Bell A

Berezantzev VG

Bustamante M

John R. Jeffrey

Jonathan A. Knappett

Jonathan D. Ball

Karlis Caucis

Lauder K

Meyerhof GG

Michael J. Brown

Mitsch MP

Qian-qing Zhang

Shi-min Zhang

van Impe WF

Wei Cui

Xiao Zheng

Jeffrey, John R.

Brown, Michael J.

Knappett, Jonathan A.

Ball, Jonathan D.

Caucis, Karlis

Cui, Wei

Zheng, Xiao Dong

Zhang, Shi Min

Zhang, Qian Qing

Discovery Research Portal

                                                              University of DundeeDiscussionJeffrey, John R.; Brown, Michael J.; Knappett, Jonathan A.; Ball, Jonathan D.; Caucis, Karlis;Cui, Wei; Zheng, Xiao Dong; Zhang, Shi Min; Zhang, Qian QingPublished in:Proceedings of the Institution of Civil Engineers: Geotechnical EngineeringDOI:10.1680/jgeen.16.00216Publication date:2017Document VersionPublisher's PDF, also known as Version of recordLink to publication in Discovery Research PortalCitation for published version (APA):Jeffrey, J. R., Brown, M. J., Knappett, J. A., Ball, J. D., Caucis, K., Cui, W., ... Zhang, Q. Q. (2017). Discussion:CHD pile performance: Part I – Physical modelling. Proceedings of the Institution of Civil Engineers:Geotechnical Engineering, 170(2), 186-187. [1600216]. https://doi.org/10.1680/jgeen.16.00216General rightsCopyright and moral rights for the publications made accessible in Discovery Research Portal are retained by the authors and/or othercopyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated withthese rights. • Users may download and print one copy of any publication from Discovery Research Portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain. • You may freely distribute the URL identifying the publication in the public portal.Take down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediatelyand investigate your claim.Download date: 05. Apr. 2019Discussion: CHD pile performance:part I – physical modellingJohn R. Jeffrey MEng, PhDGeotechnical Engineer, Technip UK Limited, Westhill, UKMichael J. Brown BEng, PhDReader, School of Science and Engineering, University of Dundee,Dundee, UKJonathan A. Knappett MA, MEng, PhDReader, School of Science & Engineering, University of Dundee,Dundee, UKJonathan D. Ball BSc, CGeol, FGSChief Geotechnical Engineer, Roger Bullivant Ltd, Burton Upon Trent, UKKarlis Caucis MEngGraduate Engineer, Arup, South Queensferry, UKWei Cui BEngAssociate Professor, Research Center of Geotechnical and StructuralEngineering, Shandong University, Jinan, P. R. ChinaXiao Zheng BEngMaster Student, Research Center of Geotechnical and StructuralEngineering, Shandong University, Jinan, P. R. ChinaShi-min Zhang MPhilProfessor, Department of Civil Engineering, Zhejiang University CityCollege, Hangzhou, P. R. ChinaQian-qing Zhang MPhil, PhDAssociate Professor, Research Center of Geotechnical and StructuralEngineering, Shandong University, Jinan, China; State Key Laboratory forGeoMechanics and Deep Underground Engineering, China University ofMining and Technology, Xuzhou, P. R. ChinaContribution by W. Cui, X. Zheng, S. Zhangand Q. ZhangIn Equation 1 of Jeffrey et al. (2016), the full flight diameterDf (see Figure 2) was used to calculate the base area, and theeffective diameter De (see Figure 2) was selected to determinethe shaft area of Equation 2. However, in the numerical analy-sis of the performance of a continuous helical displacement(CHD) pile (Knappett et al., 2016), the full flight diameter Dfwas used to calculate the shaft area, and the core diameter Dcwas selected to determine the base area. Could the authorsprovide the reason why different diameters were chosen todetermine the base and shaft area in the two papers?The failure of the pile side may occur along the interfacebetween