Exploration of the Advantages and Commercial Viability of Using Wheat Straw and Lime as Soil Stabilizing Agents.

Abstract

The purpose of this study was to explore the advantages and commercial viability of using wheat straw (WS) and lime as soil stabilizing agents. The work included the assessment of the effectiveness of WS and lime qualitatively and quantitatively and their performance in the local environment. The clayey soil was used as a base material and blended with lime and wheat straw for the determination of the effects on the engineering properties of the soil. The major investigations are comprised of difficulties in sample preparation, consistency characteristics, compaction, CBR, uniaxial compression, consolidation, shear strength, conductivity, and chemical characteristics of clayey soils blended with lime and wheat straw. A comparative cost evaluation based on the aforementioned characteristics were also made. The major findings of the present study are summarized as follow: Experimental setups of electrical conductivity and thermal conductivity characteristics of stabilized reinforced soils were indigenously developed. The design of this newly developed thermal conductivity setup is based on the basic principle of steady state heat flow. The two experimental setups were designed in order to measure the thermal and electrical conductivity of various materials such as soils, rocks, concrete and any type of unbonded and bonded materials. The design has been kept very simple, adjustable for varying type and size of specimens and easy to operate with an excellent level of accuracy and precision. For the modified soils treated and blended with stabilizing and reinforcing agents, the conventional method of sample preparation may not work adequately and therefore, requires some special treatment such as breaking of lumps, mixing, finishing of specimens, preparation of remoulded samples, uniform compaction efforts, density control etc. The effect of wheat straw and lime on the consistency characteristics have shown that the shrinkage and swelling of clayey soils which causes to several problems in the civil engineering infrastructures may adequately be managed by mixing an appropriate amount of lime and wheat straw as soil stabilizing agent for immediate and long-term effects. The addition of lime and wheat straw into clayey soils has resulted in a slight decrease in the compaction characteristics. More careful and intelligent use of lime and wheat straw would result in a slight improvement in the CBR characteristics. Typically, 4% lime, 2% wheat straw and 6% (lime + wheat straw) resulted in improving the CBR value. The addition of lime and wheat straw resulted in an increase in the uniaxial compressive strength of clayey soils at an optimum content of 6% lime and 2% wheat straw by about 40% and 71% respectively. The content on the consolidation settlement is surcharge load dependent. At lower surcharge loads the effect of lime content is relatively more prominent as compared to that of high surcharge loads. The higher surcharge loads may result in suppressing the cementation effect of lime. As a whole, the addition of lime resulted in delays in the consolidation process which could be the bonding of the soil grains due to lime cementation. From e-log curves it can be seen that there is an upward shift in the field consolidation line due to the increase in the lime and wheat straw contents. At lower surcharge loads the addition of lime resulted in delaying the consolidation and reduction in the consolidation settlement. There is an upward shift in the e-logp curve, the maximum reduction in the Cc value is at 2% lime and wheat straw content each. There is a maximum decrease in the Cv value at 4% wheat straw and maximum increase at 2% lime content. The general perception that the presence of natural and organic materials in the soil should be minimum is not always true. As from the literature and present studies, it is evident that wheat straw is a natural fibre and lime as a natural resource is going improve the several clayey soil properties when used intelligently at optimum contents. From the results of conductivity characteristics of clayey soils, it can be seen that the optimal amount at which a maximum increase in the hydraulic conductivity is 2% of both lime and wheat straw. Further increase in the wheat straw or lime content resulted in a gradual decline in the hydraulic conductivity. There is a gradual decline in the electrical conductivity of soil due to the addition of lime and/or wheat straw. The rate of decrease is high up to 6% lime and wheat straw contents each; however, thereafter, the rate of decrease is comparatively low. The soil sample with wheat straw content has shown dominant behaviour on lime content samples in the reduction of thermal conductivity characteristics of the soil. The lime and wheat straw (used as soil stabilizing and reinforcing agents respectively) has an important effect on the chemical and biological properties of water and soil. The addition of wheat straw resulted in an increase in odour level and colour darkness due to decomposition in water and soil, increase in pH due to lime and wheat straw, increase in the TDS of water due to wheat straw decomposition, decrease in the water hardness due to lime, an increase in the organic matter content due to addition of wheat straw into soil.For the exploration of the advantages and commercial viability of using lime and wheat straw as soil stabilizing agents, the exploration was based on the literature review and the testing results of lime and wheat straw on fifteen (15) different soil parameters comprising of the physical, mechanical and chemical characteristics. The outcome of the present investigations indicate that the use of lime as compared to other stabilizing agents (cement, gypsum, fly ash and volcanic ash) and use of wheat straw as compared to other natural fibres (rice husk, palm fibre, burned olive waste and sisal fibre) are equally and some cases advantageously significant in terms of improving the number of parameters as well as the quantity of the material required. Based on the relative performance, quantity and cost comparison, this would be of significant interest of the research community while selecting a suitable type of soil stabilizing and reinforcing agents. The data is provided for the feasibility, comparative performance/effectiveness, percentage use and cost evaluation based on local market rates.