International Journal of Civil Engineering
Volume:9 Issue: 2, Jun 2011

The use of by-products such as blast furnace slag, steel slag (i.e. electric arc) furnace slag, basic oxygen steel (BOS) slag and ground granulated blast furnace slag) is well established in civil engineering applications. However, the use of BOS slag in the area of soil stabilization has not been fully researched and developed despite having similar chemical composition and mineralogy to that of Portland cement. This paper reports on efforts to extend the use of BOS slag to soil stabilization by determining possible beneficial effects it may have on compressive strength, plasticity characteristics and durability. The paper presents the results of laboratory tests conducted on kaolinite samples stabilized with lime and treated with treated with various percentages of BOS slag. Tests determined strength development of compacted cylinders, moist cured in a humid environment at 35 C, their plasticity characteristics together with durability by freezing and thawing method. Results showed that additions of BOS slag to kaolinite samples singularly or in combination with lime increased unconfined compressive strength and durability and reduced plasticity characteristics. These characteristics were significantly enhanced by the concurrent use of lime and BOS slag for stabilization of kaolinite.

When geotechnical engineers are faced with soft clayey soils, the engineering properties of those soils may need to be improved to make them suitable for construction. The aim of this paper is to study the effect of using lime, natural pozzolana or a combination of both on the geotechnical characteristics of soft soils. Lime or natural pozzolana were added to soft soils at ranges of 0-8% and 0-20%, respectively. In addition, combinations of lime-natural pozzolana were added to soft soils at the same ranges. Test specimens were subjected to compaction tests and shear tests. Specimens were cured for 1, 7, 28 and 90 days after which they were tested for shear strength tests. Based on the experimental results, it was concluded that the combination lime-natural pozzolana showed an appreciable improvement of the cohesion and internal friction angle with curing period and particularly at later ages for both soft soils.

Geotextiles are one of the most widely used synthetic materials in filtration and drainage applications. Since in real applications, geotextiles are subjected to various hydraulic gradients and confining stresses, hydraulic behavior of geotextiles under different circumstances is of great practical importance. In this study filtration and drainage properties of several nonwoven needle-punched geotextiles with different properties and unit mass per area of 200g/m2, 400g/m2, 500g/m2 and 800g/m2, under various confining stresses and hydraulic gradients, were studied using standard permittivity and transmissivity equipments. Prepared samples were subjected to hydraulic heads in the range of 10cm to 60cm and confining stresses up to 1000kPa and their hydraulic behavior was investigated accordingly. In this study the flow regime through the geotextile fibers and also the anisotropic behavior of geotextile permeability were investigated. The results show that transmissivity will decrease exponentially with increasing the normal stress until a residual value is reached, and permittivity and transmissivity coefficients were seen to decrease with increasing the hydraulic gradient. The flow regime has found to be non-turbulent in all cases. The Geotextile hydraulic behavior is of great usage in the design of landfill covers, design of embankments and irrigation structures drainage systems, and in the design of protection systems in river engineering.

The main task in the design and construction of impermeable liners in landfills is to block the migration of pollutants to the groundwater systems or to reduce its rate to a reasonable amount. That is why environmental regulations force governments to construct engineered waste dumps for waste management purposes. These liners are exposed to various types of chemical, biological, and physical processes and are affected by the leachate which is produced from decomposition of waste materials accompanying methane gas. The leachate includes a lot of components such as water and different types of salts. For this reason, the geotechnical characteristics of clay liners which are evaluated in laboratories using distilled water or tap water might be far different from the representative sample of the in-situ conditions. There are some evidences regarding the effect of these salts on the physical and mechanical properties of clay barriers which could affect the long-term performance of these liners. Since the main criterion for impermeable bottom liners in landfills is their hydraulics conductivity, the increase of this parameter could have a considerable environmental impact. This paper embraces the results of a recent study on the effect of three inorganic salts, NaCl, CaCl2 and MgCl2 on some geotechnical properties of a common used clay soil in impermeable bottom barrier in Kahrizak landfill, the main waste disposal center of the Tehran Metropolitan. Also the effect of bentonite content by adding different percentage of this special clay mineral, 10 and 20 percent, on these properties was investigated. Laboratory tests like liquid limit, compaction, 1D consolidation and free swell tests were performed for this purpose. Results indicated that all of these salts could have a considerable effect on the geotechnical properties of the mixtures. The main reason of such effects is the changes which occur in diffuse double layer of clay particles.

The present paper is devoted to a new critical state based plasticity model able to predict drained and undrained behaviour of granular material. It incorporates a bounding surface plasticity model describing in multilaminate framework to capitalize on advantages of this mathematical framework. Most of the models developed using stress/strain invariants are not capable of identifying the parameters depending on directional effects such as principal stress rotation and fabric; this is mainly because stress/strain invariants are scalar quantities. The principal features of this model can be postulated as considering both inherent and induced anisotropy, principal stress rotation. Since the local instability of saturated sand within post-liquefaction is highly dependent on the residual inherent/induced anisotropy, bedding plane effects and also the stress/strain path the new mode is competent to be employed in this regard. The constitutive equations of the model are derived within the context of non-linear elastic behaviour for the whole medium and plastic sliding of interfaces of predefined planes. As follows, the constitutive equations are described in detail and then the experimental results and sensitive analysis of key material constants are shown which all imply the power of the model in predicting of soil behaviour under any condition in soil structures.

This paper discusses the applicability of a simple model to predict pore water pressure generation in non-plastic silty soil during cyclic loading. The model was developed by Seed et al. in the 1970s and relates the generated pore pressure to the cycle ratio, which is the ratio of number of applied loading cycles to the number of cycles required to cause liquefaction. Several Stress-controlled cyclic hollow torsional tests were conducted to directly measure excess pore water pressure generation at different levels of cyclic stress ratios (CSR) for the specimens prepared with different silts contents (SC=0% to 100%). The soil specimens were tested under three different confining pressures (σ′3= 60, 120, 240 kPa) at a constant relative density (Dr=60%), with different silts contents. Results of these tests were used to investigate the behavior of silty sands under undrained cyclic hollow torsional loading conditions. In general, beneficial effects of the silts were observed in the form of a decrease in excess pore water pressure and an increase in the volumetric strain. Modified model for pore water pressure generation model based on test results are also presented in this paper.

Laboratory data, which relate the liquefaction resistance of Firoozkooh sand and non-plastic silt mixtures to shear wave velocity are presented and compared to liquefaction criteria derived from seismic field measurements by Andrus and Stokoe [1]. In the work described herein, cyclic triaxial and resonant column tests were conducted on specimens of clean sand and sand-silt mixtures with silt content up to 60%, prepared at different densities. Cyclic undrained strength and small strain shear wave velocity were determined for identical specimens formed by undercompaction method. It was found that silt content affects cyclic resistance and shear wave velocity. In addition, the laboratory results indicated that using the existing field-based correlations will overestimate the cyclic resistance of the Firoozkooh sand-silt mixtures when silt content is 60%. For clean sand and the specimens containing up to 30% fines, results of this study on cyclic resistance are fairly consistent with Andrus and Stokoe correlations. These findings suggest the need for further evaluation of the effects of non-plastic fines content upon liquefaction criteria derived from seismic field measurements.