Bored Piling Construction Methodology

NARRATIVE BORED PILE CONSTRUCTION METHODOLOGY

(this is specific Bored pile Methodology in one of our bridge foundation piling works)

                                                By : Dionysus Maguayan

The Technology of Bored piling is basically very simple and consists of the following operations:

a. Location Setting Out and Referencing

The ground must be level or undisturbed before setting out the center points of the bored pile location. This prevents difficulty in placing center marks.  This also ensures convenience in the positioning of the equipment such that incidents of overturning and the like are prevented. 

b. Driving of Permanent Casing

After the center marks have been established, the permanent steel casing will be driven. The steel casing is used so that the topsoil, which carries overburden loads such as the equipment weight, excavated soil and others, will not collapse. The steel casing also serves as guide for the drilling bucket and to make sure that the center of the hole will not move.

c. Boring/Drilling Vertical Hole

For boring a hole, an RT3-S rotary drilling machine will be used. The machine is mounted on a LINKBELT Crawler Crane Capacity 45 Ton Model LS-1O8-BJ.  Before the start of drilling, we make sure that the kelly bar attached to the drilling machine is vertical to ensure that the drilled hole is precisely perpendicular to the level ground.

d. Cleaning of Bored Hole

After drilling the vertical hole, the drilling bucket will be replaced by a cleaning bucket. This process will ensure that the bottom of the hole is free from settled silt or loose materials.  Initially, these settled loose materials came from the suspended materials acquired during drilling.

e. Fabrication and installation of rebar cages

The fabrication of reinforcing bar cages is done by segments. The fabrication is composed of making spiral ties, stiffening ring, and spacers. After fabricating the stiffening ring, the vertical bars will be welded around the ring forming the rebar cages.  Then, the spiral ties will be installed depending on the specified pitch or spacing.  These are tied to the vertical bars by means of the common wire.  Lastly, the spacers will be attached on the segmental fabricated rebar cages. The completed cages will be ready for installation after cleaning the bored hole. The splicing of segmental cage is performed after the first segment is brought down the hole.  Welding works will follow to execute the splicing of the cages.  This process is repeated until the last segment is installed.

f. Pouring of Tremie Concrete

The first step is to position the platform centered to the bored hole.  Placing the tremie pipes reaching the bottom of the hole follows this.  After finishing the set-up, a cloth, sack or any light material will be placed at the chute.  This means that the first concrete that reaches the bottom will be the first concrete to come out of the bored hole.  Tremie pipes will be maintained embedded to fresh concrete at minimum of two (2) meters and a maximum of six (6) meters. Extraction of tremie pipes is done if the embedment reaches maximum but before extracting, tamping is performed.  After the tremied concrete reaches the pile head elevation, an extra length of at least two (2) meters is added to the pile head.  This is done so that dirty concrete will come out, thus, assuring that the pile head has pure fresh concrete.

 

BRIDGE BORED PILING WORKS 

Pictures of Bored piling works (not in chronology)

Settting Out and installation/driving of temporary steel casing

 Bore-hole drilling

Slurry (bentonite) preparation or (depending on soil conditions)

 Tremie pipe concreting (tremie pipe in the bored hole)

 Ultrasonic testing(using embedded 2" pipe)