HOW TO DO STANDARD PENETRATION TEST (SPT) OF SOIL ON SITE?

Target

To enter standard to obtain penetration resistance (n-value) with depth at a given location.

tools and equipment

  • Tripod (to give an apparent height of about 4 meters; one of the legs of the tripod should have a ladder to allow the person to reach the head of the tripod.)
  • tripod head with hook
  • winch
  • guide pipe assembly
  • Standard Divided Spoon Sampler
  • A drill rod for mounting the test to a deeper depth
  • Heavy Duty Post Hole Auger (100mm to 150mm Dia)
  • heavy duty helical auger
  • heavy duty auger extension rods
  • sand baler
  • Rope (about 15 meters long and strong enough to repeatedly lift 63.5 kg)
  • A light duty rope for operating the sand baler
  • chain pulley block
  • casing pipe
  • Casing Couplings
  • cover clamp
  • measuring tape
  • a straight edge (50 cm)
  • tool box
Standard Penetration Test Setup
Standard Penetration Test Setup

Process

  1. Identify the location of the test in the field
  2. Stand the tripod so that the top of the tripod head is centered on the test site. This can be ensured by passing a rope over a winch attached to the tripod head and letting the free end of the rope come down and adjusting the tripod legs such that the end of the rope is at the test site. When erecting and adjusting the tripod legs, care should be taken that the load is evenly distributed on all three legs. This can be achieved by ensuring that the lines joining the tips of the tripod legs to the ground form an equilateral triangle. In addition, it should be ensured that the three legs of the tripod rest firmly on the ground (i.e. the soil under the legs should not be loose and should not be supported on a sloping rock surface or on small boulders, which may be used for this purpose). may bend during the test.)
  3. Using the auger, move the bore hole forward, at the test location. Initiate the borehole to a depth of 0.5 m beforehand and clear the loose soil from the borehole.
  4. Clean the split spoon sampler and apply a thin film of oil to the inside face of the sampler. Connect the A-drill extension rod to the split spoon sampler.
  5. Slide the 63.6 kg weight onto the guide pipe assembly and connect the guide pipe assembly to the other end of the A-drill rod.
  6. The chain attached to the driving weight is tied to a rope passing over the pulley on the tripod head. The other end of the rope is pulled down by hand or with the help of a mechanical winch. The drive weight, guide pipe assembly, A-drill rod and split spoon sampler will stand vertically by pulling the rope down.
  7. A person should hold the guide pipe assembly split spun sampler vertically to reduce the falling weight to the bottom of the guide assembly.
  8. Now place a straight edge across the bore touching the A-drill rod. Mark the level of the straight edge around the A-drill rod with chalk or another marker. From this mark, measure with an A-drill rod and mark 15cm, 30cm and 45cm above the level of the straight edge. Lift the driving weight to reach the top of the guide pipe assembly travel and let it fall freely. The drop in driving load will transfer the impact load to the split spun sampler, which drives the split spun sampler into the ground. Again lift the weight of the drive to the top of the travel and let it fall freely under its own weight from a height of 75 cm. As the number of blows is applied, the split spoon sampler will penetrate the ground and the first mark (15 cm mark) on the drill rod will reach the straight edge.
  9. Count the number of blows required for the first 15 cm, second 15 cm and third 15 cm marks to cross the straight edge.
  10. The first 15 cm of penetration is considered as the seating drive and the number of blows required for this penetration is noted but not accounted for in the calculation of the penetration resistance value. Total number of blows required for penetration of split spoon sampler 2Ra and 3third 15 cm is recorded as the penetration resistance or n-value.
  11. After the Split Spoon Sampler 45cm is complete, take out the entire assembly. Detach the split sampler from the A-drill rod and open it. Collect the soil sample from the split spoon sampler into the sampling bag. Securely store the sample bag with an identification tag for laboratory examination.
  12. Extend the borehole another 1 meter or so until the soil level changes, whichever is sooner.
  13. The test is repeated with the progress of the bore hole until the required depth of exploration is reached or a denial condition is encountered. A state of denial is said to exist when the number of blows required for the last 30 cm penetration exceeds 100.
  14. The test will be repeated in the number of boreholes covering the site depending on the variation in the construction area, the importance of the structure and the soil properties at the site.
  15. SPT values ​​are presented either in the form of a table or as bore log data.

Also read: Reforms Applicable On SPT Values

Also read: How To Calculate Carrying Capacity Of Soil From Standard Penetration Test?

Also read: 20 Factors Affecting Standard Entrance Test Result

Read also: 9 Precautions to be taken while conducting Standard Penetration Test

Also read: How To Calculate Pile Load Capacity Using SPT Or N Values?


Er. Mukesh Kumar

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Er. Mukesh Kumar is Editor in Chief and Co-Funder at ProCivilEngineer.com Civil Engineering Website. Mukesh Kumar is a Bachelor in Civil Engineering From MIT. He has work experience in Highway Construction, Bridge Construction, Railway Steel Girder work, Under box culvert construction, Retaining wall construction. He was a lecturer in a Engineering college for more than 6 years.