Study On The Unloading Tunnel Rock Deformation And Damage Mechanisms Of Quartz Mica Schist In Danba

Quartz mica schist is a typical metamorphic which have wavy foliation structure,low rock strength, belonging to soft rock. Its main minerals are quartz, muscovite,biotite,plagioclase, hornblende, etc, resulting in a microscopic view inside the rockitself in terms of a polycrystalline structure. Deformation of rock foliationdevelopment, quartz, mica and other minerals in the rock oriented stress the role ofmetamorphism occurs or recrystallization, which are arranged according to certainrules directional anisotropy obvious damage to the surrounding rock deformationsignificantly. In this paper, Danba hydropower plant adit CPD1quartz mica schist asthe research object, through indoor and outdoor macro and micro-mechanicaldeformation test section morphology scan, combined with on-site analysis ofsurrounding rock deformation and failure characteristics, mainly achieved thefollowing results:（1）The study area is mainly distributed medium-high mountain landformeroded, temperature regional metamorphism and strong orogenic event it becomesextremey complicated geological structure, ground water development is weak, withbedrock fissure watermain, flatmaximum principal stress directions cave nearlyhorizontal, is a medium to high power. Adit rock quartz mica schist over all stability isbetter, convergence small amount of deformation, the main tunnel rock deformationlowd amage, high stress area along the foliation plane adit excavation of rockdeformation destructive phenomenon is obvious.（2）Through the rock grinding qualification test sreveal: the rock mineral ofadit is based inflakes, grains and columnar mineral-based, which is a flaky mineralmuscovite and biotite; granular, columnar minerals are quartz, plagioclase feldspar,hornblende, etc.; metamorphic minerals si based inalmandine, kyanite, staurolite.Inaddition, it also contains a small amount of apatite, tourmaline, zircon and otherminerals. Mineral composition with increasing depth of the hole was a certain changeregularly.（3）Through a series of indoor and outdoor rock, rock testing of mechanicaldeformation characteristics quartz mica schist were studied. Point load test results showed that: the basic rock strength within30MPa, and with the increase in deep holeshowing a rising trend, the loading direction perpendicular to foliation plane loadedwith pressure-induced fracturing of rock damage based. Direct shear tests and liverock in situ direct shear test results showed that: sections were cut along the surface ofthe pre-shear failure, when the plane perpendicular to the foliation shear, The shearstrength of the anti-body f ’=1.03, c’=2.10MPa, shear (friction) strength of f=0.69,c=0.18MPa; when the direction of shear along the foliation plane, the shear strengthof the anti-rock f ’=0.61, c’=0.84MPa shear (friction) strength of f=0.56, c=0.10MPa. Uniaxial compression test results show that quartz mica schist andmechanical parameters of uniaxial compressive deformation and failure modes arecontrolled by the state, showing a clear anisotropy: rock uniaxial compressive strengthand flexibility modulus with loading direction foliation plane angle β was "U" shapechange (perpendicular or parallel to the maximum load, when bias becomes smaller, β=30°is minist), along foliation plane loaded to bedding crack damage mainlyintersect at around30°to the interlaminar shear slippage along the main intersectionwhen about60°angle to the main shear failure to wear layers, vertical foliation planeloaded to wear Layer crack damage. Triaxial unloading test results show: quartz micaschist in unloading its strength and deformation are present anisotropic properties, andwith the increase of confining pressure anisotropy quartz mica schist graduallyweakening trend, the sample failure mode both tensile failure.（4）By scanning electron microscopy(SEM) tests showed that the quartz micaschist mineral crystals are carried out orientation according to certain rules, anisotropyis obvious, and there are some rocks internal cleavage and micro-defects, themacroscopic damage is the results of its internal cracks extended through. Underdifferent stress state quartz mica schist samples fracture macro and micromorphological pattern also has some differences, including morphology typicalpattern: river-like pattern, grain boundary-intergranular fracture pattern, parallel slippatterns, step-like pattern, flat surface pattern, herringbone pattern, pattern sheet totalof seven kinds of fracture patterns.（5）According to the results of the field geological survey that Adit betteroverall stability of surrounding rock, a small amount of deformation convergence, themain tunnel and adit rock types boils down to the main damage can be divided intothree categories: shear slip type, bend the drum, splitting toppling its damaging effectsof factors including: the angle between the surface and the foliation, geologicalstructure, characterized by the hole axis to stress. After the cavern excavation, stress redistribution, when there is jointed or fault zones, resulting in a low shear strengthand easy rock face along the shear structure slippage; high stress zone foliationsurface toward the hole axis When a small angle to both sides of the side wall flexuralstrength due to the lower parts of the rock mass, easily bending the drum damageoccurred; high stress zone foliation plane with a large angle to the axis of the hole, thespandrel, arch and side wall parts are prone to splitting or peeling damage dumping.