: PROJECT SITE :

HIDCO CONVENTION CENTRE,

NARKELBAGAN, KOLKATA,

WEST BENGAL

PROJECT UNDERTAKEN BY:

LARSEN & TOUBRO LTD.

The complex at night from the entrance

Plan of the whole project (Schematic diagram)

DMC PILING

PREFACE: The report is prepared after the training and observation done at Project-site of WBHIDCO Convention Centre, being an engineer trainee under Geotreat Ltd. The project is undertaken by Larsen & Toubro Ltd. A part of piling works is being conducted by Geotreat Ltd.

The start date of the construction project was 16.06.2014 & the expected end date is 15.09.2016. Over 2,600 piles are to be constructed among which 500 number of pilling is conducted by Geotreat Ltd. All of them are done by DMC piling methods.

The whole project report is subdivided in the following sections:

1. Introduction2. Objectives and classification of piles and piling

methods3. Principle of DMC piling4. Apparatus used5. Field procedure DMC piling 6. Conclusion

1. INTRODUCTION

Piles are the columnar structure, the most common type of deep foundation, that safely transfer loads from the super structure to more competent subsurface strata by means of friction, end bearing or a combination of both. Piles can be broadly classified based on the following parameters.

1. Method of installation of piles – Driven (displacement) piles or bored (replacement) piles.

2. Type of material used for piling – Concrete, steel, timber piles etc.

Among these, concrete piles can be classified further as pre-cast and cast in situ concrete piles. Though there are a variety of piling options, the most common type of piles used for majority of construction works in India are bored cast in situ concrete piles.

2 . Objectives and classification of piles and piling methods

Functions of piles:

The major uses of piles are:1. To carry vertical compression load, eg. bearing piles,

friction pile. (FIG. 1)2. To resist uplift pressure, eg. tension piles or uplift piles or

anchor piles. (FIG. 2)3. To resist horizontal or inclined loads, eg. Batter piles.

(FIG. 3)

Setting up piles

Depending up on the setting up principle, piles can be of two types, eg. Displacement type and Replacement type, each has its own advantages and disadvantages. For displacement piling

method, piles are driven into the ground pushing the soil out of its way. Displacement piling is good for contaminated sites where it costs a lot to move the soil out. Using the replacement piling method, muck is dug out and replaced with the pile. Much bigger piles can be casted by replacement method.

Direct Mud Circulation (DMC) piling method or simply DMC Piling method is an example of replacement piling method. This method is the principle subject of interest in this report.

The advantages of displacement piling are:- Self testing as driven to refusal or "set" No pile arising to dispose of Little disturbance Limited access High productionThe disadvantages of displacement piling are:- Cannot penetrate obstructions Cannot always penetrate desiccated clay Vibration and noise may be an issueThe advantages of replacement piling are:- Effectively vibration free Installed into non cohesive and water bearing soils High production Restricted accessThe main disadvantage of replacement piling is that:- it produces excavated material which requires removal off site

3. Principle of DMC piling

DMC piling is a typical wash bored piling method, ie. the piles are of REPLACEMENT type. For this type of piling method, the sub soil must be of cohesive nature. The basic principle of DMC piling

lies in the fact that the soil layers becomes harder to penetrate with depth, so to soften the hard soil layers deep below the ground level, water jet streams are used and then a typical chisel cuts the relatively softer soil. Bore holes of several depths (for example 10m, 15m, 20m, 25m, 30m, etc.) and diameter (for example 500mm 750mm, 1000mm etc.) are dug as per design requirements. It can be understood quite clearly that the nearby soil can collapse. To prevent the collapse some special safety measures are considered during the operation which will be discussed in later sections. After the bore hole is dug and the collapse of subsoil around the hole is safely prohibited, a reinforcement cage is entered into the borehole and concrete is filled from the bottom of the hole with the help of pipes, typically designed for this operation, called the Tremie pipes. Usually concrete is left 28 days to harden and gain full strength, but sometimes using admixtures they are prepared within 21 days.

4. Apparatus used I. DMC rig

THE TRIPOD SYSTEM

Main shear leg: it is the longer leg than the other two that carries the load.

The length is 7.5m.

The length can be adjusted. With the help of 20mm dia pins

The side shear legs: there are two side shear legs, 6.3m long and they mainly support the tripod system.

The side legs must be placed at least 1.5m away from the centre of the piles.

BASE CHANNEL

These are standard I section, 2cm thick and there are grooving in it that holds the shear legs onto the ground with the help of base cannel pin.

SLIP OVER WHEEL

Diameter 450mmThickness 50mmOperation The rope slips over this wheel

or Pulley

SLIP OVER WEEL HOLDERDiameter = 500mm

S.O. WHEEL PIN

Diameter 65mmLength 200mmOperation This is very important pin,

because it holds the S.O. Wheel with the tripod system and the entire vertical loads act on it.

