Cyclic shear strength of artificially prepared cementitious sands and their liquefaction susceptibility

Abstract

ABSTRACT

The present experimental investigation involves the study of liquefaction susceptibility of sands of varying coarseness collected from three selected locations of Bangladesh and the samples were designated as Soil A (FM = 3.17, D50 = 0.98 mm and F200 = 0%), Soil B (FM = 1.66, D50 = 0.37 mm and F200 = 3.4%) and Soil C (FM = 0.96, D50 = 0.21 mm and F200 = 15.15%). Collected sand samples were treated with lime, fly ash plus lime, rice husk ash plus lime, clay plus lime, bentonite and cement to generate cementitious properties in the sand samples. The samples were prepared by dry mixing and compacting them at 10% moisture content in a standard compaction mold of 71 mm diameter and 142 mm height at a constant relative density of 50% by moist tamping method. A series of isotropically consolidated cyclic and monotonic triaxial tests were performed on the soil specimens both in untreated and treated conditions. All the tests were conducted at an effective confining pressure of 50 kPa and frequency of 1 Hz with 10% double amplitude axial strain for cyclic test, and axial strain rate of 0.1 percent per minute for monotonic test. The tests were carried out on lime stabilized samples at 7 and 28 days with different cyclic stress ratio, whereas, with fly ash-lime, rice husk ash-lime, clay-lime, bentonite and cement stabilized samples they were carried out at 7 days with a cyclic stress ratio of 0.40. The testing procedure involved saturation, isotropic consolidation and a uniform sinusoidal compressive loading. Experimental results revealed that the Soil A of fineness modulus 3.17 and mean particle size of 0.98 mm were more susceptible to liquefaction as compared to the Soil B and Soil C of fineness modulus of 1.66 and 0.96 and mean particle size of 0.37 mm and 0.21 mm. The cyclic shear resistance of lime stabilized sand specimens continues to increase with increasing lime percentages and curing periods. The number of cycles required to cause liquefaction were greater for cement, lime, fly ash-lime, rice husk ash-lime and clay-lime stabilized specimens whereas the bentonite stabilized sands have no significant resistance to liquefaction compared to untreated sands. From monotonic triaxial tests of 5 percent lime and 10 percent lime, fly ash-lime and rice husk-lime treated sands were found dense specimens where 0 and 2 percent lime treated sands behaves like loose specimens. The compaction effort was found greater for Soil B and Soil C than for Soil A. The compaction energy were decreases with lime, fly ash-lime, rice husk ash-lime, clay-lime and bentonite mixed sands than for untreated sands. The mixture of lime, cement, fly ash-lime, rice husk ash-lime and clay-lime with sands and water reacts and binds the sand grains together thus reduce soils permeability and improve soils pH and their liquefaction strength.