07 1 iok a1 BORED PILES

CHAPTER I : DESCRIPTIONAll specifications for this work item will be in accordance with Division 7: Concrete and Bridge Works of the Specification, specially section 07300 “Bored Pile” T

CONSTRUCTION OF BRIDGE WORKS

CONSTRUCTION METHOD STATEMENT FOR BORED PILES

TABLE OF CONTENTS CHAPTER I : DESCRIPTION

CHAPTER II : MATERIALS FOR PILING

I CONCRETE

II REINFORCING STEEL

III TEMPORARY CASINGS

IV BENTONITE AND BENTONITE SLURRY (DRILLING FLUID)

CHAPTER III: CONSTRUCTION OF BORED PILES

I PREPARATION WORKS

II CONSTRUCTION SITE PREPARATION

III MIXING OF BENTONITE

IV DRILLING HOLE

V CLEANING OF BORED HOLE

VI INSERTING OF STEEL CAGE AND CONCRETE PLACING

VII EXTRACTION OF CASING

VIII FINAL PILE TOE LEVEL

IX QUALITY CONTROL OF PILING

CHAPTER I : DESCRIPTION

All specifications for this work item will be in accordance with Division 7: Concrete and Bridge Works of the Specification, specially section 07300 “Bored Pile”

The construction of Bored Piles shall use the reverse circulation drilling method, crab type hammers, and steel casing or any other earth drill method approved by the Engineer, in accordance with the Specification Section and in conformity with the Drawings or as may be required by the Engineer

The work to be performed as specified in this Specification Section shall be carried out after any required subsoil investigations have been completed by the Contractor in accordance with this Specification Section, the Drawings, or as may

be required by the Engineer

Reference standards:

The most recent edition of the following Vietnamese Standards shall be applied

to the Works covered by this Specification

Vietnamese Standard:

TCVN 9395:2012 Bored Piles- Construction, Check and Acceptance

TCVN 9396:2012 Bored Piles - Determination of Homogeneity of Concrete - Sonic Pulse Method

TCVN 9393:2012 Piles - Standard Test Method for Insitu Piles Under Axial

Compressive Load

International Standard:

ASTM D4945 Pile Testing Using Large Deformation Method

CHAPTER II : MATERIALS FOR PILING

I Concrete

Concrete shall conform with the applicable provisions of Specification Section

07100 - Concrete and Concrete Structures

II Reinforcing Steel

Reinforcement shall conform with the requirements of Specification Section

07500 - Reinforcing Steel

III Temporary Casings

Temporary casings shall be used to maintain the stability of pile excavation, which might otherwise collapse

Temporary casings shall be free from significant distortion They shall have a uniform cross section throughout each continuous length During concreting they shall be free from internal projections and encrusted concrete which might prevent the proper formation of piles

IV Bentonite and Bentonite Slurry (Drilling Fluid)

1 Supply

Bentonite shall be in accordance with Vietnamese Standard TCVN 9395:2012

2 Mixing

Bentonite shall be mixed thoroughly with clean fresh water to make a suspension which will maintain the stability of the pile excavation for the period necessary to place concrete and complete construction

Where chemically contaminated groundwater occurs, special precautions shall be taken to modify the bentonite in all respects for the construction of piles

CHAPTER III: CONSTRUCTION OF BORED PILES

I Preparation works

Construction equipment includes :

Drilling equipment: is a self-propelled crane for craning casing, equipment and erecting the drilling machine

Drilling equipment includes of grab buckets as mechanical or hydraulic dredging buckets

Mixing equipment, tanks and bentonite pumps

Vibrating hammer with hydraulic power 170KW is enough capacity for lowing the casing into the hard ground

Cleaning equipment: betonite pumps, compressors 10m3/minutes

Other construction equipment such as tremie pipes, concrete vehicles, welding equipment, etc

II Construction site preparation

The main purpose of preparing site plan is creating space for the installation and operation of drilling equipment and construction of bored piles

Positioning the pile centre by Total Sation and marker is made by wooden piles

to avoid the lost during construction process,

Drawing a circle with diameter the same with casing on the ground and take this ring to locate the casing when lowering Pile center under water shall be located based on the casing and positioning frame

Mobilization of material, equipment for bored pile (installation of drilling equipment, crane, casing, positioning pile, air compressor, manufacture of rebar for pile)

Checking the operation of equipment, concrete supply, water and power

III Mixing of bentonite

Bentonite is mixed with cleaned water to create the slurry, maintain the stability

of the drilling work in the concrete placing and completion of execution The temperature of the water used for mixing Bentonite is not less than 5 degrees C Bentonite grout is mixed and operation in a specialized equipment in a closed process includes all stages of mixing, filtering, pumping to drilling holes and gather mortar for reusing

