Soils age Their engineering properties often improve significantly during aging times of practical interest to engineers This paper provides examples from research and practice It includes a review of the triaxial IDS test, followed by examples of its use to investigage the question of whether the aging improvements result from frictional or cohesive effects Contrary to most current thinking, the soil stiffening and strengthening appears entirely frictional in effect The aging effects described appear mechanical, resulting from dispersive particle movements and internal stress arching under drained conditions The paper concludes with suggestions for using these mechanical aging effects in practice

The Mechanical Aging of Soils

Piles driven in sand can show remarkable increases in their axial shaft capacities in the months that follow installation. Many practical benefits follow if service capacities can be relied upon to exceed the levels proven in site tests, which are usually performed within a few days of driving. This paper reports findings from a programme of mainly tension tests on steel pipe piles performed in dense sand at Dunkirk, northern France. The tests demonstrated more marked shaft capacity growth with time than expected. The aged piles also showed surprisingly brittle failure modes; prior testing to failure both degraded capacity and modified the ageing processes, leading to non-monotonic shaft capacity–time traces that fall far below the intact ageing characteristic (IAC) defined by tests on fresh, previously unfailed, piles. Capacity–time trends inferred from repeatedly tested piles can give misleading results. The new findings allow the ageing effects to be characterised more clearly, and permit a re-evaluati...

https://www.icevirtuallibrary.com/doi/pdf/10.1680/geot.2006.56.4.227

Some observations of the effects of time on the capacity of piles driven in sand

Investigations into pile behavior in dense marine sand have been performed at the Institut Francais du Petrole and Imperial College at Dunkirk, northern France. In the most recent series of tests, strain-gauged, open-ended pipe piles, driven and statistically load tested in 1989, were retested in 1994. An 85% increase in shaft capacity took place between six months and five years after installation. The possible causes are evaluated in relation to previous case histories, laboratory soil tests, pile corrosion, and new effective stress analyses developed using smaller, more intensively instrumented piles. The available evidence suggests that a circumferential arching mechanism develops during pile driving that limits the radial stresses acting on the pile shaft. It is concluded that creep leads to a breakdown of these arching stresses, allowing increases in radial stress and hence gains in shaft capacity. Increased dilation due to sand aging may also contribute. Finally, the measured pile shaft capacities are compared to predictions made using existing design methods.

Effects of Time on Capacity of Pipe Piles in Dense Marine Sand

The available literature indicates that pile side shear increases almost linearly with the logarithm of time elapsed after driving, sometimes described using a dimensionless setup factor. A test pile program conducted by the University of Florida measured side shear setup (SSS) for up to 4.7 years on five, 457-mm (18-in), square, prestressed, concrete piles driven into coastal plain soils at different sites. Dynamic tests performed during initial driving and two restrikes measured short-term SSS. Osterberg cells, the first installed in driven concrete piles, measured long-term SSS starting within 24 h of driving and continuing with two to five additional, staged tests. Extensive instrumentation, including vibrating wire strain gauges, Marchetti total stress cells, and vibrating wire piezometers, divided the five piles into 28 segments by soil type with horizontal effective stress measurements for 18 of the segments. This paper describes the University of Florida test pile program and its results. A companion paper analyzes the test results and recommends procedures for implementing SSS in design.

Side Shear Setup. I: Test Piles Driven in Florida

This paper summarizes the parameters that influence the axial capacity of pipe piles driven into sands. The parameters that affect pile behavior are for convenience divided into four categories: (1) Soil characteristics; (2) pile characteristics; (3) method of pile installation; and (4) type of loading. When possible, the influence that these parameters have on the capacity is quantified. In addition, the paper describes supporting evidence from pile load test data, small‐scale laboratory tests, and in situ cone probings that has been used to justify limiting values for unit shaft and toe resistances. The use of limiting values has significant economic impact on long piles, especially those used for offshore applications. This information is, therefore, evaluated and critiqued to place the use of limiting values in proper perspective. The results of this paper are based on a synthesis of literature on (1) pile load test data on piles in sand, (2) data from cone penetrometer tests in sands, and (3) informa...

Performance of axially loaded pipe piles in sand

It has often been shown by previous investigators that the existing pile driving formulas yield bearing capacities which usually do not stand in good correlation to the actual bearing capacities of...

R. Audy

Papers

Limitations of the Driving Formulas for Predicting the Bearing Capacities of Piles in Sand