Fracture Grouting to Lift Structure in Clayey Sand

An seven-story reinforced concrete building on an unevenly thick clayey sand layer became inclined due to differential consolidation settlement triggered from a nearby deep excavation site, and was leveled by fracture grouting with quick-setting grout through the end of grout pipes. Although sand is the primary component and clay is the secondary component of clayey sand, the permeability and strength of this foundation soil are controlled by clay. This suggests that fracture grouting is a proper grouting method. A grout mixture of Portland cement and sodium silicate with gel time of 10 to 15 seconds was injected into foundation soil. The elevations of building's basement were closely monitored to evaluate the heaved volume of mat foundation immediately after grouting, and the settled volume of mat foundation during pore pressure dissipation. The elevation of nearby ground surface and lateral movements of subsoil were also monitored. All these results indicate that the grouting process can be separated into two stages. During the first stage, the building elevation remains unchanged and the anisotropic foundation soil is densified laterally by repeatedly fracturing with grouts. When foundation soil becomes near isotropic, the building starts to lift and this is the second stage. The factors to control grouting efficiency consist of soil type, soil stress history, and building weight. A final grouting efficiency of 27% and a linear relationship between grout take and elevated percentage are obtained after this building was successfully and permanently leveled.