USE OF CPT/CPTU FOR SOLUTION OF

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USE OF CPT/CPTU FOR SOLUTION OF PRACTICAL PROBLEMS Tom Lunne, NGI USE OF CPT/CPTU FOR SULUTION OF PRACTICAL PROBLEMS Indirect design method: Interprete CPT/CPTU

1 USE OF CPT/CPTU FOR SOLUTION OF PRACTICAL PROBLEMS Tom Lunne, NGI USE OF CPT/CPTU FOR SULUTION OF PRACTICAL PROBLEMS Indirect design method: Interprete CPT/CPTU results to arrive at soil design parameters Classical foundation analysis Direct design method: Use CPT/CPTU results directly without intermediate step of soil parameters

2 DIRECT APPLICATIONS OF CPT/CPTU RESULTS Correlations to SPT (standard d penetration ti tests) t Axial capacity of piles Bearing capacity and settlement of shallow foundations Ground improvement - quality control Liquefaction potential evaluation SPT Standard penetration test One of the most used in situ tests in the world The basis of the test consists of driving a sampler by dropping a hammer of 63,5 kg mass on to an anvil or drive head from a height of 760 mm. The number of blows (N) necessary to achieve a penetration of the sampler of 300 mm is the penetration resistance. A disturbed sample of 38 mm diameter is obtained 2

3 Standard Penetration Test (SPT) After Kovacs and Salamone, 982 Need for SPT/CPT correlations It is now recognized that the CPTU gives much more reliable and useful data compared to the SPT Still many engineers have a lot of experience with the SPT and asks for N values when CPTs have benn performed In many projects earlier investigations included SPT data and it is very useful to convert the N-values to q c in order to compare the old and new data 3

4 CPT/SPT CORRELATIONS Depends on several factors: Energy level delivered to SPT - use N 60 Grain size distribution (D 50 ) Fines content (FC) Overburden stress + other factors Comment: Single most important factor influencing N value is energy delivered to SPT sampler, expressed as rod energy ratio. Energy ratio of 60% is generally accepted to represent average SPT energy. Results should be corrected to N 60. CPT/SPT CORRELATIONS Correlations most used: - Robertson et al Kulhawy and Mayne, 990 4

5 CPT/SPT CORRELATIONS P a = reference stress = atm = 00 kpa Robertson and Campanella (983) CPT/SPT CORRELATIONS Effects of fines content Mayne and Kulhavy (990) 5

6 Normalized soil behaviour classification chart Normally Increasing OCR, age cementation u o vo qt u 6 6 Q t 0 5 y consolidated 4 Increasing sensitivity 3 Increasing OCR, age 2 Q t Zone Soil behaviour type. Sensitive, fine grained 2. 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 CPT/SPT CORRELATIONS In lack of soil grain size data, use Robertson (990) soil classification chart to define soil behaviour type index: Q I t c logq logf q ' t v 0 t v 0, F r r q t f s q p N 8.5 I 4.6 q c p a 60 c v 0 p a = atm. Press. = 00 kpa N 60 : SPT value corresponding to energy ratio of 60% 6

Bhd A lot of old investigations with SPT CPT/SPT correlations If grain size distribution data are available Use (q c /p

7 Example CPT/SPT Correlations Westport Warehose facility outside Kuala Lumpur Soil investigation by Soils and Foundations Sdn.Bhd A lot of old investigations with SPT CPT/SPT correlations If grain size distribution data are available Use (q c /p a )/N 60 from Robertson et al.,983 (Fig.6.)(D 50 ) and/or (q c /p a )/N from Fig. 6.3 ( Fines content) If grain size distribution data are not available Use soil behaviour index, I C ( = f(q t,f r ) (q c /p a )/N 60 =8.5( - I C /4.6) 7

8 Pile bearing capacity Earliest application of CPT data Compicated by large variety of pile types and installation procedures Most design techniques based on empirical methods PILE BEARING CAPACITY Q ult = pile bearing capacity = f p * A s + q p * A p A s = pile side area A p = pile tip area f p = unit side friction f p and q p can be estimated from either in situ or laboratory test data q p = unit tip resistance 8

9 PILE BEARING CAPACITY Several studies: Robertson et al., 988; 8 cases Briaud, 988; 78 pile load tests Tand and Funegård, 989; 3 cases Sharp et al.,988; 28 cases NGI, 998. All show CPT methods better than laboratory based methods. French method by Bustamante and Gianesseli (982) proved to be most consistent AXIAL PILE CAPACITY Q ult = f p A s + q p A p (side friction plus tip resistance) Bustamante and Gianeselli (982) f p = q c / q p = k c q ca and k c empirical constants for different pile and soil types Based on a large number of case histories (97) in France tables have been made with and k c factors according to soil type and to type of pile 9