pile and soil or in the soils around pile. Therefore, thefull flight diameter Df may be used to determine the shaftarea. As to the calculation of the base capacity, the full flightdiameter Df may also be selected to calculate the base area.In the paper of Jeffrey et al. (2016), the calculated result tendsto under-predict the measured pile capacity by an average of25% at higher relative densities. This may due to the fact thatthe full flight diameter Df and the effective diameter De areused to calculate the base and the shaft area, respectively.When the full flight diameter Df is used to calculate the basearea and the shaft area, the calculated shaft and bearingcapacity may be well consistent with the measured result.Authors’ replyThe authors would like to thank Professors Cui and Zhangand colleagues for their interest in this work on understandingthe performance of continuous helical displacement piles(CHD), a type of cast-in-situ auger displacement pile devel-oped in the UK. Raising this discussion has indicated that itwould be beneficial to clarify the points raised, so that anyapparent confusion in the original paper can be clarified andto confirm that the approach adopted in Knappett et al.(2016) is consistent with the findings and recommendations inJeffrey et al. (2016).The authors would like to clarify that in Section 4 of Jeffreyet al. (2016) the text initially refers to the approach used in prac-tice for the design of CHD piles prior to undertaking thisresearch, where it has been normal to calculate the pile shaftcontribution to the pile’s resistance using an effective diameter(De), which has typically been taken as 0·75Df (where Df is theouter flight diameter for an auger displacement pile). Thisapproach was recognised as conservative when compared withother approaches adopted in Europe – for example, van Impe(2004) recommends that De =Df and Bustamante and Gianeselli(1993) propose adopting a value of De = 0·9Df (see also Section1 in the original paper). These differences in approach providedone of the original motivations for undertaking the researchdescribed in Jeffrey et al. (2016) and Knappett et al. (2016).In Sections 4 and 5 of Jeffrey et al. (2016) it is recommendedthat the contribution of the pile base (Equation 1) is calculatedusing an area based upon the pile core diameter (Dc) ratherthan Df. This approach was recommended based upon theresults shown in Figure 13, where a back-calculated basebearing capacity factor (Nq) showed much better correlationwith the work of Berezantzev et al. (1961) when core diameter(Dc) rather than flight diameter (Df ) was used (Figure 13(b) inthe original paper). This is consistent with the shape of theCHD pile, which tapers from Dc below the lowest flight toa point at the base of the pile, explaining why this gives abetter correlation for this pile type. This is consistent withEquation 5 in Knappett et al. (2016).When considering the shaft contribution, the full flight diam-eter Df was used, initially based upon the observations of the1Geotechnical EngineeringDiscussionJeffrey, Brown, Knappett et al.Proceedings of the Institution of Civil Engineershttp://dx.doi.org/10.1680/jgeen.16.00216Paper 1600216Received 30/11/2016 Accepted 06/01/2017ICE Publishing: All rights reservedDownloaded by [ UNIVERSITY OF DUNDEE] on [16/02/17]. Copyright © ICE Publishing, all rights reserved.exhumed model piles where the sand was tightly packedbetween the flights of the pile and the exhumed pile resembleda straight shafted pile of diameter Df with a sand–sand shearsurface (Figure 7). Second, when comparing the CHD pileswith jacked piles of diameters equivalent to the core or flightdiameter of the CHD it was found that the results for a jackedpile with base diameter Df were far closer in capacity thanthose for Dc (Figure 6).The determination of the earth pressure coefficient, K, inFigure 14 was based upon the use of Df rather than Dc, as thisrepresents the diameter along the shaft of both CHD andjacked piles and is consistent with the approaches of Bell(2010), Meyerhof (1976) and Mitsch and Clemence (1985).This is also consistent with Equation 3 in Knappett et al.