Method bored pile onland REV b english

Cleaning borehole shall be performed before the installation of reinforcementrebar cage, and then the casting concrete of the bored piles will be taken place.. The following diagram show

PROJECT TITLE:

Ho Chi Minh City Urban Railway Construction Project Ben Thanh - Suoi Tien Section (Line 1)

Construction Package 2 : Civil (Elevated & Depot)

Method Statement of Bored Pile Construction on

Land

REVISION STATUS

B 19th Feb 2013 SECOND ISSUE

PREPARED BY CHECKED BY APPROVED BY NAME

SIGNATURE

DATE

1 INTRODUCTION

1.1 OVERALL OF PROJECT

- 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 toKm19+591.37 (including 5 special bridges) and 1 depot

- Location: Starting at District 1 and ending at Long Binh Ward, District 9, Ho Chi MinhCity

1.3 WORK SCOPE

This method statement includes below scope of works

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

- Installation of Rebar Cage

- Casting Concrete

Temporary steel casing, of which diameter is 50~100mm larger than designed bored pilediameter, will be installed The boring works will be carried out until the designated toelevel Bored hole is filled with Bentonite slurry once the boring works commenced

Upon completion of the boring works, the reinforcement rebar cage will be lowered into theborehole Cleaning borehole shall be performed before the installation of reinforcementrebar cage, and then the casting concrete of the bored piles will be taken place

Bored piles with different diameters and lengths will be constructed in accordance with theconstruction working drawings

2 CONSTRUCTION PROCEDURE

2.1 WORK FLOW-CHART

The work sequence of the bored pile construction is depicted by the following flow-chart

The following diagram shows the continuous sequence of bored piling works

Preparation WorksSetting center point of bored pile

Assembling Guide frame

- Vertical of bored

KODEN Test

1st Cleaning of the Bottom Hole Inspection:

-Rebar cages (at yard)

-Sonic and core tubes

-Depth of bored hole by using rebar cages

Installation of the Rebar Cage (including Sonic

and core tubes)

Inspection:

-Property of Bentonite

-Depth of bored hole

2nd Cleaning of Bottom Hole (if necessary)

- Slump of concrete

- Level of concrete rising

- Center of Pile

-Level of top concrete

- Depth of bored pile by

Removal of the Temporary CasingBackfill with suitable material

SONIC TestCore test (if necessary) Grouting SONIC and core tubes

Completion

1.Pre-boring for temporary

casing installation 1 Temporary casing 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

1.Desanding the complete bored hole

2.Bentonite in bored hole will be pumped back to

bentonite plant for treatment

Stage 5

1.Lowering of reinforcement to the bored hole

2 Hanging the rebar cage at the designed level

Stage 6

1.Concreting of bored pile

2.Pumping of displaced bentonite back to bentonite

2 Backfilling the bored hole with suitable backfilling material 1 to 2 hours after the completion of concreting

Fig.1 Sequence of Bored Piling Works

Temporary drainage system shall be provided around the platform so that the platform andthe surrounding area are kept dry and accessible all the time

The temporary access road shall be made in case that existing road is not available forsupplying material and mobilizing to equipment

Bentonite mixing tank will be installed for fluent execution of the work maintaining includingconnection of pipe or hose to supply bentonite for the bored pile location It will be checkedfrom time to time for any possible spillage of bentonite slurry as per environmental

The density and consistency of the concrete for the bored piles shall conform to the tremiecasting method and the maintenance of sufficient workability (slump) of all the concreteduring the casting and handling period, including calculated allowance delay time, shall besecured by a design mix (including the necessary retarders and plasticizers) which istested by trial mixes prior to the pile construction.

