Abstract:
Static load tests on cast?in?place grouted piles are often implemented to characterize surrounding geomaterial response to applied loads to further evaluate foundation design parameters. Embedded instrumentation, such as strain gauges, are advantageous for assessing the internal force distribution along an embedded pile’ s length, and in turn calculating external resisting forces. Since external resisting forces cannot be measured directly, several pile properties must be determined for appropriate calculation of foundation design values. Critically, pile geometry and composite elastic modulus at each strain gauge level must be reasonably assessed. Pile geometry (in particular total cross?sectional area, A) along the embedded length is not necessarily known, but is often estimated from installation records and/or some quality assurance methods. The grout modulus of elasticity, E, is very likely not known to a reasonable degree of certainty, being commonly estimated from laboratory tests conducted on grout samples. Therefore, significant shortcomings and a large degree of uncertainty remains in existing estimation methods for these properties for grouted piles. The Incremental Rigidity method uses applied test loads and measured strains to determine the relationship between axial rigidity, EA, and measured strain at individual interpretable strain-gauge levels. This in turn determines a direct relationship between measured strains and internal forces. This method provides significant improvement in calculating axial rigidity directly from static load test measurements through an internal calibration sequence and engineering justification. Shortcomings in existing methods to determine axial rigidity in grouted piles are discussed. Several case histories are presented to demonstrate critical details and significant benefits in applying the Incremental Rigidity method for converting strain to internal force on cast?in?place grouted piles. Recommendations for improving industry standards in implementing instrumented static load tests on cast?in?place grouted piles are presented.