(2016). Therefore, the under-prediction noted is not as a resultof the approach adopted with respect to diameter selectionfor the various contributions to pile capacity, but is morelikely to be due to the method proposed for determinationof the earth pressure coefficient (Equation 2, Figure 14). Basedupon the results shown in Figure 14 it is clear that thereis greater scatter in the data with increasing peak frictionangle (or relative density). Based upon this scatter and thelarge peak friction angles experienced at small scale andlow stress levels in the laboratory (Lauder and Brown, 2014)that are unlikely to be encountered in the field (at full scale)it was decided to adopt the Mitsch and Clemence (1985)approach (Figure 14, Equation 4). This approach representsa lower bound to K at higher friction angles (laboratoryscale), but is a better representation of displacement pilebehaviour at lower friction angles (field scale) and is thus amore appropriate recommendation for adoption in designpractice.REFERENCESBell A (2010) Foundation solutions for the urban regeneration ofGlasgow city centre. In Proceedings of the DFI and EFFC 11thInternational Conference:Geotechnical Challenges in UrbanRegeneration, London, UK. EMAP Networks, Peterborough, UK,pp. 120–129.Berezantzev VG, Khristoforov VS and Golubkov VN (1961) Load bearingcapacity and deformation of piled foundations. Proceedings of the5th International Conference on Soil Mechanics and FoundationsEngineering, Paris, France, pp. 11–15.Bustamante M and Gianeselli L (1993) Design of auger displacementpiles from in situ tests. In Proceedings of the 2nd InternationalGeotechnical Seminar on Deep Foundations on Bored and AugerPiles, BAP II, Ghent, Belgium (van Impe WF (ed.)). Balkema,Rotterdam, the Netherlands, pp. 21–34.Jeffrey JR, Brown MJ, Knappett JA, Ball JD and Caucis K (2016) CHD pileperformance: part I – physical modelling. Proceedings of theInstitution of Civil Engineers – Geotechnical Engineering 169(5):421–435, http://dx.doi.org/10.1680/jgeen.15.00131.Knappett JA, Caucis K, Brown MJ, Jeffrey JR and Ball JD (2016)CHD pile performance: part II – numerical modelling.Proceedings of the Institution of Civil Engineers – GeotechnicalEngineering 169(5): 436–454, http://dx.doi.org/10.1680/jgeen.15.00132.Lauder K and Brown MJ (2014) Scaling effects in the 1g modelling ofoffshore pipeline ploughs. In Proceedings of the 8th InternationalConference on Physical Modelling in Geotechnics, Perth, WesternAustralia (Gaudin C and White D (eds)). CRC Press, Boca Raton,FL, USA, pp. 377–383.Mitsch MP and Clemence SP (1985) The uplift capacity of helix anchorsin sand. Uplift Behavior of Anchor Foundations in Soil, Proceedingsof a Session held in conjunction with the ASCE Convention,Detroit, MI, USA, pp. 26–47.Meyerhof GG (1976) Bearing capacity and settlement of pilefoundations. ASCE Journal of the Geotechnical EngineeringDivision 102(GT3): 197–228.van Impe WF (2004) The Overview of Almost Two Decades of Full ScaleResearch on Screw Piles. Laboratory of Soil Mechanics, GhentUniversity, Ghent, Belgium.2Geotechnical Engineering DiscussionJeffrey, Brown, Knappett et al.Downloaded by [ UNIVERSITY OF DUNDEE] on [16/02/17]. Copyright © ICE Publishing, all rights reserved.

