HCMC Metro Cp-2 Project
TITLE :

Method Statement of
Bored Pile Construction
On Land

Ho Chi Minh City Urban Railway Construction Project
PROJECT TITLE:

Ben Thanh - Suoi Tien Section (Line 1)
Construction Package 2 : Civil (Elevated & Depot)

Method Statement of Bored Pile Construction on
Land

REVISION STATUS
REV. No.

DATE

B

19th Feb. 2013

DESCRIPTION
SECOND ISSUE

PREPARED BY
NAME
SIGNATURE

(5) Drilling work..........................................................................................................9
(6) 1st Cleaning bottom of the holes & Changinh Bentonite...................................12
(7) Fabrication and Installation of the rebar cage....................................................13
(8) Setting of Tremie Pipe and Re-cleaning (2nd Time Clearing) of Bored hole.....15
(9) Casting concrete................................................................................................16
(10) Removal of Temporary Casing.........................................................................18
2 RESOURCES TO BE USED........................................................................................18
3.1 EQUIPMENT TO BE USED...............................................................................18
* The equipment (type and quantity) might be changed depending on the site
situation. ......................................................................................................................19
3.2 ORGANIZATION....................................................................................................20
2.1 RESPONSIBILITY OF STAFF...............................................................................20
3 CONTINGENCY AND SOLUTION...............................................................................21
3.1 CONTINGENCY OF DRILLING WORK................................................................21
3.2 CONTINGENCY OF SUCCESSIVE WORK..........................................................22
4 GROUND MOVEMENT AND SOLUTION....................................................................22
4.1 GROUND MOVEMENT.........................................................................................22
4.2 SOLUTION.............................................................................................................23
5 QUALITY CONTROL....................................................................................................23
5.1 QUALITY CONTROL.............................................................................................23
5.2 SEQUENCE OF Inspection and Test ....................................................................23
5.3 Tolerance / Ranges................................................................................................26
5.4 Inspection and Test Personnel...............................................................................26
5.5 Laboratory..............................................................................................................27
5.6 Quality Control Plan for Bored Piling Works..........................................................27
6 HEALTH, SAFETY AND ENVIRONMENT...................................................................28
6.1 HSE Training..........................................................................................................28
6.2 PPE........................................................................................................................29
6.3 Tool Box Meeting (TBM).........................................................................................29
6.4 HSE Inspection......................................................................................................29


Project name: Ho Chi Minh City Urban Railway Construction Project Line 1, Ben Thanh
- Suoi Tien Section.
The project comprises about 17,24 km of elevated rail way from Km2+360 to
Km19+591.37 (including 5 special bridges) and 1 depot.
Location: Starting at District 1 and ending at Long Binh Ward, District 9, Ho Chi Minh
City.

GENERAL
The objective of this method statement is to describe the construction methodology and
procedure for bored pile work on land of HCMC Metro Project.
The bored pile construction technique is to construct independent circular cast in-situ
reinforced concrete piles from the designed depth to the designed cut-off level.
Required site management controls for cast-in-place concrete piling works by using Earth
Drilling Machine, the type of bored piling rig shall be so selected as to suit the required
drilling length and/or underground condition. The sizes of the piles to be covered by this
method statement are diameter 1500mm, 1200mm & 1000 mm.

0.3

WORK SCOPE
This method statement includes below scope of works.
-

Drilling works: D=1,500mm, 1200mm & 1000 mm.

-

Installation of Rebar Cage.


If necessary

Drilling Works
KODEN Test
1st Cleaning of the Bottom Hole
Installation of the Rebar Cage (including Sonic
and core tubes)
2nd Cleaning of Bottom Hole (if necessary)
Casting Concrete
Removal of the Temporary Casing
Backfill with suitable material

Inspection:
- Center point Deviation
- Vertical of casing
- Level of casing top
Inspection:
- Depth of bored hole
- Property of Bentonite
Inspection:
Diameter of bored
hole
Vertical of bored
Inspection:
- Rebar cages (at yard)
- Sonic and core tubes
- Depth of bored hole by
using rebar cages
Inspection:
- Property of Bentonite

1.Pre-boring for temporary casing 1. Temporary casing
installation
installation by vibro hammer.

1.Pumping of bentonite slurry
for maintaining bored hole
2.Drilling of bored hole from
EGL to Design Toe Level

Stage 4

Stage 5

1.Desanding the complete bored hole
2.Bentonite in bored hole will be pumped back to
bentonite plant for treatment.

1.Lowering of reinforcement to the bored hole.
2. Hanging the rebar cage at the designed
level.