The number of tank used for bentonite mixing plant shall be calculated to make sure thatthe 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

* This layout could be changed according to site condition

Fig.2 Layout of equipment and facilities set up

Precipitation Tank 1 Precipitation Tank 2

Waste Tank Withdrawal Tank

(2) Setting center point of the bored piles

Positioning drilling hole is based on the approved drawings, positioning benchmarks andpiling arrangement layout for specifying positions of pile center in compliance with theapproved design Specifying the position of the pile center is performed by electronic totalstation 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 centerand the pile center shall be checked again upon sinking temporary well casing Thesepositions shall be protected and maintained until sinking and completing inspection of thewell casing

Checking of the bored hole location shall also be carried out for all the piles after thecommencement of boring, but not later than when boring has reached the top of the firststiff layer

Fig.3 Setting out center of Bored pile

(3) Assembling Guide frame

Assembling guide frame will be prepared before Setting of the temporary casing

(4) Setting of the temporary casing

Bored pile construction will be commenced from setting out pile location and pre-drillingand installing temporary casing The length of the casing will be considered and justifiedbased on the soil condition and underground water level for maintaining the stability of thepile excavation holes against collapse, the casing length is from 6m to 9m The top oftemporary casing will be extended about 0.5 meter above the ground level

In installation of temporary casing, the verticality and stability will be checked and movement during drilling shall be kept Inner diameter of casing pipe will be at least 5 ~10cm larger than bored hole diameter The casing will be plumbed and checked foreccentricity against reference pegs, or it will be checked with survey equipment at the top

non-of the casing with the same elevation aside from the location frame installed above groundlevel

Pile center Subsidiary benchmark

Datum point

Fig.4 Installation of temporary casing

(5) Drilling work

The design length of piles will be specified in approved drawings During drillingexcavation, all holes for cast-in-place concrete pile should be excavated to the designlength Excavated holes will be protected from collapse by the provision of bentonite slurryand temporary steel pipe casing

Fig.5 Casing

Bentonite will be mixed thoroughly with clean fresh water to make a suspension which willmaintain the stability of the drilled hole for the period of casting concrete and completeconstruction Dry powder Bentonite is mixed with clean water according to required ratio bymixing machine and stored in the tanks which will supply to bored hole The drilling fluidproperties of bentonite slurry will be measured by taking samples before concreting Thedensity of freshly mixed bentonite slurry will be measured as a check on the quality of thesuspension 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

Pre-mixing of bentonite slurry on site

c) Bentonite Slurry Mix Design

Basic function of bentonite is to act as a stabilizing agent for the bored hole

In soil with high clay content, the bentonite slurry becomes very thick during excavationdue to the suspended clay particles The thick slurry becomes difficult to pump fordesanding To avoid this problem, a polymer / sodium bi-carbonate is added to the slurry

d) Testing Bentonite Slurry

Bentonite Slurry Testing:

The following tests will be conducted on bentonite slurry at the beginning and during boredpile construction period

1 Viscosity test - test on site

2 Sand Content – test on site

3 Density test - test on site

4 pH meter test - test on site

Bentonite characteristics have to meet the requirement (refer to Sub-clause 6.3Tolerance/Range, page 24-25)

The bentonite properties shall be measured by taking samples at the bottom of bored holebefore concreting All checking of bentonite slurry shall be carried out complying with thecriteria proposal The measuring device shall be calibrated to read in the minimum unit of0.01gm/ml

Fig.7 Bentonite Slurry

0.5-1.0 m above G.L

Bentonite

e) Drilling works

Temporary casings shall be free from any significant distortion They shall be of uniformcross- section throughout each continuous length During concreting, they shall be freefrom 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 drillingwithout stabilization bentonite The measurement of the depth of drilling bucket shall beclosely monitored when it gets near of the toe of the temporary casing

After putting bentonite into the borehole, drilling work will be continued and the top level ofbentonite slurry will be maintained 1.5m higher than ground water level or equal withground level for prevention of cave-ins or bored hole collapses

Based on the soil properties, drilling speed is adjustable in order to maintain the drillingaccuracy

The soil materials encountered in the bored pile drilling shall be checked to confirmwhether the actual soil conditions are similar to those assumed based on the geotechnicalinvestigation boreholes or not

During the drilling work, the verticality of bored hole will be checked by plumb with stringline or theodolites from two directions in 90 degree And the depth of bored hole will bechecked for the conformation of borehole condition When the bucket is lifted up, thebucket is to be rotated reversibly to release from the bottom and to be lifted up slowly toprotect the hole from collapse

Kelly-Bar shall be kept at the centre of the casing because drilled holes start to bend withKelly-Bar’s deviation from the centre In case any the deviation is found, the drilling should

be operated slower than usual and to correct the Bar’s verticality

After a borehole is formed to the designated depth, sonic caliper test (Koden Test) shall becarried out for checking the depth, diameter and verticality of the boreholes