Discussion:CHD pile performance: Part I – Physical modelling

                                                                    University of DundeeDiscussionJeffrey, John R.; Brown, Michael J.; Knappett, Jonathan A.; Ball, Jonathan D.; Caucis, Karlis;Cui, WeiPublished in:Proceedings of the Institution of Civil Engineers: Geotechnical EngineeringDOI:10.1680/jgeen.16.00216Publication date:2017Document VersionPublisher's PDF, also known as Version of recordLink to publication in Discovery Research PortalCitation for published version (APA):Jeffrey, J. R., Brown, M. J., Knappett, J. A., Ball, J. D., Caucis, K., Cui, W., Zheng, X. D., Zhang, S. M., & Zhang,Q. Q. (2017). Discussion: CHD pile performance: Part I – Physical modelling. Proceedings of the Institution ofCivil Engineers: Geotechnical Engineering, 170(2), 186-187. Article 1600216.https://doi.org/10.1680/jgeen.16.00216General rightsCopyright and moral rights for the publications made accessible in Discovery Research Portal are retained by the authors and/or othercopyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated withthese rights.Take down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediatelyand investigate your claim.Download date: 30. Oct. 2025Discussion: CHD pile performance:part I – physical modellingJohn R. Jeffrey MEng, PhDGeotechnical Engineer, Technip UK Limited, Westhill, UKMichael J. Brown BEng, PhDReader, School of Science and Engineering, University of Dundee,Dundee, UKJonathan A. Knappett MA, MEng, PhDReader, School of Science & Engineering, University of Dundee,Dundee, UKJonathan D. Ball BSc, CGeol, FGSChief Geotechnical Engineer, Roger Bullivant Ltd, Burton Upon Trent, UKKarlis Caucis MEngGraduate Engineer, Arup, South Queensferry, UKWei Cui BEngAssociate Professor, Research Center of Geotechnical and StructuralEngineering, Shandong University, Jinan, P. R. ChinaXiao Zheng BEngMaster Student, Research Center of Geotechnical and StructuralEngineering, Shandong University, Jinan, P. R. ChinaShi-min Zhang MPhilProfessor, Department of Civil Engineering, Zhejiang University CityCollege, Hangzhou, P. R. ChinaQian-qing Zhang MPhil, PhDAssociate Professor, Research Center of Geotechnical and StructuralEngineering, Shandong University, Jinan, China; State Key Laboratory forGeoMechanics and Deep Underground Engineering, China University ofMining and Technology, Xuzhou, P. R. ChinaContribution by W. Cui, X. Zheng, S. Zhangand Q. ZhangIn Equation 1 of Jeffrey et al. (2016), the full flight diameterDf (see Figure 2) was used to calculate the base area, and theeffective diameter De (see Figure 2) was selected to determinethe shaft area of Equation 2. However, in the numerical analy-sis of the performance of a continuous helical displacement(CHD) pile (Knappett et al., 2016), the full flight diameter Dfwas used to calculate the shaft area, and the core diameter Dcwas selected to determine the base area. Could the authorsprovide the reason why different diameters were chosen todetermine the base and shaft area in the two papers?The failure of the pile side may occur along the interfacebetween pile and soil or in the soils around pile. Therefore, thefull flight diameter Df may be used to determine the shaftarea. As to the calculation of the base capacity, the full flightdiameter Df may also be selected to calculate the base area.In the paper of Jeffrey et al. (2016), the calculated result tendsto under-predict the measured pile capacity by an average of25% at higher relative densities. This may due to the fact thatthe full flight diameter Df and the effective diameter De areused to calculate the base and the shaft area, respectively.When the full flight diameter Df is used to calculate the basearea and the shaft area, the calculated shaft and bearingcapacity may be well consistent with the measured result.Authors’ replyThe authors would like to thank Professors Cui and Zhangand colleagues for their interest in this work on understandingthe performance of continuous helical displacement piles(CHD), a type of cast-in-situ auger displacement pile devel-oped in the UK. Raising this discussion has indicated that itwould be beneficial to clarify the points raised, so that anyapparent confusion in the original paper can be clarified andto confirm that the approach adopted in Knappett et al.(2016) is consistent with the findings and recommendations inJeffrey et al. (2016).The authors would like to clarify that in Section 4 of Jeffreyet al. (2016) the text initially refers to the approach used in prac-tice for the design of CHD piles prior to undertaking thisresearch, where it has been normal to calculate the pile shaftcontribution to the pile’s resistance using an effective diameter(De), which has typically been taken as 0·75Df (where Df is theouter flight diameter for an auger displacement pile). Thisapproach was recognised as conservative when compared withother approaches adopted in Europe – for example, van Impe(2004) recommends that De =Df and Bustamante and Gianeselli(1993) propose adopting a value of De = 0·9Df (see also Section1 in the original paper). These differences in approach providedone of the original motivations for undertaking the researchdescribed in Jeffrey et al. (2016) and Knappett et