al maryah central
DESCRIPTION
pile reportTRANSCRIPT
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Al Maryah Central Project UAE-Abu Dhabi
Piling Work Report
Prepared by : Karam Ahmad Jaradat
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Introduction
The aim of this report is to introduce and explain the engineering practice
or the implementation of one of the most common types of foundations
used for high-rise buildings, which is the deep foundations, there are many
reasons a geotechnical engineer would recommend 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 the pile (which is analogous to a pole),
the pier (which is analogous to a column), and drilled shafts . Piles are
generally driven into the ground in situ ; other deep foundations are
typically put in place using excavation and drilling ( which is the case here
in our project ). The naming conventions may vary between engineering
disciplines and firms. Deep foundations can be made reinforced concrete (
which is the case here in our project ) , timber , steel or even prestressed
concrete .
Our project foundations are made of in-situ cast piles ( using excavations
and drilling ) , one advantage here over the driven piles is to avoid the
noise resulting from the hammering or driving the pile into the soil .
Another one , driven piles are made of steel sections ( usually W-section
with a shoe ) , this limits the use of concrete ( which is an excellent
material for resisting compression loads ) , while the in-situ cast piles
using drilling and excavations can be made from different materials such
like R.C , timber , steel or prestressed concrete .
Prestressed concrete piles are used to resist the lateral force developed in
the soil resulting from excavations , also its used to resist tension forces
resulting from the buoyant force developed due to the uplift pressure of
the soil .
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Description and fine details of the project
The project consists of 898 in-situ cast piles with length ranging from 15 m
to 27.5 m , the diameter of the piles also varies from 500 mm up to 1500
mm , of course the choice of length and diameter depends on the loads to
be supported by the pile .
Piles were uniformly distributed across the whole site area , which is
approximately 500m X 100 m , with some piles designed as a group to
support shear walls , core walls , … etc .
Our main duty was to witness the rebar installment and checking the pile
reinforcement to be consistent with the drawings provided from the
designers . Also we were responsible of checking the validity of the
concrete ( which was provided by Reem ready mix ) by supervising
concrete testing at the site ( slump test and temperature test ) .
A- Steel Cages .
The steel cages was fabricated in the site , the sub-contractor used two
methods of fabricating the cages :
1- Manually : which is the usual .
2- Mechanically : This was done by an excellent machine which can
fabricate spiral reinforcement with excellent quality , see the below photo .
Figure (1) : Spiral reinforcement fabrication machine .
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Figure (2) : Steel Cage .
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B- Concrete .
Concrete was provided to the project by Reem ready mix concrete
company , another team from ACES was responsible of testing the concrete
and verifying the validity of the concrete according to the ASTM .
Two main tests were conducted in the site :
1- Slump Test .
There is no acceptable test will directly measure workability as defined (
as energy or work ) . However , some tests are conducted to measure some
properties related to workability .
Slump test is considered the most universally used test due to its
simplicity , the test is done according to ASTM C143 , the mold used is a
frustum of a cone (305 mm high , 203 mm base and 102 mm top opening )
, the tamping rod is 16 mm steel rod .
Concrete is be placed in 3 layers in the mold , each layer should be hit 25
times , and then the slump value is measured , slump test will measure the
consistency of the concrete mix which is a good measure of concrete
workability .
According to the ASTM , the slump value for fresh concrete should be
ranging from 160 mm to 240 mm .
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Figure (3) : Slump test conducted in the site .
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2- Temperature test .
The acceptable temperature for the fresh concrete should be less than 34 C
, this will guarantee the cohesiveness and consistency of the concrete mix .
Also , concrete must not remain in the concrete truck more than 2 hours (
1.5 hours in the code ) , since the heat of hydration of the mixing will raise
gradually and then , the concrete mix temperature will raise above 34 C ,
which is not acceptable .
Figure (4) : Temperature Test .
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3- Excavation and drilling
As mentioned before , our project consists of 898 in-situ cast piles , the
drilling process was the longest step in the piling work , although the rock
layer appears at a depth of 20 m approximately at al Maryah island , and
the soil profile was consisting of sand ( with zero cohesion ) , but installing
the casing and insuring that its straight was the hardest and the most
critical step for the contractor .