10 Scale effect for unit end bearing Computation of q c for tip resistance Pile end bearing is dependant on soil above and below pile tip. Need to evaluate average q c to represent this influence area. Bustamante and Gianesseli(982) 0

11 BEARING CAPACITY FACTORS, k c (BUSTAMANTE AND GIANESELLI, 982) Factors k c Nature of soil q c (Mpa) Group I Group II Soft clay and mud < Moderately compact clay to Silt and loose sand q p = k c q ca Compact to stiff clay and > compact silt Soft chalc Moderately compact sand and 5 to gravel Weathered to fragmented > chalk Compact to very compact sand and gravel > Group I: plain bored piles; mud bored piles; micro piles (grouted under low pressure); cased bored piles; hollow auger bored piles; piers; barrettes. Group II: cast screwed piles; driven precast piles; prestressed tubular piles; driven cast piles; jacked metal piles; micropiles driven; grouted driven metal piles; driven rammed piles; jacket concrete piles; high pressure grouted piles of large diameter. FRICTION COEFFICIENT, (BUSTAMANTE AND GIANESELLI, 982) Category Coefficients, Nature of soil q c (Mpa) I II A B A B Soft clay and mud < Moderately compact clay to Silt and loose sand Compact to stiff clay and compact clay > Soft chalk Moderately compact sand and gravel 5 to Weathered to fragmented chalk > Compact to very compact sand and gravel < f p = q c / f p should not excced given maximum values

FRICTION COEFFICIENT, (BUSTAMANTE AND GIANESELLI, 982) Ctd. Category Maximum limit of f p (Mpa) Nature of soil q c (Mpa) I II III A B A B A B Soft clay and mud < 0.05 0.05 0.05 0.05 0.035 Moderately compact to 5 0.

12 FRICTION COEFFICIENT, (BUSTAMANTE AND GIANESELLI, 982) Ctd. Category Maximum limit of f p (Mpa) Nature of soil q c (Mpa) I II III A B A B A B Soft clay and mud < Moderately compact to clay (0.08) (0.08) (0.08) Silt and loose sand Compact to stiff clay > and compact clay (0.08) (0.08) (0.08) Soft chalk Moderately compact 5to sand and gravel (0.2) (0.08) (0.2) f p = q c / Note: Maximum limit unit skin friction, f p: bracket values apply careful execution and minimum disturbance of soil due to construction. Pile Capacity from CPT Example from Westport, Kuala Lumpur Cone resistance in sand for pile bearing capacity calculation 2

13 Pile Capacity from CPTU Example from Westport Kuala Lumpur Pile tip resistance in sand by CPT method Pile bearing capacity from CPTU data It is recommended to use several methods and to adopt a conservative value for evaluation of pile bearing capacity Bustamante and Gianeselly(982) ( French method) de Ruiter and Beeringen (979) (European method) Almeida et al (996) (clay only--- uses q t ) If local experience exist, may use only method that has shown to give the best prediction 3

14 Pile bearing capacity from CPTU data Recent methods for offshore applications Imperial College Method (996) NGI (2005) Fugro (2005) UWA (2005) Included in Commentary of API 20. Comprehensive comparison published at ISFOG conference in Perth (2005), all accepted by API Other key references: Schneider et al. (2008) and Knudsen et al. (202) Fugro -05 Formulation of shaft friction f From Schneider et al.(2008) 4

15 Fugro -05 Formulation of shaft friction f From Schneider et al.(2008) Fugro -05 Formulation of shaft friction f From Schneider et al.(2008) 5

16 Fugro -05 Formulation of shaft friction f From Schneider et al.(2008) Fugro -05 Formulation of shaft friction f From Schneider et al.(2008) 6

17 ICP -05 Formulation of shaft friction f From Schneider et al.(2008) NGI-05 Formulation of shaft friction f p ref ) 0.25 Nominal relative density, may be > q cn = (q c /p ref )(p ref / v0 ) 0.5 From Schneider et al.(2008) 7

18 UWA-05 Formulation of shaft friction f From Schneider et al.(2008) CPT based formulations for tip resistance NGI-05 From Schneider et al.(2008) 8

19 Pile bearing capacity using the 4 CPT methods (French method) Geometric mean Standard deviation of ln (Q c /Q m ) From Schneider et al.(2008) Comparison of 4 CPT pile bearing capacity methods Plugged open-ended steel piles, driven From paper by: Knudsen, Langford, Lacasse and Aas, 202 9

