Dynamic damage characteristics of mudstone around hammer driven pile and evaluation of pile bearing capacity

Abstract

The bearing capacity of the driven pile in the mudstone bearing layer is consistently lower than the design value. In this paper, the uniaxial compression test, pile driving model test, and needle penetration test were carried out on the mudstone samples before and after driving, and the influence of driving on the mudstone around the pile was studied. Based on the test results, the pile-bearing capacity evaluation method was proposed, and a numerical simulation was carried out. The findings revealed that the mudstone around the field piles was damaged by hammer pile driving, and the strength and elastic modulus reduced by 28.2% and 41.40%, respectively. The damage range of mudstone caused by dynamic pile driving was noted as 2d (pile diameter). For area within 0∼2d, 4 damage zones were defined every 0.5d. The strength of mudstone in four zones decreased by 66%, 40.5%, 17%, and 7%, and the elastic modulus decreased by 80.5%, 54.5%, 26.5%, and 11%, respectively. Besides, the reduction factors of damaged zones were determined, and the evaluation method of bearing capacity of mudstone considering damaged zones was proposed. The bearing capacity evaluated by this method was found to be consistent with the measured value with a 10.5% difference in measured mean value, and the conventional method overestimated the pile's bearing capacity by 57.9%. In addition to providing a specific method for the pile design and bearing capacity evaluation, this study clarified the dynamic damage characteristics of mudstone after the pile driving process has been completed.