GGU-OEDOM: Compression index evaluation

This evaluation method makes use of the following data and relationships, beside the stresses and settlements of the individual loading stages:

Input data:

h₀ = initial height
A = sample area
mf = wet mass
S = grain density
w0 = initial water content

Relationships:

Mass of solid substance m_S = m_f / ( 1.0 + w₀)
Solid volume VS = mS / S
Void volume VW = A * h0 – VS
Void ratio e = VW / VS

Compression index CC = (ei – ei – 1) * ln( / – 1)

e_i = void ratio at loading stage i
ei - 1 = void ratio at loading stage i – 1
i = stress at loading stage i

- 1 = stress at loading stage i – 1

The graphical visualisation of the test results is shown in Figure 2.

In contrast to the evaluation by means of constrained moduli, the void ratio is shown in the above diagram instead of the settlement. In the lower diagram the compression indices are drawn instead of the constrained moduli.

An evaluation by means of compression indices is generally very useful for normally consolidated soils, when the void ratio changes linearly with increasing stress on a semi-logarithmic scale. In this case the compression index remains constant. This makes a time-settlement analysis, for example, using compression indices, quite useful. This can be done using the GGU-CONSOLIDATE program, for instance.