【作者】 徐德敏；

【导师】 黄润秋；

【作者基本信息】 成都理工大学 ， 岩土工程， 2008， 博士

【摘要】 工程中涉及到高水压条件的情况越来越多，国内外由于岩石（体）渗流而造成工程失事的实例已有很多，高渗压下岩石（体）力学、渗透特性研究已成为岩土工程中急待解决的前沿性课题。为研究高水头压力作用下岩石（体）的渗透特性、破坏机理和力学特性，笔者与课题组同志一起，开发研制了大型岩石渗透试验仪器。依托该套试验仪器，针对不同渗透、力学特性试样进行了较为系统的测试研究。本文取得的主要研究成果如下：（1）关于试验仪器方面，具有以下特点和创新：以成都液压伺服厂专利产品-静态伺服阀为主要控制元件，实现了试样进水端水压在完全脱离计算机控制条件可长期保持不变；以精确测定渗出水体积变化量的方法，达到提高测试精度，缩短测试时间目的；试样出水端水压采用管路过滤器、调速阀系统控制流量大小基本不变，进而在试样进水端形成稳定的水压大小，实现了对高孔隙水压、小水力梯度的真实模拟；而试样的轴向荷重、侧向压力分别采用两套调速阀控制系统，实现了试验过程的稳定、精确控制。通过对计算机控制程序的改造升级，可通过实时曲线或历史曲线无限放大监控试验过程，根据实测数据变化特点可任意修改、加长操作命令而不影响整个试验过程，真正实现了高渗压条件可控的各种加、卸载路径试验测试研究。针对试样渗透性测试，笔者提出了高水压下试样的密封，方柱体、重塑试样高围压下渗透性测试方法。（2）详细阐述了高渗压下各种应力路径渗透、力学特性试验的具体操作方法，为室内渗透性及相关力学特性测试研究提出了一套行之有效的试验测试方法。（3）试验证实了低渗透岩非达西渗透现象是普遍存在的，根据其非线性曲线特点，按压力梯度从高到低顺序排序，提出以“三次平均法”进行拟启动压力梯度推算，并通过实例说明这种推算方法是可行的。（4）试验发现，孔隙性介质，不论试样的渗透性大小，围压升、降渗透性变化均处于同一数量级，说明渗透性越大的试样受围压条件的影响性就越大；试样轴向位移在围压升高时呈负值（拉伸状态）变化，围压降低时呈压缩状态，并且在围压降低各个阶段的轴向位移值均可恢复到最初时的轴向位移大小，而试样的渗透性却低于最初时围压升高时的大小；说明围压升、降过程渗透性变化主要受试样侧向弹塑性变形的影响。而裂隙性岩体围压升、降后渗透性变化特点却完全不同，围压升高裂隙闭合，围压降低时并不能使闭合的裂隙渗流通道重新张开使渗透性增大。（5）首次提出了在全应力-应变过程中，侧向应力是影响岩石（体）渗透性变化幅度大小的主要因素：在三轴加载应力状态下，侧向应力越小，其渗透性变化幅度越大；侧向应力越大，变化幅度则越小。针对同一岩性试样，加载与卸载过程渗透性变化特征差别不大，只要保持一定的侧向应力，全应力-应变过程渗透系数变化存在一个极限值：针对一般岩石（体）试样，渗透系数变化最大值不会超过10^-5cm／s量级；而对于低渗透性大理岩，最大值一般不超过10^-7cm／s量级。（6）围压、压力梯度的大小是影响岩石渗透性的主要外界因素。针对孔隙性介质而言，压力梯度对岩石渗透性影响远大于围压条件的影响；而出水端水压大小对岩石的渗透性影响不大，可根据现场实测水压差，采用出水端水压力为零的方式进行渗透、力学试验研究。（7）提出了高渗压下岩石（体）抗剪强度的计算方法：首先把高渗压下实测得到的一组σ₁、σ₃值转化为相应有效应力值，再加上这组数据峰值强度时的平均孔隙水压后，进行抗剪强度计算。（8）根据常规饱水三轴压缩实测的σ₁、σ₃值，提出了按实际工程高渗压条件进行抗剪强度计算的方法，并通过试验验证，认为从应力角度进行抗剪强度换算可以反映高渗压状态下岩石（体）的强度特征。（9）通过对试样弹性阶段不同应力路径下的应力、应变变化特征研究发现，当侧向应力保持不变时轴向应力的加载或卸载，其应力、变形特征符合胡克弹性定律；而当侧向应力处于加载或卸载状态时，其应力-应变特征则不符合胡克弹性定律。基于此，提出岩体的工程力学参数取值应基于试验基础上，模拟工程实际所处的应力状态进行相应的试验研究。（10）在试验和莫尔一库仑定律的基础上，提出了卸载（包括高渗压卸载）条件下岩石（体）的强度计算准则：σ₁+σ₃=k（σ₁-σ₃）-b，相应强度计算公式为：C=b/2tgφ，（?）=arcsin1/k。更多还原

