Experimental Research On Crack Propagation In Jointed Rock Mass Based On Energy Principle

A large number of engineering practice shows that the rock slopes andunderground cavern’s instability is closely related to the internal fracture of jointedrock mass. When stress environment changes, the joint end produces stressconcentration, cracks start to craze and expand, and then failure of rock mass happens.Therefore, studies the mechanical behavior of joint rock crack and the crackinteractions are particularly important. The traditional elastic-plastic mechanics in thestudy of rock mass mechanics is circumscribed. In fact, the damage of rock mass isessentially the result of energy dissipation and release, use energy principle to analyzedeformation and failure process is an effective method. This paper use rock-likematerial and designs different open flaw joint rock mass model, by biaxialcompression and cyclic loading-unloading compression, discuss the crack propagationprocess and energy evolution law. Mainly work are as follows:(1) Using barite powder, quartz sand, gypsum, cement and other rock-likematerials, design the single flaw rock mass model with low-angle dip, middle-angledip, and high-angle dip, which represents the geometry distribution for collinear,non-collinear and non-collinear overlap. And design the double flaw rock mass modelwith different connectivity.(2) Using rock mechanics multifunctional tester, analyze the strength anddeformation characteristics of joined rock model. Under biaxial compression, thestress strain curve is divided into four typical phases:①small deformation elasticstage;②elastic stage;③micro fracture stable development stage;④unstable fracturedevelopment stage. Under cyclic loading-unloading biaxial compression:①with theincrease of cycles stage, the curve is from dense to sparse, distance is from small tolarge, and the area formed by loading and unloading curve is becoming more and more "plump";②the stress strain curve of the two measure points have the samechanging trends, but not overlap;③when vertical stress is less than11.0MPa, thestress strain curve of most specimens show the approximate characteristics of upright,but with the increase of cycles stage, this phenomenon disappears;④before destroythe stress strain curve appeared strain lag phenomenon;⑤When σ1-σ3is smallerthan a certain value, the specimens show tensile on vertical and compression onlateral, as the same, with the increase of cycles stage, this phenomenon disappears.(3) Wing crack initiation angle is affected by the flaw angle, ligament angle,ligament length and confining pressure etc. Initiation angle in cyclicloading-unloading biaxial compression is greater than biaxial compression. For singleflaw specimens initiation angle is80-110degree, for double flaw specimens is65-105degree. And initiation stress is always at70%-90%of the peak stress.(4) Crack coalescence mode is also affected by flaw angle, ligament angle,ligament length and confining pressure etc. According to crack propagation path andcrack properties, the crack coalescence mode of single flaw rock mass can be dividedinto three kinds and eight classes: tension coalescence, tension-shear coalescence,shear coalescence. And of double flaw rock mass can be divided into two kinds andeight classes: tension-shear coalescence, shear coalescence. Flaw angle and ligamentangle have a greater influence on the crack coalescence mode; ligament length has alittle effect; yet confining pressure effect is not obvious.(5) The process of crack initiation, propagation and coalescence has a certaincorrelation with energy evolution. During the load process:①the energy evolvingcurve increases by non-linear;②growth rate changes from small to big, the curveslope increases gradually and finally tends to be stable;③at first, elastic energydensity is greater than dissipative energy density, but when failure the dissipationenergy density increases suddenly and dramatically, its value will exceed elasticenergy density. As the energy distribution:①with the increase of cycles stage,dissipative energy ratio increase, but elastic energy ratio decrease;②At thebeginning of the loading, the elastic energy ratio may be larger than, less than, or beequal to the dissipative energy ratio. It also shows that jointed rock with differentgeometry and stress state has different limit energy storage.