Abstract
In this contribution the hydro-mechanically coupled behaviour of a sand is experimentally investigated with the focus on settlements induced by changes in degree of saturation and suction. This phenomenon, referred to as collapse behaviour, is attributed to rearrangements of the grain skeleton due to changing capillary effects on wetting of the soil. For the experimental investigation of the collapse behaviour of a medium coarse sand cyclic drying-wetting tests are performed under oedometric conditions. In the test set-up a sand specimen, subjected to a constant small vertical stress, is cyclically dried and wetted by volume control of the pore water, whereas matric suction is measured using a tensiometer implemented to the specimen loading plate (topcap tensiometer). The test procedure, originally designed to investigate the hysteretic nature of the soil-water characteristic curve of the sand, allows to measure the one dimensional volume change of the specimen as evoked by the applied hydraulic paths under constant net stress. By varying the specimen void ratio the impact of density on the collapse behaviour can be assessed. The test data is important for the development of a mechanical constitutive model which can take the volume change behaviour due to suction changes into account.
Highlights
The hydraulic and mechanical behaviour of unsaturated soils is closely related due to capillary effects
In the presented tests sand specimens under oedometric stress state have been investigated by prescribing pore water volume-controlled changes in degree of saturation and by applying simultaneous suction measurements with a tensiometer
It could be shown that the presented test method, originally meant to investigate the hysteretic nature of the soil-water characteristic curve of sandy soils, can be expanded to study specimen settlements induced by changes in degree of saturation and suction
Summary
The hydraulic and mechanical behaviour of unsaturated soils is closely related due to capillary effects. Up to today the coupling mechanisms are not fully understood and no model has been found to describe both stress state and volume change behaviour properly at the same time for different soil types Jommi (2000). In this contribution an experimental method is presented to study the coupling effects in granular soils leading to settlements as a result of changes in saturation and suction, in order to gather more data on this phenomenon. The measured results will be interpreted in terms of changes of the effective stress for unsaturated soils and may be used in further studies to develop or improve a constitutive model to take the hydromechanical coupling into account
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