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Cong. SS. Sh. and engineering

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1 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

3 Exploration Hydrological properties Physical properties
Mechanical properties Structural geology

4 Exploration need to determine:
Physical properties: geometry bedding shear zones joints faults

5 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

6 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

7 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

8 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.

9 permeability or conductivity
Why is this important with respects to groutability?

10 Question ?? expected permeability of sandstone and conglomerate?
??What physical properties affect permeability?

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12 Porosity <> Permeability
pores size number unconnected open cement

13 cement > unconnected
Permeability cement > unconnected

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15 Joints frequency and interconnection

16 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

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

18 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

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

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

21 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.

22 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.

23 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

24 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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28 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

29 Surface excavations Blasting can damage the rock, create boulders which are difficult to handle

30 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

31 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

32 Dam foundations All types of dams have been founded on sandstone.

33 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

34 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

35 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??

36 Dam foundations concrete embankment, earth fill differential settling
concrete embankment, earth fill differential settling withstands deformability ability very low extensive deformation seepage path gradient high – greater risk for piping low – less risk for piping uplift pressure not good OK piping – internal erosion due to upward directed flow lines

37 Underground works in sandstone
problems: soft rocks: collapse subsidence in overlying material water inflow “making ground caves” hard rocks wear on drill silicoses

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

39 Tunnel problems – collapse / water inflow
strength joints and joint nature and frequency permeability variable permeability particle composition, variable bolting pre grout shortcret

40 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

41 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

42 Corrosion of metal and concrete by acid and sulfate ions

43 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

44 Aggregate material / dimension stone
Good in general for dimension stone few fractures and bedding plane discontinuities

45 Chapter 4.6 Engineering properties of shales and mudstones
Exploration Landslide Hazards Excavations Dams Tunnels Fills and embankments

46 Exploration need to determine:
Physical properties: geometry bedding shear zones joints faults

47 Exploration need to determine:
classify cemented compacted expansive slaking weathering effects mylonite bentonite gassy potential conductivity

48 Exploration problems:
breakage and deterioration core recovery difficult field moisture needs to be preserved by bagging or coating the cores

49 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 < 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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51 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

52 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.

53 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

54 Dams – generally clay and shale are not ideal
1. earth-fill or embankment dams – several successful dams even on expansive compacted shale

55 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

56 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

57 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

58 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

59 Exploration Landslide Hazards Excavations Foundations
Chapter 4.7 Engineering properties of sites with both sandstone and shale Exploration Landslide Hazards Excavations Foundations

60 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

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

62 Exploration different for each rock type
1. ground water relation in each rock 2. contacts described 3. differences in weathering

63 Landslides block slides Fig. 4.33

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

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

66 Chapter 4.8 Case 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

67 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

68 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

69 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

70 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

71 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

72 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

73 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

74 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

75 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

76 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

77 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

78 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


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