Bentonite introduced into the borehole achieves the stabilizing effect by ensuring that thepressure inside the borehole is greater than the horizontal soil pressure and groundwaterpressure, at all depths

Piles shall not be bored so close to the piles, which have been casted not long ago withworkable or unset concrete The piling may disturb the fresh concrete in the neighboringpiles Boring and excavation for a pile shall only be commenced 24 hours after completion

of any pile within a radius of 6.0m, center to center, and only after the concrete strength ofthe neighboring pile reaches 15N/mm2

The excavated material and disposal bentonite will be kept in tanks or containers thentransported to approved disposal areas by special trucks The proposed disposal areas will

be submitted to the Employer’s Representative for approval later and separately

(6) 1 st Cleaning bottom of the holes & Changinh Bentonite

For the supply of fresh bentonite slurry, tank for fresh bentonite slurry will be installed atthe position which is separated apart from the bentonite pit.

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 thebottom of the borehole Then,

- Using reverse circulation method or air lifting method for replacing sedimentation ofslime with good slurry

After cleaning work, the depth of hole will be measured by measuring tape connected to aplump 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 theapproved construction working drawing

After the completion of fabrication for one segment of rebar cage, this segment shall becarefully kept in the dry and stable condition at stockyard which is elevated about 20 cmhigher than ground surface level Condition of re-bar cage will be checked and cleanedconstantly If some soil or rust are pound remained on the re-bar cage, all of them shall beremoved before the installation of re-bar cage

Additional reinforcing ring will be used for hanging of rebar cage segment and for the cagestabilized against distortion

Fig.9 Reinforcement fabricationInstallation of rebar cage and sonic tubes and core tube:

After the 1st cleaning of borehole is completed, the rebar cage will be installed carefully inorder to avoid the wall of the borehole from collapsing The lowest rebar cage segment will

be put into the casing and temporarily fixed at the section to be spliced with the next rebarcage segment When the rebar cage reaches the designed level, it will be suspended fromtop of the casing The top level of the rebar cage will be confirmed in comparison to that ofthe casing

The ultra-sonic tubes and core tube will be fixed to rebar by additional bar and ties to therebar cage Top level of the sonic tubes and core tube will be positioned approximately15cm above the ground level and checked for the rigidity and watertight of tubes duringinstallation The sonic tubs and core tube will be poured with water and covered on the top

of tubes prior to casting concrete

(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 arubber gasket will be used therein to watertight, these are lowered piece by piece until itreaches to the bottom of the borehole And the tip of tremie pipe will be at least 300mmaway from the bottom of bored hole in order to have enough clearance in discharging ofconcrete The top of tremie pipe is fitted with a head hopper

The length of each tremie pipe and the sequence of installation shall be recordedcompletely

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 thebentonite slurry will be tested once again, and the second time cleaning of pile base will becarried out if required by the Employer’s Representative with 1 of 2 methods:

1 1 Airlifting method: Air-lift system will be used as second measure to take all slime out

of the bottom of bored hole, before casting concrete The pressure of compressed airhas to be properly checked Since stabilizing fluid is supplied to the piling hole, thecompressed air will create an upward jet flow which carries the bottom sludge out of thehole The circulating time of airlift varies depending on the amount of bottom sludge

2 2 Reverse circulation method: using the capable submerged pump connected to tremiepipe for removing the slime sedimentation at the bottom of bored hole and replacing byfresh slurry.

A measurement tape is to be used for the re-confirmation of drilling depth and effect ofcleaning work The concrete placing will be started as soon as possible (approx in 30minutes) after second cleaning of bottom of bored hole And before casting concrete, it will

be confirmed by measurement tape that the sedimentation has been removed completely

Slump(cm)

Compressivestrength at 28days (Cylinder)

* 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 specialequipment and testing shall be performed before pouring concrete

Concrete will be placed and poured directly to the bored hole in one continuous operationfrom tip to cut-off elevation by tremie pipes and this operation will be carried out in such amanner that segregation of concrete is avoided The tip of the tremie will generally beapproximately 2.0m lower than the casting concrete surface A sliding plug or similarbarrier will be placed within the tremie pipe to prevent direct contact between the firstcharge of concrete and the water or bentonite