Pile Foundation

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Pile Foundation

  1. 1. Civil Engineering Practice Chapter # 4 Pile Foundation 1 Pile Foundation
  2. 2. CHAPTER # 04 CHP # 04: Pile Foundation ---(Pile Foundation)--- * * * Piles are relatively long and slender members used to transmit foundation loads through soil strata of low bearing capacity to * * deeper soil or rocky strata having a high bearing capacity. I th d th l d i l t itt d t th il bIn other words, the load is properly transmitted to the soil by driving long vertical members of either timber or concrete or steel called “Piles”. 2 Civil engineering practice
  3. 3. Depth at which rocky or hard strata is available can normally be CHP # 04: Pile Foundation Depth at which rocky or hard strata is available can normally be 60 to 80 ft, showing the range of depth for the piles. Piles usually carry excessive loads as load of traffic on a bridge where the underneath strata can be of sand and silt fully saturated with watersaturated with water. Bore logs drawn after soil investigation is used to find out depthg g p of piles, diameter of piles and the numbers of piles required. Pile can also be defined as an element of construction placed in the ground either vertically or slightly inclined to increase the load carrying capacity of the soil. 3 d c y g c p c y s Civil engineering practice
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  6. 6. Piles are required for setting out of towers for high power CHP # 04: Pile Foundation Piles are required for setting out of towers for high power transmission lines and in some cases are also used for supporting the multistory buildings. 4.1 Types of Piles (Based Upon Use) 1- Sheet Piles Sheet piling is used primarily to resist lateral pressures such asSheet piling is used primarily to resist lateral pressures such as flow of water and loose soil. Typical uses include cut-off walls under dams, cofferdams, trench sheeting, etc. 6 Civil engineering practice
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  11. 11. warehouse ship sheet pile 11
  12. 12. 2- Load Bearing Piles CHP # 04: Pile Foundation These are used primarily to transmit loads through soil formations with poor supporting properties into or onto formations that are capable of supporting the loads Dependingformations that are capable of supporting the loads. Depending upon how load is transferred to the soil, load-bearing piles can be further classified into: (a) End Bearing Piles If l d i i d h il h h h l i h il iIf load is transmitted to the soil through the lower tip, the pile is called an “End Bearing Pile”. These piles transmit the superimposed load to stronger strata such as a rock bed. End area of pile times the bearing capacity of h k i h l l d hi h b li d 12 the rock is the total load, which can be applied. Civil engineering practice
  13. 13. Considering reasonable factor of safety, we can find diameter of CHP # 04: Pile Foundation the pile required. 13 Civil engineering practice
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  15. 15. P I L E weak soil bed rock 15
  16. 16. (b) Friction Piles CHP # 04: Pile Foundation These are designed to transmit the loads by the frictional force existing between the sides of the pile and the ground such as the stuff clays or dense sandy depositstuff clays or dense sandy deposit. Friction can be developed for full length as in first figure or it canp g g be developed in lower portions only depending upon the stratification of soil. Surface area times the safe friction which can be developed per unit area determines the load to be carried by the pile. Selectingy p g diameter or length of pile, the other quantity can be calculated. 16 Civil engineering practice
  17. 17. (b) Friction Piles CHP # 04: Pile Foundation 17 Civil engineering practice
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  22. 22. (c) End Bearing and Friction Piles CHP # 04: Pile Foundation These are the piles that dissipate part of the load by friction and transfer the remaining load to firm strata. 3- Piles as Soil Compactor Sometimes closely spaced piles are driven to compact theSometimes closely spaced piles are driven to compact the surrounding soil. 22 Civil engineering practice
  23. 23. 4.2 Types of Piles (Based on material used and method of CHP # 04: Pile Foundation construction) On the basis of the material from which they are made and the method of constructing and driving them load bearing pilesmethod of constructing and driving them, load-bearing piles may be classified as follows: – Timber U da. Untreated b. Treated with a preservative – Concrete a. Pre-cast b. Cast-in-place S l– Steel a. I-section b. Steel-pipe 23 p p – Composite Civil engineering practice
