Two Piles Foundation Design Examples - R. Frank EUROCODE 7

FRANK  R. (2005). "Evaluation of Eurocode 7 – Two pile foundation design examples".  Proceedings ISSMGE/ERTC10 and GeoTechNet/WP2 Workshop on Evaluation of Eurocode 7 , Trinity College Dublin, 31 March-1 April 2005

Evaluation of Eurocode 7 – Two pile foundation design examples R. Frank  CERMES (ENPC-LCPC), Paris, France

ABSTRACT Two example of design of piles under compressive loadings are examined : one from ground test results and one from pile static load test results. The solutions which are compared follow Eurocode 7 - Part 1 (EN 1997-1, 2004), as well as a number of National codes. The reasons for discrepancy or for consistency are analysed. EXAMPLES At the occasion of the workshop for the evaluation of Eurocode 7, held in Dublin on 31st March and 1 st April 2005, held jointly by ERTC 10 of ISSMGE and by WorkPackage 2 of  the GeoTechNet network (funded by EC), 10 design examples have been prepared by Orr  (2004). Examples 3 and 4 deal with the design of pile foundations under compressive loadings from ground test results (Example 3) and from pile static load tests results (Example 4). They are the subject of the present report.

1.1  Pile design from ground test results (Example 3) The problem to be solved, as sent to the participants, is given in Figure 1. Pile Foundation designed from soil parameter values

Gk  = 1200kN Qk  = 200 kN

GWL

• 2.0m

Design situation

- Bored Bored pile for a building, building, 600mm 600mm diameter  diameter  - Groundwate Groundwaterr level level at depth depth of 2m below the ground ground surface

•

Soil conditions

- Sand: c'k  = 0, φ 'k  = 35o, γ  = 21kN/m3 SPT N = 25

•

- Charac Character terist istic ic perma permanen nentt load Gk  = 1200kN - Charac Characteri teristi sticc varia variable ble load load Qk  = 200kN - Weight Weight dens density ity of concr concrete ete = 24kN/m 24kN/m3

L=? Sand φ 'k  = 35o γ  = 21kN/m3

Actions

•

Require

- Pil ilee len lengt gthh, L

Figure Figu re 1. Data for example example of pile design from ground ground test results (Example (Example 3 of ERTC10-WP2 ERTC10-WP2 Workshop) 1 R. Frank. Evaluation of Eurocode 7 - Two pile foundation design examples  ERTC10 and WP2-GeoTechnet Workshop , Trinity College, Dublin, 31st March & 1st April 2005

FRANK  R. (2005). "Evaluation of Eurocode 7 – Two pile foundation design examples".  Proceedings ISSMGE/ERTC10 and GeoTechNet/WP2 Workshop on Evaluation of Eurocode 7 , Trinity College Dublin, 31 March-1 April 2005

1.2  Pile design from static load test results (Example 4) The problem to be solved, as sent to the participants, is given in Figure 2. Pile Load (MN) 0

1

2

3

4

5

6

7

Pile Foundation designed from pile load tests

Pile Load Test Results

0

20

Load Test 1

  m   m40    (    t   n   e 60   m   e    l    t    t 80   e    S

Load Test 2

100

120

•

•

Load (MN)

Settlement Pile 1(mm)

Settlement Pile 2 (mm)

0 0.5 1.0 1.5 2.0 3.0 4.0 5.0 5.6 6.0 6.4

0 2.1 3.6 5.0 6.2 10.0 18.0 40.0 63.0 100.0

0 1.2 2.1 2.9 4.1 7.0 14.0 26.0 40.0 56.0 80.0

Design Situation

-Pile foundation, driven piles, pile diameter D = 0.4m and length = 15m. The building supported by the piles does not have the capacity to transfer the load from weak to strong piles. The allowable  pile settlement is 10mm Pile Resistance

- 2 static pile load test results provided on driven piles of same diameter and length as design  piles. Piles were loaded beyond a settlement of 0.1D = 40mm to give the limit load.

