A TECDOC on Seismic Soil Structure Interaction – IAEA draft TECDOC (Chapter 1-7 of the R0 Version))COMMENTS BY REVIEWER
Reviewer: Celine Gelis (GC); Maria Lancieri (LM); Christophe Clement (CC)
Country/Organization: FRANCE / IRSN Date: February 2017 / RESOLUTION
JJJohnson (Issues remaining = 7)
Alain (Issues to be addressed = 16)
Boris (Issues to be addressed = 6)
Boris, JJJ, and Alain (Issues to be addressed = 17)
Comment No. / Page/Section / Comment / Accepted / Accepted, but modified as follows / Rejected / Reason for modification/rejection
GC3 / 20/2.1 /
- Spatial variation of motion. Typically, defined by an assumed wave propagation mechanism.
GC4 / 29/3.1 / For soil-structure interaction (SSI) analyses, description of the soil configuration (layering or stratigraphy) and characterization of the dynamic (material) properties of the subsurface materials, including the uncertainties associated to them, shall be investigated and a soil profile for the site, in a form suitable for design purposes, shall be determined together with associated uncertainties.
What about lateral variations? / Alain
GC5 / 29/3.1 / Therefore, large scale geological investigations are required to define the lateral and in-depth extent of the various strata, the underground topography, the possible existence of basins (large-scale structural formation of rock strata formed by tectonic warping of previously flat-lying strata, structural basins are geological depressions, and are the inverse of domes), the depth to the bedrock, the elevation of the water table, etc.
See IRSN1 reviewer comments. / Alain
GC6 / 30/3.1 / “….simplified rules proposed in the outcome of the European research project NERA (2014) ”
The NERA project was intended to propose simplified aggravation factors for EC8 revision. It is based on simple basin shape filled with soil defined by smoothly varying velocities with depth.
Other studies aim at assessing such aggravation factors based on simple basins like the following ones and others :
Bard and Bouchon (1985)
Meza-Fajardo et al. (2016) / Alain
GC7 / 30/3.1 / “….Pitilakis et al, (2015)  tentatively concluded the following based on extensive numerical analyses, involving linear and equivalent linear soil constitutive models:”
Pitilakis et al. (2015) do not mention equivalent linear modelling but only linear elastic analysis. In the NERA final document (deliverable D11.5 “Code cross-check, computed models and list of available results”), it is mentioned that wave propagation modelling in nonlinear soils is performed with one code (ABAQUS) and for clays (page 9: “The material non-linearity is described according to the constitutive model of Anastasopoulos et al. (2011) and degradation curves corresponding to the Ishibashi and Zhang model for clays with a plasticity index of 50 and a mean confining pressure of 10 kPa.”) / Alain
GC8 / 30/3.1 /
- The aggrevation factors for locations close to the valley edges are smaller than 1.0,
GC9 / 30/3.1 /
- The aggrevation factors for location in the central part of the valley depend on the fundamental period of the valley: they are slightly larger than 1.0 if the basin period is small, typically less than 3.0s, and therefore 2D effect may be considered of minor importance; they may reach high values if the basin period is large.
The proposed aggravation factor should multiply in each period range the spectral value of the design elastic response spectrum of EC8. Spatial distribution of AGFS and AGFL along the basin showed that for the region above the inclined part of the basin, both AGFS and AGFL are in general below 1.0, thus, in order to be on the safe side, the design response spectrum, (i.e. normally the seismic code values) can be used without any further modification for basin edge effects. On the contrary, for the region above the constant-depth part of the basin, median short-period aggravation factors AGFS are around 1.1 with 84th percentiles not greater than 1.2; median long-period aggravation factors AGFL are around 1.0 for basins with low T0, while vary from 1.1 to 1.4 for basins with higher T0. Corresponding AGFL 84th percentiles are 1.1 for low-T0 basins and can be as high as 1.8 for high-T0 basins. The limit value of T0 for the distinction between low- and high-T0 basins could be indicatively set to 3.0s (Figure 9). These aggravation factors should be mainly used for ordinary structures, while detailed site-specific analyses should be performed for important structures.
And in conclusions : Extensive parametric 2D numerical analyses of the seismic response of homogeneous alluvial basins were performed at a second stage to explore the basin-induced amplification and its sensitivity to parameters related to the basin geometry and the properties of the soil sediments. The computed maximum AGF were found as high as 2.8 for some specific geometries and soil conditions. Median and 84th percentiles values are proposed for ordinary engineering applications with the introduction of a short- (for periods T≤0.75T0, where T0 is the fundamental period at the center of the basin) and a long-spectral period (T>0.75T0) aggravation factor, which should multiply the present spectral value of the elastic response spectrum in order to account for the extra amplification in case of basins. The extra median factors vary from 1.0 to 1.4 with the largest values corresponding to the deeper basins, with corresponding 84th percentiles ranging from 1.1 to 1.8. / Alain
GC10 / 30/3.1 / “….constitute helpful guidelines to estimate the potential for 2D effects.smaller than 0.5.”
