, though concrete piles can be spliced with difficulty.
Driving piles, as opposed to drilling shafts, is advantageous because the soil displaced by driving the piles compresses the surrounding soil, causing greater friction against the sides of the piles, thus increasing their load-bearing capacity.
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Foundations relying on driven piles often have groups of piles connected by a pile cap (a large concrete block into which the heads of the piles are embedded) to distribute loads which are larger than one pile can bear. Pile caps and isolated piles are typically
I Английский язык для студентов строительных специальностей
UNIT 10. FOUNDATIONS OF BUILDINGS
I 231
connected with grade beams to tie the foundation elements together; lighter structural elements bear on the grade beams while heavier elements bear directly on the pile cap.
Rotary boring techniques offer larger diameter piles than any other piling method and permit pile construction through particularly dense or hard strata. Construction methods depend on the geology of the site, in particular, whether boring is to be undertaken in diy ground conditions or through water-logged but stable strata, i.e. wet boring. Boring is done until the hard rock or soft rock layer is reached in the case of end bearing piles.
If the boring machine is not equipped with a rockauger, then
socketing of the hard rock layer is done with the help of a heavy
chisel which is dropped from a height of about 1.5 metres by
suspending it from a tripod stand attached to a winch crane. The
socketing is carried out until the desired depth within the rock layer
has been attained. The depth within the rock layer is considered to
be equal to the diameter of the pile in hard rock layers and is taken
to be equal to 2.5 times the diameter of the pile in soft rock layers.
Dry boring methods employ the use of a temporary casing to
seal the pile bore through water-bearing or unstable strata overlying
suitable stable material. Upon reaching the design depth, a
reinforcing cage is introduced, concrete is poured in the bore and
brought up to the required level. The casing can be withdrawn or
left in situ.
Wet boring also employs a temporary casing through unstable ground and is used when the pile bore cannot be sealed against water ingress. Boring is then undertaken using a digging bucket to drill through the underlying soils to design depth. The reinforcing cage is lowered into the bore and concrete is placed by a tremie pipe.
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