For this , a casing of length 8 m was used to ensure the straightness of the
pile , and after casting the pile , this case is removed , the casing diameter
was according to the pile diameter .
The location of the pile was determined using a total station , with a
surveying team provided by the contractor .
Figure (5) : Casing .
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Figure (6) : Drilling machine .
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4- Installing the steel cage .
After completing the drilling and ensure the total length of the pile is
drilled , the steel cage is installed , and since it's hard to fabricate a steel
cage with 27 m length , its divided into top and bottom cages .
The process of splicing the top and bottom cage was the most important
step in this stage , at first ; the bottom cage is installed and its anchored
with the casing as it completely installed , and then ; the workers ties a rod
around the bottom cage and tightens it so that its easily to install the top
cage .
Once the top cage is installed , bottom and top steel cages are welded and
the total cage is then downed to the pile .
Figure (7) : installing the Steel Cage ( top and bottom ) .
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5- Casting the pile
Perhaps this is the easiest and simplest step in piling , after the steel cage
is installed , a tremie pipe is installed in the pile and then a concrete pump
pipe is installed in the tremie pipe and the casting process in started .
(while the pile is being casted , dewatering process is started also to
remove the water from the pile ( water appears after digging 1 m ! ) .
Figure (8) : Casting process .
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Note : The tremie pipe is used to cast long-depth structures like piles ,
silos , .. etc . It's used to ensure proper casting and to prevent the
segregation of the concrete during casting .
Figure (9) : The Tremie Pipe .
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In-Situ pile testing
1- Sonic Test .
2- Caliper Test .
3- Compression test .
4- Dynamic Test .
1- Sonic Test ( Pile Integrity Test , PIT )
This is a non-destructive test method to determine some properties of the
pile , this test was carried on 91 piles with different size and length .
The test measures:
Pile length, or depth to anomalies , Pile head stiffness , Pile shaft mobility
– which is dependent on pile section and concrete properties . The
software also produces computer simulations and impedance profiles of
the test result , to analyze in detail any intermediate pile shaft responses .
Figure (10) : Steel Cage prepared for sonic test .
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2- Caliper Test .
This test was carried on 109 piles , its used to verify the size of the pile
( diameter ) , it's conducted through inserting a caliper into the pile , and
this device or caliper will measure the size and the variation of it along the
pile .
Figure (11) : Caliper Test .
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3- Compression test ( Static Test )
This test can be carried out static tests in any possible configuration:
vertical (compression and tension), lateral and raked piles load tests.
The tests are performed by applying a maintained load method or a CPR
(Constant Rate of Penetration) type tests to measure the capacity of the
pile either in compression , tension or lateral , this test was carried on 9
piles in the site .
The test will measure the settlement and deformation occur to the pile due
to the applied static load ; and this data will correlated to determine the
load bearing capacity of the pile .
Figure (12) : A pile being prepared for the compression test .
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4- Dynamic Test .
Dynamic load testing (or dynamic loading) is a method to assess a pile's bearing capacity by applying a dynamic load to the pile head (a falling mass) while recording acceleration and strain on the pile head. Dynamic load testing is a high strain dynamic test which is applied after pile installation . The procedure is standardized by ASTM D4945-00 Standard Test Method for High Strain Dynamic Testing of Piles. It may be performed on all piles, regardless of their installation method. In addition to bearing to bearing capacity ; dynamic test also gives information about shaft resistance ( Skin friction resistance ) which is important for the determination of the pile capacity .
This test was carried on 45 piles .
Figure (13) : Dynamic test .
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Non-Working Test for piles
This Test is carried basically to determine the shaft resistance (skin
resistance) and the factor of safety for the pile being tested , the piles
might be designed without taking into account the end bearing of each pile
due to the limitation of verifying the end material which support each pile ,
thus ; only skin friction with a factor of safety ranging from 2.5-3 is used .
The pile is prepared by installing a hydraulic jack into the pile with some
strain gages along the pile ( 3 or 4 layers of strain gages ) , which will
measure the shaft friction of each pile and then ; to compare these values
with the design values , the most important step here is the installment of
the pile it self and since it has many small strain gages , it will sensitive to
any mistake or wrong placement .
Figure (14) : A hydraulic jack installed to a pile .
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Figure (15) : Strain gages attached to a pile for a non-working test .
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Figure (16) : Piles after hardening .