EVALUATION OF PILE TENSION LOADS USING PULL-OUT AND PUSH-OUT METHODS

Abstract

Strain gauge instrumented static tension load testing in bored piles can give the designers a variety of useful information based on the geotechnical conditions. Traditional tension or uplift tests are performed using the pull-out method, which is sometimes inappropriate economically and technically. For the past few decades, Bidirectional Static Load Testing method (BDSLT, commonly known as the O-cell method) has been proven advantageous over the conventional pile load testing method for compression piles. However, the application of BDSLT in tension load tests (push-out), an alternative to the traditional method (pull-out), is seeking wide acceptance in the construction industry. This push-out method provides the facility to install sacrificial jacks within the toe level of the pile and extend an additional reaction pile below the design toe level. In this article, a comparison of the upward behavior of the shaft using instrumented pull-out and push-out methods is studied. The piles of 900mm diameter, 6.0m length were instrumented with 4 levels of vibrating wire strain gauges and tested up to 5000kN for a high-rise building project in Qatar. The maximum settlement observed was 4.60 mm for the pull-out test and 4.20 mm for the push-out test, respectively. The unit shaft friction shows a maximum of 312 kPa for the pull-out test and 395 kPa for the push-out test, indicating that the outcomes are fairly similar. The results of this study suggest that push-out tests can be used as an innovative alternative to conventional technique to bring economic and project executional benefits.