Eiffel 101: Basic Principles of Pile Foundations
Pile foundations can be split into two main categories: shallow foundations and deep foundations.
When a foundation has a depth that is less than the width of the building and is also less than 10 feet deep, it's considered a shallow foundation. Shallow foundations work to support structures when surface soils aren't strong enough.
If the foundations depth is greater than the width of the building, it's considered a deep foundation. Deep foundations enable a structure’s load to be transferred from the surface to the stronger soil or rock in the deep ground below.
Here are a few additional conditions which will require a deep foundation:
- When the soil near the surface has a relatively weak bearing capacity
- When the soil near the surface contain expansive clays
- When the soil near the surface is vulnerable to being removed by erosion or scour
Deep Pile Foundation Principles
Piles are long cylinders often made of steel or concrete used to create foundations. A pile foundation is a series of columns (piles) inserted into the ground to transmit loads to a deeper level of subsoil.
Pile foundations are best used in two situations. First, if there is a weak layer of soil at the surface of a construction site, the soil will not be able to support the weight of a new structure and therefore piles must be used. Second, if the surface soil cannot support the building regardless of the soil’s strength, piling must be used. In both situations, foundation piles will transfer the weight of the structure from the soil’s surface to the stronger soil or rock below.
To install a pile foundation, the piles are first cast at ground level and then hammered or driven into the ground using a pile driver. Piles are hammered into the ground until refusal, which is when a pile cannot be driven into the soil any farther. This method of installing piles is ideal because it doesn't disturb the supporting soil around the pile and it results in the highest bearing capacity for each pile.
Deep Pile Foundation Classifications
Piles can be classified as bearing piles, friction piles, friction-cum-bearing piles, batter piles, guide piles, and sheet piles. Depending on the composition of their materials, piles can also be classified as timber piles, concrete piles, sand piles, or steel piles.
Bearing piles are driven into the ground and rest on the deep soil or rock below the surface. Similar to columns on a house, bearing piles act as pillars to support the structure.
Friction piles can be used when there isn't a strong enough deep layer for a bearing pile to rest on. Friction piles are long with roughened surfaces to increase the surface area and resistance of the pile. Friction piles use the soils friction more like a wedge to bear the weight of the structure above.
Batter piles are driven at an incline to resist inclined loads.
Guide piles create cofferdams to provide stable foundations for under-water construction.
Sheet piles are used to make sheet pile walls and work as a retaining structure.
Common Deep Foundation Pile Beam Sizes
Piles come in a wide range of sizes and styles. Some of the most common sizes include:
W8: W8x18, W8x21, W8x24, W8x28, W8x31, W8x35, W8x40, W8x48, W8x58, W8x67
W10: W10x22, W10x26, W10x30, W10x33, W10x39, W10x45, W10x49, W10x54, W10x60, W10x68, W10x77, W10x88, W10x100, W10x112
W12: W12x26, W12x30, W12x35, W12x40, W12x45, W12x50, W12x53, W12x58 ,W12x65, W12x72, W12x79, W12x87, W12x96, W12x106, W26x120, W12x136, W12x152, W12x170, W12x190, W12x210, W12x230, W12x252
W14: W14x22, W14x26, W14x30, W14x34, W14x38, W14x43, W14x48, W14x53, W14x61, W14x68, W14x74, W14x82, W14x90, W14x99, W14x109, W14x120, W14x132, W14x145, W14x159, W14x176, W14x193, W14x211, W14x233, W14x257, W14x283
W16: W16x26, W16x31, W16x36, W16x40, W16x45, W16x50, W16x57, W16x67, W16x77, W16x89, W16x100
W18: W18x35, W18x40, W18x46, W18x50, W18x55, W18x60, W18x65, W18x71, W18x76, W18x86, W18x97, W18x106, W18x119, W18x130, W18x143, W18x158, W18x175, W18x192, W18x211, W18x234
W21: W21x44, W21x50, W21x57, W21x58, W21x55, W21x62, W21x68, W21x73, W21x83, W21x93, W21x101, W21x111, W21x122, W21x132, W21x147, W21x166, W21x182, W21x201, W21x223, W21x248, W21x275
W24: W24x55, W24x62, W24x68, W24x76, W24x84, W24x94, W24x103, W24x204, W24x117, W24x131, W24x146, W24x162, W24x176, W24x192, W24x207, W24x229
W27: W27x84, W27x94, W27x102, W27x114, W27x129, W27x146, W27x161, W27x178, W27x194
W30: W30x90, W30x99, W30x108, W30x116, W30x124, W30x132, W30x148
W33: W33x118, W33x130, W33x141, W33x152, W33x169
W36: W36x135, W36x150, W36x160, W36x170, W36x182, W36x194, W36x210, W36x232, W36x256
HP10: HP10x42, HP10x57
HP12: HP12x53, HP12x63, HP12x74, HP12x84, HP12x89, HP12x102, HP12x117
HP14: HP14x73, HP14x89, HP14x102, HP14x117
HP16: HP16x88, HP16x101, HP16x121, HP16x141, HP16x162, HP16x183
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