Abstract: For many high rockfill dams, which are constructed or will be constructed in Southwest China, deep overburden is one of the most complex engineering problems. The deformation and stress status play an important role in the safety of dams. For the traditional methods, because it’s almost impossible to collect gravel overburden layer samples, the original density cannot be determined exactly. Thus, it is very difficult to get the reliable mechanical and seepage properties of overburden layer in laboratory tests. A new method that indirectly calculates the original density of overburden gravel using pressuremeter tests (PMT) or dynamic penetration tests (DPT) is proposed. In the construction period of Wudongde, this method is successfully applied to the determination of the density of overburden layer. Furthermore, based on the indoor model tests, it is verified that the correction factor of rod length in DPT follows the description of Newton elastic collision theory. Therefore, a new pressuremeter probe with high pressure and side expansion is developed in order to conduct the whole-process pressuremeter tests on deep overburden. The proposed whole set method provides an important technical support for further studies on the engineering properties of deep overburden of dam foundation.