20 Pile bearing capacity using the 4 CPT methods From Knudsen et al.(202) Variation with pile diameter and D r Ground improvement - quality control Purpose of deep compaction is often to fulfill one of the following: Increase bearing capacity (i i.e. shear strength) Reduce settlements ( i.e.increase modulus) Increase resistance to liquefaction (i.e. density) Cone resistance in cohesionless soils is governed by factors including soil density, in situ stresses, stress history and soil compressiblity Changes in cone resistance can therefore be used to document effectiveness of compaction 20

method to monitor and document effect of deep compaction Important

21 Deep compaction vibrocompaction vibro-replacement dynamic compaction compaction piles deep blasting CPT is found to be best method to monitor and document effect of deep compaction Important to consider time effect Suitability of soil for vibrocompaction Massarsch(994) 2

22 Example vibropiling Port of Gijon. Spain Example vibropiling Port of Gijon. Spain 22

23 Example vibropiling CPT before and after compaction Port of Gijon. Spain Compaction control Range of cone penetration test values before and after compaction and surface compaction with vibrating plate Lindberg and Massarsch(99) 23

24 Effect penetration resistance after dynamic compaction From Woeller et al. (995) The aging effects of sands Effect of vibrocompaction at Chek Lap Kok airport in Hong Kong. From Ng, Berner and Covil (996) 24

25 Compaction by blasting Effect of time From Mitchell and Solymar(984) Days after dynamic compaction 0 m silty sand (Schmertmann, 99) 6 drops 4 drops 2 drops Time in days Diagram developed for correcting cone resistance measured just after compaction large project in Florida 25

26 Ground improvement - quality control For large projects: Develop experience with increase in cone resistance with time after compaction took place. Use this experience to make criteria for acceptance or rejection based on CPT/CPTUs carried out just after compaction took place Where resistance to liquefaction is major issue, measurement of shear wave velocity will provide additional data Results of CPTs before and after compaction may be used to evaluate increase in D r CPTU data can be used to evaluate if compaction will be efficient or not ( ref. soil behaviour chart) Liquefaction resistance Major concern for structures constructed with or on sand and sandy silt. Cyclic loads from : earthquakes, wave loading, machine foundations and other Effect is to increase pore pressure causing loss of effective stress and soil strength To evaluate potential for soil liquefaction important to determine soil stratigraphy and in situ soil state CPT/CPTU ideal because of its repeatablity, reliability, continuous data and cost effectiveness 26

27 Evaluation of liquefaction potential CPT/CPTU provide valuable data detect even thin sand layers that could liquefy pore pressure data tells usabout groundwater conditions and additional information to estimate grain size and fines content ( together w/sleeve friction) cone resistance gives input to in situ state of sandy soils SCPTU can give valuable additional data soil type state of soil in situ SCPTU is seismic cone: can measure shear wave velocity, v s Liquefaction evaluation based on CPT/CPTU results Different approaches :. a) Estimate D r from q c, vo D,D r relationship b) Perform cyclic triaxial and/or direct simple shear tests in laboratory on samples reconstituted to estimated D r and relevant cyclic stress level ( cy / vo ) 2. Estimate directly from CPT/CPTU results using empirical methods developed in North America and Japan 27

28 Liquefaction potential directly from CPT/CPTU results. Correct q c for overburden stress effect Q c = C*q c 2. Estimate t average cyclic stress ratio (due to wave loading or earthquake or other source) cy / vo 3. Establish D 50 by grain size analysis on obtained samples - or estimate from CPT/CPTU results using soil classification charts 4. Check liquefaction by cy / vo, Q c, D 50 diagram Liquefaction potential directly from CPT/CPTU results Correction factor for cone resistance to predict liquefaction potential of sand (from Shibata and Teparaksa, 988) 28

29 Liquefaction potential directly from CPT/CPTU results Liquefaction potential from cone resistance (after Shibata and Teparaksa, 988) Liquefaction potential directly from CPT/CPTU results Comparison of q c with estimated (q c ) cr value in 983 Nihonkaichuba earthquake (from Shibata and Teparaksa, 988) 29

30 Vibratory cone for liquefaction evaluation Vibratory cone for liquefaction evaluation Evaluation of liquefaction potential in Japanese soil 30

31 CPTU and evaluation of liquefaction Detailed methodology given by: Robertson, P.K. and Wride, C.E. (998) Evaluating cyclic liquefaction potential using the cone penetration test. Canadian Geotechnical Journal, 35(3): Robertson, P.K. (200) Evaluation of flow lquefaction and liquefied strength using the cone penetration test. Journal of Geotechnical and Geoenvironmental Engineering, ASCE, 36(6): SUMMARY: PERCEIVED APPLICABILITY OF THE CPT/CPTU FOR VARIOUS DIRECT DESIGN PROBLEMS Pile design Bearing Settlement Compaction Liquefaction capacity control Sand Clay Intermediate soils Reliability rating: =High 2=High to moderate 3=Moderate 4=Moderate to low 5=Low 3