【Abstract】 Because of the more high water pressure condition in engineering and rock mass seepage, there were many engineering accident examples. The rock or rock mass mechanics and permeability characteristics studies had become the front-subject which should be solved urgently. In order to study the rock and rock mass permeability, failure mechanism and mechanical properties under high seepage pressure, the Rock High Pressure Permeability Testing System had been designed and produced by author and studying team clerks. By means of the device, relatively systematical test was completed, aiming at different sample with different permeability and mechanics property. Corresponding study achievements are presented as follows:（1） Followings are the characteristics and innovations about the test machine: Because the patent product - Static Servo-Valve of Chengdu Servo Hydraulic Pressure Equipment had been used as the main controlling element, it was completed that the inlet water pressure of sample could keep stability for a long term although there was no control by computer. Because the volume change of spilling water had been accurately measured, the test time was shortened and test precision was improved. The outlet water pressure of sample could keep basically stability under the controlling system of the special pipeline filter and velocity adjust valve. Therefore, the stable water pressure was gotten at the outlet, and the simulation for high pore water pressure and low hydraulic gradient was truly achieved. Both the axial load and lateral pressure of the sample were respectively controlled by two Speed Control Valves, which made sure the test process stability and precision. Through the modification and improvement of computer controlling program, the visual monitor of test process could be enlarged infinitely by time curve or history curve. According to the changing characteristics of test data, the operation command could be modified and prolonged at will, but this would not at all influence the whole test process. The mechanics test under loading or unloading path was really achieved under controllable high permeability pressure. Aiming at the permeability test of sample, the author put forward the method of the sample waterproof under high water pressure and the test method of the square prism permeability and remodeled sample permeability under high confining pressure.（2）The detailed different stress path test operation methods to measure and calculate the permeability and mechanics characteristics of sample had been illustrated, which would be effective for the further studying.（3）The test results demonstrated that the non-Darcy flow phenomenon was ubiquitous for low permeability rocks. According to the non-linearity seepage characteristics, the Averaged Three Times Method to reckon quasi-threshold pressure gradient had been given and proved to be effective method by the examples.（4）According to the test result, whether the porosity sample permeability was high or low, the values of permeability coefficient all changed in same magnitude along with the confining pressure and axial pressure increasing or decreasing, which showed that the bigger permeability of the sample was, the higher value change value was along with the external pressure. The axial displacement of sample showed the negative value change with the external pressure increasing, which implied the sample was in the tensional state. And when the external pressure dropped, the sample showed compressed state. Furthermore, the axial displacement value could all return to the original value at each fall back phase of the external pressure, but the permeability would get lower than the original value that was tested during external pressure increased, which showed that the lateral elastic-plastic deformation of the sample was the main influence factors for the sample permeability value change during external pressure increase or decrease. But the fractured rock mass permeability change characteristics were different from the rules above. Namely, once the fission of the sample was closed by compression, its permeability could not increase any more even if external pressure was reduced.（5）According to the test result, the change scope of permeability for the same lithology sample during the complete stress-strain path was mainly controlled by confining pressure, which had been put forward for the first time. The lower value of the confining pressure was, the higher change scope of permeability was during the triaxial loading process, and vice versa. As for the same lithology sample, the permeability change characteristics had little different during loading and unloading process. As long as the confining pressure was constant, there was a limit value of the permeability change during complete stress-strain process, which was the maximal permeability coefficient, not more than the magnitude of 10^-5cm/s, and the low permeability marbles was not more than 10^-7cm/s.（6）The main external effective factors for the rock permeability were the value of external pressure and hydraulic gradient. As for the porosity medium, the hydraulic gradient influential action was more than the external pressure. Whereas, the water pressure of the sample outlet had little effect on the permeability. According to the factual water pressure difference, zero value could be given to the water pressure at the sample outlet for test studying.（7） The calculation method of shear strength under high seepage pressure was put forward: firstly, converting the measured values ofσ₁、σ₃ into the corresponding effective stress and adding the average pore water pressure to the effective stress. The average pore pressure was got from a group of samples, which are measured when the strength arrived to the peak value. Secondly, using the sum of the effective stress and the average pore water pressure to calculate the shear strength under high seepage pressure.（8） The saturation water sample test value ofσ₁、σ₃ through conventional triaxial compression could be calculated as the shear strength value according to the actual engineering high seepage pressure conditions. On the basis of checkout by actual test, it was proved that the calculation result from this method that only considered stress conversion could represent the rock or rock mass shear strength characteristics.（9） On the basis of the mechanical characteristics studying of different test path triaxial compression, the rules had been found that when the confining pressure was invariant, the shear strength and deformation characteristics accorded with Hooke elastic laws, but when the confining pressure was in loading or unloading state, the shear strength and deformation characteristics were inconformity to Hooke elastic laws. The engineering parameter value should be in accordance with the test result, which should simulate the factual stress condition.（10） On the basis of test and theory of Mohr-Coulomb, the rock or rock mass strength calculation criterion under confining pressure unloading condition had been given:σ₁+σ₃ = k （σ₁-σ₃） -b, and the corresponding strength calculation formula wasC =b/2tgφ,（?）= arcsin 1/4更多还原