Research in Geotechnical Engineering

Submitted by:- Er.Abhineet godayal (B.Sc. Non Med.,B.Tech Civil, Mtech Geotechnical Engineering)

Research in Geotechnical Engineering

INTRODUCTION :-Ground improvement is the most imaginative field of the geotechnical engineering. It is the field in which the engineer forces the ground to adopt the project requirements by altering its natural state , instead of alter in design.The result usually include saving in construction cost and reduction of implementation time

NEED TO IMPROVE GROUND..To reduce settlement of structureImprove shear strength of soil and thus increasing bearing capacity of soilIncrease the factor of safety against possible failure of embankment.Reduce the shrinkage and swelling of soilsIncrease the liquefaction resistance

SIMPLE METHOD TO DESCRIBE GROUND IMPROVEMENTDrop a handful of sand from certain height. You will get a heap of sand. Keep your foot over it, sand will disperse in all directions. Measure this dispersion as xDrop again handful of sand on the leap of sand . Keep your handkerchief on the top and then keep your foot . Dispersion of sand will again be there , but less than previous one.Reason :- Friction developed between handkerchief and soil due to which adhesion took place between cloth and soil particles, thus soil did not flow away

Research in the use of Geosynthetic productGeosynthetics like geotextiles, geogrid, geomembrane can lead to less deformation and high strength to road and can reduce thickness of the pavementFunctions GeotextileGeogridsGeomembraneGeocompositsseparation---filtration--reinforcement--Drainage--Erosion control---Slope protection--

GeogridsGeogrid are integrally polymer meshes. The meshes are made of high tensile polymer (HDPE/PP) and are totally on biodegradable and anticorrosive. They have fused or thermally welded joints having high dimensional stability and strength. These grids are immune from naturally occurring soil alkalies,acids and mineral salts

Geogrid usage in road construction

Techniques for Slope Protection

Types of Riverbank ProtectionVegetation Windrows and TrenchesSacks and BlocksGabions and MattressesArticulated concrete mattressesSoil-CementRetaining WallsMany others possible

Fig. Showing Types of Riverbank Protection

Vegetation - Main TypesShrubTreesGrasses

Vegetation Structure- FascinesBundles of cuttings tied together, placed in shallow trenches parallel to the bankPartially buried and staked in placeCreates log-like structure that will quickly root, grow and provide plant coverHolds soil in place to protect stream bank from erosion

Stream bank Revegetation and Protection

Windrows and Trenches

Conventional Windrow placementTrench

Sacks

Filled with soil or sand-cement mixturePrimarily used for emergency work during floodsProtects stream banks when proper riprap isnt available Advantages compared to stone riprap Allow placement on steep slopesUse locally available materialsCreates smooth boundaryCobblestone effect may be more aesthetic

Sacks and Blocks

Blocks Sacks-Manufactured with local materials or obtained commercially Cast with openings to provide for drainage-Openings also allow vegetation to grow so that the root structure can strengthen the bank-Can be used with a filter if erosion is a concern Advantages -Durable, less susceptible to freeze/thaw-Easy pedestrian access to river -Low channel boundary roughness -Sufficient flexibility to conform to minor changes in bank shape

Gabions

About GabionsRectangular wire boxes (baskets) filled with small-sized stonesUsed where flow velocities are too high for riprap of small stonesMade of heavy galvanized steel with PVC coating for corrosive environmentsStacked on relatively steep slopes to resist river flows and unstable banksNeed to be periodically inspected and maintained from damage

Mattress GabionsShaped into shallow, broad baskets tied together side by side to form continuous blanket of protectionPlaced on a smoothly graded riverbank slope May still allow some natural vegetation growth

Comparison between geogrid reinforced section & unreinforced sectionUnreinforced Reinforced40 mm Bituminous concrete 40 mm75 mm Dense bituminous concrete 55 mm250 mm Granular base(WBM) 200 mm250 mm Granular sub base 235 mmNatural subgarde Geogrid + sub gradeTotal thickness- 615 mm 525 mm

PROPERTIES COMMON TO GEOTEXTILESGood resistance to chemicalsResistance to biological degradationThermal stability 0 to 120cMaterial 100% polypropyleneSpecific gravity- 0.91Weight/sq m-206-303gm/mThickness-0.58-0.78Tear strength- wrap way-21-69kg -weft way-18-71kgBreaking strength- wrap way-245-500kg - weft way-181-333kg

PROPERTIES OF GEOTEXTILES continued..Pore size:- 60-243 micronsWater permeability:- 4.2-55 litre/sec/metre @ 10 cm water head