Geotechnical Investigation , laboratory Testing & Design of Foundations Collected by
Ing. Jaafar Mohammed 2011-2012
[email protected]
The Five “W’s” • Who?
• What? • Where? • When? • Why? (HOW?)
In this presentation some of the most effective or popular methods for Geotechnical Investigation and laboratory Testing in the field , and design of Foundations will be described. For many engineering projects it is very useful to take a sample of the soil, and to investigate its properties in the laboratory.
Site Characterization Methods Drilling & Sampling Soil Borings Rock Coring
In Situ Tests Standard Penetration Test (SPT) Cone Penetration Test (CPT + CPTu) Flat Plate Dilatometer (DMT) Pressure meter (PMT) Vane Shear (VST)
Geophysical Methods Mechanical Waves (P-, S-, R-waves) Electromagnetic (radar, resistivity, dielectric)
Some In Situ Tests
Aspects of foundation engineering Foundations of Building & Structures [Pile , raft, and footing ]
Design Specifications or Keywords I.
AASHTO (American Association of State Highway and Transportation Officials). I. FHWA ( Federal Highway Administration ). II. LRFD (Load and Resistance Factor Design), III. ASD (Allowable Stress Design), IV. LFD (Load Factor Design),
Site Exploration Overview 1. Review of Background Information.
2. Field Reconnaissance. 3. Field Exploration (Drilling, Sampling, In-situ Testing). 4. Laboratory Testing. 5. Geotechnical Interpretations, Analysis. 6. Report of Exploration.
Review of Background Information Information about the project. o Type of structure, magnitude of loads, structure layout. Geologic reports.
Soil survey reports. Aerial photographs. Existing structures-at the site, adjacent sites.. Previous geotechnical reports.
Field Exploration- Intrusive Geotechnical drilling. Auger drilling (solid stem auger; hollow stem auger). Rotary drilling (rotary wash boring). Rock coring. Soil (and rock) sampling. In-situ testing (SPT, CPT and other).
Aerial Photos Online: TerraServer
Soil boring locations in La Colina Vineyard (July 2003 sampling )
These risk maps are used by Town Planning, for finalisation of land use. Benefits to the Town Planning
Boreholes provides strata details
Field Explorations
Exploration Log
Soil Sampling There are two types of soil samples: Disturbed samples . These types of samples may be used for some types of soil tests as sieve analysis, water content and Attreberge limits. The major equipment used to obtain disturbed samples is “Split spoon” which is a steel tube has inner diameter of 34.93mm and outer diameter of 50.8mm
Undisturbed samples . These types of samples may be used for some types of soil tests as shear strength tests and permeability. The major equipment used to obtain disturbed samples is “thin wall tube” In general as we obtain soil samples, there will be degree of disturbance, if it was so high we will be compelled to take additional number of soil samples. The degree of disturbance can be expressed from the following relation:
Foundation Design Process Field Explorations
Undisturbed Sample (Shelby Tube)
Field Drilling and Sampling
Hollow Stem Auger o Casing with outer spiral. o Inner rod with plug/or pilot assembly. o For sampling, remove pilot assembly and insert sampler. o Typically 5ft sections, keyed, box & pin connections. o Maximum depth 60150ft.
Hollow Stem Auger
Rotary Drilling 1. Bit at the end of drill rod rotated and advanced . 2. Soil/rock cuttings removed by circulating drilling fluid. 3. Common drilling fluid; bentonite in water with slurry density 68-72pcf. 4. Air may be used as drilling fluid .
Split Spoon (Barrel) Sampler • Suitable for stiff soil, sand gravel. • Thick-wall Steel Tubes. • 1.5” ID, 2.0” OD, 18”-30” long.
Shelby Tube Sampler • Suitable for Soft Soil. • Thin-wall Steel Tubes. • 3.0" OD, 2.875" ID, 30.0" long, 7.2 lbs .
Rock Coring Double-tube core barrel is typical. Diamond or tungstencarbide tooth bit. Size of core samples varies (NX, NQ, HQ, etc.).
Groundwater Monitoring Groundwater level must be determined during geotechnical exploration. Measure at time of drilling and later (24 hrs, 1 week, etc.). Can be accomplished by leaving selected soil borings open. Or, install a piezometer.
Ground Water Piezometer. Monitor Wells & Sampling. Permeability Tests.
Soil Testing
Vane Shear Test Standard Penetration Test
How Many Borings? Structure or Project Highway Subgrade
Multistory Building
Subsurface Variability
Spacing of Borings (ft)
Irregular
100-1000 (200, typical)
Average
200-2000 (500, typical)
Uniform
400-4000 (1000, typical)
Irregular
25-75
Average
50-150
Uniform
100-300
How Deep?
Soil sampling A simple method to take a sample is to drive a tube into the ground, and then recovering the tube with the soil in it. The tube may be about 1 meter long, and may have a valve at its bottom, to prevent loosing the sample. The tube may be brought into the soil by driving it into the ground using a falling weight, or a hammer . The sample is not very well suited for a refined test, however, as the initial state of stress is disturbed, and perhaps also the density. To take a deep sample the sampling tube may be of smaller diameter than the borehole, which is supported and deepened by a special boring tube.
