Grouting techniques that can prevent groundwater leakage and can improve the ground are widely used in earth structures. In cohesionless soils in particular, cement-based permeation grouting is usually adopted and the behavior of grout injection varies depending on the relative relationship between the size of grout particles and the pore size of grounds. Moreover, variation of the viscosity of grout suspension with time and decrease in the porosity of the ground due to clogging phenomena dominantly affect the behavior of the cement-based permeation grouting.
This thesis studied the behavior of the cement-based permeation grouting in cohesionless soils considering clogging phenomena. Firstly, an one-dimensional grout penetration program was developed and used to estimate the grout injection volume with time, the deposition amount of cement-based grout particles, and the permeability and porosity reduction of the ground considering the variation of viscosity and clogging phenomena. Then, laboratory chamber tests were performed for Joomoonjin sand with various grain size distributions using ordinary portland cement (OPC) as the grouting material. Applied injection pressures were 100kPa and 200kPa, respectively; water-cement ratios (w/c ratio) were 1.25, 1.65 and 2.0, respectively, within these ranges of w/c ratios the cement-based grout may behave as a Newtonian fluid.
The test results showed that the behavior of cement-based permeation grouting is divided into three different groups depending on the grain size distribution of the soils: (1) zone of cement-based permeation grouting not feasible; (2) zone of cement-based permeation grouting feasible; and (3) zone in which an accelerating agent should be added to limit the penetration depth. In the cement-based permeation grouting feasible zone, the concept of a representative pore radius was proposed to be used for figuring out the clogging phenomena, and the ratios of the representative pore radius to the mean pore radius of the cohesionless soil were experimently obtained and were in the range of 1.07 and 1.35 depending on the grain size of the soils. This ratio was smaller as the size of the soil was larger. In addition, using the experimental results and by performing a back-analysis, a functional relationship between the lumped parameter (), of which is also needed to figure out the clogging phenomena, and the representative pore radius and the w/c ratio was derived.
In the zone of larger grain sizes in which the accelerating agent should be added during grouting process, accelerating agent (liquid A) and cement-based grout suspension (liquid B) were injected by 2-shot system. The controlling process of gel time to limit the penetration depth was experimentally verified. The results of the chamber injection tests matched well with those obtained from theory utilizing the developed grout penetration program on condition that the viscosity increasing tendency of grout suspension with time is properly taken into account. In summary, the injection behavior of the cement-based permeation grouting in cohesionless soils can be predicted and analyzed in advance using the outcome of this study, if the grain size distribution of the base soil is known.