Data are presented concerning the shear modulus and damping ratios of sands and gravelly soils as determined by laboratory and field tests. A simple relationship is proposed to relate the shear modulus of a cohesionless soil to a modulus stiffness coefficient, which is a soil property and depends on the characteristics of the soil, and the effective mean principal stress at any point in the soil. Values for the modulus coefficient at low strains are suggested, and it is shown that these values for sands can be estimated from the standard penetration resistance of the sand. Values for gravels are generally greater than those for sands by factors ranging from 1.35–2.5. Suggestions are also made for determining the variation of shear modulus with shear strain and the damping ratios for both sandy and gravelly soils.

Moduli and Damping Factors for Dynamic Analyses of Cohesionless Soils

Clayey soils are usually stiff when they are dry and give up their stiffness as they become saturated. Soft clays are associated with low compressive strength and excessive settlement. This reduction in strength due to moisture leads to severe damages to buildings and foundations. The soil behavior can be a challenge to the designer build infrastructure plans to on clay deposits. The damage due to the expansive soils every year is expected to be $1 billion in the USA, £150 million in the UK, and many billions of pounds worldwide. The damages associated with expansive soils are not because of the lack of inadequate engineering solutions but to the failure to identify the existence and magnitude of expansion of these soils in the early stage of project planning. One of the methods for soil improvement is that the problematic soil is replaced by suitable soil. The high cost involved in this method has led researchers to identify alternative methods, and soil stabilization with different additives is one of those methods. Recently, modern scientific techniques of soil stabilization are on offer for this purpose. Stabilized soil is a composite material that is obtained from the combination and optimization of properties of constituent materials. Adding cementing agents such as lime, cement and industrial byproducts like fly ash and slag, with soil results in improved geotechnical properties. However, during the past few decades, a number of cases have been reported where sulfate-rich soils stabilized by cement or lime underwent a significant amount of heave leading to pavement failure. This research paper addressed the some fundamental and success soil improvement that used in civil engineering field.

/pdf/fundamentals-of-soil-stabilization-4djewn9bar.pdf

Fundamentals of soil stabilization

The effectiveness of fly ash use in the stabilization of organic soils and the factors that are likely to affect the degree of stabilization were studied. Unconfined compression and resilient modulus tests were conducted on organic soil–fly ash mixtures and untreated soil specimens. The unconfined compressive strength of organic soils can be increased using fly ash, but the amount of increase depends on the type of soil and characteristics of the fly ash. Resilient moduli of the slightly organic and organic soils can also be significantly improved. The increases in strength and stiffness are attributed primarily to cementing caused by pozzolanic reactions, although the reduction in water content resulting from the addition of dry fly ash solid also contributes to strength gain. The pozzolonic effect appears to diminish as the water content decreases. The significant characteristics of fly ash that affect the increase in unconfined compressive strength and resilient modulus include CaO content and CaO/SiO2...

Stabilization of Organic Soils with Fly Ash

The objective of this study was to evaluate the effectiveness of self-cementing fly ashes derived from combustion of sub- bituminous coal at electric power plants for stabilization of soft fine-grained soils. California bearing ratio CBR and resilient modulus Mr tests were conducted on mixtures prepared with seven soft fine-grained soils six inorganic soils and one organic soil and four fly ashes. The soils were selected to represent a relatively broad range of plasticity, with plasticity indices ranging between 15 and 38. Two of the fly ashes are high quality Class C ashes per ASTM C 618 that are normally used in Portland cement concrete. The other ashes are off-specification ashes, meaning they do not meet the Class C or Class F criteria in ASTM C 618. Tests were conducted on soils and soil-fly ash mixtures prepared at optimum water content a standardized condition, 7% wet of optimum water content representative of the typical in situ condition in Wisconsin, and 9-18% wet of optimum water content representative of a very wet in situ condition. Addition of fly ash resulted in appreciable increases in the CBR and Mr of the inorganic soils. For water contents 7% wet of optimum, CBRs of the soils alone ranged between 1 and 5. Addition of 10% fly ash resulted in CBRs ranging between 8 and 17 and 18% fly ash resulted in CBRs between 15 and 31. Similarly, Mr of the soil alone ranged between 3 and 15 MPa at 7% wet of optimum, whereas addition of 10% fly ash resulted in Mr between 12 and 60 MPa and 18% fly ash resulted in Mr between 51 and 106 MPa. In contrast, except for one fly ash, addition of fly ash generally had little effect on CBR or Mr of the organic soil.

