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Part  B  -  Minimum  Requirements  on  geological  survey

Part  B  -  Minimum  Requirements  on  geological  survey  with  geophysical ­
  methods
1  General
Geological  survey  is  one  of  the  requirements  for  identifying  ground  types  (sediment  types),
describing  their  characteristics  and  for  assessing  their  suitability  for  construction  work.  It
makes  use  of  modern,  high-performance  geophysical  processes,  the  results  of  which  must  be
verified  based  on  direct  explorations  (drillings).  Due  to  the  lack  of  accessibility  to  the  seabed,
geophysical  processes  are  an  extremely  efficient  method  to  get  a  general  overview  of  the
ground  conditions  in  selected  areas  within  a  short  period  of  time  and  therefore  the  sediment
distribution  and  tectonic  elements  are  detected  in  such  a  manner  which  enables  e.  g.  the  identification ­
  of  areas  with  heterogeneous  or  problematic  ground  conditions.
Geological  exploration  is  the  basis  for  preliminary  and  main  geotechnical  survey  and  investigation ­
  (see  Part  C,  section  2).
Geological  investigations  can  be  divided  into  two  steps:
•  Geological  reconnaisance  should  prove  the  general  suitability  of  an  area  and  also  allow  for
detailed  geological  interpretation  within  an  offshore  construction  site  on  the  basis  of  a  sufficient ­
  number  of  geological  sections.  In  such  cases  the  local  conditions  for  the  components ­
  of  an  offshore  construction  project  should  be  drawn  up  for  all  sites  as  this  ensures
that  unsuitable  local  ground  conditions  are  identified  and  if  necessary,  relocation  or  optimisation ­
  of  individual  sites  is  supported.
Different  regulations  are  illustrated  for  geological  survey  of  offshore  stations  in  Part  B,  section ­
  6.
•  During  inspection  individual  sites  must  be  monitored  after  erection  of  the  structures  with
regard  to  potential  scouring  as  well  as  checking  that  the  minimum  cover  of  submarine
power  cables  is  adhered  to.  In  such  cases  the  use  of  geophysical  methods  such  as  e.  g.
high-performance  sonars  corresponding  to  the  state  of  the  art  should  be  allowed  for  in  order ­
  to  adequately  detect  the  local  influence  of  structures  on  the  seabed.  The  findings  must
be  submitted  in  a  inspection  report  to  the  approval  authority  in  the  prescribed  time  periods
(see  Tables  3  and  4).

2  Quality  assurance
•  The  persons  in  charge  must  be  able  to  prove  that  they  have  sufficient  qualifications  and
proven  experience.  Their  names  must  be  listed  in  the  geological  report.
•  he  data  and  the  assessment  thereof  must  be  correct  and  verifiable.
•  Measurement  protocols  are  to  be  kept;  these  contain  i.  e.  the  external  conditions  during  survey ­
  (e.  g.  wind  and  ocean  conditions,  stratification  of  water  bodies,  algal  bloom),  vessel,
measurement  equipment,  measurement  configurations  and  the  person  in  charge  for  such.
•  Position  and  depth  accuracy  must  conform  to  the  specifications  of  the  International  Hydrographic
  Organisation  (2008)  for  Order  1  a  and  1  b  Surveys.  Detailed  requirements  can  be
seen  in  Tables  3  and  4.
•  The  measurement  conditions  must  adhere  to  the  required  quality  standard  in  all  cases.
Based  on  previous  experiences,  data  quality  is  no  longer  guaranteed  with  a  sea  state  of  5
or  higher.