7 1 ok CW2C BORED PILES

ASTM A36 Carbon Structural Steel OCMA DFCP4 Drilling Fluid Materials Bentonite Oil Companies Materials Association OCMA API S13A Specification for Oil Well Drilling Fluid Materials APIS:

CONSTRUCTION METHOD STATEMENT FOR

BORED PILES

TABLE OF CONTENTS

I MATERIALS FOR PILING

II REBAR WORKS

III CONSTRUCTION OF BORED PILES

Reference standards:

The following Standards in their latest edition shall be particularly

applied to the works covered by this Specification

ASTM A36 Carbon Structural Steel

OCMA DFCP4 Drilling Fluid Materials Bentonite Oil

Companies Materials Association (OCMA)

API S13A Specification for Oil Well Drilling Fluid Materials (APIS: American Petroleum Institute Standard)

TCXDVN 326-04 or 22TCN 257-2000 Construction and Measurement of Bored Piles

I MATERIALS FOR PILING

1 CONCRETE

Bored piles shall be constructed in accordance with the details shown on the drawings using the class of concrete noted on the drawings and in accordance with Specification - Concrete and Concrete Structures

Concrete shall be mixed and placed in accordance with the applicable provisions of Specification - Concrete and Concrete Structures

2 REINFORCING STEEL

Reinforcement shall comply with the provisions of Specification - Reinforcing Steel

3 TEMPORARY CASINGS

Bored piles shall be excavated with a temporary steel casing through water and upper soil layers 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

4 PERMANENT CASINGS

Permanent casings required for construction purposes shall be of the thickness and length proposed by the Contractor, and shall be of steel grade ASTM A36 unless otherwise approved

Steel casings shall be furnished in appropriate lengths approved by the Engineer

The casings shall be handled and stored in a manner that prevents buckling and other deformation and the accumulation of dirt, oil and paint When placed in the work they shall be free from dirt, oil, grease, paint, millscale and loose or thick rust

5 BENTONITE AND BENTONITE SLURRY (DRILLING FLUID)

(a)Supply

Immediately prior to mixing Bentonite shall be in accordance with Specification DFCP4 of the Oil Companies Materials Association (Drilling Fluid Materials Bentonite), or the American Petroleum Institute Standard 13A

(b)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

II REBAR WORKS

All reinforcement steel shall comply with the requirements of Specification Section 07500 “ Reinforcing steel ”

III CONSTRUCTION OF BORED PILES

1 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 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, mix truct, welding equipment, etc

List of main equipment

Item of work Uni

ts

Num ber Remark

Reverse circulation piling

equipment D1,5m

Reverse circulation piling

equipment D1,0m

Crawler or Moblie Cranes ≥50T nos 02

Crawler or Mobile Cranes ≥25T nos 04

Excavator with bucket capacity ≥

0.7m3

Item of work Uni

ts

Num ber Remark

Sand separation system for

betonite fuid

Concrete Batching Plant 60m3/h nos 02

Main and standby generator nos 02

Set of pipe for cleaning bored

hole

Cutting and bending machine nos 04

2 Construction site preparation

For the abutment, pier on land: remove organic soil and leveling to create construction site

For the pier next to river side: Driving sheet pile system, leveling to create construction site

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

3 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 Benonite 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

Property to be Range of results at

20°C Test method measured

Density Less than 1.10g/ml Mud density balance

(ASTMD4380)

D6910) Shear strength

(10 minute gel

strength)

1.4-10 N/m2 or 4-40 N/m2 Shearometer Fann viscometer

Sand content <4% at time of

introduction Sand content set (ASTM

<2% at pile base prior

electrical

pH meter

4 Drilling hole

a Driving casing

The Contractor uses the temporary steel casing to guide and stabilize the hole wall Using the crane 35 tons in combination with vibration hammer 170 KW and excavation to lower the casing

b Drilling hole

- Use ED rotary 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, 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 which contain workable or unset concrete such that a flow of concrete could be induced from or damage caused to any of the piles Typically, boring of a new pile within three diameters edge to edge should not commence until 24 hours of completion of concreting of the previous pile

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

The bentonite slurry shall be premixed thoroughly with clean fresh water, and adequate time shall be allotted for hydration prior to introduction into the shaft excavation Adequate slurry tanks shall be provided No excavated slurry pits shall be allowed when slurry tanks are required on the project without written permission of the Engineer Adequate desanding equipment shall be provided Steps shall be taken as necessary to prevent the slurry from "setting up" in the shaft excavation, such as, agitation, circulation, and adjusting the properties of the slurry

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 material from pile excavation and waste bentonite shall be in accordance with the Contractor’s approved environmental management plan

Pumping from a bored hole will not be permitted unless a casing has been placed into a stable stratum which prevents the flow of a significant quantity of water from other strata into the bore, or unless it can be shown that pumping will not have a detrimental effect on the surrounding soil or adjacent property

5 Cleaning of bored hole

On completion of boring, loose, disturbed or remoulded soil shall be removed from the base of the pile, using appropriate and approved methods, which may include airlifting, and which shall be designed to clean while at the same time minimizing ground disturbance below the pile base

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 End

of air pipe is laid 10m distance from the bottom of tremie pipe 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)

6 INSPECTION

For a boring without casing, the diameter of the boring hole for a representative number of piles will be measured by calipers prior to the placing of concrete into

it The Contractor’s Quality Control personnel shall do the measurement using approved equipment

The Contractor shall provide an approved means by which inspection of the verticality of bored piles and reinforcement cages can be performed

7 FINAL PILE TOE LEVEL

Where indicated on the drawings or as instructed by the Engineer proposed pile toe levels shall be confirmed by site investigation boreholes (prebores) located at

or near pile positions Boreholes shall be in accordance with requirements and procedures of Specification - Soil Investigation Borings and/or as required by the Engineer Where so required, prebore results shall be submitted to the Engineer,

at least one month in advance of the piling work, to confirm the design of the piles

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

Excavations required for shafts shall be performed through whatever materials are encountered, to the dimensions and elevations in the Contract Documents or ordered by the Engineer The methods and equipment used shall be suitable for the intended purpose and materials encountered The first pile in a group of a pile cap shall be constructed to demonstrate the suitability of construction methods

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

The Engineer will confirm the final pile toe level after his inspection of the earth layers penetrated by the pile

The Contractor shall prepare for carrying out sampling and tests to check bottom soils and excavation geometry

8 REINFORCEMENT

Steel reinforcement shall be fabricated in accordance with the sizes and dimensions shown on the drawings, and shall be placed, centered and braced in the pile hole to the approval of the Engineer

Particular care shall be taken in locating projecting "column dowel bars", with a tolerance not exceeding 10 mm in any direction, and pouring will not be permitted until the Engineer is satisfied that adequate provisions have been made

Adequate "shoes" or spacers shall be firmly anchored to the reinforcement to ensure that the reinforcement is kept centered in the concrete, and the minimum cover requirements as specified on the Drawings are achieved

The Contractor shall include in his construction method for pile construction submitted to the Engineer for his approval, the working drawings and details related to the placing of the reinforcement cage, splicing procedures, measures and equipment to prevent damage to the bored hole and maintain the stability of the bore while the cage is being placed and procedures to control the verticality and consistency of the cage during placing operations

Reinforcement shall not be placed in the complete pile excavation until it has been inspected and approved by the Engineer

9 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