{"id":464,"date":"2025-03-07T04:19:46","date_gmt":"2025-03-07T04:19:46","guid":{"rendered":"https:\/\/libraryresources.nse.org.ng\/fundamentalsoffoundationengineering\/chapter\/6-11-ultimate-geotechnical-strength-of-piles-subjected-to-axial-compressive-load-from-spt-test-results\/"},"modified":"2026-03-16T14:08:06","modified_gmt":"2026-03-16T14:08:06","slug":"6-11-ultimate-geotechnical-strength-of-piles-subjected-to-axial-compressive-load-from-spt-test-results","status":"publish","type":"chapter","link":"https:\/\/libraryresources.nse.org.ng\/fundamentalsoffoundationengineering\/chapter\/6-11-ultimate-geotechnical-strength-of-piles-subjected-to-axial-compressive-load-from-spt-test-results\/","title":{"raw":"6.11 Ultimate geotechnical strength of piles subjected to axial compressive load from SPT test results","rendered":"6.11 Ultimate geotechnical strength of piles subjected to axial compressive load from SPT test results"},"content":{"raw":"Given difficulties (and costs) associated with obtaining undisturbed coarse-grained soil samples for laboratory testing, as discussed in <a href=\"https:\/\/libraryresources.nse.org.ng\/fundamentalsoffoundationengineering\/chapter\/5-7-bearing-capacity-from-standard-penetration-test-spt-results\/\">Chapter 5.7<\/a>, the collapse load of piles in homogeneous coarse-grained soil can be estimated directly from SPT test results, skipping the intermediate step of interpreting characteristic values of soil parameters. While such methods are rather obsolete, and have been replaced by CPT-based methods described in the next section, the relevant formulas are provided below for completeness.\n\nThe skin friction resistance (units: force) is correlated to the average SPT value along the length of the pile<em> N<sub>60,shaft<\/sub><\/em> as:\n\n<strong>(6.21)<\/strong> [latex]{Q_{sf}} = \\left( {0.01{\\rm{ \\:to \\:}}0.02} \\right){p_a}{N_{60,shaft}}\\pi DL[\/latex]\n\nThe upper bound of Eq. 6.21 corresponds to driven piles, while the lower bound corresponds to drilled shafts.\n\nIn addition, the end-bearing resistance (units: force) is correlated to the average SPT value at the vicinity of the pile toe <em>N<sub>60,toe<\/sub><\/em>, considering blow counts about 6 to 10<em>D<\/em> above and 2 to 4<em>D<\/em> below the pile toe (Meyerhoff, 1976).\n\n<strong>(6.22)<\/strong> [latex]{Q_b} = 0.4{p_a}{N_{60,toe}}\\dfrac{L}{D}\\left( {\\pi {{\\left( {\\dfrac{D}{2}} \\right)}^2}} \\right) \\le 4{p_a}{N_{60,toe}}\\left( {\\pi {{\\left( {\\dfrac{D}{2}} \\right)}^2}} \\right)[\/latex]\n\nIn the above Eqs. 6.21-6.22 <em>L<\/em> is the length of the pile, <em>D<\/em> is its diameter and <em>p<sub>a<\/sub><\/em> is the atmospheric pressure, equal to <em>p<sub>a <\/sub><\/em>= 100 kPa. The pile length over which <em>N<sub>60<\/sub><\/em> are averaged to find <em>N<sub>60,toe<\/sub><\/em> (from 6<em>D<\/em> to 10<em>D<\/em> above to 2<em>D<\/em> to 4<em>D<\/em> below the pile toe) covers the extent of the possible failure surface developing below the pile toe (<a href=\"https:\/\/oercollective.caul.edu.au\/app\/uploads\/sites\/143\/2025\/03\/6.22-extent-of-possible-failure-surface.png\">Figure 6.22<\/a>).\n\n[caption id=\"attachment_463\" align=\"aligncenter\" width=\"295\"]<img class=\"wp-image-463 size-full\" src=\"https:\/\/libraryresources.nse.org.ng\/wp-content\/uploads\/sites\/9\/2025\/03\/6.22-extent-of-possible-failure-surface.png\" alt=\"Schematic showing a pile of diameter D loaded with an axial compressive force at its head. A generalised failure surface develops underneath the pile's toe. This failure surface extends 2 to 4D below the pile toe, and 6 to 10D above the pile toe.\" width=\"295\" height=\"274\"> Figure 6.22. Geometry of a possible failure surface developing below the pile toe.[\/caption]","rendered":"<p>Given difficulties (and costs) associated with obtaining undisturbed coarse-grained soil samples for laboratory testing, as discussed in <a href=\"https:\/\/libraryresources.nse.org.ng\/fundamentalsoffoundationengineering\/chapter\/5-7-bearing-capacity-from-standard-penetration-test-spt-results\/\">Chapter 5.7<\/a>, the collapse load of piles in homogeneous coarse-grained soil can be estimated directly from SPT test results, skipping the intermediate step of interpreting characteristic values of soil parameters. While such methods are rather obsolete, and have been replaced by CPT-based methods described in the next section, the relevant formulas are provided below for completeness.