PREdiction of NOn-LINear soil behavior (PRENOLIN) is an interna-
tional benchmark aiming to test multiple numerical simulation codes that are capable
of predicting nonlinear seismic site response with various constitutive models. One of
the objectives of this project is the assessment of the uncertainties associated with
nonlinear simulation of 1D site effects. A first verification phase (i.e., comparison
between numerical codes on simple idealistic cases) will be followed by a validation
phase, comparing the predictions of such numerical estimations with actual strong-
motion recordings obtained at well-known sites. The benchmark presently involves
21 teams and 23 different computational codes.
We present here the main results of the verification phase dealing with simple cases.
Three different idealized soil profiles were tested over a wide range of shear strains with
different input motions and different boundary conditions at the sediment/bedrock inter-
face. A first iteration focusing on the elastic and viscoelastic cases was proved to be
useful to ensure a common understanding and to identify numerical issues before pursu-
ing the nonlinear modeling. Besides minor mistakes in the implementation of input
parameters and output units, the initial discrepancies between the numerical results
can be attributed to (1) different understanding of the expression
“
input motion
”
in dif-
ferent communities, and (2) different implementations of material damping and possible
numerical energy dissipation. The second round of computations thus allowed a con-
vergence of all teams to the Haskell
–
Thomson analytical solution in elastic and visco-
elastic cases. For nonlinear computations, we investigate the epistemic uncertainties
related only to wave propagation modeling using different nonlinear constitutive mod-
els. Such epistemic uncertainties are shown to increase with the strain level and to reach
values around 0.2 (log
10
scale) for a peak ground acceleration of
5
m
=
s
2
at the base of
the soil column, which may be reduced by almost 50% when the various constitutive
models used the same shear strength and damping implementation.