Cong. SS. Sh. and engineering

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Cong. SS. Sh. and engineering

• Organization
• Sandstones and Conglomerates
• Shales and Mudstones
• Both sandstones and shales

2
Engineering properties

• Exploration
• Landslide Hazards
• Excavations
• Foundations
• Underground works
• Material properties

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Exploration

• Hydrological properties
• Physical properties
• Mechanical properties
• Structural geology

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Exploration need to determine

• Physical properties
• geometry
• bedding
• shear zones
• joints
• faults

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tests and observations at the site

• groutability - the ability to pump or inject a
  mixture of grout into the rock an thus make it
  impervious. This is often difficult in
  fine-grained sandstone
• morphology of the sandstone is the assumption of
  equal thickness true or does it thin or thicken
  in some direction

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tests and observations at the site

• degree of cementation related to rock
  durability and permeability
• stability of cementation is the cement soluble
  or reactive
• moisture content -
• poorly cemented/high moisture content
• well cemented/low moisture content

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permeability

• permeability is a property of the rock or soil,
• the ease of which liquids or gas can move through
  the formation
• related cohesion and friction size
• volume of pores and
• degree of openness or connection between pores
  and fractures

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conductivity

• conductivity is a property of rock or soil
  together with a given liquid or gas at a specific
  temperature
• it takes into consideration the viscosity of the
  liquid or gas.

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permeability or conductivity

• Why is this important with respects to
  groutability?

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Question

• ?? expected permeability of sandstone and
  conglomerate?
• ??What physical properties affect permeability?

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Porosity ltgt Permeability

• pores
• size
• number
• unconnected
• open
• cement

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Permeability
cement gt unconnected
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Joints frequency and interconnection
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problems associated with field tests

• orthoquartzite - is often fractured and
  extremely hard
• drill water is lost in fractures need to case
  the hole
• quartz content wears heavy on the drill bit
• loss of diamonds
• frequent drill bit replacement required

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• 2.  miss identification granite is similar to
  arkose sandstone in sandstone dikes fig 4.23

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• 3.  case hardening occurs in dry climates, the
  upper 25 cm is extremely hard
• This results in the misinterpretation of the rock
  hardness and durability

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• 4. cross bedding misinterpretation of the
  orientation of bedding can result in 3d
  projection problems

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Questions

• ?? How are sandstone dikes formed? In what type
  of rocks (metamorphic, sedimentary, igneous) do
  they occur?

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• Clastic dikes form when sediment is partially
  consolidated but under high pressure.
• If a water-laden layer can find a weak spot in
  the overlying layers, it squirts upward.
• Earthquakes are a common trigger.

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slopes

• Sheet joint development in sandstone along cliffs
  
• Compare to exfoliation of granite,
• heaving of shale in excavations,
• popping rock or squeezing ground in tunnels.

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Landslide hazards

• Friction material thus in general risk is
  uncommon
• Exception
• When the beds are underlain by weaker rock
• Slab formation due to sheet jointing and bedding
  planes

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Landslide hazards

• Friction material thus in general risk is
  uncommon
• Exception
• When the beds are underlain by weaker rock
• Slab formation due to sheet jointing and bedding
  planes

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Surface excavations

• rippability the ability to break the rock without
  blasting
• rippability is related to p-wave velocity which
  is related to hardness and durability of the
  rock fast p-waves/strong rock/not rippable vs
  slow p-waves /weak rock/rippable

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Surface excavations

• Blasting can damage the rock, create boulders
  which are difficult to handle

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Surface excavations

• Foundations
• bearing capacity usually good in sandstones and
  conglomerates, compressive strength test
  inversely proportional to moisture content
• friable sandstones - erosion and weathering risk,
  durability is proportional to cement

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Surface excavations

• Foundations
• bearing capacity usually good in sandstones and
  conglomerates, compressive strength test
  inversely proportional to moisture content
• friable sandstones - erosion and weathering risk,
  durability is proportional to cement

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Dam foundations

• All types of dams have been founded on sandstone.
  

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Dam foundations associated problems

• 1. scour erosion by running water
• 2. poorly cemented ss not suitable for concrete
  dams
• 3. uplift pressure due to permeability can cause
  problems
• 4. strength of the ss must be greater than the
  stress applied
• 5. piping can occur due to internal erosion

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Dam foundations associated problems

• 6. bearing capacity vs erodability even if the
  rock is strong enough to support the weight it
  may be very susceptible to scour
• 7. under seepage causes high uplift pressures
  this can be remedied by a grout curtain
• 8. bank storage if the rock is highly permeable
  a great part of the water that fills in the
  reservoir will move into the rock, up to 1/3 to
  total inflow volume for highly permeable
  sandstones

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Dam foundations

• Question
• Which type of dam would be most suitable in an
  area with
• porous, friable un-cemented sandstone and
  siltstone?
• hard sandstone, well-cemented with silica cement?
• calcite cemented sandstone?
• What are the main risks??

