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Piles Engineering

Why is bentonite slurry commonly used in diaphragm wall construction?

Bentonite slurry is one of the most common excavation fluid used in constructing diaphragm wall. Bentonite clay (in powder form) and water are combined in a colloidal mixer and clay particles bond to each other and set to form a gel when left to stand for a period of time. When the bentonite is set in motion, it reverts back to the fluid state rapidly.

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What is the difference between pad foundation, strip foundation and raft foundation?

Shallow foundation is commonly accepted as foundation with founding level less than 3m from ground surface. In case surface loads or surface conditions could still affect the bearing capacity, the foundation which sits on it is called shallow foundation.

Pad foundation refers to the foundation which is intended for sustaining concentrated loads from a single point load such as structural columns.

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What are the components in contributing the bearing capacity of shallow foundation?

Based on Terzaghi’s bearing capacity equation, there are three components in contribution to the bearing capacity:

(i) Surcharge pressure
Foundations are normally not placed directly on the ground level. Instead, they are installed at a depth below the existing ground level. The soil pressure arising from the depth of soils serves as a surcharge imposing a uniform pressure at foundation level.

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In driven piles, the allowable set is limited between 25mm and 50mm per 10 blows. Why?

In final set table it is commonly to limit pile set between 25mm/10 blows and 50mm/10 blows. The reason of the provision for lower limit of set value of 25mm/10 blows is to avoid possible damage at pile toe owing to compressive stress reflected at the bottom of pile.

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Some piling contractors incline to use drop hammer instead of hydraulic hammers in setting of piles. Why?

The use of high grade and heavy steel pipes may not warrant the use of drop hammer. For pile driving of Grade 55C steel section, it requires heavier drop hammer with increased drop height so as to comply with penetration resistance at final set. As such, it is possible that such heavy hammer may damage the pile and endangers the worker who takes the final set record.

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