  24. 24. Driven timber piles, Pacific Highway 24 p g y
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  28. 28. 4.3 Factors Affecting Selection of Piles CHP # 04: Pile Foundation Among the factors that will influence the selection of type of piles for a given project are the following: 1. Type, size, and weight of the structure to be supported.1. Type, size, and weight of the structure to be supported. 2. Physical properties of the soil at the site. 3. Depth to a stratum capable of supporting the piles. 4. Possibility of variations in the depth to a supporting stratum. 5. Availability of materials for piles. 6 Number of piles required6. Number of piles required. 7. Facilities for driving piles. 8. Comparative costs in place. 9. Durability required. 10. Types of structures adjacent to the project. 11 Depth and kind of water if any above the ground into which 28 11. Depth and kind of water, if any, above the ground into which the piles will be driven. Civil engineering practice
  29. 29. 4.4 Significance of Pile Foundation CHP # 04: Pile Foundation Pile foundation is suitable for works over water such as bridge`-piers, foundation of transmission towers and foundation of multistory buildingsfoundation of multistory buildings. From head or cap of piles, we can construct the grids with beams and columns. 29 Civil engineering practice
  30. 30. 4.4 Significance of Pile Foundation CHP # 04: Pile Foundation The number of piles depends on the type of pile and the load coming from the buildings. 30 Civil engineering practice
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  32. 32. CHP # 04: Pile Foundation ooden Pilesooden Piles 32 Civil engineering practice
  33. 33. 4.5 Wooden Piles CHP # 04: Pile Foundation These piles, if used below the ground water level, last for a very long period but ordinarily they last no longer than 30 years or so even if treated.yea s o so eve t eated. The circular piles vary in diameter from 12 inch to 16-inch. If square sizes are used, they also vary in size fro 12 inch to 16- inch square. The length of the piles is about 20 times the top width.width. The timber point may be protected or replaced by a metallic shoe; shoes are used while driving through soils containing boulders, gravels, hard clays etc. 33 Civil engineering practice
  34. 34. 4.5 Wooden Piles CHP # 04: Pile Foundation They may be of C.I. and should have sufficient length of wrought iron straps to connect them with the pile. The head of the pile is subjected to a heavy impact of the driving machine; hence, rings of wrought iron are fitted to theg ; , g g pile head. They vary in cross-section from 2 in. to 4 in. Timber piles should not be loaded above 15 to 20 tons and should be carefully driven. Whenever it is necessary to use a longer pile than available in usual lengths, it is necessary to splice the piles together, with 34 their ends abutting each other. Civil engineering practice
  35. 35. 4.5 Wooden Piles CHP # 04: Pile Foundation Additional strength can be obtained by the use of steel fishplates bolted to the sides of the piles. Among the advantages of timber piles are the following: 1. The more popular lengths and sizes are available on short notice. 2. They are economical in cost. 3. They are handled easily, with little danger of breakage. 4. They can be cut off to any desired length after they are driven. 5. They can be pulled easily in the event removal is necessary. 35 Civil engineering practice
  36. 36. 4.5 Wooden Piles CHP # 04: Pile Foundation Among the disadvantages of timber piles are the following: 1. It may be difficult to obtain piles sufficiently long and straight for some projects. 2. It may be difficult or impossible to drive them into hard formations. 3 I i diffi l li h i h i l h3. It is difficult to splice them to increase their lengths. 4. While they are satisfactory when used as friction piles, they are not suitable for use as end-bearing piles under heavy loads.g p y 5. The length of life may be short unless the piles are treated with a preservative. 36 Civil engineering practice
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  38. 38. CHP # 04: Pile Foundation oncrete Pilesoncrete Piles 38 Civil engineering practice
  39. 39. download.mp4 39
