Effect of Injection Pressure on Permeability and Strength of Microfine Cement Grouted Sand

The type and level of injection pressure used during permeation grouting with microfine cement suspensions can influence the extent of improvement in permeability and strength of grouted sand, the mass of cement particle deposition, and the grout flow rate. Laboratory experiments were conducted using constant pressure, variable pressure, and oscillating pressure with different pressure levels, ranges, and cyclic durations. Microfine cement grout at three different w:c ratios was injected into sand-packed columns of two different lengths; the longer column length allowed assessment of property improvement with distance from the injection point. Effluent flow rates decreased as the grouting process continued and the response was dependent on the type and level of injection pressure. Although a relatively large mass of cement particles may be deposited in the intergranular space, the grouted sand may not necessarily exhibit corresponding improvements in permeability and strength. Results from the longer columns showed sand grouted with oscillatory injection pressure exhibited somewhat greater mean strength, lower mean permeability, and larger mean cement content than sand grouted with increasing pressure or constant pressure.