This paper deals with the orientation ability of clay minerals and its effects on landslides using the result of x-ray diffraction for clay mineral in sliding-zone soil. At first, the basic measured principles for the orientable arrangement of clay minerals were discussed and the methods of the quantitative appraisement for the orientation ability of clay minerals are given. And then, according to the result of x-ray diffraction of the clay minerals in the sliding-zone soil, the orientation ability of clay minerals had been quantitatively analyzed and calculated. Results show that the sliding-zone soil has the orientation ability of clay minerals,...