Ground improvement & foundation engineering

Ground Improvement & Foundation EngineeringConstruction aspectsSize of projectAvailability of resourcesExpertise available at siteSpecificationsGuidanceTime availableUse of accelerated construction techniquesPossible damage to ground water and adjacent structureTolerable level of loading and deformationCorrosion and aggressive soil conditionsDurability of materials Toxicity of any chemical additivesGovernment regulationReversibility or irreversibility of process: lime added to soil reacts in presence2Reliability of methods of testing, analysis and designGood methods of testing, proven methods of design and analysis should be used and empirical approaches need to be avoided

Feasibility of construction control and performance measurements

Documents of quality control and performance are required in major ground improvement projectsBenefits of Ground ImprovementIncrease of strengthReduce distortion under stress (Increases stress-strain modulus)Reduce compressibility (volume decreases due to a reduction in air voids or water content under loads)Prevent detrimental physical or chemical changes due to environmental conditions (freezing / thawing, wetting / drying)Reduce susceptibility to liquefactionReduce natural variability of borrow materials and foundation soilsBasics of Geotechnical Engineering Void ratio

Porosity

Degree of saturation

Bulk density

Saturated mass density

Consistency limitsAtterberg LimitsAtterberg Limits & indicesLiquid limit

Plastic limit

Shrinkage limit

Plasticity index: Flow indexToughness indexConsistency indexLiquidity indexLl by casegrande apparatus- moisture content @25 blows to move the soil sample through 13mmcone penetration test: 80 g cone with sliding shaft metal cut of 55m dia and 40mm deep water content @ penetration between 15 to 35 mm in 5 seconds

PL- 3mm thread first sign of crcking

6SOIL INVESTIGATIONDetermination of surface and subsurface soil conditions and features in an area of proposed construction that may influence the design and construction and address expected post construction problems.777SCOPE OF INVESTIGATIONSimple visual examination of soil at the surface or from shallow test pits

Detailed study of soil and groundwater to a reasonable depth (influence zone) by samplingfrom bore holes, shafts and audits and in-situ and laboratory tests.

8PURPOSE OF SOIL INVESTIGATION: Selection of foundation type.Design of foundations.Contractors to quote realistic and competitive tenders.Planning construction techniques.Selection of appropriate construction equipment (especially for excavation and foundations).Feasibility studies of the site.Estimating development cost for the site.Study of environmental impacts of the proposed construction.

999PURPOSE OF SOIL INVESTIGATION: Selection of borrow areas for embankments.Need for any suitable soil improvements.Requirement of any surface or subsurface drainage.Suitable and economical route for highways with respect to soil conditions.Selecting areas (better soil) for engineering structures for foundation cost reductionDesign of extension worksFailure investigation

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Boring Logs12METHODS OF INVESTIGATIONThe methods to determine the sequence, thickness and lateral extent of the soil strata and, where appropriate the level of bedrock.

The common methods include Test pits Shafts and audits

Boring or drilling1212Test Pits The excavation of test pits is a simple and reliable method.

The depth is limited to 4-5m only.

The in-situ conditions are examined visually

It is easy to obtain disturbed and undisturbed samples

Block samples can be cut by hand tools and tube samples can be taken from the bottom of the pit.1313131414

1234Walls of the test pit indicate four layers (1) Clayey silt (2) Sandy silt (3) Clean sand (4) Sandy gravel1414Boring or DrillingTo obtain representative soil and rock samples for laboratory tests.

To identify the groundwater conditions.

Performance of in-situ tests to assess appropriate soil characteristics.

Some of the common types of boring are as follows

Auger boring

Wash boring

Percussion boring

Rotary drilling1515151616Auger Boring Hand Auger

For hard soil and soil containing gravels boring with hand auger becomes difficult. Hand-augered upto about 20m depth, greater than 8-10m is usually not practical.The length of the auger blade varies from 0.3-0.5m.The auger is rotated until it is full of soil, then it is withdrawn to remove the soil and the soil type present at various depths is noted.Disturbed samples and can be used for classification testAuger boring may not be possible in very soft clay or coarse sand hole tends to collapse when auger is removed

Hand Auger Mechanical Auger1616It is the simplest method of boring used for small projects in soft cohesive soils.

17a. Helical (worm types) Augers b. Short flight Auger c. Iwan (posthole) Auger

abc171718Mechanical Auger

Mechanical Auger means power operated augers. depends on the type and size of auger and the type of soil.Downwards pressure can be applied hydraulically, mechanically or by dead weight

aabcda. Continuous Flight Auger b. Hallow-stem auger plugged during advancing borec. Plug removed and sampler inserted d. Truck mounted auger boring machine1818Auger BoringThe diameter of the flight auger usually is between 75 to 300mm up to 1m dia

Shell Auger (bucket auger)up to2m are available.

Borehole depths up to 50m are possible with continuous-flight augers.

