What is Dry density of Soil?
Dry density of compacted soil is a measure of the amount of the compaction achieved during the construction. Knowing the field density and field moisture content, the dry density can be calculated. The unit weight of the soil in its field condition is known as field density or in-situ density. The common methods of determination of field density are core cutter, sand replacement, and rubber balloon method. Here we briefly discuss the Core Cutter method.
Applications of Field Density Test
Density is a measure of the strength of the soil. It is useful in estimating bearing capacity of soils, settlement of footings, earth pressure behind the retaining walls and embankments. The field compaction is controlled by the density. The relative density of cohesionless soils is determined by knowing the dry density of soils in its natural, loosest and densest states. The determination of voids ratio, porosity, and degree of saturation need the help of the density of soils.
Determination of field Density test of soil by Core Cutter Method.
In this method, a cylindrical core cutter with a dolly of known dimensions as shown in fig. is used. A dolly is placed over the cutter to prevent damage to the edges of the cutter. Cyclinder is embedded into the ground for its full height and is taken out. The surplus soil at both ends is trimmed and the weight of the cylinder is found out. From the known dimension of the cutter, volume and the moisture content of the soil is determined.
The dry density of soil is computed as follows:
Weight of cutter = W1
Weight of soil + cutter = W2
Wt. of soil = W2-W1
Volume of cutter = V
Bulk density ϒ= (W2-W1)/ V
Dry density ϒd=ϒ/(1+w)
Apparatus for core cutter method
- Cylindrical core cutter (ht= 2·74 cm, dia= 10 cm),
- Steel dolly (2·5· cm high and 10 cm internal dia).
- Steel rammer,
- Balance -2 Nos of accuracy O .01 g and 1 g,
- Others-Palette Knife, Straight edge, Spade.
Procedure of Core Cutter method
1. Find the volume of core cutter by measuring its internal dimensions.
2. Find the weight of the core cutter (without dolly).
3. Place the dolly over the cutter and drive the cutter into the soil with the help of rammer
4. Take out the cutter containing soil.
5. Remove the dolly and trim off the excess soil above the edges of the cutter.
6. Take the weight of cutter filled with soil.
7. Take some representative sample for water content determination by the oven.
8. Repeat the test at two/three locations and find the average density.
Observations and Calculations of Core Cutter method
|(A) Determination of Field-Density|
|I. Wt. of core cutter (g)|
|2. Wt. of cutter+wet soil (g)|
|3. Wt. of wet soil (g) (2-1)|
|4. Volume of core cutter (cm3)|
|5. Field density ϒ= (3)/(4) (g/cm3 = (kN/m3)|
|(B) Determination of Water Content|
|6. Container No. (g)|
|7. Wt. of container+moist soil (g)|
|8. Wt of container+ dry soil (g)|
|9. Wt. of container (g)|
|1 0. Wt. of water ((7) – (8)] (g)|
|1 1. Wt. of dry soil [(8)- (9)] (g)|
Water content w=(10)/(11) (ratio)
|13. In-place dry density ϒd=ϒ/(1+w) (g/cm3) = KN/m3|
Dry density ϒd = ϒ/(1+w)
Where, w = Water content
This method is suitable for soft, fine-grained soils. The method is practicable only at paces where the surface of the soil is exposed and the cutter can be easily driven.
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