2) Pile Execution Method

Classification of piles based on execution method

Pile Foundation: Execution methods • Piles can be executed either - by driving or by boring • Driven piles are those formed by driving precast piles and those made by casting concrete in a hole formed by driving. • Bored piles are those formed by casting concrete in hole previously bored or drilled in the subsoil.

Driven Piles

Drilled/Bored Piles

Driven piles • Pile driving is the process by way of which a pile is forced or driven into the ground without excavation or boring • Driven piles are considered to be displacement piles. In the process of driving the pile into the ground, soil is moved radially as the pile shaft enters the ground. There may also be a component of movement of the soil in the vertical direction. • There are several types of pile driving method in the piling construction, type of pile driving method used is depending on the condition of soil and location of the site. However, different piling machine will be used with different pile driving methods too.

• Generally Piles are driven by means of a hammer supported by a crane or by a special device known as a pile driver. • The hammer is guided between two parallel steel members known as leads. • The leads are carried on a frame in such a way that they can be supported in a vertical position of an inclined position. • Driving hammers are of the following types: 1. Drop Hammer 2. Single acting hammer 3. Double acting hammer 4. Diesel hammer 5. Vibratory hammer

Driven Piles

• Driven piles are either wood, reinforced concrete, or steel. • Wooden piles are made from trunks of tall trees.

• Concrete piles are available in square, octagonal, and round cross-sections. They are reinforced with rebar and are often prestressed. • Steel piles are either pipe piles or some sort of beam section (like an H-pile). • Driving piles, as opposed to drilling shafts, is advantageous because the soil displaced by driving the piles compresses the surrounding soil, causing greater friction against the sides of the piles, thus increasing their load-bearing capacity.

Bored piles • Bored piles (Replacement piles) are generally considered to be non- displacement Piles: a void is formed by boring or excavation before piles is produced. • Piles can be produced by casting concrete in the void.

• Some soils such as stiff clays are particularly amenable to the formation of piles in this way, since the bore hole walls do not requires temporary support except cloth to the ground surface.

• In unstable ground, such as gravel the ground requires temporary support from casing or bentonite slurry. Alternatively the casing may be permanent, but driven into a hole which is bored as casing is advanced. • A different technique, which is still essentially nondisplacement, is to intrude, a grout or a concrete from an auger which is rotated into the granular soil, and hence produced a grouted column of soil. • There are three non-displacement methods: bored cast- in place piles, particularly pre-formed piles and grout or concrete intruded piles.

The following are replacement piles: • Augered • Cable percussion drilling • Large-diameter under-reamed • Types incorporating pre caste concrete unite • Drilled-in tubes • Mini piles

Drilled/Bored piles •

Also called drilled piers or Cast-in-drilled-hole piles (CIDH piles) or Cast-in-Situ piles. Rotary boring techniques offer larger diameter piles than any other piling method and permit pile construction through particularly dense or hard strata. Construction methods depend on the geology of the site. In particular, whether boring is to be undertaken in 'dry' ground conditions or through water-logged but stable strata - i.e. 'wet boring'.

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Boring is done until the hard rock or soft rock layer is reached in the case of end bearing piles. If the boring machine is not equipped with a rock auger, then socketing of the hard rock layer is done with the help of a heavy chisel which is dropped from a height of about 1.5 metres (depends on the weight of the chisel and design requirements) by suspending it from a tripod stand attached to a winch crane. The socketing is carried out until the desired depth within the rock layer has been attained. Usually, the required depth within the rock layer is considered to be equal to the diameter of the pile in hard rock layers and is taken to be equal to 2.5 times the diameter of the pile in soft rock layers.

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'Dry' boring methods employ the use of a temporary casing to seal the pile bore through water-bearing or unstable strata overlying suitable stable material. Upon reaching the design depth, a reinforcing cage is introduced, concrete is poured in the bore and brought up to the required level. The casing can be withdrawn or left in situ.

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'Wet' boring also employs a temporary casing through unstable ground and is used when the pile bore cannot be sealed against water ingress. Boring is then undertaken using a digging bucket to drill through the underlying soils to design depth. The reinforcing cage is lowered into the bore and concrete is placed by tremmie pipe, following which, extraction of the temporary casing takes place.

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The reinforcement cage may need to be lapped with another cage if the depth of the pile exceeds 12 metres as that is the standard length of reinforcement bars of diameter 16mm and above.