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Dam foundations
piping internal erosion due to upward directed
flow lines
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Underground works in sandstone

• problems
• soft rocks
• collapse
• subsidence in overlying material
• water inflow
• making ground caves
• hard rocks
• wear on drill
• silicoses

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Questions

• ??What tunnel problems are associated
• with hard sandstone or conglomerates
• with soft sandstone?
• What measures can be taken?

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Tunnel problems collapse / water inflow

• strength
• joints and joint nature and frequency
• permeability
• variable permeability
• particle composition, variable

• bolting
• pre grout
• shortcret

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Aggregate material / dimension stone

• hardness important
• extremely soft rocks are not suitable as
  aggregates or dimension stone
• Good in general for both concrete and asphalt
  are
• hard / strong / wear resistant /durable /
  resistant to weathering

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Aggregate material / dimension stone

• Good in general for concrete
• free mica content should be low to insure good
  rheology in concrete
• reactive minerals such as flint, gypsum, salt,
  pyrite can cause problems in concrete

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Corrosion of metal and concrete by acid and
sulfate ions
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Aggregate material / dimension stone

• Good in general for asphalt
• quartz rich rocks often do not have an excellent
  grip in asphalt additives make it possible to
  use
• light color desired safety

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Aggregate material / dimension stone

• Good in general for dimension stone
• few fractures and bedding plane discontinuities

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Chapter 4.6 Engineering properties of shales and
mudstones

• Exploration
• Landslide Hazards
• Excavations
• Dams
• Tunnels
• Fills and embankments

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Exploration need to determine

• Physical properties
• geometry
• bedding
• shear zones
• joints
• faults

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Exploration need to determine

• classify
• cemented
• compacted
• expansive
• slaking
• weathering effects
• mylonite
• bentonite
• gassy potential
• conductivity

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Exploration problems

• breakage and deterioration
• core recovery difficult
• field moisture needs to be preserved by bagging
  or coating the cores

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Landslide hazards

• Landslide hazards two types common in
  argillaceous rocks
• 1. cemented shale
• a. glide along bedding planes when the planes dip
  less than the slope, enhanced by the occurrence
  of bentonite layers or mylonite zones (dip lt 5
  degree required)
• b. dislocation common between weathered and non
  weathered zones
• c. topple when bedding is very steep, often in
  more brittle rocks

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Landslide hazards

• Landslide hazards two types common in
  argillaceous rocks
• 2. compacted shale and clay soils slump their
  weight is greater than their strength
• a. slaking a continuous process. Surface
  material slakes and is eroded exposing new fresh
  material. The process is repeated

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Landslide hazards slaking

• Question
• ?? Which glacial sediment has a problem with
  slaking in surface excavations?
• Tills that are rich in silt are notorious for
  slaking. They flow in open cuts, especially when
  there is a high groundwater pressure due to the
  excavation slope.

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Heaving and rebound

• Heaving upward and inward into excavations
• Fig 4.30
• especially common in expansive mudstone, expands
  due to the removal of the confining stress not
  due to swelling with added water
• inward expansion is common in areas with high
  initial horizontal stress

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Dams generally clay and shale are not ideal

• 1. earth-fill or embankment dams several
  successful dams even on expansive compacted shale

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Dams generally clay and shale are not ideal

• 2. concrete dams very difficult
• a. seepage difficult to determine and is
  generally high
• b. hydraulic gradient can be difficult to
  monitor
• c. uplift pressure difficult to control by
  either grouting or drainage holes
• d. location of bentonites and mylonites are
  difficults
• e. faults, joints and other such dislocations
  are difficult to locate
• f.   calcareous shales can give rise to piping
  and solution cavities

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Tunnels

• squeezing ground approximately the same as
  heaving
• a. inward creep of rock
• b. damage of supports
• c. lining broken
• d. depth dependent, occurs at depths, h?1/2
  qu/?, where qu is the compressive strength and ?
  is the weight

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Tunnels

• squeezing ground approximately the same as
  heaving
• e. expansive clays are more likely to squeeze
• f. slaking can also occur
• g. bolting difficult
• h. short creat difficult
• i. lining may be necessary immediately
• j. block fall common in cemented shale along
  joint systems

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Fills and embankment problems

• 1. deterioration of the slopes continuous and
  causes compaction
• a. expansive clay stone shale
• b. highly slaking clay stone shale
• c. weathered clay stone shale
• d. fissil clay stone shale
• 2. slides common due to low shear strength

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Chapter 4.7 Engineering properties of sites with
both sandstone and shale

• Exploration
• Landslide Hazards
• Excavations
• Foundations

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Chapter 4.7 Engineering properties of sites with
both sandstone and shale

• two different types of rocks are more difficult
  and create more problems than does one rock type
  alone

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Exploration

• The combination of rhythmic bedded sandstone and
  shale is common - Flysch

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Exploration different for each rock type

• 1. ground water relation in each rock
• 2. contacts described
• 3. differences in weathering

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Landslides

• block slides Fig. 4.33

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excavation

• 1. blasting causes damage easily
• 2. slides
• 3. payment rock or soil
• 4. classification difficult, rippability etc.

