Richard S. Olsen, PhD, PE Acting Principle Geotechnical Engineer

Transcription

1 The Cone Penetrometer Test (CPT) for Earth Dams 2016 Feb 18 NDSP Technical Seminar No. 23 Internal Evaluation Techniques for Earthen Dams FEMA and National Dam Safety Review Board Richard S. Olsen, PhD, PE Acting Principle Geotechnical Engineer Geotechnical & Materials CoP Lead Headquarters Engineering & Construction Division US Army Corps of Engineers (USACE) Washington DC

2 CPT measurements Sleeve Friction Resistance, f s Cone Resistance, q c Measured pore pressure

3 20 TON TRUCK CPT Sounding Data Plot Cone Resistance, (tsf) q c Sleeve Friction Resistance (tsf) f s Speed of Push 2cm/sec (~4ft/minute) Sleeve Friction Resistance, f S Cone Resistance, q C 1-meter connecting rod Reporting the Cone Penetrometer Test (CPT) f s Friction Ratio = 100 q c The sleeve percentage of the cone resistance!

4 Meaning of the CPT Measurements Sleeve Friction Resistance is proportional to large strain effects and lateral stress conditions Cone Resistance is proportional to the initial structure Lateral Stress Conditions Soil Remolding and Grain Rearrangement

5 The CPT is the most cost effective tool for site investigation of soil sites! The CPT is probably the best tool for estimating geotechnical properties!

6 Borings$ = CPT$ x 7 (ranges from 5 to 10) Boring and lab testing Drilling borings 60 to 155 $/foot Lab testing 5 to 120 $/foot Evaluation 1 to 10 $/foot Cone Penetrometer Test (CPT) CPT testing 10 to 25 $/foot Evaluation 0 to 15 $/foot 300 to 600 feet/day 40 to 90 feet/day

7 What if and why is critical for the CPT DON T JUST USE SIMPLE DATA PROCESSING SOFTWARE think Remember geotechnical engineering is not about crunching numbers Most geotechnical failures and issues are due to problems that COULD have been found rather than computed

8 What is the propose of CPT? 1) to find isolated weak zones (the first CPT sounding defines the site conditions - all other soundings either confirm or show geological change) 2) to provide estimates of soil properties, 3) to generate cross sections, and 3) for comparison to nearby borings (verification or to establish correlations)

9 The Initial sand structure is dependent on the deposition environment The CPT is the best tool for indexing the relative structure of the sand structure Flowing river Not flowing

10 Sand-silt-clay mixtures can be potentially unstable This type of metastable structure can be detected with the CPT, specifically using the sleeve friction resistance The sleeve resistance can detect this condition

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12 Weak and soft soil The Cone stress bulb is maybe only one probe diameters below the tip Cone can detect and measure thin layers but the sleeve 5 inches long Stiff and dense soil approx. 20 cm (7.8 inch) approx. 8 cm (3.4 inch) The Cone stress bulb is many Probe diameters below the tip Weak Soil The sleeve at 5 inches long can detect 5 inch soil layers however the cone can influencing a depth of 10 or more inches Stiff Soil Zone of plastic flow

13 We are using the Academic Quality Index (AQI) at all levels (i.e. great data has an A grade (or AQI of 95%) and a ok data is a C or 75%) AQI is better than saying pick a quality index from 0 to 10 AQI is also repeatable AQI can also be a sum of many sub-aqi items, For example; AQI for CPT zero load issues, AQI for CPT stratigraphy issues, AQI for cone type

14 CPT Equipment

15 Compression designed cone Sleeve load cell (compression loading) (not loaded in tension) Sleeve loading Cone load cell (loaded in compression and tension) Subtraction cone The inside of a typical CPT probes Tension cone

16 Between cone and sleeve Seal Face Standard Tip Porous Filter

17 Silt can get into these joints and cause zero load offset problems Measure the pre- and post- zero loads to identify possible zero load offset problems

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19 ERDC SCAPS CPT truck system

20 Terracon s Swamp CPT WES first CPT

21 GeoStaff CPT boat for near shore soft soil testing (1995)

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24 Suitcase CPT system 1994 SCAPS system GeoStaff boat

25 USACE Vicksburg Panama Canal ERTEC in long Beach WES SCAPS at Jacksonville Army base WES SCAPS SWAMP rig - AB

26 Greg CPT on Sacramento levees

27 FUGRO all terrain CPT rig UGRO special purpose rig

28 Four leg jack up (spud barge) for performing CPT soundings

29 Clark s Field vane shear and mini penetrometer rig (Seattle, Washington 1973)

30 CPT Cone Resistance Stress Normalization (determining equivalent value at a vertical effective stress of 1 atm)

31 CPT Boring Normalization Stress Normalization q q c q 1= σ ' c1 = c v q c σ ( σ ' ) total c Stress exponent ( variable, 0.1 to 1 ) v Normalized CPT Parameters CPT estimation of geotechnical properties f s q c f sle q cle Stress Normalization Normalized geotechnical property Use Stress normalization techniques to include stress effects Geotechnical property CPT Measurements