<\/p>\n<p>The skin friction resistance (units: force) is correlated to the average SPT value along the length of the pile<em> N<sub>60,shaft<\/sub><\/em> as:<\/p>\n<p><strong>(6.21)<\/strong> [latex]{Q_{sf}} = \\left( {0.01{\\rm{ \\:to \\:}}0.02} \\right){p_a}{N_{60,shaft}}\\pi DL[\/latex]<\/p>\n<p>The upper bound of Eq. 6.21 corresponds to driven piles, while the lower bound corresponds to drilled shafts.<\/p>\n<p>In addition, the end-bearing resistance (units: force) is correlated to the average SPT value at the vicinity of the pile toe <em>N<sub>60,toe<\/sub><\/em>, considering blow counts about 6 to 10<em>D<\/em> above and 2 to 4<em>D<\/em> below the pile toe (Meyerhoff, 1976).<\/p>\n<p><strong>(6.22)<\/strong> [latex]{Q_b} = 0.4{p_a}{N_{60,toe}}\\dfrac{L}{D}\\left( {\\pi {{\\left( {\\dfrac{D}{2}} \\right)}^2}} \\right) \\le 4{p_a}{N_{60,toe}}\\left( {\\pi {{\\left( {\\dfrac{D}{2}} \\right)}^2}} \\right)[\/latex]<\/p>\n<p>In the above Eqs. 6.21-6.22 <em>L<\/em> is the length of the pile, <em>D<\/em> is its diameter and <em>p<sub>a<\/sub><\/em> is the atmospheric pressure, equal to <em>p<sub>a <\/sub><\/em>= 100 kPa. The pile length over which <em>N<sub>60<\/sub><\/em> are averaged to find <em>N<sub>60,toe<\/sub><\/em> (from 6<em>D<\/em> to 10<em>D<\/em> above to 2<em>D<\/em> to 4<em>D<\/em> below the pile toe) covers the extent of the possible failure surface developing below the pile toe (<a href=\"https:\/\/oercollective.caul.edu.au\/app\/uploads\/sites\/143\/2025\/03\/6.22-extent-of-possible-failure-surface.png\">Figure 6.22<\/a>).<\/p>\n<figure id=\"attachment_463\" aria-describedby=\"caption-attachment-463\" style=\"width: 295px\" class=\"wp-caption aligncenter\"><img decoding=\"async\" class=\"wp-image-463 size-full\" src=\"https:\/\/libraryresources.nse.org.ng\/wp-content\/uploads\/sites\/9\/2025\/03\/6.22-extent-of-possible-failure-surface.png\" alt=\"Schematic showing a pile of diameter D loaded with an axial compressive force at its head. A generalised failure surface develops underneath the pile's toe. This failure surface extends 2 to 4D below the pile toe, and 6 to 10D above the pile toe.\" width=\"295\" height=\"274\" srcset=\"https:\/\/libraryresources.nse.org.ng\/fundamentalsoffoundationengineering\/wp-content\/uploads\/sites\/9\/2025\/03\/6.22-extent-of-possible-failure-surface.png 295w, https:\/\/libraryresources.nse.org.ng\/fundamentalsoffoundationengineering\/wp-content\/uploads\/sites\/9\/2025\/03\/6.22-extent-of-possible-failure-surface-65x60.png 65w, https:\/\/libraryresources.nse.org.ng\/fundamentalsoffoundationengineering\/wp-content\/uploads\/sites\/9\/2025\/03\/6.22-extent-of-possible-failure-surface-225x209.png 225w\" sizes=\"(max-width: 295px) 100vw, 295px\" \/><figcaption id=\"caption-attachment-463\" class=\"wp-caption-text\">Figure 6.22. Geometry of a possible failure surface developing below the pile toe.<\/figcaption><\/figure>\n","protected":false},"author":1,"menu_order":11,"template":"","meta":{"pb_show_title":"","pb_short_title":"6.11 Ultimate geotechnical strength of piles subjected to axial compressive load from SPT test results","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"class_list":["post-464","chapter","type-chapter","status-publish","hentry"],"part":421,"_links":{"self":[{"href":"https:\/\/libraryresources.nse.org.ng\/fundamentalsoffoundationengineering\/wp-json\/pressbooks\/v2\/chapters\/464","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\/464\/revisions"}],"predecessor-version":[{"id":465,"href":"https:\/\/libraryresources.nse.org.ng\/fundamentalsoffoundationengineering\/wp-json\/pressbooks\/v2\/chapters\/464\/revisions\/465"}],"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\/464\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/libraryresources.nse.org.ng\/fundamentalsoffoundationengineering\/wp-json\/wp\/v2\/media?parent=464"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/libraryresources.nse.org.ng\/fundamentalsoffoundationengineering\/wp-json\/pressbooks\/v2\/chapter-type?post=464"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/libraryresources.nse.org.ng\/fundamentalsoffoundationengineering\/wp-json\/wp\/v2\/contributor?post=464"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/libraryresources.nse.org.ng\/fundamentalsoffoundationengineering\/wp-json\/wp\/v2\/license?post=464"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}