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ch 5 Soluble rocks

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Information about ch 5 Soluble rocks
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Published on January 14, 2008

Author: Biaggia

Source: authorstream.com

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Chapter 5 Soluble rocks:  Chapter 5 Soluble rocks Solubility – threatens water storage and water conveyance projects with sever problems involving potential leakage and ground collapse Question: :  Question: What is the most common soluble rock type? Question: :  Question: What are the 3 groups or classes of limestone? The divisions are based on their mode of formation? Biochemical Chemical Detrital Biochemical limestone:  Biochemical limestone Rocks formed from living organisms – shells of microscopic planktonic foraminifera and plates of calcareous algae Slide12:  Beige limestone with rounded intraclasts and fossils (gastropods, corals) Biochemical limestone:  Biochemical limestone Bedded and jointed Hardness 3 to 4, mineral calcite and dolomite Chert horizons hardness 6 - silica Chert concretion from Boom Clay Belgium:  Chert concretion from Boom Clay Belgium Chert:  Chert Chalk:  Chalk one unusual example of biochemical limestone is chalk – compacted but not lithified Chalk:  Chalk white friable and very porous shells of microscopic planktonic foraminifera and calcareous algae Chalk:  Chalk massive uniform layers or very thick beds separated by shale partings not typical to be jointed as is most limestone Horizons of chert concretions common Chalk:  Chalk Chalk:  Chalk Other names dependent upon content of clay and chalk Chalk > 95% CaCO3 Clay Chalk >5%<13% clay Clay Marl >13%<25% clay Calcareous mudstone >25%clay Chemical limestone:  Chemical limestone Precipitate of calcite CaCO3 (uncommon), occurs in warm CaCO3 rich seas oolites. Oolites:  Oolites Concentric radial structure 1. Precipitation of CaCo3 :  1. Precipitation of CaCo3 sea water is almost saturated in CaCO2 – decrease in the content of CO2 by warming or by the action of plants in shallow water can cause calcium carbonate to precipitate 2. Precipitation of CaCo3 :  2. Precipitation of CaCo3 rivers saturated in CaCO2 precipitate it when they enter saline environments, called travertine 3. Precipitation of CaCo3 :  3. Precipitation of CaCo3 groundwater saturated in CaCO3 precipitates it when the groundwater emerges into the atmosphere, springs called tufa brick in a church 4. Precipitation of CaCo3 :  4. Precipitation of CaCo3 evaporation in arid and semiarid regions leads to the precipitation of CaCO3 called caliche Detrital limestone :  Detrital limestone particles of CaCO3 cemented together, very porous Names are dependent upon the size and nature of the particles clay – calcilutite sand – calcarenite gravel – calcirudite shell fragments – coquina or shell-hash limestone calclutite:  calclutite calcarenite:  calcarenite sand size grains of CaCO3 calcirudite:  calcirudite Question::  Question: Compare the strength of calcarenite with orthoquartzite with respect to their particles, and cement. What is the expected difference in porosity? Dolostone or Dolomite:  Dolostone or Dolomite recrystallized limestone which contains Mg composed 90% of the mineral dolomite, less soluble than calcite composition changes after deposition – type of chemical re crystallization Dolostone or Dolomite:  Dolostone or Dolomite dolomitization is not always uniform Dolostone or Dolomite:  Dolostone or Dolomite Fractures in the dolostone bedrock  conduct groundwater Dolostone or Dolomite:  Dolostone or Dolomite Mountain range called dolomites Marble:  Marble What type of rock is it? Marble – metamorphic rock formed from limestone – complete recrystallization Evaporate rocks:  Evaporate rocks Gypsum CaSO4 2H2O Anhydrite CaSO4 Halite NaCl Evaporate rocks:  Evaporate rocks Gypsum CaSO4 2H2O Anhydrite CaSO4 Halite NaCl Evaporate rocks:  Evaporate rocks Gypsum CaSO4 2H2O Anhydrite CaSO4 Halite NaCl Gypsum:  Gypsum massive or bedded associated with rock salt, shale, dolomite and limestone bituminous material common often intensely folded and brecciated – due to its formation: Anhydrite + hydration results in Gypsum and EXPANSION and deformation highly soluble – 170 times more soluble than calcite but only 1% that of NaCl lacks strength for caverns to form Anhydrite :  Anhydrite stable form of CaSO4 above 43 degrees stable at any temperature when there is no H2O present Hydration – volume expansion of 35% Hydration depth is less than 150 m (fig 5.9) Hydration changes the anhydrite to Gypsum 3.5 Mpa pressure due to hydration Halite or Rock Salt :  Halite or Rock Salt massive beds with inclusions of brine salt dome formation – diapirs Fig. 5.8 – intrusions of salt into overlying rocks salt domes – up to 3 km diameter steep and vertical joints impermeable – trap for oil cap rock deformed source as much as 5 km deep salt diapirs that pierce the ground become salt glaciers salt dome:  salt dome Salt glacier:  Salt glacier Solution processes and effects:  Solution processes and effects Common in limestone, dolostone and marble Stages of Karstification:  Stages of Karstification Youth Maturity Old age Stages of Karstification:  Stages of Karstification Youth Maturity Old age Two kinds of subsidence:  Two kinds of subsidence dissolved slow subsidence sinkholes densification of sediments collapsed – p166 fig 5.17, 5.16 loss of support triggered by: lowered groundwater level heavy rain storms – wash out of sediments vibrations increased infiltration Two kinds of subsidence:  Two kinds of subsidence dissolved slow subsidence sinkholes densification of sediments collapsed – p166 fig 5.17, 5.16 loss of support triggered by: lowered groundwater level heavy rain storms – wash out of sediments vibrations increased infiltration Geologic Controls on the Formation of Karst:  Geologic Controls on the Formation of Karst Cavities occur in almost all soluble rocks – but their size and shape is dependent upon the composition, texture, and structure of the rock, its strength and its geological history Residual Soils :  Residual Soils limstone gives terra rosa a soil red due to the high content of hematite and limonite, FeO; clay rich and fissured thus well drained Residual Soils :  Residual Soils dolominte gives a soil called wad rich in magnesium rich minerals such as clorite and montmorillonite are highly compressible and swelling Natural water content of more than 200% (greater than bentonite) Volcanic tuff - montmorillonite :  Volcanic tuff - montmorillonite Engineering properties:  Engineering properties Case study Vajont slide in Italy Engineering properties:  Engineering properties Exploration targets and problems:  Exploration targets and problems subsurface cavities and sinkhole areas location determination of the surface of the solid rock below the residual soil, top of rock (SAME for Sweden) location of highly soluble layers gypsum – drilling to determine occurrence anhydrate – gypsum contact Water supply :  Water supply water plentiful but the system is very sensitive to pollution water will result in CaCO3 deposits on pipes Rock salt:  Rock salt impermeable – proposed site for deposit of burnt atomic fuel Foundation :  Foundation karsts – each bearing point must be studied cavities – collapse potential must be studied – drill plan dependent upon the risk pinnacle rock top § differential settling § differential support § pinnacles undermined § piles - glide off pinnacle Foundation :  Foundation gypsum and water leads to settling, collapse and solution anydydrate leads to heaving calcarenite and chalk have limited bearing capacity weathered products extremely compressable Dams and Reservoirs:  Dams and Reservoirs All the same problems as mentioned for Foundations above Dams and Reservoirs:  Dams and Reservoirs IMPOUNDMENT of WATER not obvious no lake may form if water flows through the ground dissolve new channels washout of old channels dissolution of gypsum and salt foundation stability endangered by clay seams high pore pressures can occur if the foundation is located on an upwardly discharging spring Tunneling :  Tunneling limestone relatively strong – caverns with considerable size can form naturally in them karsts – are a problem – collapse and sudden inflow of water Tunneling:  Tunneling evaporate rocks salt · massive - good, bedded – poor · easily dissolved · organic materials common – risk for explosions · oils and gas outbursts gypsum · fractured · disturbed bedding and voids · squeeze common · dissolvable Tunneling:  Tunneling chalk, calcarentites, and cacirudites weak – requires additional supports due to collapse risk >15 Mpa >300 m plastic ductile deformation <300 m elastic brittle deformation Materials of construction :  Materials of construction Aggregates: limestone and dolomite – good in both asphalt and concrete given a reasonable strength they give good particle shape good particle size distribution NOTE – strength in asphalt is not sufficient for cold climates where studded tires are used >15% argillite not good Materials of construction :  Materials of construction Aggregates: chert – reactive in concrete and fractures in extreme cold gypsum is a SO4 – not allowed in concrete!! too weak for asphalt Materials of construction :  Materials of construction Dimention stone limestone, dolomite and marble are all very common – not always good on exteriors (warping) Case Study :  Case Study Failures and Near Misses from surface Collapse over Cavities