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IN SITU TESTS & INTERPRETATION Madhira R. Madhav JNTU madhavmr@gmail.com

"In-Situ" : 

"In-Situ" Latin: In its original position Why perform in-situ testing?

Outline of Geotechnical Site Characterization Methods : 

Outline of Geotechnical Site Characterization Methods Drilling & Sampling In-Situ Tests Standard Penetration Test (SPT) Cone Penetration Test (CPT + CPTu) Flat Plate Dilatometer (DMT) Pressuremeter (PMT) Vane Shear (VST) Geophysical Methods Mechanical Waves (P-, S-, R-waves) Electromagnetic (radar, resistivitity)

In-Situ Geotechnical Tests for Soils : 

In-Situ Geotechnical Tests for Soils

In-Situ Testing - Objectives : 

In-Situ Testing - Objectives Select in-situ tests for augmenting, supplementing, and even replacing borings. Realize the applicability of various in-situ methods to different soil conditions. Recognize the complementary nature of in-situ direct push methods with conventional rotary drilling & sampling methods. Recognize values for utilizing these methods and quality implications for their use.

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Objectives of field tests Knowing the general suitability of the site for the proposed works. Assessing local conditions and problems likely to be encountered in foundation construction. Acquiring data for adequate and economic design of foundation.

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Information extracted from field tests General topography Location of buried services General geology of the area Previous history and use of the site Any special features such as possibility of earthquake, flooding, seasonal swelling etc. A detailed record of soil or rock strata, ground water condition etc. Strength and compressibility characteristics.

Slide 11: 

Stages of field tests

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Boring Definition Drilling or driving a hole into the earth's surface. Types Trial pits Shafts and headings Percussion boring Mechanical auger Wash borings Hand and portable augers Rotary drilling

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Boring (Detailed Soil Investigation) Trial Pits

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Boring (Detailed Soil Investigation) Wash Borings

Slide 15: 

Boring (Detailed Soil Investigation) Wash Borings

Hollow Stem Auger Plugged for Auguring and Used for Sampling : 

Hollow Stem Auger Plugged for Auguring and Used for Sampling Sampler Rod Auger Shaft Auger Flight Plug Center Rod Sampler Auger Flight

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Hand Auger Used for: Depths of around 5m. Fine particles Cohesive Soil

Augers : 

Augers

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Boring (Detailed Soil Investigation) Advantages: - Progress is faster than other methods - Disturbance of the soil is slight Rotary drilling

Rotary Drilling : 

Rotary Drilling Boring (Detailed Soil Investigation)

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Sampling Definition Taking samples from the filed or site to determine soil types and in-place characteristics of soil . Types Disturbed sample Undisturbed sample

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Sampling Techniques Disturbed samples: Drill tools Drive sampling Rotary sampling Undisturbed samples : Trial pit.

Slide 24: 

Sampling Samples Disturbed Undisturbed Remolded Representative (The structure of soil is disturbed to a considerable degree by the action of boring tools and excavation equipment.) (Retains as closely as practicable, the true in-situ structure and water content of the soil.)

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Test Pit Sampling

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Sampling Sampling from trail pits

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Sampling Sampling from Boreholes

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Sampling Samplers Piston Sampler Sampling tube

Thin Wall Sampler: Shelby Thin Tube : 

Thin Wall Sampler: Shelby Thin Tube Sampling

Split Barrel Sampler : 

Split Barrel Sampler Sampling

Single Tube Core Barrel : 

Single Tube Core Barrel Sampling

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Disturbed Sample

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Undisturbed Sample

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Preservation of Samples Block sample Tube sample

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Disturbed Sample: Test pit Cuttings from bottom of auger Split spoon Auger boring Wash boring Used to determine: Grain size analysis Liquid limit/plastic limit Specific gravity Compaction Undisturbed Sample: Recovered completely intact Test pits: Limited depth Water table problems Shelby thin tube Pushed in soil Sample Preserved with wax: Used to Determine: Soil strength Compressibility permeability Field Soil Sampling Categories

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Testing of soils Field testing of soils:

Slide 37: 

Field Tests

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Testing The main tests: Standard Penetration Test (SPT) Cone Penetration Test (CPT)

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Most common geotechnical test Been in use for over 50 years Universal availability of equipment Fairly well known outside of geotechnical community Standard Penetration Test

Standard Penetration Test (SPT) : 

Standard Penetration Test (SPT) Very common test worldwide 1902 - Colonel Gow of Raymond Pile Co. Split-barrel sample driven in borehole Conducted on 5-ft depth intervals (1.5-m). ASTM D 1586 guidelines Drop Hammer (140-lbs falling 30 inches) (63.5-kg hammer falling 0.76 meters) Three-increments of 150-mm each; Sum last two increments = "N-value" (blows/ft)

Sample by Driving With a Drop Weight : 

Standard Penetration Test Sample by Driving With a Drop Weight

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Standard Penetration Test It aims to determine the SPT N-value, which gives an indication of the soil stiffness.

