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SITE

SITE. EXPLORATION. Contents. INTRODUCTION METHODS OF SITE EXPLORATION CHOICE OF EXPLORATION METHOD. INTRODUCTION.

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SITE

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  1. SITE EXPLORATION

  2. Contents • INTRODUCTION • METHODS OF SITE EXPLORATION • CHOICE OF EXPLORATION METHOD

  3. INTRODUCTION • The Object of the site exploration is to provide reliable, specific and detailed information about the soil and ground water conditions of the site which may be required for a safe and economic design of foundation.

  4. METHODS OF SITE EXPLORATION The various methods of site exploration may be grouped as follows :- • Open excavations • Boring • Sub-surface sounding • Geo-physical methods.

  5. Open Excavations • Trial pits are the cheapest method of exploration in shallow deposits. • This method is use for all type of soils. • The big advantage of this method is the soil strata can be inspected in their natural condition and samples can be conveniently taken. • The cost of open excavation increases rapidly with depth. • The method is generally considered for shallow depths, say upto 3m. • Through this method we take disturbed sample.

  6. Methods of Boring:- The following are the various boring methods commonly used : • Auger Borings • Auger and shell boring • Wash boring • Percussion boring • Rotary boring

  7. Auger Borings: • Simplest method of exploration and sampling. • Auger are used in cohesive and other soft soils above water table. • This method is operated manually or mechanically. • Hand auger are used upto a 6 metre depth. • Hollow stem augers used for sampling or conducting Standard Penetration Tests.

  8. Hand operated augers Power driven augers

  9. a a b c d a. Continuous Flight Auger b. Hallow-stem auger plugged during advancing bore c. Plug removed and sampler inserted d. Truck mounted auger boring machine Mechanical Auger

  10. Auger and shell boring: • This method is use for deep borings. • Hand operated rings are used for depths upto 25m and mechanised ring up to 50m. • Shells are use for very stiff and hard clays, and send pumps for sandy soils. • Small boulders, thin soft strata or rock or cemented gravel can be broken by chisel bits attached to drill rods.

  11. shells Auger and shell boring

  12. Wash Boring: • Water with high pressure pumped through hallow boring rods is released from narrow holes in a chisel attach to the lower end of the rods. • The soil is loosened and broken by the water jet and the up-down moment of the chisel. • The soil particles are carried in suspension to the surface between the rock and the borehole sites. • The rods are raised and drop for chopping action of the chisel by means of winch. • Wash boring can be used in most type of soil but the progress is slow in coarse gravel strata.

  13. Schematic for wash boring

  14. Rotary Boring: • Rotary boring is a very fast method in all boring. • This process is also known as mud rotary drilling. • The drilling tool, (cutting bit or a coring bit) is attached to the lower. • The coring bit is fixed to the lower end of a core. • Water or drilling fluid is pumped down the hollow rods and passes under pressure through narrow holes. • There are two forms of rotary drilling, open-hole drilling and core drilling. • Open- hole drilling, which is generally used in soils and weak rock.

  15. Rotary Drilling rig

  16. GEOPHYSICAL METHODS1) Seismic Refraction Method: • Seismic waves have different velocities in different typesofsoil. • Waves are generated either by explosives, or striking a metal plate with a hammer (geophone & seismograph ). • Two types of stress waves: • P Waves : plane waves • 200 m/s in sands to 2500 m/s in clays • S Waves : shear waves

  17. Seismic Refraction Method - • • Principle: • Longitudinal waves travel in straight lines in a medium of constant density. • Waves are reflected when they come in contact with soil strata of different density. • Determine seismic velocities & compare with known values.

  18. 2) Electrical Resistivity Method: • Differences in electrical resistance of different soil types. • Method • * Place 4 electrodes with equal spacing ‘A’. • * Apply a direct current to outer electrodes ‘I’. • * Measure potential drop in inner electrode.

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