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Field density by core cutter method

Determination of in-situ density by core cutter method

Aim:

To determine the field density of soil by Core cutter method.

Specification:

This test is done to determine the in-situ dry density of soil by core cutter method as per IS-2720-Part-29 (1975). Core cutter method in particular, is suitable for soft to medium cohesive soils, in which the cutter can be driven. It is not possible to drive the cutter into hard and boulder soils.

Equipments Required:

  • Cylindrical core cutter, 100mm internal diameter and 130mm long.
  • Steel dolley, 25mm high and 100mm internal diameter.
  • Steel rammer mass 9kg, overall length with the foot and staff about 900mm.
  • Balance, with an accuracy of 1gm.
  • Palette knife, Straight edge, steel rule etc.
  • Square metal tray- 300mm x 300mm x 40mm.
  • Trowel.

Theory:

Field density is defined as weight per unit volume of soil mass in the field at insitu conditions. In the spot adjacent to that where the field density by sand replacement method has been determined or planned, drive the core cutter using the dolly over the core cutter. Stop ramming when the dolly is just proud of the surface. Dig out the cutter containing the soil out of the ground and trim off any solid extruding from its ends, so that the cutter contains a volume of soil equal to its internal volume which is determined from the dimensions of the cutter. The weight of the contained soil is found and its moisture content is determined. Equation for γd is

\[\mathop \gamma \nolimits_d = \frac{{\mathop \lambda \nolimits_t }}{{\left( {1 + \omega } \right)}}\]

Where,
  • γd = Dry unit weight in g/cm3.
  • γt = Field moist unit weight in g/cm3.
  • ω = Water content in ( Percentage % ).

Field density is used in calculating the stress in the soil due to its overburden pressure. It is needed in estimating the bearing capacity of soil foundation system, settlement of footing, earth pressures behind the retaining walls and embankments. Stability of natural slopes, dams, embankments and cuts is checked with the help of density of soil. It is the density that controls the field compaction of soils. Permeability of soils depends upon its density. Relative density of cohesionless soils is determined by knowing the dry density of soil in natural, loosest and densest states. Void ratio, porosity and degree of saturation need the help of density of soil.

Precautions:

  • Core cutter method of determining the field density of soil is only suitable for fine grained soil (Silts and clay). That is, core cutter should not be used for gravels, boulders or any hard surface. This is because collection of undisturbed soil sample from a coarse grained soil is difficult and hence the field properties, including unit weight, cannot be maintained in a core sample.
  • Core cutter should be driven into the ground till the steel dolly penetrates into the ground half way only so as to avoid compaction of the soil in the core.
  • Before lifting the core cutter, soil around the cutter should be removed to minimize the disturbances.
  • While lifting the cutter, no soil should drop down.

Procedure:

  1. Measure the height and internal diameter of the core cutter to the nearest 0.25 mm.
  2. Calculate the internal volume of the core-cutter Vc in cm3.
  3. Determine the weight of the clean cutter accurate to 1 gm (W1 in gm).
  4. Select the area in the field where the density is required to be found out. Clean and level the ground where the density is to be determined.
  5. Place the dolley over the top of the core cutter and press the core cutter into the soil mass using the rammer. Stop the pressing when about 15mm of the dolley protrudes above the soil surface.
  6. Remove the soil surrounding the core cutter by digging using spade, up to the bottom level of the cutter. Lift up the cutter and remove the dolley and trim both sides of the cutter with knife and straight edge.
  7. Clean the outside surface of the cutter and determine mass of the cutter with the soil (W2 in gm).
  8. Remove the soil core from the cutter and take the representative sample in the water content containers to determine the moisture content.
  9. The field test may be repeated at other places if required.
  10. The water content of sample collected is determined in the laboratory as per oven drying method.
  11. Use the above equation, given the theory section, for determining density of soil γd.

Table:Weights of core cutter

Sl.No Particulars Test No.1 Test No.2 Test No.3
1. Internal diameter of cutter (cm)
2. Internal height of cutter (cm)
3. Cross sectional area of cutter (cm2)
4. Volume of core cutter (Vc), cm3
5. Weight of empty core cutter (W1), gm
6. Weight of core cutter + wet soil (W2), gm
7. Moisture content container No.
8. Weight of empty container(W3), gm
9. Weight of container + wet soil (W4), gm
10. Weight of container + dry soil (W5), gm
11. Water content ω=(W4-W5)/(W5-W3)
12. Field moist density γt (g/cm3)=(W2-W1)/Vc
13. Dry density γd (g/cm3)=γt/1+ω
14. Average γd = (γd1+γd2+γd3)/3

Result:

Average in-situ field dry density, ρd = __________

Verification/ Validation:

The dry density of most soils varies within the range of 1.1-1.6 g/cm3. In sandy soils, dry density can be as high as 1.6 g/cm3; in clayey soils and aggregated loams, it can be as low as 1.1 g/cm3.

Conclusion:

The value of dry density of the soil is ____. The type of soil is ____.

Viva Questions:

  1. What are the main factors which affect in-situ density of soil? Explain.
  2. Beside the density, what other properties do you need to calculate the void ratio and degree of saturation of soils ?
  3. What are the other methods to calculate the field density of soil ?
  4. Which is the most accurate method to determine the field density ?
  5. Can we use core cutter method on stony or non-cohesive soils ?
  6. Which method is more accurate, sand replacement method or core cutter method ?
  7. What is the practical application of the current test ?
  8. Do we get undisturbed sample using core cutter ?
  9. Why is field density required ?
  10. Out of wet density, dry density, and saturated density, which one of them is maximum and minimum? Explain.