It may be interesting to note that samples can also be taken from the bottom of the sea. One possible method is by using a diving bell, in which the air pressure is kept at the same level as the water pressure. From this diving bell a sample can be taken by the operators, or they can make a cone penetration test. Another method is to use a heavy frame, that is submerged in the water from a ship. Using a remote control system a cone can be made to penetrate the soil, or a sample can be taken. This method can even be used in water depths of 1000 meter, or more. An example of a continuous Begemann boring is shown in Figure.
Begemann sample.
Choice of method depends on budget, sampling requirements, extent of investigation, and often site conditions
Cone Penetration Test (CPT) This test, CPT, has been developed from a simple tool, that was pushed into the ground by hand or a manual pressure device, into a sophisticated electronic measuring device, with an advanced hydraulic loading system. The load is often provided by the weight of a heavy truck. Originally the CPT was a purely mechanical test, as shown schematically in Figure
I. First only the cone is pushed into the ground, over a distance of 35 mm. II. Clay layers have a much smaller cone resistance than sand. III.A typical cone resistance qc for a sand layer is 5 MPa or 10 MPa, or even higher, whereas the cone resistance of soft clay layers is below 1 MPa. IV.The ratio of friction to cone resistance for clays is much higher than for sand. V. In sands the friction usually is only about 1 % of the cone resistance, whereas in clays this ratio usually is 3 % to 5 %. Higher values (8 % 10 %) may suggest a layer of peat. In peat the friction usually is substantial, but it has a very small cone resistance.
Cone Penetrometers
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 Details
Cone Penetration Tests (CPT) Cone Trucks
Mobile 25-tonne rigs with enclosed cabins to allow testing under all weather conditions
CPT Truck
Friction ratio and cone resistance
An example of the results of as cone penetration test is shown in Figure . At a depth of 7 meter a sand layer of about 2 meter thickness can be observed. At a depth of 18 meter the top of a thick sand layer is found. The low values above the first sand layer, and between the two sand layers indicate soft soil, probably clay. A simple building (a house) can be founded on the top sand layer, provided that the presence of this layer is general.
Result of CPT
Dynamic Cone Penetrometer tests(DCPT) The Dynamic Cone Penetrometer (DCP) is an instrument which can be used for the rapid measurement of the in situ strength of existing flexible pavements constructed with unbound materials. Measurements can be made down to a depth of 800 mm or to a maximum depth of 1500mm by adding an extension rod.
TRL Dynamic Cone Penetrometer
Prior to testing, site details should also be recorded on the Test Data Form. These include: 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16.
Location - either Carriageway, Shoulder, Verge or other Lane number – 1/2/3/4 if the location is carriageway Offset (m) As defined by user Direction Cone angle – either 30o / 60o cone Zero error (mm) Test date Remarks, if any to a maximum of 60 spaces Layers removed – None, One or Two Surface type – either Thin Bituminous Seal, Hot Mixed Asphalt, Unpaved, Concrete or Other Thickness of surfacing, if removed (mm) Surface condition – where the road has a bituminous surfacing Strength coefficient of surface, if surface condition unknown Base type – either Bituminous, Cement treated or Coarse granular (Water Bound Macadam) Thickness of base, if removed (mm) Strength coefficient of base, if removed
Dynamic Cone Penetrometer in operation
Vane test The shear strength of soils can be measured reasonably accurately in situ using the vane test. In this test a small instrument in the shape of a vane is pushed into the ground, through a system of rods, just as in the cone penetration test. The vane is connected, by a central steel axis, to a screw at the top of the rods. This screw can be rotated, so that the soil in a cylindrical element of soil is sheared along its surface, against the soil outside the cylinder.
Down-hole Shear Wave Velocity
Anchoring System Automated Source Polarized Wave Down-hole Vs
Standard Penetration Test(SPT) In this test a sampling tube is driven into a borehole in the ground using a standardized hammering weight. The actual test consists of measuring the number of blows needed to achieve a penetration of 300 mm (1 foot) into the ground. This is denoted as N, the blow count, the number of blows per foot.
For many projects the initial soil data often may be restricted to a series of SPT results. Then it is useful to know that a characteristic blow count for sand is N = 20 , and that for soft clay the value may be N = 5 , or even lower, down to N = 1. A first indication can be obtained from Table 3-4, derived from Terzaghi & Peck.
Interpretation of SPT according to Terzaghi &Peck.
Standard Penetration test (SPT) Advantages Many existing correlations Most contractors are capable of SPT testing Obtain sample (when using the spoon) of material that is tested Relatively cheap Robust Suitable for most soils
Disadvantages Ground at base of borehole is disturbed by drilling process Prone to errors by drillers (e.g. water head, depth measurement errors) Device imposes very complex strain paths to the soil and no theory at present is capable of predicting what are the most influential factors affecting the N value
Standard Penetration Test (SPT)
Standard Penetration Test Rotary-drilled Borehole
Standard Penetration Test (SPT) Procedures: ASTM D 1586 N = measured Number of Blows to drive sampler 300 mm into soil.
