Quality Control of Jet Grouting at Basement by Measurements of Flow Rate and Gravity of Spoil Return

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JSG high pressure jet grouting method that was introduced to Taiwan more than 20 years ago, in general, is conducted on the ground or above groundwater table. There is no risk of water gushing or sand boiling during drilling and grouting operations. However, if drilling and grouting operations are performed in confined layer or in the basement and the groundwater level is above the platform of drilling and grouting operations, it is necessary to install pumping well to lower the groundwater level below operation platform before drilling and grouting in order to avoid the risk of water ingress, sand boiling, ground settlement and building tilting. This study to cusson how to install point wells and pumping wells when the jet grouting is conducted in the basement and the groundwater level is higher than the working platform of drilling and grouting operations. This study also proposes a quality control skill by measuring the volumes and unit weights of spoil returns twice for each column. The diameter of column is back calculated from these results of volumes and unit weights of returned spoil greater. This study also found that the greater the unit weight of spoil return, the greater the unit weight or better quality of column in the field. Since grouting sequence can affect the unit weight of spoil, optimum design of grouting layout and grouting sequence is important. By observing the variation trend of spoil volumes, sand boiling can be effectively detected. Based on the results of this study, it is recommended that the measurement of volume and unit weight of returned spoil should be listed in the standard operation procedure, especially when jet grouting platform is below the groundwater table.