  40. 40. 4.6 Concrete Piles CHP # 04: Pile Foundation (a) Pre-cast Concrete Piles Square and octagonal piles are cast in horizontal forms, while round piles are casts in vertical forms. After the piles are cast, they should be cured for the period required by specifications, frequently 21 days. With the exception of short lengths, Precast concrete piles t b i f d ith ffi i t t l t t dmust be reinforced with sufficient steel to prevent damage or breakage while they are being handled from the casting beds to the driving positions. 40 Civil engineering practice
  41. 41. 4.6 Concrete Piles ( ) P C Pil CHP # 04: Pile Foundation (a) Pre-cast Concrete Piles Among the advantages of Pre cast concrete piles are theAmong the advantages of Pre-cast concrete piles are the following: 1. High resistance to chemical and biological attacks. 2. High strength. 3. A pipe may be installed along the center of a pile to facilitate driving. 41 Civil engineering practice
  42. 42. 4.6 Concrete Piles ( ) P C Pil CHP # 04: Pile Foundation (a) Pre-cast Concrete Piles Among the disadvantages of Pre cast concrete piles are theAmong the disadvantages of Pre-cast concrete piles are the following: 1. It is difficult to reduce or increase the length. 2. Large sizes require heavy and expensive handling and driving equipment. 3 I bili b i il b h d l h i f3. Inability to obtain piles by purchase may delay the starting of a project. 4. Possible breakage of piles during handling or driving producesg p g g g p a delay hazard. 42 Civil engineering practice
  43. 43. 4.6 Concrete Piles CHP # 04: Pile Foundation (b) Cast-in-Place Concrete Piles These piles are constructed by depositing the freshly mixed concrete in place in the ground and letting it cure there. The two principal methods of constructing such piles are:p p g p 1. Driving a metallic shell, leaving it in the ground and filling it with concrete. 2 D i i t lli h ll d filli it ith t th h ll2. Driving a metallic shell and filling it with concrete as the shell is pulled from the ground. 43 Civil engineering practice
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  45. 45. 4.6 Concrete Piles CHP # 04: Pile Foundation (b) Cast-in-Place Concrete Piles Among the advantages of cast in place concrete piles are theAmong the advantages of cast-in-place concrete piles are the following: 1. The lightweight shells may be handled and driven easily. 2. Variations in length do not present a serious problem. The length of a shell may be increased or decreased easily.g y y 3. The shells may be slipped in short lengths and assembled at the job. 4 E i f i t i t t d b h dli l4. Excess reinforcing, to resist stresses caused by handling only, is eliminated. 5. The danger of breaking a pile while driving is eliminated. 45 6. Additional piles may be provided quickly if they are needed. Civil engineering practice
  46. 46. 4.6 Concrete Piles CHP # 04: Pile Foundation (b) Cast-in-Place Concrete Piles Among the disadvantages of cast-in-place concrete piles are the following: 1. A slight movement of the earth around an un-reinforced pile may break it. 2. An uplifting force, acting on the shaft of an uncased and un- reinforced pile, may cause it to fail in tension. 3 Th b tt f il t b t i l3. The bottom of pile may not be symmetrical. 46 Civil engineering practice
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  48. 48. CHP # 04: Pile Foundation teel Pilesteel Piles 48 Civil engineering practice
  49. 49. 4.7 Steel Piles CHP # 04: Pile Foundation Steel piles may be of I-section or hollow pipe section 10 inches t 24 i h di t ith 3/8 i h thi kto 24 inches diameter with 3/8 inches thickness. Because of a small sectional area steel piles are easy to driveBecause of a small sectional area, steel piles are easy to drive. The pipes are driven with open ends. Compressed air with a pressure of 100 psi in a 2½ inches or more diameter pipe and h f ili h d i ithus facilitates the driving. These piles are later on filled with concrete Steel piles areThese piles are later on filled with concrete. Steel piles are mostly used as end bearing piles because of their less available surface area to take the loads by frictional forces. 49 Civil engineering practice
  50. 50. 4.7 Steel Piles CHP # 04: Pile Foundation In constructing foundations that require piles driven to great depths, steel I-section probably are more suitable than anydept s, stee sect o p obab y a e o e su tab e t a a y other type. Steel piles may be driven through hard materials to a specified depth to eliminate the danger of failure due to scouring, such as under a pier in a river.as under a pier in a river. Also, steel piles may be driven to great depths through poor soils to bear on a solid rock stratum. 50 Civil engineering practice
