A method for determining the long-term strength of rock by multi-stage stress loading creep mechanical test

Abstract

The invention discloses a method for determining the long-period strength of rock through a multistage stress staged loading creep mechanic test. The method comprises the following steps that the in-site sampling is carried out, and a rock core test piece is manufactured; the test piece is arranged into a rock three-axis rheological mechanic test instrument, and an axial stress and annular stress system is regulated to an initial value; the test piece is subjected to multistage stress staged loading creep mechanic test in a stress load control mode until a specimen is damaged, and in the process, the change of the axial compression stress and the annular volume expanding stress along with the time in the whole test process under the effects of different stress is measured; the change of the size of the test piece along with the time is calculated; a rock creep curve is drawn, and the weakening creeping stage and the steady-state creep stage of the creep curve under the effect of each stage stress load are judged; the steady-state creep speed under the effect of each stage of stress load is calculated, the relationship curve of the change of the axial, annular and size steady-state creep speed along with the stress level is drawn, a crossing point is determined, and the stress corresponding to the crossing point is the long-period intensity of the rock.

Description

technical field [0001] The invention relates to a method for determining the long-term strength of rock through a multi-stage stress graded loading creep mechanics test. Background technique [0002] With the gradual expansion of the scale of rock engineering construction in my country, more and more attention has been paid to its long-term stability and safety. Long-term strength is an important aspect of long-term stability and safety analysis of rock engineering. Engineering experience and monitoring data show that many rock works have no conventional damage during the construction period. As time goes by, the deformation and stress show a phenomenon of slowly changing with time. This phenomenon has a great impact on the long-term stability of the project. directly cause instability and destruction. It is necessary to provide accurate long-term strength of rock to study the change law of stress-strain state of rock engineering under the action of aging, and to solve and ...

AI Technical Summary

Problems solved by technology

[0005] In the complex stress state, the stress-strain isochronous curve cluster method is mainly used to determine; Xu Weiya and Wang Rubin disclosed the use of stress-strain isochronous curves in the patent "Determining the Long-term Strength Parameters of Underground Water-sealed Petroleum Cavern Surrounding Rock" (201410399007.5). The method for determining the long-term strength of rock by the rheological rate in the curve or the steady-state rheological stage; the method described in this patent only considers the axial strain change of the rock, and does not consider the influence of the circumferential and volumetric strain changes on the long-term strength of the rock

In view of the fact that most rocks show significant volume expansion and axial compression when they fail, there are certain errors in the determination of long-term strength by the two methods only considering axial strain; in addition, the stress-strain isochrone As a parameter, a cluster of stress-strain isochronous curves is obtained. When the time tends to infinity, the corresponding stress level is the long-term strength; however, for a specific rock mechanics test, the time is 48h or 72h, and there is a certain distance from tending to infinity. Therefore, this method has certain limitations in determining the long-term strength; while the rheological rate method in the uniform steady-state rheological stage describes the steady-state creep rate of the rock sample through an exponential function, and then considers that the inflection point of the exponential function is the rock’s Long-term strength; since the exponential function is a smooth curve, the inflection point is not clear, and intuitive observation of its inflection point will inevitably cause certain errors; and because there are certain differences in the changing laws of the rheological rate curves in the three directions, the inflection point is not the same , which direction the inflection point of the rheological rate curve is used to determine the long-term strength in actual engineering is a controversial topic

[0006] In summary, the existing methods for judging long-term strength are somewhat subjective

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