an assessment of the effect of calcium dosage injection on the mechanical strength of fine grain soils

1. introduction adding lime to increase the geotechnical characteristics of fine-grained soils, to achieve different goals always been done from ancient time. there are many techniques for stabilizing unstable slopes, among them lime treatment is a quick, simple and cost-effective operation that can be incorporated into any unstable slopes. some scientific techniques of soil treatment have been introduced by bell (1996). the effect of lime on maximum compressive strength were studied by indraratna (1996). he concluded that the addition of only 2% of lime results in a 50% increase in compressive strength and if this amount increases to the 5% of lime, the increase is doubled. although lime stabilizes the soil rapidly after the treatment, the mechanical properties and strength of soil change over a long period of time (bell, 1996; sivapullaiah, sridharan, & ramesh, 2000). recently a new method has been developed by which lime is injected into soil in the form of saturated solution. as it penetrates into the soil due to the gravity, it improves soil strength through pozzolanic reaction (davoodi, 2007). limited studies have been conducted to investigate the suitability of using saturated lime solution in slope stability. optimum concentrations of lime solution and lime dosage were investigated by pui ling (2005) and pedarla, chittoori, puppala, hoyos, & saride, (2010). moreover, it is known by the studies of khelifa (2010) that the curing time influences the physical properties of soil stabilized by lime, and considerably increases the shear strength of cohesive soils stabilized by lime. this study intends to assess the effect of calcium dosage on uniaxial strength of clayey soils stabilized by saturated lime solution in order to be applied in unstable slope stability and sediment control. 2. material and methods soil: the clay soil chosen in this study was a fine grain soil, classified as ml–cl in the unified soil classification system, underwent laboratory tests. the soil properties are as follow. maximum dry mass density of approximately 1.88 g/cm3 at optimum moisture content of approximately 10.9%.the specific gravities of soil, liquid limit and plastic limit were 2.63, 21.64, and 18.92 respectively. 3. saturated lime solution the lime used for preparing the saturated lime solution was a commercially available lime typically used for construction purposes. the simple method for preparing the saturated lime solution is to thoroughly stir 5 grams of hydrated lime into one liter of water, allowing the excess to settle; the excess in the bottom will ensure that the solution remains saturated. 4. methods laboratory tests consisting of compaction and uniaxial strength were conducted on the specimens with a controlled humidity and temperature. each specimen was compacted at optimum moisture content and maximum dry density and after preparation of specimens, 15 soil samples in five set were placed in saturated lime solution for 48 hours, then they were kept in the controlled chambers for a period of, 3, 7, 28, and 60 days and then mechanical properties were tested. one set for 48 hours only influenced by the water as a representative sample and comparison. by measuring the amount of calcium ions in the sample before and after the treatment, the calcium ion consumption was computed. 5. results and discussion it is generally accepted that the penetration of lime solution in clayey based soils readily lead to the pozzolanic reaction that may cause increasing geotechnical characteristics. different values of calcium consumption in the specimen after the mixture of lime solution with soil specimen showed the evolution of lime consumption with curing time. the initial consumption of lime can be used as an indication of the minimum quantity of lime that must be added to the soil in order to achieve a significant change in soil properties in short time. in this study, determination of this minimum percentage of lime is based on measurement of calcium ion concentration in soils before and after solution affect. average calcium consumption for short term treatment (3 day) was found 27 milligram per liter, for 7 day 34 milligram per liter, 28 days curing period 45 milligrams per liter and for 60 days curing period also 45 were found. this demonstrates that there is no important effect of lime addition after 28 days and it also demonstrates the minimum lime consumption for short term soil improvement. uniaxial strength of specimens with 3 days curing time increased by 180% compared to the control sample. with increased calcium consumption and pozzolanic reactions, the permeability of the samples also showed a downward trend. this is due to the decrease in porosity and is due to pozzolanic reactions. 6. conclusion by comparing the results of the absorption of calcium in the treated samples and the relationships between them as well as the relationship between the curing time and strength of the samples, it was concluded that the minimum and maximum lime needed to increase the mechanical properties of soil resistance can be calculated. also it was concluded that the most effective curing time for injection and increasing the mechanical properties of the soils with saturated lime solution is 28 days. this study has led to the valuable insights regarding the treatment of the soil by saturated lime solution in order to sediment and landslide control