: 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. Introduction
2. Objectives and classification of piles and piling
methods
3. Principle of DMC piling
4. Apparatus used
5. 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 production
The disadvantages of displacement piling are:-
Cannot penetrate obstructions
Cannot always penetrate desiccated clay
Vibration and noise may be an issue
The advantages of replacement piling are:-
Effectively vibration free
Installed into non cohesive and water bearing soils
High production
Restricted access
The 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 450mm
Thickness 50mm
Operation The rope slips over this wheel
or Pulley
SLIP OVER WEEL HOLDER
Diameter = 500mm
S.O. WHEEL PIN
Diameter 65mm
Length 200mm
Operation This is very important pin,
because it holds the S.O.
Wheel with the tripod system
and the entire vertical loads
act on it.
PLUNGE
Inside 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 3
Diesel consumption 2.1 lit/hr 1.75 lit/hr
Mobil consumption 0.5 lit per 7 days 0.5 lit per 7 days
(fresh engine)
Mobil consumption 0.5 lit per 12 hours 0.5 lit per 12 hours
(older engine)
USED IN PUMP (KILOSKER MAKE)
Number of cylinder 2
Diesel consumption 1.25 lit/hr
Mobil consumption 250ml per 12 hours
IV. Bailer or Slush Pump
Length 2700mm
Inside Diameter 450mm
Weight 0.5 Ton
V. Guide casing
Length 2750mm
Inside Diameter 550mm
Thickness of casing 30mm
Thickness of collar 20mm
VI. Chisel or Chopper
Thickness of sheet 80mm
Inside Diameter 400mm
Length 2500mm
Number of nozzle 4
7. DMC rod
Length (m) 2.7 3 3.25
Diameter (mm) 95 75 65
Thread length (mm) 120
Thread type Tapered
ID of tapered king end (mm) 80
ID of queen end (mm) 120
Tapered thread end of DMC rods
8. Rope
Diameter – 20mm
9. Tremie pipe
ID 5 inch
OD 6 inch
Thickness of sheet 12mm
10. Vertical pump
Power source Electrically operated
Power 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.
