Examples of : CPTU profiles other soil types Unusual behaviour Use of non-standard equipment Examples of CPTU results in other soil types Peat Silt/ clayey sands Mine tailings Underconsolidated clay Other Engineering properties in peat from CPTU? Landva( 986) concluded that due to the very fibrous nature of peat, and the frequent obstructions like stumps and roots, small scale in situ tests like CPT are normally of little engineering use for design of road embankments (experience from East Canada mainly) CPTU good for identification of peat layers In organic soils of non-fibrous nature, CPT and possibly other in situ tests can be useful. Example of CPT profile from Holland with peat layers Example of CPTU profiles from coast of Germany with peat layers Intermediate soils - clayey sands to silt Interpretation methods valid for sands or clays may not be applicable for silts since penetration can be partially drained According to Bugno and McNeilan (984) undrained response for standard CPT will occur if permeability of soil is < 0-7 to 0-6 cm/sec. Soils with permeability between 0-6 and 0-3 cm/sec will probably behave as partially drained Vos (98) Is silts it may be advantageous to do tests at nonstanderd rates
Soil profile and CPTU results in Stjoerdal silt, Norway CPTU profile in Keilisnes silt, Iceland Sand Interpretation in terms of effective stresses Silt q t - σ vo = N m (σ vo +a) N m = cone resistance number a = attraction = c/tanφ β = degree of plastification a = attraction = c/tanφ After Senneset et al.(988) From Janbu and Senneset(989) Interpretation in terms of effective stresses q t - σ vo = N m (σ vo +a) N m = cone resistance number a = attraction = c/tanφ β = degree of plastification For Norwegian silts: a = 5-0 kpa β = 5-0 degrees Interpretation in terms of effective stresses For Stjørdal silt : 0 m depth : q t =. MPa σ vo = 70 kpa N m = 5 tanφ = 0.65 φ = 35 degrees Stjoerdal silt Effective stress friction angle from CPTU and from laboratory tests
Constrained moduldus,m o, vs cone resistance for silty soils 5 CPTU in silts Rough conservative estimates of constrained modulus: for q t <.5 MPa M o = q t Mpa.5 MPa < q t < 5 MPa M o = (4 q t -5) MPa Gullfaks C CPTU profile and correlation with clay content 0 From Senneset et al.(988) Hight et al.(994) Assessment of in situ variation of clay content, Gullfaks C Clay content is very important for penetration behaviour General guidance on interpretation of CPTU in silt/ clayey sand soils Important to identify drainage conditions expected in foundation design problem and during cone penetration General guidance on interpretation of CPTU in silt/ clayey sand soils Important to identify drainage conditions expected in foundation design problem and during cone penetration If design problem requires undrained shear strength and cone penetration is also undrained CPTU data can be used similar to clays Hight et al.(994)
General guidance on interpretation of CPTU in silt/ clayey sand soils Important to identify drainage conditions expected in foundation design problem and during cone penetration If design problem will undrained shear strength and cone penetration is also undrained CPTU data can be used similar to clays If design problem involves drained loading and cone penetration is also drained, CPT data can be treated as in sand General guidance on interpretation of CPTU in silt/ clayey sand soils Important to identify drainage conditions expected in foundation design problem and during cone penetration If design problem will undrained shear strength and cone penetration is also undrained CPTU data can be used similar to clays If design problem involves drained loading and cone penetration is also drained, CPT data can be treated as in sand If design problem is expected to involve drained loading but cone penetration is undrained or partially drained, interpretation is more complicated : use effective stress strength parameters. May consider to do tests at non-standard speeds CPTU in mine tailings Stability is frequently a geotechnical problem Deposits are often very stratified and CPTU is particularly useful Example from Zelazny Most in Poland Żelazny Most Mine Tailings Dam: )Situated between Lubin and Głogów, Poland )The biggest hydrotechnical construction in Europe, 3)Dimensions: a) diameter app. 5 km, b) height of dams over 45 m (east dam), c) length of dams app. 4 km, 4) Accumulation from 977, 5) Hydrotransportation with dumping towards the center. DEPARTMENT OF GEOTECHNICS, AGRICULRAL UNIVERSITY, POZNAŃ, Poland Zelazny Most Tailings dam, Poland Żelazny Most reservoir (source: KGHM) DEPARTMENT OF GEOTECHNICS, AGRICULRAL UNIVERSITY, POZNAŃ, Poland Zelazny Most Tailings Dam INVESTIGATIONS Due to the technology of deposition three parts in the cross section: )Dams mainly noncohesive soils, )Beaches both non- and cohesive material, 3)Pond cohesive material, the finest fractions, covers significant part of the reservoir. Investigations: )dams and beaches easy access, ) pond difficult access, out of interest DEPARTMENT OF GEOTECHNICS, AGRICULRAL UNIVERSITY, POZNAŃ, Poland
