Table of Contents
Vibro piles are the type of pile foundation utilized where the soil is soft, thus contributing slight frictional resistance to the discharge of concrete. The standard and expandable pile can be pushed by the Vibro technique.
1. Vibro Piles
These piles are made by pushing a steel tube and shoe, filling it with concrete, and removing the steel tube.
Standard Vibro piles are made in the size of 45 and 50 cm in diameter for loads of 60 to 70 tonnes. They can be formed in lengths of 25 m and over.
A steel tube containing a cast-iron shoe included at the bottom is pushed by a 2 to 2.5 tonnes hammer run by steam or compressed air providing up to 40 blows per minute, with a stroke of approximately 1.4 m.
2. Advantages of Vibro Piles
The advantages of Vibro Piling are as follows:
✔ Useful treatment for soft/weak soils at depths of 2m>20m.
✔ Optimized and localized treatment solution for varying soils.
✔ Highly cheap and usually results in more significant time savings.
✔ Decreases the danger of seismically generated liquefaction.
✔ Minimal noise and vibration.
✔ Permits high manufacture rates to be faster to complete than piling.
✔ Cost-effective option to piling.
3. Disadvantages of Vibro Piles
The disadvantages of the Vibro pile are as follows:
✔ Vibro-compaction is only effective on granular and non-cohesive soils.
✔ Densification generally cannot be achieved when the granular soil contains more than 12 to 15 percent silt or more than 2 percent clay.
✔ A comprehensive analysis of the soil profile is needed with continuous sampling or in-situ testing.
✔ Not suitable for sites with contaminated land if vibratory techniques use water jetting.
4. Vibratory Techniques
There are two vibratory techniques used in the UK known as the ‘dry bottom feed’ and the ‘dry top feed’.
Each work precisely for varying soil conditions, therefore it is necessary to aspire to the guidance of a structural engineer at the design stage in order to select the most useful technique.
It is also necessary to take into consideration the following when evaluating vibratory techniques for ground advancement:
The design done should be in accordance with appropriate Building Regulations and Codes of Practice.
Only two types of foundations are appropriate for use with Vibro ground advancement: reinforced concrete strip foundation or a raft or semi raft foundation.
Their design should be undertaken by a Structural Engineer and comply with the minimum requirements for areas of reinforcement as defined in BS EN 1992. For a reinforced strip foundation, this is likely to comprise top and bottom mesh fabric held in place with shear link bars.
Suspended ground floors should be provided for all dwellings where vibratory ground advancement has been carried out.
Where the treated soil composes cohesive soils, steps must be carried out to rescue the potential effects of vegetation (i.e. subsidence or heave).
5. Cast-in-Place Concrete Piles
Cast-in-place concrete is made by boring the soil up to a particularly preferred depth, filling it with freshly mixed concrete, and permitting it to dry on the field itself.
Normally, an outer metallic shell is first pushed into the ground and loaded with a fresh mix of concrete.
It is then allowed to be set and cured.
Finally, the outer metallic shell is removed or pulled out.
1. Advantages of Cast-In-Situ Concrete
Some of the advantages of cast-in-situ concrete piles can be listed as follows:
✔ They are more flexible in terms of length variation.
✔ Handling such piles is easier.
✔ Additional piles may be provided easily.
✔ The installation process is simple with no possibility of breakage.
2. Disadvantages of Cast-In-Situ Concrete
Some of the disadvantages of cast-in-situ concrete piles can be listed as follows:
✔ Since the pile is cast in situ, a proper storage place must be arranged for storing the construction materials safely.
✔ Quality control must be ensured during installation.
✔ The difficulty may arise in casting the concrete where the underground flow of water is relatively heavy.
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