| In spite of the study and application of rock hydraulic fracturing started at 20th century 50s early, its mechanism is not known well and there are many study topics. Most studies on rock hydraulic fracturing are focussed on artifical hydraulic farcturing applied in field of petroleum and nature gas. The hydraulic fracturing problems in field of water conservancy and hydropower and mining are producted by nature hydraulic power. The mechanism of nature hydraulic fracturing is more complex than that of artifical fracturing, so its studies are not enough ,espeically, the study on a single fracture.Fristly, In this paper the study level of hydraulic fracturing is divided into two based on study measure. The rock is considered as a homogeneous medium based on rock macroscopical, synthrtic and statistical characteristics in frist study level. But the secondary study level is focussed on a single fracture based on rock microcosic characteristics. Secondly, the differences between the artifical and nature hydraulic fracturing are analyzed and concluded. Thirdly, the mechanism of nature hydraulic fracturing is studied from two aspects of theortical analysis and numerical simulation according to its characteristics and study level. Finally, after deeply studyed on hydraulic fracturing simulation of higher pressure tunnel, the Influence laws of hydraulic fracturing on tunnel surrounding rock stability are proposed. The major studies and conclusions are followed.(l)The elastic and elasto-plastic problems of deep-buried circle tunnel considering influence of seepage field is studied based on rock macroscopical, synthrtic and statistical characteristics. The elasto-plastic analytical solution of deep-buried tunnel are obtained. Further, the influence laws of seepage field on stress field and plastic radius surrounding tunnel are studied according to different ratio of inner and outer water head. The study shows that the influence of seepage field on stress field is intensive along with the gradient increment of inner and outer water head of tunnel, and the influence degree on tangent stress is more than that on radial stress. The distribution law of stresses is not coincided with situation of without considering fluid flow. The compressive stresses and plastic radius are gradually decreased along with the increasing inner head, and plastic radius may be zero value if the inner head continually to some extent. But the new plastic radius will be reappeared along with the increment of inner head further, the first principle stress is alreadly turnned to tangent stress at that time. The plastic radius with considering influence of fluid flowis larger than that without considering the influence.(2)Using fracture propagation engineering criterion, calculation formulae of critical inner water pressure of two kinds of failure model are obtained respectively and its effect laws as fracture direction and lateral geo-stress coefficient are studied. The study shows that critical inner pressure of two kinds of model is not varied as fracture direction changing when the lateral coefficient equals 1.0. Under tension-shear mixed model, fracture is most easily fracturing when fracture direction is parallel with direction of principle stress. Under compression-shear mixed model, distribution law of critical inner water pressure is same as tension-shear complex model when (λ-tanφ) large than 1.0 .But fracture is most easily fracturing when (λ-tanφ) less than 1.0 and fracture direction are 45° or 135° angle with principle stress.(3)It is assumed that fracture shape is a half ellipse-shaped in hydraulic fracturing of rock and concrete material. Based on boundary condition of natural hydraulic pressure, the mass conservation and momentum principle, the concrete formulae of liquid mass conservation and differential equation of water pressure distribution due to hydraulic fracturing are obtained using the finite control volume approach. The theoretical formula at any time of fracture stable propagating is obtained also. The theoretical formula is...
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