This research project deals with the fracturing phenomena of ground in the cases of chemical grouting, backfill grouting, pressurization of slurry in slurry type shield tunneling, pressurization of cement milk in ground anchor and so on.
When the injection pressure is larger than the fracturing pressure of ground, the fracturing occurs. And the fracturing pressure depends upon the soil type, confining pressure, types of grouts. The author studies some factors related to the fracturing pressure of sandy and cohesive soils. In experiments, the effects of soil type (permeability, and strength), viscosity of grouts, and confining pressure were clarified and the equation which gives the fracturing pressure was supposed. Main conclusions were summarized as follows.
1) The fracturing pressure generally increases as the viscosity of injection materials increase. However, the fracturing pressure become constant when the flow value of injection material exceed 30 sec.
2) The fracturing pressure with injection materials which flow value is larger than about 30 sec can be reach to the cavity expansion pressure, irrespective of types of ground.
3) The fracturing pressure which have a tunnel-face-shaped cavity is a little larger than that have a cylinder-shaped cavity.
4) The fracturing pressure increases as the diameter ratio (=diameter of specimen/diameter of borehole) increases when the ratio is less than about ten. And the pressure become constant when the ratio is larger than ten.