Al Maryah Central Project UAE-Abu Dhabi

Piling Work Report

Prepared by : Karam Ahmad Jaradat

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 .

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 .

Figure (2) : Steel Cage .

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 .

Figure (3) : Slump test conducted in the site .

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 .

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 .

Figure (6) : Drilling machine .

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 ) .

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 .

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 .

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 .

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 .

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 .

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 .

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 .

Figure (15) : Strain gages attached to a pile for a non-working test .

Figure (16) : Piles after hardening .