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St. Francis Dam, Ca. 1926.EngineeringGeology

Concrete gravity dam constructed in 1926 inCalifornia collapsed 1928

Rock was Schists and soft argillaceous conglomerateseparated by a distinct fault

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Other dam failures

Engineering GeologyIntelligent and useful application of geologicalknowled e to different branches of en ineerinconstitutes the subject matter ofENGINEERINGGEOLOGY

Includes- Geological studies in the fieldand laboratory, Safety and economic

p ann ng an execu on. s s anextensive field where the science of theearth and the art of engineering mergeinto each other

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Condition required to successof dam.

Water tight reservoir basin

Low rate of accumulation of silt

A narrow river channel

Safe foundation

Provision for disposal of surplus waterthrough suitable gateway

Availability of the required material forconstruction nearby

Geology of dam sites and reservoir

Reservoir may fail due to excessiveleakage or as a result of rapidaccumulation of silt.

Some rocks are porous and pervious and

.Unconsolidated or partially consolidatedcourse sandstones are highly porous andpermeable.

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Geology of dam sites and reservoircontd

Massive igneous or metamorphic rocks.

contain well developed joints and otherweakness planes, shear zones, faults

the nature and position of water table

and also the nature and structure of therocks forming the region

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Geology of Bridge structure

A railway bridge is being constructed at a height of 186m from bed level,

between chainages 38.430 Km on left abutment to Katra side and chainage

39.087 Km on right abutment to Reasi side.

Chainage :38.430 Chainage :38.510

P1

River is flowing SW

O = Center point of

Katra Side

Steel arch

O

Viaduct span

Viaduct spans

Chainage :39.087

Chainage :38.775

(P10)

River

bridge

Lat 31o0445

Long 74o5452

Viaduct towards katra = 80 mSteel arch span = 265 mViaduct towards Reasi = 312 mTotal length of bridge80 + 265 +312 = 657 m

E

N

Reasi Side

Reasi sideKatra side

740

760

780

800

Figure showing left abutment at Katra

side with foundation locations of P1b and P1.

-50

0

5038.46

38.4838.5

38.5238.54

660

680

700

720

Figure showing right abutment on Reasi

side with foundation locations of P10 to P21View of left and right abuttment

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Sound rock profile underneath the floor

Geology of Bridge structure

and walls of natural depression

Foundation and abutment should bestrong

Geolo ical structure of the countr rockshouldnt create any stability problem

Erosional action of the fast runningwater should be significant

Geology of Bridge structure

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Geology of tunnel site

Governing Geological factors

The nature of the country rock alongthe ali nment of the tunnel

The geological structure of the region

Position of the water table andprevailing ground water table

condition along the length of thetunnel

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Tunneling in rocks

depends upon the nature of rock. Hardcrystalline rocks are very good but verydifficult to excavate

Moreover they may also contain planes ofweakness. Proper profiling is difficult.

Consolidated massive sandstones aregood but softer ones need some linings

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Lining should varypoint to point

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Nature of rock, orientation and spacing ofdiscontinuity, orientation of bedding planes with

respect to the alignment

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Overbreak

overbreak than hard rock with welldefined and closely spaced discontinuityplanes

In sedimentary rock more over breakoccurs along the strike than the dip

Too much overbreak increases the costof tunnelling

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Stability of Hill slopes

The nature of the rocks occurring alongthe slope or cutting wall

The geological structure of the countryrock

The prevailing ground water conditions

along the slope or cutting wall

Stability of Hill slopes

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Different kinds of U/gwater- a) soil water b)

pellicular water in fracturedrock, c) pellicular water in

sedimentary rocks d)Vadose water p) perchedwater WT-Water table E)

Ground water e) Free

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Building stonesStrength and durability mineralcom osition texture and structure

Colour and beauty

Cost

,mica are st carbonate rocks marble,limestone are relatively weak and wornout easily rong and durable where as

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Building material(aggregates)road metals

durable and there shouldnt betendency to react with cement

For good road metals a) hard b) toughc) resistant to abrasion d) high

cementing value