Determination of in-situ density by core cutter method

Aim:

To determine the field density of soil by Core cutter method.

Specification:

This test is done to determine the in-situ dry density of soil by core cutter method as per IS-2720-Part-29 (1975). Core cutter method in particular, is suitable for soft to medium cohesive soils, in which the cutter can be driven. It is not possible to drive the cutter into hard and boulder soils.

Equipments Required:

  • Cylindrical core cutter, 100mm internal diameter and 130mm long.
  • Steel dolley, 25mm high and 100mm internal diameter.
  • Steel rammer mass 9kg, overall length with the foot and staff about 900mm.
  • Balance, with an accuracy of 1gm.
  • Palette knife, Straight edge, steel rule etc.
  • Square metal tray- 300mm x 300mm x 40mm.
  • Trowel.

Theory:

Field density is defined as weight per unit volume of soil mass in the field at insitu conditions. In the spot adjacent to that where the field density by sand replacement method has been determined or planned, drive the core cutter using the dolly over the core cutter. Stop ramming when the dolly is just proud of the surface. Dig out the cutter containing the soil out of the ground and trim off any solid extruding from its ends, so that the cutter contains a volume of soil equal to its internal volume which is determined from the dimensions of the cutter. The weight of the contained soil is found and its moisture content is determined. Equation for γd is

\[\mathop \gamma \nolimits_d = \frac{{\mathop \lambda \nolimits_t }}{{\left( {1 + \omega } \right)}}\]

Where,
  • γd = Dry unit weight in g/cm3.
  • γt = Field moist unit weight in g/cm3.
  • ω = Water content in ( Percentage % ).

Field density is used in calculating the stress in the soil due to its overburden pressure. It is needed in estimating the bearing capacity of soil foundation system, settlement of footing, earth pressures behind the retaining walls and embankments. Stability of natural slopes, dams, embankments and cuts is checked with the help of density of soil. It is the density that controls the field compaction of soils. Permeability of soils depends upon its density. Relative density of cohesionless soils is determined by knowing the dry density of soil in natural, loosest and densest states. Void ratio, porosity and degree of saturation need the help of density of soil.

Precautions:

  • Core cutter method of determining the field density of soil is only suitable for fine grained soil (Silts and clay). That is, core cutter should not be used for gravels, boulders or any hard surface. This is because collection of undisturbed soil sample from a coarse grained soil is difficult and hence the field properties, including unit weight, cannot be maintained in a core sample.
  • Core cutter should be driven into the ground till the steel dolly penetrates into the ground half way only so as to avoid compaction of the soil in the core.
  • Before lifting the core cutter, soil around the cutter should be removed to minimize the disturbances.
  • While lifting the cutter, no soil should drop down.

Procedure:

  1. Measure the height and internal diameter of the core cutter to the nearest 0.25 mm.
  2. Calculate the internal volume of the core-cutter Vc in cm3.
  3. Determine the weight of the clean cutter accurate to 1 gm (W1 in gm).
  4. Select the area in the field where the density is required to be found out. Clean and level the ground where the density is to be determined.
  5. Place the dolley over the top of the core cutter and press the core cutter into the soil mass using the rammer. Stop the pressing when about 15mm of the dolley protrudes above the soil surface.
  6. Remove the soil surrounding the core cutter by digging using spade, up to the bottom level of the cutter. Lift up the cutter and remove the dolley and trim both sides of the cutter with knife and straight edge.
  7. Clean the outside surface of the cutter and determine mass of the cutter with the soil (W2 in gm).
  8. Remove the soil core from the cutter and take the representative sample in the water content containers to determine the moisture content.
  9. The field test may be repeated at other places if required.
  10. The water content of sample collected is determined in the laboratory as per oven drying method.
  11. Use the above equation, given the theory section, for determining density of soil γd.

Table:Weights of core cutter

>
Sl.No Particulars Test No.1 Test No.2 Test No.3
1. Internal diameter of cutter (cm) 10 10 10
2. Internal height of cutter (cm) 12.95 12.95 12.95
3. Cross sectional area of cutter (cm2)
4. Volume of core cutter (Vc), cm3
5. Weight of empty core cutter (W1), gm 1130 1130 1130
6. Weight of core cutter + wet soil (W2), gm 3120 3122 3119
7. Moisture content container No. 14. 28. 31.
8. Weight of empty container(W3), gm 20.12 20.21 20.15
9. Weight of container + wet soil (W4), gm 44.84 44.90 44.86
10. Weight of container + dry soil (W5), gm 41.25 41.21 41.17
11. Water content ω=(W4-W5)/(W5-W3)
12. Field moist density γt (g/cm3)=(W2-W1)/Vc
13. Dry density γd (g/cm3)=γt/1+ω
14. Average γd = (γd1+γd2+γd3)/3



Result:

Average in-situ field dry density, ρd = g/cm3.

Verification/ Validation:

The dry density of most soils varies within the range of 1.1-1.6 g/cm3. In sandy soils, dry density can be as high as 1.6 g/cm3; in clayey soils and aggregated loams, it can be as low as 1.1 g/cm3.

Conclusion:

The value of dry density of the soil is g/cm3. The type of soil is .

1. First video

2. Second video

3. Third video


Blogs

1. First blog

2. Second blog

Refrence

1. Venkataramaiah, C. (2018). Geotechnical Engineering (6th ed.). New Age International Publishers Pvt Ltd.

2. Punmia, B.C( 2017)Soil mechanics and foundations(17th ed.).Laxmi publications Pvt Ltd.

3. Gopal R, Rao, A, S, R( 2016)Basic and applied Soil mechanics(3rd ed.).New Age International Publishers Pvt Ltd.

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