•

Characteristic values of actions

•

Require number of piles needed to satisfy both ULS and SLS

-

Permanent vertical load Variable vertical load

Gk  = 20,000kN Qk  = 5,000kN

Figure 2. Data for example of pile design from static load test results (Example 4 of ERTC10-WP2 Workshop)

EUROCODE REQUIREMENTS The general requirements for ultimate limit states applicable to pile foundations (compressive or tensile resistance) are given in clauses 2.4.7.3.4.2(2)P for    Design Approach 1, 2.4.7.3.4.3(1)P for  DA 2 and 2.4.7.3.4.4(1)P for  DA 3. The corresponding recommended values of the partial factors γ  are given in Table A.3 for  the actions, Table A.4 for the   ground parameters and Tables A.6 through A.8 for the resistances for piles. Clause 7.6.2.2 applies to the ' Ultimate compressive resistance from static load tests'. Clause 7.6.2.3 applies to the ' Ultimate compressive resistance from ground test results', in   particular, clause 7.6.2.3(5)P and Equation 7.8 for the 'model pile' method, and clause 7.6.2.3(8) for the ' alternative' method (see Frank et al., 2004). Clause 7.6.4 deals with the vertical displacements of pile foundation (Serviceability of  supported structures). 2 R. Frank. Evaluation of Eurocode 7 - Two pile foundation design examples  ERTC10 and WP2-GeoTechnet Workshop , Trinity College, Dublin, 31st March & 1st April 2005

FRANK  R. (2005). "Evaluation of Eurocode 7 – Two pile foundation design examples".  Proceedings ISSMGE/ERTC10 and GeoTechNet/WP2 Workshop on Evaluation of Eurocode 7 , Trinity College Dublin, 31 March-1 April 2005

ANALYSIS OF THE SOLUTIONS 3.1 Example of pile design from ground test results For the design example of Figure 1, ten contributions were received from Europe (Denmark, France, Germany (x2), Ireland, Lithuania, Poland, Portugal, Romania and Switzerland). Four  contributions were received from Japan, among which one uses Eurocode 7. The solutions were derived using the following design approaches : - Eurocode 7-Part 1 together with its recommended values (Annex A) or national application of Eurocode 7 ; - other National standards usually based on limit state design (LSD); - traditional. For three cases using Eurocode 7, two solutions were given by the same author, either   because two calculation models were used (design from N values and from φ 'k  values), or    because the 'alternative' method of Eurocode 7 was used with and without recourse to a model factor (the latter are the reporter's solutions given in the Appendix to this report). Thus, 14 different (sets of) solutions are available for comparison. 3.1.1

Ultimate limit states (in permanent and transient situations)

Eleven solutions were received using Eurocode 7 – Part 1 (EN 1997-1, 2004) with its recommended values or values used at national level. The range of the results is from L = 10.0 m to L = 42.8 m (with 8 solutions between 10 m and 20 m). The Design Approach used (DA1, DA2 or DA3) does not play any significant role (see below). It is to be stressed that the calculation models used are mainly responsible for this very large range of values obtained. This can be illustrated by comparing the calculated values of   base resistance q b,cal and of shaft friction q s,cal, on the one hand, and the correlation factors ξ  and/or partial factors γ  subsequently applied to the calculated values, on the other hand. The following calculation models have been used - Tomlinson (1995) and Berezantzev et al. (1961) rules from φ 'k  values - Fleming et al. (1992) for shaft friction from base resistance q  b,cal and of shaft friction qs,cal, and Japanese experience for base resistance from N (SPT) - Romanian code STAS 2561/3-90 from φ 'k  values - Danish standards DS409/DS415 - Meyerhof (1976) rules with N (SPT) (2x) - correlation between N (SPT) and q c (CPT) and then DIN 1054 rules (x2) - correlation between N (SPT) and p l (PMT) and then French 'Fascicule 62-V' rules (see Frank, 1999) (x3) (Other solutions using a National standard including also the Tomlinson-Berezantzev model, the Russian SNIP 2.02.03-85 model and the Polish standard model). The ranges of calculated values, when stated, are the following : - base resistance q b,cal : from 1,32 MPa to 5 MPa - shaft friction q s,cal : from 25 kPa to 100 kPa when using a correlation with N (SPT), qc (SPT) or p l (PMT); β s = K stanδ vary from 0.20 to 0.49 when using φ 'k  values (together  with qs = β σ 'v). These ranges are indeed very large. To derive the design values of base and shaft resistances, the solutions usually apply one or several of the following factors : - correlation factor  ξ  = 1.4 (when assuming one soil profile, i.e. n = 1, and using equation (7.8) of EN 1997-1) - partial factors γ   b and γ  s (see equation (7.7) in EN 1997-1) - model factor  γ  Rd It is interesting to check for each solution, when feasible, the ratio of R d/R cal which is a 'summary' (composition) of the various factors applied on the calculated resistance. The comparison is interesting, because the factors on the actions are similar for all the solutions and design approaches (i.e. γ  G = 1.35 and γ  Q = 1.5, which leads to a mean load factor  3 R. Frank. Evaluation of Eurocode 7 - Two pile foundation design examples  ERTC10 and WP2-GeoTechnet Workshop , Trinity College, Dublin, 31st March & 1st April 2005