And what about 3D ? what about 2D SV and 2D SH ? / Alain
GC11 / 33/3.2 / “However, it is frequently assumed that a one-dimensional situation prevails and simpler models can then be used to describe the salient features of the soil response.”
What if 2D/3D effects take place? Link with part 6.3.3 (page 101-104) should be done / Alain / .
GC12 / 33/3.3.2 / “High frequency motions induce smaller strains and therefore should be assigned less damping.”
Add references to the paper of Kausel and Asimaki (2002) that introduced Frequency-Dependent Shear Modulus and Damping ? / Alain
GC13 / 43/3.4 / The essential parameters that need to be determined are the parameters entering the constitutive models described in Section 3.2.
See table. (JJJ-cannot connect with table unless it is the table to be produced) / Alain, Boris,
GC14 / 43/3.4 / Boris’s note: Add a bit on other parameters that are important, like density, void ratio, number of loading cycle…
Provide table. / Alain, Boris,
GC15 / 45/3.5.1 / As indicated in Section 3.1, this parameter is a good proxy to decide of the importance of 2D effects in presence of a basin.
See table. (JJJ-what table?) / Alain, Boris,
GC16 / 45/3.5.1 / This method consists in measuring the ambient noise in continuous mode with velocity meters (not accelerometers) and then computing the ratio between the horizontal and vertical Fourier amplitude spectra (Nakamura, 1989) . Guidelines were produced by the SESAME research programme (SESAME 2004)  to implement this technique, which is now reliable and robust. H/V measurements can provide the fundamental frequency of the studied site under some conditions (but not the associated response amplitude) but can also be used to assess the depth to bedrock and its possible lateral variation when the technique is implemented along profiles. However, in this case, care should be taken when interpreting along the edge of basins, where the bedrock is significantly sloping, because 1-D geometry is assumed in the interpretation of measurements. The knowledge of the soil profile natural frequency is also important to validate the numerical model used for the analyses.
See table. (JJJ-what table?) / Alain, Boris,
GC17 / 45/3.5.1 / What about arrays using ambient noise to get 1D soil profiles?
See table. (JJJ-what table?) / Alain
GC18 / 45/3.5.1 / Measurement of seismic events is recommended with installation of instruments that allow recording, on site or in the vicinity, ground motions induced by real earthquakes. Based on these free-field records, "site to reference" transfer functions can be determined at various locations across the site. The site to reference transfer functions are useful to assess site amplification with respect to the reference and to calibrate the numerical model, at least in the linear range, provided that the “reference” site is characterized.
See table. (JJJ-what table?) / Alain, Boris,
GC19 / 45/3.5.1 / What about installing accelerometers for strong motion recording ?
See table. (JJJ-what table?) / Alain, Boris,
GC20 / 46/3.5.2 / “….interpretation of MASW measurements implicitly assumes that the site is horizontally layered; therefore, they are not accurate for subsurface sloping layers.”
Other techniques, like array measurements or high resolution seismic reflexion, allow to reach higher depths. / Alain
GC21 / 47/3.5.3 / “….retrieving truly undisturbed samples in cohesionless uniform materials is still a challenge. Laboratory tests can be classified in three categories:”
The authors should add that it is physically impossible, in a strict sense, to obtain undisturbed samples in borings because of the undesirable effects resulting from the unloading caused by removal from confinement, and from shipping or handling.
About cohesionless soils, there are no standard, or generally accepted, methods for undisturbed sampling.
Such soils can be recovered by in situ freezing or chemical stabilization to preserve the natural structure. / Alain
GC22 / 49/3.6 /
3.6 CALIBRATION AND VALIDATIONAnd code verification. / Alain / BORIS code verification is described in chapter 9, available software, section 9.4 quality assurance
GC23 / 50/3.6 / “However, validation shall not be overlooked: results should be critically examined since, as indicated previously, those constitutive models are only valid for strains smaller than a given threshold v. If results of analyses indicate larger strains, then the constitutive models should be modified and nonlinear models should be advocated.
More precision about this threshold parameter v and how to measure/calculate it should be given. / Alain
LM24 / 62/5.1.1 / Earthquake Source: the slippage (shear failure) of a fault. Initial slip propagates along the fault and radiates mechanical, earthquake waves. Depending on predominant movement along the failed fault,
There is not an initial slip propagating.
An earthquake is produced by a rapid stress drop in the crustal medium with a consequent release of energy. Part of this energy alows the rupture propagation along the fault plane.
An other part of energy propagates in the crustal medium as elastic waves.
Under a kinematic pov, the seismic source is described as a slip distribution starting from a nucleation point and propagating along the fault plane at a given velocity rupture.
The seismic moment is defined as the product between the crust rigidity, the fault area and the average slip. The moment magnitude is given by log10(M0) = 1.5 Mw +9.1 (if M0 is expressed in Nm)
The source mechanism is described using 3 angles: strike (orientation of the fault plane respect to the north), dip (orientation respect to the vertical) and rake (orientation of the slip). / X / Boris changed – excellent.
LM25 / 62/5.1.1 / Depending on predominant movement along the failed fault, we distinguish (a) dip slip and (b) strike slip sources. Size and amount of slip on fault will release different amounts of energy, and will control the earthquake magnitude.
