PILE FOUNDATION and METHODS OF INSTALLING PILE FOUNDATIONS

Pile foundation, Uses, Types pf Pile Foundation, Methods of Installing Pile Foundation, Pile Driving Equipments

1. PILE FOUNDATION & METHODS OF INSTALLING PILE FOUNDATIONS Shivananda Roy

2. PILE FOUNDATION Pile foundation, a kind of deep foundation, is actually a slender column or long cylinder made of materials such as concrete or steel which are used to support the structure and transfer the load at desired depth either by end bearing or skin friction . They are formed by long, slender, columnar elements typically made from steel or reinforced concrete, or sometimes timber. A foundation is described as 'piled' when its depth is more than three times its breadth . Pile foundations are usually used for large structures and in situations where the soil at shallow depth is not suitable to resist excessive settlement, resist uplift, etc.

3. When to Use Pile Foundation When the groundwater table is high. Heavy and un-uniform loads from superstructure are imposed. Other types of foundations are costlier or not feasible. When the soil at shallow depth is compressible. When there is the possibility of scouring, due to its location near the river bed or seashore, etc. When there is a canal or deep drainage systems near the structure. When soil excavation is not possible up to the desired depth due to poor soil condition. When it becomes impossible to keep the foundation trenches dry by pumping or by any other measure due to heavy inflow of seepage.

4. Types of Pile Foundation

5. Types of Pile Foundation Sheet Piles Usually , they resist lateral pressure from loose soil, the flow of water, etc. They are used for cofferdams , trench sheeting, shore protection, etc. They are not used for providing vertical support to the structure. They are usually used to serve the following purpose- Construction of retaining walls. Protection from river bank erosion. Retain the loose soil around foundation trenches. For isolation of foundation from adjacent soils. For confinement of soil and thus increase the bearing capacity of the soil. Load Bearing Piles This type of pile foundation is mainly used to transfer the vertical loads from the structure to the soil. These foundations transmit loads through the soil with poor supporting property onto a layer which is capable of bearing the load.

6. Types of Pile Foundation End Bearing Piles The loads pass through the lower tip of the pile. The bottom end of the pile rests on a strong layer of soil or rock. Usually, the pile rests at a transition layer of a weak and strong slayer. The total capacity of end bearing pile can be calculated by multiplying the area of the tip of the pile and the bearing capacity of at that particular depth of soil at which the pile rests. Friction Pile Transfers the load from the structure to the soil by the frictional force between the surface of the pile and the soil surrounding the pile such as stiff clay, sandy soil, etc. Friction can be developed for the entire length of the pile or a definite length of the pile, depending on the strata of the soil. The surface area of the pile multiplied by the safe friction force developed per unit area determines the capacity of the pile.

7. Types of Pile Foundation Timber Piles Timber piles are placed under the water level. They last for approximately about 30 years. They can be rectangular or circular in shape. Their diameter or size can vary from 12 to 16 inches. The length of the pile is usually 20 times of the top width. They are usually designed for 15 to 20 tons. Additional strength can be obtained by bolting fish plates to the side of the piles. Steel Piles Steel piles may be of I-section or hollow pipe. They are filled with concrete. The size may vary from 10 inches to 24 inches in diameter and thickness is usually ¾ inches. Because of the small sectional area, the piles are easy to drive. They are mostly used as end-bearing piles.

8. Types of Pile Foundation Pre-cast Concrete Pile The precast concrete pile is cast in pile bed in the horizontal form if they are rectangular in shape. Usually, circular piles are cast in vertical forms. Precast piles are usually reinforced with steel to prevent breakage during its mobilization from casting bed to the location of the foundation. After the piles are cast, curing has to be performed as per specification. Generally curing period for pre-cast piles is 21 to 28 days. Cast-in-Place Concrete Piles This type of pile is constructed by boring of soil up to the desired depth and then, depositing freshly mixed concrete in that place and letting it cure there.

9. METHODS OF INSTALLING PILE FOUNDATIONS Methods of pile driving can be categorized as follows: Dropping weight Explosion Vibration Jacking (restricted to micro-piling ) Jetting

10. Drop Hammer Method of Pile Driving A hammer with approximately the weight of the pile is raised a suitable height in a guide and released to strike the pile head. This is a simple form of hammer used in conjunction with light frames and test piling, where it may be uneconomical to bring a steam boiler or compressor on to a site to drive very limited number of piles . There are two main types of drop hammers: Single-acting steam or compressed-air hammers Double-acting pile hammers

11. Drop Hammer Method of Pile Driving Single-acting steam or compressed-air comprise a massive weight in the form of a cylinder. Steam or compressed air admitted to the cylinder raises it up the fixed piston rod. At the top of the stroke, or at a lesser height which can be controlled by the operator, the steam is cut off and the cylinder falls freely on the pile helmet. Double-acting pile hammers can be driven by steam or compressed air. A piling frame is not required with this type of hammer which can be attached to the top of the pile by leg-guides, the pile being guided by a timber framework .

12. Pile Driving by Vibrating Vibratory hammers are usually electrically powered or hydraulically powered and consists of contra-rotating eccentric masses within a housing attaching to the pile head . The amplitude of the vibration is sufficient to break down the skin friction on the sides of the pile. Vibratory methods are best suited to sandy or gravelly soil.

