Seepage failure test means the foundation soil instability caused by underground water perturbation, which is one of the most common methods to evaluate a site seepage resistance, but it is time consuming. High water pressure is always applied to shorten the test time. However, significant error is generated as calculating the seepage failure slope (SPS), the gradient, due to the nonlinear characteristics as the pressure increases. The Darcy law and the permeability coefficient are no longer applicable. Here, an analytical method for confined aquifer is proposed to investigate the nonlinear permeability coefficient and SPS. The in situ tests were conducted on the dislocation interfaces at the reservoir banks of the Baihetan hydropower station to verify the proposed method. The test results indicate that the SPS calculated values by nonlinear equation is much smaller than that by linear equation, which means that the conventional linear calculation results will overestimate the resistance of the site seepage failure. Moreover, the results calculated by steady and nonsteady nonlinear equations are very close, while the storativity is between 1 × 10⁻³ and 1 × 10⁻⁵, which is the ordinary storativity of most aquifers in this region. Hence, in general, the steady nonlinear equation can be used to calculate the site SPS to simplify the calculation.

渗流破坏试验是指由地下水扰动引起的地基土不稳定性，这是评估场地渗流阻力的最常用方法之一，但很费时间。始终施加高水压以缩短测试时间。但是，由于压力增加时的非线性特性，在计算渗流破坏斜率（SPS）梯度时会产生明显的误差。达西定律和渗透系数不再适用。在此，提出了一种用于承压含水层的分析方法，以研究非线性渗透系数和SPS。对白鹤滩水电站库岸错位界面进行了现场测试，验证了该方法的有效性。测试结果表明，非线性方程计算得到的SPS值远小于线性方程计算出的值，这意味着传统的线性计算结果会高估现场渗流破坏的抵抗力。而且，由稳态和非稳态非线性方程式计算得到的结果非常接近，而储磁率在1×10之间^-3和1×10 ^-5，这是该区域大多数含水层的普通储水比。因此，通常，可以使用稳态非线性方程来计算站点SPS，以简化计算。