FOUNDATION

foundation အေၾကာင္း၊ သိေကာင္းစရာ။
(1) အလုပ္လုပ္ပံုေပၚမူတည္ၿပီး၊ ခြဲျခားထားေသာ၊ Pile (၅)မ်ိဳးရွိပါသည္။ ၄င္းတိုမွာ_
1.1 end bearing pile - ေအာက္ေထာက္ပိုင္
1.2 friction pile - ေဘးပြတ္ပိုင္
1.3 compaction pile - ေျမသိပ္ပိုင္
1.4 tension pile - ဆြဲပိုင္
1.5 anchor pile - ေဘးတြန္းေဘးေထာက္ပိုင္တို႔၊ ျဖစ္ၾကပါသည္။
1.1 end bearing pile - ေထာက္ပိုင္
ဝန္ထမ္းအားေကာင္းေသာေျမ၊ သို႔မဟုတ္၊ ေက်ာက္လႊာကိုေထာက္၍၊ column တေခ်ာင္းကဲ့သို႔၊ အေပၚမွ၊ အေဆာက္ အအံု၏၊ အေလးဝန္ခ်ိန္ကို၊ ထမ္းေသာ pile ကို၊ "end bearing pile - ေထာက္ပိုင္" ဟု၊ ေခၚပါ သည္။
In end bearing piles, the bottom end of the pile rests on a layer of especially strong soil or rock. The load of the building is transferred through the pile onto the strong layer. In a sense, this pile acts like a column.
1.2 friction pile - ပြတ္ပိုင္
Pile ၏၊ မ်က္ႏွာျပင္ႏွင့္၊ ၄င္းႏွင့္ထိေတြ႕ေသာ၊ ေျမသားတို႔၏၊ ပြတ္အားက၊ အေလးဝန္ခ်ိန္ကို၊ ထမ္းေဆာင္လ် င္၊ "friction pile - ပြတ္ပိုင္"ဟု၊ ေခၚပါသည္။
A load-bearing pile that receives its principal vertical support from skin friction between the surface of the buried pile and the surrounding soil.
1.3 compaction pile - ေျမသိပ္ပိုင္
ေျမႀကီးကိုသိပ္သည္းေစၿပီး၊ ထိုေျမ၏၊ bearing capacity ကို၊ တိုးပြားေစေအာင္၊ ရိုက္သြင္းေသာ pile ကို "compaction pile - ေျမသိပ္ပိုင္"ဟု၊ ေခၚပါသည္။
A pile driven into the ground to compact soil and increase its bearing capacity is compaction pile.
1.4 tension pile - ဆြဲပိုင္
ေျမငလၽွင္လႈပ္သည့္အခါ၊ footing foundations မ်ားကို၊ uplift ေခၚ၊ အေပၚသို႔ႂကြတက္မလာေအာင္ႏွင့္၊ overturning ေခၚ၊ တိမ္းေစာင္းမသြားေစရန္အတြက္၊ ကာကြယ္ထားေသာ pile ကို၊ "tension pile - ဆြဲပိုင္" ဟု၊ ေခၚပါသည္။
Tension Piles are used, in general, to address uplift concerns in seismic zones and for seismic retrofitting of existing footing foundations where uplift and overturning must be prevented.
1.5 anchor pile - တြန္းေထာက္ပိုင္
lateral load -ေဘးတိုက္တြန္းအားကို၊ ခုခံကာကြယ္ရန္၊ တည္ေဆာက္ထားေသာ၊ pile ကို၊ "anchor pile - တြန္းေထာက္ပိုင္"ဟု၊ ေခၚပါသည္။
Anchor Piles are required to resist lateral loads with or without being braced depending on circumstances and an ordinary or standard house pile is required to carry a vertical load.