Zelazny Most tailngs Dam Zelazny Most Mine Talings Dam Zelazny Most Mine Tailings Dam Parts of the cross section DEPARTMENT OF GEOTECHNICS, AGRICULRAL UNIVERSITY, POZNAŃ, Poland Beach profile: ) mainly sand fraction, laminations of silt and clay fractions, ) result high values of q c and f s, u c close to hydrostatic, 3) parameters for sediments close to values for natural soils. Pond profile: ) very weak sediments, ) mainly silt fraction, 3) result low values of q c and f s, high excess pore pressure u c. Interpretation like in clay Zelazny Most Tailings dam, Poland DEPARTMENT OF GEOTECHNICS, AGRICULRAL UNIVERSITY, POZNAŃ, Poland CPTU chosen as main test for contiously monitoring stability. Thousands of tests have been carried out Identification of underconsolidated clay In many cases it is important to determine if a clay is fully consolidated or not. Alternative approaches :. Install piezometer and measure directly in situ pore pressue. Carry out piezocone dissipation tests until equilibrium pore prssuers have been reached 3. Empirical approach by Tanaka and Sakagami (989) based on tests in Osaka clay ( Japan) Identification of underconsolidated clay Tests carried out in NC and underconsolidated Osaka clay Tanaka and Sakagami(989)
CPTU profiling can be useful in most soils Examples of other materials not covered in presentation: Residual soils ( e.g. Mayne, 003) Calcareous soils ( see book + some new) Chalk (book) Slurry walls (book) Loess soils (book) Permafrost (book) Examples of unusual behaviour and effects of non-standard procedures Cavitation of pore water Effect of stones on u penetration pore pressures Cone size and scale effects Cone penetrometer geometry Rate of penetration Limiting negative pore pressures due to cavitation If pore pressures in a soil becomes equal to minus atmosphere ( about 00 kpa), cavitation occurs and it cannot become lower However, much larger values of Δu ( = u - u o ) can be obtained depending on initial pore pressure in a soil For offshore soils, at a given depth below seabed the min value of Δu depends on water depth CPTU at Sleipner, North Sea, 05 m wd CPTU at Sleipner, North Sea, 05 m wd CPTU at Sleipner, North Sea, 05 m wd Effect of cavitation At 05 m water depth: back pressure of about 050kPa; i.e. Absolute negative pore pressure is about 50-050 = 00 kpa - cavitation Effect of cavitation At 05 m water depth: back pressure of about 050kPa; i.e. Absolute negative pore pressure is about 50-050 = 00 kpa Note loss of saturation and sluggish response Effect of cavitation
Negative u pore pressures du to stones in stiff clays Pushing the stone aside creates a vacuum behind the stone and pore pressure becomes negative Filter u Example of CPTU measurements with u pore pressure in glacial till at cowden in UK Exposed glacial clay till at Cowden, UK Effect of rate of penetration on u readings in a glacial till at Cowden, UK Effect of cone size Considerations related to minicones Example of light mini-rig for use in deep waters Global, UK
Mini Cone Effects of cone size Effect of cone size in layered soils cm cone with pore pressure sensor and friction sleeve Investigations have shown that tests with cone diameters in range 5 cm to 5 cm gives very similar results Smaller cones should be checked for scale effects, especially in layered soils; ref. recent investigation in Louisiana soils (Titi et al.,999.): q c,cm =.* q c,5cm f s,cm = 0.9 * f cs5cm Effects of cone size on cone resistance Depth (m) Corrected Cone Resistance q (MPa) t 0.0 0. 0.4 0.6 0.8.0 0 3 4 5 6 7 8 9 0 Cone 5 sq cm Cone 5 sq cm Cone 3 0 sq cm Cone 4 5 sq cm Cone 0 sq cm Cone 5 sq cm Bothkennar, UK Powell,00 Effects of cone size on cone resistance Depth (m) 0 3 4 5 6 7 8 9 0 Cone Resistance qc (MPa) 0 3 4 5 Cone 3 0 sq cm Cone 3 0 sq cm Cone 0 sq cm Cone 0 sq cm Cone 0 sq cm Cone 0 sq cm Cone 5 sq cm Cowden, UK Powell, 00 Recommendations on cone size IRTP : the cross-sectional area of cone shall nominally be 0 sq.cm, which corresponds to a diameter of 35.7 mm. Cones with diameters between 5 mm( A c =500 sq.mm) and 50 mm (A c =000 sq.mm) are permitted for special purposes, without the application of correction factors. Cones outside this range should not be used for deriving soil design parameters before documentation with parallel tests of standard size
Sleeve friction and friction ratio along shaft in sand ( McDonald Farm) Sleeve friction and friction ratio along shaft in sand ( McDonald Farm) Influence of rate of penetration on cone resistance Sleeve friction is now standardised to be just behind cone and 34 mm long, but for special purposes it may be more optimal with different location and length Bemben and Myers(974) Influence of rate of penetration on cone resistance Roy et al.,98 CPT/CPTU equipment and procedures Results depend very much on details in equipment and procedures We should as far as possible stick to IRTP or ASTM If we deviate notes should be clearly marked on each plot showing results In some cases it may be beneficial to deliberately use non-standard procedures Normalized soil behaviour classification chart 000 000 7 ϕ 8 σ Increasing vo qt OCR, age 7 u o cementation u 9 00 00 6 6 Q t Q 5 0 t 0 4 5 Increasing OCR, age 4 3 Increasing sensitivity 3 0. 0-0.4 0 0.4 0.8. Normally consolidated Zone Soil behaviour type. Sensitive, fine grained. Organic soils-peats 3. Clays-clay to silty clay Zone Soil behaviour type 4. Silt mixtures clayey silt to silty clay 5. Sand mixtures; silty sand to sand silty 6. Sands; clean sands to silty sands Zone Soil behaviour type 7. Gravelly sand to sand 8. Very stiff sand to clayey sand 9. Very stiff fine grained Robertson,990
CPTU profile in Japanese volcanic soil CPT creep test results in permafrost Takesue et al. (995) Soil classification from CPTU data compared to laboratory test results Takesue et al. (995) Ladanyi et al. CPT results on the moon CPT result in Dutch cheese CPT profile in middle chalk at Munford, UK Mitchell and Houston (974) Power,98
Classification of chalk grade Example of cavitation phenomenon on CPT tests : CPTU profiling in mine tailings showing ice lenses plus use of dissipation data to aid soil classification Powell and Quarterman, 994 Another water depth From British Columbia, Canada Campanella et al, 984