Stabilizing Soft Fine-Grained Soils with Fly Ash

This report presents information on the characterization of cementitiously stabilized layers and the properties that influence pavement performance. It also contains recommended performance-related procedures for characterizing these layers and performance-prediction models for incorporation into the mechanistic–empirical pavement analysis methods. Individual chapters highlight pavement distresses of hot-mix asphalt pavements and concrete pavements, laboratory tests and model development, and model calibration. The material contained in the report will be of immediate interest to state materials, pavement, and construction engineers and others involved in the different aspects of pavement design and construction.

Characterization of Cementitiously Stabilized Layers for Use in Pavement Design and Analysis

This publication presents the results of research involving different types of self-cementing fly ashes (without any other activators) for the stabilization of four different types of soft subgrades from various road sites in Wisconsin, USA. The strength approaches were applied to estimate the optimum mixture design and to determine the thickness of the stabilized layer. The stabilized soil samples were prepared by mixing fly ash at different contents at varying water contents. The performance of fly ash stabilized subbase depends both on the specific source of fly ash and the engineering properties of soils. It is suggested that the performance analysis of fly ash should be based upon the laboratory tests such as index properties, compaction, unconfined compressive strength and CBR tests of a specific site. This is suggested rather than using the study of the physical properties and chemical composition of fly ash and soil. As disclosed in the literature, the strength gain due to stabilization depends mainly upon three factors; ash content, molding water content and compaction delay. The samples were subjected to unconfined compression strength and California bearing ratio (CBR) tests after 7 days curing time to develop water content–strength relationship. To evaluate the impact of compaction delay that commonly occurs in the field during construction, the sets of samples were compacted 2 h later after mixing with water. The unconfined compression strength and CBR tests were performed and used to determine the thickness of the stabilized layer in pavement design. All of these factors were taken into account throughout this research.

Soft subgrades' stabilization by using various fly ashes

Alternative methods for providing a stable platform over soft subgrades were evaluated using a 1.4-km section along a Wisconsin State highway that incorporated 12 test sections to evaluate 9 different stabilization alternatives. A variety of industrial by-products and geosynthetics were evaluated for stabilization. The industrial by-products included foundry slag, foundry sand, bottom ash, and fly ash as subbase layer materials. The geosynthetics included geocells, a nonwoven geotextile, a woven geotextile, a drainage geocomposite, and a geogrid. The same pavement structure was used for all test sections except for the subbase layer, which varied depending on the properties of the alternative material being used. All test sections were designed to have approximately the same structural number as the conventional pavement structure used for the highway, which included a subbase of granular excavated rock. Observations made during and after construction indicated that all sections provided adequate support for the construction equipment and no distress was evident in any part of the highway. Each of the alternative stabilization methods, except a subbase prepared with foundry sand, appear to provide equivalent or greater stiffness than that provided by control sections constructed with excavated rock. However, the foundry sand subbase is providing adequate support. Analysis of leachate collected from the base of the test sections shows that the by-products discharge contaminants of concern at very low concentrations.

