{"id":493,"date":"2025-03-11T04:50:26","date_gmt":"2025-03-11T04:50:26","guid":{"rendered":"https:\/\/libraryresources.nse.org.ng\/fundamentalsoffoundationengineering\/chapter\/6-15-ultimate-geotechnical-strength-of-piles-subjected-to-axial-tensile-loads\/"},"modified":"2026-03-16T14:10:01","modified_gmt":"2026-03-16T14:10:01","slug":"6-15-ultimate-geotechnical-strength-of-piles-subjected-to-axial-tensile-loads","status":"publish","type":"chapter","link":"https:\/\/libraryresources.nse.org.ng\/fundamentalsoffoundationengineering\/chapter\/6-15-ultimate-geotechnical-strength-of-piles-subjected-to-axial-tensile-loads\/","title":{"raw":"6.15 Ultimate geotechnical strength of piles subjected to axial tensile loads","rendered":"6.15 Ultimate geotechnical strength of piles subjected to axial tensile loads"},"content":{"raw":"In the simplest yet most common case of a pile without an enlarged base, its resistance to uplift axial loads is directly estimated as the sum of the skin friction resistance and the dead weight of the pile:\n\n<strong>(6.74)\u00a0<\/strong>[latex]{Q_{f,t}} = {Q_{sf,t}} + {W_p}[\/latex]\n\nIf the <em>\u03b1<\/em>-method or the ICP method is used to determine the pile\u2019s tensile collapse load <em>Q<sub>f,t<\/sub><\/em>, the skin friction resistance developing during uplift of piles installed in soft fine-grained soils is assumed to be equal to the friction resistance in compression, and is estimated with the formulas presented in <a href=\"https:\/\/libraryresources.nse.org.ng\/fundamentalsoffoundationengineering\/chapter\/6-9-ultimate-geotechnical-strength-of-piles-subjected-to-axial-compressive-load-under-undrained-conditions-%ce%b1-method\/\">Chapter 6.9<\/a> (<em>\u03b1<\/em>-method) and Section 6.12.7 (ICP method for piles in fine-grained soils).\n\n[caption id=\"attachment_492\" align=\"aligncenter\" width=\"400\"]<img class=\"wp-image-492 size-full\" src=\"https:\/\/libraryresources.nse.org.ng\/wp-content\/uploads\/sites\/9\/2025\/03\/6.43-hr-e1743553325866.png\" alt=\"The figure on the left shows a pile subjected to compression. The pile's length decreases and its radius increases. Vertical and horizontal stresses on a soil element near the pile shaft are denoted as \u03c3'z0 and \u03c3'hf. The figure on the right shows a pile subjected to uplift. The pile's length increases and its radius decreases. Vertical and horizontal stresses on a soil element near the pile shaft are denoted as \u03c3'z0 and \u03c3'hf. The horizontal stress in the case of uplift is lower than the horizontal stress in the case of compression.\" width=\"400\" height=\"348\"> Figure 6.43. Reduced interface normal stress during pile uplift.[\/caption]\n\nUnder drained conditions, the skin friction resistance to pile uplift <em>f<sub>sf,t<\/sub><\/em> is reduced due to the Poisson effect (<a href=\"https:\/\/oercollective.caul.edu.au\/app\/uploads\/sites\/143\/2025\/03\/6.43-hr.png\">Figure 6.43<\/a>), which results in lower confining stress at the side of the shaft and thus reduced friction compared to <em>f<sub>sf<\/sub><\/em> (Reese <em>et al., <\/em>2006, AS 2159). In that case, the skin friction stress developing at the interface to resist tensile an axial load may be computed as:\n\n<strong>(6.75)\u00a0<\/strong>[latex]{f_{sf,t}} = {\\psi _t}{f_{sf}}[\/latex]\n\nwhere the reduction