Sinkholes associated with lowered ground water table West Driefontein mine – south African mine :  West Driefontein mine – south African mine increased rate of ground-water with drawl caused the main surface stream to go dry cavern had developed 117m deep boring in residual soils grouted in 171 holes, 9-15 m deep surface paved to prevent infiltration around the plant 60 m in all directions the entire crushing plant disappeared into a sinkhole – with 29 people – never found the hole was 55 m in diameter and more than 30 m deep South Africa train 1975 – near the Driefontein mine:  South Africa train 1975 – near the Driefontein mine ground water lowered in the Dolomite railroad was closed for passenger trains over a year during which remedial measurements were taken 8 days after the rout was re opened a sinkhole formed the train driver could not stop the train in time 3 coached derailed – 2 left hanging over the sinkhole Failure of the Tarpon Strings Bridge – Florida :  Failure of the Tarpon Strings Bridge – Florida 1969 – 3 foundation units were swallowed into a sinkhole the railroad traffic did not stop in time – one person was killed Palermo airport, Sicily :  Palermo airport, Sicily cavity of 12,000 m3 volume 2 m below the pavement cavity extended over the entire width of the runway just at the place where aircraft touch down cavity was plugged with concrete through holes drilled from the pavement Kentucky Dam :  Kentucky Dam 10 potential sites studied bedrock was flat lying limestone – overlain by 30m of tertiary sediments – overlain by cherty residual soil karsts in the limestone weathered down 95 m (Fig. 5.23) solution more intense at changes in bedding orientation due to the higher frequency of joints Kentucky Dam :  Kentucky Dam both dam abutments were situated on thick sequences of soils and alluvium bedrock had numerous caves 65 m deep and 18 m wide most partially filled with residual clay solution cavities were very continuous laterally along certain beds with unstable minerals Kentucky Dam :  Kentucky Dam solved drillings were made so miners could go down and clean the cavities of clay and soil the cavities were filled with grout material this formed an underground cutoff 50 km of diamond core holes 2.3 km of calyx holes 20,000 m3 grout Great falls dam :  Great falls dam horseshoe formed river leakage through the divide of 10 % the capacity leakage increase by 1% per year the lake level was lowered and 96 inlets were detected trace elements were used to trace the flow these were then grouted and leakage cut off UCSC :  UCSC Karstic limestone where an Olympic size swimming pool was to be constructed Relocated to miss karts filled with silt – Since this is an earthquake area, near the San Andreas Fault Zone, liquefaction would be probable over silt new location in a collapsed dolline the base was filled, lined and under the liner a collector for leakage water installed Grout Curtain at El Cajon Dam :  Grout Curtain at El Cajon Dam thin arch dam 238 m high to be built in karstic area overlain with volcanics and 4 major faults in the area drillings revealed caves 200 m lateral extent grout curtain made in form of a bathtub 514 km of drillings 14 km galleries grout curtain area 530 000 m2 2 ½ years to complete 10,000 m3 cave detected during exploration resulted in the relocation of the bathtub grout curtain New Mexico Mc Millan reservoir 1893 :  New Mexico Mc Millan reservoir 1893 gypsum beneath the reservoir abutment soon after filling the cliff began to crack and collapse 1909 embankment built parallel with the cliff to cut off the contact with the water 12 m subsidence 1942 underground caves and chanels 60 million m3 Oklahoma 1965 – 11 m high dam:  Oklahoma 1965 – 11 m high dam soon after construction a sinkhole formed volume of 2 000 m3 under the spillway Pollution in karst – Australia – Mount Gambier, :  Pollution in karst – Australia – Mount Gambier, town with 20 000 inhabitants located on limestone The karstic limestone aquifer overlies a clay bed which is impermeable (aquiclude) which in turn overlays a delta mollase aquiclude The upper aquifer is polluted with waste from industry and sewage The lower aquifer is the source of ground water Pollution in karst – Australia – Mount Gambier, :  Pollution in karst – Australia – Mount Gambier, the state of leakage between the two aquifers is threatened if the amount of ground water pumped out of the lower aquifer exceeds the infiltration there is a risk that the direction of leakage through the aquiclude will change so leakage will be from the upper polluted aquifer down to the confined aquifer today the lower aquifer is artesian and under high pressure but if the pressure gradient is lowered this will change

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