Ground Improvement with Geotechnical Site Investigation

202 Pages·2019·20.297 MB·English

by  Patel, Anjan

Geotechnical Investigations
and Improvement of Ground
Conditions
Geotechnical
Investigations and
Improvement of
Ground Conditions
Anjan Patel
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1
Introduction
1.1 Introduction
Groundimprovementisrequired,whereverproblematicsoils/rocksareencountered.
Thebasicpurposeistomakethesubsurfaceconditionssuitableforconstructionpur-
poses.Therearevariousmethodsofgroundimprovementavailableandtheselection
ofatechniqueoracombinationoftechniquesdependsuponseveralfactors.Thedif-
ferent purposes of ground improvement and a brief description of the different
methods andtheir selection criteria is presentedin thischapter.
1.1.1 Purpose of ground improvement
Ground-improvement methodsarethosethatarecapableofimprovingcertainchar-
acteristics(e.g.increaseinbearingcapacity,reductionintotalaswellasdifferential
settlement,reductioninpermeability,slopestability,preventionofsoilerosioncaused
bypipingandseepage,reductionofupliftpressure,decreaseinliquefactionpotential
ofsoil,reductionofswellingandcrackingofsoils,identificationofsuitabilityofsite
to facilitate construction works, etc.) of poor ground for civil engineering construc-
tions and various infrastructure developments. So a ground improvement method
ortechniqueisrequiredtoalterthestate,nature,ormassbehaviourofgroundmate-
rialsinacontrolledmannerinordertoachieveanexpectedandsatisfactoryresponse
toexisting orprojectedenvironmental and engineering actions.
There are alternate options toground improvement as well. These are
a. toremoveandreplace thesoilmasswithanothertypeofsoilsorothergeomaterialsofa
suitablequalityfortheconstructionwork
b. tobypassthepoorsoilwiththehelpofasuitabletechniquelikepilefoundation
c. to alter the design (height and configuration) of structures to overcome the ground
limitations
d. tochangetheconstructionsiteandlookforanewone.
However,duetothescarcityoflandinpresentconditions,heavyloadingstructures,
competitive design,the need for speedy construction,andvarious politicalandeco-
nomic issues, a ground-improvement technique may be the only feasible option for
civil engineering constructions. This situation is outlined in Fig. 1.1, which demon-
stratesthatwhenthegroundisproblematicinmostofthecasesweneedtoimprove
thesoilmassbyselectingaproperground-improvementtechnique(s).Theselectionof
ground-improvementtechniquesdependsuponvariousfactorslikethecostandtime
GeotechnicalInvestigationsandImprovementofGroundConditions.https://doi.org/10.1016/B978-0-12-817048-9.00001-9
©2019ElsevierInc.Allrightsreserved.
2 GeotechnicalInvestigationsandImprovementofGroundConditions
Problematic cases
Collapsible soil
Options available
Liquefiable soil
1. Remove and replace Constraints
Filling materials
2. Bypass Technical, practical, political
Loose deposits
3. Change site location and economical issues
Swelling soil 4. Design alteration
Soft and marshy ground
Karst topography Selection criteria
Nonuniform soil/rock strata Cost, time, purpose, volume
Potential for slope instability of treatment area, soil
5. Improve in situ soil properties properties, accessibility,
Excessive seepage
(ground improvement) availability of materials,
High lift pressure
equipment and manpower,
Erosion, piping environmental factor, local
experience and preference
Fig.1.1 Necessityandselectionofground-improvementtechniquesforconstructionprojects.
availabletocompletetheproject,reasonsforimprovingtheground,extentanddepth
of ground to be treated, geotechnical properties of the existing in situ soils/rocks,
accessibility to the project site, availability ofmaterials, equipments and manpower
requiredtoimprovetheground,environmentalfactors,localexperience,andprefer-
ence ofcontractors and engineers.
1.1.2 Preliminary evaluation for ground improvement
As mentioned previously, the requirement for and selection of various ground-
improvementtechniquesarepurelysiteandprojectspecific.Itisessentialthatthesite
characterizationiscompletedbeforeimplementationoftheground-improvementpro-
cess.First,itneedstobedecidedwhethergroundimprovementisrequiredforthespe-
cificprojectattheparticularsiteornot?Inordertodecidethisweneedtoanalyzethe
variousparametersrelatedtothegroundthataffectthestabilityandserviceabilityof
thestructures.Asimpleexampleofapreliminaryevaluationforgroundimprovement
toconstructabuildinghasbeenpresentedasaflowchartinFig.1.2.Similarmatrices
canbeformedfordifferentstructurestobeconstructedindifferentsitestoevaluatethe
necessity ofground improvement.
1.1.3 Methods of ground improvement
Aclassificationofvariousground-improvementtechniquescanbedonebasedupon
their basic principlesand this is presentedinTable 1.1.