factor <em>\u03c8<sub>t\u00a0<\/sub><\/em>is given by the formula (Reese\u00a0<em>et al.,<\/em> 2006):\n\n<strong>(6.76a)<\/strong> [latex]{\\psi _t} = 1 - 0.2\\log \\left( {\\dfrac{{100D}}{L}} \\right)\\left[ {1 - 8n + 25{n^2}} \\right][\/latex]\n\n<strong>(6.76b)<\/strong> [latex]{\\rm where\\:}n = {v_p}\\tan \\left[ {{\\varphi _i}\\left( {\\dfrac{L}{D}} \\right)\\left( {0.385\\dfrac{{{E_{s,aver}}}}{{{E_p}}}} \\right)} \\right][\/latex]\n\nwhere <em>\u03c6<\/em><sub>i<\/sub> is the interface friction angle; <em>E<sub>s,aver <\/sub><\/em>is the average Young modulus of the soil along the pile; <em>E<sub>p<\/sub><\/em> is the Young modulus of the pile\u2019s material; <em>v<sub>p <\/sub><\/em>is the Poisson ratio of the pile\u2019s material; <em>L <\/em>is the pile\u2019s length; <em>D <\/em>is the pile\u2019s diameter.\n\n\u03a4he reduction factor <em>\u03c8<\/em><sub>t<\/sub> estimated from Eq. 6.76 ranges from 0.75 to 0.85 for typical piles, and can be conservatively taken equal to 0.75. The above formulas were originally proposed for coarse-grained soils, but can be used conservatively for fine-grained soils under long-term uplift loading.\n\nThe ICP-05 method for piles in coarse-grained soils, presented in Section 6.12.5 can also be used to estimate the skin friction resistance <em>f<sub>sf,t<\/sub><\/em> developing in piles subjected to axial tensile loads. For <em>closed-end<\/em> cylindrical piles Eq. 6.35 that provides the skin friction stress becomes:\n\n<strong>(6.77)<\/strong> [latex]{f_{sf,t}} = \\left( {0.8{{\\sigma '}_{he}} + \\Delta {{\\sigma '}_{rd}}} \\right)\\tan {\\varphi _{i,cs}}[\/latex]\n\ni.e., the normal stress acting at the soil-pile interface after equilibration is reduced by 20%, which is comparable with Eq. 6.76 and the recommended <em>\u03c8<\/em><sub>t<\/sub> values.\n\nFor <em>open-ended<\/em> pipe piles Jardine <em>et al.<\/em> (2005) recommend further reducing <em>f<sub>sf,t<\/sub><\/em> by another 10%, as:\n\n<strong>(6.78)\u00a0<\/strong>[latex]{f_{sf,t}} = 0.9\\left( {0.8{{\\sigma '}_{he}} + \\Delta {{\\sigma '}_{rd}}} \\right)\\tan {\\varphi _{i,cs}}[\/latex]","rendered":"<p>In the simplest yet most common case of a pile without an enlarged base, its resistance to uplift axial loads is directly estimated as the sum of the skin friction resistance and the dead weight of the pile:<\/p>\n<p><strong>(6.74)\u00a0<\/strong>[latex]{Q_{f,t}} = {Q_{sf,t}} + {W_p}[\/latex]<\/p>\n<p>If the <em>\u03b1<\/em>-method or the ICP method is used to determine the pile\u2019s tensile collapse load <em>Q<sub>f,t<\/sub><\/em>, the skin friction resistance developing during uplift of piles installed in soft fine-grained soils is assumed to be equal to the friction resistance in compression, and is estimated with the formulas presented in <a href=\"https:\/\/libraryresources.nse.org.ng\/fundamentalsoffoundationengineering\/chapter\/6-9-ultimate-geotechnical-strength-of-piles-subjected-to-axial-compressive-load-under-undrained-conditions-%ce%b1-method\/\">Chapter 6.9<\/a> (<em>\u03b1<\/em>-method) and Section 6.12.7 (ICP method for piles in fine-grained soils).