Effect of Preparation Technique on Permeability and Strength of Cement-Grouted Sand
The effectiveness of cement grouting is generally evaluated in terms of the improvement attained in the engineering properties of the grouted soil. Although this degree of improvement should logically be related to the amount of cementitious particles present in the pore spaces of the grouted sand, and indeed is to some extent, the method of preparing the specimens can exert an even stronger influence. Two significantly different preparation procedures—injection and hand mixing—were used to combine sand with a microfine cement grout at three different water-to-cement ratios. In the hand-mixing technique, a measured volume of grout (relative to the total void volume of the sand) was mixed mechanically with the sand, whereas in the injection method the grout permeated the sand through interconnected pore channels. Immediately after preparing the injected specimens, they were disassembled and an elutriation and filtration procedure was used to quantify the mass of cement particles deposited in the voids of the sand. For grouts with corresponding water-to-cement ratios, the injected specimens manifested higher cement contents than their hand-mixed counterparts with voids completely filled with grout. However, permeability and strength tests on companion specimens cured for 7 or 48 days indicated that injected specimens were generally somewhat stronger, but considerably more permeable, than hand-mixed specimens; this is attributed to the vastly differing mechanisms that govern the distribution and packing arrangement of the cement particles within the void spaces and on the sand grains.