• SCE-CSSM model is adequate to capture the general trend of CPTu readings in clayey soils

• Key parameters in fitting models of CPTu readings: sp’ and IR. Other parameters (gt, f’, L, Ko and d’) have lesser significance

• SCE-CSSM model is inadequate to represent mixed soil types (partially drained conditions)

Piezocone penetration test (CPTu) readings of tip resistance

(qt), sleeve friction (fs), and shoulder porewater pressure (u2)

in fine-grained soils can be modeled using spherical cavity

expansion (SCE) theory and critical state soil mechanics

(CSSM) concepts. The predicted profiles can be fitted to the

measured CPTu response using input of soil parameters:

preconsolidation stress (sp'), total unit weight (gt), effective

friction angle (f'), rigidity index (IR = G/su; G = operational

shear stiffness), and compressibility parameters (L = plastic

volumetric strain potential = 1–Cs/Cc; Cs = swelling index,

and Cc = virgin compression index). The application of such

a formulation is presented for CPTu representation

obtainable using a hybrid SCE-CSSM model to a variety of

clays sites which have been field tested by CPTu. These

deposits have known profiles of gt, f', sp‘, Cs, Cc and L

determined from laboratory tests, and initial shear stiffness

(Gmax) obtained from field measurement of shear wave

velocity (Vs). Undrained shear strength (su) evaluated via

critical-state concepts is used together with G to evaluate IR

over a range of applicable strains.

RESULTS AND CONCLUSIONS CLOSED FORM SOLUTION

CALIBRATION OF HYBRID SCE-CSSM ANALYTICAL MODEL FOR PIEZOCONE PENETRATION IN CLAYS

Fawad S. Niazi1, Paul W. Mayne1, and David J. Woeller2 1Georgia Institute of Technology; 2ConeTec Investigations Ltd.

OVERVIEW OF CPT CALIBRATIONS

ABSTRACT

Figure 3. Fitted OCR and CPTu profiles: NGES Amherst

Table 1. SCE-CSSM input parameters at selected clay sites

REFERENCES

• Historic evolution of CPT-based correlations: mechanical to electrical CPT; single reading to hybrid SCPTu

• Continuous need for improved correlations

• Alternate approach – utilize fundamental soil properties to model CPTu readings

• Analytical model for clay – a framework of SCE by Vesic (1977) + Cambridge CSSM concepts

• Forward evaluations of CPTu (3 readings) in clays

Site Name Location Sounding depth (m)

Predominant soil type

zw (m)

Dsp' (kPa)

OCR f' (deg.)

L IR

Cowden N. Humberside, UK 26 Glacial clay till 1.0 800 3–15 27 0.9 850

FMC Calgary, AB, Canada 30 Sandy silt layers

overlying very stiff to hard silty clay till

6.0 850 3–15 32–40 0.9 100

GEB: North Maple Ridge, BC,

Canada 77 silty clay/clayey silt 2.1 60 1–4 29 0.7 600

GEB: South– I Langley, BC, Canada 47 Stiff clay 2.1 115 1–3 28 0.80 450 GEB: South– II Langley, BC, Canada 94 Sitly sand over clay 3.0 100 1–3 30 0.85 350 Grimsby Waltham, UK Glacial clay till 1.5 700 3–15 28 0.9 900

High Prairie N. AB, Canada Soft to stiff clay with

silty sand/sand lenses

4.5 95 1–2 30 0.7 40

Sarapui clay Rio de Janeiro, Brazil 6 Soft clay over hard

silty clay 0.0 25 2-7 26 0.8 30

Amherst NGES

UMASS, Amherst, USA

15 Alternating layers of

silt and clay 1.5 25–300 1–8 25 0.9 300

Northwestern NGES

Evanston, IL, USA 27 Sand fill over soft to medium to stiff clay

4.0 25–80 < 2 29–35 0.8 65

Treporti Test Site

Venice, Italy 40 Predominant silty

clay, combined with sand

0.5 30 1–2 36 0.85 250

US-95 Sandcreek Byway Project

Sandpoint, ID, USA 60 Sandy/silty soil over clay with seams of

sand/silt 4.0 80 1–3 27 0.8 70

qt

u2

fs

qt u2 fs

Tip Resistance: qt = svo + [(4/3)(lnIR + 1) + p/2 + 1+∙(M/2)(OCR/2)L∙svo' Shoulder Porewater Pressure: u2 = uo+(4/3)∙(lnIR)∙(M/2)∙(OCR/2)L∙svo’+*1 – (OCR/2)L+∙svo ‘ Sleeve Friction: fst = [Ko – {1 – (OCR/2)L}]∙svo'∙tand'

