{"id":408,"date":"2025-03-31T03:20:47","date_gmt":"2025-03-31T03:20:47","guid":{"rendered":"https:\/\/libraryresources.nse.org.ng\/fundamentalsoffoundationengineering\/chapter\/example-5-6-design-capacity-from-in-situ-tests-spt\/"},"modified":"2026-03-16T14:05:26","modified_gmt":"2026-03-16T14:05:26","slug":"example-5-6-design-capacity-from-in-situ-tests-spt","status":"publish","type":"chapter","link":"https:\/\/libraryresources.nse.org.ng\/fundamentalsoffoundationengineering\/chapter\/example-5-6-design-capacity-from-in-situ-tests-spt\/","title":{"raw":"Example 5.6","rendered":"Example 5.6"},"content":{"raw":"Estimate the design capacity of the footing shown below according to AS 5100.3, using directly the SPT measurements in the loose-to-medium sandy foundation soil.\n\n[caption id=\"attachment_407\" align=\"aligncenter\" width=\"700\"]\"The Example 5.6. Problem description and input parameters.[\/caption]\n

Answer:<\/h2>\nBefore applying Eq. 5.53 to estimate the bearing capacity, we must first find the corrected N\u2032 <\/em>values for overburden stress, and the average corrected value N\u2032<\/em>\u00a0over a depth 1.5B <\/em>= 6 m. Application of Eqs. 5.51 and 5.52 for calculating the overburden stress correction factor CN<\/sub><\/em> and accordingly the average N<\/em>\u2032 <\/em>value for 6 m is presented in the table below.\n\n\n\n\n\n\n\n
Example 5.6. Calculation of average N<\/em>\u2032\u00a0 <\/em>value.<\/caption>\n
Depth (m)<\/th>\nN<\/em><\/th>\nTotal stress (kPa)<\/th>\nPore pressure (kPa)<\/th>\nEffective stress (kPa)<\/th>\nCN<\/sub><\/em><\/th>\nN\u2032 = NCN<\/sub><\/em><\/th>\n<\/tr>\n
1<\/td>\n8<\/td>\n17<\/td>\n0<\/td>\n17<\/td>\n2.373<\/s> 2.0*<\/td>\n16<\/td>\n<\/tr>\n
2.5<\/td>\n16<\/td>\n42.5<\/td>\n0<\/td>\n42.5<\/td>\n1.501<\/td>\n24<\/td>\n<\/tr>\n
4<\/td>\n12<\/td>\n68<\/td>\n10<\/td>\n58<\/td>\n1.285<\/td>\n15.4<\/td>\n<\/tr>\n
5.5<\/td>\n6<\/td>\n93.5<\/td>\n25<\/td>\n68.5<\/td>\n1.182<\/td>\n7.1<\/td>\n<\/tr>\n
N'average<\/sub><\/em><\/strong><\/td>\n15.62<\/th>\n<\/tr>\n<\/tbody>\n<\/table>\n*Note: Use of CN<\/sub> values higher than 2.0 is not recommended<\/em>\n\nSubstituting in Eq. 5.53 while taking the groundwater table factors Cw1<\/sub><\/em>, Cw2<\/sub><\/em> from Table 5.7 yields:\n\n[latex]{q_f} = 9.57{N'_{average}}B\\left( {1.0 + 1.0 \\times \\dfrac{0}{4}} \\right) = 598{\\rm{ \\:kPa}}[\/latex]\n\nAs the bearing capacity is determined from SPT test results, the appropriate range of the geotechnical strength reduction factor \u03c6<\/em>g <\/sub>from Table 5.1 is \u03c6<\/em>g <\/sub>= 0.35 to 0.40. Selecting conservatively the lower bound of the proposed range, the design capacity is determined in terms of stress as:\n\n[latex]{\\varphi _g}{q_f} \\ge {S^ * } \\Rightarrow 0.35 \\times 598 \\ge {S^ * } \\Rightarrow {S^ * } \\le {\\rm{209 \\:kPa}}[\/latex]","rendered":"

Estimate the design capacity of the footing shown below according to AS 5100.3, using directly the SPT measurements in the loose-to-medium sandy foundation soil.<\/p>\n

\"The
Example 5.6. Problem description and input parameters.<\/figcaption><\/figure>\n

