SPECIFIC GRAVITY DETERMINATION METHODS
October 30, 2019
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(1) Density bottle method
(2) Pycnometer method
(3) Measuring flask method
(4) Gas jar method
(5) Shrinkage limit method
➤ The last method of determining the specific gravity of solid particles from the shrinkage limit discussed !!
(1) Density bottle method:-
➤ The specific gravity of solid particles can be determined in a laboratory using a deformity boule fined with a stopper having a hole (Fig. 212). The density bottle of 50 ml capacity is generally used.
➤ The diversity bottle is cleaned and dried at a temperature of 105 to 110 C and cooled.
➤ The mass of the bottle,, including that of stopper, is taken. About 5-10g of &y sample of soil is taken in the boule and weighed Ir the sample contains particles of large sure.
➤ it shall be ground to pass a 2-mm sieve before the iest Distilled water is then added to cover the sample.
➤ The soil is allowed to souk water for about 2 hours.
➤ More water is added until the bottle is half full.
➤ Air entrapped in the soil is expelled by applying a vacuum pressure of about 55 cm of mercury for about one hour in a vacuum desiccator.
➤ Alternatively, the entrapped air Can be removed by gentle heating.
➤ More water is added to the bottle to make I full The stopper is Inserted in the bottle and its masa is taken.
➤ The temperature is also recorded -Hole -Stopper gas formed.
➤The samples of sand and plastic soils.
➤ gives the specific gravity of water at different temperatures.
➤ The specific gravity of solids is reported as the average of the two tests, to the nearest 0.01, provided the difference between the two tests docs not differ by 0.03. Kerosene is a better wetting agent than water and is sometimes used in place of water.
➤ If Gs the specific gravity of kerosene at the test temperature.
(2) Pycnometer Method.
➤The method is similar to the density boule method, As the capacity of the Pycnometer is larger, about 200-300 g
➤oven-dry soil is required for the test. he method can be used for all types of soils but is more suitable for medium-grained soils, with more than 90% passing a 20 mm
➤Coane-grained soils with more than 90% possing a 40 mm IS sieve. (See Chapter 30, Sect. 30.4 for the laboratory experiment). ) Measuring Flask Method.
➤A measuring flask is of 250 ml (or S00 ml) capacity, with a graduation mark at that level.
➤I am fitted with an adaptor for connecting it to a vacuum line for removing entrapped sir The method is similar to the density boule method.
➤About 80-100 g of dry soil is required in this The method is suitable for fine-grained and medium-grained soils (4) Gas Jar Method.
➤In this method, a gas jar of liter capacity is used.
➤ The jar is finished with a rubber bung jar serves as a pycnometer.
➤ The method is similar to the pycnometer Rubber bung method.
➼ MEASUREMENT OF MASS DENSITY:-
➤ The bulk mas density of a soil sample, as per is the mass per unit volume. Although the mss of a soil sample can be determined to a high degree of precision.
➤ it is rather difficult to determine the volume of the sample accurately.
➤ The methods discussed below basically differ in the procedure for the measurement of the volume.
➤7m Once the bulk mass density has been determined, the dry mass density is found using Thus.
➤The volume of the specimen used in various tests can be computed from the measured dimensions a they have regular shapes, such as a cylinder or a cube.
➤ However, precise measurements are not possible I the sample is made in a container of known dimensions, much more accurate measurements are possible.
➤The following methods are generally used for the determination of mass density.
(1) Water Displacement Method.
(2) Submerged mass density Method.
(3) Core Cutter Method.
(4) Sand Replacement Method.
(5) Water Balloon Method.
(6) Radiation Method. methods.
➤The methods are discussed below. The first two methods are laboratory methods !!
(1) Water Displacement Method:-
➤The volume of the specimen is determined in this displacement.
➤As the soil mass disintegrates when it comes in contact with water, the sample wax to make it impervious.
➤ A test specimen is trimmed to more or less a regular shape and weighed. It is then coated with a thin layer of paraffin wax by dipping it in a molten method by water Coated with paraffin wax.
➤ The specimen is allowed to cool and weighed. The difference between the two observations is equal to the mass of the paraffin.
➤The waxed specimen is then immersed in a water- displacement container.
➤The volume of the specimen is equal to the volume of water which comes out of the outflow tube.
➤The actual volume of the soil specimen is less than the volume of the waxed specimen.
➤ The volume of the wax is determined from the mass of the wax pealed off from the specimen after the test and the mass density of wax.
(2) Submerged Mass Density method:-
➤ This method is based on Archimedes' principle that when a body submerged in water.
➤ the reduction in mass is equal to the mass of the volume of water displaced.
➤The sample is first trimmed and weighed and then it is immersed in molten wax and again weighed, as in the water displacement method.
