Determination of in-situ density by sand replacement method
Aim:
To determine in-situ density of natural or compacted soil using Sand replacement method.
Specification:
This test is done to determine the in-situ dry density of soil by core cutter method as per IS-2720-Part-28 (1975). In order to conduct the test, select uniformly graded clean sand passing through 600µ and retained on 300µ IS sieve.
Equipments Required:
- Sand pouring cylinder of about 3 litre capacity (Small pouring cylinder as per IS 2720 Part 28).
- Cylindrical calibrating container 10 cm internal diameter and 15 cm depth
- Glass plate, trays, containers for determining water content.
- Tools for making of a hole of 10 cm diameter and 15 cm deep, knife and other accessories.
- Metal container to collect excavated soil.
- Metal tray, 300mm square and 40mm deep with a hole of 100mm in diameter at the centre.
- Weighing balance.
- Moisture content cans.
- Glass plate about 450 mm/600 mm square and 10mm thick.
- Oven.
- Dessicator.
Theory:
The in-situ density of natural soil is needed for the determination of bearing capacity of soils, for the purpose of stability analysis of slopes, for the determination of pressures on underlying strata for the calculation of settlement and the design of underground structures. Moreover, dry density values are relevant both of embankment design as well as pavement design.
By conducting this test, it is possible to determine the field density of the soil. The moisture content is likely to vary from time and hence the field density also. So it is required to report the test result in terms of dry density. In sand replacement method, a small cylindrical pit is excavated and the weight of the soil excavated from the pit is measured. Sand whose density is known is filled into the pit. By measuring the weight of sand required to fill the pit and knowing its density, the volume of pit is calculated. Knowing the weight of soil excavated from the pit and the volume of pit, the density of soil is calculated. Therefore, in this experiment there are two stages, namely
- Calibration of sand density.
- Measurement of soil density.
Field density is defined as weight per unit volume of soil mass in the field at in-situ conditions. Equations are:
\[\mathop \rho \nolimits_d = \frac{{\mathop \rho \nolimits_t }}{{1 + \omega }}\]
Where,- γd = Dry unit weight in g/cm3.
- γt = Field moist unit weight in g/cm3.
- ω = Water content in ( Percentage % ).
The basic equations in determination of density using sand replacement method are:
\[\mathop V\nolimits_h = \frac{{\mathop W\nolimits_s }}{{G \times \mathop \rho \nolimits_w }}\]
\[\mathop \rho \nolimits_t = \frac{W}{{\mathop V\nolimits_h }}\]
Where,- Ws = weight of the sand that fills the hole.
- W = moisture content of soil removed from the hole.
- ρt = moist soil in-situ density.
- G = specific gravity of the solids.
- ρw = density of the water.
- Vh = Volume of hole made in the field.
Precautions:
- If for any reason it is necessary to excavate the pit to a depth other than 12 cm, the standard calibrating can should be replaced by one with an internal height same as the depth of pit to be made in the ground.
- Care should be taken in excavating the pit, so that it is not enlarged by levering, as this will result in lower density being recorded.
- No loose material should be left in the pit.
- There should be no vibrations during this test.
- It should not be forgotten to remove the tray, before placing the SPC over the pit.
Procedure:
- Soil sample must be taken as air dried sand which is passed through 1mm sieve and retained on 600µ sieve for filling sand pouring cylinder.
- Fill the sand pouring cylinder with clean sand so that the level of the sand in the cylinder is with in about 10mm from the top, find out the initial weight of the cylinder plus sand (W1) and this weight should be maintained constant throughout the test for which the calibration is used.
- Allow the sand of volume equal to that of the calibrating container to run out the cylinder on the glass plate and open the shutter to allow the sand to run out and close the cylinder shutter when there is no movement of sand and remove the cylinder carefully. Weigh the sand collected on the glass plate. Its weight (W2) gives sand filling the cone portion of the sand pouring cylinder.
- Determine the volume (V) of the container be filled it with water to the brim. Check this volume by calculating from the measured internal dimensions of the container.
- Place the sand pouring cylinder centrally on the calibrating container making sure that constant weight (W1) is maintained. Open the shutter and permit the sand to run into container. When no further movement of sand is seen close the shutter. Remove the pouring cylinder and find its mean weight (W3).