<\/p>\n<figure id=\"attachment_492\" aria-describedby=\"caption-attachment-492\" style=\"width: 400px\" class=\"wp-caption aligncenter\"><img decoding=\"async\" class=\"wp-image-492 size-full\" src=\"https:\/\/libraryresources.nse.org.ng\/wp-content\/uploads\/sites\/9\/2025\/03\/6.43-hr-e1743553325866.png\" alt=\"The figure on the left shows a pile subjected to compression. The pile's length decreases and its radius increases. Vertical and horizontal stresses on a soil element near the pile shaft are denoted as \u03c3'z0 and \u03c3'hf. The figure on the right shows a pile subjected to uplift. The pile's length increases and its radius decreases. Vertical and horizontal stresses on a soil element near the pile shaft are denoted as \u03c3'z0 and \u03c3'hf. The horizontal stress in the case of uplift is lower than the horizontal stress in the case of compression.\" width=\"400\" height=\"348\" srcset=\"https:\/\/libraryresources.nse.org.ng\/fundamentalsoffoundationengineering\/wp-content\/uploads\/sites\/9\/2025\/03\/6.43-hr-e1743553325866.png 400w, https:\/\/libraryresources.nse.org.ng\/fundamentalsoffoundationengineering\/wp-content\/uploads\/sites\/9\/2025\/03\/6.43-hr-e1743553325866-300x261.png 300w, https:\/\/libraryresources.nse.org.ng\/fundamentalsoffoundationengineering\/wp-content\/uploads\/sites\/9\/2025\/03\/6.43-hr-e1743553325866-65x57.png 65w, https:\/\/libraryresources.nse.org.ng\/fundamentalsoffoundationengineering\/wp-content\/uploads\/sites\/9\/2025\/03\/6.43-hr-e1743553325866-225x196.png 225w, https:\/\/libraryresources.nse.org.ng\/fundamentalsoffoundationengineering\/wp-content\/uploads\/sites\/9\/2025\/03\/6.43-hr-e1743553325866-350x305.png 350w\" sizes=\"(max-width: 400px) 100vw, 400px\" \/><figcaption id=\"caption-attachment-492\" class=\"wp-caption-text\">Figure 6.43. Reduced interface normal stress during pile uplift.<\/figcaption><\/figure>\n<p>Under drained conditions, the skin friction resistance to pile uplift <em>f<sub>sf,t<\/sub><\/em> is reduced due to the Poisson effect (<a href=\"https:\/\/oercollective.caul.edu.au\/app\/uploads\/sites\/143\/2025\/03\/6.43-hr.png\">Figure 6.43<\/a>), which results in lower confining stress at the side of the shaft and thus reduced friction compared to <em>f<sub>sf<\/sub><\/em> (Reese <em>et al., <\/em>2006, AS 2159). In that case, the skin friction stress developing at the interface to resist tensile an axial load may be computed as:<\/p>\n<p><strong>(6.75)\u00a0<\/strong>[latex]{f_{sf,t}} = {\\psi _t}{f_{sf}}[\/latex]<\/p>\n<p>where the reduction factor <em>\u03c8<sub>t\u00a0<\/sub><\/em>is given by the formula (Reese\u00a0<em>et al.,<\/em> 2006):<\/p>\n<p><strong>(6.76a)<\/strong> [latex]{\\psi _t} = 1 - 0.2\\log \\left( {\\dfrac{{100D}}{L}} \\right)\\left[ {1 - 8n + 25{n^2}} \\right][\/latex]<\/p>\n<p><strong>(6.76b)<\/strong> [latex]{\\rm where\\:}n = {v_p}\\tan \\left[ {{\\varphi _i}\\left( {\\dfrac{L}{D}} \\right)\\left( {0.385\\dfrac{{{E_{s,aver}}}}{{{E_p}}}} \\right)} \\right][\/latex]<\/p>\n<p>where <em>\u03c6<\/em><sub>i<\/sub> is the interface friction angle; <em>E<sub>s,aver <\/sub><\/em>is the average Young modulus of the soil along the pile; <em>E<sub>p<\/sub><\/em> is the Young modulus of the pile\u2019s material; <em>v<sub>p <\/sub><\/em>is the Poisson ratio of the pile\u2019s material; <em>L <\/em>is the pile\u2019s length; <em>D <\/em>is the pile\u2019s diameter.