Concreting of bored piles marks the final stage of of the construction. Once the required depth or design depth is drilled the drilling stops. The drilling auger is then changed into a cleaning bucket to clean up any loose debris left at the bottom of the hole. This process will take place for a few times until the bottom is reasonable cleaned.
Cleaning bucket can be used in both dry holes and holes under drilling fluid. In some instances, an inspection of the base will be required in large diameter dry holes. This will be done manually by lowering a competent inspector down the hole. This process can be dangerous and it would be better to send cameras down. In fluid filled hole, inspection will not be possible, but the drilling depth will be continued to be monitored for any soil collapse.
Lowering of Reinforcement cage
When all is fine, the reinforcement cage is lowered into the drilled hole. Sometimes the cage does not go down all the way thus it will need to be suspended at the top. There are designs where the cage goes all the way, ie as in tension piles, thus there is a need to provide a clearance between the bottom of the cage and the bottom of the hole. Round spacers are used to spaced out the cage from the soil surface.
When the reinforcement cage is in, the next phase is to lowered in the tremie pipe. In a wet hole the tremie pipe is installed all the way down. However if it is a dry hole, the tremie pipe will be install 1/3 to 1/2 of the drilled depth. A tremie pipe is used to allow concrete ( tremie mix) to be poured right to the bottom of the bored piles without segregation. This is it when the cement and stones separated during a free falling situation.
By this time the concrete truck will have arrived at the site , once the cubes taken and slump test done and passed, the truck will then proceed to the respective bored piles and poured out the concrete. The concreting process duration is dependent on the size of the piles. After each pour, the depth of the concrete rise is determined by lowering a measuring tape. Every so and then, small sections of the tremie pipe is removed during the concreting process.
During concreting, the drilling fluid in the hole is also displaced, this fluid is pumped back to the storage silos for reuse or to be de-sanded when it becomes to contaminated with drilling debris of fine sand, silt, etc.
Once the process of concreting is completed, any casing used is taken out by using a vibratory hammer and the area cordoned off to indicate a freshly concreted pile. The tremie pipes are cleaned and ready for another concreting session. During all this, a service crane is used with an excavator standing by for general light lifting.
Dry hole concreting of Bored Pile
Wet hole concreting of bored pile
As can be noted from the above 2 photos, once can tell what types of concreting is being done. In the wet hole situation, drilling fluid is being displaced why none is observed in the dry hole situation. A sump pump is always used in wet hole situation as can be seen there is a pump head next to the bored pile casing in the wet hole concreting. Judging from the picture, well a dry hole working environment is preferred as the work site will not be turning up messy.
Round Spacers used along the reinforcement cage
And this is what I meant about using round plastic spacers. These are hardy, consistent and easily installed. It is sage too if anyone of the space is dislodged. Using this is preferred to own fabrications of concrete spacer cast on site.