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In some cases there may be a need to employ drilling fluids (such as bentonite suspension) in order to maintain a stable shaft. Rotary auger piles are available in diameters from 350 mm to 2400 mm or even larger and using these techniques, pile lengths of beyond 50 metres can be achieved.

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Such piles commonly fail due to the collapse of the walls of the shaft resulting in the formation of a reduced section which may not be able to bear the loads for which it had been designed. Hence at least a third of piles in projects with a large number of piles are tested for uniformity using a "Pile Integrity Tester". This test relies on the manner in which low intensity shock waves are affected as they pass through the pile and are reflected to judge the uniformity and integrity of the pile. A pile failing the integrity test is then subjected to a pile load test

Drilled Piles

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Bored pile is a cast-in-place concrete pile where the bored piles have to be cast on construction site. Bored piling is cast by using bored piling machine which has specially designed drilling tools, buckets and grabs, it’s used to remove the soil and rock. Normally it can be drilling into 50metres depth of soil. The advantage of bored piling is its’ drilling method, little vibration and lower noise level. Usually bored pile is used for those tall buildings or massive industrial complexes, which require foundations which can bear the load of thousands of tons, most probably in unstable aor difficult soil conditions. The method of drilling bored pile is different from RC Square pile or spun pile which are using driving method, the piling machine to be used will be different too. Bored piling works required specialist bored piling contractor to follow up instead of hiring general piling contractor. There is a simple step-by-step method on how to drill the bored pile in construction site.

How To Drill Bored Pile?

Bored Piles Construction – How Bored Piles Are Drilled

1.The first step is to drill a hole of the require diameter into the ground. 2.When the design depth or foundation bearing layer is reached, drilling stopped. 3.The hole is then cleaned. 4.Steel reinforcement cage is lowered into the hole. 5.Concrete is then poured into the hole until the designed cutoff level of the pile. 6.After Step5, the construction of bored pile is completed. Thus it can be seen that bored piles are constructed by first drilling into ground. Drilling is one of the most important step in bored pile construction. Only successful drilling can lead to the next construction step to be carried out. Thus drilling requires experience and the use of the right tools and equipment.

1) Adjust the piling machine on the pile axis2) Start drilling until the auger is filled. and haul with the auger to the drilling place.

3) Return from the drilling level to the top of the pile hole

4) Swing to the uploading area.

5) Unload the dirt in the unloading area

7) Relocate the machine and start steps 1 to 6 Repeat steps 2 to 7 until the pile is completely drilled.

6) Swing back to the top of the hole

8 ) Start erecting rebar cage using a crane.

9) Use funnel for dry method and tremie for wet method. Start pouring the concrete and finish the pile

Drilling methods for bored piles The drilling method is depending on the condition of soil, piling contractor has to do soil investigation and decide which drilling technology has to be carried on. Piling contractor decide the correct drilling technology and minimize disturbance of the surrounding soil. For cohesionless soils such as sands, gravels, silts etc, whether it’s under the water table or not, the pile bore hole must be supported using steel casing or stabilizing muds such as bentonite suspension. After these, reinforcement bar will be put into the bore hole and concrete will be poured into the bore hole.

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Bored piles can be drilled by using an auger ( see attached picture of an auger) that is powered mechanically. There will be an auger attached to a the tip of a telescopic Kellybar.

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Telescopic means the Kellybar is extensible, there by enabling drilling to greater depths.

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Drilling rigs can be crane mounted or as a single unit known as rotary drilling rig. Both of which is discussed in greater details below.

Crane Mounted Drilling Rig •

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The drilling rig is a power unit that rotates the Kellybar which in turn rotates the auger. The power unit is normally diesel powered. The Kellybar is slotted through the power unit at the front end known as the “Table”. Horizontal rotation of the diesel engine is converted to vertical rotation which rotates the Kellybar. There is also a pair hydraulic arms at the “table”. These arms can clamped to the Kellybar and are use to raise or lower the the it slowly over a short lenght. Rotation can be either anticlockwise or clockwise. The whole power unit, Kellybar and auger assembly is then mounted onto a base crane. Drilling starts by pressing and rotating the auger at the same time. Once the initial hole is formed and depending on the soil material, the weight of the Kellybar pushes the drilling deeper. The Kellybar is raised and lowered into the hole by a separate lifting cable of the base crane. This enables the Kellybar and auger to be lifted up quickly to the surface to dispose of the drilled material and later lowered back again to the hole to continue drilling. This processes is repeated until the desired depth is reached.