Continuous flight augers can be solid stem or hollow stem with internal diameter of 75-150mm.

Hollow stem augers are used when undisturbed samples are required.

Plug is withdrawn and sampler is lowered down and driven in to the soil below the auger.

Drill through hollow stem in bed rock.

Auger boring for sand below water table

191919The most common method is to use continuous flight augers. As the auger acts as a casing it can be used in sand below water table. The possibility of rising sand in to the stem by hydrostatic pressure can be avoided by filling the stem with water up to the water table

20Auger BoringThe soil rises to the surface along the helical blades,

Not suitable for soil bore that require casing

Possibility that different soil types may become mixed as they rise to the surface

Difficult to determine the depths of changes of strata. Experienced driller can however detect the change of strata by the change of speed and the sound of drilling.

2021Wash boring Water with high pressure pumped through hollow boring rods

Released from narrow holes in a chisel attach to the lower end of the rods.

The rods are raised and drop for chopping action of the chisel by means of winch.

Wash boring can be used in most type of soil

Progress is slow in coarse gravel strata.

2121The soil is loosened and broken by the water jet and the up-down moment of the chisel.The soil particles are carried in suspension to the surface between the rock and the borehole sites.

22Wash boringThe accurate identification of soil strata is difficult due to mixing of the material has they are carried to the surface.

Used for advancing the borehole to enable tube sample to be taken or field test to be carried at the hole bottom.

The advantage is that the soil immediately below the hole remains relatively un-disturbed

The method is unacceptable for obtaining soil samples2223

Wash boring rig2323Rotary DrillingThe rig consists of a derrick, power unit, winch, pump and a drill head to apply high-speed rotary drive and downward thrust to the drilling rods.

Primarily intended for investigation in rock, but also used in soils.

The drilling tool, (cutting bit or a coring bit) is attached to the lower end of hollow drilling rods

Water or drilling fluid is pumped down the hollow rods and passes under pressure through narrow holes in the bit or barrel

The drilling fluid cools and lubricates the drilling tool and carries the loose debris to the surface between the rods and the side of the hole.242424Rotary DrillingThe fluid (bentonite slurry) also provides some support to the sides of the hole if no casing is used

There are two forms of rotary drilling, open-hole drilling and core drilling.

Open- hole drilling, which is generally used in soils and weak rock, just for advancing the hole

The drilling rods can then be removed to allow tube samples to be taken or in-situ tests to be carried out. In core drilling, which is used in rocks and hard clays, the diamond or tungsten carbide bit cuts an annular hole in the material and an intact core enters the barrel, to be removed as a sample. Typical core diameters are 41, 54 and 76mm, but can range up to 165 mm.

2526Advantages

The advantage of rotary drilling in soils is that progress is much faster than with other investigation methods and disturbance of the soil below the borehole is slight.

Limitations

The method is not suitable if the soil contains a high percentage of gravel/cobbles, as they tend to rotate beneath the bit and are not broken up.

The natural water content of the material is liable to be increased due to contact with the drilling fluid 262627

Rotary Drilling rig

272728GEOPHYSICAL METHODAlthough boring and test pits provide definite results but they are time consuming and expensive.

Subsurface conditions are known only at the bore or test pit location.

The subsurface conditions between the boring need to be interpolated or estimated.

Geophysical methods are more quick and cheaper.

They provide thorough coverage of the entire area.

The results of Geophysical testing however are less definitive and require subjective interpretation.

Therefore both methods are important. In case geophysical testing in major in scope, few borings and sampling will be required for accurate determination of soil properties.

If boring is major in scope then few geophysical lines will be required to know the conditions in-between the borings.

28282929Site Evaluation Direct MethodsBoreholes/Probes

Test Pits/Trenches

Cores

30Geophysical Techniques Indirect Methods

Ground Penetrating Radar (GPR) Electromagnetic (EM) Magnetic Utility Locating Seismic Electrical Resistivity Gravity Very Low Frequency (VLF)

3131Geophysical Techniques Indirect MethodsAdvantagesNon-Destructive Cost Effective Provides Preliminary or Supplemental Information

32Soil SamplingSplit Spoon/SPT samplerThin-wall tube/Shelby tubeAugers33Soil SamplingDisturbedIn situ structure not retainedWater content, classification, compactionUndisturbedLess disturbedShear strength, consolidation, permeability34Soil SamplingDisturbancesShearing and compressionIn situ stress releaseDryingVibrations

35How do we Sample Soil?Is it just digging holes?36Soil Analysis Ch 836Amount of samplingDepends upon;Time constraintsTopographyCost factorsReasons for samplingThere are no specific guidelines

3737Soil SamplingHow many samples do we take?At least 20 single samples per 10 000m2 must be taken with an earth boring tool (or spade) and combined to a mixed sample. To what depth do we sample?The usual sampling depth is up to 20 cm in arable land or 10cm in pasture. Undisturbed soil samples are obtained with a cutting cylinder with minimum capacity of 100cm3 .

