Shallow vs Deep foundation and Sheet Pile 2 Q2

Thomas Sim PEA2066

Q.
a) List five (5) differences between shallow and deep foundation. (10 marks)

b) Sheet pile walls are constructed by driving prefabricated sections into the ground. With the aid of sketches, explain the method of installing sheet pile. (15 marks)

(25 marks, 2014 Q2)

A.

Shallow foundation:


A type of foundation that is used when the earth directly beneath a structure has sufficient bearing capacity to sustain the loads from the structure . 
1. Light, flexible structure: older residential construction, residential construction which include a basement, and in many commercial structures,
2. Nice soil condition: hard, uniform soil.
3. Cheaper than deep foundation
4. Easier construction
5. Typically types: spreading footing foundation, slab-on-grade foundation, pad foundation, strip foundation, and raft foundation.
Spreading footing foundation: controlled by several factors: lateral and vertical capacity, penetration through near surface layers likely to change volume due to frost heave or shrink-swell.
Mat-slab foundation: the distribution of loads in a mat slab helps reduce differential settlement due to the non-uniform building loads. 

 

Deep Foundation:

The characteristics of the deep foundations are as follow. 

A type of foundation that is used when the soil near the ground surface is weak.
1. Heavy, rigid structure: other uncommon building, such as large bridge, tower, and the empire state building.
2. Poor soil condition: liquefaction, soft clay and sands.
3. Typically more expansive
4. More complex to construct and more time than shallow foundation.
5. Typically types: battered piles, bearing piles, caissons, and friction piles
Friction piles: Friction piles obtain a greater part of their carrying capacity by skin friction or adhesion. This tends to occur when piles do not reach an impenetrable stratum but are driven for some distance into a penetrable soil. Their carrying capacity is derived partly from end bearing and partly from skin friction between the embedded surface of the soil and the surrounding soil. 
End bearing piles: End bearing piles are those which terminate in hard, relatively impenetrable material such as rock or very dense sand and gravel. They derive most of their carrying capacity from the resistance of the stratum at the toe of the pile
Ref:
How to differentiate Shallow Foundation from Deep Foundation, available at
http://www.bayt.com/en/specialties/q/140692/how-to-differentiate-shallow-foundation-to-deep-foundation/
(b)
Sheet Pile

 

 

Properties of steel sheet-pile walls

Sheet-pile walls are made from linked sheet piles that are long steel plates with a Z or U shape. These piles are connected together to make a sealed wall. Sheet piles are often connected together in pairs and installed using one of three methods:

  • Vibration: this is the most common method. The first sheet pile of the wall is installed into the ground. A vibratory hammer with clamp is attached to the top of the second sheet pile, which is then interlocked with the first sheet pile, and the sheet pile is vibrated into the ground.
  • Pressing: sheet piles can also be pressed into the ground when noise hindrance and vibration would otherwise cause problems. This, however, takes longer and is expensive. The sheet piles are pressed into the ground by a hydraulic machine.
  • Excavation: sheet piles can also be excavated into the soil. A long trench is excavated which is then filled with cement bentonite (a thin concrete slurry) to prevent the walls from collapsing. The sheet piles are then installed in the trench and the cement bentonite is allowed to set.

Steel sheet-pile walls can retain both soil and water. The retaining height of the sheet-pile wall can be increased by driving anchors or MV piles into the ground. This increases the strength of the structure: the anchors prevent the sheet-pile wall from being forced inwards by the force of the soil or water.

Use of sheet-pile walls
Sheet-pile walls are used for both temporary and permanent purposes. They are, for example, suitable for creating a sufficiently deep workplace in the form of an excavation pit below ground level; they retain the soil or water to enable the construction. Sheet-pile walls are used in permanent structures such as quay walls or tunnel walls.

Ref:
Steel Sheet Pile Wall, available at
http://www.bnft.nl/page_2526.asp