TOPIC 5 : Piling

MANGROVE PILES

The mangrove piles are widely used in peninsular Malaysia for low-rise building.

Although the use of mangrove piles is not recognized in other countries, Malaysia

contractors and developers are very confident that the mangrove piles can actually being

used for piling in the low-rise buildings due to the mangrove wood nature density and

strength.

ADVANTAGES

The mangrove piles are not only cheap, but also easy to be handled in pilling work.

The buildings using the mangrove piles as foundation can at least stand for 10 years, and the

mangrove piles are very easy to be cleared off when the other type of foundation is to be

used.

The minimum length of the mangrove piles use is only 6.0m and they can be joint

with a pile joint, which is made up by a steel box.

The lengthening of pile may increase the soil bearing capacity and make sure then the piles are stand on a firm or stiff clay, so that the downward movement of piles will not happen.

Drop hammer is used for the driver of the mangrove piles. To install the piles into

soft clay, the drop hammer just pushes the piles with small force. The clay is excavate

before the installation of piles.

DISADVANTAGE

the mangrove piles may be damaged if they are not fully submerged under the water table level.

Timber Piles

Transmission of load through timber piles takes place by the frictional resistance of the ground and the pile surface. Timber piles prove economical hit supporting light structures to be located in compressive soils constantly saturated with water. The timber piles are made from timber obtained from trees like sal, teak, deodar, babul, Khair etc. It has been found that piles made from Khair wood can stand action of sea water better and are thus commonly used for marine works. Timber piles may be circular or square in cross-section. Piles are driven with the help of pile-driving machine in which a drop hammer delivers blows on the pile head. To prevent the pile head from brooming, an iron ring about 25 mm less in diameter than the pile head is provided at the pile top. To facilitate driving, the lower end of the pile is pointed and is provided with a cast iron conical shoe. Piles should not be spaced less than 60 cm centre to centre. By driving piles much closer, the frictional resistance is destroyed. The best spacing for timber piles is 90 cm c/c. Maximum load on a wooden pile should normally not exceed 20 tonnes. Piles made from sound timber free from any defect or disease and driven in the soils which are either permanently wet or permanently dry, will remain in good condition for centuries. However, when subjected to alternate dry and wet conditions (on account of variations in ground water level) they get decayed. It is on this account that timber piles are cut a little below the lowest water-mark and capped with concrete, steel grillage, stone or timber. If timber capping is used, the cap should be permanently under water.

Advantages of timber piles:1. They are economical.2. They can be driven rapidly and as such there is great saving in time in execution of piling

work.3. On account of their elasticity timber piles can be recommended for sites where piles are

likely to the subjected to unusual lateral forces.4. They do not need heavy machinery and elaborate technical supervision.

Disadvantages of timber piles:1. Timber piles must be cut off below the permanent ground water level to prevent them from

decay and thus if the water table at a site is at a greater depth, extra cost of excavation needed to provide the pile cap may render the choice uneconomical.

2. Timber piles can not be driven in filled up ground without injury and as such they cannot be recommended for such sites.

3. They are liable to decay or deteriorate by sail water or insects.4.  On account of their restricted length, they cannot be used for jobs  where long piles are

needed.5. They have low bearing capacity.

Sheet Piles – Types of Sheet Piles

Sheet piles may he made up of wood, concrete or steel. Steel piles are driven side by side into the ground to form a continuous vertical wall for retaining soil. The alignment and resistance or thrusts are normally provided by horizontal wallers, braces or tiebacks. Factors affecting the choice of a particular type of pile include nature of ground, cost, ease of installation, availability of material, ability to withstand driving, lateral strength and ease of making connections. Depending upon the material used in their manufacture, some of the types of sheet piles are,1. Wooden sheet piles2. Precast concrete Sheet piles3. Prestressed concrete sheet piles4. Steel sheet piles