CASE STUDY APPLICATIONS

NGES Amherst, MA NGES Northwestern Univ., IL US-95 Bypass Project,

Sandpoint, ID

Cowden, North Humberside, UK Grimsby, Waltham, UK

Sarapui Clay Site, Rio de Janeiro, Brazil www.mapcruzin.com

Foothill Medical Center, AB Golden Ears Bridge, BC High Prairie, AB

Treporti Test Site, Venice, Italy

OCR = overconsolidation ratio = sp'/svo'; M is the frictional parameter of Cambridge

q–p' space = 6sinf'/(3−sinf'); svo' = effective vertical stress = svo–uo; svo = total

overburden stress = Sgti∙zi; uo = hydrostatic porewater pressure = gw∙hw; zi = depth of

ith soil layer, respectively; hw = height of water; gw is the unit weight of water; tand =

interface friction ≈ 0.4∙tanf' and Ko = lateral stress coefficient = sho'/svo'.

Figure 2. Locations of selected clay sites

Figure 1. CPTu evaluations of geotechnical properties

Mayne, P.W. (1991). "Determination of OCR in clays by piezocone tests using cavity expansion and critical state concepts." Soils and Foundations 31(1): 65–76.

Mayne, P.W. (1993). "In-situ determination of clay stress history by piezocone model." Predictive Soil Mechanics, Thomas Telford, London: 483 – 495.

Mayne, P.W. (2007). "Overview Paper: In-situ test calibrations for evaluating soil parameters", Characterisation & Engineering Properties of Natural Soils, Vol. 3, Taylor & Francis Group, London: 1601– 1652.

Vesic´, A.S. (1977). Design of pile foundations. NCHRP Synthesis 42, Transportation Research Board, National Research Council, Washington, D.C., 68p.

0 0.5 1 1.5 2

OCR

Oedometer

Geologic prestress est.

0

5

10

15

20

25

30

0 0.1 0.2 0.3 0.4

Dep

th (

m)

svo' and sp' (MPa)

Effective overburden stressOedometerGeologic prestress est.

0 1 2 3 4

qt (MPa)

Measured qtSCE-CSSM qt

0 0.01 0.02 0.03 0.04

fst (MPa)

Measured fstSCE-CSSM fst

0 0.25 0.5 0.75 1

u2 (MPa)

uoMeasured u2SCE-CSSM u2

Figure 4. Fitted OCR and CPTu profiles: NGES NWU

Figure 5. Fitted OCR and CPTu profiles at High Prairie

0 1 2 3 4

qt (MPa)

Measured qt

SCE-CSSM qt

0 0.01 0.02 0.03 0.04

fst (MPa)

Measured fst

SCE-CSSM fst

0 0.25 0.5 0.75 1

u2 (MPa)

uoMeasured u2SCE-CSSM u2

0

5

10

15

20

0 0.1 0.2 0.3 0.4

Dep

th (

m)

svo' and sp' (MPa)

Effective Overburden Stress

Preconsol. via oedometer

Geologic prestress est.

0 2.5 5 7.5 10

OCR

Via Oedometer

Geologic prestress est.

0 2 4 6

OCR

Via SCPTu

Via DMT

Geologic prestress est.

0

5

10

15

20

25

0 0.1 0.2 0.3 0.4

De

pth

(m

)

svo' and sp' (MPa)

Effective overburden stress

Preconsol. via SCPTu

Preconsol. via DMT

Geologic prestress est.

0 2 4 6

qt (MPa)

Measured qtSCE-CSSM qt

0 0.05 0.1 0.15

fst (MPa)

Measured fstSCE-CSSM fst

0 0.5 1 1.5

u2 (MPa)

uoMeasured u2SCE-CSSM u2

0

10

20

30

40

50

60

10 15 20 25 30

De

pth

(m

)

gt (kN/m3)

Mayne et al. (2010): fn(z, fs, qt)

Mayne et al. (2010): fn(svo', fs, gw)

25 30 35 40 45 50

f' (degree)

Kulhawy & Mayne (1990): fn(qt, svo')

Senneset et al. (1989): fn(Q, Bq)

0 250 500 750 1000

sp' (kPa)

Mayne (2009): fn (qt, svo)

Mayne (2007): fn (Gmax, svo')