Qw<\/sub><\/em><\/td>\n| [latex]\\left( {\\dfrac{{{Q_w}L}}{{{E_p}{A_p}}}} \\right) + 0.01D[\/latex]<\/td>\n<\/tr>\n | \n| S2<\/td>\n | 0<\/em><\/td>\n| [latex]\\max \\left( {0.01D;5{\\rm{ \\:mm}}} \\right)[\/latex]<\/td>\n<\/tr>\n | \n| G1<\/td>\n | Qf<\/sub><\/em><\/td>\n| [latex]\\left( {\\dfrac{{{Q_f}L}}{{{E_p}{A_p}}}} \\right) + 0.05D + 10[\/latex]<\/td>\n<\/tr>\n | \n| G2<\/td>\n | 0<\/em><\/td>\n| [latex]0.05D + 10[\/latex]<\/td>\n<\/tr>\n | \nD is the pile diameter; L is the pile length; Ap<\/sub> is the area of the pile\u2019s section; Ep<\/sub> is the Young\u2019s modulus of the pile\u2019s material<\/em><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\nAlternatively, one case use the \u201coffset limit\u201d<\/em> method proposed by Davisson (1972) (FHWA 2006). As illustrated in Figure 6.62a<\/a>, the elastic shortening of the pile head under the in situ<\/em> collapse load Qf,test<\/sub><\/em> is estimated as:\n\n(6.79)<\/strong> [latex]{\\rho _{short}} = \\dfrac{{{Q_{f,test}}L}}{{{E_p}{A_p}}}[\/latex]\n\nFor piles with diameter D <\/em>< 0.60 m the failure load is the one that results in a pile toe settlement equal to:\n\n(6.80)<\/strong> [latex]{\\rho _f} = {\\rho _{short}} + 0.381 + \\dfrac{D}{{120}}{\\rm{ }}\\left( {{\\rm{units:\\: cm}}} \\right)[\/latex]\n\nFor piles with diameter D <\/em>> 0.60 m the failure load is the one that results in a pile toe settlement equal to:\n\n(6.81)<\/strong> [latex]{\\rho _f} = {\\rho _{short}} + \\dfrac{D}{{30}}{\\rm{ }}\\left( {{\\rm{units: \\:cm}}} \\right)[\/latex]\n\n \n\n[caption id=\"attachment_531\" align=\"aligncenter\" width=\"600\"]![\"Figure](\"https:\/\/libraryresources.nse.org.ng\/wp-content\/uploads\/sites\/9\/2026\/03\/6.62-hr-e1743553757467.png\") 60cm. Figure (b) on the right presents a load-pile head settlement curve obtained during a pile load test. The load Qf,test is found from the intersection of the tangent lines drawn from the initial and final part of the load-pile head settlement curve.\" width=\"600\" height=\"317\"> Figure 6.62. Alternative methods for determining the ultimate geotechnical strength of piles from ultimate tests: (a) offset limit method, and (b) double tangent method.[\/caption]\n\nFor drilled shafts, the graphical double tangent <\/em>method can be used (Figure 6.62b<\/a>) to determine Qf,test<\/sub><\/em>. The load-displacement curve is plotted, and the in situ<\/em> collapse load Qf,test<\/sub><\/em> is defined at the intersection of the tangent lines of the initial and final part of the curve. When applying this method one should bare in mind that the elastic shortening of the pile (Qf,test<\/sub>L<\/em>\/Ep<\/sub>Ap<\/sub><\/em>) is not considered. Thus, the in situ<\/em> collapse load of short piles may be over-estimated, and the in situ<\/em> collapse load of long piles may be under-estimated, if the elastic shortening of the pile (Eq. 6.79) is significant.\n\n
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![\"The](\"https:\/\/oercollective.caul.edu.au\/app\/uploads\/sites\/143\/2025\/03\/6.58-hr.png\")
Figure 6.58. Outline of a compression static pile load test following AS2159 loading sequence.[\/caption]\n![\"The](\"https:\/\/oercollective.caul.edu.au\/app\/uploads\/sites\/143\/2025\/03\/6.59-hr.png\")
max(5D, 2.5m) according to AS2159, where D is the diameter of the tested pile.\" width=\"600\" height=\"458\"> Figure 6.59. Pile load test setup and AS2159 spacing requirements.[\/caption]\n\n![Figure 6.62b<\/a>) to determine Qf,test<\/sub><\/em>. The load-displacement curve is plotted, and the in situ<\/em> collapse load Qf,test<\/sub><\/em> is defined at the intersection of the tangent lines of the initial and final part of the curve. When applying this method one should bare in mind that the elastic shortening of the pile (Qf,test<\/sub>L<\/em>\/Ep<\/sub>Ap<\/sub><\/em>) is not considered. Thus, the in situ<\/em> collapse load of short piles may be over-estimated, and the in situ<\/em> collapse load of long piles may be under-estimated, if the elastic shortening of the pile (Eq. 6.79) is significant.\n\n\n\n6.16.4 Geotechnical strength reduction factor \u03c6<\/em>g<\/sub> according to AS2159 accounting for pile load test results.<\/h2>\nAs discussed earlier, when static pile load tests are performed to verify in situ <\/em>the design assumptions, AS2159 allows for the adoption of a higher value for the geotechnical strength reduction factor<\/em> \u03c6<\/em>g<\/sub>. The basic geotechnical strength reduction factor \u03c6<\/em>gb<\/sub> derived via the risk assessment procedure described in Chapter 6.8<\/a>, is increased as:\n\n(6.82)<\/strong> [latex]{\\varphi _g} = {\\varphi _{gb}} + \\left( {{\\varphi _{tf}} - \\,{\\varphi _{gb}}} \\right)K \\ge {\\varphi _{gb}}[\/latex]\n\nwhere \u03c6<\/em>tf <\/sub>= 0.9 for static load tests, and\n\n](\"https:\/\/oercollective.caul.edu.au\/app\/uploads\/sites\/143\/2025\/03\/6.62-hr.png\"){kind=link}