Field density test
- 1. FIELD DEKSITY TE ST BY SAND REPLACEMENT METHOD. INTRODUCTION: The dry density of the compacted soil is a common measure of the amount of the compaction achieved during the construction. Knowing the field density and field moisture content, the drydensity is calculated. Therefore, field density test is important as a field control test for the compaction ofsoil. Several methods, such as core cutting method, sand replacement method etc. is used for the determination of field density of soil. But core cutter method is not suitable for soil containing coarse-grained particle, such as gravel, stones etc. Under such circumstances, field density test is determined by sand replacement method. The basic principle of sand replacement method is to measure the in-situ volume of hole from which the soil was excavated. In-situ volume of hole = weight of pouring sand x known density of pouring sand in the hole. In-situ density of excavated soil = weight of excavated soil/In-situvolume. Apparatus: a) Sand pouring cylinder b) Tools for leveling and excavating c) Containers d) Sand:Dryand clean test sand of uniform gradation, passing 1.0mm and retained 600- micron sieve. e) Balance Procedure: The test is conducted in two stages - (i) calibration of apparatus (ii) measurement of field density (i) Calibration of apparatus: Volume of excavated hole = weight of pouring sand x density of the pouring sand. Calibration of apparatus includes - (a) determination of density of test sand (that is used in the test) (b) determination of the weight of the sand occupying the cone of the sand-pouring cylinder. Clean and dry test sand is collected. The top cap of the sand-pouring cylinder is removed, the shutter is closed, the cylinder is filled with dry test sand & the cap is replaced. The weight of the cylinder + sand is determined = WI. In all the subsequent tests for calibration as well as for the field density tests, eve1y time the sand is filled into the cylinder such that the initial weight of the cylinder with sand is exactly = WI. The sand pouring cylinder is placed over the calibration cylinder, the shutter is opened and the sand equal to the volume of the calibration cylinder is allowed to flow out and
- 2. the shutter is closed. The sand pouring cylinder is now placed on a clean plane surface, the shutter is kept open till the sand fills up the cone fully and there is no visible movement of sand as seen from the top of the cylinder by removing the cap. The shutter is closed, the cylinder is removed and the sand, which is occupied the cone is carefully collected from the plate and weighed = W2. The sand pouring cylinder is refilled with sand such that the initial weight is again Wl. Now the cylinder is placed centrally on the top of the calibration container and the shutter is opened. When the sand fills up the calibration container and cone completely, and there is no movement of sand, the shutter is closed and the sand pouring cylinder and the remaining sand is weighed = W3. The above steps are repeated three times and the mean values of W2 and W3 are determined. The volume of the calibrating container, V is determined either by measuring the internal dimensions. From the weight of sand Wa and its volume V in the calibrating container, the density of sand, is determined. (ii) Measurement of field density: The metal tray central hole is placed on the prepared surface. The soil is excavated using a trowel up to a required depth and the loose material that is removed is carefully collected in the metal container and is weighed = W. The sand-pouring cylinder is refilled with calibrated sand such that its weight is again W1. The metal tray with central hole is removed and the sand-pouring cylinder is placed centrally over the excavated hole. The shutter is opened till the sand fills the excavated hole and the cone completely and there is no further movement of sand in the cylinder. The shutter is closed and the cylinder is weighed again = W4. The weight of sand filling the excavated hole alone = Wb can be found. The moisture content of the excavated soil, w% is determined by taking a sample of soil, weighing, drying in oven at 110°c and re-weighing. Alternatively, the moisture content (w%) is determined by placing the entire excavated soil collected from the hole (of weight W) in the oven and finding its dry weight = Wd. Calculations and Results: W1 = weight of sand pouring cylinder + sand filled up to 10mm from top edge W2 = weight of sand in the cone W3 = weightof cylinder + sand after pouring into the calibration container and cone W4 = weight of cylinderand sand after pouring into the excavated holeand cone, g Va = volume of the excavating container W = weight of the soil from the excavated hole Wd =oven dry weight of thesoil excavated fromthehole w= moisture content of thesoil, %