To clarify the strength of fault gouge with preset structural plane after strengthening by cement and sodium silicate grout, a test device was developed. The grouting tests were therefore conducted under the conditions of different structural plane angle, ratio of C-S grout and injection pressure. It can be concluded that the uniaxial compressive strength of samples with α=0°, 45° and 90° increased by 156%, 400% and 50% after grouting, respectively. The strength of samples with α=45° were relatively low both before and after grouting. By the extremum difference analysis method, ratio of C-S grout is confirmed to be the most important factor followed by structural plane angle and injection pressure to influence the strength of samples. Compression failure characteristics of typical samples were analyzed. It was found that grout veins played a role of skeleton during the compression process. In terms of strengthening mode, strengthening effect and the dominant factor, the strengthening characteristics of cement grout, and C-S grout are contrasted. By using the cement grout, structural plane angle is the most important factor to influence the strength of samples, which is different from C-S grout.
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