HCMC Metro Cp-2 Project
TITLE :

Method Statement of
Bored Pile Construction
On Land
Stage 7


from time to time for any possible spillage of bentonite slurry as per environmental
requirement.
The density and consistency of the concrete for the bored piles shall conform to the tremie


HCMC Metro Cp-2 Project
TITLE :

Method Statement of
Bored Pile Construction
On Land

casting method and the maintenance of sufficient workability (slump) of all the concrete
during the casting and handling period, including calculated allowance delay time, shall be
secured by a design mix (including the necessary retarders and plasticizers) which is
tested by trial mixes prior to the pile construction.
The number of tank used for bentonite mixing plant shall be calculated to make sure that
the volume of mixed bentonite slurry is enough for carrying out drilling work continuously.
Typical layout of equipment and facilities set up for bentonite solution is shown below.

Precipitation Tank 3

Precipitation Tank 2
Precipitation Tank 1

Circulation Tank

Withdrawal Tank

Mixing Tank

Positioning drilling hole is based on the approved drawings, positioning benchmarks and
piling arrangement layout for specifying positions of pile center in compliance with the


HCMC Metro Cp-2 Project
TITLE :

Method Statement of
Bored Pile Construction
On Land

approved design. Specifying the position of the pile center is performed by electronic total
station. The position shall be approved by the Employer’s Representative.
In addition, subsidiary benchmarks shall be set up by steel piles for direction of pile center
and the pile center shall be checked again upon sinking temporary well casing. These
positions shall be protected and maintained until sinking and completing inspection of the
well casing.
Checking of the bored hole location shall also be carried out for all the piles after the
commencement of boring, but not later than when boring has reached the top of the first
stiff layer.

Pile center

Subsidiary benchmark

Datum point

Fig.3 Setting out center of Bored pile
(3) Assembling Guide frame
Assembling guide frame will be prepared before Setting of the temporary casing.

HCMC Metro Cp-2 Project
TITLE :

Method Statement of
Bored Pile Construction
On Land

Fig.6 Casing
a) Bentonite slurry
All properties of chosen bentonite shall be tested and the test results shall be submitted to
the Employer’s Representative to get approval before using.
During drilling process of bored hole, the soil wall will be protected from collapse by the
provision of bentonite slurry and temporary steel pipe casing. Prior to drilling works, the
stabilization liquid as the bentonite suspension will be prepared and tested to meet the
criteria which will be proposed before commencement.
Bentonite will be mixed thoroughly with clean fresh water to make a suspension which will
maintain the stability of the drilled hole for the period of casting concrete and complete
construction. Dry powder Bentonite is mixed with clean water according to required ratio by
mixing machine and stored in the tanks which will supply to bored hole. The drilling fluid
properties of bentonite slurry will be measured by taking samples before concreting. The
density of freshly mixed bentonite slurry will be measured as a check on the quality of the
suspension being formed.
b) Setting up of Bentonite Plant
The following are the various stages of works in the setting up of site facilities:
Setting up
Installation of desander unit.
Preparation and levelling of ground.
Installation of bentonite silos.
Setting up of bentonite plant facilities.
Layout of bentonite and water piping systems.

pH meter test - test on site

Bentonite characteristics have to meet the requirement (refer to Sub-clause 6.3
Tolerance/Range, page 24-25).
The bentonite properties shall be measured by taking samples at the bottom of bored hole
before concreting. All checking of bentonite slurry shall be carried out complying with the
criteria proposal. The measuring device shall be calibrated to read in the minimum unit of
0.01gm/ml.

0.5-1.0 m above G.L

Bentonite

Fig.7 Bentonite Slurry


HCMC Metro Cp-2 Project
TITLE :

Method Statement of
Bored Pile Construction
On Land

e) Drilling works
Temporary casings shall be free from any significant distortion. They shall be of uniform
cross- section throughout each continuous length. During concreting, they shall be free
from internal projections and encrusted concrete which might disturb the proper formation
of piles.
From the ground level to one meter above the toe of the temporary casing will be drilling
without stabilization bentonite. The measurement of the depth of drilling bucket shall be

(6) 1st Cleaning bottom of the holes & Changinh Bentonite
For the supply of fresh bentonite slurry, tank for fresh bentonite slurry will be installed at
the position which is separated apart from the bentonite pit.


HCMC Metro Cp-2 Project
TITLE :

Method Statement of
Bored Pile Construction
On Land

The sequence of cleaning work for the bottom of hole is as below:
- Using cleaning bucket to remove lumps of clay, coarse sand and gravels at the
bottom of the borehole. Then,
- Using reverse circulation method or air lifting method for replacing sedimentation of
slime with good slurry.
After cleaning work, the depth of hole will be measured by measuring tape connected to a
plump bob. Measuring of hole will be carried out at the center and four corners of the hole.

