Abstract: It was found that in shallow depth in magma and metamorphic rocks, the value of lateral coefficient is higher relative to sedimentary rocks. Taking the granitic rocks for examples, which is widely exposed in ground surface and regarded as originally intruded to form a dome at larger depth, this paper presents the computation result of denudation thickness. The method is started from two kinds of suppositions for representation of dominant stress in 3D in large depth before obvious denudation. One is hydrostatic head, another is Hooke’s law and then the horizontal strain is zero during denudation process. The lateral coefficient formula is used to infer the denudation thickness, which is commonly larger for both of the two suppositions. Statistic results of in-situ stress data of 254 groups in granitic rocks are of a new fitting formula to the average counterparts. From the 2nd supposition, it is inferred the denudation thickness, which is seemed to closed to the updated high limitary values of denudation thickness whether from geological judgment or fission-track data of apatite. To check the feasibility of this method, two case histories are presented. The denudation thickness as Daya Bay is between 1 500 m and 3 000 m, closed to 1300m from geological judgment. The denudation thickness at the shiplock of the Three Gorges Project is 1 700-3 200 m, similar to that test result of fission track analysis. The results further prove that the denudation thickness is relatively larger than most of the buried depth of underground rock engineering.

Key words: granite, in-situ stress, lateral coefficient, buried depth, denudation thickness