Dr Naveen uses Oasys software to address the gap in codes when seeking an understanding of how larger diameter piles (over 1m) will perform, and lays the foundations for building knowledge bank of their limitations. Dr Naveen’s paper uses field data from the existing bifurcated HSR flyover in his home country – India.
At present, IS (Indian Standard) Codes, voluntary international ASTM codes and Eurocodes only relate to small diameter piles (less than 1.0m diameter). It is Dr Naveen’s hope that his research will act as a catalyst for the development of new codes for larger diameter piles. His research was presented in 2016 at the 7th International Conference on “Scientific Computing to Computational Engineering”, 7th IC-SCCE in Athens, and we are pleased to give it another audience through the Oasys Competition.
How Oasys proved invaluable
Dr Naveen BP used the Oasys Geotechnical Unipac Suite for teaching and research for several years. The core objective was to understand the limitations of the large diameter bored cast in-situ piles by validating bored cast in situ pile results with the numerical simulations like Oasys Alp, analytical and field testing.
Field tests were carried out. The bored cast-in situ pile considered in this study is of diameter (D) 1m, length 17m and of M35 grade concrete. The site soil is composed of layers of sandy clay and soft-weathered rock. A hydraulic jack, fixed horizontally between an immovable wall and the top of the pile, was used to apply lateral loads (Pz), in stages, up to 120kN. A displacement of 4.12 mm was observed as against the permissible settlement of 12mm as per IS 2911 – Part – IV.
Closed view of laterally loaded pile test
Results obtained from the field test have been used to validate the modelling results in Alp. In the Alp model, the soil is composed of 2 layers namely sandy clay and soft-weathered rock. There is no ground water data for the problem being considered.
The curve obtained using Alp simulations is close to field test results when compared with the analytical method (i.e Winkler’s). However, a link in the field test results attributed some problems in field tests. The issues in large diameter piles in residual soils are:
Presently, know-how on prediction of load-displacement relationships of large diameter piles in residual soils is scarce. Here, Dr Naveen showed that the prediction of the adopted method is reasonably close to the field test results.
- IS 2911–Part IV says that the maximum permissible displacement is 12mm. Testing should be conducted until such displacements are reached to determine ultimate bearing capacity. This has not been carried out in the field test presented here due to unavailability of jacks and supports of adequate capacity. This has become more common due to large diameter piles.
- Codes suggest the load produced a deflection of 10% of the diameter as the ultimate bearing capacity. Required Loads are not large enough to produce 12 mm, let alone 10% of diameter, i.e., 100 m displacement has not been used in the field test
- Accurate numerical simulations can be used for this purpose, to simulate pile behaviour for large loads, until failure, conditions for which existing field test techniques cannot be used.
Highly Commended entry within the Geotechnical Academics category Oasys Project of the Year 2016.