Project on Ground Improvement using Stone Column

In order to enhance infrastructure projects, large civil engineering projects are executed in India. Due to space constraints and time limits infrastructure facilities have to often build on site where the soil conditions are not ideal. This is where the geotechnical engineer plays a critical role in improving the soil conditions. The method of ground improvement adopted depends upon the nature of strata and the purpose of improvement. Under different improvement techniques, ground improvement using stone columns offers a proven and economical solution. In this project, you are going to make a stone column with different composition to know which composition gives more strength to the soil.

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Stone columns have been used as a technique for improving both cohesive soils and silty sands to increase strength and decrease compressibility. Stone columns can improve a soil deposit by densification, reinforcement and drainage functions. Out of several techniques available for improving soft clay, stone columns are ideally suited for structures with widespread loads. In case of soil having medium to low safe bearing capacity, ground improvement with the help of stone columns has been found economical and faster in construction. The main aim of soil improvement is to increase the shear strength, loading capacity, stability and settlement control.

An improvement in the bearing and reduction in settlement of soft deposit can be affected by the installation of stone columns. The method consists of forming vertical holes in the ground when being filled with compact crushed stone, gravel, and sand or a mixture of soil improvement occurs in two ways,

• The stone columns provide strength reinforcement to the soil and due to their relatively high modulus a large portion of the load applied to the ground surface is transferred to them.
• Column acts as vertical strains and accelerates consolidation. The stone column has been used up to about 20m depth and about 1.0 diameter.

Main advantages of using stone column are, Increased strength to improve stability, reduced deformation due to distortion or compressibility of the soil mass, Reduced susceptibility to liquefaction, the reduced natural variability of soils, to make it more economical, Settlement reduction, to increase the load bearing capacity.

Project Description:

1. Sand: Sand is a naturally occurring particle composed mainly of silica and these have a particle size range of 0.0625mm-2mm.
2. Fly ash: After combustion of coal there is two kinds of solids residue that is obtained, one is bottom ash, it is heavy and the other one is fly ash, so it flies and hence the name!. It can be captured using electrostatic precipitator or any other particle filter technology.
3. Geogrid: These are geosynthetic materials used Reinforce Soil and used for reinforcing Retaining Walls. As Soil pulls apart in Tension Geogrids are strong in tension. These are made of polymers such as Polyester or Polyethylene.
4. Jute: It is a type of natural fiber used to strengthen composites. In this project, you will use this for the same purpose.

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Project Implementation:

1. At first collect all the materials (Sand, Stone aggregate, Fly ash, Jute) from your locality.
2. Then perform a Sieve analysis test to characterize various types of soil according to the grain size.
3. Then perform specific gravity test, Liquid limit test, Plastic limit test, Standard Proctor test, of various soils which you characterized in the previous test. Keep a record of all the data you obtained for each soil.
4. Obtain screened stone aggregate from the local crusher. Wash them and over dry them at a temperature around 1100 degree Celsius. Perform specific gravity test on these stones.
5. Perform specific gravity test on Fly ash too and keep noting the data you obtained from these tests.
6. After performing these tests determine which soil is rich in the mechanical property.
7. Perform an unconfined test using that soil sample with the various composition of fly ash, geogrid, Jute, Water, and stone. Few of the test cases are given here for your reference,
• Soil + 30% of water
• Soil + 20% of water
• Soil+ geogrid at a height of 3.8 cm from the bottom
• soil+ geogrid at height of 2.5cm and 5cm from the bottom
• Soil+ 20% of the stone sample
• soil + 20 % stone sample+ jute at 3.8 cm from bottom
• Soil + 20 % stone sample+ jute at 2.5 cm and 5cm from bottom
• Soil + 20 % stone + 20 % fly ash
• Soil + 20 % stone + 20 % fly ash + jute at height of 3.8 cm from bottom
• Soil + 20 % stone + 20 % fly ash + jute at height of 2.5 cm and 5cm from bottom
8. Plot stress-strain curve for all the above test cases and note down the uni-axial compressive test value for each of them.
9. Observe the result and try to analyse which composition is cost effective and efficient.

Project Brief: After successful completion of the project, you can observe the following things,

• The replacement of 20% (by weight) of stones by fly ash can be possible without affecting the strength and performance of the system.
• When Jute was used in single layer (at 3.8cm from bottom) and double layer (at 2.5cm and 3.8cm from bottom) in the specimen of the stone columns, it was found that the stone column gained maximum strength when fly ash was used in the stone column and jute was used at 2.5cm and 3.8cm from bottom.

Software requirements:

Minitab: You can use this software for plotting and comparing your result data.

• Soil
• Water
• Stone
• Geo-grid
• Testing apparatus

• Ground improvement

Ground Improvement using Stone Column