Foundation Part 02

Excavation For Pile Cap

Shoring is provided around the proposed pile cap with 600mm working space. Excavation is carried out up to certain level by using backhoe. Then excavation was carried out manually. Excavation is very difficult below ground water level. De watering system should be provided.

Excavation With Jcb

Shoring Is Provided

Difficulties in excavation below the ground water level.

• Difficult to remove the soil
• Need continuous de watering process
• Density of soil will increased
• Erosion or collapse of the sides of the excavation

Pile Hacking

Pile is casted up to above required level. Then it is broken up to required level. This is known as pile hacking. Top concrete is weaken so pile should be casted above required level. Normally height above required level, it is equal to the diameter of the pile. But during the concreting ensure the concreting whole pile, normally concreting the ground level. Then excavate soil and pile should hacking required level.

 

Pile Hacking Process

Pile was hacked by using Air breaker. Pile hacking can be carried out by using two methods.

1) Start to pile hack from top of the pile.

2) Break at above required level.

Second method is suitable for if large length to be hacked. For other cases first method is used. In second method pile is hacked horizontally up to reinforcement gage at just above required level. Then pile is connected to the crane. Reinforcement bars are cut. And small force is applied horizontally by crane or JCB. At this stage pile should break fully. To reference the pile cutting level the cutoff level marked on existing reinforced bar of pile.

There were used main three of tools to hacking piles. All are working with air compressor.

1. Driller – To making hole on pile, it make crack along the hole

2. breaker - To break the pile components as small peaces

3. chipper - To level the break surface

Pile Breaking With Breaker

Eccentricity Of Pile

After the hacking piles the eccentricity of piles was taken. Actual co-ordinate of the centre of the pile sometimes, which may vary from co-ordinate, which is according to the drawing.

Eccentricity of pile = (Actual co-ordinate) – (co-ordinate according to the drawing)

Determination Of Centre Of Pile

The geometrically method as shown in the figure, pile center was obtained most possible position. Most of times the casted pile or reinforcement cage of pile not in actual circle, but we were take the most probable circle shape in cut surface

Plan view of pile

If pile is regular shape, we find centre of pile by triangulation method.

If pile is irregular shape, we find centre of reinforcement gage by triangulation method.

Pile Caps

Pile caps are usually constructed of concrete to such depth as will ensure full transfer of load to piles, at the same time, resist punching shear. Since it is almost impossibility to bore or drive piles exactly vertical. The pile cap should be large enough in plan to accommodate any deviation in the final position of the pile heads.

Concreted Pile Cap

  Section Of Pile Cap

Pile Cap Re- Design

Sometimes piles are not installed at correct position. That deviation is over to allowable limit that make additional moment in the structure. Due to above problem pile cap dimensions have to re-design. In our site the pile cap F6 2P1A of piles are shifted over the allowable limit. Therefore its pile cap was redesigned.

Re-bar arrangement and spacing between bars are not changed. Additional reinforcement is taken by pro-rata basis from earlier one.