PROBLEMS IN BOREDPROBLEMS IN BOREDPILE PILE

CONSTRUCTION CONSTRUCTION

PRESENTED BY:PRESENTED BY:

MUHAMMAD NAVEEDMUHAMMAD NAVEED

2007-MS-GEO-052007-MS-GEO-05

SCOPESCOPE

1. EXCAVATION OF PILE BORE

2. DESIGN AND LOWERING OF PILE REINFORCEMENT

3. CONCRETING THE PILE

TABLE OF CONTENTSTABLE OF CONTENTS

1.EXCAVATION OF PILE BORE

1.1 DRY DRILLING OF PILE BORE

1.2 WET DRILLING OF PILE BORE

1.3 OVERBREAK

1.4 BASE OF BOREHOLE

1.5 EFFECT OF WATER IN BOREHOLES

2.DESIGN AND LOWERING OF PILE REINFORCEMENT

2.1 DESIGN OF PILE REINFORCEMENT

2.2 LOWERING OF PILE REINFORCEMENT

3. CONCRETING THE PILE BORE

3.1 QUALITY OF CONCRETE

3.2 PLACING OF CONCRETE

3.3 EXTRACTING TEMPORAEY CASING

3.4 PROBLEMS IN SOFT GROUND

1.EXCAVATION OF PILE BORE

1.1 DRY DRILLING OF PILE BORE HOLLOW BUCKET TYPE AUGER/CONTINUOUS

SUITABLE FOR STIFF TO V. STIFF/MEDIUM DENSE SOIL

SUITABLE ONLY WHEN W/T IS DEEP

1.2 WET DRILLING OF PILE BORE BY REVERSE ROTARY METHOD OF DRILLING

SUITABLE FOR ANY TYPE & CONSISTENCY OF STRATA

SUITABLE FOR ALL W/T DEPTHS

WET DRILLING BY REVERSE ROTARY

1.3 OVERBREAK

The formation of cavities outside the nominal diameter of the pile is known as overbreak as shown in Fig.:

It may occur in cohesion less soil below W/T

Reduces Skin Friction & End Bearing

May overcome by using Temporary Casing or drilling under bentonite drilling fluid

OVER BREAK

1.4 BASE OF BOREHOLE1.4 BASE OF BOREHOLE

To develop the available end bearing it is essential that bottom of borehole is clean and undisturbed.

IN CLAYEY SOILS

IN SANDY SOILS

To avoid the falling of debris, cover the borehole properly before concreting

1.5 EFFECT OF W/T1.5 EFFECT OF W/T

In dry drilling of borehole ingress of small quantity of water from sides of the borehole reduces the Skin Friction and from the bottom of borehole reduces the End Bearing.

In this condition concreting should be carried out with Tremmie Pipe otherwise segregation of concrete may occur as shown in Fig.

SEGREGATION OF CONCRETE

2. DESIGN & LOWERING OF PILE

REINFORCEMENT

2.1 DESIGN OF PILE REINFORCEMENT

The major problem in design of pile reinforcement is its detailing.

A minimum spacing of 100mm is required otherwise concrete will not flow outside the cage & proper cover could not be provided.

A few large diameter bars are preferred in place of small dia bars

This problem is visible during concreting when cage drags downward into the borehole.

SPACING DRAGS DOWNWARD

2.2 LOWERING OF PILE REINFORCEMENT

The steel cages should be lowered after providing proper laps so that there will no slippage of cages while lowering.

When weight of cages is more in deep piles, cages should be welded at the laps before lowering as shown in Fig.

LAP OF CAGE

3. CONCRETING THE PILEConcreting of cost-in-situ piles is a special operation and it requires considerable skill and correct concrete mix design.

3.1 QUALITY OF CONCRETE

Mixes are designed having sufficient workability so that they are self compacting and should not on falling.

Slump test in field is adequate to asses the former properties.

To achieve above use

1. Rounded Aggregates

2. High Sand Content

3. Plasticizers

Super plasticizers should not use because this reduce the setting time of concrete.

SLUMP TEST

3.2 PLACING OF CONCRETE3.2 PLACING OF CONCRETE The concrete is placed in boreholes using The concrete is placed in boreholes using tremmie tremmie pipepipe to to avoid segregation & impinging of avoid segregation & impinging of concrete on the sides of the concrete on the sides of the borehole. borehole.

The concreting The concreting process should be continuousprocess should be continuous and and completed completed without any break. without any break.

The tremmie pipe should be atleast The tremmie pipe should be atleast 1.5m embedded1.5m embedded in in concrete during concreting process otherwise concrete during concreting process otherwise bentonite bentonite mixes in concrete and results in the mixes in concrete and results in the weakness of the pile weakness of the pile shaft.shaft.

If If slight delaysslight delays occur b/w batches then cement slurry occur b/w batches then cement slurry comes comes over surface and causes weakness of the over surface and causes weakness of the pile shaft.pile shaft.

If If prolonged delaysprolonged delays occur b/w batches then so that concrete occur b/w batches then so that concrete has has reached their final setting timereached their final setting time

Overflow of concreteOverflow of concrete should be sufficient otherwise should be sufficient otherwise bentonite bentonite remains in concrete which weakens the pile remains in concrete which weakens the pile shaft as shown in Fig.shaft as shown in Fig.

OVERFLOW OF CONCRETE

3.3 EXTRACTING TEMPORARY CASING

After concreting, extraction of temporary casing can create problems particularly if delays occur and partial separation of pile shaft may occur as shown in Fig.

This is due to

Use of dirty and dented casing.

Delay in extracting.

Use of poor workable mix.

CONDUCTOR PIPE

3.4 PROBLEMS IN SOFT GROUND

In soft ground having undrained shear strength less than 15kn/m2 causing the squeezing of the pile section near the head because lateral pressure of soil is more than the lateral pressure of concrete as shown in Fig.

SQUEEZING OF THE PILE SECTION

CONCLUSIONSFull time supervision of pile construction should be carried out by an experienced Engineer which gives us the designed pile capacity

THANKSTHANKSTHANKSTHANKS

THANKS

ANY QUESTION?