FRANK  R. (2005). "Evaluation of Eurocode 7 – Two pile foundation design examples".  Proceedings ISSMGE/ERTC10 and GeoTechNet/WP2 Workshop on Evaluation of Eurocode 7 , Trinity College Dublin, 31 March-1 April 2005

γ  F = 1.37) , except for DA1-Combination 2 (for which the partial factors on the actions are, in principle, near 1.0). The ratio R d/R cal varies from to 1.1 to 1.54, which is a relatively narrow range. No link between large values of the γ  and ξ factors and low (conservative) values of  calculated resistance, or vice versa, seems to exist… The minimum value of R d/R cal (1.1) is obtained, for instance, for DA2 (with γ  Rd = 1.0 and ξ  = 1.0); the maximum value (1.54) is obtained for DA2 and using ξ = 1.4 (as if the soil test results were obtained from one soil  profile). In some cases, for Eurocode 7 – Part 1, two or three of the design approaches have been compared (i.e. DA 1, DA2, and DA3). The following results are obtained : - DA 2 appears to be slightly more conservative than DA1 (but never more than 8 %), except in one case ; - for DA1, combination 1 is more conservative than combination 2 and rules the design (this comes directly from the fact that the overall partial factor on the actions for combination 1 is greater than the partial factor on the resistance for combination 2) ; - the most conservative approach is DA3 (note that there are only 2 answers). When other national LSD standards have been used, the range is from L = 10.2 m to 17.6 m (5 solutions from Europe and 3 from Japan). Only in 3 cases, it has been compared to a Eurocode 7 design and no real trend appears. Finally, only one solution with the traditional design (i.e. using a global factor of safety) has been proposed. The value obtained is L = 14.8 m, which is near the LSD solutions given in the same contribution. 3.1.2

Serviceability limit states

The check of serviceability limit states (SLS) was not explicitly asked for and no allowable settlement had been indicated in the example.  Nevertheless, the reporter indicated the solution according to the French code 'Fascicule 62-V', which requires to check SLS by means of a bearing capacity calculation, even if no settlement criteria are specified (see Appendix). 3.2 Pile design from static load test results For the design example of Figure 2, eleven contributions were received from Europe (Denmark, France, Germany (x2), Ireland (x2), Lithuania, Poland, Portugal, Romania, and Switzerland). Five contributions were received from Japan, among which one uses Eurocode 7. The solutions were derived using the following design approaches : - Eurocode 7-Part 1 together with its recommended values (Annex A for ULS) or  national application of Eurocode 7 (10 solutions); - other National standards, usually based on LSD (10 solutions). 3.2.1

Ultimate limit states (in permanent and transient situations)

The application of Eurocode 7 – Part 1 (EN 1997-1, 2004) with its recommended values (Annex A) or values used at national level, leads to : - 9 piles for DA1 for all solutions ; - 9 or 10 piles for DA2 (always 10 piles when the recommended values are used).   Note that DA3 is not applicable (the partial factors being applied to the ground strength  parameters, and not to the total, base or shaft resistance provided for by pile load tests). The very satisfactory consistency of these results comes from the fact that Eurocode 7 –  Part 1 gives quite precise rules for deriving the characteristic resistance R c,k  from measured resistances R c,m in pile static load tests (equation 7.2 together with recommended values of  Table A.9). For 2 pile static load tests (n = 2), the correlation factors for deriving R  c,k  from measured R c,m are ξ 1 = 1.3 (on R c,m,mean) and ξ 2 = 1.2 (on R c,m,min). These values seem to have   been used in most contributions. The following assumptions are also mentioned in the contributions : 4 R. Frank. Evaluation of Eurocode 7 - Two pile foundation design examples  ERTC10 and WP2-GeoTechnet Workshop , Trinity College, Dublin, 31st March & 1st April 2005