al. (2016).In Sections 4 and 5 of Jeffrey et al. (2016) it is recommendedthat the contribution of the pile base (Equation 1) is calculatedusing an area based upon the pile core diameter (Dc) ratherthan Df. This approach was recommended based upon theresults shown in Figure 13, where a back-calculated basebearing capacity factor (Nq) showed much better correlationwith the work of Berezantzev et al. (1961) when core diameter(Dc) rather than flight diameter (Df ) was used (Figure 13(b) inthe original paper). This is consistent with the shape of theCHD pile, which tapers from Dc below the lowest flight toa point at the base of the pile, explaining why this gives abetter correlation for this pile type. This is consistent withEquation 5 in Knappett et al. (2016).When considering the shaft contribution, the full flight diam-eter Df was used, initially based upon the observations of the1Geotechnical EngineeringDiscussionJeffrey, Brown, Knappett et al.Proceedings of the Institution of Civil Engineershttp://dx.doi.org/10.1680/jgeen.16.00216Paper 1600216Received 30/11/2016 Accepted 06/01/2017ICE Publishing: All rights reservedDownloaded by [ UNIVERSITY OF DUNDEE] on [16/02/17]. Copyright © ICE Publishing, all rights reserved.exhumed model piles where the sand was tightly packedbetween the flights of the pile and the exhumed pile resembleda straight shafted pile of diameter Df with a sand–sand shearsurface (Figure 7). Second, when comparing the CHD pileswith jacked piles of diameters equivalent to the core or flightdiameter of the CHD it was found that the results for a jackedpile with base diameter Df were far closer in capacity thanthose for Dc (Figure 6).The determination of the earth pressure coefficient, K, inFigure 14 was based upon the use of Df rather than Dc, as thisrepresents the diameter along the shaft of both CHD andjacked piles and is consistent with the approaches of Bell(2010), Meyerhof (1976) and Mitsch and Clemence (1985).This is also consistent with Equation 3 in Knappett et al.(2016). Therefore, the under-prediction noted is not as a resultof the approach adopted with respect to diameter selectionfor the various contributions to pile capacity, but is morelikely to be due to the method proposed for determinationof the earth pressure coefficient (Equation 2, Figure 14). Basedupon the results shown in Figure 14 it is clear that thereis greater scatter in the data with increasing peak frictionangle (or relative density). Based upon this scatter and thelarge peak friction angles experienced at small scale andlow stress levels in the laboratory (Lauder and Brown, 2014)that are unlikely to be encountered in the field (at full scale)it was decided to adopt the Mitsch and Clemence (1985)approach (Figure 14, Equation 4). This approach representsa lower bound to K at higher friction angles (laboratoryscale), but is a better representation of displacement pilebehaviour at lower friction angles (field scale) and is thus amore appropriate recommendation for adoption in designpractice.REFERENCESBell A (2010) Foundation solutions for the urban regeneration ofGlasgow city centre. In Proceedings of the DFI and EFFC 11thInternational Conference:Geotechnical Challenges in UrbanRegeneration, London, UK. EMAP Networks, Peterborough, UK,pp. 120–129.Berezantzev VG, Khristoforov VS and Golubkov VN (1961) Load bearingcapacity and deformation of piled foundations. Proceedings of the5th International Conference on Soil Mechanics and FoundationsEngineering, Paris, France, pp. 11–15.Bustamante M and Gianeselli L (1993) Design of auger displacementpiles from in situ tests. In Proceedings of the 2nd InternationalGeotechnical Seminar on Deep Foundations on Bored and AugerPiles, BAP II, Ghent, Belgium (van Impe WF (ed.)). Balkema,Rotterdam, the Netherlands, pp. 21–34.Jeffrey JR, Brown MJ, Knappett JA, Ball JD and Caucis K (2016) CHD pileperformance: part I – physical modelling. Proceedings of theInstitution of Civil Engineers – Geotechnical Engineering 169(5):421–435, http://dx.doi.org/10.1680/jgeen.15.00131.Knappett JA, Caucis K, Brown MJ, Jeffrey JR and Ball JD (2016)CHD pile performance: part II – numerical modelling.Proceedings of the Institution of Civil Engineers – GeotechnicalEngineering 169(5): 436–454, http://dx.doi.org/10.1680/jgeen.15.00132.Lauder K and Brown MJ (2014) Scaling effects in the 1g modelling ofoffshore pipeline ploughs. In Proceedings of the 8th InternationalConference on Physical Modelling in Geotechnics, Perth, WesternAustralia (Gaudin C and White D (eds)). CRC Press, Boca Raton,FL, USA, pp. 377–383.Mitsch MP and Clemence SP (1985) The uplift capacity of helix anchorsin sand. Uplift Behavior of Anchor Foundations in Soil, Proceedingsof a Session held in conjunction with the ASCE Convention,Detroit, MI, USA, pp. 26–47.Meyerhof GG (1976) Bearing capacity and settlement of pilefoundations. ASCE Journal of the Geotechnical EngineeringDivision 102(GT3): 197–228.van Impe WF (2004) The Overview of Almost Two Decades of Full ScaleResearch on Screw Piles. Laboratory of Soil Mechanics, GhentUniversity, Ghent, Belgium.2Geotechnical Engineering DiscussionJeffrey, Brown, Knappett et al.Downloaded by [ UNIVERSITY OF DUNDEE] on [16/02/17]. Copyright © ICE Publishing, all rights reserved.

