stone column

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AN-najah National UniversityFaculty of Engineering

Civil engineering Department

Prepared by:

Eng. Imad A. F. Jarara’h.

Submitted to: Dr.Isam Gh. M.Jardaneh.

2010

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Methods for Soil Improvement?

Ground Reinforcement

Ground Improvement

Ground Treatment

• Stone Columns• Soil Nails• Deep Soil Nailing• Micro piles (Mini-piles)• Jet Grouting• Ground Anchors• Geosynthetics• Fiber Reinforcement• Lime Columns• Vibro-Concrete Column• Mechanically Stabilized

Earth• Biotechnical

• Deep Dynamic Compaction

• Drainage/Surcharge• Electro-osmosis• Compaction grouting• Blasting• Surface Compaction

• Soil Cement• Lime Admixtures• Fly ash• Dewatering• Heating/Freezing• Verification

• Stone Columns??

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Soil Improvement

&Reinforcement

“Stone Columns Method”

What is Stone Column?

stone columns are a ground improvement technique to improve the load bearing capacity of the soil.

The stone column consists of crushed coarse aggregates of various sizes.

The ratio in which the stones of different sizes will be mixed is decided by design criteria.

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What is Stone Column? (Cont.)

Vibro-Replacement Stone Columns extends the range of soils that can be improved by vibratory techniques to include cohesive soils. Densification and/or reinforcement of the soil with compacted granular columns or “stone columns” is accomplished by either top-feed or the bottom-feed method.

Cohesive, mixed and layered soils generally do not densify easily when subjected to vibration alone. The Vibro-Replacement Stone Column technique was developed specifically for these soils, effectively extending the range of soil types that can be improved with the deep vibratory process. With Vibro-Replacement Stone Columns, columns of dense, crushed stone are designed to increase bearing capacity, reduce settlement, aid densification and mitigate the potential for liquefaction, and improve shear resistance.

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The Vibro-Replacement Stone Column Process!

1. Reduces shallow foundation settlement.

2. Increases bearing capacity, allowing reduction in footing size.

3. Mitigates liquefaction potential.

4. Provides slope stabilization.

5. Permits construction on fills.

6. Permits shallow footing construction.

7. Prevents earthquake-induced lateral spreading.

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Stone Column Construction methods!

The two primary methods of Vibro Stone Column construction are:

1. Wet, Top Feed Method (Replacement and Displacement).

2. Dry, Bottom Feed Method (Displacement).

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Stone Column Construction (cont.)

**Wet, Top Feed Method (Replacement and Displacement):In this technique, jetting water is used to remove soft material, stabilize the probe hole, and ensure that the stone backfill reaches the tip of the vibrator.

This is the most commonly used and most cost-efficient of the deep vibratory methods. However, handling of the spoil generated by the process may make this method more difficult to use on confined sites or in environmentally sensitive areas.

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Stone Column Construction (cont.)

**Top-Feed Construction Method:

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Stone Column Construction (cont.)

**Dry, Bottom Feed Method (Displacement):

This technique uses the same vibrator probes as standard Vibro-Replacement Stone Columns, but with the addition of a hopper and supply tube to feed the stone backfill directly to the tip of the vibrator.

Bottom Feed Vibro-Replacement is a completely dry operation where the vibrator remains in the ground during the construction process.

The elimination of flushing water in turn eliminates the generation of spoil, extending the range of sites that can be treated. Treatment is possible up to a depth of 80 feet and is not inhibited by the presence of groundwater.

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Important Stone Columns Parameters?

1. Ground conditions.

2. Relative density (RD).

3. Degree of saturation.

4. Permeation.

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Stone Columns Acceptance Testing?

1. Standard Penetration Testing (SPT).

2. Cone Penetrometer Testing (CPT).

3. Dilatometer Testing (DMT).

4. Load Testing.

5. Shear Wave Velocity Profiling .

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Stone Columns Quality Control!

1. Stone column location ( the spacing between the stone column usually 1.5-3 m c/c).

2. Resistance level as measured by amp meter (Vibrator draws more current in denser sols).

3. Quality and quantity of stone added -- friction angle and size of stone columns.

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Stone Columns Design Steps:

1. Perform site investigationSoil type, gradation, consolidation, and strength important.

2. Calculate predicted improvement.(Problem understood)

3. Establish requirements of ground improvement(What settlements, factor of safety, etc., are allowable).

4. Design Vibro-Replacement scheme(Number of stone columns, diameter of stone column and/or performance requirements required to achieve desired results).

5. Establish testing criteria(Load test, SPT, area of stone columns).

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Fig. Step Construction procedure of aggregate pier element!

Drill cavity

using augers, install casing

IF cave-ins occur.

Place crushed stone

at the bottom of

the cavity.

Ram bottom stone with beveled

tamper to produce bulb.

densify crushed stone

in layers of 30cm

with tamper.

Preload top of rap element. 15

Method to Estimate Settlement Reduction Using Stone Columns in Cohesive Soils !!

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Vibroflotation and stone column??

From Das, 1998

Vibroflotation is a technique for in situ densification of thick layers of loose granular soil deposits. It was developed in Germany in the 1930s.

Stone column can be used instead of sand drains and it is the same as Vibroflotation.

Pictures for stone column?

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Pictures for stone column (cont.)

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Pictures for stone column (cont.)

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Expected Stone Columns Results!!

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DO YOU HAVE ANY

QUESTIONS??

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THANK YOU

FOR

YOUR ATTENTION!