Experimental results and discussion The uniaxial compressive strengthresults of the specimen is shown in Table 1. The elastic modulus and Poisson’sratio of the rock in the table are calculated by selecting 50% of the peakstrength value (M.H.
B, Rao, & Ramamurthy, 2002). For the uniaxial strength andelastic modulus, we can see that the variation of uniaxial strength variesgreatly, with the maximum reaching 206.168MPa and the minimum of only99.841MPa. The average elastic modulus of the rock is 86.835GPa, shows that theelastic modulus of the rock is large which will cause more elastic deformationduring the load process. The average Poisson’s ratio (0.
274) of all samples asseen in table 1.At the later stage of the loadingprocess, the rock samples were peeled off and accompanied by splashing anddestruction. The rock samples emitted a loud sound and accompanied with thesplashing of the rock, which indicated that the rock samples showed strongbrittleness.
During the loading process, large elastic energy is stored, andthe energy is quickly released at the moment of failure of rock specimen. Based on this study, the failure modeof slate caused byuniaxial compression can be summed up in 3 categorieswhich are Tensile Failure (TF), X shear failure (XSF) and Shear Failure (SF) asillustrated in figure 7. Tensile failure is dominant at angle ?=90° and it isparallel to the direction of laminations and thesamples had multiple splitting failures along the axis of surface tension asshown in figure 9a. Under the influence of the axial compressive stress,the Poisson’s effect will cause the transverse stress to be greater than therock’s compressive strength which will cause the destruction of the rock.
Thecracks from the sample are similar to that obtained by (Khanlari, Rafiei, & Abdilor, Evaluation of strength anisotropy and failure modes of laminated sandstones, 2015) but the cracks wereobserved at angle ? =0 °. When ? =30°£ ?£ 60°, Shear Failure (SF) occurs.In this type, the shear failure occurs along the axial to the laminations andgives rise to two separate shear planes in the middle. The shape of the samplefailure is a ?-shaped which resembles the one of (Khanlari et al, 2015) but intheir experiment it occurs at ? =900 asshown in fig. 9b. In X Shear Failure (XSF), the failure cutsacross the laminations perpendicularly. The transverse stress produced by thePoisson effect is larger than that of the tensile Strength which will cause thedestruction of the rock.
This fallsunder ? =00as shown in fig. 9c. Q from my explanations, does these diagramscorrespond to the failure modes?The rock samples in uniaxial failure forms are complexand changeable. It is generally assumed that most of the final rockdestructions are parallel to the axis of fracture (failurealong foliation plane).
Similar studies were conducted by (MingTien, Chuan Kuo, & HseinJuang, 2006) and (Saroglou & Tsiambaos , 2007), to determine the uniaxial compressivestrength variations of rocks. In this study, the type I and type II maximumcompressive strength occurs when ? =0°, while in type III the maximumcompressive strength occurs when ? =90° as shown in figure 6.