Offshore Technology Research Center

 

OTRC Project Summary

Project Title:

An Experimental Facility to Model the Behavior of Steel Pipe Piles in Sand

Prinicipal Investigators:

Roy Olson

Sponsor:

National Science Foundation, American Petroleum Institute and Fugro McClelland

Completion Date:

March, 1996

Final Report ID#

B78(Click to view final report abstract)

This project is part of a joint study which was conducted at The University of Texas at Austin (UT), Texas A&M University (A&M), The University of Houston (UH), and Fugro McClelland Marine Geosciences (FM).  The overall objectives of the study were to:

  • Identify the sources of inaccuracy in RP-2A’s provisions for predicting the axial capacity of piles in sand.
  • Compile, catalog, and assess the validity of the criticisms directed at RP-2A guidelines for piles in sand.
  • Perform three original research studies to investigate the effects of the installation process, in situ conditions, and loading details on the capacity of piles driven in siliceous sands.
  • Generalize and otherwise improve the methods used to design piles in sand.

The purpose of this study is to identify the effects of the installation process on the capacity of piles.  The project also for identifies, catalogs, and assesses the validity of RP-2A criticisms for piles in sand (Iskander and Olson, 1992).  In addition the data base of load tests on piles in sand (Templeton and Hamilton, 1993) is updated and enlarged and the accuracy of pile capacity predictions (Olson and Iskander, 1994) is assessed.

Although this study has been geared to solve some of the difficulties encountered in marine geotechnology, is findings are equally relevant to traditional terrestrial geotechnical engineering.  In the terrestrial environment, many uncertainties in pile capacity predictions can be avoided by driving piles to “refusal” in deep layers of hard clay, dense sand, or rock.  When strong layers are not available, and driving piles to refusal is not possible, engineers often apply conservative assumptions and rely on proof test to verify the design capacity. Strong layers are typically absent in the offshore environment.  Load tests on large piles of sizes used in the offshore are often prohibitively expensive, and hence the importance of precise capacity predictions.  One of the objectives of this study is to develop a body of knowledge which will aid the designers of both offshore and terrestrial pile to obtain more precise capacity predictions.  The possible cost savings incurred for offshore piles are indeed larger than those for terrestrial piles, Nevertheless, the potential savings for terrestrial piles may be substantial in many cases.

The objectives of this dissertation research are to:

  • Develop the experimental facilities necessary to identify the physical mechanisms which control the behavior of piles during installation and subsequent loading. 
  • Perform load tests to identify the effects of the installation process on the capacity of pipe piles in sand, with emphasis on the phenomenon of pile plugging.

This investigation used methods that are fundamentally different from previous experimental studies, in a number of ways.  First, a double-walled pile is used to delineate the frictional stresses acting against the external and internal surfaces of the pile wall.  Second, a fast automatic laboratory pile hammer capable of representing the phenomena which occur during pile driving was developed and used.  Their, a data acquisition system capable of collecting data at a scale that has never been accomplished in foundation engineering in terms of the combined number of channels and sampling rate was built.  Fourth, this study is the first to provide continuous measurements of the elevation of the soil inside the pile during installation and loading.  Fifth, a pressure chamber, feedback control system, loading frame , sand handling, pluviating, saturating, and drying apparatus have been integrated to allow convenient load testing of piles under simulated field conditions.

In the short term, the developed apparatus will be used to identify the physical mechanisms which control the behavior of piles during installation and loading.  In the long term the identified mechanisms should provide a framework for developing a theoretically sound model to predict the capacity of piles.

Related Publications: Iskander, M. and Olson, R.E., "Review of API Guidelines for Pipe Piles in Sand," Civil Engineering in the Oceans V, ASCE Specialty Conference, pp. 798-812, 1992.

Jones, W.C., Iskander, M.G., Olson, R.E. and Goldberg, A.D., "Axial Capacity of Suction Piles in Sand," ASCE Session on Offshore Pile Foundations, Dallas, October 1993.

Iskander, M.G., Olson, R.E. and Pavlicek, R.M., "Installation and Pull Out Tests on Suction Piles," ASCE Session on Offshore Pile Foundations, Dallas, October 1993.

Iskander, M.G., Olson, R.E. and Pavlicek, R.W., "Behavior of Suction Piles in Sand," Design and Performance of Deep Foundations, Geotechnical Special Publication No. 38, pp 157-171, 1993.

Olson, R. E., and M. G. Iskander (1994), “Axial Load Capacity of Piles in Sand”, Advanced Technology in Civil Engineering, ASCE-Saudi Arabian Section, Manama, Bahrain, pp. 383-394.

Iskander, M. G., and R. E. Olson (1997), “Behavior of Open Ended Pipe Piles in Sand During Installation and Loading”, Proc., XIV Intern. Conf. on Soil Mechanics and Foundation Engineering, Hamburg, Germany, pp. 991-995.

Olson, R. E., and Iskander, M. G., "Axial Load Capacity of Piles in Sand", Proc., Fourth Intern. Conf. on Case Histories in Geot. Engr., Vol. 1, pp. 293-300, 1998.

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