Problems in Piling ?

In this article we are going to discuss some more terms related to the process of Piling.
What’s a under ream ?
A SINGLE PILE  [ HAMMER METHOD ]
A SINGLE PILE
[ HAMMER METHOD ]
It is a bulb made on the pile shaft. This type of bulb is called as ” Under-ream ” and it increases the load carrying capacity of piles.
There can be either a single Under-ream or a double under-ream. The single Under-ream piles are designated as SUR and double under-ream  piles are designated as DUR on the drawings. This arrangement is only done in manually augured Piles.
You must be wondering as to how this bulb is dug on the pile shaft at a lower depth ?
There is a special tool for making an Under-ream which cuts the soil and creates the Hollow  bulb.
Diameter of under-ream is generally kept 2.5 times the diameter of the Pile.
For example, for a 12′ diameter Pile, the under-ream diameter shall be 12 x 2.5 = 30 “.


Spacing between 2 piles:

When the capacity of a single pile is not adequate , it may be needed to have more than one Pile under the columns. In such a case, a cluster of Piles is made which may include , depending on the total load , 2 , 3 , 4 or more Piles.
When ever, there is a cluster of Pile, the load is transferred to the individual piles through a Pile cap .
The distance between two adjacent piles shall not be less than 2.5 times the pile diameter.

CLUSTER OF TWO PILES
CLUSTER OF TWO PILES
CLUSTER OF THREE PILES READY TO RECEIVE THE PILE CAP
CLUSTER OF THREE PILES READY TO RECEIVE THE PILE CAP

Water During Piling ?
Often we encounter water during piling.This is sub soil water which seeps through  when the piling is in progress.

As such water is not harmful ,but it loosens the adjoining soil which collapses inside the Pile hole .
In such cases, there are two methods to manage the progress of Piling :
Option 01: Casing pipe:
A casing pile of adequate diameter is inserted into the Pile Hole which retains the soil.
There are practical limitations to casing pipe since it is difficult to  procure the exact diameter of the mild steel casing pipe at a short notice and secondly, it is again difficult to retrieve the pipe from its position after the pile hole is completed.
Option 02: Bentonite slurry.
Bentonite is a chemical powder which stabilizes the cohesive soil.
Bentonite powder is just poured inside the pile hole. This mixes with the water and forms a protective layer on inner surface.
TREMIE READY TO RECEIVE THE CONCRETE. [ Photo source : Unknown from Web .The author extends his gratitude ]
TREMIE READY TO RECEIVE THE CONCRETE.
[ Photo source : Unknown from Web .The author extends his gratitude ]
Use of Tremie:
The concreting in the Piles offers a special challenge.Unlike the columns, the concrete cannot be simply poured from the top of the pile .Because if the concrete is dropped from a height of more than 2.5 meters, it shall result into ” segregation . Segregation happens when sand & aggregate get disengaged from a common bond. the concrete looses its strength.
In such cases, a Tremie is convenient. it is a big size metallic funnel which receives the concrete. There is a long mild steel pipe connected to the funnel. the concrete smoothly travels from the funnel to the pipe and gets slowly deposited on the bottom of the pile shaft. the pipe is lifted slowly as the concrete work progresses upwards.
How it is used ?
Precautions during Piling :
In case of Piles there is a safety hazard of someone falling in the freshly dug pile shaft.
Even in hand augured ,Under-reamed piles, there are cases where a child has fell inside . Due to the small diameter, the rescue is very difficult. Therefore ,it is advisable to follow a policy of ” Dig & cast“.  So, when boring of first pile is complete , immediately put the reinforcement cage inside it and begin the Pile casting. Start a second piling only after the concreting is completed.
If due to rains or some other reason , it is not possible to do concreting , then it must be made compulsory that the Pile hole be covered with strong plates 
Advertisements

2 thoughts on “Problems in Piling ?”

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s