Determination Of Compliance Ratio And Application Improvement Of Anelastic Strain Recovery Method

The acknowledge of in-situ stress becomes more important as more and more deep underground engineering are constructed in our country.The creep of rock will be more obvious if the stress is higher,and this is the principle of which the anelastic strain recovery method(ASR)based to determine in-situ stress.ASR method is economical and more suitable for determination in deep drills and fields with complicated geological conditions,which compensate the flawless in overcoring method and hydraulic fracturing method.Even though,there are less applications of ASR in the world,the principle and procedure of ASR still need to be improved.The application of traditional ASR method was based on the assumption of “the compliance ratio is 0.5”which was usually used in the determination of stress magnitude.Actually,there were less investigation on the compliance ratio and the assumption itself is not objective.This paper described the principle and the traditional process of calculation of ASR method in detail in the basis of reviewing the domestic and foreign research status.The experiments were performed on the red sandstones to investigate the variation of compliance.Focus on the flawless of the application of ASR method,improvements were proposed and applied.The improved ASR method was applied on the Pingdingshan No.4 coalmine.The main progress and achievements are as follows:1.In reviewing of domestic and foreign research status,this paper analyzed the advantages of ASR method on the determination of deep stress.The principle of ASR was introduced in the basis of rheology mechanics and elastic mechanics.The expressions of rock compliances of different rock rheology models were deduced in details and the fundamental framework of rheology models that adapted to ASR methods was proposed;2.ASR tests were performed on red sandstones that retrieved from coalmine in Huainan.The anelastic recovery strain curves of red sandstones were analyzed and proved the reasonability of the theory model.The variation of compliances of red sandstones were investigated.The traditional ways of hypothesizing the compliance ratio is 0.5 is incorrect.Analyzing the examples of ASR method and the selfexperiences,proposing theoretical and practical improvements.3.Analyzing the reasonability of the improvements and presenting the theory formulas.Proposing two kinds of improvements from the viscoelastic models to solve the theory flawless.Developing anelastic strain recovery models for rocks and set corresponding rheology parameters to simplify the constitutive equations.4.Improving traditional ASR procedure.Developing a set of photogrammetry apparatus to determine orientation of strain gauges,solving the problem of long time waste in the procedure of measuring strain and improving the accuracy of the strain orientation measurement.5.The improved ASR method was firstly applied in the Pingdingshan No.4coalmine.The corresponding process were described in this paper.Combined with the error discussion of anelastic recovery strain curves,the final results of stress were carried out.Compared with the stress data that from the overcoring method,the orientation of principle stress was close to N—S,and the practicability of improved ASR method was testified.