➤The specimen is then placed in the cradle of special type balance.
➤The cradle dips in the water contained the bucket placed just below.
➤The apparent mass of the waxed specimen in water is determined.
➤ The volume of the specimen is determined as below.
(3) Core Cutter Method:-
➤ It is a field method for the determination of mass density.
➤A core caters an open cylindrical barrel with a hardened sharp cutting edge.
➤ A dolly is placed o cutter and it is rammed into the soil.
➤ The dolly is required to prevent burring of the edges of the can cutter containing the soil is taken out of the ground.
➤ Any soil extruding above the edges of the cutter is removed.
➤The mass of the cutter filled with soil is taken.
➤A representative sample is taken for water content determination.
➤ The volume of the soil is equal to the internal volume of the cutter which can be determined from the dimensions of the cutter or by filling.
➤ the culter with water and finding the mass of water.
(4) Sand Replacement Method :-
➤ sand-pouring cylinder, which has a pouring cone a it's base.
➤ The cylinder shown is placed with its base at the ground level.
➤ There is a screen between the chamber and the cone.
➤ The chamber is first aligned to decide the mass thickness of sand.
➤For good results the sand used should be uniform, dry and clean, passing a 600-micron sieve and retained on a 300 mico sieve.
(a) Calibration of the apparatus:-
➤The cylinder is filled with sand and weighed.
➤A calibrating containers then placed below the pouring cylinder and the shutter is opened.
➤The sand fills the calibrating container and the cons.
➤The shutter is closed, and the mass of the cylinder is again taken.
➤The mass of the sand in the Container and the cone is equal to the difference of the two observations.
➤The pouring cylinder is again filled to the initial mass.
➤ The sand is allowed to run out of the cylinder equal to the volume of the calibrating container and the shutter is closed.
➤ The cylinder is then placed over a plain surface and the shutter is opened.
➤ The sand runs out of the cylinder and fills the cone.
➤ The cylinder is removed and the sand filling the collected and weighed The mass density of the sand is determined as under.
(b) Measurement of Volume of Hole-A:-
➤tray with a central hole is placed on the prepared ground surface which has been cleaned and properly levelled.
➤ A hole about 100 mm diameter and mm deep is excavated in the ground, using the hole in the tray as a pattern.
➤The soil removed is carefully collected and weighed.
➤The sand pouring cylinder is then placed over the excavated hole.
➤The shutter is opened and the sand is filled in the cone and the hole.
➤When the sand stops running out, the shutter is closed.
➤The cylinder is removed and weighed.
➤The volume of the hole is determined from the mass of sand filled in the hole and the unit mass density of sand.
5. Rubber Balloon Method:-
➤The volume of the hole in this method determined using a rubber balloon or by filling water in the hole after covering it with a plastic sheet.
➤The rubber balloon method is explained below The apparatus consists of a density plate and a graduated cylinder made of lucite enclosed in an airtight aluminum case.
➤The cylinder is partially filled with water.
➤ There is an opening in the bottom of the case, which is sealed by a rubber balloon.
➤The balloon can be pulled up into the cylinder or maybe pushed down through the bottom.
➤ A pump is attached to the cylinder for this purpose When the pressure is applied, the balloon comes out of the aluminum case through the hole in the density plate.
➤ When a vacuum is applied, the balloon is pulled up into the cylinder.
➤ For determination of the volume of the hole, the density plate is placed on the leveled ground.
➤The cylinder is then placed over the plate The pressure is applied to the balloon.
➤The balloon deflates against the surface of the soil.
➤The volume of water in the cylinder is observed. The cylinder is removed from the base plate. The soil is taken out.
(6) Radiation Method:-
➤ The bulk mass density of in-situ soil can be determined using the ratio method.
➤The meter consists of two probes, one containing a radioisotope source and the other a gamma a detector.
➤ The meter is placed on the surface which had been carefully cleaned and leveled. probe e to a maximum depth of 200 mm to 300 mm into the ground, and, therefore, gives an average mass de for that depth.
➤ The detector records the amount of radiation which passes through the soil from the pro attached to the meter when inserted into the ground.
➤The denser the soil, the greater is the absorption gamma rays, and the lesser will be the gamma rays energy at the detector.
➤The method is known as the dr transmission method There is another method, known as the backscatter method Both the source and the detector contained in one probe.
➤ The detector records radiations which had been reflected by the soil.
➤The bulk density of the soil is determined in from the radiation count over a fixed time period.
➤The mass density obtained is for the top 40 to 50 mm.
➤The method is simpler than the direct transmission method, but it requires greater source strength Radiation methods for determination.
➤the mass density of soils is quick and convenient and gaining popularity.
➤However, precautions must be taken against the radiation hazard.