38GROUND INVESTIGATION TESTING

Selection of Testingfor SPECIFIERS38This presentation is intended for people specifying:-geotechnical testsanalytical tests

39Laboratory TestingTesting by a laboratory accredited to ISO 17025 is an essential part of soil and rock testing

Competency of staff Control of test conditions Accuracy of test measurements Traceability of measurements to national standards Control of test material Repeatability of results

39In the UK accreditation is by external audit undertaken by UKAS.

If a UKAS accredited laboratory is not used you should audit the laboratory that is used against ISO 17025 before you use it

Data from chemical testing on soils for EA consideration MUST come from MCERTS accredited laboratories40Laboratory TestingSoil and Water testingRock Testing Chemical Testing (for effect on construction materials)Contamination (Analytical) Testing40Chemical testing to BS 1377 Contamination testing to EA specified methods41Types of Laboratory TestsClassification testsChemical TestsCompaction TestsShear strength and triaxial testsConsolidation TestsPermeability TestsSpecialist TestsRock TestsContamination Tests41See the AGS Guide to the Selection of Geotechnical Soil Laboratory Testing for elaboration42Structuring the Test ScheduleDesign data required and for what purpose Identification of material characteristicsIdentification of contamination levelsType of sample neededMinimum mass of sampleMultiple tests on samples

4242Re-emphasise AGS Guide

NB: It is too late to consider the mass of the sample when scheduling. This should have been addressed at the sampling stage, otherwise some tests will be impossible. eg 3-4kg needed for WAC testing43Classification Tests Moisture content DensityAtterberg limitsParticle size distribution

4343Why do these tests?Aid description of materialsIdentify expected behaviour of materials

Index to material behaviour and potential use

PracticalitiesEnsure sample is suitable for test type egVolumeTypeDisturbed or undisturbed

44Rock TestingClassification (moisture, density, porosity, slake durability)Point load strengthUniaxial compressive strength and modulusTriaxial strengthPermeability

4444Why do these tests?

To determine the strength and integrity of rock mass.

Clarify what methods to use, since no British Standard tests

PracticalitiesBe clear about the test specification because there is no British Standard (ISRM and ASTM standards are often used)The first three are routine the last two are specialist testsSchedule against specific core depth45Chemical TestsTo provide design parameters for civil engineering materials in the groundpH, sulphate, chloride, carbonateOrganic content and mass loss on ignitionSpecial testing (eg SD1)4545Why do these tests?

Age of sampleIssue of conversion (eg sulphur to sulphates)

PracticalitiesRefer to BRE Special Digest 1 (NB: must be specific about parameters wanted)

Storage and shelf life of samplesSD1 = BRE document, and analytical methods used

46Compaction TestsDensity/moisture content relationshipsCalifornia bearing ratio (CBR)Moisture condition value tests (MCV)Maximum/minimum densityCombined relationship testing

4646Why do these tests?To obtain information likely to be used very specifically for design and for the construction of earthworks. Therefore quality data is needed that is specific to the construction project and the use to which the data will be put.

PracticalitiesQuantity and/or volume of samplesOn re-moulded samples need significant sized samples

Specialist tests could include:-Frost susceptibilityRing shearSaturate and moisture contentChalk crushing value47Shear Strength and Triaxial TestsShear Box Laboratory vane shearQuick undrained triaxial test (total stress)Consolidated undrained triaxial test (effective stress)Consolidated drained triaxial test (effective stress)Ring shear for residual strength

4747Why do these tests?

To determine the short term and long term strength of soils for design parameters.

Practicalities

Appropriate samplesTime (NB consolidated triaxial tests take a long time compared to the first 3 tests)Sample preparationOn undisturbed samples.If re-moulded then at what moisture content and densityShort and long term testsEffective stress tests take longer to do

48Consolidation TestsOne dimensional consolidationTriaxial consolidationHydraulic cells (Rowe)Swelling tests

4848Why do these tests?

To predict settlement and/or swell

Practicalities

Specify loading stages

What load/unload/re-load cycles49Permeability TestsConstant head permeameterFalling head permeameterTriaxial permeability49Why do these tests?

To determine the permeability of soils for the design of soakaways, landfill liners, groundwater control, etc

PracticalitiesTest conditionsAppropriate sample materialsTime period and test conditionsMarket availability50Contamination TestingpHOrganicsInorganicsMetalsAsbestos

50Why do these tests?

To assess contamination in relation to published guidelines to determineWhat can be left on siteWhat treatment might be neededWhat to do with material removed from site

Lead by risk assessment and the ultimate use of the site.

PracticalitiesSample sizeContainers usedPretreatment on siteTemperature controlNeeds to be scheduled before physical tests (for heath and safety reasons ie to ensure safe to handle)Total and/or leachateCheck with Project Risk AssessmentSample pre-treatment and storageLimits of detection

Seek specialist advice!