- Clean and level the ground where field density is required.
- Fill the pouring cylinder with dry sand within about 10mm of the top and weigh it.
- Place the metal tray with the central hole over the soil to be tested.
- Excavate approximately 10cm diameter and 15cm deep with bend spoon. The hole in the tray will guide the diameter of the hole to be made in the soil.
- Collect the excavated soil in the metal tray and weigh it (Ww) to nearest gram.
- Determine the moisture content of excavated soil.
- Place the pouring cylinder over the hole so that base of the cylinder covers the hole concentrically.
- Open the shutter and allow the sand to run into the hole, where there is no movement of the sand, close the shutter. Remove the cylinder and determine its mean weight (W3).
Calibration of apparatus
Determination of bulk density of soil
Determination of dry density of soil in field
Table: Caliberation of appratus and calculate bulk density
| Sl.No | Particulars | Test No.1 | Test No.2 | Test No.3 |
|---|---|---|---|---|
| 1. | Internal diameter of calibrating cylinder (cm) | |||
| 2. | Internal height of calibrating cylinder (cm) | |||
| 3. | Cross sectional area of calibrating cylinder (cm2) | |||
| 4. | Volume of calibrating cylinder (Vc), cm3 | |||
| 5. | Weight of cylinder + sand (before pouring) (W1), gm | |||
| 6. | Weight of cylinder + sand (after pouring) (W2), gm | |||
| 7. | Mean weight of sand in cone (W3), gm | |||
| 8. | Weight of sand to fill the calibrating cylinder (Wa), gm | |||
| 9. | Bulk density of sand (γb),=Wa/Vc,(g/cm3) |
Table: Determination of dry density
| Sl.No | Particulars | Test No.1 | Test No.2 | Test No.3 |
|---|---|---|---|---|
| 1. | Weight of wet sand from hole (Ww), gm | |||
| 2. | Weight of cylinder + sand (before pouring) (W1), gm | |||
| 3. | Weight of cylinder + sand (after pouring) (W4), gm | |||
| 4. | Mean weight of sand in hole (Ws), gm | |||
| 5. | Volume of calibrating cylinder (Vc), cm3 | |||
| 6. | Bulk density (γb),=Wa/Vc,(g/cm3) | |||
| 8. | Average (γb) = (γb1+γb2+γb3)/3 | |||
| 7. | Dry density (γd)=γt/1+ω,(g/cm3) | |||
| 8. | Average (γd) = (γd1+γd2+γd3)/3 | |||
Table: Measurement of water content
| Sl.No | Particulars | Test No.1 | Test No.2 | Test No.3 |
|---|---|---|---|---|
| 1. | Moisture content container No. | |||
| 2. | Weight of empty container(W5), gm | |||
| 3. | Weight of container + wet soil (W6), gm | |||
| 4. | Weight of container + dry soil (W7), gm | |||
| 5. | Water content ω=(W6-W7)/(W7-W5) | |||
| 8. | Average (%W) = (%W1+%W2+%W3)/3 | |||
Result:
The Bulk density of soil is ___________.
The Water content of soil is ___________.
The Dry density of soil is ___________.
Verification/ Validation:
Sand replacement method is an indirect method of finding the density of soil. The basic principle is to measure the in-situ volume of hole from which the material was excavated from the weight of sand with known density filling in the hole. The in-situ density of material is given by the weight of the excavated material divided by the in-situ volume. The dry density of most soils varies within the range of 1.1-1.6 gm/cm3. In sandy soils, dry density can be as high as 1.6 gm/cm3. In clayey soils and aggregated loams, it can be as low as 1.1 gm/cm3.
Conclusion:
The value of dry density of the soil is ______________ g/cm3.Comparing with the in-situ density by core cutter method, more or less the same value is achieved. The type of soil is ____________ .
Viva Questions:
- What is the objective of sand replacement method ?
- What is the relationship that can be established between the dry density with known moisture content ?
- What are the apparatus that are needed in this test ?
- What is the significance of determining the in-situ density of the soil ?
- Why Depth of hole is kept to 15 cm in the field ?
- Why we need to determine the unit weight of sand to determine the unit weight of soil?
- Which method is the accurate one, core cutter or sand replacement method as per you? And why?
