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Research hinges on sheet piles tests Dutch researchers seek design predictions for sheet pile wall behaviour in soft clay.

PERFORMANCE PREDICTIONS of a hinged sheet pile wall design in soft clay are being sought by two Dutch research organisations which will then construct the wall at full scale and monitor its performance.

The test aims to establish the validity of design rules on steel bearing piles and steel sheet piles given in the recently issued Eurocode 3 part 5. 'One of the new aspects of this Eurocode is the ultimate limit state design of steel sheet piles with plastic hinges' says Fred Jonker of CUR, the Netherlands centre for civil engineering research and codes, which is organising the test in conjunction with Delft University.

The test will be carried out near Rotterdam at a soft clay and peat site, where groundwater is 1m below surface. The strutted test pit will be constructed with a hinged Z-profiles on one wall and double U-profiles on the opposite. The other two walls will be formed from soft bentonite to create as close as possible a two dimensional plane strain situation in the ground.

During the test the hinged wall will be loaded to its ultimate serviceability state, while the other will be loaded to its serviceability limit state.

The test aims to investigate the behaviour of the steel sheet piles in both the short and long term. It will also look at the effects of the plastic hinges on the Z-profile wall, and 'oblique bending' in the U-profile wall. The latter is because Eurocode 3 gives directives to account for the loss of strength and stiffness due to oblique bending, but a practical verification of these effects has never been undertaken, explains Jonker.

Once the test elements have been installed, the pit will be excavated in phases involving dewatering to allow excavation in the dry to 4m. Groundwater will then be allowed to return to its original level, and wet excavation will continue to about 6.5m. The groundwater will again be lowered to the new pit base, and the test pile walls will be loaded and monitored for about six months.

Monitoring during the test will include earth and water pressures on the wall, wall displacements at various depths, rotation of the wall, vertical displacement of the ground surface, pore water pressure in the clay, and heave in the bottom of the pit.

The organisers openly invite predictions on the behaviour of the wall, which should be submitted by 15 August. For further information email: fred.jonker@cur.nl.

The test is a follow up to a full scale sheet pile trial undertaken in Germany in 1993. This trial, organised by CUR and University of Karlsruhe looked at the performance of a simply supported sheet pile wall in dry sand. For this 43 predictions were submitted from research organisations, universities, consultants and contractors. The predictions and test results were released through a workshop (GE July/August 1995), and will be published in report form in the near future, promised Jonker.

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