Answer:<\/h2>\n

Before applying Eq. 5.53 to estimate the bearing capacity, we must first find the corrected N\u2032 <\/em>values for overburden stress, and the average corrected value N\u2032<\/em>\u00a0over a depth 1.5B <\/em>= 6 m. Application of Eqs. 5.51 and 5.52 for calculating the overburden stress correction factor CN<\/sub><\/em> and accordingly the average N<\/em>\u2032 <\/em>value for 6 m is presented in the table below.<\/p>\n\n\n\n\n\n\n\n\n
Example 5.6. Calculation of average N<\/em>\u2032\u00a0 <\/em>value.<\/caption>\n
Depth (m)<\/th>\nN<\/em><\/th>\nTotal stress (kPa)<\/th>\nPore pressure (kPa)<\/th>\nEffective stress (kPa)<\/th>\nCN<\/sub><\/em><\/th>\nN\u2032 = NCN<\/sub><\/em><\/th>\n<\/tr>\n
1<\/td>\n8<\/td>\n17<\/td>\n0<\/td>\n17<\/td>\n2.373<\/span> 2.0*<\/td>\n16<\/td>\n<\/tr>\n
2.5<\/td>\n16<\/td>\n42.5<\/td>\n0<\/td>\n42.5<\/td>\n1.501<\/td>\n24<\/td>\n<\/tr>\n
4<\/td>\n12<\/td>\n68<\/td>\n10<\/td>\n58<\/td>\n1.285<\/td>\n15.4<\/td>\n<\/tr>\n
5.5<\/td>\n6<\/td>\n93.5<\/td>\n25<\/td>\n68.5<\/td>\n1.182<\/td>\n7.1<\/td>\n<\/tr>\n
N’average<\/sub><\/em><\/strong><\/td>\n15.62<\/th>\n<\/tr>\n<\/tbody>\n<\/table>\n

*Note: Use of CN<\/sub> values higher than 2.0 is not recommended<\/em><\/p>\n

Substituting in Eq. 5.53 while taking the groundwater table factors Cw1<\/sub><\/em>, Cw2<\/sub><\/em> from Table 5.7 yields:<\/p>\n

[latex]{q_f} = 9.57{N'_{average}}B\\left( {1.0 + 1.0 \\times \\dfrac{0}{4}} \\right) = 598{\\rm{ \\:kPa}}[\/latex]<\/p>\n

As the bearing capacity is determined from SPT test results, the appropriate range of the geotechnical strength reduction factor \u03c6<\/em>g <\/sub>from Table 5.1 is \u03c6<\/em>g <\/sub>= 0.35 to 0.40. Selecting conservatively the lower bound of the proposed range, the design capacity is determined in terms of stress as:<\/p>\n

[latex]{\\varphi _g}{q_f} \\ge {S^ * } \\Rightarrow 0.35 \\times 598 \\ge {S^ * } \\Rightarrow {S^ * } \\le {\\rm{209 \\:kPa}}[\/latex]<\/p>\n","protected":false},"author":1,"menu_order":13,"template":"","meta":{"pb_show_title":"","pb_short_title":"Example 5.6","pb_subtitle":"Design capacity from in situ tests: SPT","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"class_list":["post-408","chapter","type-chapter","status-publish","hentry"],"part":325,"_links":{"self":[{"href":"https:\/\/libraryresources.nse.org.ng\/fundamentalsoffoundationengineering\/wp-json\/pressbooks\/v2\/chapters\/408","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\/408\/revisions"}],"predecessor-version":[{"id":409,"href":"https:\/\/libraryresources.nse.org.ng\/fundamentalsoffoundationengineering\/wp-json\/pressbooks\/v2\/chapters\/408\/revisions\/409"}],"part":[{"href":"https:\/\/libraryresources.nse.org.ng\/fundamentalsoffoundationengineering\/wp-json\/pressbooks\/v2\/parts\/325"}],"metadata":[{"href":"https:\/\/libraryresources.nse.org.ng\/fundamentalsoffoundationengineering\/wp-json\/pressbooks\/v2\/chapters\/408\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/libraryresources.nse.org.ng\/fundamentalsoffoundationengineering\/wp-json\/wp\/v2\/media?parent=408"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/libraryresources.nse.org.ng\/fundamentalsoffoundationengineering\/wp-json\/pressbooks\/v2\/chapter-type?post=408"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/libraryresources.nse.org.ng\/fundamentalsoffoundationengineering\/wp-json\/wp\/v2\/contributor?post=408"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/libraryresources.nse.org.ng\/fundamentalsoffoundationengineering\/wp-json\/wp\/v2\/license?post=408"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}