Maybe you mean the rake ? / X / Changed
LM26 / 62/5.1.1 / “….mechanical waves propagate….”
Should be “elastic” / X / Changed
LM27 / 62/5.1.1 / “Spatial distribution (deep geology) and stiffness of rock will control wave paths, which will affect amplitude of waves that radiate toward the surface.
I would write that the crust is characterised by heterogenous mechanic and rheological properties; such an heterogeneity affect the elastic wave propagations. / X / Changed
LM29 / 62/5.1.1 / Shallow, surface layers Response: seismic body waves propagating from rock and deep soil layers to the surface and interacting with the ground surface create surface seismic waves.
Pay attention, surface waves play an important role in site response, but they are not limited at this framework. When a strong event occurs somewhere on Earth, the teleseimic records are dominated by surface waves and you can include them in the path term.
Here you are specifically writing about the soil effects. This passage deserve a carefully redaction. / Boris, JJJ, Alain / Need to discuss
BORIS Yes, however surface waves are also important at the SSI location, not just for measuring far away earthquakes…
LM30 / 63/5.1.1 / In general, seismic motions at surface and shallow depths consist of (shallow) body waves (P, SH, SV) and surface waves (Rayleigh, Love, etc.). It is possible to analyze SSI effects using a 1D simplification, where a full 3D wave field is replaced with a 1D wave field. It is advisable that effects of this simplification on SSI response be carefully assessed.
Too generic to be informative. / Boris, JJJ, Alain / Need to discuss. Boris added some clarification. Why use term (shallow)?
BORIS: surface as in top few meters and shallow depth can be one wave length in dept (that is where surface waves are ;felt the strongest, about 2 wave lengths, they are gone
LM31 / 63/5.1.1 / A usual assumption about propagation of seismic waves (P and S) is based on Snell’s law about wave refraction.Seismic waves travel from great depth (many kilometers) and as they travel through horizontally layered media (rock and soil layers), where each layer features different wave velocity (stiffness) that decreases toward surface, waves will bend toward vertical (Aki and Richards, 2002). However, even if rock and soil layers are ideally horizontal, and if the earthquake source is very deep, seismic waves will be few degrees off vertical, depending on layering (usually 5-10 degrees off vertical) when they reach the surface.
If the scope of the paragraph is to describe a phenomenon, occurring at hundreds of meters of depth why go back to the crustal scale?
As result, the sentence become confusing. Moreover, the shallow geology can have a predominant role on the surface wave generation.
For a sake of clarity, I suggest: first to introduce the different kind of waves (body and surface) in the Path term. Then in the surface layer term discuss the aspects related to the locale surface waves generation (the site response). / Boris, JJJ, Alain / Need to discuss. JJJ concurs with change.
BORIS changes together wiith previous comment
GC32 / 63/5.1.1 / However, such deviation from vertical will produce surface waves, the presence of which can have practical implications for SSI analysis.
Or generated at valleys/basin edges. / X / Added. / BORIS, changed!
LM33 / 65/5.1.2 / “Prior to the early 1990s, skepticism existed in some quarters as to the wave propagation behavior of seismic waves in the free-field and their spatial variation with depth in the soil.”
This sentence should be supported by citations. / BORIS: resolved with citations / In this time period, there was significant scepticism about near surface variations of motion, especially when implementing deconvolution analyses and the results thereby produced. In addition, there was even scepticism concerning convolution results when taking into account earth berms that were constructed on site. Limitations on reductions of free-field motion at depth was strictly enforced for all site conditions not simply the envelope of the various soil cases analyzed.
LM34 / 65/5.1.2 / “This skepticism arose from several sources; one of which was the lack of recorded data to provide evidence of a general variability of motion with depth in the soil profile due to wave propagation phenomena.
This sentence is unclear and sounds as the author personal pov.
The influence of soil property on seismic waves is analytically described in the elasticity equations.
Moreover during the 1977 san Fernando earthquakes sites effects were observed.
Or I’m misunderstanding the sentence. / X / Modified: “This skepticism arose from several sources; one of which was the lack of recorded data at shallow depths to provide recorded evidence of the variability of motion with depth in the soil profile as predicted by wave propagation theory.”
LM35 / 65/5.1.2 / A non-vertical incident plane wave will created a horizontally propagating(surface) wave at some apparent phase velocity, and will induce ground motion having identical amplitudes but with a shift in phase in the horizontal direction associated with the apparent horizontal propagation velocity of the wave.
Repetition / X / Boris considered this and concluded it was appropriate.
GC36 / 67/5.3 / For example, earthquake records from different geological settings are used to develop GMP equations for specific geologic settings (again, different from those where recordings were made) at locations of interest.
What is it refered to ? Host-to-target ? single station sigma ? This should go to chapter 4. / Boris, JJJ, Alain / Need to discuss
BORIS: well this is a really hot topic, what is sigma, is it properly calculated, are PSHA variables statistically independent…
Will leave it as it is, will add some recent references for sigma, etc…
LM37 / 68/5.3.1 /