GROUND IMPROVEMENT TECHNOLOGY- STONE COLUMN TECHNOLOGY- BAND DRAIN TECHNOLOGY

Sravan MVEngineer

ALTERNATIVES FOR INADEQUATE GROUND?

Abandon the site and locate the structure elsewhere

Design deep foundations to carry the weight of the structure to competent stratum

Redesign the structure according to the ground conditions

Improve the properties of the ground prior to construction

BASIC PRINCIPLE OF GROUND IMPROVEMENT

Densification of the ground , E.g.: Compaction Accelerate the consolidation, E.g.: Vertical drains Usage of geo synthetics, E.g.: Geotextiles Usage of admixtures, E.g.: Cement stabilization Preloading Mechanical Stabilization

Ground improvement is the modification of the ground properties in order to achieve the required ground conditions for the particular use of the ground.

STONE COLUMN TECHNOLOGY

STONE COLUMN TECHNOLOGY It is also known as Vibro replacement

or Vibro displacement Compacted aggregates form as a

vertical columns to improve the soil conditions.

Resulting in considerable increase in vertical load capacity and to an extent contribute to as drains to dissipate pore water pressure.

Two methods of stone columns:

Wet / Top Feed Method

Dry / Bottom Feed Method

STONE COLUMN TECHNOLOGY

STONE COLUMN : WET / TOP FEED METHOD

Step 1 : Penetration of probe Step 2 : Backfilling of aggregate and

compacting Step 3 : Consolidation of granular fill and

finishing the column

Vibro Probe

STONE COLUMN : DRY / BOTTOM FEED METHOD

Step 1 : Penetration of probe Step 2 : Installation of aggregate through

separate duct along the vibro probe Step 3 : Consolidation of granular fill and

finishing the column

Technically and potentially economical alternative for deep compaction.

Alternative for dynamic compaction, deep blasting etc.,

Quicker than preloading the site It increases the bearing capacity,

reduces the settlements, liquefaction potential.

STONE COLUMN : ADVANTAGES

CASE STUDY: Four Lane National Highway Connectivity to ICTT – Vallarpadam, Kochi

Connects NH - 47 and NH - 17. Project cost was revised from 329.46 cr to 571.20 cr due

to ground improvement, bridges and retaining walls. Road Length – 17.2km, total length of bridges – 2.93km. Ground improvement works – 10km. Wet /Top method of installation was used. Stone columns where installed in 15 locations

between Ch, 0.245 and 16.210

CASE STUDY: INSTALLATION

CASE STUDY : INSTALLATION

CASE STUDY :STONE COLUMN Quantity of stone aggregate used : 28,774 cum. Geo grid consumed: 35,536. 12 sq.m Bulk density considered : 1.8 MT/m3

App. Quantity of aggregate for one column : 35MT

Total number of stone columns : 22,166 no's Time required for each stone column : 60 min No. of stone columns installed per day : 15 no's Total running meter of all the columns :

91,641 Rm

BAND DRAIN TECHNOLOGY

BAND DRAIN TECHNOLOGY - PVD Used in loose, compressible and water

saturated clay and silty clays. Soils are characterized by very loose

skeleton and a large pore sizes filled with water

Requires about ten or more years to consolidate on preload.

PVD – Prefabricated Vertical Drain.

WHAT IS VERTICAL DRAIN? Consolidation takes

place in only one direction

Vertical drainage path may be substantially longer

It may take 10+ years to consolidate Pore water will flow laterally

Pore water pressure dissipates as the layer drains and water is conveyed through vertical drains

It takes only about 6months or so to consolidate

COMPONENTS OF PVD? Core : It is called drained body

corrugated, flexible and made of polypropylene, designed to provide high discharge capacity, high tensile and compressive strength.

Filter Jacket: Non – woven ,thermically bonded polypropylene wrapped around the core. Acts as the filter to allow ground water to the core.

Filter

Core

ADVANTAGES OF BAND DRAIN TECHNOLOGY:

Minimum disturbance to the soil layers during installation

High water discharge capacity High tensile strength prevents the

collapse of flow path. Fast and easy installation Deep installation up to 40m.

CASE STUDY: Four Lane National Highway Connectivity to ICTT – Vallarpadam, Kochi

Connects NH- 47 and NH – 17. Project cost was revised from 329.46 cr to 571.20 cr

due to ground improvement, bridges and retaining walls.

Road Length – 17.2km, total length of bridges – 2.93km.

Ground improvement works – 10km. PVD were installed in 8 locations between

Chainage 8.400 – 15.000

CASE STUDY: INSTALLATION EQUIPMENT

Hydraulic Stitcher Mandrel Base Hydraulic Machine

CASE STUDY: BAND DRAIN INSTALLATION

CASE STUDY: BAND DRAIN INSTALLATION

Total length of band drains : 56,21,780 Rm Total Granular blanket : 1,23,386 Cum Total Geotextiles used : 3,90,714 sq.m Time taken for install one band drain of 25m :

1min Time taken for splicing the wick : 1 min

CASE STUDY: BAND DRAIN TECHNOLOGY

After the installation of band drains, Casagrande peizometer and plate type settlement recorders where installed in order to check the settlements

CASE STUDY: BAND DRAIN TECHNOLOGY

Description ValuesCumulative Heights Stage 1 : 3.0m ( i.e., 1.0m above

the top of reclamation)Stage 2 : 5.5m ( includes 1.5m of additional surcharge)

Waiting period of each stage Stage 1 : 6.0 monthsStage 2 : 6.0 months

CASE STUDY: BAND DRAIN TECHNOLOGY

The water coming out of the vertical drains is collected in temporary ditch. The water collected is regularly dewatered to the adjoining area.

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