Papers by Author: Tian Hong Yang

Abstract: first of all, this paper intensive studies the hydraulic fracturing mechanism of heterogeneous material resultant from the seepage – damage coupling, based on which, the coupled seepage and damage effects during hydraulic fracturing is investigated, and the difficulties of hydraulic fracturing study are how to determine failure modes and breakdown pressure. By using numerically testing method, the mechanical mechanism of hydraulic fracturing under asymmetric distribution of pore pressure with three holes, including fracture patterns, stress flied distribution, initial fracturing pressure and breakdown pressure, was studied by using the FSD model. According to the results of this research, crack extension direction of hydraulic fracturing is influenced not only by the local pore pressure around crack tip, but also by the gradient distribution of macro pore water pressure. The fracturing direction always propagates towards the regions of higher local pore pressure and breakdown pressure decreases with the increasing of local pore pressure. These results are well aggress with the results in the experiments. This research has important theoretical and engineering value. In engineering practice, we can use the porous asymmetric hydraulic fracturing technology to control the direction of crack propagation. Keywords: hydraulic fracturing; numerical simulation; heterogeneous material; asymmetrical

Abstract: Concrete is a heterogeneous composite material. The heterogeneity consists of the distribution and shape of aggregate, interfacial transition zone (ITZ) and the inhomogeneity of each component materials. The key in numerical models for simulating the fracture behaviors is how to describe the heterogeneity actually. In this paper, at meso-scale level general-purposed digital image processing technologies are utilized to characterize the heterogeneity resulting from the shape and distribution of aggregates and ITZ, and at micro-scale level, a statistical method (e.g. Weibull distribution) is used to describe the heterogeneity of each phase. And then a multi-scale numerical model based on digital image is proposed to simulate fracturing process of concrete under loading condition. The proposed model can take the actual distribution and shape of aggregate into account. The fracturing process of concrete in uniaxial compressive tests is simulated by using the model. The results show that the shape of aggregates plays an important role in stress distributions to influence the damage evolution during loading. The proposed model is capable of capturing the complete failure process of concrete materials that includes the initiation, propagation and coalescence of microcracks as well as cracking pattern associated with different loading stages, which is a new tool to study the fracturing behaviors of concrete in more detail. Key words: digital image; heterogeneity characterization; fracturing process; concrete

Abstract: In general, rock mass is anisotropic because of presence of stratification, foliation or joints in it. In this paper we considered how the angle of anisotropy influences the stability of tunnel. By using COMSOL Multiphysics, fluid and 2D plane models are coupled to analyze stress-strain state, failure shape and water flow characteristic around tunnel for angle range from 0° to 90° with a interval of 15°. Results show that in condition of vertical force of initial stress field larger than horizontal one, failure district is maximum for θ=40° and minimum for θ=90° where the strength of horizontal direction in anisotropic rock is smaller than the vertical one. In this case failure is mainly developed in roof and bottom. When the horizontal strength of anisotropic rock is larger than the vertical, results reverse. In anisotropic rock, the more the direction of larger permeability is coincident with one of source underground water acted, the more water flows into tunnel.