(2) တည္ေဆာက္ပံုေပၚမူတည္ၿပီး၊ ခြဲျခားထားေသာ၊ Pile (၃)မ်ိဳးရွိပါသည္။ ၄င္းတိုမွာ_
2.1 Driven piles -
2.2 Cast-in-situ piles, and
2.3 Driven and cast-in-situ piles
2.1 Driven pile ဆိုသည္မွာ_
အသင့္သြန္းေလာင္းထားေသာ၊ ကြန္ကရစ္တိုင္မ်ား၊ ပံုသ႑ာန္အမ်ိဳးမ်ိဳးရွိေသာ၊ steel မ်ား၊ သစ္လံုးတိုင္မ်ား ကို၊ ေျမႀကီးထဲသို႔၊ တူျဖင့္ရိုက္သြင္းျခင္း၊ ဝန္ျဖင့္ဖိသြင္းျခင္းျဖင့္၊ တည္ေဆာက္အပ္ေသာ၊ pile မ်ားကို၊ "Driven pile" ဟု၊ ေခၚပါသည္။
2.2 Cast-in-situ piles ဆိုသည္မွာ_
ေျမႀကီးကို၊ အေပါက္ေဖာက္ၿပီး၊ သံဆင္ကာ၊ ကြန္ကရစ္သြန္းေလာင္းေသာpile ကို၊ "Cast-in-situ pile"ဟု၊ ေခၚပါသည္။ (bore pile)
2.3 Driven and cast-in-situ pile ဆိုသည္မွာ_
ေျမႀကီးထဲသို႔၊ steel pipe လံုးႀကီးမ်ားရိုက္သြင္းၿပီး၊ ပိုက္လံုးႀကီးမ်ားအတြင္းမွ၊ ေျမႏွင့္ေရမ်ားဖယ္ရွားကာ၊ သံဆင္ၿပီး၊ကြန္ကရစ္သြန္းေလာင္းေသာ၊ pile အမ်ိဳးအစားျဖစ္ပါသည္။ ပင္လယ္ကမ္းစပ္၊ ေရႏွင့္ရႊံ့ႏြံရွိေသာ ေနရာမ်ားတြင္၊ ဤနည္းကို၊ အသံုးျပဳၾကသည္။
3. အသံုးျပဳ ေသာ၊ ပစၥည္းေပၚမူတည္ၿပီး၊ pile ကို၊ ေအာက္ပါအတိုင္း၊ ၅မ်ိဳးခြဲျခားႏိုင္ပါေသးသည္။
3.1 Timber piles
3.2 Steel piles
3.3 Concrete Piles
3.4 Plastic pile
3.5 Composite piles
Plastic sheet Pile တြင္_a. Vinyl sheet pile, b. PVC sheet pile, c. Plastic sheet pile ဟူ၍၊ ထပ္မံခြဲျခားႏိုင္ပါေသးသည္။
(2) There are three types of pile foundations according to their construction methods:
2.1 Driven piles,
2.2 Cast-in-situ piles, and
2.3 Driven and cast-in-situ piles.
2.1 Driven Pile Foundations:
Driven pile foundations can be made from concrete, steel or timber. These piles are prefabricated before placing at the construction site. When driven piles are made of concrete, they are precast. These piles are driven using a pile hammer.
When these piles are driven into the granular soils, they displace the equal volume of soil. This helps in compaction of soil around the sides of piles and results in the densification of soil. The piles which compact the soil adjacent to it is also called as compaction pile. This compaction of soil increases its bearing capacity.
Saturated silty soils and cohesive soils have poor drainage capability. Thus these soils are not compacted when driven piles are drilled through it. The water have to be drained for the soil to be compacted. Thus stresses are developed adjacent to the piles have to be borne by pore water only. This results in increase in pore water pressure and decrease in bearing capacity of the soil.
2.2 Cast-in-situ Pile Foundations:
Cast-in-situ piles are concrete pile. These piles are constructed by drilling holes in the ground to the required depth and then filling the hole with concrete. Reinforcements are also used in the concrete as per the requirements. These piles are of small diameter compared to drilled piers.
Cast-in-situ piles are straight bored piles or with one or more bulbs at intervals are casted. The piles with one or more bulbs are called as under-reamed piles.
2.3 Driven and Cast-in-situ Piles
Driven and cast-in-situ piles have the advantages of both driven and cast-in-situ piles. The procedure of installing a driven and cast-in-situ pile is as follows:
A steel shell of diameter of pile is driven into the ground with the aid of a mandrel inserted into the shell. After driving the shell, the mandrel is removed and concrete is poured in the shell.