- How many samples are to be collected ?
- What is the advantage of sand replacement method over core cutter method ?
- What is the practical application of the test ?
Determination of in-situ density by sand replacement method
Aim:
To determine in-situ density of natural or compacted soil using Sand replacement method.
Specification:
This test is done to determine the in-situ dry density of soil by core cutter method as per IS-2720-Part-28 (1975). In order to conduct the test, select uniformly graded clean sand passing through 600µ and retained on 300µ IS sieve.
Equipments Required:
- Sand pouring cylinder of about 3 litre capacity (Small pouring cylinder as per IS 2720 Part 28).
- Cylindrical calibrating container 10 cm internal diameter and 15 cm depth
- Glass plate, trays, containers for determining water content.
- Tools for making of a hole of 10 cm diameter and 15 cm deep, knife and other accessories.
- Metal container to collect excavated soil.
- Metal tray, 300mm square and 40mm deep with a hole of 100mm in diameter at the centre.
- Weighing balance.
- Moisture content cans.
- Glass plate about 450 mm/600 mm square and 10mm thick.
- Oven.
- Dessicator.
Theory:
The in-situ density of natural soil is needed for the determination of bearing capacity of soils, for the purpose of stability analysis of slopes, for the determination of pressures on underlying strata for the calculation of settlement and the design of underground structures. Moreover, dry density values are relevant both of embankment design as well as pavement design.
By conducting this test, it is possible to determine the field density of the soil. The moisture content is likely to vary from time and hence the field density also. So it is required to report the test result in terms of dry density. In sand replacement method, a small cylindrical pit is excavated and the weight of the soil excavated from the pit is measured. Sand whose density is known is filled into the pit. By measuring the weight of sand required to fill the pit and knowing its density, the volume of pit is calculated. Knowing the weight of soil excavated from the pit and the volume of pit, the density of soil is calculated. Therefore, in this experiment there are two stages, namely
- Calibration of sand density.
- Measurement of soil density.
Field density is defined as weight per unit volume of soil mass in the field at in-situ conditions. Equations are:
\[\mathop \rho \nolimits_d = \frac{{\mathop \rho \nolimits_t }}{{1 + \omega }}\]
Where,- γd = Dry unit weight in g/cm3.
- γt = Field moist unit weight in g/cm3.
- ω = Water content in ( Percentage % ).
The basic equations in determination of density using sand replacement method are:
\[\mathop V\nolimits_h = \frac{{\mathop W\nolimits_s }}{{G \times \mathop \rho \nolimits_w }}\]
\[\mathop \rho \nolimits_t = \frac{W}{{\mathop V\nolimits_h }}\]
Where,- Ws = weight of the sand that fills the hole.
- W = moisture content of soil removed from the hole.
- ρt = moist soil in-situ density.
- G = specific gravity of the solids.
- ρw = density of the water.
- Vh = Volume of hole made in the field.
Precautions:
- If for any reason it is necessary to excavate the pit to a depth other than 12 cm, the standard calibrating can should be replaced by one with an internal height same as the depth of pit to be made in the ground.
- Care should be taken in excavating the pit, so that it is not enlarged by levering, as this will result in lower density being recorded.
- No loose material should be left in the pit.
- There should be no vibrations during this test.
- It should not be forgotten to remove the tray, before placing the SPC over the pit.
Procedure:
- Soil sample must be taken as air dried sand which is passed through 1mm sieve and retained on 600µ sieve for filling sand pouring cylinder.
- Fill the sand pouring cylinder with clean sand so that the level of the sand in the cylinder is with in about 10mm from the top, find out the initial weight of the cylinder plus sand (W1) and this weight should be maintained constant throughout the test for which the calibration is used.
- Allow the sand of volume equal to that of the calibrating container to run out the cylinder on the glass plate and open the shutter to allow the sand to run out and close the cylinder shutter when there is no movement of sand and remove the cylinder carefully. Weigh the sand collected on the glass plate. Its weight (W2) gives sand filling the cone portion of the sand pouring cylinder.
- Determine the volume (V) of the container be filled it with water to the brim. Check this volume by calculating from the measured internal dimensions of the container.
