Cement Grout Nonlinear Flow Behavior through the Rough-Walled Fractures: An Experimental Study

This research experimentally studied the effects of various fracture roughness (characterized by the fractal dimension D) and normal stress (normal loads FN) applied to fracture on ultrafine cement grout nonlinear flow behavior through rough-walled plexiglass fractured sample. A high-precision and effective sealing self-made apparatus was developed to perform the stress-dependent grout flow tests on the plexiglass sample containing rough-walled fracture (fracture apertures of arbitrary variation were created by high-strength springs and normal loads according to design requirements). The real-time data acquisition equipment and high-precision self-made electronic balance were developed to collect the real-time grouting pressure P and volumetric flow rate Q, respectively. At each D, the grouting pressure P ranged from 0 to 0.9 MPa, and the normal loads FN varied from 1124.3 to 1467.8 N. The experimental results show that (i) the Forchheimer equation was fitted very well to the results of grout nonlinear flow through rough-walled fractures. Besides, both nonlinear coefficient (a) and linear coefficient (b) in Forchheimer's equation increased with increase of D and FN, and the larger the FN was, the larger the amplitude was. (ii) For normalized transmissivity, with the increase of Re, the decline of the T/T0-beta curves mainly went through three stages: viscous regime, weak inertia regime, and finally strong inertia regime. For a certain D, as the normal load FN increased, the T/T0-beta curves generally shifted downward, which shows good agreement with the single-phase flow test results conducted by Zimmerman. Moreover, with the increase of D, the Forchheimer coefficient beta decreased. However, within smaller FN, beta decreased gradually with increasing D and eventually approached constant values. (iii) At a given FN, Jc increased with increasing D.