Mechanical Response of Castlegate Sandstone under Hydrostatic Cyclic Loading

The stress history of rocks in the subsurface affects their mechanical and petrophysical properties. Rocks can often experience repeated cycles of loading and unloading due to fluid pressure fluctuations, which will lead to different mechanical behavior from static conditions. This is of importance for several geophysical and industrial applications, for example, wastewater injection and reservoir storage wells, which generate repeated stress perturbations. Laboratory experiments were conducted with Castlegate sandstone to observe the effects of different cyclic pressure loading conditions on a common reservoir analogue. Each sample was hydrostatically loaded in a triaxial cell to a low effective confining pressure, and either pore pressure or confining pressure was cycled at different rates over the course of a few weeks. Fluid permeability was measured during initial loading and periodically between stress cycles. Samples that undergo cyclic loading experience significantly more inelastic (nonrecoverable) strain compared to samples tested without cyclic hydrostatic loading. Permeability decreases rapidly for all tests during the first few days of testing, but the decrease and variability of permeability after this depend upon the loading conditions of each test. Cycling conditions do affect the mechanical behavior; the elastic moduli decrease with the increasing loading rate and stress cycling. The degree of volumetric strain induced by stress cycles is the major control on permeability change in the sandstones, with less compaction leading to more variation from measurement to measurement. The data indicate that cyclic loading degrades permeability and porosity more than static conditions over a similar period, but the petrophysical properties are dictated more by the hydrostatic loading rate rather than the total length of time stress cycling is imposed.

EXPERIMENTAL VERIFICATION OF CONSTRUCTIVE SOLUTION OF A NEW TYPE FRAMEWORK

Experimental verification is an integral part of the study for both new designs and new materials and technologies. To assess the features of deformation of the lightweight frame, a series of tests using the method of hydrostatic loading, developed at the Department of Building Structures O.M. Beketov national university of urban economy in Kharkiv. A fragment of a monolithic reinforced concrete frame with a floor slab with a span of 6.0 m and a thickness of 500 mm (thickness of both claddings 100 mm, liner thickness 300 mm) was selected as the object of study. The purpose of the study is to assess the deformability of lightweight frame structures. The tests were implemented under the action of short-term and long-term evenly distributed loads, and were carried out in accordance with the method of hydraulic tests of plates and shells on the basis of the requirements of DSTU B B.2.6-7: 95. For research the research method based on hydrostatic loading of object when loading is set by weight of water is used, and its size is regulated by height of a water column. To carry out the described test procedure on the mezzanine floor of the seventh floor was assembled inventory pool of formwork panels with dimensions in terms of 5.2x2.8 m and a board height of 1.15 m. To register the measured displacements, sensors are supplied to the object under study, which allow to establish the characteristics of the stress-strain state of the object of study. Use of this method, in comparison with other existing, allows to define durability and deformability of various full-scale designs at short-term and long loading without their destruction and a stop of production process. The obtained results of field testing of a fragment of a lightweight frame indicate that the nature of the deformation of the floor under load correlates with the results of similar studies that have been repeatedly conducted for the frames of buildings with load-bearing elements with a continuous cross section.

ALTERNATIVE METHOD FOR QUALIFICATIONS OF GLASS FIBRE REINFORCED EPOXY PIPES (GRE)

This paper discusses the Ultimate Elastic Wall Stress (UEWS) test for GRE pipes under pure hydrostatic loading. UEWS appears to provide an attractive alternative to the currently used procedure laid down in ISO 14692, which involves an expensive series of long term constant pressure tests, as described in ASTM 2992, running for a period in excess of 10,000 hours. The pipes were subjected to biaxial loading, which was attained by combinations of hoop and axial stress. Loads were applied as groups of cycles which, were gradually increased until the UEWS had been determined. UEWS test has proved to be one of the most effective in terms of accuracy and speed. Moreover, it has been found to be sensitive to changes in key manufacturing and raw material parameters. Modelling results are also showed a harmonic approach and accepted to that obtained experimentally. This encourages to apply the proposed modelling for further biaxial load ratios.