KOLEJ KEMAHIRAN TINGGI MARA PASIR

MAS

PRESENTATION GROUND IMPROVEMENT(STONE COLUMN)

PREPARE BY:1. NUR AZIRA BINTI MASSIM @

KASSIM2. NOOR SYAKIRAH BINTI KHALID3. NUR HASLINA BINTI ZAKARIA4. SITI AMIRA BINTI MUSA

STONE COLUMNS

Soils with appreciable silt or clay content do not respond to deep vibratory compaction. To improve these cohesive soil types to allow building and other heavy construction, it is necessary to create stiff reinforcing elements in the soil mass. The stone column technique, also known as vibro-replacement or vibro-displacement, is a ground improvement process where vertical columns of compacted aggregate are formed through the soils to be improved. These columns result in considerable vertical load carrying capacity and improved shear resistance in the soil mass.Stone columns are installed with specialized vibratory probes, generally having a horizontal mode of vibration. Column diameters of 2 to 5 feet can be achieved, depending upon soil conditions and design requirements.

CONCEPT OF DESIGN

Stone columns are essentially designed to take load when the columns bulgeunder loading and the surrounding soil offers passive resistance. In a cohesivesoil, when stone columns are constructed, a considerable portion of improvedground can be reduced to as much as 30% of the natural ground. In addition,the stone columns act as a drainage path, which would accelerate further settlement under loading.In a cohesion less soil like loose silty sand,when stone columns are constructed by vibro-floatation, the ground is densified by the reduction invoids and the intrusion of gravel and stones. Thus, in totality, the bearing capacity increases. The drainage and residual settlements are not important in such soil conditions.

VIBRO REPLACEMENT STONE COLUMNS

Are a ground improvement technique to improve the load bearing capacity and reduce the settlement of the soil. On many occasions, it is noted that the local soil is by nature, unable to bear the proposed structure. Hence the use of ground improvement techniques may be necessitated. Use of stone columns is one such technique. 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.

The aforementioned crushed aggregates in the definite proportion are to be placed into the soil at regular intervals throughout the area of the land where the soil bearing capacity is to be improved. This is done either by using the dry or the wet top feed vibrators which are forced into the ground. The aggregates are then allowed to take the place of the displaced soil which exerts a pressure on the surrounding soil, hence helping to improve the soil's load-bearing capacity.

The vibrating pore breaks down the pores of the surrounding soil, thereby densifying the soil. The crushed aggregates or the gravel that is poured in takes the place of the soil and keeps up the pressure on the soil that was created by the vibrating probe. These columns are made across the area to be built on in a grid pattern at regular intervals.

PURPOSE/ OBJECTIVE

i. The stone column technique of ground improvement is extensively used to improve the strength of weak soil layers.

ii.To improve the stability of embankments and natural slopes.

iii.To increase the bearing capacity of a site to make it possible to use shallow foundation on the soil.

iv.the reduction of total and differential settlements.

v.For the reduction of liquefaction potential of cohesion less soil.

vi. To increase the time rate of settlement.

PROCEDURES

BOTTOM FEED METHOD OF STONE COLUMN CONSTRUCTION

Step 1:With the vibrocat stabilized on hydraulic outriggers the leaders are elevated to the vertical and the vibrator located on the ground at the stone column position. The skip is charged with stone.Step 2 :The skip travel up the leaders and automatically discharges stone into thye reception chamber at the top of the vibrator.Step3:The vibrator penetrates the weak soils to the design depth under the action of the vibrations compressed air and pull- down winch facility.

Step4:At the required depth. Stone is released and compacted by small upward and downward movements of the vibrator the pull-down being employed on the downward compacting action.

Step 5:With stone being added to the system as necessary at any stage of the construction procedure a stone column of very high integrity,tighly interlocked with the surrounding soil is built up to ground level.

EQUIPMENTMain equipment used to form Stone Columns comprises of the following:

i. The Vibratorii. The Crane or Base Machineiii. Stone Delivery Systems and Water-Jet Systemsiv. The Control and Verification Device

Other ancillary equipment include:

i. Pay Loaderii. Dumpersiii. Survey equipment like Theodolite, Dumpy Level and

leveling Equipmentiv. Low Bed Trailerv. Tractor

Benefits of Vibroflotation Stone Columns are a technical and potentially economical alternatives todeep foundation.

Stone Columns are more economical than the removal and replacementof deep poor bearing soil on a large site.

Very useful where infrastructure does not permit high vibrationtechnique such as dynamic compaction, deep blasting or piling.

Where time is critical to project start-up site improvement can beachieved quicker by vibroflotation than by pre-loading the soils.• Stone Columns provide a vertical drainage path for excess pore waterpressure dissipation.

With Vibroflotation differential settlements are often in the order of 10%to 15% of total settlement

REFERENCES

1.Principles of foundation engineering2.Internet :ground improvement3.“Reinforcing of Soft Cohesive Soils with Stone Columns”,4.Ground Engineering5.“Building Structures Supported by Stabilized Ground”,

Geotechnique6.Soil mechanics and foundation engineering

CONCLUSION1. Understanding the limits to which the stone columns can improve the ground capacity and reduce the settlement irrespective of the behavior of the individual stone column.

2. Choice of the correct technique of the stone column construction depending upon the soil properties.

3. Assessment of the properties of the soil layers that can be improved by stone column.

4. Proper execution of the stone column to take sure that the functions of the stone columns is not blocked by the technique of construction adopted.