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On the basis of in situ direct shear tests the effect of roughness, concrete strength and normal stress on the shear strength of the cemented interface between concrete and bedrock has been systematically studied. As a result of this study, an efficient method for assessing the shear strength of the cemented interface is presented.Due to the varieties of concrete strengths the test results of τ-σn seem to be scattered.An apparent nonlinear relation of normal stress versus shear stress is obtained... On the basis of in situ direct shear tests the effect of roughness, concrete strength and normal stress on the shear strength of the cemented interface between concrete and bedrock has been systematically studied. As a result of this study, an efficient method for assessing the shear strength of the cemented interface is presented.Due to the varieties of concrete strengths the test results of τ-σn seem to be scattered.An apparent nonlinear relation of normal stress versus shear stress is obtained after determining the relationship between non-dimensional ratio τ/Rc--σn/Rc. By using the equation of the curve fitting, the shear strength of the cemented interface between any concrete strength required in construction and bedrock can be obtained.The study shows that the roughness is a major factor which influences shear strength. The shear strength for design can be basically estimated according to the basic friction angle and the peak dilation angle of the interface, and the shear strength of the cemented interface without normal stress.Therefore, in order to determine the shear strength of the cemented interface between concrete and bedrock, it is extremely important to obtain the basic friction angle of concrete against the plane-surface of the bedrock; make measurement of the peak dilation angle and the shear strength without normal stress; and determine the concrete strength during the direct shear tests under appropriate roughness. 通过现场直剪试验,比较系统地研究了糙度、混凝土强度和正应力对混凝土与基岩胶结面抗剪强度的影响,从而提出了对混凝土与基岩胶结面抗剪强度进行评价的有效方法。 由于混凝土强度不同,造成τ与σ_n关系点群分散。用无因次比τ/R_c与σ_n/R_c的关系,得到正应力与剪应力的明显非线性关系,拟合其曲线方程,从而得到工程所需的任一混凝土标号的抗剪强度。 研究表明,粗糙度是影响抗剪强度的主要因素,根据混凝土与基岩接触面的基本摩擦角和峰值剪胀角,以及胶结面的抗切强度,对设计采用抗剪强度可作出基本的估计。 因此,确定混凝土与基岩平整面的基本摩擦角;在直剪试验中准确地测定峰值剪胀角、不加正应力的抗切强度和混凝土的强度;以及选择适当的糙度,对最终确定混凝土与基岩胶结面的抗剪强度极为重要。 Corresponding to various shear strength with even stress distribution,the real shear strength of cemented interface between concrete and bedrock is studied in this paper by elasto plastic FEM.The effect of Young's modulus of concrete and rock upon the real shear strength is analyzed,and the influence of sample shape on the test result about shear strength is studied too.Some propositions that can be taken as references for engineering practice and in situ shear test are put forward. 采用弹塑性有限元法,分析研究了混凝土与基岩胶结面的不同平均应力抗剪断强度对应的真实抗剪断强度,以及混凝土和基岩弹性模量取值对计算真实抗剪断强度值的影响.提出了一些可供现场抗剪断试验和工程设计时选择抗剪断强度的参考意见. In the fracturing process for making the horizontal fractures, the interlayer channeling often takes place. In order to investigate the causes of interkyer channeling, the finite element numerical simulations were carried out by means of the software ANSYS. The results demonstrate that the interkyer channeling is resulted from the shear destruction of the second cemented interfaces nearby. The shear destruction is induced by the imbalance of pressures acted on the upper and lower surfaces of interlayer.... In the fracturing process for making the horizontal fractures, the interlayer channeling often takes place. In order to investigate the causes of interkyer channeling, the finite element numerical simulations were carried out by means of the software ANSYS. The results demonstrate that the interkyer channeling is resulted from the shear destruction of the second cemented interfaces nearby. The shear destruction is induced by the imbalance of pressures acted on the upper and lower surfaces of interlayer. The lowest limits of interlayer thickness for the balance fracturing technology and the ordinary fracturing technology were determined on a series of calculations. When the thickness of interlayers is over the limits for these two technology,the interlayer channeling would probably take place in the practice. This result may provide a quantitative reference for putting the balance fracturing technique into practice. 在形成水平裂缝的压裂施工中,常会发生薄层间窜流的现象。借助于有限元分析软件ANSYS,对层间窜流的原因进行了深入的模拟分析。模拟结果表明,在压裂施工中,水平主裂缝附近第二胶结面会发生受拉张开和压裂液渗入的现象,但这并不会直接导致层间窜流,隔层上、下压力差使附近的第二胶结面产生剪切破坏才是层间窜流的直接原因。在此基础上,针对平衡压裂和常规压裂两种工艺,对不同厚度的隔层进行了抗压强度计算,给出两种工艺下隔层不发生窜流的下限厚度,为平衡压裂技术的实施提供了量化的参考标准。
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