The sand replacement method is used to determine field density of soils and the sand replacement method of determination of in situ density uses a sand-pouring cylinder, tray with a central circular hole, chisel, and cylindrical calibrating container.
To measure the in-situ volume of the hole from which the material was excavated from the weight of sand with known density filling in the hole, sand replacement method is used and this is the basic principle of this method.
There are three steps in the determination of field density using the sand replacement method, the first step involves calibration of the sand-pouring cylinder, and in the second step soil density is measured, and in the third step water content and dry density is measured.
The major object is the determination of field density by sand replacement method.
there are the following apparatus used in the sand replacement method such as;
Sand Pouring Cylinder Equipment
Tools for Leveling and Excavating
Sand Pouring Cylinder Equipment:
There are three types of cylinders in sand replacement method such as;
Small Pouring Cylinder:
The small pouring cylinder is one type of cylinders used in the sand replacement method and suitable for medium-grained and fine soils and consists of the metal cylinder of 3 liters capacity, 100 mm in diameter, and length of 380 mm. At one end it is with an inverted funnel or cone and a shutter to open and close the entry of sand and on another end, there is a cap.
To excavate the hole with suitable shape and size metal tray is available and 100 x 150 mm size calibration cylinders provided.
Large Pouring Cylinder:
For fine, medium, and coarse-grained soils large pouring cylinders are suitable, and this consists of 16.5 liters capacity of the metal cylinder, 200 mm in diameter, and with all arrangements, 610 mm in length and 200 x 250 mm size of calibration container.
Medium Pouring Cylinder:
For fine, medium, and coarse-grained soils medium pouring cylinders are also suitable and this cylinder has 150 mm diameter 450 mm length and 150X200 mm calibration container size.
Tools for Leveling and Excavating:
There are many hand tools used for leveling the surface such as scraper with handle, elongated trowel or, a dibber for digging.
For collecting the excavated material metal containers of any convenient size about 150 mm diameter and 200 mm depth with removable lid are used.
Uniform grade dry and clean test sand, passing 0.1 mm and retained micron sieve.
A suitable balance with the necessary set of weights and a suitable balance of capacity 15 or 30 kg accuracy 1.0 g are used.
There are two stages of sand replacement method as given below;
Calibration of Apparatus
Measurement of field density
Calibration of Apparatus:
The volume determination of the excavated hole is based on the weight of sand filling the hole, the density of the sand and the cone and calibration of apparatus includes;
Density determination of test sand used in the experiment under pouring conditions of sand into the test hole and under identical height.
Weight determination of the sand occupying the sand-pouring cylinder cone.
For at least three to four sets of tests clean and dry sand passing 1.0 mm sieve and retained 600-micron sieve is collected in sufficient quantity and the top cap of the sand-pouring cylinder is removed and the shutter is closed.
Then with dry test sand from the top cylinder is filled up to about 100 mm and cap is replaced and to one gram the weight of the cylinder with the sand is determined accurately as W1.
Now on a clean plane surface the sand pouring cylinder is placed and till the sand fills up the cone fully the shutter is kept open and by removing the cap there is no visible movement of sand. Then the shutter is closed, the cylinder is removed and from the plate, the sand which occupied the cone is carefully collected and weighed as W2.
Now on top of the calibration container the cylinder is placed centrally and the shutter is opened and when the calibration container and the cone are filled by sand and there is no movement of sand then the shutter is closed and the remaining sand is weighed as W3.
The mean values of W2 and W3 are determined by repeating the above steps and by measuring the internal dimensions the volume of calibration container is determined and the density of sand is determined from the weight of sand Wa and its volume V in the calibrating container.
Measurement of Field Density:
Another stage of sand replacement test is the measurement of field density and in this, the site where the field density test is to be conducted is cleaned and leveled using a scraper for about 450 mm square area and on the prepared surface, the metal tray central hole is placed.
Using a dibber or trowel up to a required depth the soil material is excavated and removed loose material is carefully collected in the material container and weighed as W and with sand, the sand-pouring cylinder is refilled and again weighed as W1.
Over the excavated hole the sand-pouring cylinder is placed centrally and till the sand fills the excavated hole the shutter is opened and in the cylinder, there is no further movement of sand and shutter is closed then and the cylinder is weighed as W4 and Wb can be found by the weight of sand filling the excavated hole alone.
By taking a sample of soil from it in moisture content dish, weighing, drying in an oven at 110c, and re-weighing the moisture content of the excavated soil is determined as W% and by this, the dry weight is determined as Wd.
The above process must be repeated three times and for the determination of field density values, the average values are taken.
Formulas for Calculations in Sand Replacement Method:
W1 is the weight of the sand-pouring cylinder and from top edge ‘g’ sand filled up to 10 mm.
W2 is the weight of sand in the cone.
W3 is the weight of the cylinder and sand after pouring into the calibration container and cone.
W4 is the weight of the cylinder and sand after pouring into the excavated hole.
Va is the volume of the excavating container in cm3.
W is the weight of the soil excavated from the hole.
Wd is the oven-dry weight of the soil.
w is the moisture content of the soil in percentage.
There are following formulas used in the sand replacement method;
The weight of sand filling the calibrating container = Wa = (W1-W3-W2), g
Sand Bulk Density
Weight of excavating hole sand filling = Wb = (W1-W4-W2), g
Excavated hole sand filling volume = V = weight of dry soil/ bulk density, cm3.