分形计算方法能较准确地计算膨润土的膨胀变形，但系数K没有确切的计算方法，限制了该方法的广泛应用。基于双电层（DDL）理论和分形方法在双电层膨胀下都适用的理论事实，提出在双电层膨胀条件下采用DDL理论推导出分形方法中系数K的方法，并计算出商用膨润土的K值为9.15。对商用膨润土进行了N2吸附试验，利用等温吸附数据计算出该膨润土的表面分维为2.65，然后根据得出的系数K和表面分维采用分形方法计算了膨润土的最大膨胀率并与膨胀试验结果作对比。结果表明，分形方法的理论计算和试验结果基本一致，尤其是在施加压力较大而膨胀变形较小的情况下，分形计算方法计算结果比起双电层理论更符合试验数据。

Although fractal method performs well in calculating the swelling deformation of bentonite, it does not provide an effective method to calculate coefficient K, which limits the application of the fractal theory. Because both the DDL theory and the fractal theory are applicable in analyzing the behavior of compacted bentonite, a method is proposed to determine coefficient K in the fractal theory based on the DDL theory, by which a value of 9.15 is determined for coefficient K of commercial bentonite. N2 adsorption tests are the performed on the commercial bentonite, and the measured isotherm data are used to determine a surface fractal number of 2.65. Then, the so-determined K and the surface fractal number are used to calculate the maximum swelling deformation through the fractal method, and the calculations are compared to the experimental measurements. It is shown that the results of the fractal method agree well with the experimental data, especially when the applied loading is large and the swelling deformation is small. It is also shown that the fractal theory yields better results than the DDL theory.