FRANK  R. (2005). "Evaluation of Eurocode 7 – Two pile foundation design examples".  Proceedings ISSMGE/ERTC10 and GeoTechNet/WP2 Workshop on Evaluation of Eurocode 7 , Trinity College Dublin, 31 March-1 April 2005

- R c,m values are read on the load-settlement curves for settlement s = 40 mm ; - no group effect is taken into account. The reporter's solution given in the Appendix to this report is an example of application of  Eurocode 7 – Part 1 following these lines. On the other hand, the following national codes have been used : - Danish standard DS415 - French code 'Fascicule 62-V' - Russian SNIP 2.02.03-85 - Polish standard - Romanian code STAS 2561/3-90 - Swisscode SC7 - RLSDB, SHB4, RSDS and TSPH Japanese codes The number required is also 9 or 10 piles for four of the six solutions from Europe. For the Japanese codes, the number is between 11 and 15 piles. 3.2.2

Serviceability limit states

Most of the solutions deal explicitly with the SLS checks. For the 10 mm allowable pile settlement criterion, the number of piles needed is also found equal to 9 or 10. When Eurocode 7 - Part 1 is used here again the solutions are quite consistent one with each other : - the serviceability load is G k + Qk  = 25 MN; - the two load-settlement curves are analysed to check that the settlement for the load carried  per pile is lower than 10 mm ; - the group effect is ignored, except in one solution (which leads to a larger number of piles) ; - usually, the two load-settlement curves are 'combined' in the same manner as for the limit loads for ULS, in order to obtain a characteristic load for the SLS criterion (s < 10 mm). Only four solutions from Europe mention the use of a National code for checking SLS. The results are also 9 or 10 piles. The four Japanese codes have specific provisions for SLS checks, which lead to the same number or a slightly greater number of piles than for ULS checks. CONCLUSION The solutions given for two pile design examples have been examined. The solutions come from 9 European countries and from Japan. Eurocode 7 – Part 1 (EN 1997-1, 2004) is used, as well as a number of National codes. For the ULS design example from ground test results the range of the results is very large. The discrepancy is attributed to the models used for calculating the base and shaft resistances from the test results, rather than to the ULS verification format and values of partial factors used. In the case of the design from pile static load test results, the solutions are remarkably consistent both for ULS and SLS verifications. This is attributed to the precise guidelines given by Eurocode 7 – Part 1 for ULS and to the straightforward analysis of the loadsettlement curves for SLS. REFERENCES Berezantzev V.G., Khristoforov, V.S. & Golubkov V.N. (1961). "Load-bearing capacity and deformation of piled foundation", Proc. 5th Int Conf Soil Mechanics and Found Engng , Paris, vol. 2, 11-15. EN 1997- 1 (2004).  Eurocode 7: Geotechnical design – Part 1 : General rules, EN 1997-1:2004(E), European Committee for Standardization (CEN), Brussels, November, 168 p. Fleming , W.G.K, Weltman, A..J., Randolph, M.F. & Elson, W.K. (1992).  Piling Engineering . Surrey University Press, London. 5 R. Frank. Evaluation of Eurocode 7 - Two pile foundation design examples  ERTC10 and WP2-GeoTechnet Workshop , Trinity College, Dublin, 31st March & 1st April 2005

FRANK  R. (2005). "Evaluation of Eurocode 7 – Two pile foundation design examples".  Proceedings ISSMGE/ERTC10 and GeoTechNet/WP2 Workshop on Evaluation of Eurocode 7 , Trinity College Dublin, 31 March-1 April 2005 Frank, Roger (1999). Calcul des fondations superficielles et profondes, Presses de l’École Nationale des Ponts et Chaussées, 141 p. Frank, R., Bauduin, C., Driscoll, R., Kavvadas, M., Krebs Ovesen, N., Orr, T., Schuppener, B. (2004).  Designer's guide to EN 1997-1 Eurocode 7: Geotechnical design - General rules , Thomas Telford, London, 216 p. Meyerhof G.G.(1976). "Bearing capacity and settlement of pile foundations", J Geot Engng Div, Am. Soc. Civil Engrs, 102, No. GT3, March. Orr, T. (2004). Design Examples for Eurocode 7 Workshop at Trinity College on 31 March and 1 April  2005, ISSMGE/ERTC10 and GeoTechNet/WP2 document, 23/12/2004, 7 p. Tomlinson M.J. (1995). Foundation design and construction, 6th ed., Longman, Harlow.