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foundations

• 1. differential settling
• 2. differential expansion
• 3. difficult to predict rock type at depth
  sandstone or shale

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Chapter 4.8Case histories

• Portage Mountain Dam and Powerhouse
• Damage to a housing development by mustone
  expansiion
• Shale foundations in TVA dams
• Foundation in Melange scott dam
• Excavaations in shales for Bogata, Colombia

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Portage mountain dam powerhouse

• peace river, Canada
• embankment dam
• 200 m high
• 2 km long
• underground chamber
• 46m high
• 300 m long
• 27 m wide

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Portage mountain dam powerhouse

• Gething Formation, Cretaceous sandstone and shale
  with coal beds. The coal had burnt naturally and
  still had cavities where there was ash and
  cavities and was still burning
• Moosebar Formation, black shale, highly weathered
  up to 70 m deep
• Dunlevy Formation, thick bedded sandstone

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Portage mountain dam powerhouse

• The dam site selection was finally on the Dunlevy
  Formation and Gething Formation
• The shales did not swell but did slake slightly
• Problems occurred in the underground powerhouse
  deflection of up to 20cm of the roof strata
• This was supported by bolts and grout

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Damage to a housing development by mudstone
expansion Fig 4.35

• Unprecedented wetting of expansive clay inter
  bedded with sandstone resulted in 15 cm heave
• The claystone was impervious but highly
  fractured. Fractures conducted water into the
  rock and thus swelling occurred down to more than
  2.5 m depth
• Remedy drainage, exclude claystone in
  embankments, foundations on beams 10 to 15 m deep

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Shale foundations in Tennessee valley

• lower to middle Paleozoic limestone/dolomite
  sandstone and shale with some metamorphic rocks.
• Dams founded on the shale foundations difficult
• open joints
• mud filled joints
• pyrite rich black shales

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Shale foundations in Tennessee valley

• a. Chickamauga project
• folded limestone with some shale layers and
  bentonite
• Shale layer impervious, protected from
  weathering it did not slake badly

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Shale foundations in Tennessee valley

• b. Watts Bar dam
• Rome formation sandstone, shaley sandstone,
  sandy shale, compacted 1.5 Mpa, limb of an
  anticline
• Clean up to a sound bearing level
• grouting attempted but little grout accepted by
  the rock
• rock had differential strength and settlement
• Remedy steeped foundation so that each of the
  monoliths would be on a Bearing layer

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Shale foundations in Tennessee valley

• c. Fort Loudoun limestone and dolomite with
  some calcareous shales and argillaceous limestone
• uniform bed dip
• bedding plane cavities filled with insoluble
  yellow clay
• recurrant down to 40 feet
• Remedy concrete filled grout trench, cavities
  filled with grout

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Shale foundations in Tennessee valley

• d. South holston dam - folded shales, calcareous
  sandstone and conglumerate
• Few outcrops pre investigations important
• exploration results significant core hole loose,
  either drill wash out or solution cavies,
  numerous slickensides
• Problems
• slip into tunnels resulting in considerable
  overbreak
• strong when unweathered, but weathered rock
  slaked quickly

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Foundation in melange scott dam, eel river
California

• Franciscan melange predominately graywacke and
  shale with sheared serpentine
• construction started on right bank but after
  2/3 complete the proposed stable left bank slid
• Stability is still a question the dam was not
  complete at the time the book was written

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Excavation in shales, Bogata, Columbia, 2600 m
above sea level

• dam and 70 km long conveyance system, sewage and
  power supply
• Rocks intensely folded Paleozoic and Cretaceous
  massive orthoquartzite sandstone interbedded
  siliceous shale and siltstone with bituminous
  black shale overlain by tertiary coal bearing
  sediments. Chemical weathering has softened the
  sandstone in the upper 30 m and the shale has
  changed to a sticky clay soil.
• Landslides common on the steep slopes

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Excavation in shales, Bogata, Columbia, 2600 m
above sea level

• Moved the site several times but landslides
  continued to threaten the construction.
• Attempt to lower the pore pressure in the shale
  difficult due to the low permeability proved to
  be successful.
• Years later leakage was noted from a steel
  pipeline and a slide diagnosed
• The pads of the pipeline were greased and thus
  allowed the slide to slip without damaging the
  structure