What is Under Reamed Pile?
A cast-in-situ solid pile with an expanded base called bulb (bulb has shape of triangle) at the base made by one or the other removing or digging soil or by some other appropriate method is called Under-Reamed Pile. Another name for under-Reamed Piles is bored cast-in-situ concrete piles.
These piles are most relevant in soils where strong ground developments happen because of occasional varieties or delicate soil layers. Under reamed pile is a simple concrete pile that has one or more bulbs at the lower end. This bulb is named under ream.
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Types Under Reamed Piles
- Single Under Reamed pile
- Multiple bulbs Under Reamed pile
When just a single bulb is given at the lower part of the pile, it is known as a single Under-Reamed Pile establishment. When at least two bulbs are given at the lower part of the heap, it is known as multiple bulbs Under-Reamed Pile establishment. The use of multiple bulbs enhances the weight-bearing capability of the Foundation.
The most crucial and critical part of a building is its Foundation. A strong foundation makes a structure more stable, Strong, and resistant to a natural disaster. Depending upon different factors of the building, environment, and part of the earth on which it stands. Constructors lay down a different type of Foundation. Two basic types are: –
- Shallow Foundation
- Deep Foundation
Pile Foundations is a type of deep foundation but under reamed pile is a different case. It is not laid down so deep.
Application of Under Reamed Pile
Under-Reamed Piles Foundation is an answer in zones where dark cotton soil could cause primary insecurity. Commonly, soils go through volumetric changes because of the dampness variety under the ground surface. This development and shrinkage can cause disastrous trouble, especially when there is a question about the Foundation’s bearing. The truth is that Under Reamed Piles are considered generally protected establishments for such dark cotton soils or sweeping soils.
Additionally, under reamed piles likewise, increment the bearing limit, give legitimate anchorage, and disregard the effect of settlement and elevate because of shrinkage and expanding because of the presence of a bulb-like construction. Additionally, these piles are suggested for the sandy soil with the high groundwater table and a design where elevating powers like a breeze and critical factors are comparatively high.
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Features of Under Reamed Pile Foundation
- The diameter of the pile is 20 to 50cm.
- Bulb Diameter is 2 to 3 times of the diameter of the pile.
- Pile Length is 3 to 8m
- Spacing between two piles is generally 2 to 4m.
- Distance between 2 bulbs is 1.25 to 1.5 times bulb diameter.
- The load-carrying capacity of Under reamed pile is 20 to 40 tons.
- The under-reamed pile volume relies on the diameter of the pile and the size of the bulbs.
Under Reamed Pile Construction
The machine used for the installment of under reamed pile is lightweight and two of its important parts are
- Spiral Auger
- Under reamer
A spiral auger is a device used in construction works. It consists of a sharp twisting blade and is used for boring purposes. The under-reamed pile utilizes a spiral auger to the ground’s opening, with a unique sharp edge used to burrow the dirt at the lower end of the drill.
Furthermore, a basket is hanged for filling the exhumed soil underneath the two cutters. Auger is introduced in the part of the earth to be bored and rotated by hand. When spirals get full of soil auger is taken out. This process is continued until the required depth is achieved.
Under – Reamer
Under reamer is a rotatory cutting device used for boring. It has cutters that can be extended or shrunk by mechanical methods or by hand and are used to develop or ream a borehole underneath. Underreaming is a method of widening the bottom area of a drilled hole and thus increasing load-bearing capacity.
The utilization of a boring guide is important to keep the bore opening vertical and in position. Each guide is given a round collar and four arms. The collar is fixed to the drilling guide on the lower side, and it doesn’t permit the mouth of drill openings to expand because of frequent insertion and evacuation of the drill and other drilling equipment.
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Steps involved in Under Reamed Pile Construction
- The first step is to set guide assembly.
- The opening or bore for under reamed pile is finished by utilizing a spiral auger.
- Soil dug by spiral auger is taken out with the help of a bucket.
- Unique cutters are utilized for making the bulb. The dia. of the bulb can be expanded by applying more significant pressure. The drill is set up on a tripod after the burrowing is finished. So, the excavating is done the vertical way.
- As arriving at adequate profundity, the drill is pulled out. The support is then embedded into the opening. Cementing is finished. On the off chance that more than one pile, the bar is developed, which associates the piles and makes them act like a solitary unit.
Under Reamed Piles Bulb Calculation
The width of the under-reamed bulbs might be 2 to 3 times the width of the stem. The distance between bulbs is 1.25 to 1.5 times the stem breadth. The topmost bulb’s distance from the surface should not be less than 2 to 3 times the bulb’s diameter.
Increasing Load-Carrying Capacity of Under Reamed Pile
The load-bearing capacity of under-reamed piles can be increased by controlling various factors.
- By expanding quantities of bulbs. More bulbs will provide more fabulous anchorage.
- By expanding the diameter of bulbs.
- By expanding the Length of the pile.
- By proper designing of piles
Advantages of under reamed pile
- Diminishes the vertical settlement and furthermore differential settlement.
- It is utilized when soil expands because of the dampness variety or sweeping nature of the dirt.
- Arrangement of under-reams or bulbs has the upside of expanding the bearing and inspire limits.
- When the quantity of bulbs is expanded from one to two, the pile conveying limit of the Under-Reamed Pile is expanded.
- The arrangement of bulbs is of unique benefit in Under-Reamed Piles to oppose uplift, and they can be utilized as anchors.
- Under-Reamed Piles are cheaper comparatively because less amount of concrete is required to fill the excavated area.
Disadvantages of under Reamed Pile
- Under a depth where soil nature differs with a climatic condition, Under-Reamed Piles are not appropriate for waterlogged soil, as they take load by contact.
- These piles need critical supervision and concentration during the development.
- A large portion of the occasions, Under Reamed Piles, are driven physically with a hand-worked machine.
Under Reamed Piles PDF Download
Download IS Code IS 2911-3 (1980): Code of practice for design and construction
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