1 / 28

SITE INVESTIGATION

Soil Investigation: Object of soil investigation for new and existing structures. Depth of<br>exploration for different structures. Spacing of bore Holes. Methods of soil exploration and<br>relative merits and demerits. Types of soil sample. Design features of sampler affecting sample<br>disturbance. Essential features and application of the following types of samplesOpen Drive samples, Stationery piston sampler,. Rotary sampler, Geophysical exploration by<br>seismic and resistivity methods.

Télécharger la présentation

SITE INVESTIGATION

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. TABLE OFCONTENTS • Objectives • Stages in Sub-SurfaceExploration • Extent ofExploration • Methods ofExploration • Samplers • GeophysicalMethods

  2. OBJECTIVES • To classify thesoil • To check the properties ofsoil • To select type and depth offoundation • To check the water level beneath theground • To check the site preferred for “BorrowPits” • To identify the stratification of soil below ground surface • To investigate safety of existingstructures

  3. STAGES INSUB-SURFACE EXPLORATION • Reconnaissance • To know general topography and existence ofdrains • To observe settlement cracks in existingstructure • To observe evidence oflandslides • Location of high floodmarks • To know about drainage pattern and type ofvegetation • PreliminaryExploration • To determine the depth,thickness,extent and composition of each soil stratum at the site. • The depth of the bed rock and the ground water is also determined.

  4. STAGES INSUB-SURFACE EXPLORATION • Detailed exploration • To determine the engineering properties of the soils in different strata. • It includes an extensive boring programme, sampling and testing of sample in a laboratory. • For complex project involving heavy structures such as bridge, dams, multi-storeybuiliding ,it is essential to have detailed exploration. • For small projects ,detailed investigation may not be require.

  5. EXTENT OFEXPLORATION • The Depth of soil exploration is carried out upto “Significant Depth” i.e. where stresses due to the loading are reduced to 20%. Depth of soil exploration dependson: • Type ofstructure • Depth and type offoundation • Height ofembankment • Scour Depth in case of flowingwater • Capillary Rise

  6. EXTENT OFEXPLORATION • Minimum 5 boreholes are required for an area ofabout • 0.4 hectares that can be reduced to 1 in case of compact sites. The spacing of boreholes is kept as following: • 10 to 30 m depending upon subsurfacecondition • 150 to 300 m incase ofhighways • 40 to 80 m in case of concretedams

  7. METHODS OFEXPLORATION • DirectMethods • Trenches and Pits • Drifts andShafts • Boring • AugerBoring • WashBoring • RotaryDrilling • PercussionDrilling • CoreBoring • IndirectMethods • SeismicMethod • ResistivityMethod

  8. METHODS OFEXPLORATION

  9. METHODS OFEXPLORATION

  10. METHODS OFEXPLORATION Rotary Drilling by MAITMachine

  11. METHODS OFEXPLORATION Trenches and pits are excavated at the site to inspect the strata. The size of the pit should be sufficient to provide necessary working space IS 4453-1967 recommend a clear working sapce of 1.2 *1.2 m at the bottom of pit. Trenches and pits are normally preferred in case depth of exploration does not exceed6m. Shallow pits upto a depth of 3m. Drifts and Shafts. Drifts are horizontal tunnels made in the hill side to determine the nature and structure of the geological formation. IS:4453-1980 recommends that a drift Should have the minimum clear dimensions of 1.5 m width and 2.0 m height in hard rock.

  12. METHODS OFEXPLORATION In soft rock an arch roof is more advantages tha a flat roof. Shafts are large size vertical holes made in the geological formation. These may be rectangular or circular in section. The min width of a rectangular shaft is 2.4 m and circular shaft min dia is 2.4 m. Shaft are also used to extend the exploration below the river bed. In other hand Boreholes are meant for exploring the soil where significant depth is more than 6m. In this method the sample of soil which is collected with the help of samplers, is tested inlaboratory

  13. METHODS OFEXPLORATION • Auger Boring preferred for maximum depth of 12m. • Auger boring is not used when there are large cobbles, boulders or other obstructions areencountered. • In wash boring hole is advanced by chopping bit and water jet. • Wash Boring is not preferred in hard soils, rocks or soils containingboulders. • Rotary Drilling make use of cutting bit byrotation • Rotary Drilling is not preferred for soils containing large percentage of gravels as they start rotating along withbit.