Name of Parts 1 KellyBar 2 Auger 3 Diesel Powered Drilling Rig 4 Base Crane 5 Table 6 Hydraulic arms

Crane Mounted Drilling Rig • A crane mounted rig requires on site assembly and requires the help of another crane to mount and set up. As for rotary drilling rigs, there is no such requirement. • Once mobilized to site it is just a matter of raising up the leader , attached the auger and drilling can start.

The drilling rig can also be mounted onto a heavy truck like what is shown in the picture.

Rotary Drilling Rigs •

A compact design in which the drilling rig is permanently mounted onto a crawler unit. The drilling rig is hydraulic powered giving it a very powerful drilling capability. The drilling process is the same as what is mentioned above.

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However rotary drilling unit is easy to deploy. There is no setting up required compared to crane mounted drilling rig.

Drilling by Using Continuous Flight Auger •Drilling of bored piles can also be carried out by using continuous flight auger (CFA). CFA is used when bored piles depths are fixed and the diameter not larger than 1500mm. The construction of bored piles using CFA is different from the auger and Kellybar drilling. •The major difference is this, when the bored pile desired depth is reached, the hole can be filled by injecting concrete down the hollow stem of the CFA. In this way the bored pile is concreted as the auger is slowly raised.

• After completing the concreting and the auger had been removed, a reinforcing cage is pushed down the shaft while the concrete has not set. It is not uncommon to push down cage length of 12m. Thus it can be seen that the final steps of bored piles construction by CFA is different from the Kellybar and auger process. • However if the drilled hole depth is shallow and the ground stable ( the drilled hole does not collapse), the CFA can be completely removed. In this case, the concreting can be carried out like those of the Kellybar and auger method. • Modern drilling rigs can drill bored piles of diameters ranging from 600mm to 4000mm. Due to the convenience of the rotary drilling rigs, they have become more common nowadays as compared to the crane mounted drilling rigs. Rotary drilling rigs are self-mounting and also easily transportable. On the whole this capability which reduces cost of mobilization.

Sometime referred to as drilled piers, bored piles are cast-in-place piles ranging from 600mm to 6000mm in diameter with depth that can reach down to 100 meters. Bored piles are installed by first removing the soil by a drilling process and then constructing the pile by placing concrete in the hole. The simplest form of construction consists of drilling an unlined or unprotected hole and filling it with concrete. Complications that may arise such as difficult ground conditions and the presence of ground water have led to the development of special drilling technologies. The choice of the correct drilling technology must be done in a way as to minimize disturbance of the surrounding soil. For cohesionless soils (sands, gravels, silts), whether under the water table or not, the pile borehole must be supported using steel casing or stabilizing muds such as bentonite suspension.

2.5 m diameter off shore piles for Del Pan Bridge

Off-shore piles for LRT-1 bridge crossing Pasig River

Driving of steel casing for Aloragat Bridge bored piles

Grouping of piles and Pile caps: • • •

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Piles may be used to support pad, strip or raft foundation. Normally, pile foundations consist of pile cap and a group of piles. Where a group of piles is used to support a column or pier base. The individual piles are spaced and connected to the pile cap or tie beams and trimmed in order to connect the pile to the structure at cut-off level, and depending on the type of structure and eccentricity of the load, they can be arranged in different patterns. The load from the column or pier is transmitted to the piles through a concrete pile cap which is cast over the pile. The pile cap distributes the applied load to the individual piles which, in turn,. transfer the load to the bearing ground. To provide structural continuity the reinforcement of the pile caps through starter bars protruding from the top of the cast in situ piles or through reinforcement exposed by breaking off the top concrete from precast piles.

•Figure bellow illustrates the three basic formation of pile groups.

Figure 2-1 Basic formation of pile groups Q = Vertically applied load H = Horizontally applied load

Single Piles

Pile Groups

Vertical And Raked Piles

Piled Wall

SELECTION OF THE TYPE OF PILE • Different types of piling have been devised to suit different ground conditions. • Hence the nature of the ground, where the piling operation is to be carried out, determines to a large extent the choice of type of pile to be used.

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The other important factors in this regard: The nature of the structure. Loading conditions Elevation of the ground water level with respect to the pile cap. Probable length of pile required. Availability of materials and equipment. Factors which may cause deterioration of pile Probable cost of pile.