English

                                                                    University of DundeeDiscussionJeffrey, John R.; Brown, Michael J.; Knappett, Jonathan A.; Ball, Jonathan D.; Caucis, Karlis;Cui, WeiPublished in:Proceedings of the Institution of Civil Engineers: Geotechnical EngineeringDOI:10.1680/jgeen.16.00216Publication date:2017Document VersionPublisher's PDF, also known as Version of recordLink to publication in Discovery Research PortalCitation for published version (APA):Jeffrey, J. R., Brown, M. J., Knappett, J. A., Ball, J. D., Caucis, K., Cui, W., Zheng, X. D., Zhang, S. M., & Zhang,Q. Q. (2017). Discussion: CHD pile performance: Part I – Physical modelling. Proceedings of the Institution ofCivil Engineers: Geotechnical Engineering, 170(2), 186-187. [1600216]. https://doi.org/10.1680/jgeen.16.00216General rightsCopyright and moral rights for the publications made accessible in Discovery Research Portal are retained by the authors and/or othercopyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated withthese rights. • Users may download and print one copy of any publication from Discovery Research Portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain. • You may freely distribute the URL identifying the publication in the public portal.Take down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediatelyand investigate your claim.Download date: 30. Jul. 2023Discussion: CHD pile performance:part I – physical modellingJohn R. Jeffrey MEng, PhDGeotechnical Engineer, Technip UK Limited, Westhill, UKMichael J. Brown BEng, PhDReader, School of Science and Engineering, University of Dundee,Dundee, UKJonathan A. Knappett MA, MEng, PhDReader, School of Science & Engineering, University of Dundee,Dundee, UKJonathan D. Ball BSc, CGeol, FGSChief Geotechnical Engineer, Roger Bullivant Ltd, Burton Upon Trent, UKKarlis Caucis MEngGraduate Engineer, Arup, South Queensferry, UKWei Cui BEngAssociate Professor, Research Center of Geotechnical and StructuralEngineering, Shandong University, Jinan, P. R. ChinaXiao Zheng BEngMaster Student, Research Center of Geotechnical and StructuralEngineering, Shandong University, Jinan, P. R. ChinaShi-min Zhang MPhilProfessor, Department of Civil Engineering, Zhejiang University CityCollege, Hangzhou, P. R. ChinaQian-qing Zhang MPhil, PhDAssociate Professor, Research Center of Geotechnical and StructuralEngineering, Shandong University, Jinan, China; State Key Laboratory forGeoMechanics and Deep Underground Engineering, China University ofMining and Technology, Xuzhou, P. R. ChinaContribution by W. Cui, X. Zheng, S. Zhangand Q. ZhangIn Equation 1 of Jeffrey et al. (2016), the full flight diameterDf (see Figure 2) was used to calculate the base area, and theeffective diameter De (see Figure 2) was selected to determinethe shaft area of Equation 2. However, in the numerical analy-sis of the performance of a continuous helical displacement(CHD) pile (Knappett et al., 2016), the full flight diameter Dfwas used to calculate the shaft area, and the core diameter Dcwas selected to determine the base area. Could the authorsprovide the reason why different diameters were chosen todetermine the base and shaft area in the two papers?The failure of the pile side may occur along the interfacebetween pile and soil or in the soils around pile. Therefore, thefull flight diameter Df may be used to determine the shaftarea. As to the calculation of the base capacity, the full flightdiameter Df may also be selected to calculate the base area.In the paper of Jeffrey et al. (2016), the calculated result tendsto under-predict the measured pile capacity by an average of25% at higher relative densities. This may due