In consideration of the weak rock conditions of rock-socketed piles and taking the dilatancy of the interface into account，the constant normal stiffness conditions (CNS) were applied to simulate the lateral constraints provided by weak rock，and laboratory model tests were conducted to inquire the mobilization of the side resistance. The asperity of the concrete-rock interface can be idealized as regular sawtooth asperities，and sandstone and concrete specimens were manufactured with different half-chord lengths，respectively. The relevant measurements were observed，such as shear load，shear displacement，normal load and normal displacement. In addition，the observations showed that the dilatancy angle of the interface gradually decreased with the development of shear displacement. The shear strength of interface is closely related with the normal constant stiffness and the half chord of the rough body as well as the shear displacement. Based on the consideration of elastic compression of the asperity，the empirical relationship for the shear strength of weak rock was fitted by power functions. On the other hand，the observations were compared with the predictions of an existing theoretical model，and it was shown that the theoretical model can overestimate the side resistance of the rock-socketed piles，due to the disregard of nonlinear variation of the dilatancy angle.