AbstractSoil reinforcement using synthetic fibers is a proven technique for enhancing engineering properties to meet the requirements of subgrade materials for pavement projects. The safe and ...economical design of fiber-reinforced pavement layers requires better insights into their unsaturated behavior. The soil–water characteristic curve (SWCC) is a measure of the water content inside soil pores at a given suction and is considered an essential property to better understand or predict the behavior of unsaturated fiber-reinforced soils. This paper centers on investigating the soil–water characteristic curves for typical expansive clay reinforced with two different types of polypropylene fibers having different surface morphological properties. The effect of an increase in the fiber dosage (0.2% and 0.6% by dry weight of soil) and fiber lengths (6 and 12 mm) on the resultant SWCC patterns is investigated. The addition of lime is considered to enhance the bonding between clay particles and fiber elements to ensure better friction mobilization levels. SWCCs were determined for all experimental mixtures using a combination of axis translation and filter paper techniques that cover the entire matric suction range during measurements. Volume changes undergone during suction measurements have been duly highlighted and discussed. Furthermore, the one-dimensional deformation (swelling/consolidation) characteristics of these lime-blended fiber-reinforced mixtures at different levels of initial matric suction are studied, and the correlations between initial matric suction with both compression index (Cc) and swell index (Cs) are established. The results indicate a significant change in the shape of the SWCC for lime-blended fiber-reinforced mixtures compared with the shape of the SWCC for natural clay. The contribution of fiber inclination to altering the shape of the SWCC curve is observed as slight regardless of the type, length, and dosage of fiber. Compression and swell indices for tested mixtures increased proportionately with an increase in initial matric suction levels. Doubling the length of the fiber also induced an increase in the compression index. Under no stress conditions did both fiber type and fiber length have a marginal effect on the swell potential and SWCCs.
AbstractThe current study aims at examining the effect of different calcium-based stabilizers {calcium hydroxide Ca(OH)2, calcium carbonate CaCO3, and calcium chloride CaCl2} on the geotechnical ...properties and lime-leaching behavior of expansive clay. The lime-leaching tests were conducted on clay samples that were compacted at maximum Proctor dry density values relying on specially fabricated molds and subjected to water flow conditions for a specific period (up to 7 days). In order to study the effect of pore fluid on the lime-leachability patterns, the pH of the leaching solution was kept at 7 (pH of deionized double-distilled water) and at 4 (adjusted using 0.1 N HNO3). The effect of curing period (1, 7, 14, and 28 days) on the lime-leaching pattern and unconfined compression strength (UCS) behavior were also studied. One-dimensional fixed-ring consolidation tests were performed to quantify the effect of various stabilizers (at fixed dosage of 4% by weight of dry sample) on the swell and deformation characteristics. The results of the study indicate that with an increase in curing period, irrespective of the type of stabilizer, the calcium concentration in the leachate reduced. The flow duration (7 days was adopted in the study) had an insignificant effect on the resultant lime-leaching values. When acidic water was used as flushing solution, relatively higher concentrations of calcium were noticed, which further establishes the fact that amorphous pozzolanic compounds formed in the early hydration reaction stages are easily soluble. Furthermore, the associated anions in respective stabilizers have a direct bearing on the resultant UCS and consolidation behavior.
The hydraulic properties of expansive soils are affected due to the formation of visible cracks in the dry state. Chemical stabilization coupled with fiber reinforcement is often considered an ...effective strategy to improve the geotechnical performance of such soils. In this study, hydraulic conductivity tests have been conducted on expansive clay using two different types of fibers (fiber cast (FC) and fiber mesh (FM)) exhibiting different surface morphological properties. The fiber parameters include their dosage (added at 0.2% to 0.6% by dry weight of soil) and length (6 and 12 mm). Commercially available lime is added to ensure proper bonding between clay particles and fiber materials, and its dosage was fixed at 6% (by dry weight of the soil). Saturated hydraulic conductivity tests were conducted relying on a flexible wall permeameter on lime-treated fiber-blended soil specimens cured for 7 and 28 days. The confining pressures were varied from 50 to 400 kPa, and the saturated hydraulic conductivity values (ksat) were determined. For FC fibers, an increase in fiber dosage caused ksat values to increase by 9.5% and 94.3% for the 6 and 12 mm lengths, respectively, at all confining pressures and curing periods. For FM fibers, ksat values for samples mixed with 6 mm fiber increased by 12 and 99.2% for 6 and 12 mm lengths, respectively for all confining pressures at the end of the 28-day curing period. The results obtained from a flexible wall permeameter (FWP) were compared with those of a rigid wall permeameter (RWP) available in the literature, and the fundamental mechanism responsible for such variations is explained.