APPENDIX : SOLUTIONS OF THE REPORTER  Pile Foundation designed from soil parameter values  I. Introduction : calculation of compressive resistance from soil parameter values

The compressive resistance is determined below from the pressuremeter (PMT) rules used in France, after using a correlation between the PMT limit pressure pl and SPT blow count N, i.e. : for sands pl = N/20 (in MPa), thus for N = 25, p l = 1.25 MPa a) The unit base resistance is q b = k  p pl(at z= L), where k  p is taken equal to 1.1 (bored pile in medium dense sand B), thus: q b = 1.1x1.25 = 1.37 MPa The total base resistance is : R  b,cal = Π (B²/4)q p = 3.14x(0.36/4)x1.37 = 387 kN  b) The unit shaft friction at all depths z is : qs = 70 kPa (line Q2 for bored piles under bentonite mud or temporary casing, in medium dense sand B) The total shaft friction is (B = 0.6 m is the pile diameter) : R s,cal = Π Β ∫  qsdz = 1.885x70 L = 132 L (in kN and m) c) The total compressive resistance is : R c,cal = R  b,cal + R s,cal = 387 + 132 L ( in kN and m)  II. Eurocode 7 

Eurocode 7-Part 1 (EN 1997-1, 2004) requires checking ultimate and serviceability limit states. In this example, as no limitation is set on the settlement of the pile, nor any accidental action is to be taken into account, the following is restricted to ULS for persistent and transient design situations.  Design Approaches 1 and 2 for ULS in persistent and transient design situations

In the case of ultimate limit states (ULS) for persistent and transient design situations, Design Approaches 1 or 2 may be used. Design Approach 3 is not relevant to semi-empirical models like the PMT rules, as it means factoring ‘at the source’ the parameters of shearing resistance by γ  M > 1.0 (and not the base and shaft resistances themselves, i.e. γ   b = 1.0 and γ  s = 1.0); these models use, on the contrary, γ  M = 1.0, together with γ   b ≥1.0 and γ  s ≥ 1.0). The relevant recommended values are given in Tables A.3, A.4 and A.7 of  Annex A in EN 1997-1. For  Design Approaches 1 and 2 , the 'alternative' procedure of  clause 7.6.2.3(8) in EN 1997-1 has to be used, because we only have the soil parameter values, with no indication of the number of soil  profiles (the 'model pile' procedure of  clause 7.6.2.3(5) is not applicable). In the following two different assumptions will be made: A. qs and q b calculated above can be considered to be characteristic values, because they are derived from a cautious estimate of N (and pl) and some conservatism has been input in the calculation rules. Therefore, it is believed that the recommended values of  Annex A of EN 1997-1 are applicable, without recourse to a resistance model factor larger than 1.0, see Note  below clause 7.6.2.3(8) in EN 1997-1; B. qs and q b calculated above cannot be considered to be characteristic values, because they are derived from N (and pl) values which are not meant to be cautious and no real conservatism has been input in the calculation rules . Therefore, it is believed that the recommended values of  Annex A of EN 1997-1 are applicable, but with recourse to a resistance model factor larger  6 R. Frank. Evaluation of Eurocode 7 - Two pile foundation design examples  ERTC10 and WP2-GeoTechnet Workshop , Trinity College, Dublin, 31st March & 1st April 2005