1.Wooden sheet piles:Wooden sheet piles are made in various sizes and forms. The nature of site conditions determine, the choice of a particular type, In places where excavation is small and the ground water problem is not serious, 5 cm x 30 cm to 10 cm x 30 cm wooden planks arranged in a simple row will serve the purpose. If the water-tightness is required to a great extent, lapped sheet piling is used. In this case, each pile is made up of two planks, either spiked or bolted to one another. Thus if only earthen banks of small height are to be supported, a single or double row of  planks properly erected will perform the function of sheet piling. If complete water tightness is desired or pressure of the retained material wakefield or tongue and grooved sheeting is generally used. To facilitate the driving of the piles, they are usually bevelled at foot. This not only assists in driving but also prevents bruising, if the piles encounter hard stratum.

Wakefield piles:This type of pile is made with three planks, 5 cm, 8 cm or 10 cm in thickness. The planks are nailed together with the middle plank offset forming a tongue on one edge and a groove on the other. The planks are connected by using a pair of staggered bolts at 80 cm centre to centre at intermediate points. The triple lap piles prove stronger in driving. There is no wastage in forming the tongue and groove joints and the piles have less tendency to warp. Timber sheet piles have light weight and as such the equipment required for pile driving is also light. This is considered to be an important advantage timber piles have over piles of other materials.

Sectional Plan of a Wakefield Pile

2. Precast concrete sheet piles:Precast concrete piles are made in square or rectangular cross-section and are driven similar to wooden piles to form a continuous wall. The interlock between two piles is normally provided with the help of tongue and groove joint. The tongue and groove extend to the full length of the piles in most of the cases.An alternative method of providing joint between two piles is shown below. In this method, after the piles are driven to the required. depth, the joint is grouted with cement mortar 1: 2 (1 cement : 2 sand).

Sectional Plan of Different Types of Precast Concrete Piles

The piles are reinforced to avoid formation of cracks due to rough handling or shrinkage stresses. In order to reduce the possibility of damage due to driving impact, the stirrups should be spaced closely near the top and bottom of the piles. The piles are normally bevelled at their feet to facilitate tightly close driving of a pile against the already driven one.  Reinforced concrete sheet piles are bulky and heavy and as such they are gradually being superseded byprestressed concrete piles.

3. Prestressed concrete sheet piles:On account of the numerous advantages the prestressed concrete members have over the conventional type of reinforced concrete members, prestressed concrete sheet piles are commonly used for sheet piling jobs. Similar to concrete sheet piles, they are reinforced on both the faces so that they could be handled from either side. They are comparatively lighter in weight, more durable and economical in the long run. They are advantageously used in sea water, since the danger of cracking of concrete is negligible and also the corresponding danger of corrosion of pile reinforcement is reduced.

4. Steel sheet piles:Steel sheet pile is a rolled steel section consisting of a plate called the web with integral interlocks on each edge. The interlocks consist of a groove, one of whose legs has been suitably flattened.This flattening forms the tongue which fits into the groove of the second sheet. Commonly used sheet piles can be broadly divided into the following three categories, Straight-web type Shallow or deep arched-web type Z web typeSpecial shapes and sizes of steel sheet piles are manufactured for meeting the requirement of junctions and other similar situations. Each of the above mentioned type of piles is manufactured in varying widths and lengths. The selection of the type of pile and the section to be adopted depend upon the depths up to which the pile is to be driven, the nature of soil to be penetrated the elevation of the earthen embankment, ground water level etc.In general, Straight web type of piles are used where the piles are liable to he subjected to tensile forces and interlocking strength is of prime importance (Cellular cofferdam etc); Arched-web type are used where the piles are required to resist bending stresses (in cantilever retaining walls etc,) and Z-web type of piles arc used where the piles are required to resist bending stresses of very large magnitude.