AllofthetechniquesmentionedinTable1.1haveoneormorethanoneofthefol-
lowing main functions:
a. Toincreasethebearingcapacity
b. Tocontroldeformationsandaccelerateconsolidation
c. Toprovidelateralstability
Introduction 3
Fig.1.2 Necessityofground-improvement:preliminaryevaluation.
d. Toformseepagecut-offandenvironmentalcontrol
e. Toincreaseliquefactionresistance
f. Tofacilitatetheworkingsiteconditions.
Depending upon the specific project requirements, it is necessary to select one, or
morethanone,oftheground-improvementtechniquesforaparticularsitebyconsid-
eringotherfactorsliketimeandcost,volumeanddepthofwork,etc.,asmentionedin
the previous section.Someofthecommonmethods alongwiththeir basic purposes
are summarized inTable 1.2.
Itisworthmentioningthataparticularground-improvementtechniquecanbeused
only for aparticular type ora group of soils, as shown inFig. 1.3.
4 GeotechnicalInvestigationsandImprovementofGroundConditions
Table1.1 Classificationofground-improvementtechniquesbasedupontheirbasic
principles
Basicprinciples Someofthemethods
Consolidation Wickdrainsorprefabricatedverticaldrains(PVD),
vacuumconsolidation,preloading,surchargefill,
electro-osmosis
Densification Vibro-compaction,vibro-flotation,dynamiccompaction,
blasting
Reinforcement Applicationofgeosyntheticmaterialsandnaturalfibres,
retainingwalls,soilnailing,soilanchoring,micropiles,
stonecolumns
Chemicalstabilizationby Chemicallimeandcementpiles
deepmixingmethods
Chemicalstabilizationby Permeationgroutingwithparticulateorchemicalgrouts,
grouting compactiongrouting,jetgrouting,hydro-fracture
grouting,etc.
Thermalstabilization Groundfreezing,vitrification
Electro-treatment Electro-kineticremediation,electro-heating,
electro-kineticfencing,bioelectro-kineticinjection
Loadreduction UseofEPS(expandedpolystyrene)geofoams,crumb
rubbertire,sawedlumberwaste,foamglassaggregates,
clamshells,LECA(lightweightexpandedclay
aggregate),expandedshellclayandslates,cellular
concrete,pumiceandindustrialwasteslikeslag,etc.
Similarly,themaximumeffectivedepthandtheeconomicalsizeofthetreatment
area variesfrom method to method, as summarized in Table 1.3.
1.1.4 Scope
l Developing new machinery to execute the work in less time, particularly for deep
compaction
l Automationofequipmentforinsitumonitoringandqualitycheck
l Developmentofproperguidelinessoastoenhancetheeffectivenessofdifferentground-
improvementtechniques.Also,theregularrevisionoftheexistingguidelinesisrequired,
baseduponnewsitecondition,climaticconditions,andnewchallenges
l Innovatingnewconstructionmaterials,particularlyfromdifferentwastes
l Developmentofnewcost-effectivetechniquestoreplacetheexpensiveones,likefreezing,
electro-osmosis,vacuumconsolidation,etc.Interdisciplinaryworktoexplorenewmethods
likenanotechnologyandmicrobialgeotechniques,biorockformations,inventionofcatalyst
andenzymesthatcanconvertsoilintorocklikematerials,etc.
l Tomakethesetechnologiesmoreenvironmentallyfriendly
l Analysisoftheeffectofclimatechangeonperformanceofdifferentsoilstabilizers,etc.
Introduction 5
Table1.2 Purposesofsomeofthecommonmethodsforgroundimprovement
Improve
bearing Settlement Lateral Environmental Liquefaction
Methods capacity control stability control resistance
√ √ √
Vibro-
compaction,
blasting,
preloading
√ √ √ √
Dynamic
compaction
√
Soilnailing
√ √ √
Mechanical
stabilization,
micropiles,fibre-
reinforcement
√ √
Vacuum
consolidation,
electro-osmosis
√
Lightweightfill
√ √ √ √
Stonecolumns
√ √ √
Permeation
grouting
√ √
Electro-heating
√ √ √ √ √
Jetgrouting,deep
soilmixing,lime
column
√ √
Groundfreezing
√
Vitrification
6 GeotechnicalInvestigationsandImprovementofGroundConditions
Gravel Sand Silt Clay
Vibro-compaction
Vibro-displacement compaction
Particulate grout
Chemical grout
Displacement grout
Preloading
Dynamic compaction
Electro-osmosis
Reinforcement
Thermal treatment
Remove and replace
Prewetting
10 1.0 0.1 0.01 0.001 0.0001
Particle size (mm)
Fig.1.3 Variousground-improvementmethodsaspertheirapplicabilitytodifferentsoilmass.
BasedonMitchell,J.K.,1981.Soilimprovement:stateoftheartreport.In:Proceedingsof10th
InternationalConferenceonSoilMechanicsandFoundationEngineering,Stockholm,4,
pp.509–565.
Table1.3 Maximumeffectivedepthandeconomicalsizeoftreatmentareaforsomeofthe
ground-treatmentmethods
Maximumeffective Maximumeffectivedepth
depth/economicalsizeof andeconomicalsizeof
Method treatmentarea Method treatmentarea
Blasting About20–25mbutnot Preloading Economicalforsmallarea
neartogroundsurface/
smallarea
Vibratory 3m/anysize Dynamic 30m/largearea
roller compaction
Grouting Unlimited/smallarea Vibro- 30m/largearea
flotation
Electro- 20m/smallarea Stone 20m/mediumtolargearea
osmosis columns
Heating/ 15m/smallarea Chemical 45m/mediumtolargearea
freezing limepiles