4 Exploration need to determine: Physical properties:geometrybeddingshear zonesjointsfaults
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 sandstonemorphology 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 permeabilitystability of cementation – is the cement soluble or reactivemoisture content -poorly cemented/high moisture contentwell 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 formationrelated cohesion and friction sizevolume of pores anddegree of openness or connection between pores and fractures
8 conductivityconductivity 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?
16 problems associated with field tests: orthoquartzite - is often fractured and extremely harddrill water is lost in fractures – need to case the holequartz content wears heavy on the drill bitloss of diamondsfrequent 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” rockSlab 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” rockSlab formation due to sheet jointing and bedding planes
28 Surface excavationsrippability 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 excavationsBlasting 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 contentfriable 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 contentfriable sandstones - erosion and weathering risk, durability is proportional to cement
32 Dam foundationsAll types of dams have been founded on sandstone.
33 Dam foundations – associated problems 1. scour – erosion by running water2. poorly cemented ss not suitable for concrete dams3. uplift pressure due to permeability can cause problems4. strength of the ss must be greater than the stress applied5. 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 scour7. under seepage causes high uplift pressures – this can be remedied by a grout curtain8. 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 withporous, 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 concreteembankment, earth filldifferential settlingwithstandsdeformability abilityvery lowextensive deformationseepage path gradienthigh – greater risk for pipinglow – less risk for pipinguplift pressurenot goodOKpiping – internal erosion due to upward directed flow lines
37 Underground works in sandstone problems:soft rocks:collapsesubsidence in overlying materialwater inflow“making ground caves”hard rockswear on drillsilicoses
38 Questions ??What tunnel problems are associated with hard sandstone or conglomerateswith soft sandstone?What measures can be taken?
39 Tunnel problems – collapse / water inflow strengthjoints and joint nature and frequencypermeabilityvariable permeabilityparticle composition, variableboltingpre groutshortcret
40 Aggregate material / dimension stone hardness importantextremely soft rocks are not suitable as aggregates or dimension stoneGood 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 concretefree mica content should be low to insure good rheology in concretereactive 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 asphaltquartz rich rocks often do not have an excellent grip in asphalt – additives make it possible to uselight color desired – safety
44 Aggregate material / dimension stone Good in general for dimension stonefew fractures and bedding plane discontinuities
45 Chapter 4.6 Engineering properties of shales and mudstones ExplorationLandslide HazardsExcavationsDamsTunnelsFills and embankments
46 Exploration need to determine: Physical properties:geometrybeddingshear zonesjointsfaults
47 Exploration need to determine: classifycementedcompactedexpansiveslakingweathering effectsmylonitebentonitegassy potentialconductivity
48 Exploration problems: breakage and deteriorationcore recovery difficultfield moisture needs to be preserved by bagging or coating the cores
49 Landslide hazards:Landslide hazards – two types common in argillaceous rocks1. 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 zonesc. topple when bedding is very steep, often in more brittle rocks
51 Landslide hazards:Landslide hazards – two types common in argillaceous rocks2. compacted shale and clay soils – slump; their weight is greater than their strengtha. 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 4.30especially common in expansive mudstone, expands due to the removal of the confining stress not due to swelling with added waterinward 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 difficulta. seepage difficult to determine – and is generally highb. hydraulic gradient – can be difficult to monitorc. uplift pressure difficult to control by either grouting or drainage holesd. location of bentonites and mylonites are difficultse. faults, joints and other such dislocations are difficult to locatef. calcareous shales can give rise to piping and solution cavities
56 Tunnels squeezing ground approximately the same as heaving a. inward creep of rockb. damage of supportsc. lining brokend. depth dependent, occurs at depths, h1/2 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 squeezef. slaking can also occurg. bolting difficulth. short creat difficulti. lining may be necessary immediatelyj. block fall common in cemented shale along joint systems
58 Fills and embankment problems 1. deterioration of the slopes continuous and causes compactiona. expansive clay stone & shaleb. highly slaking clay stone & shalec. weathered clay stone & shaled. fissil clay stone & shale2. slides common due to low shear strength
59 Exploration Landslide Hazards Excavations Foundations Chapter 4.7 Engineering properties of sites with both sandstone and shaleExplorationLandslide HazardsExcavationsFoundations
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 ExplorationThe combination of rhythmic bedded sandstone and shale is common - Flysch
62 Exploration different for each rock type 1. ground water relation in each rock2. contacts described3. differences in weathering
64 excavation 1. blasting causes damage easily 2. slides 3. payment – rock or soil4. 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 PowerhouseDamage to a housing development by mustone expansiionShale foundations in TVA damsFoundation in Melange – scott damExcavaations in shales for Bogata, Colombia
67 Portage mountain dam & powerhouse peace river, Canadaembankment dam200 m high2 km longunderground chamber46m high300 m long27 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 burningMoosebar Formation, black shale, highly weathered up to 70 m deepDunlevy Formation, thick bedded sandstone
69 Portage mountain dam & powerhouse The dam site selection was finally on the Dunlevy Formation and Gething FormationThe shales did not swell but did slake slightlyProblems occurred in the underground powerhouse – deflection of up to 20cm of the roof strataThis 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 heaveThe claystone was impervious but highly fractured. Fractures conducted water into the rock and thus swelling occurred down to more than 2.5 m depthRemedy – 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 difficultopen jointsmud filled jointspyrite rich black shales
72 Shale foundations in Tennessee valley a. Chickamauga projectfolded limestone with some shale layers and bentoniteShale layer – impervious, protected from weathering it did not slake badly
73 Shale foundations in Tennessee valley b. Watts Bar damRome formation – sandstone, shaley sandstone, sandy shale, compacted 1.5 Mpa, limb of an anticlineClean up to a sound bearing levelgrouting attempted but little grout accepted by the rockrock had differential strength and settlementRemedy – 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 limestoneuniform bed dipbedding plane cavities filled with insoluble yellow clayrecurrant down to 40 feetRemedy – concrete filled grout trench, cavities filled with grout
75 Shale foundations in Tennessee valley d. South holston dam - folded shales, calcareous sandstone and conglumerateFew outcrops – pre investigations importantexploration results: significant core hole loose, either drill wash out or solution cavies, numerous slickensidesProblemsslip into tunnels resulting in considerable overbreakstrong when unweathered, but weathered rock slaked quickly
76 Foundation in melange – scott dam, eel river California Franciscan melange predominately graywacke and shale with sheared serpentineconstruction started on right bank – but after 2/3 complete the proposed stable left bank slidStability 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 supplyRocks – 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 diagnosedThe pads of the pipeline were greased and thus allowed the slide to slip without damaging the structure