# Porosity and Density Determination of Rock Using Saturation And Buoyancy Techniques

## Aim

To determine porosity and density of rock using saturation and buoyancy techniques as per IS-13030-1991.

## Apparatus

• Oven (capacity 105±30C)
• Balance (Accuracy of 0.01% of the sample weight)
• Non corrodible sample container
• Vacuum vessel for immersion of sample (capacity 0.8 kPa)
• Immersion bath, wire basket for determination of saturated-submerged weight)

## Procedure

• Take at least 10 lumps of regular or irregular geometry, each having a mass of minimum 50 g.
• Wash the sample if it contains any dust.
• Saturate the sample by immersing it in the vacuum vessel (maintained at 0. 8kPa) for a period of 1 hour.
• Record the temperature, t, of the water in the immersion bath to the nearest degree centigrade.
• Determine the mass, M1, of the wire basket submerged in the immersion bath.
• Transfer the sample under water to the basket in the immersion bath. Determine the saturated-submerged mass, M2, of the basket plus sample to an accuracy of 0.01% of the sample mass.
• Determine the mass, M3, of a clean, dry sample container and lid.
• Remove the sample from the immersion bath and surface dry the sample with a moist cloth, care being taken to remove only surface water. Transfer the sample to the sample container and replace the lid. Determine the mass M4, of the saturated surface dry sample plus container.
• Remove the lid and place the container with contents and lid in the oven and dry at 105±30C, until it attains a constant mass.
• Replace the lid, remove the container from the oven and place the whole in the desicator to cool for 30 minutes.
• Determine the dry mass, M5, of the container with the oven dry sample.

## Observation

Record all the observations in a table as shown below.

 Sample No Date Determination No 1 2 3 Saturated-submerged mass of basket alone, M1, in kg Saturated submerged mass of basket + specimen, M2, in kg Mass of container and lid, M3, in kg Saturated surface dry mass of the sample plus container, M4, in kg Dried mass of the container with sample, M5, in kg

## Calculations

• Msub = M2-M1 (kg)
• Msat = M4-M3 (kg)
• Ms = M5-M3 (kg)
• V = Msat-Msub/ρw (m3)
• Vv = Msat-Msw (m3)
• η = (Vv/V)*100 (%)
• or, η = [(Msat-Ms)/(Msat-Msub)]*100
• ρd = Ms/V

Where,

Msub = Saturated submerged mass

Msat = Saturated surface dry mass

Ms = Dry mass (only grain weight)

V = Bulk volume

ρw = Density of water at temperature t

Vv = Pore volume of the sample

η = Porosity

ρd = Dry density o f rock sample

## Reporting of Result

Report the porosity and dry density values or the sample to the nearest 0.1% and 10kg/m3 respectively.

Report that the bulk volume was obtained by a buoyancy technique and that the pore volume was obtained by water saturation.