FRANK  R. (2005). "Evaluation of Eurocode 7 – Two pile foundation design examples".  Proceedings ISSMGE/ERTC10 and GeoTechNet/WP2 Workshop on Evaluation of Eurocode 7 , Trinity College Dublin, 31 March-1 April 2005 than 1.0 (see Note below clause 7.6.2.3(8) in EN 1997-1): for the purpose of this example the value γ  Rd = 1.25 is selected. Thus, for the purpose of using EN 1997-1, the two following sets of calculations will be  performed (kN and m are used): Assumption A. R c,k  = R c,cal = R  b,k  + R s,k  = 387 + 132 L, and Assumption B. R c,k  = R c,cal/γ  Rd = R  b,k  + R s,k  = (387 +132 L)/1.25 = 309.6 + 105.6 L Assumption A : R c,k  = R c,cal Design Approach 1 Combination 1: According to clause 2.4.7.3.4.2 (2) P , sets A1, M1 and R1 of Tables A.3, A.4 and A.7 are used. The design load is : Fc,d = G.Gk  + Q. Qk  = 1.35 x 1200 + 1.5 x 200 = 1920 kN The design resistance of the pile is : R c,d = R  b,k / b + R s,k / s = 387/1.25 + 132 L/1.0 = 309.6 + 132 L The condition Fc,d ≤ R c,d leads to L ≥ 12.2 m . Combination 2:

Sets A2, M1 and R4 are used. The design load is : Fc,d = G.Gk  + Q.1,5 Qk  = 1.0 x 1200 + 1.3 x 200 = 1460 kN The design resistance of the pile is : R c,d = R  b,k / b + R s,k / s = 387/1.6 + 132 L/1.3 = 241.9 + 101.5 L The condition Fc,d ≤ R c,d leads to L ≥ 12.0 m. In conclusion, for Design Approach 1, the result is L ≥ 12.2 m (the larger of the two lengths, given  by Combination 1). Design Approach 2 Only one combination is relevant, with sets A1, M1 and R2 (see clause 2.4.7.3.4.3 (1) P and Tables  A.3, A.4 and A.7 ). The design load is : Fc,d = G.Gk  + Q.1,5 Qk  = 1.35 x 1200 + 1.5 x 200 = 1920 kN The design resistance of the pile is : R c,d = R  b,k / b + R s,k / s = 387/1.1 + 132 L/1.1 = 351.8 + 120 L The condition Fc,d ≤ R c,d leads to L ≥ 13.1 m. Design Approach 3 : not relevant to PMT model Assumption B : R c,k  = R c,cal/γ  Rd Design Approach 1 Combination 1: According to clause 2.4.7.3.4.2 (2) P , sets A1, M1 and R1 of Tables A.3, A.4 and A.7 are used. The design load is : Fc,d = G.Gk  + Q. Qk  = 1.35 x 1200 + 1.5 x 200 = 1920 kN The design resistance of the pile is : R c,d = R  b,k / b + R s,k / s = 309.6/1.25 + 105.6 L/1.0 = 247.7 + 105.6 L The condition Fc,d ≤ R c,d leads to L ≥ 15.8 m. Combination 2:

Sets A2, M1 and R4 are used. The design load is : Fc,d = G.Gk  + Q.1,5 Qk  = 1.0 x 1200 + 1.3 x 200 = 1460 kN The design resistance of the pile is : R c,d = R  b,k / b + R s,k / s = 309.6/1.6 + 105.6 L/1.3 = 193.5 + 81.2 L The condition Fc,d ≤ R c,d leads to L ≥ 15.6 m. In conclusion, for Design Approach 1, the result is L ≥ 15.8 m (the larger of the two lengths, given  by Combination 1). Design Approach 2 Only one combination is relevant, with sets A1, M1 and R2 (see clause 2.4.7.3.4.3 (1) P and Tables  A.3, A.4 and A.7 ). The design load is : Fc,d = G.Gk  + Q.1,5 Qk  = 1.35 x 1200 + 1.5 x 200 = 1920 kN 7 R. Frank. Evaluation of Eurocode 7 - Two pile foundation design examples  ERTC10 and WP2-GeoTechnet Workshop , Trinity College, Dublin, 31st March & 1st April 2005

