Numerical analysis of lime stabilized capping under embankments based on expansive subgrades

Evaluation of swelling pressure of an expansive soil stabilized with lime and lignosulphonate as overlay cushion: an experimental and numerical quantification

Expansive soils are one of the most problematic soils faced by civil engineers in various construction activities. It has the property to swell with the addition of water and shrink on water removal. The volume change behavior of expansive soil occurs vastly during seasonal changes in moisture conditions and can be significantly attenuated by chemically stabilizing the soil. In this study, calcium lignosulphonate (LS), a biopolymer, is added to the soil to curtail the swelling nature of the soil. Lime (L) is also used to treat the soil, and a comparative study is carried out to examine the effectiveness of LS. The expansive soil is treated with several combinations of cushion layers with 1.5% LS, 2% L, 4% L, and combination of 1.5% LS and 2% lime. To counter the swell pressure of the expansive soil, the treated soil and additive composites are placed as a cushion layer over the expansive soil with the replacement ratio of 1:1 and 1:2, represented as configuration "a" and "b." The swelling pressure of the proposed arrangement is evaluated through the constant volume swell apparatus. The soil layers are inundated from the bottom upwards, and the swell pressure is determined for the various configuration adopted. The effectiveness of the stabilized soil cushion over expansive soil is analyzed through the numerical software PLAXIS 2D for further extension to field conditions. As the replacement thickness of stabilized soil increases, the swell pressure decreases. Nevertheless, the lime-treated soil layer depicted lesser swell than the LS-treated soils. Analyzing the conditions for field situations in numerical analysis yielded consistent results with the laboratory inferences.

Studying the Properties of Chromium-Contaminated Soil Solidified by Polyurethane

The solidification of chromium-contaminated soil using polyurethane (PU) was systematically investigated. The unconfined compression test was conducted to investigate the effects of the curing time, PU dosage and the content of chromium ions on the unconfined compressive strength (UCS) of chromium-contaminated soil. The effect of the PU dosage on the pore structure was investigated using nuclear magnetic resonance (NMR) and scanning electron microscopy (SEM), and the mechanism of strength change was revealed by combining the strength law with the pore structure development law. In addition, the ability of the PU to solidify the chromium-contaminated soil was studied by the toxicity characteristic leaching procedure (TCLP). According to the above test results, the UCS and the ability of the PU to solidify the chromium ions increased with the increase in curing time. The NMR tests showed that with the increase in PU dosage, the porosity decreased and the soil became more compact, hence increasing the strength. When the chromium ion content was 2000 mg/kg and the PU dosage was 8%, the strength of the sample was 0.37 MPa after curing for 24 h, which met the requirement of 0.35 MPa set by the U.S. Environmental Protection Agency. Consequently, PU is a solidification agent with high-early strength.

Evaluating the Performance of Lateritic Soil Stabilized with Cement and Biomass Bottom Ash for Use as Pavement Materials

From the perspective of sustainable waste management and its environmental impact, waste biomass bottom ash (BA) remains problematic and challenging to use as a recycling material for civil engineering infrastructures. This study evaluated the performance of lateritic soil (LS), stabilized with cement and biomass BA, as a subbase material. BA has been considered a replacement material in LS prior to the introduction of hydraulic cement stabilization means. The geotechnical engineering tests comprised the modified Proctor test, the California Bearing Ratio (CBR) test, and the unconfined compression test. X-ray fluorescence (XRF) and X-ray diffraction (XRD) tests were conducted to investigate the mineralogical properties of the stabilized soil samples. The leachate test was performed with a permeability mold to measure the release of heavy metals. Finally, the benefits of using the stabilized subbase material were assessed using the mechanistic–empirical (M–E) pavement design approach. Based on the results obtained, the strength and stiffness characteristics of the stabilized soils indicate that the efficiency of the mix satisfied the Thailand highway specification. The admixture of 80% BA and 5% cement is suggested for use as a soil–cement subbase material for flexible pavements, due to its good engineering and environmental properties. The results of the M–E design demonstrate the effectiveness of the stabilized soil presented herein. The study’s outcomes are predicted to promote the utilization of waste BA as a promising pavement material.

Experimental and numerical assessment of efficacy of lime stabilized capping material in controlling swelling displacements within flexible pavement embankments

The performance of flexible pavements constructed on embankments founded on expansive clay subgrade is greatly affected by the distress caused in these embankments as they are subjected to swelling displacements. These are caused by the volume changes in expansive subgrade soil due to moisture variation. The authors have suggested the technique of ‘C’-shaped lime stabilized capping in their earlier studies which is useful for controlling swelling displacements within the expansive subgrade. In the present study, the authors have attempted to assess the efficacy of the capping material itself for controlling swelling displacements at the top and bottom of embankment which is directly responsible for improving the performance of pavements on these embankments. This assessment is carried out with respect to stiffness and reduction in permeability of capping material. Stiffness of the buffer layer controls swelling displacements within the embankment under flexible pavement and the reduced permeability of the capping will control moisture variations and the corresponding pavement distress. The stiffness assessment is carried out through laboratory Unconfined Compression Strength (UCS) tests for modulus estimation by curing the samples for short-term and long-term strength gain. Assessment of permeability reduction is carried through the study of permeability of expansive soils after lime stabilization. Swelling displacements are estimated using Finite Element Analysis (FEA) of the numerical model. The experimental and numerical analysis results indicate that with the increased modulus and reduced permeability of the buffer layer material the swelling displacements at the top and bottom of pavement embankment have reduced. This will help in improving the performance of pavement constructed on the embankment founded on the expansive subgrade.

Evaluating the toxicity of polyurethane during marine clay stabilisation

In civil engineering, many geotechnical and forensic projects employ polyurethane (PU) for ground improvement, and the results have shown to be effective in terms of time and cost savings. However, similar to many other chemical stabilisers, the use of PU for soil stabilisation may have environmental repercussions. Therefore, this paper utilised a toxicity characteristic leaching procedure (TCLP) to investigate the potential for ground contamination resulting from the application of PU for the stabilisation of marine clay. Furthermore, the hazardousness of PU during the stabilisation of marine clay was investigated by testing its reactivity, ignitability, corrosivity and physical properties. The results reveal that the quantity of heavy metals present in PU is far below the regulatory limits. The results further confirm that PU is odourless and non-corrosive and that it is non-cyanide and non-sulphide-bearing. However, PU is capable of igniting. Overall, the potential application of PU for ground improvement is promising due to its environmental friendliness.