Representative SPT Profile Downtown Memphis SPT-N (bpf) 0
20
40
60
Soil Profile 80
100
0
Depth (meters)
4 8 12 16
1982 B1 1982-B3
Fill Silty Sand
1982-B5 Sandy Silt Gravelly Sand
20 Desiccated OC Clay
24
Clayey Sand
28
OC Clay Gravelly Sand
Corrections to SPT N-value Effect
Variable
Term
Value
CN
(Pa/svo')0.5 but < 2
Safety Hammer Donut Hammer Automatic Hammer
CE
0.6 to 0.85 0.3 to 0.6 0.85 to 1.0
65 to 115 mm 150 mm 200 mm
CB
Standard sampler Sampler without liner
CS
1.00 1.05 1.15 1.0 1.1 to 1.3
CR
1.0 0.95 0.85 0.75
Particle Size
10 m to 30 m · 6 to 10 m · 4 to 6 m · 3 to 4 m Median Grain Size (D50) of Sand in mm
CP
60 + 25 log D50
Aging
Time (t) in years since deposition
CA
1.2 + 0.05 log (t/100)
COCR
OCR0.2
Overburden Stress
svo'
Energy Ratio1
·
Borehole Diameter
·
Sampling Method
·
Rod Length
·
Overconsolidation
1
· · · ·
·
OCR
Obtain by energy measurement per ASTM D4633
Seismic Piezocone Test Obtains Four Independent Measurements with Depth: Cone Tip Stress, qt Penetration Porewater Pressure, u Sleeve Friction, fs Arrival Time of Downhole Shear Wave, ts
Vs fs u2 u1
60o
qc
Seismic cone measures tip and sleeve resistance, pore water pressure, and shear and compression waves
Automated Seismic Source • Electronically-actuated • Self-contained • Left and right polarization • Modified beam uses fin to enhance shear wave generation
• Successfully tested to depths of 20m • Capable of being used with traditional impulse hammer
Concrete Spread Footings Shear failure
One way shear
Two way shear
Reinforcement Length Need length, ld – bond – development of yield strength
Examples of anchoring
Foundation Design Process
Sheet Piles ~ sheets of interlocking steel or timber driven into the ground, forming a continuous sheet
warehouse
warehouse
ship
sheet pile sheet pile
Design and Construction of Steel Sheet Pile
Sheet Piles ~ resist lateral earth pressures ~ used in excavations, waterfront structures, ..
HZ King Piles High Capacity Port Systems.
H pile sheet used for pier construction. (Courtesy of Skyline Steel, Inc. Gig Harbor, WA)
Cofferdam ~ sheet pile walls enclosing an area, to prevent water seeping in.
Bridge Abutment Comparison - Conventional Vs Sheet Piling
Completed Underground Parking garage using Steel Sheet Piling – Designed for a 120 year life
Examples of pier supports
Earthwork and walls: ASD
Superstructure: LRFD Substructure: LRFD/ASD
Foundations: ASD
Installing Micro-piles
Large storage tanks
Sheet piles marked for driving
Sheet pile wall
Sheet Pile
During installation
Sheet pile wall
Kansai Airport Aerial View
Bore Hole Locations
Seawall After Completion
Seawall Construction
The official website of KIA
http://www.kald.co.jp/eindexframe.html
Gravity platforms
Gullfaks C W=1.5 million tones Total height =380m
Troll East - Total height 450m
Repair Viaduct Between Columbia and Yesler
Total vs. Differential Settlement
Do not put too much reinforcement in the footings and ground beams. It is just a waste of money.
Failed Sheet-pile Wall Near Bridge
Collapse of highway due to retaining wall failure – Singapore, 2004
Pile installation using Drop Hammer
Pile Driving Rig - temporarily support the pile that being driven and to support the pile hammer.
Jacking Method Of Insertion Jacked Piles are most commonly used in underpinning structures By excavating underneath a structure short lengths of pile can be inserted and jacked into the ground using the underside of the existing structure as a reaction.
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NON DISPLACEMENT PILES
There are four types: a) b) c) d)
Small Diameter Cast-In- Situ Large Diameter Cast-In-Situ Partially Preformed Piles Grout or Concrete Intruded Piles
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Thank You
CPT-Related Websites • The Liquefaction Site (and CPT site): www.liquefaction.com
• Link page to manufacturers, suppliers, and CPT services: http://www.usucger.org/insitulinks.html
• Listing of available videos on CPT and other in-situ tests: http://www.geoinstitute.org/in-situ.html
• The book Cone Penetration Testing in Geotechnical Practice (Lunne, Robertson, & Powell, 1997):
–
Review: http://geotech.civen.okstate.edu/magazine/books/
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Order: http://www.routledge-ny.com/