Fig.8 Cleaning by cleaning bucket
(7) Fabrication and Installation of the rebar cage
Fabrication of rebar cage:
Steel bar shall be tested when delivery to site and only approved steel bar will be used.
Rebar cages, sonic tube and core tube will be fabricated and assembled according to the
approved construction working drawing.
After the completion of fabrication for one segment of rebar cage, this segment shall be
carefully kept in the dry and stable condition at stockyard which is elevated about 20 cm
higher than ground surface level. Condition of re-bar cage will be checked and cleaned
constantly. If some soil or rust are pound remained on the re-bar cage, all of them shall be

Method Statement of
Bored Pile Construction
On Land

Fig.10 Installation of the rebar cage
(8) Setting of Tremie Pipe and Re-cleaning (2nd Time Clearing) of Bored hole
a) Setting of Tremie Pipe
Tremie pipes of dia. 8-10 inches shall be used. The tremie pipes with standard length,
such as 0.5M, 1M, 2M, 3M and 6 M, shall be used.
Since the tremie pipes are segmented and connected by bolts as a flange type and a
rubber gasket will be used therein to watertight, these are lowered piece by piece until it
reaches to the bottom of the borehole. And the tip of tremie pipe will be at least 300mm
away from the bottom of bored hole in order to have enough clearance in discharging of
concrete. The top of tremie pipe is fitted with a head hopper.


HCMC Metro Cp-2 Project
TITLE :

Method Statement of
Bored Pile Construction
On Land

The length of each tremie pipe and the sequence of installation shall be recorded
completely.

Fig.11 Tremie Pipe
b) Re-cleaning of the Borehole (2nd Time Cleaning)
Prior to placing concrete, the depth of bored hole will be measured carefully and the
bentonite slurry will be tested once again, and the second time cleaning of pile base will be

aggregate
(mm)
20

Method Statement of
Bored Pile Construction
On Land

Slump
(cm)
18 to 25

Compressive
strength at 28
days (Cylinder)
30 N/mm2

Cement Contents
356Kg/m3

Prior to commencement of the concrete casting work, the following checking will be
executed for preventing the tremie pipe from blocking.
* Workability of concrete.
* Selection of the suitable tremie pipe (diameter, length per pipe and joint)
* Check of pipe joints leakage (visual Inspection)
Once again taking of Bentonite samples at the bottom of the bored hole by special
equipment and testing shall be performed before pouring concrete.
Concrete will be placed and poured directly to the bored hole in one continuous operation
from tip to cut-off elevation by tremie pipes and this operation will be carried out in such a
manner that segregation of concrete is avoided. The tip of the tremie will generally be

Temporary casing shall be withdrawn 15 minutes to 20 minutes after concreting by using
the draw and spin system of drilling machine or using vibro-system in vertical direction to
make sure the stability of pile head and degree of accuracy of pile center.
After removal of temporary casing, from 1 hour to 2 hours, the bored hole will be filled by
soil and/or sand.
2

RESOURCES TO BE USED
3.1

EQUIPMENT TO BE USED

For the successful implementation of bored piling works, the following equipment will be
mobilized. The list of equipment for a typical working party is shown below. Bored pile
works will be carried out with the following equipment.

The List of Equipment for One Typical Working Party
No.

Item

1

Drilling machine

Kelley
or
RCD
equivalent machine


Pouring concrete
platform
Bar
Cutter
machine
Bar
Bending
Machine

11

Air Compressor

12

Tremie Pipe

Remarks
or

For excavation of bored hole
For handling of steel cages and
concreting works

For casting bored pile
For fabricating rebar cages
For fabricating rebar cages
For airlifting (Cleaning)
80m


D = 1050~1550mm

For excavating of borehole

16

Bentonite Tank

17
18
19
20

Concrete Mixer
Truck
Bentonite
Desander
Survey
Equipment
Measuring Tape
with Plumb Bob

21

Empty tanks

22

Excavator


(Mr. Kim Dong Wan)
Quality Manager
(Mr. Myung Jai Sin)

Safety Manager
(Mr. Hwang Ki Ha)

Environmental Manager
(Mr. Tran Thanh Lap)

Survey Team
Site Manager
(Mr. Lee Jung Sun)

Site Engineer
(Mr. Mai Song Thao)

Subcontractor’s Project Manager

Subcontractor’s Engineer

Operator

2.1

Skill Labor

Common Worker

Electrician

CONTINGENCY AND SOLUTION
The possible contingency and solution during piling work will be described below.

3.1

CONTINGENCY OF DRILLING WORK

(1) Sand piping
The steel standing casing will be installed into the ground to protect the drilled hole from
collapsing due to the weight of working machines. However, piping may occur due to
insufficient penetration depth or penetrating into a sand layer. This occurrence may result
in water level dropping suddenly, drilling surface collapsing, and the standing casing
lowering or tilting. To solve this situation, either increases the casing length or withdraws
the casing and backfill immediately and re-excavate after the backfill consolidated.

