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Geomechanics and Engineering
  Volume 8, Number 1, January 2015 , pages 113-132

Improvement of bearing capacity of footing on soft clay grouted with lime-silica fume mix
Mohammed Y. Fattah, A'amal A. Al-Saidi and Maher M. Jaber

    In this study, lime (L), silica fume (SF), and lime-silica fume (L-SF) mix have been used for stabilizing and considering their effects on the soft clay soil. The improvement technique adopted in this study includes improving the behaviour of a square footing over soft clay through grouting the clay with a slurry of lime-silica fume before and after installation of the footing. A grey-colored densified silica fume is used. Three percentages are used for lime (2%, 4% and 6%) and three percentages are used for silica fume (2.5%, 5%, 10%) and the optimum percentage of silica fume is mixed with the percentages of lime. Several tests are made to investigate the soil behaviour after adding the lime, and silica fume. For grouting the soft clay underneath and around the footing, a 60 ml needle was used as a liquid tank of the lime-silica fume mix. Slurried silica fume typically contains 40 to 60% silica fume by mass. Four categories were studied to stabilize soft clay before and after footing construction and for each category, the effectiveness of grouting was investigated; the effect of injection hole spacing and depth of grout was investigated too.It was found that when the soft clay underneath or around a footing is injected by a slurry of lime-silica fume, an increase in the bearing capacity in the range of (6.58-88)% is obtained. The footing bearing capacity increases with increase of depth of grouting holes around the footing area due to increase in L-SF grout. The grouting near the footing to a distance of 0.5 B is more effective than grouting at a distance of 1.0 B due to shape of shear failure of soft clay around the footing.
Key Words
    soft clay; stabilization; lime-silica fume; grouting
(1) Mohammed Y. Fattah:
Building and Construction Engineering Department, University of Technology Baghdad, Iraq;
(2) A'amal A. Al-Saidi, Maher M. Jaber:
Department of Civil Engineering, College of Engineering, University of Baghdad, Baghdad, Iraq.

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