Design Parameters

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Design Parameters
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Classification in Design Stage and Assessment of
Design Parameter

• All the efforts of the engineering geological
  investigation steps already performed in previous
  stages of the project are the basis for the
  establishment of geological models and later on
  to the assesment of design criteria.
• The establishment of the geological model has the
  scope to define where and which geotechnical rock
  mass properties to be used as design parameters
  to be applied for the coming design steps.
• The values obtained by site and laboratory
  investigations represent characteristics for the
  special point where they were taken from.

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• The rock mass is affected by a number of impacts
  converting the physical and rock mechanical
  properties to the worst. These may be for
  example
• Weathering
• Volcanic or postvolcanic processes
• Tectonic processes
• Influences of pore- and groundwater
• Slope instabilities
• After collecting all data by desk studies, field
  survey, subsurface investigations, laboratory and
  in situ testing, the geological model and
  geotechnical rock mass properties have to be
  established.

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• The empirical methods help to establish
  geological models by the use of statistical and
  probabilistic analysis of the collected data
  (structural data, data on mechanical properties
  and mineralogical analysis of samples,
  hydrogeological data as well as data on
  seismicity etc.).
• After the collection of the data is finished, an
  evaluation of the different impacts of these
  parameters (as mechanical behavior of
  discontiniuities, pore water pressure, activity
  of fault zones, distribution of swelling
  clayminerals, tectonic stress fields etc.) on the
  concerned project has to be performed.
• The empirical approach with the use of matrices
  for the introduction of the relative importance
  of the individual parameter sets requires an
  appropriate geological model and further on leads
  to the classification of the design stage.

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How to achieve this geological model

• The first step is the evaluation of all
  available investigation results being elaborated
  in the previous working steps, such as
• Desk study reports concerning published papers,
  geological maps, seismicity maps, other
  geological or geotechnical project reports
• Analysis of aerial photos
• Results of detailed geological mapping
• Results of subsurface investigations as trial
  pits and trenches, drill holes, adits etc.
• Results of geophysical studies
• Results of insitu tests
• Hydrogeological studies
• Results of laboratory tests on physical
  properties and mechanical parameter of soil and
  rock samples
• Results of laboratory tests concerning minerology
  and petrography of soil and rock samples
• Results on slope monitoring by survey

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• Next step is the preparation of the
• Geological longitudinal sections and
• Geological cross sections.
• Based on the results of the detailed geological
  mapping, the subsurface investigation results and
  the knowledge on the geological situation.
• The products of this step must give a clear
  information on, which different rock (soil) types
  occur in the project, their physical properties
  and mechanical parameters and locations.

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• Assesment of Design Parameters and
  Classification
• The next step will be converting this knowledge
  into geotechnical terms applicable for the
  assesment of design parameters.
• The emphasis lies on gaining clear understanding
  concerning the geomechanical conditions before
  the design object is implemented,
• -changes that may arise during the excavation and
  construction and
• -the state after the completion of the project

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• Since geological conditions vary from site to
  site an examination of their impacts on the
  project must be done.
• The most advanced way to do this is to set up a
  matrix which highlights the individual geological
  parameters such as
• distribution of discontinuities,
• shape and position of keyblocks,
• mechanical behavior along discontinuities,
• ground or pore water conditions,
• tectonic stresses,
• expected deterioration of rock mass properties
  during excavationdue to minerological conditions
  like swelling etc.

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• For each project the influence of each geology
  related parameter must be rated indivudually as
  it depends on the size of the opening, the
  construction method, the orientation of the
  opening towards discontinuities.
• After the preparation of this matrix the
  geotechnical longitudinal profile has to be
  prepared.
• Parts of the tunnel with similar geotechnical
  behavior are now recognizable in this
  longitudinal profile. Change points and
  classification for the assesment of design
  parameters at the design stage are more clear at
  that point.

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• Selection of Design Zones (Longitudinal
  Section)
• By the selection of design zones, the tunnel is
  divided, along its alignment, in longitudinal
  sections. Within one zone a similar behavior of
  the ground and the structure is expected. In the
  evaluatiion of design zones following steps are
  followed
• - estimate of the size of the influence zone of
  construction
• - evaluation of the dominating construction
  specific parameters (required information!)
• - selection of the design zones

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• In relation to the surface and sub-ground
  condition and with respect to the structural
  layout required information
• topography and overburden
• surface structures
• surface hydrological conditions
• stratification
• classification of soil layers (classification
  parameters, density, stiffness)
• assessment of the groundwater condition (GW flow,
  water pressure distribution, aquifer system)
• Tunnel geometry
• Conditions at the portal zones of the tunnel
• Zones of enlargement of the standard tunnel
  section
• Cross passages
• Connection with ventilation shafts, tunnels or
  similar structural constraints

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• Soil Parameters
• Using the results of field and laboratory
  investigations, soil properties and soil
  parameters are evaluated according to the defined
  design zones and stratification system. This
  includes direct use of factual data and the
  direct assesment on the basis of correlation to
  other soil parameters. A sound local experience
  of the ground and engineering judgement may be
  needed for the verification of the data.

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• Design sections and Design parameters
• The number of design sections will be defined on
  the basis of changes of the surface and subground
  condition and with respect to the structural
  layout.
• Design parameters are design specific soil
  parameters and are determined for the particular
  design section according to the input
  requirements of the calculation method. They
  comprise the following information
• thickness of the individual layer
• unit weight
• Water table and water pressure distribution
• Modulus of the ground
• Poissons ratio
• Shear parameters (friction, cohesion)
• Coefficient of the earth pressure at rest
• Subgrade reaction
• Design section represents an average section, so
  there is no need to assume the lowest value for
  all design data. In general the average soil
  parameters within the respectve design zone and
  the average layering system will be adopted for
  the design.

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• For the definition of different load cases short
  and long term conditions as well as a possible
  range of design parameters must be considered.
  Such as drained or undrained conditions, low and
  high groundwater table.
• For the determination of the shear parameters,
  it will be necessary to consider both, short term
  and long term ground behavior with respect to the
  time of consolidation in relation to stress
  changes.
• The permanent design should be based on the less
  favourable condition. As in most of the soils
  fully undrained conditions will be for a very
  short period only. Undrained shear strength might
  be used for the estimate of the stand up time of
  the unprotected soil face during excavation,
  while the actual temporary support system will be
  determined also by the less favourable condition

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• Design methods and engineering classification of
  rock masses for the design of tunnel supports
• Basically there are four different groups of
  design methods
• Empirical
• Observational
• Analytical
• numerical

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• Rock classifications
• Rock classifications were developed to provide
  the design aids forming only a part of the tunnel
  engineers bag of tools.
• Describing the rock through which a tunnel has
  an importance to choose the support system and
  the excavation method. Different classification
  system are used commonly in practical
  applications.
• In general there are 3 applications
• Geologic, geotechnical descriptions where one or
  several parameters are standardized
• Quantitative descriptions of significant
  parameters of the rock mass which can directly or
  indirectly be used as design support
• Description of the qualitative behavior of the
  rock mass during and after excavation, including
  the influence of the support