DMC piling method procedure

DMC piling method procedure

Direct Mud Circulation method of pile foundation installation is used for bored cast in-situ piles. Direct Mud Circulation method is best suited when working-space is a huge constraint. In Industries and power plants where there is a labyrinth of pipelines snaking all around, DMC comes to the rescue.

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 precast
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

   

•      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.

SLIP OVER WHEEL 

•      SLIP OVER WEEL HOLDER

Diameter = 500

•      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.

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.

                                                              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

II.       Diesel engine •      USED IN WINCH (RUSTON MAKE)

Number of cylinder	4	3
Diesel consumption	2.1 lit/hr	1.75 lit/hr
Mobil 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	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

7.                          Rope 

Diameter – 20mm

8.                          Tremie pipe 

ID	5 inch
OD	6 inch
Thickness of sheet	12mm

9.                          Vertical pump  

Power source	Electrically operated
Power	10 Hp

10.                   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

7.                          Wash vat

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

8.                          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.

Ø 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.

     

        Ø         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. 

Ø 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. 

Ø 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.

Ø  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. 

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.