饱和尾矿稳态特性试验研究

发布时间：2018-11-26 19:55

【摘要】：饱和尾矿的稳态强度是尾矿坝能否发生流滑破坏的关键因素，因此，为了揭示尾矿坝流滑破坏机理，有必要先弄清尾矿的稳态强度特性。动荷载作用引起孔隙水压力上升和土体有效应力下降，而地震液化后发生的流滑破坏通常是由静载荷引起的，故稳态强度（或称残余强度）可在静载条件下确定。本文采用固结不排水三轴试验，通过配制6组不同相对密度的尾矿试样，经饱和后分别在100kPa、200kPa、300kPa的围压下进行试验。在进行剪切时保持围压不变，逐渐加大轴向剪切力。在剪切力达到最大值后，继续进行试验，当试样产生25%的轴向应变时停止。另按照《土工试验方法标准》中的筛析法，以尾矿粒径平均大小为变量，人工配制3种颗粒级配的尾矿试样。在初始相对密度和围压一致的情况下，分别进行固结不排水剪切试验，直至进入稳定状态。根据试验结果，绘制出不同围压、试样密实度、颗粒级配下尾矿的应力—应变—孔隙水压关系曲线，，建立饱和尾矿的稳态线，求出尾矿的稳态内摩擦角及稳态强度表达式。主要得到了以下研究成果：饱和尾矿的固结不排水剪切曲线有三种典型类型：软化型、准软化型、硬化型。其中饱和松散尾矿的剪切曲线具有明显的软化特性，试样在轴向应变增长到15%—20%左右达到变形的稳态。在剪切初期，轴向应变及孔隙水压随着剪应力的增大而增大。剪应力达到峰值后随之下降，最后保持稳定，孔隙水压力则在达到最大值后一直保持稳定。同一级配、同一孔隙比的试样，随着试验围压的增大，剪切曲线软化程度逐渐降低，尾矿稳态点则随之上升。同一级配、不同孔隙比的试样在200kPa围压下的剪切曲线均表现出应变软化，且随着孔隙比的减小，剪切曲线的软化程度逐渐减弱。稳态是尾矿的固有属性，不受外界条件的影响，与尾矿的颗粒级配有关。在孔隙比与剪应力的算术坐标内，尾矿的稳态线是一条直线，线以上的部分，代表剪缩性尾矿，在实际情况下则有可能发生液化流滑。平均粒径大的尾矿，其稳态内摩擦角大，稳态线的空间分布位置高。因此，细粒尾矿在外力条件下更容易诱发液化流滑破坏。
[Abstract]:The steady-state strength of saturated tailings is the key factor for the failure of tailings dam. Therefore, in order to reveal the mechanism of fluid-slip failure of tailings dam, it is necessary to find out the steady strength characteristics of tailings. Dynamic load causes pore water pressure to rise and soil effective stress to decrease, but the flow slip failure after earthquake liquefaction is usually caused by static load, so the steady-state strength (or residual strength) can be determined under static load condition. In this paper, six groups of tailings samples with different relative densities were prepared by undrained triaxial test. After saturation, the tests were carried out under the confining pressure of 100kPa200kPa-300kPa respectively. The confining pressure is kept constant and the axial shear force is gradually increased. After the shear force reaches the maximum value, the test continues and stops when the specimen produces 25% axial strain. In addition, according to the sieve analysis method in the Standard of Geotechnical Test methods, three kinds of tailings samples with particle gradation were artificially prepared with the mean size of tailings as variables. Under the same initial relative density and confining pressure, the undrained shear tests were carried out respectively until they entered a stable state. According to the test results, the stress-strain-pore water pressure relationship curves of tailings with different confining pressures, sample compactness and particle gradation are drawn, the steady state curves of saturated tailings are established, and the steady state friction angles and steady strength expressions of tailings are obtained. The main results are as follows: there are three typical types of undrained shear curves of saturated tailings: softening type, quasi-softening type, and hardening type. The shear curve of saturated loose tailings has obvious softening characteristics, and the specimen reaches the steady state of deformation at the axial strain of 15% -20%. At the early stage of shear, the axial strain and pore water pressure increase with the increase of shear stress. When the shear stress reaches the peak value, it decreases and then keeps stable, while the pore water pressure remains stable after reaching the maximum value. With the increase of test confining pressure, the softening degree of shear curve decreases gradually, and the steady point of tailings increases with the increase of test confining pressure. The shear curves of samples with different porosity ratios show strain softening at 200kPa confining pressure, and the softening degree of shear curves decreases with the decrease of void ratio. Steady state is the inherent property of tailings, which is independent of external conditions and is related to the particle gradation of tailings. In the arithmetic coordinates of void ratio and shear stress, the steady state line of tailings is a straight line, the part above the line, representing shear-shrinkage tailings, may occur liquefaction flow slip in practice. The tailings with large average particle size have large steady state internal friction angle and high spatial distribution of steady state line. Therefore, fine tailings are more likely to induce liquefaction flow slip failure under external force.
【学位授予单位】：江西理工大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TV649;TD926.4

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