to the fact thatthe full flight diameter Df and the effective diameter De areused to calculate the base and the shaft area, respectively.When the full flight diameter Df is used to calculate the basearea and the shaft area, the calculated shaft and bearingcapacity may be well consistent with the measured result.Authors’ replyThe authors would like to thank Professors Cui and Zhangand colleagues for their interest in this work on understandingthe performance of continuous helical displacement piles(CHD), a type of cast-in-situ auger displacement pile devel-oped in the UK. Raising this discussion has indicated that itwould be beneficial to clarify the points raised, so that anyapparent confusion in the original paper can be clarified andto confirm that the approach adopted in Knappett et al.(2016) is consistent with the findings and recommendations inJeffrey et al. (2016).The authors would like to clarify that in Section 4 of Jeffreyet al. (2016) the text initially refers to the approach used in prac-tice for the design of CHD piles prior to undertaking thisresearch, where it has been normal to calculate the pile shaftcontribution to the pile’s resistance using an effective diameter(De), which has typically been taken as 0·75Df (where Df is theouter flight diameter for an auger displacement pile). Thisapproach was recognised as conservative when compared withother approaches adopted in Europe – for example, van Impe(2004) recommends that De =Df and Bustamante and Gianeselli(1993) propose adopting a value of De = 0·9Df (see also Section1 in the original paper). These differences in approach providedone of the original motivations for undertaking the researchdescribed in Jeffrey et al. (2016) and Knappett et al. (2016).In Sections 4 and 5 of Jeffrey et al. (2016) it is recommendedthat the contribution of the pile base (Equation 1) is calculatedusing an area based upon the pile core diameter (Dc) ratherthan Df. This approach was recommended based upon theresults shown in Figure 13, where a back-calculated basebearing capacity factor (Nq) showed much better correlationwith the work of Berezantzev et al. (1961) when core diameter(Dc) rather than flight diameter (Df ) was used (Figure 13(b) inthe original paper). This is consistent with the shape of theCHD pile, which tapers from Dc below the lowest flight toa point at the base of the pile, explaining why this gives abetter correlation for this pile type. This is consistent withEquation 5 in Knappett et al. (2016).When considering the shaft contribution, the full flight diam-eter Df was used, initially based upon the observations of the1Geotechnical EngineeringDiscussionJeffrey, Brown, Knappett et al.Proceedings of the Institution of Civil Engineershttp://dx.doi.org/10.1680/jgeen.16.00216Paper 1600216Received 30/11/2016 Accepted 06/01/2017ICE Publishing: All rights reservedDownloaded by [ UNIVERSITY OF DUNDEE] on [16/02/17]. Copyright © ICE Publishing, all rights reserved.exhumed model piles where the sand was tightly packedbetween the flights of the pile and the exhumed pile resembleda straight shafted pile of diameter Df with a sand–sand shearsurface (Figure 7). Second, when comparing the CHD pileswith jacked piles of diameters equivalent to the core or flightdiameter of the CHD it was found that the results for a jackedpile with base diameter Df were far closer in capacity thanthose for Dc (Figure 6).The determination of the earth pressure coefficient, K, inFigure 14 was based upon the use of Df rather than Dc, as thisrepresents the diameter along the shaft of both CHD andjacked piles and is consistent with the approaches of Bell(2010), Meyerhof (1976) and Mitsch and Clemence (1985).This is also consistent with Equation 3 in Knappett et al.