Evaluation Of True Triaxial Strength Criteria On Prediction Of In-suit Stresses With Borehole Breakout

Stress concentration is easily happened on borehole wall, it will arouse borehole breakout when the concentrated stress exceeds strength of rock on the borehole wall. The edge of breakout is on the critical state of destroy, so the principal stress of breakout edge will satisfy strength criterion. Conversion can be carried on between in-suit stresses and the principal stress on borehole wall according to the Kirsch equation, if Kirsch equation is substituted into strength criterion, the maximum horizontal in-situ stress can be predicted. The distinction between vertical stress and minimum horizontal stress on borehole wall is large, so it's suitable to select true triaxial strength criteria which consider the effect of intermediate principal stress for the prediction of in-suit stresses.This paper adopts test data in literatures, make use of Drucker-Prager criterion, Murrell criterion,3D Hoek-Brown criterion, Mogi-Coulomb criterion, modified LADE criterion and EXP criterion, six strength criteria in all to fitting true triaxial test datum and borehole breakout test data, to make sure of the correlation parameter in criteria, and then the maximum horizontal in situ stress can be predicted by Fitting relationships.It's discovered that:true triaxial strength criteria are suitable to be used for prediction of maximum horizontal in-suit stresses on borehole wall which breakout span less than 75°; it's not accuracy for the prediction of maximum horizontal in-suit stresses on borehole wall which breakout span is bigger than 75°. Base on the prediction of maximum horizontal using borehole breakout, it's not found a true triaxial strength criterion which is fitted for all rock types. Different true triaxial strength criteria are suitable different rock types. If a true triaxial strength criterion can fit test data well, it's not mean it can predict in-situ stresses precisely.