  14. METHODS OFEXPLORATION • In Percussion method a heavy chisel is alternately lifted and dropedin a vertical hole. • The material gets pulverised. • Percussion Drilling is preferred where soils consist of rocks orboulders. • Percussion Drilling is also used for constructing Tube Wells. • Core Drilling is preferred to collect the core by rotating the hollow drilling rod.

  15. SAMPLERS Terminology:

  16. SAMPLERS Terminology:

  17. SAMPLERS • Types ofSamples: • Disturbed SoilSample. • Change in stress condition. • Change in water content and void ratio. • Disturbance of the soil structure. • Chemical changes. • Mixing and segregation of soil constituents. • Undisturbed SoilSample • No change in stress condition. • No change in water content and void ratio. • No disturbance of the soil structure. • No change in constituents and Chemical properties.

  18. SAMPLERS • Requirement of GoodSampler: • Considering different types of soil samplers available in the market to collect soil samples while boring, a good sampler should have following properties: • The inside clearance should be 0.5% to3% • Sands, silts, soft clay should have0.5% • Stiff and hard clays below water table should have1.5% • Stiff expansive clays should have3% • The Area Ratio should be less than10% • The Outside Clearance should be less than2%

  19. SAMPLERS • Requirement of GoodSampler: • Maximum Inside diameter should be75mm • Cutting edge angle should be less than20o • The sampler tube should be uniform andsmooth • Recovery Ratio should be 96% -98% • Inside wall should be properly oiled to reduce wall friction

  20. SAMPLERS • Types: • Split Spoon Sampler • Stationery Piston Sampler • Rotary sampler

  21. SAMPLERS • Split Spoon Sampler • It consists of tool-steel driving shoe at the bottom, a steel tube (that is split longitudinally in to halves) in the middle, and a coupling at the top. • The steel tube in the middle has inside and out side diameters of 34.9mm and 50.8mm, respectively. • When the bore hole is advanced to a desired depth, the drilling tools are removed. • The split-spoon sampler is attached to the drilling rod and then lowered to the bottom of the bore hole. The sampler is driven into the soil at the bottom of the bore hole by means of hammer blows.

  22. SAMPLERS • The hammer blows occur at the top of the drilling rod. The hammer weights 623N. For each blow, the hammer drops a distance of 0.762m. • The number of blows required for driving the sampler through three 152.4mm interval is recorded. • The sum of the number of blows required for driving the last two 152.4mm intervals is referred to as the standard penetration number; N. it is also commonly called the blow count. • After driving is completed, the sampler is with drawn and the shoe and coupling are removed. • The soil sample collected inside the split tube is then removed and transferred to the laboratory in small glass jars. Determination of the standard penetration number and collection of split-spoon samples are usually done at 1.5m.

  23. SAMPLERS

  24. SAMPLERS • Stationery PistonSampler • A piston sampler consists of a thin walled tube with a piston inside. • The piston keeps the lower end of the sampling tube closed when the sampler is lowered to the bottom of the hole. • After the sampler has been lowered to desire depth , the piston is prevented from moving downwards by a suitable arrangement , which differs in different types of piston sample. • The thin tube sampler is pushed past the piston to obtain the sample. • The piston remains in close contact with the top of the sample.

  25. SAMPLERS • The presence of the piston prevents rapid squeezing of the soft soil into the tube and reduce the disturbance of the sample. • A vacuum is created on the top of the sample, which helps in retaining the sample. • During the withdrawal of the sampler, the piston provides protection against the water pressure otherwise would have occurred on the top of sample. • Piston sampler are used for getting undisturbed soil sample from soft and sensitive clays.

  26. SAMPLERS PistonSampler

  27. SAMPLERS • Rotary sampler • A Rotary Sampler is a double –walled tube sampler with an inner removable liner. • The outer tube or the rotating barrel is provided with a cutting bit. • The bit cuts an annular ring when the barrel is rotated. • The inner tube which is stationary, slides over the cylindrical sample cut by the outer rotating barrel. The sample is collected in the inner liner. • Rotary samples are useful for sampling in firm to hard cohesive soils and particularly in rocks

  28. GEOPHYSICALMETHODS • Resistivitymethod • Limitations • Valid only for strata having different electricalresistivity • Results are influenced by surface irregularities, wetness ofstrata • Expertise isrequired • Electrical resistivity changes gradually rather abruptly asassumed • SeismicMethod • Limitations • Cannot be used if harder surface overlies softlayer • Cannot be used for areas covered by concrete or asphalticpavement • Cannot be used when surface isfrozen • Requires costlyequipment • Expertise isrequired

More Related