This paper addresses a fundamental question in rock mechanics:Are there Class Ⅱ rocks?The historical development of servo-controlled rock testing machines is reviewed,followed by a brief review of some stiff testing ...This paper addresses a fundamental question in rock mechanics:Are there Class Ⅱ rocks?The historical development of servo-controlled rock testing machines is reviewed,followed by a brief review of some stiff testing machines.The pioneering work of some researchers is reviewed,and the misconception of classifying rocks into Class Ⅰ and Class Ⅱ is discussed.The mechanism of post-peak Class Ⅱ behavior is discussed based on some recent test results.When a brittle hard rock is tested using a soft testing machine under axial-strain-controlled loading,violent failure can occur when the peak strength is reached,and the post-peak stress-strain curve cannot be obtained.However,a Class Ⅱ post-peak stress-strain curve can be obtained when the rock is tested under lateral-strain-controlled loading.If a stiff testing machine is used,Class Ⅰ and Class Ⅱ post-peak stress-strain curves will be obtained under axial-and lateral-strain-controlled loadings,respectively.It is therefore not appropriate to classify rocks into Class Ⅰ or Class Ⅱ rocks.The influences of other conditions,such as rock type,confinement,and specimen height-to-diameter ratio,on the type(Class Ⅰ or Class Ⅱ)of post-peak stress-strain curves are also discussed.Finally,some misconceptions in the rock mechanics community,stemming from the concept of“Class Ⅱ rock”,are discussed.By clarifying these concepts related to Class Ⅰ and Class Ⅱ behaviors,this paper seeks to clarify misunderstandings and misapplications related to post-peak strength and deformation properties in the field.展开更多
基金the Natural Science and Engineering Research Council of Canada(RGPIN/4052-16,ALLRP 560390-20).
文摘This paper addresses a fundamental question in rock mechanics:Are there Class Ⅱ rocks?The historical development of servo-controlled rock testing machines is reviewed,followed by a brief review of some stiff testing machines.The pioneering work of some researchers is reviewed,and the misconception of classifying rocks into Class Ⅰ and Class Ⅱ is discussed.The mechanism of post-peak Class Ⅱ behavior is discussed based on some recent test results.When a brittle hard rock is tested using a soft testing machine under axial-strain-controlled loading,violent failure can occur when the peak strength is reached,and the post-peak stress-strain curve cannot be obtained.However,a Class Ⅱ post-peak stress-strain curve can be obtained when the rock is tested under lateral-strain-controlled loading.If a stiff testing machine is used,Class Ⅰ and Class Ⅱ post-peak stress-strain curves will be obtained under axial-and lateral-strain-controlled loadings,respectively.It is therefore not appropriate to classify rocks into Class Ⅰ or Class Ⅱ rocks.The influences of other conditions,such as rock type,confinement,and specimen height-to-diameter ratio,on the type(Class Ⅰ or Class Ⅱ)of post-peak stress-strain curves are also discussed.Finally,some misconceptions in the rock mechanics community,stemming from the concept of“Class Ⅱ rock”,are discussed.By clarifying these concepts related to Class Ⅰ and Class Ⅱ behaviors,this paper seeks to clarify misunderstandings and misapplications related to post-peak strength and deformation properties in the field.
