Assessment of Suspension and Chemical grout’s Stabilization Effects on Sandy Soils

Muhammed, Shellas M and Saride, Sireesh (2017) Assessment of Suspension and Chemical grout’s Stabilization Effects on Sandy Soils. Masters thesis, Indian Insitute of Technology Hyderabad.

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Abstract

Grouting t echniques are widely used in improving the performance of weaker soils . Among the various grouting technics available , permeation grouting is more economical due to it process and technic. Permeation grouting do not alter the soil ‟s virgin structure during the process as it uses little or no jetting pressures. Current study focuses on the permeation grouting using suspension grout and chemical grout materials to improve loose sand deposits . An attempt has been made t o prepare a nano sized fly ash based suspension grout material . A class F fly ash obtained from Neyveli Lignite Corporation, Tamil Nadu was used to prepare a nano size fly ash for preparing a suspension gro ut material, whereas sodium s ilicate solution was used as a chemical grout. Graded Ennore sand was used to prepare a loose soil deposit (30% relative density) to be grouted with suspension and chemical grouts . Firstly, to check the groutability of nano f ly ash as a po ssible grout material , to improve loose sand deposits, h ydrometer analysis was performed. The grain size distribution of sand and nano fly ash confirms that a consistent grouting is possible. It was observed that after a series of trials, a minimum water to solid (stabilizer) ratio of 8:1 is consistently yieldin g a grouted san d column . A series of sand specimens were prepared with different dosages of fly ash and NaOH concentrations. Sodium hydroxide is adopted to activate the fly ash. Corresponding unconfined compressive strength tests at different curing interv als indicated that the shear strengths are very low (15 kPa). The reason for low shear strength can be attributed to the weak stabilization effect of class F fly ash and high bleeding values. It was also observed that a cake was forming on top of the sand surface, which vii confirms that the void spaces are smaller than that of the suspended grout particle (nano) size. To re - verify the grout size, particle size analyzer was used. It was found that repeatedly that the ball milled grout particle size s are predominantly of the size 50  m. Hence, the modified groutability ratio indic ated that the consistent grouting is not possible. Secondly , sodium silicate solution was used as a chemica l grout and the specimens were prepared at different combinations of sodium silicate and sodium hydroxide concentrations. The specimens were subjected to air dried curing before performing the UCS testing . The undrained shear s trength s of these samples w ere much higher and are comparable with that of the literature. However, the air dried samples slowly d issolv ed in a water retention test indicating that the crystallization of sodium silicate on the sand surface is incomplete. To understand the crystallization temperatures (formation of glass) of sand specimens grouted with sodium silicate a nd sodium hydroxide, Differential Scanning Calorimetry (DSC) tests were performed. It was found that the critical curing temperature for all the combinations is about 100 o C . Hence, the samples were then cured at the corresponding critical temperature s to verify the ir undrained compressive strengths. Overall, a nano based fly ash suspended grout material could not be produced due to the limitation of the ball milling apparatus. Sodium silicate based chemical grouts are consistently possible for treating sa ndy soil deposits. However, a curing critical temperature needs to be identified. To reduce the curing temperatures, accelerators , catalysts and/or super plasticizer are necessary.

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