Steel Sheet Piles

Steel sheet piles are driven with the help of pile drivers which may be of drop hammer type or single or double acting hammer driven by steam or compressed air. The outstanding feature of steel sheet piles is that they  can be used for greater depths. The continuous interlocking arrangement of the piles gives strength and rigidity to the supported structure. A wall made from properly driven sheet piles leaks very little, hence steel sheet piling is used with advantage in the  construction  of deep cofferdams. They are commonly used in coastal defence works which are likely to be subjected to tidal action.

Precast Concrete Piles

Precast Concrete Piles may be defined as a reinforced concrete pile which is moulded in circular, square, rectangular or octagonal form. The precast concrete piles are cast and cured in a casting yard and then transported to the site for driving. In case space is available, pile can also be cast and cured near the site of works. They are driven in a similar manner as timber pileswith the help of pile drivers. The diameter of the pile normally varies 1mm 35 cm to 65 cm and their length varies from 45 in to 30 m.

Precast Concrete PilesThe function of reinforcement in a precast concrete piles are to resist the stresses produced on account of its handling, driving and the loading which the pile is finally expected to receive. Longitudinal reinforcement usually consists of one bar 20 mm to 50 mm in diameter at each angle of the section of the pile. The vertical rods are tied horizontally by bars 6 mm to 10mm in diameter. The horizontal bars may be provided in the form of stirrups wound around the verticals. For lengths of approximately 90 cm at head and toes, the spacing of the stirrups should be 8 cm c/c. Circular piles are seldom tapered but when tapering of the piles becomes necessary due to site conditions, their length is restricted to 12 m.

Precast Piles supporting Column footing

The most common pile type in many parts of the world, such as Scandinavia, is the precast concrete pile. Precast concrete piles are commonly manufactured in square and ranging from about 250 mm to about 450 mm, with a maximum section length of up to about 20 m. Other pile sections exist and may include hexagonal, circular, triangular and H shapes.

The piles have generally been driven with a drop hammer of 3 to 4 tons, although in recent years, hydraulic hammers have become very common for driving precast concrete piles. I some countries, diesel hammers and occasionally also vibrators are used. Maximum allowable axial loads can be up to about 1 000 kN. The length of pile sections is often dictated by practical considerations including transportation, handling problems in sites on restricted area and facilities at the casting yard.

Precast concrete piles can be constructed either in the factory or on site. The quality of the pile is very much affected by the construction and production process. A typical section of a Swedish precast concrete pile is shown.

Extending precast piles without joints is a lengthy process. It requires breaking down the projecting pile head to provide a suitable lap for the steel reinforcement and casting concrete to form the joint. Piles can also be connected by epoxy to form the joint. Good alignment of the pile sections is required to prevent excessive bending stresses developing on subsequent re-driving.

The pile length can be equipped with prefabricated joints. Other splicing methods commonly adopted include welding of steel end plates or the use of epoxy mortar with dowels.

Precast concrete piles are not suitable for soil deposits containing a significant amount of boulders. In such cases, the pile may be equipped with a pile shoe, which protects the pile tip during hard driving.

BORED PILE

Bored pile is another type of reinforced concrete pile which is used to support high building which has heavy vertical load. Bored pile is a cast-in-place concrete pile where the bored piles have to be cast on construction site, while other concrete piles like Spun Pile and Reinforced Concrete Square Pile are precast concrete pile which they’re cast in the factory.

Normally bored piling has be to carried on those tall buildings or massive industrial complexes, which require foundations which can bear the load of thousands of tons, most probably in unstable or difficult soil conditions. 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.

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.

Bored piling is popular to be used in construction as a foundation especially for bridge work and tall building as well. Bored piling work has to be done by specialist bored piling contractor, normal piling contractor can’t be done without experience and knowledge about bored piles.