32 Reserve overheads Rapid impact compactor 32

33 t t Effect of rapid impact compactor Depth below com mpaction level (m) q c (MPa) Upper reclamation fill - Med to dense SAND with some gravel Reclamation fill - Soft CLAY/SILT Lower reclamat ion f ill - M ed t o Dense SAND with gravel M arine sediment - Loose to medium dense silt y SAND M arine silt - Soft to firm sandy SILT / CLAY wit h gravel Highly t o completely weathered LIM ESTONE to design GWL (m) Elevation related Trial CPT 4 pretreatment Trial CPT 9 pretreatment Trial CPT 4 posttreatment Ti Trial lcpt9 posttreatment Target qc Site investigation data 6 Weak t o moderat ely weak LIM ESTONE -4 If no grain size data available- use Soil behaviour classification chart Cone resistance, q (MPa) , 0, or vo u o OCR q t u2 u-u 2 o B= q q- t vo S Cone resistance, q (MPa) S t Pore pressure parameter, B q Friction ratio (%) t Dr. 5 4 OCR e 3 Zone: Soil Behaviour Type:. Sensitive fine grained 2. Organic material 3. Clay 4. Silty clay to clay Soil Behaviour Chart (Robertson et al, 986) 5. Clayey silt to silty clay 6. Sandy silt to clayey silt 7. Silty sand to sandy silt 8. Sand to silty sand 9. Sand 0. Gravelly sand to sand. Very stiff fine grained* 2. Sand to clayey sand* * Overconsolidated or cemented. Robertson et al.,986 33

34 SOIL CLASSIFICATIONS AND RATIOS Zone Soil behavior type (q c /p a )/N 60 Sensitive fine grained 2 2 Organic material 3 clay 4 Silty clay to clay.5 Zone refers to Soil 5 clayey silt to silty clay 2 6 Sandy silt to clayey silt Silty sand to sandy silt 3 8 Sand to silty sand 4 9 sand 5 0 Gravely sand to sand 6 Very stiff fine grained 2 Sand to clayey sand B= 2 Behaviour type diagram o q q 6 t - vo 6 q t (MPa) Cone resistance, 00 9, 0, or vo u o OCR q t u2 u-u S q t (MPa) Cone resistance, S t Zone: 5 Pore pressure parameter, B q Soil Behaviour Type: t Dr. 5 4 OCR e Friction ratio (%) 3. Sensitive fine grained 2. Organic material 3. Clay 4. Silty clay to clay Soil Behaviour Chart (Robertson et al, 986) 5. Clayey silt to silty clay 6. Sandy silt to clayey silt 7. Silty sand to sandy silt 8. Sand to silty sand 9. Sand 0. Gravelly sand to sand. Very stiff fine grained* 2. Sand to clayey sand* * Overconsolidated or cemented. BOUNDARIES OF SOIL BEHAVIOUR TYPE INDEX Soil behaviour type Zone Soil behaviour type Index I c I c <.3 7 Gravilly sand.3 < I c < Sands clean sand to silty sand 2.05 < I c < Sand mixturees silty sands to sandy silts 2.60 < I c < Silt mixtures clayey silts to silty clay 2.95 < I c < Clays I c < Organic soils - peat Q t Increasing OCR, age cementation Normally consolidated 4 Increasing sensitivity Increasing OCR, age u o vo q t u Q t I c logq log F t r Zone Soil behaviour type. Sensitive, fine grained 2. Organic soils-peats 3. Clays-clay to silty clay Zone Soil behaviour type Zone Soil behaviour type 4. Silt mixtures clayey silt to silty clay 7. Gravelly sand to sand 5. Sand mixtures; silty sand to sand silty 8. Very stiff sand to clayey sand 6. Sands; clean sands to silty sands 9. Very stiff fine grained 34

CPT Guide 5 th Edition. CPT Applications - Deep Foundations. Gregg Drilling & Testing, Inc. Dr. Peter K. Robertson Webinar # /2/2013

CPT Guide 5 th Edition. CPT Applications - Deep Foundations. Gregg Drilling & Testing, Inc. Dr. Peter K. Robertson Webinar # /2/2013 Gregg Drilling & Testing, Inc. Site Investigation Experts CPT Applications - Deep Foundations Dr. Peter K. Robertson Webinar #6 2013 CPT Guide 5 th Edition Robertson & Cabal (Robertson) 5 th Edition 2012