Cong. SS. Sh. and engineering

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

4. 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 • morphologyof the sandstone; is the assumption of equal thickness true or does it thin or thicken in some direction

5. 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

6. 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

7. 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.

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

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

11. Porosity <> Permeability • pores • size • number • unconnected • open • cement

12. Permeability cement > unconnected

14. Joints frequency and interconnection

15. 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

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

17. 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

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

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

20. 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.

21. 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.

22. 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

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

27. 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

28. Surface excavations • Blasting can damage the rock, create boulders which are difficult to handle

29. 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

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

32. 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

33. 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

34. 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??

35. 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 Dam foundations piping – internal erosion due to upward directed flow lines

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

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

38. 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

39. 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

40. Corrosion of metal and concrete by acid and sulfate ions

41. 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

42. Aggregate material / dimension stone Good in general for dimension stone • few fractures and bedding plane discontinuities

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

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

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

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

47. 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

49. 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

50. 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.