To determine in-situ density of natural or compacted soil using Sand replacement
method.
The in-situ density of natural soil is needed for the determination of bearing
capacity of soils, for the purpose of stability analysis of slopes, for the determination of
pressures on underlying strata for the calculation of settlement and the design of
underground structures. Moreover, dry density values are relevant both of embankment
design as well as pavement design.
This test is done to determine the in-situ dry density of soil by core cutter method as per IS-2720-Part-28 (1975). In order to conduct the test, select uniformly graded clean sand passing through 600 micron IS sieve and retained on 300 micron IS sieve.
By conducting this test, it is possible to determine the field density of the soil. The moisture
content is likely to vary from time and hence the field density also. So it is required to report
the test result in terms of dry density. In sand replacement method, a small cylindrical pit is
excavated and the weight of the soil excavated from the pit is measured. Sand whose
density is known is filled into the pit. By measuring the weight of sand required to fill the pit
and knowing its density, the volume of pit is calculated. Knowing the weight of soil
excavated from the pit and the volume of pit, the density of soil is calculated. Therefore, in
this experiment there are two stages, namely
1. Calibration of sanddensit
2. Measurement of soildensity
Field density is defined as weight per unit volume of soil mass in the field at in-situ
conditions. Equations are:
*d = *t/(1+w)gm/cm³
OR *d =
*t/(1+w)kN/m³ Where,
*d = drydensity,
*d = dry unit weight,
*t = field moist density,
*t =field moist unit
weight,
w =water
constant,
w = unit weight of water = 9.81 kN/m³
The basic equations in determination of density using sand replacement method are:
Vh= Ws/ (G ** w)