(2) Collapse because of excessive loads
Potential collapse may occur due to the excessive loads. Before drilling, equipment
which is not necessary should be removed for drilling. Increasing the viscosity of slurry or
the length of standing casing may reduce the risk of collapse. When large collapse
happens, all the equipment will be removed and the hole will be backfilled immediately.
For several days, the pile could be drilling again after covering the ground of the borehole
with steel plates and increasing the casing length (if necessary).

(3) Insufficient water head
Insufficient water head in the drilled hole may result in the collapsing of the drilling
surface. Spillage leakage into ground may occur while the high permeable layer is
encountered. Therefore, the water level within the drilled hole shall be inspected regularly
and frequently. Additional slurry or other solutions may be needed to keep slurry from
flowing into the high permeable layer.


(1) Rebar cage dropping into the drilled hole
When the rebar cage drops into the drilled hole, the installation should be stopped
immediately. The dropped cage should be recovered by using the wire with hook, which
is enough to recover the falling cage. After recovering, the condition of the cage should
be check to make sure that the cage quality is still accepted for structural use. Another
section will be needed if the cage is not accepted. In order to prevent the cage from
falling or dropping, the connecting points among rebars and hanging bars should be
carefully inspected. After removing the rebar cages the depth of borehole shall be
checked again to make sure the drilled depth before re-installing rebar cages.

(2) Tremie pipe dropping into the hole before concrete placing
Care should be taken while inserting tremie pipes into the hole. When the tremie pipe is
dropped into the hole before concrete placing, the work should be stopped. A large hook
will be used for recovering the dropping pipe from the hole and resume the work.

(3) Tremie pipe out of the placed concrete
If the bottom of tremie pipe be out of the placed concrete due to the pipe blocked, it is a
practicable choice to re-penetrate the cleaned tremie pipes into the placed concrete
before the initial set of concrete, to vacuum water and slurry in the tremie pipe and to
continue placing concrete.
The procedure of work shall be checked carefully at the points of:
The taken time should less than the setting time of used concrete and as soon
as possible.
The volume of bentonite slurry inside the tremie pipe.
The toe of tremie pipe inside poured concrete at least 2m.
The procedure of the treatment shall be recorded completely and accurately. The
integrity test of the pile shall be executed after 7 days to confirm the structural capability.

(4) Collapse during concrete placing
When placing concrete, there are chances that the wall of hole has collapsed if the water


If groundwater flows into the boreholes together with soils at the base of the
boreholes (boiling of sandy soil ground at the base of the borehole)

-

If groundwater level of surrounding ground was lowered

SOLUTION
In order to prevent ground movement during piling work, these solutions will be applied:
-

In case of problem arise, bentonite shall be densified and extend the temporary
casing.

-

Bentonite shall be kept more than 1.5m above from existing groundwater level,
described in fig. 13.

Fig. 13 Bentonite and ground water level
5
5.1

QUALITY CONTROL
QUALITY CONTROL
All material will comply with the requirements in the Outline Construction Specification
and the required inspection and test on site will be carried out in compliance with the ITP
and quality control plan. ITP will be submitted to the Employer’s Representative
separately.

reinforcement shall be taken from different bars. The ends of the specimen shall be cut
square before delivery to the laboratory.
b) Ready Mixed Concrete


HCMC Metro Cp-2 Project
TITLE :

Method Statement of
Bored Pile Construction
On Land

The ready-mixed concrete shall be obtained only from a supplier agreed by the
Employer’s Representative .
Contractor shall submit the Mix Design Ready Mixed Concrete to the Employer’s
Representative for his approval.
Ready-mixed concrete shall comply with the requirements of JIS A 5308 or equivalent
Vietnamese Standards and those specified herein and shall comply with all requirements
of the Contract.
The concrete shall be carried in purpose-made agitators, or truck mixers, operate
continuously. The concrete, shall be compacted and in its final position within 2 hours of
the introduction of cement to the aggregates, unless a longer time is agreed by the
Employer’s Representative. The time of such introduction shall be recorded on the
Delivery Note, together with the weight of the constituents of each mix.
The Contractor shall make the supplier aware of all Specifications requirements and of
his program, construction methods, rates of concreting, access, and all other criteria
which may affect the supplier's performance in any way.
Sampling and Testing shall be in accordance with the following specification and
Inspection and Test Plan
No

JIS A 1102 or
AASHTO Test Method T27
JIS A 1109 or AASHTO Test
Method T84

6

Related testing for Fine Aggregate

7

Specify Gravity and Absorption of Coarse
Aggregate

and Absorption

of

Fine

Refer to sub-clause 5.1.2
(3)
JIS A 1110 or
AASHTO Test Method T85

The frequence of testing and sampling of fresh concrete at construction site are
performed by the this table
No
1
2