Abstract: An induced fracture grouting method has been developed to solve the randomness of the splitting direction of fracture grouting in soil in tunnel. The objective of the method is to control and change the splitting direction of the soil. The results can be used to guide the design and construction of induced fracture grouting. Based on the elastic theory and its basic assumptions, the mechanism of fracture grouting in a single layered soil under the condition that the vertical in-situ stress is larger than horizontal in-situ stress is analyzed. And then the necessity of changing the splitting direction into horizontal as well as the induced method is discussed. The mechanism of induced fracture grouting is analyzed according to the stress concentration theory. By using the finite element method, a research about the stress distribution around the grouting hole is performed, in order to find out how it changes with the lateral pressure coefficient and distance between the grouting hole and the induced hole. The requirements about the lateral pressure coefficient and distance between the above two holes to achieve induced fracture grouting are studied. The formula for calculating critical value of distance between the above two holes is fitted. It is concluded that it appears possible to change the stress distribution around the grouting hole by excavating symmetrically the induced holes at its top and bottom positions; and the distance needs less than 4 times the diameter of the grouting hole. While the distance between the grouting hole and induced hole is less than the critical distance, the stresses of the control points around the grouting hole transform, as a result the slurry would split horizontally. In addition, the critical distance between the induced hole and grouting hole increases if the lateral pressure coefficient increases.

Key words: induced fracture grouting, elastic analysis, distance between the induced hole and grouting hole, lateral pressure coefficient, finite element method