32 1000 Cone resistance stress exponent (for stress normalization) c=0.55 c=0.75 Fines < 5% SCN=2 Medium dense Very loose Loose SCN=1 c= 1 Soil Classification Number (SCN) (Olsen 1995 version) SCN=0 Sand clayey silt fine sand silty sand Silt Olsen & Mitchell (1995) Olsen (1988) sandy silt silty clay Dense Fines = 10 to 15% 80 Fines = SCN= -1 SCN= Friction Ratio (%) silty clay c=0.15 c=0.35 Normally to 100% Peats Sand & Gravel Normalized cone resistance (atm units) Sand mixtures Fines = 40 to 60% mixtures consolidated Clays Increasing over consolidation Increasing over consolidation Organic clay and unstable clayey silts The c stress exponent q = c1 q c σ ( σ ' ) v total c

33 Stress effects are VERY important for shallow (low stress) and deep situations Underwater shallow depths (< 2 m), F v = 0.02 to 0.1 atm Foundations for for large dams, F v = 10 to 20 atm atm. tsf. kgf/cm 2 (Vertical Effective Stress) St-hi-lw.wpg

34 CPT soil classification The changing CPT based Soil Classification chart over the last 28 years plus stress normalization Richard Olsen, PhD, PE USACE-ERDC Geo-Omaha Conference - Feb 15, 2008

35 Richard Olsen, PhD, PE USACE-ERDC Geo-Omaha Conference - Feb 15, 2008

36 Olsen & Mitchell (1995) Olsen (1988) SCN=2 Very loose Loose SCN=1 Soil 10 Classification Number (SCN) (Olsen 1995 version) SCN=0 Medium dense Sand fine sand silty sand silt clayey Fines < 5% Silt sandy silt silty clay Fines = Dense SCN= -1 SCN= Friction Ratio (%) silty clay Peats scn9703n.grf OLSEN 03/03/98 The CPT soil characterization chart for predicting soil type and estimating fines content (Olsen & Mitchell, 1995) Normalized cone resistance (atm units) Sand & Gravel Fines = 10 to 15% Sand mixtures mixtures Normally consolidated Fines = 40 to 60% 80 to 100% Clays Increasing over consolidation Increasing over consolidation Organic clay and unstable clayey silts The CPT soil characterization chart provides the means for accurate estimation of soil properties and behavior trends Silt NC Clay

37 History of Charts 38

38 Advanced Geotechnical Site Characterization CE Fall Dr Richard Olsen Class Notes 15 39

39 Advanced Geotechnical Site Characterization CE Fall Dr Richard Olsen Class Notes 15 40

40 Olsen 2007 and 2012 versions Advanced Geotechnical Site Characterization CE Fall Dr Richard Olsen Class Notes 15 41

41 2016 trending of OCR cle Olsen 2016

42 CPT prediction of earthquake liquefaction Resistance I ve spent 25+ years developing contours of predicted properties on the soil characterization chart AND Explaining the shape and location of these contours I will fully explain many of the prediction in 10 minutes. Normalized Cone Resistance (atm units) Olsen et al 1984, 1986, 1988, 1992, 1995,1998, 1999 Loose Sands Medium Dense 0.1 Dense Sand Mixtures Silt Mixtures 0.2 over consolidation Clays 0.3 CPT estimated CRR Friction Ratio (%)

43 Poor prediction of SPT The q c /N ratio Richard Olsen, PhD, PE USACE-ERDC Geo-Omaha Conference - Feb 15, 2008 Seed

44 Predicting SPT Prediction of normalized SPT blow count (N 1 ) Richard Olsen, PhD, PE USACE-ERDC Geo-Omaha Conference - Feb 15, 2008

45 An example of CPT estimated soil property versus measured values The CPT soil characterization technique is the best CPT-based technique for estimating soil properties because it uses both CPT measurements and uses the Stress Focus theory for stress normalization (Olsen, 1994)

46 Prediction of total unit weight

47 shear wave velocity Measuring Shear Wave Velocity using the Electric CPT High Capacity CPT truck Reverse hit for shear wave generation Vandehey Soil Exploration Wood plank The wood plank (or steel/wood assembly) can also be positioned under the truck leveling jacking pads Reverse wave Reverse wave Primary wave Primary hit for shear wave generation V s1 Use of primary and reverse hits are important to differentiate the shear wave first arrival from noise and compression waves, especially for tests near the ground surface. Miniature precision geophone (positioned for horizontal shear waves) Wave front Primary wave Enlarged section Sleeve Friction Resistance, f s Cone Resistance, q c Travel time to geophone The slope is the shear wave velocity, V s (feet/second) or (meters/second)