Bentonite is strictly in accordance with the technical standards by Contractor Bentonite mixing ratio dry / water is adjusted according to actual geological drilling Contractor shall conduct the tests in accordance with bentonite

specification before commencement of work The contractor will propose test methods, sampling procedures, inspection frequency and bentonite grout and submit to the Engineer Betonite's certificate Contractor’s site lab is sufficiently equipped with equipment to examine the density, viscosity, pH, shear force of the bentonite mixture to deploy test in the construction process

The tests and inspections must be taken regularly for bentonite

Testing of Materials for Drilling Fluid

1 Density 1.05 + 1.15g cm3 Hydrometer or

Bome- meter

2 Viscosity 18-5-45(8) Hopper 500 700CC

3 Sand content <6%

4 Rate of colloidal > 95% Measuring cup

5 Dehydration < 30mm 30 minutes instruments for

measuring Dehydration

6 Thickness of the

clay mantle 1 3mm 30 minutes

7 Shear strength 1 minute: 20-K30mg cm2

10 minutes: 5(H100mg cnr

Shear strength -meter

8 Stability < 0.3 g cm*

IV Drilling hole

1 Driving casing

The Contractor uses the temporary steel casing to guide and stabilize the hole wall

Using the crane in combination with vibration hammer 170 KW and excavation

to lower the casing

2 Drilling hole

Use drilling machine to drill bored piles

Bored piles will be drilled in sequence so that next bored pile will not be next to the piles having fresh concrete

The bentonite in the bored hole must be maintained so that the pressure of the fluid always exceeds the external pressure of the soil and outside water Bentonite will be maintained at a height 1 meter higher than the outside groundwater level

Excavated soil, rock, unsuitable Bentonite will be taken out of the Site to follow the provisions of Specifications

Piles shall not be bored so close to piles which have recently been cast and whichcontain workable or unset concrete such that a flow of concrete could be induced from or damage caused to any of the piles

Where the Contractor intends to bore a new pile located close to a recently Bored Pile Vietnamese Standard TCVN 9395-2012 Construction and Measurement of Bored Piles shall be applied and, unless otherwise instructed by the Engineer, the work for boring the new pile shall depend on the confirmation that the compressive strength of the recently Bored Pile has reached 70% of its design strength

3 Stability of Pile Excavation using Drilling Fluid

Where the use of drilling fluid is approved for maintaining the stability of a bore, the level of the fluid in the excavation shall be maintained so that the fluid pressure always exceeds the pressures exerted by the soils and external groundwater or at not less than 1m above the level of the external groundwater

An adequate temporary casing may be required in conjunction with the method

to ensure stability of the strata near ground level until concrete has been placed

In the event of a rapid loss of bentonite suspension from the pile excavation, the excavation shall be backfilled without delay and the instructions of the Engineer shall be obtained before excavation at that location is resumed

V Cleaning of bored hole

The Cleaning method for bored hole shall be applied by Contractor as follows: Dredging bucket is used for dredging large size of mud from bottom hole

Treatment for the sediment by circulation method :

 Using a pump with high capacity to pump clean bentonite to the bottom hole, clean and light bentonite shall be floated and pull drillcuttings out of the bored hole Dirty bentonite is led through the sediment tank, sand separator machine, the container and returning to the hole

Using the method of reverse circulation for cleaning hole may be 1 of 2 ways:

 Use air compressor: Erecting the tremie pipes into the drilled hole with a distance between head of tremie and bottom of the bored hole about 1m Inserting the air leading pipe into the tremie pipe End of air leading pipe is fitted with air nozzle and counterweight to keep the pipe from being pushed up during operation Pumping the compressed air into leading pipe to push drillcuttings and bentonite from the bottom of the hole up and pouring the clean bentonite into the bored hole

 Use water pumps with high capacity, type of full pumping to place into bottom of drilled hole to push the mud up from the bottom hole and pouring the clean bentonite into the hole

Cleaning of holes are carried out by 2 stages, first stage conducted after the completion of drilling and second stage is carried out after lowering steel cage (if any sediment beyond the requirements of technical regulations)

All reasonable steps shall be taken to prevent spillage of bentonite suspension at the Site and in areas outside the immediate vicinity of bore Disposal of discarded bentonite shall be in accordance with the Contractor’s approved environmental management plan

VI.Inserting of steel cage and concrete placing

Along with methods of bored piles, the Contractor shall submit to the Engineer for his approval the construction drawings and details related to the installation

of the steel cage and the corresponding sequences, and equipment and measurement tools to prevent and the broken of bored hole and maintain the stability of bored hole during the erection of the steel cage and control procedures in the method of vertical and firmly in the process

After completion of the drilling and installation of steel cages and cleaning the hole, the Contractor will require Engineer’s approval for conducting the placing

of concrete

The bottom of bored hole must be checked before commencement of work to ensure that there is no accumulation of silt or other materials mixed

Soon after being approved by Engineer the concrete placing must be taken and without interruption