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Standard Penetration Test

Standard Penetration Test (SPT) : 

Standard Penetration Test (SPT)

Standard Penetration TestAdvantages Disadvantages : 

Standard Penetration TestAdvantages Disadvantages Obtain Sample + Number Simple & rugged device at low cost Suitable in many soil types Can perform in weak rocks Available throughout the world Obtain Sample + Number Disturbed sample (index tests only) Crude number for analysis Not applicable in soft clays and silts High variability and uncertainty

Corrections to SPT N-value : 

Corrections to SPT N-value Nmeasured = Raw SPT Resistance (ASTM D 1586). N60 = (ER/60) Nmeasured = Energy-Corrected N Value where ER = energy ratio (ASTM D 4633). Note: 30% < ER < 100% with average ER = 60% in the U.S. N60  CE CB CS CR Nmeas = Estimated corrected N For Clean Sands: (N1)60 = CN N60 = Energy-corrected SPT N-value normalized to an effective overburden stress level of one atmosphere: (N1)60 = (N60)/(vo’)0.5 with stress given in atm. (Note: 1 atm = 1 bar = 100 kPa = 1 tsf).

Standard Penetration Test (SPT) : 

Standard Penetration Test (SPT) Data from Robertson, et al. (1983)

ADSC Load Test Site at Georgia Tech Campus : 

ADSC Load Test Site at Georgia Tech Campus

SPT Results at GT Campus : 

SPT Results at GT Campus

SPT Results at GT Campus : 

SPT Results at GT Campus

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After SPT, a disturbed sample is obtained for examination and testing. Standard Penetration Test

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Relative density from SPT blow count Testing of soils

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Modulus of Elasticity of sand Testing of soils

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Testing of soils Stress-strain modulus of sand

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More than 50 blows required for any interval If more than 100 total blows required Either of these events known as: Refusal Will be so noted on borings Stop Test If

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Extremely operator dependent (results can vary by a factor of 2) No theoretical basis Foundation design using SPT is entirely empirical (typically conservative) Problems associated with SPT

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Damaged Drive Shoe Variation in Hammer Fall Effect of Overburden Pressure Plugging End of Sampler Hollow Stem Auger Quick Condition Careless Work by Drill Crew SPT Test - Common Errors

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Very Economical Test Provides Sample for Soil Classification Long Service Life of Equipment Vast SPT Data Base Numerous Empirical Correlations with SPT SPT Test - Advantages

Gravels - What to do? : 

Gravels - What to do? SPT may not be Dependable Can Use Oversize Sample Spoon Can Use Dynamic Cone for Correlation to SPT Test SPT

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An instrumented steel cone is pushed into the ground at a rate of 2 cm/sec Measurements include: tip resistance sleeve friction pore water pressure shear wave velocity Cone Penetration Test

Cone Penetrometers : 

Cone Penetrometers

Cone Penetration Test (CPT) : 

Cone Penetration Test (CPT) Electronic Steel Probes with 60° Apex Tip ASTM D 5778 Procedures Hydraulic Push at 20 mm/s No Boring, No Samples, No Cuttings, No Spoil Continuous readings of stress, friction, pressure

Cone Penetration Testing (ASTM D 5778) : 

Cone Penetration Testing (ASTM D 5778)

Cone Penetration Vehicles : 

Cone Penetration Vehicles Mobile 25-tonne rigs with hydraulic pushing systems. Enclosed cabins to allow testing for all weather conditions Cone Trucks

Cone Penetration Vehicles : 

Cone Penetration Vehicles

Electric Friction Cone Penetrometer : 

Electric Friction Cone Penetrometer Georgia Tech Test Site

Piezocone Penetrometers : 

Piezocone Penetrometers Porewater Pressures Measured at Apex McClelland Penetrometer Design

Cone Penetrometer Types : 

Cone Penetrometer Types

Cone Penetration TestAdvantages Disadvantages : 

Cone Penetration TestAdvantages Disadvantages Fast and continuous profiling of strata Economical and productive Results not operator-dependent Strong theoretical basis for interpretation Particularly suited to soft soils High capital investment Requires skilled operator for field use Electronics must be calibrated & protected No soil samples Unsuited to gravelly soils and cobbles.

