Determining Field Density of Soil Using the Rubber Balloon Method

In the quest to assess the density of soils, especially those that have been compacted, the rubber balloon method emerges as a reliable in-situ test. This article delves into the intricacies of this method, covering the necessary apparatus, the test procedure, and the subsequent calculations.

Rubber Balloon Method Overview

The rubber balloon method stands out for its efficiency and accuracy when compared to alternative in-situ techniques. Its core involves employing rubber balloons to ascertain the volume of an excavated soil hole.

Apparatus Required

To conduct the rubber balloon test, several apparatuses come into play:

1. Balloon Density Meter
2. Rubber Bulb Pump
3. Density Plate with Fasteners
4. Rubber Balloons
5. Soil Augur or Trowel
6. Moisture Tight Container
7. Weight Balance
8. Drying Oven

The Balloon Density Meter: A Closer Look

The balloon density meter, resembling a cylinder, features graduations on its wall. At its base, a thin membrane (rubber balloon) is affixed. This balloon expands when water is pumped into it, facilitated by a control valve and a rubber bulb arrangement.

Rubber Balloon Test Procedure

The rubber balloon method unfolds through a systematic procedure:

1. Prepare a flat and smooth soil surface at the testing site.
2. Affix the density plate securely to the prepared surface.
3. Position the balloon density meter precisely on the hole provided in the density plate.
4. Pump water into the rubber balloon using the rubber bulb pump through the control valve until the water level reaches its lowest position. Record this initial volume (V1).
5. Invert the rubber bulb pump and return the water to its original position.
6. Remove the density meter and excavate a hole (4 inches in diameter, 5 inches deep) using an auger or trowel.
7. Collect the excavated soil in a moisture-tight container, noting its weight (W) for water content calculations.
8. Place the balloon density meter over the hole and pump water into the balloon until the water level reaches its lowest point. Record this as the final volume (V2).
9. Return the water to its original level using the rubber bulb pump with the vacuum side connected to the control valve.

Observations and Calculations

The weight of the excavated soil is denoted as W. The volume of the hole excavated (V) is determined by V1 – V2, where V1 represents the initial volume reading, and V2 is the final volume reading.

The field density or wet density of the soil can be calculated, along with the water content (w) and dry density of the soil.

Results

The field density of the soil is then determined in N/m³, providing a comprehensive understanding of the soil’s characteristics.