Rotary Bored Piling Specialists

Extraction Of Pile Casings & Support Of Pile Reinforcement Cages


Purpose & Scope

The purpose of this procedure is to define the risks which may be present during the extraction of casings and specify the control measures to eliminate those risks and will cover;

Risk to the reinforcement being displaced by sinking into the wet concrete.

Risk to the integrity of the pile shaft

Procedures

Step 1 /3


Risk of the reinforcement being displaced by sinking.

Once the reinforcement cage has been placed into the pile bore, suspended and concreted in accordance with the procedure.  Then the casings must be removed in a manner which avoids the cages sinking.  The cage sinking is particularly a risk when cage length and casing length are similar.

There are two approved methods for supporting the cages:

 

  • Method 1:     Cage extension legs, this is the extension of the reinforcement cage at the base by additional bars such that the cage itself can be taken on the base of the pile (See FIG 01)

  • Method 2:     Cage Hanging “Tel tale” bars, (FIG 02) These are extension bars at the top of the cage which may be used to support the cage weight by external means e.g. a crane or excavator.

 

The method which MUST NOT be used is the use of disposable straps which are then left in place.

 

 

 

 

 

Procedures

Step 2 /3


On completion of first stage concreting, casings will be removed with a Casing Extractor (FIG 03) which will be placed over the casing with the attendant crane or piling rig.  The attendant crane will then be attached to the top of the casing.

 

The casing extractor will then be clamped around the casing and the leg rams extended to “jack” the casing out of the ground.

 

At the end of the legstroke the attendant crane will take up the slack in the attached chains, so when the clamp is opened the weight of the casing does not take it back down.  The clamp is then opened and the leg rams retracted.

 

This process is repeated until the casing joint is above the top of the extractor body, the extractor leg rams retracted and the clamp is closed.  The casing plugs can be removed and the casing split with the casing joint popper. The attendant crane can then remove the casing.

 

This process is followed until all the casing is removed from the pile.

Procedures

Step 3 /3


Integrity of the pile shaft

The pile shaft is formed from fluid concrete and as such may be easily damaged whilst it is in a fluid state, or at the stage where it is just set before achieving any strength.

 

Whilst the concrete is fluid, if the ground water level is higher that the concrete level in the bore, then ground water may be forced into the concrete from the surrounding strata thereby damaging the concrete

 

During the extraction of the casing, the concrete level MUST be above the water level at all times, and the concrete shaft must finish above the water level irrespective of what the final cut off level might be.

 

Even when the ground water level is lower than the level of the concrete, the concrete must always be maintained to a minimum of 2.0m above the bottom of the casing (up to the point of reaching the finished cut off level, when it may be reduced)

Get In Touch


For more information about our services and how we can help you with your projects, please call us on 01476 570781 or leave us a message below.