Expansion Characteristics Of Rock Peak Loading And Unloading A Pilot Study

Excavation is a complicated process with loading and unloading at the same time in underground rock project, and the destruction process and the stress and strain of rock has not been sufficiently understond in loading and unloading conditions, and the formation and activity of rock rupture zone and the interactional law between frame and surrounding rock is also unclear. Therefore, the study of rock dilatancy and deformation failure characteristics has a great significance for understanding the deformation mechanism and reasonable supporting design of surrounding rock in roadway.In order to study the dilatancy of surrounding rock in some mine in Yunnan, the test methods were used, which include triaxial loading and unloading confining pressure, and the test was carried at the TAW-2000 microcomputer control servo rock compression testing machine. Eventually, the dilatancy characteristic, deformation failure mechanism, mechanics properties and mechanics parameters of rock has beenin-depth studied.By analysis of the experimental results, the important conclusions are as follows: (1) The dilatancy is mainly from deformation generated by the rock rupture in loading and unloading test, when the confining pressure less than 10MPa; (2) When the confining pressure less than 10MPa, specimens mainly occur extension breakage in the triaxial loading test, and specimens mainly occur shear breakage in the unloading confining pressure test. Extension fracture by comparison to shear breakage, bring more dilatancy; (3) The result's analysis of the unloading confining pressure test showed that plastic strain-softening properties and dilatancy characteristics of rock can be also observed, which has not been specifically discussed in the literature published; (4) Compared with the triaxial loading test, the rock mechanical properties is significantly affected by confining pressure in the unloading test (In loading test, the uniaxial compressive strength of rock (σc) is 169.127MPa, and the lithology intensity influence coefficient k is 5.087; In unloading confining pressure test, the uniaxial compressive strength of rock (σc) is139.311MPa, and the lithology strength influence coefficient k is 9.027. So, the rock uniaxial strength is obviously on the low side in the unloading test condition, and the axial stress strength(σ₁) is affected confining pressure by all the more prominence.); (5) The function between dilatancy angle and confining pressure is obtained by LR Alejano and E. Alonso in loading test, but the result of unloading test showed that dilatancy angle and confining pressure also meet the function in the unloading confining pressure test conditions; (6) Finally, the constitutive model which contain plastic strain-softening and dilatancy was improved by working in the function of dilatancy angle and confining pressure, so as to the effect of dilatancy in rock project can be more true in the simulation with the constitutive model.To sum up, the dilatancy that exist in rock engineering, was carried out a detailed study with the triaxial loading and unloading test, from the qualitative analysis to quantitative analysis. And the innovative research results has great theoretical significance and engineering value for theoretical studies, engineering design and construction.