48 Prediction of shear wave velocity Old predicting V s1 CPT-based estimation of the normalized shear wave velocity V s1 = (Olsen, 1988) V s v 0.25 V s1 proportional to f s1 But f s1 proporttional to S r Interestly, V s1 and S r are both related to steady state behavior

49 Prediction of shear wave velocity Predicting V s1 CPT-based estimation of the normalized shear wave velocity V s1 = (Olsen, 1994, 1995) V s v 0.25

50 example An example comparison of measured shear wave velocity and CPT estimated shear wave velocity

51 example Another comparison example (uniform bomb blast site)

52 Clay strength We normally look a undrained (relatively quick) failures. So, clay undrained strength is represented as; S u the US standard engineering units are pounds per square foot (psf) Normalized undrained clay strength S u1 = S u v = c/p Vertical effective stress in tsf units = 0.31 for UU test based normal clays with no organics and not illite clay (For slope stability analysis the UU is the standard test) = 0.25 for Simple shear and other specialized laboratory tests = 0.18 to 0.3 organic based clays

53 Prediction of Predicting Strength soil strength Example S u1 or c/p of version

54 Predicting Liquefaction Olsen & Koester 1995

55 Olsen 2015

56 2015 prediction of CRR e Olsen 2015

57 Olsen 2015 Going from clean sand to Normally consolidated clay For CRR 1 =0.2 i.e. CRR e = 0.2

58 Predicting S ues1 Prediction of after earthquake strength Medium dense sands Loose to medium sands Very loose sands Strength of normally consolidated clay (c/p =0.31) Normally Consolidated Clay Normalized Cone Resistance (atm units) Olsen 1987, 1994, 1998 Unpublished - WES data and correlations Friction Ratio (%) qcfr-ws-cleanedup Olsen WES

59 Predicting boil potential Prediction of Sand and Silt Boil Expression Loose sand silt Sand only boils silt Loose sand Silt and sand boils Silt erosion Silt needs to be eroded to be brought to the ground surface Normalized Cone Resistance (atm units) Richard Olsen, PhD, PE USACE-ERDC Midwest DOT Geotechnical Conference Sept 23, 2008 Loose High Pure Silts are very erosion Sands Medium Dense Moderate Dense Sand Mixtures High Moderate Silt Mixtures None Low Clays Friction Ratio (%) over consolidation None None None None

60 Predicting C c Prediction of consolidation parameter This is great for differential settlement calculations Project experience indicates that predicted total settlement can be off by a factor as much as 3 but the differential settlement (ratio) is generally within 25% of laboratory based data. C c 1 + e 0

61 Predicting volume change Prediction of VOLUME CHANGE due to shaking Normalized Cone Resistance (atm units) Very High Loose High High Sands Moderate Dense Medium Dense Sand Mixtures Moderate Low None Low Silt Mixtures None None over consolidation Clays Friction Ratio (%)

62 Predicting Modulus reduction Prediction of Modulus reduction due to liquefaction shear CRR E liquefaction E 50 (Youngs modulus) E 50 dynamic Static (loose sand) 5% strain E Liq 100 (%) strain Normalized Cone Resistance (atm units) times reduction for loose sand Loose Watch out for sensitive silts and soil mixtures 20 time reduction for dense sand - however dense sand will dilate with shear Sands Medium Dense 0.1 2% Dense Sand Mixtures Silt Mixtures 0.2 5% 3% over consolidation Clays % CPT estimated CRR 1 25% Clay Friction Ratio (%)

63 Permeability (cm/sec) SM-ML % passing #200 or D 10 (mm) Final design S u Elevation (feet) Depth below crest (feet) SM SP SM SP Laboratory permeability Laboratory measured D p + u + Trend based on measured data Laboratory based trend Estimated trend from D 10 SC FFSWdepth. Required plots that should be added to computer seepage modeling output 64

64 CPT predicted cross sections CPT Cross sections requires good CPT investigation planning CPT value requires good cross sections

65 3D volume modeling requires too many CPT soundings to properly visualize the soil. SCAPS research to test for petroleum and visualized the results However, 2D cross sections are easily to economically justify 3D volume modeling of clayey soils 1990 high tech Easy in 2016 But not used

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67 The CPT cross section concept (in this case predicted strength) CPT soundings Interpolate the strengths between the two adjacent CPTs (using one of 4 techniques) Commercial contouring software does not create proper alluvial layers watch out Water table Elevation CPT predicted strength of 750 psf for CPT 308C 450 psf for CPT 307C

68 Let us now compare the normal cross sections to CPT predicted cross sections

69 CPT predicted Soil type (Olsen method) For complete site characterization, you must have cross sections of CPT predicted; Soil type, Strength, & Normalized strength