FRANK  R. (2005). "Evaluation of Eurocode 7 – Two pile foundation design examples".  Proceedings ISSMGE/ERTC10 and GeoTechNet/WP2 Workshop on Evaluation of Eurocode 7 , Trinity College Dublin, 31 March-1 April 2005 The design resistance of the pile is : R c,d = R  b,k / b + R s,k / s = 309.6/1.1 + 105.6 L/1.1 = 281.5 + 96.0 L The condition Fc,d ≤ R c,d leads to L ≥ 17.1 m. Design Approach 3 : not relevant to PMT model Conclusion for Assumptions A and B : when using Eurocode 7-1 (EN 1997-1) for ULS in  persistent or transient design situations, Design Approach 2 is the most conservative, for this example (with dominant shaft friction), as it leads respectively to L ≥ 13.1 m (assumption A) and to L ≥ 17.1 m (assumption B). With regard to Design Approach 1, combination 1 is more conservative than combination 2.  III. Present French practice

In present French practice both ULS and SLS are derived from a condition on the bearing capacity of  the pile, if no limit on the settlements of the structure is specified. ULS in persistent and transient design situations

Present French practice is very near DA-2 of EN 1997-1, with the 'alternative' method of  clause 7.6.2.3(8) in EN 1997-1, and uses a direct determination of q sk  and q bk  from soil test result (like Assumption A above). R c,k  = R c,cal = R  b,k  + R s,k  = 387 + 132 L The load factors are the same as Set 1 of  Table A.3 (in Annex A of EN 1997-1). The resistance factor for ULS in persistent or transient design situations is applied on the total resistance (R  b,k  + R s,k ) and its value is t = 1.40. The design load is : Fc,d = G.Gk  + Q.1,5 Qk  = 1.35 x 1200 + 1.5 x 200 = 1920 kN The design resistance of the pile is : R c,d = R c,k  / t = (387 + 132 L)/ 1.4 = 276.4 + 94.3 L The condition Fc,d ≤ R c,d leads to L ≥ 17.4 m. The result is very near the results for DA-2 and assumption B with EN 1997-1. This is not surprising since the value of the factor applied to the calculated resistance is 1.4 in French practice and is 1.25 x 1.1 = 1.375 for DA-2-Assumption B (including the value of the model factor chosen equal to 1.25). The high value of the resistance factor (1.4) in French practice assumes that reasonably 'true' values of q b,cal and qs,cal are used as characteristic values.  SLS- Serviceability Limit States

The SLS load is determined through the creep load Qc which is linked to the bearing resistance through the following correlation for bored piles: Qc = 0.5 x R  b,cal + 0.7 R s,cal = 193 + 92.4 L The condition is Fc,d (SLS) ≤ Qd (SLS) = Qc/γ  SLS with γ  SLS = 1.1 for characteristic (rare) combinations and 1.4 for quasi-permanent combinations. Characteristic combinations Fc,d(rare) = Gk  + Qk  = 1200 + 200 = 1400 kN Qd(SLS) = 193/1.1 + 92.4 L/1.1 = 175.4 + 84 L The condition Fc,d ≤ Qd yields L ≥ 14.6 m. Quasi-permanent combinations Fc,d(rare) = Gk  = 1200 kN Qd(SLS) = 193/1.4 + 92.4 L/1.4 = 137.9 + 66.0 L The condition Fc,d ≤ Qd yields L ≥ 16.1 m. Conclusion Both ULS and SLS checks are fulfilled with L ≥ 17.4 m. Pile Foundation designed from pile load tests  I. Using EN 1997-1 and recommended values in Annex A

Determination of characteristic compressive resistance : The measured ultimate compressive resistances are (from readings at settlement s = 0.1D = 40 mm) : 8 R. Frank. Evaluation of Eurocode 7 - Two pile foundation design examples  ERTC10 and WP2-GeoTechnet Workshop , Trinity College, Dublin, 31st March & 1st April 2005

FRANK  R. (2005). "Evaluation of Eurocode 7 – Two pile foundation design examples".  Proceedings ISSMGE/ERTC10 and GeoTechNet/WP2 Workshop on Evaluation of Eurocode 7 , Trinity College Dublin, 31 March-1 April 2005 R c,m1 = 5.0 MN , and R c,m2 = 5.6 MN Clause 7.6.2.2(8)P is applied. Equation (7.2) reads : R c;k