Bored Pile Advantages

The main advantages of bored piles over conventional footings or other types of piles are: Piles of variable lengths can be extended through soft compressible or swelling soils, into

suitable bearing material. Piles can be extended to depths below frost penetration, and seasonal moisture variation. Large excavations and subsequent backfill are eliminated. Adjacent soil is not disturbed or remolded. Absence of vibration will not disturb adjacent piles or structures. Extremely high capacity caissons can be obtained by expanding the base of the shaft up to

three times the shaft diameter, thus eliminating construction of caps over multiple pile groups.

Membandingkan Kaedah Cerucuk Berasaskan Geseran dan Galas Hujung

Keupayaan Galas

Sekiranya tanah yang berhampiran dengan permukaan tidak berkeupayaan secukupnya untuk menyokong struktur, cerucuk digunakan untuk memindahkan bebankepada tanah yang lebih sesuai pada kedalaman yang lebih besar.

Dalam kata lain,keupayaan galas boleh didefinasikan sebagai tekanan yang dikenakan oleh asas ceucuk ke atas tanah

Cerucuk Hujung Galas

Cerucuk yang dikelaskan dalam kumpulan ini hampir semua menanggungrintangan penusukan tanah di tapak cerucuk.

Ia digunakan untuk memindahkan bebanyang sangat berat melalui permukaan tanahyang tidak stabil ke tanah yang stabil yangterletak di bawah permukaan tanah pada sesuatu jarak.

Ia memindahkan beban pada arahmenegak ke bawah kepada bahan yang mempunyai keupayaan galas tinggi yang biasanya merupakan batuan keras. Cerucuk akan dipacu sehingga mencapai ‘set’ dilapisan set tersebut.

Suatu cerucuk tidak akan gagal melalui lengkokan walaupun ia berada dalam keadaan tanah yang lemah tetapi kesan ini kan dipertimbangkan apabilasebahagian daripada cerucuk berada dalam air.

Cerucuk Geseran Kulit

Cerucuk geseran bergantung sepenuhnya pada geseran yang berlaku di antara permukaan cerucuk dengan tanah sekitarnya. Kedua-duanya perlu mempunyai permukaan yang menghasilkan geseran.

Keupayaan tanggungannya kebanyakkannyaterhasil daripada rekatan atau geseran tanah dengan cerucuk. Pemacuan cerucuk yangsecukupnya ke dalam tanah adalah untuk menghasilkan rintangan geseran yang berpadanan.

Ia merupakan lanjutan daripada cerucuk galas hujung apabila strata penanggung yang tidak keras.

Contohnya, cerucuk ini sesuai digunakan pada tanah liatyang keras. Ini kerana permukaan konkrit dapat menghasilkan geseran apabila bertemudengan tanah liat yang keras. Sebaliknya, tanah liat yang lembut atau tanah pasir yanglonggar tidak dapat mewujudkan geseran yang dikehendaki.

Cerucuk Hujung Galas dan Geseran Kulit

Dalam kajian ini, penulis akan membincangkan cerucuk terjara dengan lebihterperinci. Cerucuk terjara dibentuk daripada penjaraan dan kemudian mengisikan lubang dengan konkrit kebolehkerjaan tinggi dan tetulang.

Saiz cerucuk terjara yang biasa digunakan ialah berdiameter 400-1500mm dengan keupayaan menanggung bebanadalah sehingga 60-1000tan.

Di mana cerucuk terjara yang berdiameter lebih daripada 600mm dikenali sebagai cerucuk terjara bergaris pusat besar. Terdapat dua jenis cerucuk terjara berdasarkan kepada kaedah ataupun teknik pengorekkan tanah dalam penempatan konkrit bertetulang iaitu samaada pengorekkan lubang terjara dengan menggunakantangan atau alat mekanik.

Cerucuk terjara sesuai digunakan di kawasan yang bertanah keras apabila bebanyang tinggi dikenakan ke atasnya. Ia juga tidak menghasilkan sebarang bunyi dangegaran serta tidak mengganggu struktur bangunan yang berhampiran.

