The sand replacement test method is an important technique used in construction projects to determine the in situ dry density of soil. This method follows the Indian Standard (IS 2720 part 28) and involves certain procedures, materials, equipment, and specifications.
The test helps in estimating the field density of natural soil, which is crucial for assessing the soil bearing capacity. It also aids in evaluating the pressures on underlying strata, calculating settlement, and analyzing the stability of natural slopes.
In addition, the sand replacement test method is useful in determining the in-place density of compacted soil. This helps in comparing the degree of compaction achieved with the designated compaction degree. By doing so, it can be determined how close the soil compaction is to the designated compaction degree. Overall, this test plays a significant role in construction projects by providing valuable information on soil density and compaction.
Apparatus
To conduct a sand pouring cylinder test, several tools and equipment are needed. A calibrating container with a diameter of 100mm and a height of 150mm is necessary to measure the amount of sand poured. Soil cutting and excavating tools such as a scrapper tool and a bent spoon are also required for soil preparation.
A plane surface like a glass or Perspex plate, which is at least 450mm square and 9mm thick, is necessary to place the sand pouring cylinder during the test. A metal container is also needed to collect the excavated soil. Additionally, a metal tray with a hole of 100mm in diameter at the center is required to facilitate sand pouring.
To determine the weight of the sand poured, a weighing balance that is accurate to 1 gram is necessary. Moisture content cans are also needed to determine the moisture content of the soil. An oven is used to dry the soil samples, and a desiccator is used to keep the soil samples dry once they are removed from the oven. By utilizing these tools and equipment, a sand pouring cylinder test can be conducted accurately and efficiently.
Materials
The material needed is a sufficient quantity of clean and uniform sand that can pass through a 1mm IS sieve and is retained on a 600micron IS sieve. Additionally, it is important that the sand is free from any organic substances.
To ensure that the sand meets the required standards, it should have been dried in an oven prior to use. Afterward, it should have been stored in a suitable location for an appropriate amount of time, allowing the sand’s water content to reach equilibrium with the humidity of the surrounding atmosphere. This is an essential step in ensuring that the sand is properly prepared and ready for use in the intended application.
Calibrations
To measure the volume of a calibrating container, one needs to measure its internal dimensions and calculate its volume. To determine the weight of sand filled in a sand-pouring cylinder, one must fill the cylinder with sand up to about 10mm from the top and weigh it (M1).
To conduct the sand density test, place the sand-pouring cylinder vertically on the calibrating container and open the shutter to let the sand run out. Once there is no further movement of the sand in the cylinder, close the shutter and lift the cylinder to weigh it again (M2) to determine the weight of the sand used.
Next, place the sand-pouring cylinder on a glass plate and open the shutter to let the sand flow out until it fills the cone of the cylinder. Close the shutter and carefully remove the cylinder. Then, weigh the sand on the glass plate (M3).
Repeat the process of pouring sand into the calibrating container and weighing it two more times to obtain the mean weight (mean M2 and M3). Using the values obtained, one can calculate the dry density of the sand, as shown in Table 1.
Table 1 Calibration for Dry Density of Sand
| Sl. No. | Observations and Calculations | Determination No. | ||
| – | Observation | 1 | 2 | 3 |
| 1 | Volume of calibrating cone VC | – | – | – |
| 2 | Mass of pouring cylinder (M1), filled with sand | – | – | – |
| 3 | Mass of pouring cylinder after pouring sand into the calibrating container and cone (M2) | – | – | – |
| 4 | Mass of sand in the cone (M3) | – | – | – |
| Calculations | ||||
| 5 | Mass of sand in the calibrating container, MC=(1) – (2) – (3) | – | – | – |
| 6 | Dry density of sand, ps=MC/VC | – | – | – |
Procedure
To conduct a Sand Replacement Method Test on a soil mass, an area of approximately 450mm square on the soil surface must be exposed. This area should then be leveled using a scrapper tool, after which a metal tray is placed on the leveled surface. The soil must be excavated through the central hole of the tray, using the hole as a pattern, to a depth of approximately 150mm. The excavated soil must be collected in a metal container, and its mass must be determined.
After collecting the soil, the metal tray must be removed from the excavated hole. A sand pouring cylinder must then be filled with sand up to 10mm below its top, and its mass must be determined. The cylinder is then placed directly over the excavated hole, and the sand is allowed to run out of the cylinder by opening the shutter. The shutter should be closed when no further movement of sand is observed and the hole is completely filled. The cylinder must then be removed from the filled hole, and its mass must be determined.
A representative sample of the excavated soil must be taken to determine its water content. The dry density of the soil can then be determined using the data obtained in the test and the information in Table 2.
Fig. 2: Procedure for Sand Replacement Method Test of Soil
Table 2 Observations and Calculations for Dry Density Test of Soil
| SI. No. | Observations and Calculations | Determination No. | ||
| – | Observation | 1 | 2 | 3 |
| 1 | Mass of excavated soil (M) | – | – | – |
| 2 | Mass of pouring cylinder (M1), filled with sand | – | – | – |
| 3 | Mass of pouring cylinder after pouring into the hole and cone (M4) | – | – | – |
| Calculations | ||||
| 4 | Mass of sand in the hole, MS=M1 – M4– M3 | – | – | – |
| 5 | Volume of sand in the hole V=Ms/Ps | – | – | – |
| 6 | Bulk density =M/V | – | – | – |
| 7 | Water content | – | – | – |
| 8 | Dry density using formula | – | – | – |
Result
The formula to calculate the dry density of soil involves two parameters, the bulk density and the water content. The bulk density refers to the mass of soil per unit volume, while the water content is the ratio of the mass of water in the soil to the dry mass of the soil. The dry density can be obtained by dividing the bulk density by the sum of one and the water content, as expressed in Equation 1.
This equation is commonly used in geotechnical engineering and soil science to determine the properties of soil. The dry density is an important parameter that affects various aspects of soil behavior, such as its strength, compressibility, and permeability. By knowing the dry density, engineers and scientists can make informed decisions about construction projects, land use planning, and environmental assessments. Therefore, understanding the concept and calculation of dry density is essential in these fields.