Publication Abstract

Proceedings-DFI-India 2016: 6th Conference on Deep Foundation Technologies for Infrastructure Development in India, (DFI)

Dynamic Load Testing of Driven and Drilled Deep Foundations
Prof. Samuel G. Paikowsky; Sc.D, University of Massachusetts, Lowell. President, GeoDynamic Inc. Newton MA. USA

The design of deep foundations encounters a large degree of uncertainty due to the calculation models, the determination of soil strength parameters and site variability. This along with the uncertainty in the pile integrity due to the installation methods, typically leads to a large safety margin that translates to a high cost. Capacity and integrity testing enable to decrease the uncertainty in design and construction. Traditional static load tests are costly, time consuming and may result with unresolved questions regarding the ultimate capacity, pile integrity and load distribution. Consequently, dynamic testing is increasingly being used to examine the capacity and integrity of deep foundations. The advantages of the tests include, short testing time, low cost relative to static load tests (allowing multiple tests at a single site), and integrity/construction quality evaluation concurrent with capacity determination. In addition, the tests are being used for drilled foundations as proof tests. These tests are carried out to a limited load in order to examine existing foundations due to construction difficulties, load verification or design change. A short review of the principles, techniques and analyses of the dynamic testing is presented. While driving hammers are used for driven piles, drop weight systems are mostly used to dynamically test the capacity and integrity of drilled deep foundations. Extensive studies supported by AASHTO through the National Cooperative Highway Research Program (NCHRP 24-17 and NCHRP 21-08) had examined the dynamic methods using theoretical tools and databases for driven and drilled deep foundations, respectively. The sizeable databases allow the determination of the expected accuracy of the test results when compared to static load tests to failure. Recommendations are made regarding the application of the dynamic testing method, its accuracy and available codes. The presentation includes several case histories and a project in the port of Tema Ghana where project specific drop weight device had been utilized to mitigate great changes during construction and control the cost of special drilled foundations

 article #2207; publication #1020 (INDIA-2016)