(2016). Therefore, the under-prediction noted is not as a resultof the approach adopted with respect to diameter selectionfor the various contributions to pile capacity, but is morelikely to be due to the method proposed for determinationof the earth pressure coefficient (Equation 2, Figure 14). Basedupon the results shown in Figure 14 it is clear that thereis greater scatter in the data with increasing peak frictionangle (or relative density). Based upon this scatter and thelarge peak friction angles experienced at small scale andlow stress levels in the laboratory (Lauder and Brown, 2014)that are unlikely to be encountered in the field (at full scale)it was decided to adopt the Mitsch and Clemence (1985)approach (Figure 14, Equation 4). This approach representsa lower bound to K at higher friction angles (laboratoryscale), but is a better representation of displacement pilebehaviour at lower friction angles (field scale) and is thus amore appropriate recommendation for adoption in designpractice.REFERENCESBell A (2010) Foundation solutions for the urban regeneration ofGlasgow city centre. In Proceedings of the DFI and EFFC 11thInternational Conference:Geotechnical Challenges in UrbanRegeneration, London, UK. EMAP Networks, Peterborough, UK,pp. 120–129.Berezantzev VG, Khristoforov VS and Golubkov VN (1961) Load bearingcapacity and deformation of piled foundations. Proceedings of the5th International Conference on Soil Mechanics and FoundationsEngineering, Paris, France, pp. 11–15.Bustamante M and Gianeselli L (1993) Design of auger displacementpiles from in situ tests. In Proceedings of the 2nd InternationalGeotechnical Seminar on Deep Foundations on Bored and AugerPiles, BAP II, Ghent, Belgium (van Impe WF (ed.)). Balkema,Rotterdam, the Netherlands, pp. 21–34.Jeffrey JR, Brown MJ, Knappett JA, Ball JD and Caucis K (2016) CHD pileperformance: part I – physical modelling. Proceedings of theInstitution of Civil Engineers – Geotechnical Engineering 169(5):421–435, http://dx.doi.org/10.1680/jgeen.15.00131.Knappett JA, Caucis K, Brown MJ, Jeffrey JR and Ball JD (2016)CHD pile performance: part II – numerical modelling.Proceedings of the Institution of Civil Engineers – GeotechnicalEngineering 169(5): 436–454, http://dx.doi.org/10.1680/jgeen.15.00132.Lauder K and Brown MJ (2014) Scaling effects in the 1g modelling ofoffshore pipeline ploughs. In Proceedings of the 8th InternationalConference on Physical Modelling in Geotechnics, Perth, WesternAustralia (Gaudin C and White D (eds)). CRC Press, Boca Raton,FL, USA, pp. 377–383.Mitsch MP and Clemence SP (1985) The uplift capacity of helix anchorsin sand. Uplift Behavior of Anchor Foundations in Soil, Proceedingsof a Session held in conjunction with the ASCE Convention,Detroit, MI, USA, pp. 26–47.Meyerhof GG (1976) Bearing capacity and settlement of pilefoundations. ASCE Journal of the Geotechnical EngineeringDivision 102(GT3): 197–228.van Impe WF (2004) The Overview of Almost Two Decades of Full ScaleResearch on Screw Piles. Laboratory of Soil Mechanics, GhentUniversity, Ghent, Belgium.2Geotechnical Engineering DiscussionJeffrey, Brown, Knappett et al.Downloaded by [ UNIVERSITY OF DUNDEE] on [16/02/17]. Copyright © ICE Publishing, all rights reserved.

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Proceedings of the Institution of Civil Engineers - Geotechnical Engineering

Discussion: CHD pile performance: part I – physical modelling

http://discovery.dundee.ac.uk/ws/files/16936706/CHD_DiscussiononCHDpilepapersinICEGEjgeen.16.00216.pdf

Discussion:CHD pile performance: Part I – Physical modelling

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