Contohnya,apabila tapak binaan berhampiran dengan hospital. Walaupun cerucuk ini menjimatkankos tetapi, kos mobilisasi adalah tinggi untuk penghantaran mesin-mesin pembinaanyang besar dan mahal.

Untuk tanah yang berpasir dan berstrata terlalu lembut, sokongan ‘bentonite’ bolehlah digunakan untuk menstabilkan lubang terjara. Kapasiti cerucuk memerlukannilai fcu yang tinggi, tetapi untuk lubang jara yang lebih panjang atau dalam yangmengandungi pasir berair, nilai fcu yang rendah boleh digunakan dalam menganggar kapasiti cerucuk.Bagi lubang kering kadar kandungan simen adalah sebanyak 300 kg/m3manakala 400kg/m3untuk lubang basah.

Kebolehkerjaan yang tinggi diperlukan bagimemastikan konkrit boleh mengalir melalui dinding lubang jara tanpa perlu dipadatkandan mengelakkan pengasingan,honeycombing , penjujuhan dan lain-lain.

Konkrit jugatidak boleh dituang melebihi 2m dan walaupun lubang terjara adalah dalam keadaankering, paip tremie hendaklah digunakan.Kerj-kerja konkrit hendaklah dilakukan dalam masa 1 jam dan sekiranya kerja-kerja penjaraan dilakukan melebehi jangkamasa yang lama iaitu melebihi 3jam,makakelonggaran tanah yang dikorek akan jatuh.

Kerja-kerja konkrit hendaklah mestilahmematuhi spesifikasi dan pembaziran dan pengleheran haruslah dielakkan. Kelebihandan kelemahan cerucuk terjara telah dibincangkan

DESCRIPTION

Friction piles rely specifically on the friction created between the soil and the surface of the pile material in order to provide stability. The combination of friction and adhesion with the soil causes them to stay in place.

FRICTION PILES VERSUS END-BEARING PILES

Piles are long, thin poles that are driven deep into the soil to give support to a building's foundation. While end-bearing piles rest on a layer of rock below the soil's surface, this setup is not always possible. Since friction piles transfer the weight of the structure they support to the surrounding soil, they do not need the support of a rock layer.

CONSIDERATIONS

In order for friction piles to be effective, the soil surrounding the area must be fairly uniform in type and density. For more complex situations, construction companies sometimes rely on a combination of friction and end-bearing piles.

ADVANTAGES:

1.Even in weak soil a pile will not fail by buckling and this effect need only be considered if part of the pile is unsupported, i.e. if it is in either air or water.2.Bearing piles transfer the load through a soft soil to an underlying firm stratum.They also distribute the load through relatively soft soils that are not capable of supportingconcentrated loads.3.Typical end-bearing piles are driven through very soft soil, such as a loose silt-bearing stratumunderlain by compressible strata. This factor when determining the load the piles can support safely.  

DISADVANTAGES:

1. the soil surrounding the pile may adhere to the surface of the pile and causes "Negative Skin Friction" on the pile.

2. the pile is unsupported if is in air or water

ADVANTAGES AND DISADVANTAGES OF PILE

There are several advantages that can be obtained when using a type of pile foundation, which is as follows:

1. Guaranteed because it is made of concrete manufacturing

2. Foundation bearing capacity of soil can reach the most hard

3. Bearing capacity not only from the end of the pole, but also around the appendage on the pole.

4. Pile bearing capacity on the use of a group or groups (single pole load was arrested by two or more columns) very strong

5. Relatively cheap price of the stake when compared with the foundation sinks.

Besides its advantages, there are some deficiencies that frequently encountered in the use of piles are as follows:

1. for areas that are within a small alley, workmanship difficult because of transport factors

2. New usage in urban and surrounding areas

3. When used outside urban areas, usually the volume a bit so the price will be much more expensive.

4. Erection process will cause vibration and noise so very disturbing environment.