Ground Improvement and Ground Control including Waste Containment
with Geosynthetics
Dr. J.N.Jha, Professor and Head (Civil Engineering), Guru Nanak Dev Engineering College,
Ludhiana, Punjab-141006
Ground Improvement Tehnique: Issues, Methods and their Selection
Present Day Scenario
• Best buildable lands not available for construction• Available sites are having low strength because : Filled up sites, Low lying water logged, Waste lands, Creek lands with deep deposits of soft saturated
marine clays• Another problem: Design loads are high and the site
is situated in seismic zones
What are the options?
•Traditional foundation techniques sometimes costlier than the super structure and in many situations can’t be built•when a poor ground exists at the project site, designer faces following questions:Should the poor ground be removed and replaced with a more suitable material?Should the weak ground be bypassed laterally by changing the project’s location or vertically by the use of deep foundations? orShould the design of the facility (height, configuration, etc) be changed to reflect the ground’s limitations?
•Development of ground improvement, gives the designer/bulder has a fourth option To “fix” the poor ground and make it suitable for the project’s needs
• Now the designer/builder faces new questions:Should the problematic ground at the project site be fixed instead of bypassed?What are the critical issues that influence the successful application of a specific fixing tool? AndWhich fixing tool to be used from comprehensive and diversified set currently available in the tool box?
What are the major functions of Ground improvement in soil ?
(1) To increase the bearing capacity(2) To control deformations and accelerate consolidation (3) To provide lateral stability (4) To form seepage cut-off and environmental control(5) To increase resistance to liquefaction
• Above functions can be accomplished :
by modifying the ground’s character - with or without the addition of foreign material
The current state of the practice: •Densification•Consolidation•Weight reduction•Reinforcement•Chemical treatment•Thermal stabilization•Electrotreatment•Biotechnical stabilization
Ground Improvement by Densification
Methods of Application : VibrocompactionDynamic CompactionBlastingCompaction Grouting
Key Issues affecting densification:(a) Percent of fines in the soil, (b) Ability of the soil to dissipate excess pore water pressure, (c) Energy felt by the soil, (d) Presence of boulders, utilities and adjacent structures, and (e) Mysterious phenomenon of ageing.
Ground Improvement by Consolidation
Methods of application:
Preloading with or without vertical drainsElectro-osmosisVacuum consolidation
Key Issues associated with consolidation:
(a)stability during surcharge placement,(b)clogging of vertical drains, and (c)maintenance of the vacuum.
Ground Improvement by Weight Reduction
Methods of Application:•Placing lightweight materials over the native soil in one of three ways:spread in a loose form, then compactedcut in block forms, then stacked according to a certain arrangement, orpumped in a flowable liquid form
key issues with the weight reduction method(a) Placement of the lightweight material, (b) Longevity and long-term performance.
Ground Improvement by ReinforcementMethods of Application:Mechanical stabilizationSoil nailingSoil anchoringMirco pilesStone columnsFiber reinforcement
Key Issues Affecting Soil Reinforcement: (a)Load transfer to the reinforcing elements,(b)Failure surface of the reinforced soil mass, (c)Strain compatibility between the soil and the reinforcement, (d)Arrangement of the reinforcing elements, (e)Durability and long-term behavior of the reinforcements.
Ground Improvement by Chemical Treatment
Methods of Application:Permeation groutingJet groutingDeep soil mixingLime columnsFracture grouting
Key Issues involved in Chemical Treatment(a)soil-grout compatibility and reactivity,(b)operational parameters,(c)column verticality, and (d)weathering effects
Ground Improvement by Thermal Stabilization
Methods of Application:Ground freezingVitrification
Key Issues of thermal stabilization(a)Degree of saturation of the soil, (b)Rate of groundwater movement, (c)Creep potential of the frozen ground, (d)Post thawing behavior, (e)Heat transfer in the melted soil and (f)Impact of heat on utilities and adjacent structures.
Ground Improvement by Electrotreatment
Methods of Application:Electrokinetic remediationElectroheatingElectrokineting fencingBioelectrokinetic injection
Key Issues in Electrotreatment (a)Soil’s electrical conductivity, (b)Ionic characterization of the contaminants, and(c)Impact on buried objects and utilities
Ground Improvement by Biotechnical Stabilization
Methods of Application:Brush layering Contour wattling Reed-trench layering Brush matting Live staking and others
key issues affecting biotechnical stabilization (a)Development of artificial cohesion in the ground, (b)Effects of evapotranspiration, and (c)Durability of the vegetation
Factors affecting the selection of a ground improvement method
(a)Ground, (b)Groundwater(c)Construction considerations including schedule,
materials, accessibility, right-of- way, equipment and labor
(d) environmental concerns, (e) durability, maintenance and operational requirements(f) contracting, politics and tradition, (g) cost
Waste Containment with Geosynthetics
Large quantities of waste are being produced since 1990 due to Rapid industrialisation and Excessive urbanisationWaste needs to be disposed off and only disposal bin is ground and it occupies large chunk of land. One million ton of municipal solid waste occupies approximately one million square meter (One square kilometer of land area when waste is spread uniformly with a thickness of one meter)
Other problem associated with waste disposal
Another problem with the disposal of waste :
Source of pollutionContaminates the soil beneath the wasteContaminates the ground water as contaminants travel from the solid waste to the subsurface environment
Other sources of subsurface contamination
Ponding or impoundment of Liquid Waste : Slurry type liquid wasteLeakage from storage of liquids in underground tanks Leakage from pipelines that transport liquidAccidental spills of toxic liquidApplication of fertilizers , pesticides on large agricultural areas
How to tackle and minimise this damageDesign and implementation of solution for detection, control, remediation and prevention of subsurface contaminationProtection of uncontaminated landAnalysis of the fate of contaminants on and in the ground including transportation through geomediaUse of waste material on and in the ground for geotechnical construction
Pollution:MSW/ISWMunicipal solid waste/Industrial solid waste place on the ground: two most significant source of subsurface contaminationWater infiltrates into waste and reacts physically, chemically and biologically to produce leachateLeachate infiltrates into the ground causing subsoil and ground water contaminationSolid waste continues to stay at the location where it is placed for years Therefore the process of leachate infiltration into subsurface environment continues , slowly but surely for several yearss
Control and Remediation
Clean up of soil involves - Treatment of three phases in soil:Solid soil particle, Liquid pore fluids and Pore gases MethodsControlling the spread of polluted zone by installing impermeable vertical barriers (cut-off walls) all around and horizontal cover above the contaminated siteRemoving the source of contamination and placing it in designed facilityExcavating the affected soil, washing it or teating it and placing it back after treatment
Pumping out the contaminated ground water by using a set of tube wells installed in the Contaminated zone , treating the ground water and the injecting the purified waterback (Pump and Treat Method)Pumping out pore gas from the unsaturated zone using gas wells and allowing air to enter through injection wellsUsing micro-organism to biomediate the sub soil and ground water by transforming or immobilzing the contaminantsUsing thermal treatment e.g. incineration
Control of subsurface contamination for new facility
For solid waste: Providing impermeable flexible liners at the base and covers on top of all Solid waste disposal facilities to minimize leachate formationFor slurry type waste: Providing storage in ponds and impoundments having incrementally raised embankments and impermeable flexible liners at the baseFor liquid: providind storage in ponds with impermeable flexible linerFor underground liquid storage facility: Providing double walle tanks with leakage detention system placed between the walls
Thankyou...............
