A practical method for construction of p-y curves for liquefiable soils
Introduction
A reasonable representation of pile-soil interaction is important in the evaluation of response of pile foundation to earthquake shaking. Winkler approach (also known as Beams on Non-Linear Winkler Foundation, BNWF or p-y approach) for analysis of laterally loaded pile is widely used in the practice due to its ease of nonlinearity modelling and mathematical and computational efficiency. Fig. 1(a) schematically demonstrates the BNWF model where the lateral, axial and end bearing soil-pile interactions are modelled by lateral springs (p-y spring), axial springs (t-z spring) and end-bearing spring (q-z spring), respectively. For evaluating the lateral capacity of pile foundation, p-y springs play a vital role, and the backbone force deformation behaviour defined for this spring is known as p-y curve. In a p-y curve, p is the soil reaction per unit length of the pile and y is the corresponding relative pile-soil displacement. For liquefied soil, the p-y curve used in current practice is a factored value from its non-liquefied state, which is found to be in disagreement with the p-y curve observed from full scale, centrifuge and shaking table tests, see for example [1], [4]. Fig. 1(b) and (c) shows the shape of p-y curves in pre and post-liquefaction stage. Further details of the shape of the p-y curves for liquefied and non-liquefied soils can be found in [1], [2], [3], [4], [5], [6], [7]. This paper presents a step-by-step procedure that can be used for constructing p-y curves for liquefiable soils from a typical field bore log data.
Section snippets
Major steps in the construction of p-y curves for liquefiable soils
The construction of p-y curves for liquefiable soils involves four steps, as follows.
- 1)
Evaluation of soil parameters from bore-log data
- 2)
Consideration of dimensions of pile foundation
- 3)
Construction of simplified stress-strain curve for liquefied soil
- 4)
Generation of p-y curve for liquefied soil from stress-strain curve obtained in Step 3 above.
Example for calculating p-y curves for liquefied soil from a typical ground profile
Typically for onshore practice, SPT N value are recorded through geotechnical investigation. Fig. 4(a) shows the ground profile along with a pile for which p-y curves are to be constructed under liquefied conditions. Stepwise description is given below to obtain p-y curves for liquefied soil at a depth of 5 m.
Steps to obtain p-y curve for liquefied soil from ground profile:
Step – 1: The soil considered at a depth of 5 m with SPT value N=5 and unit weight=17 kN/m3
- (a)
The SPT value corrected for
Conclusion
In this paper a practical method for construction of p-y curves for liquefiable soils is presented. A step by step calculation procedure has been provided with an example considering a standard borelog data. The calculation uses basic soil properties such as relative density, SPT profile, basic pile geometry and material. Other required soil properties are estimated based on proposed empirical relationships. Once the stress-strain behaviour of post-liquefied soil is defined, the p-y curve can
Novelty of submission
- 1.
Mechanics based shape of p-y curves
- 2.
Proposed p-y curves for liquefiable soils.
- 3.
Understanding the parameters required for construction of p-y curves.
References (10)
- et al.
Simplified method for unified buckling and dynamic analysis of pile supported structures in seismically liquefiable soils
Soil Dyn Earthq Eng
(2009) - et al.
Undrained behaviour of two silica sands and practical implications for modelling SSI in liquefiable soils
Soil Dyn Earthq Eng
(2014) - et al.
Empirical correlation between SPT N value and relative density for sandy soils
Soil Found, Jpn Geotech Soc
(1999) Lateral pile soil interaction in liquefiable soils [Ph.D. Thesis]
(2010)- et al.
Evaluation of seismic performance of pile-supported models in liquefiable soil
Earthq Eng Struct Dyn
(2016)
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