What are Vibro stone columns?/ All about Vibro stone columns.

Let us go through the FAQs related to Vibro stone columns as follows.

1. What are Vibro stone columns?

Vibro stone columns are a process to improve the bearing capacity of weak soils by the installation of stone columns up to the required depth. 

The Vibro columns are made of crushed stones, gravel, or similar type of coarse aggregate materials. These materials are densely compacted with vibrating tools to form a column-like structure below the proposed soil. 

2. What are the different ways to install Vibro stone columns?

There are two methods to form the Vibro stone columns.

Top feed method:

The vibrator probe is penetrated into the ground up to the required depth. The tip of the vibrator tool is fitted with a water jet nozzle to pump the pressurized water. The crushed materials are added around the drilled hole at the top soil surface. The vibration makes these materials fall into the space created by the water jet & vibrator. 

The vibrator is lifted to several feet so that the aggregates occupy the empty space beneath the vibrator tool. Now, the vibrator is lowered to push & compress the aggregates to form a densified column structure. This process of Vibro replacement is repeated until the highly compacted column is formed up to the ground level.

As we use water here, this process is also known as the wet feed method.

Bottom feed method:

In this method, the aggregates are fed beneath the vibrator tool through the feed pipe. The feed pipe is attached alongside the vibrator, up to its tip level. The vibrator is lifted to a certain height to fill the voids by the aggregates. 

Once the voids are filled by aggregates, the vibrator is pushed downward for the compaction & densification of materials. This process is repeated to form an aggregate stone column up to the ground surface level.

As aggregates are fed in dry conditions, this process is referred to as the dry feed method.

3. What are the advantages & disadvantages of Vibro stone columns?

Advantages:

1. Increases bearing capacity of the soil.

2. Reduces the differential settlement of soil & foundation.

3. Helps to reduce foundation size.

4. Enhances the shear strength & friction angle of the soil.

5. Required foundation depth is minimized. 

6. Lowers soil permeability.

7. Enhances soil stiffness & stability.

8. More economical when compared to piling.

Disadvantages:

1. Not effective in all types of soils. This method works better for granular & non-cohesive soils.

2. Continuous in situ testing of the soil samples is necessary to install the Vibro stone columns.

3. Thorough soil investigation is required before preparing the construction drawing.

4. Required compaction cannot be achieved in granular soils if the percentage of clay or silt is > 15%.

4. What are the factors that affect the design of Vibro stone columns?

The factors that decide the design of Vibro stone columns are,

1. Type of soil.

2. Required installation depth.

3. The area to be treated.

4. The type of structure to be supported.

5. Required area replacement ratio.

6. In-situ soil properties.

7. The type of aggregate material used in the column & its parameter.

5. Where we can use the Vibro replacement stone columns?

The Vibro stone columns are used in several Civil engineering projects such as,

1. Bridge approaches & abutments.

2. Road embankments, retaining walls, & rail works.

3. In multi-storeyed buildings.

4. Industrial structures & warehouses.

6. Why the Vibro stone columns are used?

When we design a superstructure, we need firm strata or sub-surface soil to bear the superimposed loads. But this condition is not possible in all types of available soils.

Vibro stone columns are useful to eradicate such weak soil defects. This process helps to improve ground conditions & to enhance soil properties as per the design requirement.

7. What are the important aspects of Vibro stone columns?

1. The spacing of the columns is usually between  6' to 9' (1.8m. to 2.4m.).

2. The diameter of the vibrator probe is between 12 inches to 18 inches ( 300mm. - 450mm.).

3. The Vibro stone columns are constructed in the range of 2' to 4' ( 600mm. - 1200mm.) per lift of the vibrator probe.

4. The speed of drilling a hole ranges between  3' to 6' per min.(900mm. - 1800mm./minute).

5. The time taken by filling & compaction is between 1.5' to 3' per min. (450mm. - 900mm./minute).

For more such explanatory articles, click here.

Thank you for going through this article❤. Have a good day 😄.

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