The shell is made of corrugated and reinforced thin sheet steel (mono-tube piles) or pipes (Armco welded pipes or common seamless pipes). The piles of this type are called a shell type piles.
The shell-less type is formed by withdrawing the shell while the concrete is being placed. In both the types of piles the bottom of the shell is closed with a conical tip which can be separated from the shell. By driving the concrete out of the shell an enlarged bulb may be formed in both the types of piles. Franki piles are of this type. In some cases the shell will be left in place and the tube is concreted. This type of pile is very much used in piling over water.
(3.1) Timber piles
Timber piles are made of-tree trunks driven with small end as a point
Maximum length: 35 m; optimum length: 9 - 20m
Max load for usual conditions: 450 kN; optimum load range = 80 - 240 kN
#Disadvantages of using timber piles:
Difficult to splice, vulnerable to damage in hard driving, vulnerable to decay unless treated with preservatives (If timber is below permanent Water table it will apparently last forever), if subjected to alternate wetting & drying, the useful life will be short, partly embedded piles or piles above Water table are susceptible to damage from wood borers and other insects unless treated.
#Advantages:
Comparatively low initial cost, permanently submerged piles are resistant to decay, easy to handle, best suited for friction piles in granular material.
(3.2) Steel piles
Maximum length practically unlimited, optimum length: 12-50m
Load for usual conditions = maximum allowable stress x cross-sectional area
The members are usually rolled HP shapes/pipe piles. Wide flange beams & I beams proportioned to withstand the hard driving stress to which the pile may be subjected. In HP pile the flange thickness = web thickness, piles are either welded or seamless steel pipes, which may be driven either open ended or closed end. Closed end piles are usually filled with concrete after driving.
Open end piles may be filled but this is not often necessary., dm
Advantages of steel piles:
Easy to splice, high capacity, small displacement, able to penetrate through light obstructions, best suited for end bearing on rock, reduce allowable capacity for corrosive locations or provide corrosion protection.
Disadvantages:
Vulnerable to corrosion.
HP section may be damaged/deflected by major obstruction
(3.3) Concrete Piles
Concrete piles may be precast, prestressed, cast in place, or of composite construction
Precast concrete piles may be made using ordinary reinforcement or they may be prestressed.
Precast piles using ordinary reinforcement are designed to resist bending stresses during picking up & transport to the site & bending moments from lateral loads and to provide sufficient resistance to vertical loads and any tension forces developed during driving.
Prestressed piles are formed by tensioning high strength steel prestress cables, and casting the concrete about the cable. When the concrete hardens, the prestress cables are cut, with the tension force in the cables now producing compressive stress in the concrete pile. It is common to higher-strength concrete (35 to 55 MPa) in prestressed piles because of the large initial compressive stresses from prestressing. Prestressing the piles, tend to counteract any tension stresses during either handling or driving.
Max length: 10 - 15 m for precast, 20 - 30 m for prestressed
Optimum length 10 - 12 m for precast. 18 - 25m prestressed
Loads for usual conditions 900 for precast. 8500 kN for prestressed
Optimum load range: 350 - 3500 kN
Advantages:
High load capacities, corrosion resistance can be attained, hard driving possible
Cylinder piles in particular are suited for bending resistance.
Cast in place concrete piles are formed by drilling a hole in the ground & filling it with concrete. The hole may be drilled or formed by driving a shell or casing into the ground.
Disadvantages:
Concrete piles are considered permanent, however certain soils (usually organic) contain materials that may form acids that can damage the concrete.
Salt water may also adversely react with the concrete unless special precautions are taken when the mix proportions are designed. Additionally, concrete piles used for marine structures may undergo abrasion from wave action and floating debris in the water.
Difficult to handle unless prestressed, high initial cost, considerable displacement, prestressed piles are difficult to splice.
Alternate freezing thawing can cause concrete damage in any exposed situation.
(3.4) plastic pile
a. Vinyl sheet pile
b. PVC sheet pile
c. Plastic pile
(3.5) Composite piles
In general, a composite pile is made up of two or more sections of different materials or different pile types. The upper portion could be eased cast-in-place concrete combined with a lower portion of timber, steel H or concrete filled steel pipe pile. These piles have limited application and arc employed under special conditions.

#CREDIT