SYMPOSIA PAPER Published: 29 July 2019
STP161120170177

Soil Damping and Rate-Dependent Soil Strength Changes Due to Impact and Rapid Loads on Deep Foundations

Source

The static soil resistance of deep foundations can be measured either by static or dynamic loading tests. The dynamic test applies a load to the pile by impact of a large mass onto the highly or minimally cushioned pile top. Measuring the resulting force on top of the deep foundation (pile) and the associated motion and performing a dynamic analysis of the pile-soil system allows for the separation of static from dynamic soil resistance components and the calculation of an equivalent static load-displacement curve. This result can be compared with the same type of curve obtained by the static loading test. For certain plastic soils, it has been found that the static resistance derived by analysis from the dynamic test may not completely account for the fact that quickly loaded materials exhibit a strength greater than a slowly loaded material. The resulting static resistance should then be reduced by a rate factor that depends on basic soil parameters. This paper reviews different approaches of loading rate and damping effect identification. It also presents several examples of dynamic test results on piles driven or drilled into soils with different levels of plasticity. The effectiveness of two approaches in separating the dynamic component from the total soil resistance in addition to accounting for rate-dependent strength gains is assessed by comparison with static loading test results, considering partial resistance mobilization and soil setup. Recommendations are given aimed at both reducing the possibility of overestimations of capacity and the need for accurately knowing the soil characteristics near the location of the dynamically tested foundation.

Author Information

Rausche, Frank
PileDynamics, Inc., Cleveland, OH, US
Hannigan, Patrick
GRL Engineers, Inc., Cleveland, OH, US
Alvarez, Camilo
GRL Engineers, Inc., Los Angeles, CA, US
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Details
Developed by Committee: D18
Pages: 48–67
DOI: 10.1520/STP161120170177
ISBN-EB: 978-0-8031-7668-3
ISBN-13: 978-0-8031-7667-6