1644
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
Corner period for response spectra for this sites can be Tc=1
s or 0,7s (Fig. 2).
Figure 3 Normalized spectrum for acceleration’s elastic response
according to P100-2006
From 2012 in Romania is proposed another design code
named “
Cod de proiectare seismică – Partea 1, Prevederi de
proiectare pentru cladiri P100/1-2012
”. Main difference is that
it design value of seismic force for is defined for 225 years
average recurrence interval (probability of exceeding 20% in 50
years).
As in can be seen in Fig. 4 seismic hazard is described
through peak grouns acceleration
a
g
determined for average
recurrence interval IMR=225 years for ultimate limite state a
g
=
0,30 g ÷ 0,20 g, where g=9,81m/s
2
, a
g
=2,943 ÷ 1,962 m/s
2
.
Figure 4 Peak ground acceleration according to P100-2012.
From natural frequencies point of view (Fig. 7) it can be seen
that almost every type o wind turbine (with steel or concrete
tower) has natural period over 3,2 s, even if the soil is stiff,
average or soft.
Figure 5 Corner period according to P100-2012.
Regarding corner period (Fig. 6) the same zones will be
used.
Main differences are at T
B
=0,2T
C
, so that T
B
=0,2 s.
Figure 6 Normalized spectrum for acceleration’s elastic response
according to P100-2012.
Figure 7 Natural periods for WT (Gifford – Concrete towers for
Onshore and Offshore wind farms)
2 GEOTECHNICAL INVESTIGATIONS
Geotechnical studies show the followings three major types
of lithology:
1. Rocks layer from the top - green schists are at the
surface of terrain (0 – 4m deep)
2. Rocks layer is situated between 4m deep to 15m and
over it is a leossoidal layer.
3. Rocks layer is deeper than 15m.
Geotechnical investigation were made respecting national
standard NP 074/2007. Drillings were made, corresponding to
each wind turbine location during November 2011 to march
2012 using WIRTH HD 10S and L100 machines.
First general conclusion of this studies is that a layer of about
25m of dusty sandy clays saturated with low consistency thin
intercalations non-cohesive nature is on each site. This is also
confirmed in geoelectrical studies.
Figure 8 Geoelectrical section through P45.
It is confirmed that resistivities for the first 22m of soil is very
low between 1.5 ÷ 5.5 ohm
x
m. From 22m depth resistivities are
increasing to values between 25 ÷ 40 ohm
x
m which suggest
cohesive lithological formations with better consistency.
For low consistency clays were made also dynamic tests in
cyclic triaxial compressive machine and in resonant column.
Compression tests were performed in edometer in order to
obtain edometric modulus and unit deformation. The maximum
vertical effort of 300kPa was applied to identify stress - strain
relationship in compression area (charge) / decompression. In
terms of compressibility characteristics of site materials fall into