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Cone Penetration Test Conical point (10 cm2) Load cell Strain gauges Friction sleeve (150 cm2) Adjustment ring Waterproof bushing Cable Connection with rods Static cone penetrometer

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Cone Penetration Test Static cone penetrometer data

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Vane Shear Test

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Vane Shear Device

Vane Shear Test (VST) : 

Vane Shear Test (VST) Field Vane (FV) per ASTM D 2573 Performed at bottom of boring or by direct push placement of device Four-sided blade pushed into clays and silts to measure following: suv (peak) = Peak Undrained Strength suv (remolded) = Remolded Strength (after 10 revolutions) Sensitivity, St = suv(peak)/suv (remolded)

Vane Shear Test (VST) : 

Vane Shear Test (VST)

Vane Shear Devices : 

Vane Shear Devices Scandinavian Vanes McClelland Offshore Vane

Vane Shear Devices : 

Vane Shear Devices Dutch Vane Equipment, Holland VST in Upstate NY

Results from Vane Shear Tests : 

Results from Vane Shear Tests San Francisco Bay Mud, MUNI Metro Station

Vane Shear TestAdvantages Disadvantages : 

Vane Shear TestAdvantages Disadvantages Assessment of undrained shear strength of clays Simple test and equipment Measure in place sensitivity Long history of use in practice, particularly embankments, foundations & cuts Limited to soft to stiff clays & silts with suv < 200 kPa Slow & time-consuming Raw suv needs empirical correction Can be affected by sand seams and lenses

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Direct Shear Test (In-situ)

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Direct Shear Test (In-situ)

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Plate Bearing Test

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Pressuremeter Test

Geophysical Methods : 

Geophysical Methods Mechanical Wave Measurements Crosshole Tests (CHT) Downhole Tests (DHT) Spectral Analysis of Surface Waves Seismic Refraction Suspension Logging Electromagnetic Wave Techniques Ground Penetrating Radar (GPR) Electromagnetic Conductivity (EM) Surface Resistivity (SR) Magnetometer Surveys (MT)

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Planning of Exploration Programme Layout and Number of Boreholes

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Planning of Exploration Programme Depth of Boreholes

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More borings = better analysis Borings are expensive General Guide to spacing for borings: Multi-story bldg. – 50 to 100 ft. One story , earthen dams and borrow pits = 100 to 200 ft. Highway sub-grades – 500 to 1000 ft Boring Spacing

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SOIL DATA AND DESIGN PARAMERS

Slide 90: 

Designer Construction problems Project completion Construction agency Design Soil report Management group Soil investigation agency

Slide 91: 

Information required from Soil Investigation Engineering geology of the data General Topography Past history and land use pattern Soil stratification Depth to rock Ground water and drainage Engineering properties of different strata Design recommendations, if the scope permits

Slide 92: 

Soil Test Report Project and site description Regional and site geology Dates of field and laboratory work Layout of structures and location of boreholes/field tests Methods of investigation Field work Laboratory tests Details of field and laboratory work Ground water characteristics Field test data Laboratory test data Soil profile and stratification Interpretation of data Design parameters Design recommendations, if included in the scope of the work

Slide 93: 

Project and site description General level of the site with respect to adjacent area Problems of water logging/drainage Surface configuration Pond, rock, outcrop etc. Adjacent buildings Layout and type of structure, and Location of borehole and field tests

Slide 94: 

Layout plan showing location of boreholes

Slide 95: 

Location of filled-up pond in HUDCO project site, Kolkata

Slide 96: 

Schedule of laboratory tests Testing

Slide 97: 

Soil profile through selected boreholes and SPT data Soil profile

Slide 98: 

Variation of natural moisture content and Atterberg limits with depth Data interpretation

Slide 99: 

Spacing: buildings 10 – 30 m apart road lines 30 – 300 m apart landslides at least 5 in line for profile Depth: 1.5 x foundation width + 10 m control hole 3 m below rock head Depth & No. of boreholes