  51. 51. 4.7 Steel Piles CHP # 04: Pile Foundation The great strength of steel combined with the small displacement of soil permits a large portion of the energy fromd sp ace e t o so pe ts a a ge po t o o t e e e gy o a pile hammer to be transmitted to the bottom of a pile. As a result, it is possible to drive steel piles into soils, which could not be penetrated by any other type of pile. By weld splicing sections together, lengths in excess of 200ft have been driven. 51 Civil engineering practice
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  53. 53. CHP # 04: Pile Foundation crew Pilescrew Piles 53 Civil engineering practice
  54. 54. 4.8 Screw Piles CHP # 04: Pile Foundation Screw piles consist of iron or steel shaft h i t it d t i t t lhaving at its end a cast iron or cast steel screw, with a blade 1.5ft to 5ft in diameter. These piles can be screwed down to a great depth in clay, etc., and penetrate h h ll b kthrough small broken stones. The base area of the screw does most ofThe base area of the screw does most of the weight bearing; they can be used for bridges in riverbeds with deep clay f d i 54 foundation. Civil engineering practice
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  59. 59. 4.9 Pile Driving CHP # 04: Pile Foundation The operation of forcing a pile into ground without any previous excavation is called “Pile Driving”. Following are the various methods of pile driving: 1. Drop hammer. 2. Steam-hammer. 3 Boring3. Boring. 4. Screwing. 5. Water jet. 59 Civil engineering practice
  60. 60. 4.9 Pile Driving 1 D H M h d CHP # 04: Pile Foundation 1- Drop Hammer Method It is the simplest method of pile driving. In this method, at s t e s p est et od o p e d v g. t s et od, a hammer is dropped on the head of the pile and is guided during its fall by suitable staging. The hammer is raised by pulling a rope manually or by steam engine or electric motor. The weight of the hammer forengine or electric motor. The weight of the hammer for driving concrete or wooden piles is about 225 kg for short piles and 900 kg to 2350 kg for long and heavy piles. Hammer is generally dropped from a height of 15m to 45m and the height is limited to 6 m The pile-driving frame is kept 60 and the height is limited to 6 m. The pile driving frame is kept in vertical position by suitable ropes. Civil engineering practice
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  62. 62. 4.9 Pile Driving 2 S H M h d CHP # 04: Pile Foundation 2- Steam Hammer Method A heavy hammer is dropped on to the pile through a smalleavy a e s d opped o to t e p e t oug a s a height but in quick succession. Single acting or double acting steam hammers are available. These hammers are raised with high-pressure steam and are dropped under gravity when single acting or by steam wheredropped under gravity when single acting or by steam where there is double acting hammer. These hammers are specially used for driving sheet piles and where small vibrations are i d t b t i th ilrequired to be set up in the piles. Special devices are used to protect the heads of the piles from 62 Special devices are used to protect the heads of the piles from damage due to excessive blows, which they receive. Civil engineering practice
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  64. 64. 4.9 Pile Driving CHP # 04: Pile Foundation 3- Boring S ti ili i d b b i h l f it bl di tSometimes, piling is done by boring holes of suitable diameter to the required depth and then dropping piles in them. Generally cast-in-situ piles are laid by this method. 4- Screwing Screw piles and disc piles are generally driven by this method. They are driven into the ground by turning them round andThey are driven into the ground by turning them round and round in one direction with big levers. 64 Civil engineering practice
  65. 65. 4.9 Pile Driving 5 W J CHP # 04: Pile Foundation 5- Water Jets Pile driving can also be done by displacing the material at orP e d v g ca a so be do e by d sp ac g t e ate a at o near the foot of the pile by means of one or more water jets under pressure. Sometimes, hammer may be used to force the pile rapidly into the ground. The pressure of the jet should be sufficient tothe ground. The pressure of the jet should be sufficient to displace the soil and other removed materials for driving the piles quickly and satisfactorily. 65 Civil engineering practice
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