Geotechnical Site Characterization by Cone Penetration Testing Paul

Geotechnical Site Characterization by Cone Penetration Testing Paul W. Mayne, Ph. D, P. E. Professor, Geosystems Civil & Environmental Engineering Mid-America Earthquake Center FHWA

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

Corrections to SPT N-value Effect Overburden Stress Term vo' CN Value 0. 5 (Pa/ vo') but < 2 Energy Ratio 1 · Safety Hammer CE 0. 6 to 0. 85 0. 3 to 0. 6 0. 85 to 1. 0 Borehole Diameter · 65 to 115 mm CB Sampling Method · Standard sampler CS 1. 00 1. 05 1. 15 1. 0 1. 1 to 1. 3 · Donut Hammer · Automatic Hammer · 150 mm · 200 mm Particle Size · Sampler without liner · 10 m to 30 m · 6 to 10 m · 4 to 6 m · 3 to 4 m Median Grain Size (D 50) of Sand in mm Aging Time (t) in years since deposition Rod Length Overconsolidation 1 Variable OCR Obtain by energy measurement per ASTM D 4633 CR 1. 0 0. 95 0. 85 0. 75 CP 60 + 25 log D 50 CA 1. 2 + 0. 05 log (t/100) COCR 0. 2

Corrections to SPT N-value q Nmeasured = Raw SPT Resistance (ASTM D 1586). q N 60 = (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. q N 60 CE CB CS CR Nmeas = Estimated corrected N q (N 1)60 = CN N 60 = Energy-Corrected SPT Value normalized to an effective overburden stress of one atmosphere: (N 1)60 = (N 60)/( vo’)0. 5 with stress given in atm. (Note: 1 atm = 1 bar = 100 k. Pa = 1 tsf).

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 Penetration Tests (CPT) Cone Trucks Mobile 25 -tonne rigs with enclosed cabins to allow testing under all weather conditions

Corrections to CPT • Tip Stress correction for porewater pressures on unequal areas – Important in Intact Clays & Silts • Sleeve Friction correction for porewater pressures – Use equal end areas on friction sleeve • Baseline corrections – Obtain before & after sounding

Anchored Cone Rig Mud Island, Downtown Memphis, TN q 6 -tonne Geostar truck with 20 -tonne hydraulic pushing system q No special license q Twin earth anchors q Has penetrated to depths over 32+ meters at sites in SC, AL, MO, TN, & AL

CPT Profile, Downhole Memphis fs ub qt

Comparison CPT and SPT Downtown Memphis

Seismic Piezocone Test Obtains Four Independent Measurements with Depth: q Cone Tip Stress, qt q Penetration Porewater Pressure, u q Sleeve Friction, fs q Arrival Time of Downhole Shear Wave, ts Vs fs u 2 u 1 60 o qc

Downhole Shear Wave Velocity q Anchoring System q Automated Source q Polarized Wave q Downhole Vs

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 20 m • Capable of being used with traditional impulse hammer

Downhole Shear Waves Left Strike Right Strike CROSSOVER Method Shear Wave at 8. 15 m Shear Wave at 9. 20 m CROSSCORRELATION Maximum crosscorrelation at Dt = 6. 75 ms Shear wave velocity = 155 m/s Time shift (ms)

Sod Farm, Charleston, SC

CPT Soil Behavioral Classification Soil Behavior Type (Robertson et al. , 1986; Robertson & Campanella, 1988) 1 – Sensitive fine grained 5 – Clayey silt to silty clay 9 – sand 2 – Organic material 6 – Sandy silt to silty sand 10 – Gravelly sand to sand 3 – Clay 7 – Silty sand to sandy silt 11 – Very stiff fine grained* 4 – Silty clay to clay 8 – Sand to silty sand 12 – Sand to clayey sand* *Note: Overconsolidated or cemented

Sounding - Shelby County, TN

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/ • Order: http: //www. routledge-ny. com/