Analysis of Post-Installation Dynamic Load Test Data for Capacity Evaluation of Deep Foundations

Abstract

Construction of deep foundations causes changes to the original geotechnical condition of the surrounding soils and rock. The nature, extent, and effects of these alterations, and subsequent time-dependent modifications, on the long-term load bearing capacity of the foundation elements are mainly functions of the characteristics of the supporting geo-materials and type of installation method. Post-installation Dynamic Load Testing (DLT) is commonly used for capacity evaluation of driven and drilled deep foundation elements and is performed under impacts of the pile driving hammer or a special large drop weight loading device. Use of a large drop weight loading device is usually appropriate for cast-in-place shafts and driven piles in high-setup soils to activate the full bearing capacity. The DLT procedure consists of applying a specific number of blows (typically 2 to 10 blows) and measuring pile/shaft strain and motion time-records, and the resulting displacement. This paper presents discussions on the analysis of post-installation DLT data for capacity evaluation of driven and drilled deep foundations. Technical aspects related to the proper test record selection for analysis considering pile/shaft set per blow, changes of capacity from blow to blow with subsequent impacts, energy levels, and total penetration during the test are delineated. Analytical procedure and engineering evaluation of results are discussed with recommendations for practical use. Test records from actual case histories are utilized to demonstrate data characteristics and illustrate proposed numerical methods and recommended analytical procedures for rational evaluation of DLT results for engineering use.