Abstract: A 3D grouting model test system, which consists of bearing test rig, servo voltage supply unit, grouting unit, multivariate information monitoring unit and image acquiring unit, is developed to investigate the grouting diffusion process and reinforcement mechanism. The main functions of this system are the lacunose, multiple sequence and parameter flexible model test of the grouting and the real-time collection of the physics field information during the grouting. The major advantages of the system include: (1) The test cavity is designed as composite barrel structured, strong leak tightness and convenient disassembly, in favor of studying grouting solid details; (2) the loading method of multi-cavity control hydraulic pneumatic joint can provide continuous steady pressure groundwater environment; (3) a multi information parallel real-time monitoring system can collect the information of the total pressure, pore water pressure and displacement of different spatial positions in the injected rock body, and realize the spatial and temporal variation of physical parameters in the grouting process. The testing system is used to perform the simulation tests of single hole grouting and grouting in a single hole, and the variation of grouting pressure P and the mechanical response of soil are obtained. The p - t curve shows multiple peak - trough cycle and characterizes strengthening mode of splitting grouting. The total pressure, pore water pressure, effective stress and grouting pressure change almost synchronously under the grouting loading; reach the peak values at the end point of grouting, and then begin to attenuate and gradually to be stabilized. Compared with single-hole grouting method, the multi-hole grouting method can improve the effective stress of soil dramatically. It is demonstrated that fracturing grouting is the main clay medium. The contact relationship between different orders of slurry veins is complex, and can be divided into 3 basic modes: shear splitting, in situ splitting and intrusion splitting. The test method of porous and small grouting rate can reduce the disturbance of surrounding rock, increase the amount of grouting and the degree of consolidation of soil, and improve the effect of grouting reinforcement.

Key words: 3D grouting model test system, clay medium, single-hole grouting experiment, multi-hole grouting experiment, real-time monitoring