( R  )   ( R  ) = Min c;m mean ; c;m min  ξ 1 ξ 2  

with (R c,m)mean = 5.3 MN and (R c,m)min = 5.0 MN. From Table A.9, for n = 2 pile load tests : ξ  1 = 1.30 and ξ  2 = 1.20 ; thus,  5.3 5.0  R c;k = Min  ;  = Min {4.08 ; 4.17 } = 4.08 MN 1.30 1.20  ULS in persistent and transient situations – Design Approach 1 Combination 2 is usually leading the geotechnical design. Sets A2, M1 and R4 are used (clause 2.4.7.3.4.2 (2) P and Tables A.3, A.4 and A.6 ). The design load is : Fc,d = G.Gk  + Q.1,5 Qk  = 1.0 x 20 + 1.3 x 5 = 26.5 MN The design resistance for one pile is : R c,d = R c,k  / t= 4.08 / 1.3 = 3.14 MN. Thus, according to DA1-Comb 2, 26.5/3.14 = 9 piles are needed. Combination 1: Sets A1, M1 and R1 are used. The design load is : Fc,d = G.Gk  + Q. Qk  = 1.35 x 20 + 1.5 x 5 = 34.5 MN The design resistance for one pile is : R c,d = R c,k  / t = 4.08/ 1.0 = 4.08 According to DA1-Comb 1, 34.5/4.08 = 9 piles are also needed. ULS in persistent and transient situations – Design Approach 2 Only one combination is relevant, with sets A1, M1 and R2 (see clause 2.4.7.3.4.3 (1) P and Tables  A.3, A.4 and A.6 ). The design load is : Fc,d = G.Gk  + Q.1,5 Qk  = 1.35 x 20 + 1.5 x 5 = 34.5 MN The design resistance for one pile is : R c,d = R c,k  / t = 4.08/ 1.1 = 3.71 MN The number of piles is 34.5/3.71 = 10 piles. SLS – Serviceability check  The characteristic load Gk  + Qk  = 25 MN is relevant for the characteristic combination, which is the most severe one (used for irreversible limit states, see EN 1990). When examining the two measured load-settlement curves, the settlement is 10 mm for measured loads Fm equal to 3.0 MN and 3.5 MN (approximately), respectively. The characteristic value for  10 mm can be assessed in the same manner as the characteristic bearing resistance, i.e. F m,k  = 2.5 MN approximately. Hence, 10 piles must be used in order to keep the pile settlement lower or equal to 10 mm. Conclusion According to ULS + SLS : 10 piles are needed, whatever the Design Approach used for ULS requirements.  II. Present French practice

ULS in persistent and transient situations For ULS under persistent and transient combinations, the calculations are identical to DA2, except for  the values of ξ 'and γ  t . ξ ' The characteristic value is R c,k  = R c,min (R c,min/R c,max) , with ξ ' = 0.55 for two pile load tests. 0.55 Hence, R c,k  = 5.0 (5.0/5.6) = 4.70 MN The design value is : R c,d = R c,k  / t with t = 1.4 for persistent and transient combinations. Thus, R c,d = 4.70/1.4 = 3.36 MN On the other hand, Fc,d = G.Gk  + Q.1,5 Qk  = 1.35 x 20 + 1.5 x 5 = 34.5 MN Thus 10 piles are needed. SLS – Serviceability check  9 R. Frank. Evaluation of Eurocode 7 - Two pile foundation design examples  ERTC10 and WP2-GeoTechnet Workshop , Trinity College, Dublin, 31st March & 1st April 2005

FRANK  R. (2005). "Evaluation of Eurocode 7 – Two pile foundation design examples".  Proceedings ISSMGE/ERTC10 and GeoTechNet/WP2 Workshop on Evaluation of Eurocode 7 , Trinity College Dublin, 31 March-1 April 2005 In present French practice, SLS are checked by comparing the creep load Qc to the applied load, if there is no limiting value for the vertical displacement of the structure (i.e. no displacement calculation is explicitly required). For driven piles Qc = R c/1.5, i.e. Qc = R c,k  /1.5. Thus, Qc = 4.70/1.5 = 3.13 MN. The applied load per   pile is Gk  + Qk  = 25 MN/10 = 2.5 MN . It can be concluded that SLS requirements are satisfied. Conclusion : According to ULS + SLS : 10 piles are needed. This result is the same as for EN 1997-1.

10 R. Frank. Evaluation of Eurocode 7 - Two pile foundation design examples  ERTC10 and WP2-GeoTechnet Workshop , Trinity College, Dublin, 31st March & 1st April 2005