METHOD STATEMENT FOR DRIVEN SPUN PILES

Method Statement for driven of spun piles is generally describes the method used to the installation of  driven precast  with various size diameter of  spun piles Grade 80N/mm2. Under this method statement will describes the procedures of driven piles , penetration or set that is required within the given scope of works. 

 1.0          MATERIALS

The Precast Spun Piles shall be externally purchased and hence when receiving the piles, they must be closely inspected for:-

1.       Type of pile

2.       Lengths of piles

3.       Date/s batched or manufactured

4.       Quality (Cracks, splits, damages etc.)

5.       Straightness (No bow or hog)

6.       Support conditions during transport.

Once accepted, the piles shall be neatly and properly stacked under its designed support conditions.

They shall be serially code-numbered (according to length or date) prior to its use.

2.0          EQUIPEMENT & RESOURCES

i)                    Piling rig

ii)                   7 tonne hydraulic hammer.

iii)                 20 tonnes mobile crane

iv)                 Welding Set

3.0          METHOD

3.1    Setting Out 

Pile setting out shall be carried out jointly with the S.O. and shall include any additional reference points necessary, to enable immediate checking and cross-referencing for any problematic pile positioning.

3.2          Piling Platform 

1.      Pier pile positions shall be installed over a suitable pile installation platform, whether they be on firm ground or on an elevated staging. Any platform/staging established   shall be robust and stable enough to handle weights of piling machine, additional cranes as necessary and the working forces that will develop during pile driving. The platform must be of known elevation to enable the control of pile penetration and/or pile setting when necessary.

4.4          Pile Driving Termination Criteria

1. Pile set shall be decided through a test pile installation.
2. If pile set is the criteria, the required working load shall be agreed and stoppage of pile driving shall be based on Hiley’s pile driving formula. The graphical “set over 10-blow readings” shall be obtained. Subsequent calculation using agreed driving parameters shall determine adequacy of driving.

Hiley formula :

SET = Awh / fL x (W+Pe²) / (W+P) – C/2

Hammer Efficiency                                         A

Mass of Hammer                                             W

Drop of Hammer                                             h

Safety Factor                                                  f

Pile Working Load                                          L

Total Mass                                                       P

Coefficient of Restitution                               e

Temporary Compression                                 C

3.          3. The actual SET values will be recomputed at site based on the variable parameters of actual pile length  installed and the actual temporary compression recorded

4. If pile penetration is the criteria, the outcome of the test pile installation shall be a guide to the required depth of penetration.

4.4      Pile installation

a.            Piles shall be lifted from its stacked position utilizing its two designated lifting points (especially concrete piles). Canvass padded slings shall be used for spun piles.

b.            The toe end of the starter piles shall be pitched/planted to its exact position manually by suspending the pile from its driven end.

c.             With the toe position fixed, the required pile inclination shall then be adjusted to the required angle while the guide rails and required back supports are firmly secured.

d.            Counter checks shall be made through two survey stations, preferably at right angles to each other, to confirm the position at the pile base and inclination of pile shaft. The stations should be situated at least 30m away.

e.            Pile driving shall utilise the most suitable hammer for the purpose of driving the type of pile to the set without damage to the pile head. The type (static, vibration or dynamic), weight and mechanism (diesel, hydraulic etc.) of the hammer shall be approved by the S.O. (Kobe K35 diesel hammer or 7 tonne hydraulic hammer, mounted on P & H 85P piling rig for spun file)

f.             When driving commence, the first few blows and meter of penetration shall be closely monitored to enable any initial deviation to be physically corrected.

g.            Large deviations in terms of position and inclination (in excess of specified tolerances) shall merit an extraction and re-drive at this stage if forcible corrections are not adequate.

h.            For deviations that inevitably occur at deeper penetrations, only measurements in the final set position shall dictate, amongst other factors, the pile acceptance or otherwise.

i.              Where driving depths go below the piling rig’s base level, a suitable dolly or temporary pile extension of known length and material properties shall be used to enable proper computation of the pile set.

4.6          Pile Driving Records

Pile driving shall be recorded through an agreed format and shall detail all the relevant information including times for driving and jointing.

The records shall be comprehensive so as to discount any uncertainty or reservations as to the piles’ integrity to be part of the permanent structure.

4.7          Pile Jointing and Splicing

Piles shall be joined at the specified position using the recommended method or propriety systems as required.

The required setting and hardening times for primers and epoxies, where used, shall be adhered to when pile joints are made, to ensure a safe and effective joint.

When welding  joints, no gaps shall be allowed and full bearing at the connecting plates between the driven and the extended length shall be ensured. Pile driving will then be resumed after the required setting/hardening times for the weld to develop its strength.

 

4.8          Pile Cut-Off

Piles shall only be cut-off after securing the directive and acceptance by the S.O.  This is to ensure that any re-driving work that would be required can still be carried out when such situations warrant.

The value for pile cut-off level must be formally agreed and any piles that need to be ‘brought up’ to the required cut-off level must meet the S.O.’s agreement and guidelines.

Where pile cut-off levels are below ground, excavation sides shall either be sloped or protected by an earth retaining structure to prevent collapse of the excavated pit.

Where pile cut-off levels are below water level, suitable enclosing structures (e.g. cofferdams) shall be installed to exclude water from the works.

4.9   Fabrication of Pile Plug

Stripping of piles and fabrication of pile heads for concrete piles shall be carried out in accordance to the Drawings. The lengths of stripping and reinforcement to be provided shall be adequate to anchor the pile into the pile cap to be constructed.