PLUNGEInside Diameter = 50mm

SUSPENSION PLATE – this is called into action if somehow the chisel is stuck in the borehole. Pulleys are attached here and the chisel is pulled out.

Suspension Plate

MAIN SHEAR LEG PIN – 20mm dia.

II. Winch

Capacity 3 Ton (Other capacities can be of 1 Ton 2.5 Ton 5 Ton 7.5 Ton etc.)

Driven wheel diameter 900mm

III. Diesel engine

USED IN WINCH (RUSTON MAKE)

Number of cylinder 4 3Diesel consumption 2.1 lit/hr 1.75 lit/hrMobil consumption (fresh engine)

0.5 lit per 7 days 0.5 lit per 7 days

Mobil consumption (older engine)

0.5 lit per 12 hours 0.5 lit per 12 hours

USED IN PUMP (KILOSKER MAKE)

Number of cylinder 2Diesel consumption 1.25 lit/hrMobil consumption 250ml per 12 hours

IV. Bailer or Slush Pump

Length 2700mmInside Diameter 450mm Weight 0.5 Ton

V. Guide casing

Length 2750mmInside Diameter 550mmThickness of casing 30mmThickness of collar 20mm

VI. Chisel or Chopper

Thickness of sheet 80mmInside Diameter 400mmLength 2500mmNumber of nozzle 4

7. DMC rod

Length (m) 2.7 3 3.25Diameter (mm) 95 75 65Thread length (mm) 120Thread type Tapered ID of tapered king end (mm) 80ID of queen end (mm) 120

Tapered thread end of DMC rods

8. Rope

Diameter – 20mm

9. Tremie pipe

ID 5 inchOD 6 inchThickness of sheet 12mm

10. Vertical pump

Power source Electrically operatedPower 10 Hp

11. Bentonite tank and Bentonite slurry The Bentonite tank stores the Bentonite water which is of avg. Density of 1.04gm/cc. The minimum density is 1.03gm/cc and maximum density is 1.05gm/cc

Vertical Pump in Bentonite tank

12. Wash vat This is where the muck mix with water gets stored, the muck gets precipitated and the water becomes reusable.

13. Tremie fork

Used to insert the tremie pipes and taking out DMC rods.

5. Field procedure DMC piling

For executing DMC piling method which is approved as per IS 2911 under specifications of bored cast in situ piles. The positioning of points where the piles are proposed to set up, are checked by the surveyor.

DMC piling Rig set-up and initiation of boring using the Bailer

After the point for boring operation is set out by the surveyor the tripod is paced such that each side legs are at least 1.5m away from the point, keeping the centre of borehole exactly in the centre.

The bailer is then attached with the rope and the boring operation is initiated.

After bailer reaches its full length into the soil, the guide casing is inserted into the hole for farther operations.

Insertion of the guide casing

To prevent the side collapse and caving in, a guide casing of 550mm dia and of 2750mm length is placed on the top of the bore hole and hammered by the bailer to insert it into the soil. This will be withdrawn after concreting is over.

Boring with Chisel

Once the guide casing is placed, the boring is started with chisel.

The chisel has 4 nozzles from where water jet is forced on the hard soil layer as the boring progresses.

Progression of boring and addition of DMC rods

DMC rods are added one after another as the depth increases. The DMC head are attached on top of the DMC rods which has

the plunge which receives the water from delivery hose.

The whole system is pulled up by the rope and the D-Shackle with the help of the winch system and then left to fall free, so that the chisel at the bottom cuts the soil and the boring progresses.

The loose soil produced by boring, mixes with water and comes up and is stored in the wash vat, where the soil gets precipitated and the water is again usable.

Taking out of the DMC rods and Chisel and Insertion of the reinforcement cage

After the boring is complete up to the desired depth, the DMC rods are removed one by one using the DMC fork and the chisel is also removed.

Then the steel reinforcement cage is inserted and welded where ever there are joints.

Concreting and finalization of the process

The tremie pipes are inserted one by one using the Tremie fork and then the bore hole is washed with the Bentonite water and the Muck is completely removed and the hole is filled with bentonite slurry.

The Transit mixer arrives and the Hopper is attached on top of the tremie pipe.

The TM puts concrete mix into the hopper and the valve opens. The bore hole is gradually filled with concrete which is

compacted by gradual vibration of tremie pipes. This filling of concrete from the bottom is done to avoid segregation of the concrete mix.

As the concrete fills the hole from bottom, Bentonite slurry escapes the hole. The tremie pipes are detached one by one and thus the hole gets filled completely.

After the hole is fully filled, the concrete is left 28 days to gain full strength. After 28 days the guide casing is removed and the pile is ready.

Concreting

6. Conclusion

DMC piling is the most common piling methods used in India. For moderate sized piles, that is 450mm to 1000mm diameter and 25m to 30m depth piles; it is also most convenient and economic way of piling. Larger piles that are of diameter up to 1500mm can also be founded by this method, but those are not that convenient. Other process like Reduced Mud Circulation (RMC) is also in use.