- Place the sand pouring cylinder centrally on the calibrating container making sure that constant weight (W1) is maintained. Open the shutter and permit the sand to run into container. When no further movement of sand is seen close the shutter. Remove the pouring cylinder and find its mean weight (W3).
- Clean and level the ground where field density is required.
- Fill the pouring cylinder with dry sand within about 10mm of the top and weigh it.
- Place the metal tray with the central hole over the soil to be tested.
- Excavate approximately 10cm diameter and 15cm deep with bend spoon. The hole in the tray will guide the diameter of the hole to be made in the soil.
- Collect the excavated soil in the metal tray and weigh it (Ww) to nearest gram.
- Determine the moisture content of excavated soil.
- Place the pouring cylinder over the hole so that base of the cylinder covers the hole concentrically.
- Open the shutter and allow the sand to run into the hole, where there is no movement of the sand, close the shutter. Remove the cylinder and determine its mean weight (W3).
Calibration of apparatus
Determination of bulk density of soil
Determination of dry density of soil in field
Table: Caliberation of appratus and calculate bulk density
| Sl.No | Particulars | Test No.1 | Test No.2 | Test No.3 |
|---|---|---|---|---|
| 1. | Internal diameter of calibrating cylinder (cm) | 10 | 10 | 10 |
| 2. | Internal height of calibrating cylinder (cm) | 15 | 15 | 15 |
| 3. | Cross sectional area of calibrating cylinder (cm2) | |||
| 4. | Volume of calibrating cylinder (Vc), cm3 | |||
| 5. | Weight of cylinder + sand (before pouring) (W1), gm | 11040 | 11040 | 11040 |
| 6. | Weight of cylinder + sand (after pouring) (W2), gm | 9120 | 9120 | 9120 |
| 7. | Mean weight of sand in cone (W3), gm | 450 | 450 | 450 |
| 8. | Weight of sand to fill the calibrating cylinder (Wa), gm | |||
| 9. | Bulk density of sand (γb),=Wa/Vc,(g/cm3) |
Table: Determination of dry density
| Sl.No | Particulars | Test No.1 | Test No.2 | Test No.3 |
|---|---|---|---|---|
| 1. | Weight of wet sand from hole (Ww), gm | 2310 | 2400 | 2280 |
| 2. | Weight of cylinder + sand (before pouring) (W1), gm | 11040 | 11040 | 11040 |
| 3. | Weight of cylinder + sand (after pouring) (W4), gm | 9120 | 9120 | 9120 |
| 4. | Mean weight of sand in hole (Ws), gm | |||
| 5. | Volume of calibrating cylinder (Vc), cm3 | |||
| 6. | Bulk density (γb),=Wa/Vc,(g/cm3) | |||
| 8. | Average (γb) = (γb1+γb2+γb3)/3 | |||
| 7. | Dry density (γd)=γt/1+ω,(g/cm3) | |||
| 8. | Average (γd) = (γd1+γd2+γd3)/3 | |||
Table: Measurement of water content
| Sl.No | Particulars | Test No.1 | Test No.2 | Test No.3 |
|---|---|---|---|---|
| 1. | Moisture content container No. | 45 | 21 | 25 |
| 2. | Weight of empty container(W5), gm | 18 | 18 | 18 |
| 3. | Weight of container + wet soil (W6), gm | 74 | 74 | 74 |
| 4. | Weight of container + dry soil (W7), gm | 64 | 64 | 64 |
| 5. | Water content ω=(W6-W7)/(W7-W5) | |||
| 8. | Average (%W) = (%W1+%W2+%W3)/3 | |||
Result:
The Bulk density of soil is .
The Water content of soil is
The Dry density of soil is
Verification/ Validation:
Sand replacement method is an indirect method of finding the density of soil. The basic principle is to measure the in-situ volume of hole from which the material was excavated from the weight of sand with known density filling in the hole. The in-situ density of material is given by the weight of the excavated material divided by the in-situ volume. The dry density of most soils varies within the range of 1.1-1.6 gm/cm3. In sandy soils, dry density can be as high as 1.6 gm/cm3. In clayey soils and aggregated loams, it can be as low as 1.1 gm/cm3.
Conclusion:
The value of dry density of the soil is g/cm3.Comparing with the in-situ density by core cutter method, more or less the same value is achieved. The type of soil is .
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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