Field Evaluation of Construction Alternatives for Roadways over Soft Subgrade

i i 1 i This paper represents the results of a study aimed at using self-cementing Class C fly ash for the stabilization of soft subgrade of a city street in Cross Plains, [Wisconsin, U.S.A. Both strength and modulus-based approaches were applied to [estimate the optimum mix design and to determine the thickness of the stabilized layer.J Stabilized soil samples were prepared mixing fly ash at three different contents at varying water contents. The samples were subjected to unconfined compression test after seven days of curing to develop 'water content-strength relationship. To evaluate the' impact of compaction delay that commonly occurs in field construction, one set of the samples was compacted just after mixing with water, while the other set after two hours. CBR and resilient modulus tests were conducted and used to determine the thickness of the stabilized layer in pavement design. Some field tests were also performed after the construction, which showed that the fly ash stabilization improved the 'engineering properties significantly. !' Introduction Fly Ash is one of the most plentiful and versatile of the industrial by-products (Collins and Ciesielski 1992). It is generated in vast quantities (more than 65 million metric tons per year) as a by-product of burning coal at electric power plants. Combustion of subbituminous coal produces a fly ash (Class C) that has self-cementing characteristics and has been used in earthwork applications to improve the mechanical properties of soils for more than 20 years (Ferguson 1993). After the introduction of Clean Air Act Amendments of 1990, the utilities in the western and mid-western regions of the United States began burning sub-bituminous coal in their power plants to meet more stringent EPA sulfur emission standards, which increased the availability of Class C fly ash. The potential for using fly ash in soil stabilization has increased significantly, in Wisconsin due to increased availability and the introduction of new environmental regulations (NR 538, Wisconsin Administrative Code) that encourage use of fly ash in geotechnical applications when it is environmentally safe. Class C fly ash is usually recycled as an engineering material to take advantage of its pozzolanic characteristics. This type of fly ash provides the opportunity for applications where no other activators would be required and thus it offers more economical alternative for a wide range of stabilization applications. The primary objective of this paper is to study how Class C fly ash can be used in soil stabilization without using any other activator, and the performance of fly ash-stabilized subbase of a pavement system. Ferguson (1993) investigated soil stabilization in a racetrack with Class C fly ash without any other activator, which showed encouraging results. Improved engineering properties of fly ash-stabilized soil are also reported by Turner (1997). Edil et al. (2002) conducted research on fly ash-stabilized subbase along with nine other stabilization alternatives, such as those using a subbase layer consisting of foundry sand, foundry slag, and bottom ash or geosynthetics-reinforcement. Based on the falling weight deflectometer (FWD) data, performance of Class C fly ash-stabilized subbase seemed to be equal or better than the other stabilization alternatives. Fly Ash Chemistry Fly ash is classified into two classes, F and C, based on the chemical composition of the fly ash according to ASTM C 618 Class F fly ash is produced from burning anthracite and bituminous coals and contains small amount of lime (CaO). This fly ash has siliceous and aluminous material (pozzolans), which itself possesses little or no cementitious value but in the presence, of moisture, chemically reacts with lime at ordinary temperature to form cementitious compounds (Chu et al. 1993). Class C fly ash is normally produced from lignite and sub-bituminous coals, and usually contains significant amount of lime (Cockrell et al. 1970) along with pozzolanic materials. Formation of cementitious material by the reaction of lime with the pozzolans (AlCb, SiOj, FejOa) in the presence of water is known as hydration of fly ash. The hydrated calcium silicate gel or calcium aluminate gel (cementitious material) can bind inert material together. The pozzolanic reactions for soil stabilization are as follows (TRB 1987): CaO + H2O => Ca(OH)2 (1) Ca(OH)2 => Ca -*+ 2[OH](2) + 2[OH]+ Si02 => CSH (3) (silica) • (gel) + 2[OH]+ A12O3 => CAH (4) (alumina) (gel) For Class C fly ash, the lime present in the fly ash reacts with the siliceous and aluminous materials (pozzolans) in the fly ash. A similar reaction can occur in Class F fly ash, but lime must be added because the lime content of the ash is too low. Lime stabilization of soils occurs in a similar manner, where the pozzolanic reactions depend on the siliceous and aluminous materials provided by the soil.

Use of class C fly ash for stabilization of soft subgrade

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