Improvement of peaty clays by deep mixing and preloading

Abstract

One major problem related to construction on peaty clay deposit is the low shear strength of the soil. However previous researches have shown that the shear strength could increase significantly by mixing with cement and various stabilizers. Hence some improvement methods have been developed to increase the bearing capacity of the peaty clay deposit by mixing with stabilizers and cement. The aim of this project is to evaluate the increase of shear strength of peaty clays due to mixing with cement and the application of preloading pressure during the curing period. The initial undrained shear strength was obtained from untreated remoulded peaty clay subject to preloading pressures. For this study, samples were prepared for untreated peaty clay samples and treated peaty clay by mixing with 15% and 20% cement by wet weight and keeping under two preloading pressures of; 20kN/m2 and 40kN/m2 . The shear strength of the samples was obtained by triaxial compression test under unconsolidated undrained condition. The results proved that there is an increase in the range of 150% to 240% in shear strength due to mixing with cement and application of preloading pressure during the curing process. The other major problem related to construction on peaty clay deposit is the high settlement of the soil. The previous researches have proven that the settlement of soft soil has decreases significantly with the addition of stabilizers and cement. For the analysis of compressibility characteristics, peaty clay samples were mixed with 0%, 15% and 20% cement by wet weight and keeping under two preloading pressures of; 20kN/m2 and 40kN/m2. Consolidation characteristics of the untreated and treated peaty clay are determined through the series of laboratory consolidation testing. From the consolidation test results, coefficient of volume compressibility (mv) and the coefficient of secondary consolidation (Ca ) were evaluated in all the loading and reloading increments. The values of compression index (Cc) and recompression index (Cr) were also evaluated using the e Vs log a plot. The improvement of the stiffness is assessed and compared by the measurement of compressibility characteristics of the treated peaty clay with untreated peaty clay.