70 CPT predicted Normalized strength (Olsen method) For complete site characterization, you must have cross sections of CPT predicted; Soil type, Strength, & Normalized strength Richard Olsen, PhD, PE USACE-ERDC Geo-Omaha Conference - Feb 15, 2008 Richard Olsen, PhD, PE USACE-ERDC-GSL-GEGB Omaha District Citrus levee meeting 10Jan2008 at New Orleans

71 CPT predicted strength (using Nk = 11) Note: a higher Nk will cause a lower predicted strength For complete site characterization, you must have cross sections of CPT predicted; Soil type, Strength, & Normalized strength Richard Olsen, PhD, PE USACE-ERDC-GSL-GEGB Omaha District Citrus levee meeting 10Jan2008 at New Orleans

72 CPT predicted strength (using a Olsen method) For complete site characterization, you must have cross sections of CPT predicted; Soil type, Strength, & Normalized strength Richard Olsen, PhD, PE USACE-ERDC-GSL-GEGB Omaha District Citrus levee meeting 10Jan2008 at New Orleans

73 CPT predicted soil type - for comparison Zoomed in to compare boring based CAD cross sections to CPT cross section 20 feet Soil type Strength cross section Normalized Strength cross section 20 feet

74 LPV CPT predicted soil type Using the chimney effect with cross section - final QA on CPT data

75 CPT predicted soil type Comparing lateral stratigraphy boring based CAD approach to CPT cross sections Many CPTs (for 2000 ft) because of economics Only two borings for 2000 feet

76 Shallow near offshore project client wanted gray scale only (prediction of undrained strength) 1994

77 Richard Olsen, PhD, PE USACE-ERDC Geo-Omaha Conference - Feb 15, 2008

78 Gatun Dam (hydraulic fill dam) Cross section of soil type (red is sand and blue is clay) (this cross section was developed using custom soil tracing CAD/gridding software) Note the CONTINOUS sloping sand layer! Upstream downstream

79 A C B Complex stratigraphy can become extremely important

80 FIRST STEP - CPT predicted soil type The process of generating CPT based cross sections is not quick nor magic This is the initial output for the specialized gridding software QA, section inspection, removal of chimney effects, and DB verification are still required

81 MIDDLE STEP - CPT predicted soil type

82 FINAL CPT - predicted soil type

83 LPV CPT predicted soil type can it effect landform? Deep seated sandy deposit (i.e much lower settlement potential) Richard Olsen, PhD, PE USACE-ERDC-GSL-GEGB Omaha District Citrus levee meeting 10Jan2008 at New Orleans

84 Non linear layering due to differential settlement A A

85 This surface (A-A) was level before new sediment was added A Ground surface (but it must be level) Lets move back in time when layer interface A was being deposited A

86 This surface (A-A) level can be forced to be level A Moderate consolidation potential Level ground at deposition Moderate consolidation potential Low consolidation potential High consolidation potential A Moderate consolidation potential Shallow clay Full depth of sands and clays Deep clay Full depth of sand with clays Deep clay Shallow mixture

87 The recent sediment caused the (A-A) line that we now see A A

88 LAST TOPIC CPT measurements (with AQI) CQI) Boring Laboratory testing (with AQI) CQI) CPT (Good stratigraphic CQI) Good stratigraphy, e.g. AQI=95% (Poor stratigraphic CQI) Poor stratigraphy, e.g. AQI=60% Overall AQI = low or low average of all individual AQIs Overall CQI = CPT CQI & Laboratory/sample CQI & Stratigraphy CQI

89 Remove soil boring CPT too close CPT correct distance Maybe too far away for correlation purposes How to solve this issue? Lateral stress decreases First perform CPT soundings then borings Richard Olsen, PhD, PE USACE-ERDC Geo-Omaha Conference - Feb 15, 2008 Lower lateral stress due to nearby borehole

90 Predicted strength Cross section of strength Depth plots of strength Elevation

91 LPV 146 MER study area - CPT predicted strength vs measured dots FINAL topic

92 Excellent correlation Excellent correlation Excellent correlation Width of a typical house

93 1000 Olsen & Mitchell (1995) Olsen (1988) 100 Very loose Loose SCN=1 Soil 10 Classification Number (SCN) (Olsen 1995 version) SCN=0 Sand & Gravel Fines < 5% Dense SCN=2 Medium dense Sand fine sand silty sand clayey silt Sand sandy silt silty clay Fines = 10 to 15% Fines = 40 to 60% Fines = 80 to 100% Clays SCN= -1 SCN= -2 Increasing over consolidation Organic clay and unstable clayey silts Friction Ratio (%) silty clay Peats scn9703n.grf OLSEN 03/03/98 Normalized cone resistance (atm units) mixtures Silt mixtures Normally consolidated Increasing over consolidation Thank You Rick Olsen