13. Jetting To aid the penetration of piles in to sand or sandy gravel, water jetting may be employed. However, the method has very limited effect in firm to stiff clays or any soil containing much coarse gravel, cobbles, or boulders.

14. Boring Methods Continuous Flight Auger (CFA ) Equipment comprises of a mobile base carrier fitted with a hollow-stemmed flight auger which is rotated into the ground to required depth of pilling. To form the pile, concrete is placed through the flight auger as it is withdrawn from the ground. The auger is fitted with protective cap on the outlet at the base of the central tube and is rotated into the ground by the top mounted rotary hydraulic motor which runs on a carrier attached to the mast. On reaching the required depth, highly workable concrete is pumped through the hollow stem of the auger, and under the pressure of the concrete the protective cap is detached. While rotating the auger in the same direction as during the boring stage, the spoil is expelled vertically as the auger is withdrawn and the pile is formed by filling with concrete. In this process, it is important that rotation of the auger and flow of concrete is matched that collapse of sides of the hole above concrete on lower flight of auger is avoided. This may lead to voids in filled with soil in concrete. The method is especially effective on soft ground and enables to install a variety of bored piles of various diameters that are able to penetrate a multitude of soil conditions. Still, for successful operation of rotary auger the soil must be reasonably free of tree roots, cobbles, and boulders, and it must be self-supporting.

15. Under reaming A special feature of auger bored piles which is sometimes used to enable to exploit the bearing capacity of suitable strata by providing an enlarged base. The soil has to be capable of standing open unsupported to employ this technique. In its closed position, the under reaming tool is fitted inside the straight section of a pile shaft, and then expanded at the bottom of the pile to produce the under ream shown in fig. Normally, after installation and before concrete is casted, a man carrying cage is lowered and the shaft and the under ream of the pile is inspected.

16. Types of Pile Driving Equipments

17. Types of Pile Driving Equipments Types of Pile Driving Equipments Piling rigs Piling winches Hanging leader Hammer guides Piling hammer Helmet, driving cap, dolly, and packing

18. Piling Rigs It composed of a series of leaders, which are consist of tabular element or hard box, placed and fixed on a crane base as it can be seen from figure. Not only does the leaders support the hammer and the pile but also guide them when the pile is forced into the ground.

19. Piling Winches T he prime goal of piling winches is to left the hammer and piles in addition to support tools that responsible for leader raking and rotation. There are different piling winches with different capacity for instance winches with double or triple drums possess satisfactory controlling and pile driving speed whereas one drum winch does not have that advantage. So, the former type would be favored provided that handing and driving piles with great speed is required.

20. Hanging Leader Hanging leaders are specifically designed to be hanged from the jib of a crane. A steel strut, which its length can be varied as per requirements of construction site, provides a stiff connection from the leader foot to the machine bed frame. Moreover, crane or excavator winch units are utilized to left the hammer and piles using separate drums. Finally, it is substantially crucial to practice utmost precaution to hanging leader stiffness particularly in the case of long sloped pile driving since intolerable deformation would lead to eccentric hammer blow and possibly cause pile fracture.

21. Hammer Guides When it is intended to remove hanging leaders or piling frames completely, rope suspended leaders which are commonly guided by timber or steel formwork, would be considered. In this technique, an independent crane needed to control the pile and establishing the guide and hammer. it is necessary to set and secure the guide properly in order to avoid movements specifically in the during raking pile installation. This is because serious fatigue stress would generate if the thrust is not centered properly and the guide might deteriorate. Finally, it is required to prevent disproportionate bending stress development in guide and piles because it leads to undesired results. for example, when heavy hammer is attached to the upper end of a long pile which is driven at flat angle of rake, excessive bending stress may be generated at support point in the guide. This problem might be tackled by providing suitable support for the pile at proper position.

22. Piling Hammer There are several factors that greatly influence the decision to choose suitable piling hammer. For example, pile size and weight, the resistance of the ground which should be overcame in order to obtain specified penetration, construction site space availability, noise limitation that might be imposed at certain areas, and availability of cranes. As for input data required for drivability analysis, piling hammer producer provided necessary data about efficiency and energy feature of the piling hammer. It should be bore in mind that piling hammer efficiency is not a constant and it is affected by number of factor for example mechanical condition of the hammer and operation temperature. It should be known that the mechanical condition is not influence the efficiency of piling drop hammer. That is why dynamic pile analysis is carried out and its results would be used to assess the influence of different factor on the piling hammer efficiency.

23. Helmet, Driving Cap, Dolly and Packing Helmet is a cast steel that placed over the pile to hold the dolly that placed between the pile and the hammer to avoid pile head deterioration that may cause by pile driving hammer. Dolly , which is square at the bottom and round at the top, is placed in a square recess at the top of the helmet. Their selection is dependent on the driving force. As far as packing is concerned, it is placed between pile top and the helmet in order to protect the former from the hammer blow. Different types of packing include paper sacking, thin timber sheet, coconut mapping, and sawdust in bags. Regarding driving cap , it is provided as a protection for steel bearing piles. It is necessary to place the driving cap tightly otherwise the pile cap would suffer deterioration. That is why it is fitted with a recess for hardwood or plastic dolly and with steel wedges to fix the cap tightly on its position .

24. Thank You Shivananda Roy