# CREEP CHARACTERISTICS OF CHALK MARL UNDER UNIAXIAL AND CONFINED COMPRESSION STATE STRESS

### NURI AL-MOHAMADI

This paper studies the time-dependent deformation of chalk marl under uniaxial state of stress in a specially built creep rigs, and confined compression stress state. The tests carried out include: six uniaxial creep tests with vertical and lateral deformation measurements, at different stress levels which lasted for 75 to 268 days, six oedometer creep tests under different stress intensities and different loading conditions which lasted for 80 to 250 days. All tested samples were trimmed from 113 mm diameter cores. For uniaxial tests 0.5% axial strain occurred almost instantaneously in the first series subjected to a stress level of 80%. In the second series subjected to a stress level of 40%, the average initial strain was 0.25% which indicate clearly their stress level dependency. After 75 to 150 days creep period, the measured average creep strain was 0.33% for the first series, which represents 57% of the consolidation strain. For series 2 the average creep strain = 0.26%, which represents 54% of the consolidation strain. This implies that the proportional creep ratio Cr = (Et - E1) / E1 is independent of the applied stress level, where Et strain at any time t, E1 strain at one day. For 1-D creep tests E1 and the proportional strain (Et - E1) are not affected significantly by the intensity of applied creep stress, while both of them are highly influenced by the method of load application. From these results, it can be concluded that creep deformation constitutes an important part of the total deformation of chalk marl.

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