The concrete shall be a rich coherent mix of high workability having a maximum measured slump of 200 mm

The concrete shall be placed in such a manner that segregation does not occur The concrete placing must be done in accordance with the technology of concreting under water :

+ Using the vertical pipe to push concrete down (tremie pipe )

+ Concrete placing pipe having a diameter of 250mm or more, are connected into the 1m, 2m, 4m, 6m, the short pipe is connected to each other, at the junctions must be watertight (using high rubber washer) and pipe are manufactured exclusively used for the placing of concrete under water concrete pipe must be of sufficient thickness to prevent the distort of pipe

+ Tremie joints of pipe is easy removable The pipe lifting is done by crane

+ Funnel for concrete :

* Volume of funnel must be calculated to contain sufficiently the concrete volume to ensure the submerged concrete of pipe legs

* The slant of funnel must be calculated to ensure the concrete pouring into the casing with slant of 1:1 to 1:2

+ Barrie for water must be made in soft material, easily deformed such as rubber, spongy, waterproof with density less than 1 to its own emergence from the water when out of the tremie Barrie for water is always closely the pipe circumference, but not be stuck in any case The upper side of barrier is always in contact with concrete Using the crushed spongy D=2cm, pouring into bag with thickness of 50cm and inserting into concrete pipe

+ Productivity of placing is 25-40 m3 / h

+ Placing concrete under water:

* Concrete continuously supply concrete pump (pump capacity of 60m3 / h) this is method to ensure that no water get into the concrete pipe Concrete is a mixture with high liquid suitable slump of 125 mm - 175mm Concrete must be ensure that no segregation

Funnel and tremie pipe must be cleaned and waterproof Tremie is always submerged in poured concrete least 2 m and not greater than 5m

Measure the concrete surface elevation must be conducted immediately before and after any movement of the tremie pipe

The hopper and pipe of the tremie shall be clean and watertight throughout The pipe shall extend to the base of the pile and a sliding plug or barrier shall be placed in the pipe to prevent direct contact between the first charge of concrete and the water The pipe shall at all times penetrate the concrete that has previously been placed and shall not be withdrawn from the concrete until completion of concreting At all times a sufficient quantity of concrete shall be maintained within the pipe to ensure that the concrete pressure exceeds the water pressure The tremie pipe shall be kept at least 2.0m but never more than 5.0m under the concrete level The internal diameter of the tremie pipe shall not

be less than 150mm for concrete made with 20mm aggregate and not less than

200 mm for concrete made with 40mm aggregate It shall be so designed that external projections are minimized, allowing the tremie to pass through reinforcing cages without causing damage The internal face of the pipe of the tremie shall be free from projections

Measurement of the level of concrete surface shall be taken immediately before and after any vertical movement of the tremie pipe

The Contractor shall ensure that heavily contaminated bentonite suspension, which could impair the free flow of concrete from the pipe of the tremie, has not accumulated in the bottom of the hole

Samples of bentonite slurry should be taken from the bottom of the hole using sampling devices have been approved If density more than 1.25 then it is not

allowed to carry out the placing of concrete In this case, the Contractor shall replaced the bentonite if approved to meet the requirements of the Technical Instructions

VII Extraction of Casing

1 Workability of Concrete

Temporary casings shall be extracted while the concrete within them remains sufficiently workable to ensure that the concrete is not lifted Should a semi-dry mix have been approved the means of ensuring that the semi-dry concrete does not lift during extraction of the casing shall be subject to approval

2 Concrete level

When the casing is being extracted a sufficient quantity of concrete shall be maintained within it to ensure that pressure from external water or soil is exceeded and that the pile is neither reduced in section nor contaminated

No concrete is to be placed in the boring once the bottom of the casing has been lifted above the top of the concrete; concrete shall be placed continuously as the casing is extracted until the desired head of concrete is obtained The pile shall

be concerted with an overheight agreed by the Project Manager to allow for chiseling back to the required cutoff level and to ensure sound, uncontaminated concrete in the head of the pile

Adequate precautions shall be taken in all cases where excess hydraulic heads could be caused as the casing is withdrawn because of the displacement of water by the concrete as it flows into its final position against the walls of the shaft

The use of vibrating casing extractors shall be subject to the approval of the Project Manager

3 Water Level

In the event of the groundwater level being higher than the required pile head casting level shown on the Drawings, the Contractor shall submit his proposals for approval prior to placing concrete The pile head shall not be left below the groundwater level unless approved precautions are taken

VIII Final Pile Toe Level

During pile boring, the Contractor shall produce a boring log indicating approximate depths and types of the various earth layers found in the bore Based on the existing conditions of boring, the Engineer might require the Contractor to provide disturbed samples for visual analysis

The Contractor shall immediately notify the Engineer if, during the installation of piles, the ground conditions are different from those indicated on the Drawings

or observed in the prebore