EFFECT OF CONFINING PRESSURE ON EVOLUTION LAW OF HYSTERESIS LOOP OF SANDSTONE UNDER CYCLIC LOADING
(1. Key Laboratory for Exploitation of Southwestern Resources and Environmental Disaster Control Engineering of Ministry of
Education,Chongqing University,Chongqing 400044,China;2. State and Local Joint Engineering Laboratory of Methane
Drainage in Complex Coal Gas Seam,Chongqing University,Chongqing 400044,China)
Abstract:The effect of confining pressure on evolution law of hysteresis loop of sandstone under cyclic loading is investigated by using MTS815 rock mechanics testing system. Test results are shown as follows:(1) The hysteresis loop can be divided into two parts to perform quadratic fitting. In cyclic loading section,with the increase in cycle,fitting parameters A and B increase with the increase in confining pressure;while the fitting parameter C decreases with the increase in confining pressure. The opening of fitting curve increases gradually and tends to be stable;the greater the confining pressure is,the less the time it need to be stable is. In cyclic unloading section,with the increase in cycle,fitting parameter A decreases with increase in confining pressure;fitting parameters B and C decrease with the increase in confining pressure. The openings of fitting curves increase gradually and tend to be stable;the greater the confining pressure is,the larger the opening of fitting curve is. (2) Hysteresis loop area of sandstone increases with the increase in confining pressure,which means that with the increase in confining pressure,the dissipation energy of specimen in each cycle increases and the crack propagation energy needed also increases. (3) The relationship between the axial dissipation energy and cycle accords with the power of negative exponent function under cyclic loading;and the feature of the curve is that with the increase in cycle,the axial dissipation energy per unit volume attenuates quickly and tends to be stable gradually.
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