GROUND IMPROVEMENT TECHNOLOGY- STONE COLUMN TECHNOLOGY- BAND DRAIN TECHNOLOGYSravan 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 Ground improvement is the modification of the ground properties in order to achieve the required ground conditions for the particular use of the ground. 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
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.
STONE COLUMN TECHNOLOGYTwo methods of stone columns: Wet / Top Feed Method Dry / Bottom Feed Method
STONE COLUMN : WET / TOP FEED METHOD Vibro Probe Step 1 : Penetration of probe Step 2 : Backfilling of aggregate and compacting Step 3 : Consolidation of granular fill and finishing the column
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
STONE COLUMN : ADVANTAGES 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.
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 :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 nos Time required for each stone column : 60 min No. of stone columns installed per day : 15 nos Total running meter of all the columns : 91,641 Rm
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 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 Filter bonded polypropylene wrapped around the core. Acts as the filter to allow ground water to the 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 TECHNOLOGY 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 TECHNOLOGYDescription 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 months Stage 2 : 6.0 monthsThe water coming out of the vertical drains is collectedin temporary ditch. The water collected is regularlydewatered to the adjoining area.