<\/p>\n<p>\u03a4he reduction factor <em>\u03c8<\/em><sub>t<\/sub> estimated from Eq. 6.76 ranges from 0.75 to 0.85 for typical piles, and can be conservatively taken equal to 0.75. The above formulas were originally proposed for coarse-grained soils, but can be used conservatively for fine-grained soils under long-term uplift loading.<\/p>\n<p>The ICP-05 method for piles in coarse-grained soils, presented in Section 6.12.5 can also be used to estimate the skin friction resistance <em>f<sub>sf,t<\/sub><\/em> developing in piles subjected to axial tensile loads. For <em>closed-end<\/em> cylindrical piles Eq. 6.35 that provides the skin friction stress becomes:<\/p>\n<p><strong>(6.77)<\/strong> [latex]{f_{sf,t}} = \\left( {0.8{{\\sigma '}_{he}} + \\Delta {{\\sigma '}_{rd}}} \\right)\\tan {\\varphi _{i,cs}}[\/latex]<\/p>\n<p>i.e., the normal stress acting at the soil-pile interface after equilibration is reduced by 20%, which is comparable with Eq. 6.76 and the recommended <em>\u03c8<\/em><sub>t<\/sub> values.<\/p>\n<p>For <em>open-ended<\/em> pipe piles Jardine <em>et al.<\/em> (2005) recommend further reducing <em>f<sub>sf,t<\/sub><\/em> by another 10%, as:<\/p>\n<p><strong>(6.78)\u00a0<\/strong>[latex]{f_{sf,t}} = 0.9\\left( {0.8{{\\sigma '}_{he}} + \\Delta {{\\sigma '}_{rd}}} \\right)\\tan {\\varphi _{i,cs}}[\/latex]<\/p>\n","protected":false},"author":1,"menu_order":15,"template":"","meta":{"pb_show_title":"","pb_short_title":"6.15 Ultimate geotechnical strength of piles subjected to axial tensile loads","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"class_list":["post-493","chapter","type-chapter","status-publish","hentry"],"part":421,"_links":{"self":[{"href":"https:\/\/libraryresources.nse.org.ng\/fundamentalsoffoundationengineering\/wp-json\/pressbooks\/v2\/chapters\/493","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/libraryresources.nse.org.ng\/fundamentalsoffoundationengineering\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/libraryresources.nse.org.ng\/fundamentalsoffoundationengineering\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/libraryresources.nse.org.ng\/fundamentalsoffoundationengineering\/wp-json\/wp\/v2\/users\/1"}],"version-history":[{"count":1,"href":"https:\/\/libraryresources.nse.org.ng\/fundamentalsoffoundationengineering\/wp-json\/pressbooks\/v2\/chapters\/493\/revisions"}],"predecessor-version":[{"id":494,"href":"https:\/\/libraryresources.nse.org.ng\/fundamentalsoffoundationengineering\/wp-json\/pressbooks\/v2\/chapters\/493\/revisions\/494"}],"part":[{"href":"https:\/\/libraryresources.nse.org.ng\/fundamentalsoffoundationengineering\/wp-json\/pressbooks\/v2\/parts\/421"}],"metadata":[{"href":"https:\/\/libraryresources.nse.org.ng\/fundamentalsoffoundationengineering\/wp-json\/pressbooks\/v2\/chapters\/493\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/libraryresources.nse.org.ng\/fundamentalsoffoundationengineering\/wp-json\/wp\/v2\/media?parent=493"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/libraryresources.nse.org.ng\/fundamentalsoffoundationengineering\/wp-json\/pressbooks\/v2\/chapter-type?post=493"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/libraryresources.nse.org.ng\/fundamentalsoffoundationengineering\/wp-json\/wp\/v2\/contributor?post=493"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/libraryresources.nse.org.ng\/fundamentalsoffoundationengineering\/wp-json\/wp\/v2\/license?post=493"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}