Case studies

 

Design of pile foundations for Newark Dyke bridge (UK)

A Repute analysis was undertaken for Cementation Foundations Skanska Ltd to assess the pile-foundation requirements for the new railway bridge at Newark Dyke (UK). Further details on this case study may be found in the paper by Suckling & Lee "Piled foundation aspects of the bridge slide at Newark Dyke" (Underground Construction 2001, Int. Symposium & Exhibition, London, 2001, pp 361-372).

The 24 piles for the south-west pile cap are 8m long, 0.6m in diameter, and in the asymmetric layout shown below. The soil profile consists of 1m of Alluvium underlain by 2m of river gravels which overlie 5m of Mercia Mudstone. The applied vertical loads result from the combined effect of live and dead loads, whereas the horizontal loads and moments in X and Y directions are generated by the trains braking and accelerating.

 

 

 

 

 

 

 

 

A Repute analysis using linear elastic and non-linear soil models has been undertaken, and results for the most heavily loaded row in the group (pile Nos 1 to 5) are compared to a previous PIGLET analysis in the table below.

 

Pile axial load (kN)
Pile No PIGLET Repute (linear) Repute (non-linear) Percentage difference between PIGLET and Repute (non-linear)
1 2545 2340 2160 -15%
2 1589 1570 1590 0
3 1446 1450 1460 +1%
4 1502 1470 1470 -2%
5 2243 1970 1810 -19%

Piles were designed with a factor of safety of 2 on the average load and 1.5 on the maximum load in each row, as calculated by PIGLET. Thus, pile Nos 1 to 5 were designed with a minimum ultimate axial capacity of 3818kN. It is important to note that Repute predicts lower maximum and average pile loads. This results, for the non-linear soil model, in an increase in design factors of safety to 2.2 on the average pile load and 1.8 on the maximum pile load, compared to 2.0 and 1.5 originally desired from the PIGLET results.

Finally, it is worth noting that the maximum pile load calculated by structural methods was 1541kN. This is significantly lower than the maximum values obtained from the pile group analyses which consider pile-soil interaction, thereby showing the dangers of attempting to model a complex pile-soil system by means of a simple structural frame. For further details, download the report "Repute vs Structural analyses" (PDF format, size 19KB).

Acknowledgments

Appreciation is expressed to Cementation Foundations Skanska Ltd for permission to publish the above results.

References

Suckling, T. P. & Lee, J. (2001). Piled foundation aspects of the bridge slide at Newark Dyke. Underground Construction 2001, Int. Symposium & Exhibition, London, pp 361-372.

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