Abstract
Rapid industrialization in developed countries has led to a continuous release of heavy metals into the environment. When these effluents are discharged directly into natural surrounding ...soils, not only is the geotechnical behavior altered but the natural surface and subsurface waters become contaminated. In this study, experiments are conducted to examine the unconfined compressive strength (UCS) and compressibility behavior for two semiarid soils exhibiting different mineralogy spiked with selected heavy metals (As3+, Cr6+, Cu2+, Hg2+, Pb2+, and Zn2+) and their relative immobilization levels in the presence of a binder. Removal efficiencies of selected metal ions were estimated by performing desorption tests using different extractants acetic acid (H3COOH), nitric acid (HNO3), ethylenediaminetetraacetic acid (EDTA), and diethylenetriaminepentaacetic acid (DTPA). Analytical grade lime was used as a binder and the concentrations of spiked metal ions were maintained at 50 and 100 ppm respectively. The variations in electrical conductivity and pH for both soils spiked with selected metal ions were evaluated for the control case (absence of lime) and lime treated case and have been related to the compression behavior. Results from this study reveal that the UCS values of both soils increased for the control and lime treated cases. The compression behavior of the selected soils exhibited contrasting behavior with an increase in compression index (Cc) values for soil A and a decrement for soil B when spiked with selected metal ions. The desorption studies revealed higher removal efficiencies for EDTA compared with other extractants.
Investigation of the volume change behavior of expansive soils typically utilizes conventional oedometer which provide estimates of vertical strain and swelling pressure under fully lateral ...restrained conditions. In this study, testing was conducted on compacted highly expansive clay using a thin-walled oedometer to evaluate the state of stresses during inundation in both vertical and lateral directions in addition to the vertical strain. First, calibration, correction, and verification of the thin wall oedometer were described. Second, an experimental program was developed to evaluate the volume change behavior during inundation for a wide range of vertical stresses at inundation (σi) under two conditions: (i) constant vertical stress at inundation and (ii) constant volume. Results of tests under constant vertical stress at inundation indicate the dependency of strain state of expansive soil on the inundation vertical stress. Moreover, the vertical stress at inundation (σi) was observed to affect the vertical stress state after inundation for constant volume condition. Investigating the equilibrium vertical stress state after inundation under constant volume condition showed that there is one relation termed as “Swell-Collapse Equilibrium Line, SCEL” that represents the equilibrium condition after inundation for specimens subjected to different initial sample conditions prior to inundation. General trends of strain softening behavior for the evolution of lateral stresses with time were observed, particularly for the swelling zone. Stress path followed by tested samples was depicted. Interpretation of results in light of Barcelona Expansive Model (BExM) was also performed. An enlargement of yield envelop after loading to stresses greater than past stress history was observed.
•Dependency of inundation strain on inundation vertical stress is observed•Vertical stress at inundation affects vertical stress state after inundation•Distinct relation proposed for prediction of equilibrium condition after inundation•Strain softening behavior for the evolution of lateral stresses is observed•Loading over the past stress history tends to enlarge yield envelop at saturation
AbstractThis paper evaluates the effectiveness of stabilizing expansive soil with two different types of fibers, fiber mesh (FM) and fiber cast (FC), in conjunction with chemical stabilization. The ...intention of this study is to evaluate the effect of these fibers and lime in stabilizing expansive soil by improving its unconfined compressive strength (UCS) behavior. The effect of varying lengths (6 and 12 mm) and amounts (0.2, 0.4, and 0.6% dosage by weight of soil) of FC and FM fibers and varying curing periods (0, 7, 28, 60, 120, 180, and 360 days) on the UCS and on secant modulus of a semiarid expansive soil, in the presence of lime, was investigated. The main focus of this paper is on the determination of optimum fiber reinforcement parameters (in terms of fiber type, length, and dosage) for the stabilization of expansive soil in terms of UCS, which is of a prime importance in soil stabilization projects for practicing engineers. In deterministic optimization, the uncertainties associated with pavement system subgrade soil are not explicitly taken into account. Hence, resulting optimal solutions may lead to reduced pavement reliability levels. Therefore, this paper also focuses on determining the optimum amounts of reinforcement for desired UCS performance of lime-blended expansive soil using the target reliability approach (TRA). Experimental data were used to develop a parabolic model including factors such as length and dosage of fiber types to predict UCS as a response variable. In addition, it was concluded that TRA can be successfully employed in expansive soil stabilization applications to determine the optimum length and dosage of fiber reinforcements.
Most of the chemicals containing non-biodegradable metal pollutants from anthropogenic sources are highly mobile in nature. The only way to contain or limit their movement is through sorption and ...entrapment in the soil matrices. In this study, the sorptive response of the three most commonly found divalent metal contaminants, copper (Cu
+2
), lead (Pb
+2
), and zinc (Zn
+2
), are studied using two locally available semi-arid soils from Saudi Arabia. To enhance their retention capacity, these soils are amended with lime. The response to sorption at varying initial contaminant concentrations, pH conditions, temperature levels, and dilution ratios are investigated. Relying on empirical models (Langmuir and Freundlich), the nature of sorption (monolayer or heterogeneous) is ascertained. Further, kinetic models are employed to validate the type and nature of sorption that occurs (whether pseudo first-order or second-order). It is found that the experimental results correlate well with these empirical models for both the Al-Ghat and Al-Qatif soils when amended with lime and attenuate Cu, Pb, and Zn to satisfactory levels. The
R
2
values are close to 1 for all the tested models. The order of sorption was Pb > Cu > Zn for these heavy metals, and also for soils and soil mixtures that were considered: Al-Qatif soil amended with 6 % lime > Al-Ghat soil with 6 % lime > Al-Qatif > Al-Ghat. Lime-treated soils sorbed 73, 65, and 60 % more than the untreated soils for Pb, Cu, and Zn, respectively.
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