The August 2022 issue of Ground Improvement has been reached. As soil mechanism problems have the worldwide researchers’ attention, 5 papers make up this this third issue, discussing sulfonated oil (SO) effects on expansive soil properties, the improvement methods performance of tunnel excavation, and the performance of unpaved roads reinforced with geogrids. In addition, the improvements achieved in erosion resistance for biological soil crust (BC), and cement/lime treatments for three different soft clays are discussed.
The first paper by Soltani et al., (2022) discussed the effects of SO stabiliser on the swell–shrink properties of an expansive soil, investigated through cyclic wetting–drying tests. The cyclic wetting–drying action led to the reconstruction of the soil microstructure by inducing clay particle aggregation. The results are show 0.75% SO exhibiting the highest resistance against cyclic wetting–drying. For any given SO concentration, the equalised void ratio–moisture content curves for wetting and drying followed the same S-shaped path, further corroborating that the swelling and shrinkage processes (on achieving elastic equilibrium) become reversible.
In the second paper, Majidian et al., (2022) investigates the effects of three improvement methods – the umbrella arch method, soil nailing and micropiling – on the performance of the excavation method of the tunnel. A tunnel of uncommon square shape was chosen due to limitations caused by adjacent facilities. Based on their test results, forepoling was the most effective in settlement compared to the initial model. Combining the forepoling and nailing systems decreased the settlement by 37.5% and was the most effective synchronic system. The best results were for the model incorporating all supporting systems.
Then, El Tawati and El Naggar (2022) investigates the performance of unpaved roads reinforced with geogrids. Full-scale unpaved road tests were carried out with ten test sections in two different base course thicknesses. Traffic loading was also provided by a single-axle dump truck. Field measurements of rut depth and surface deformation were recorded at selected traffic intervals. The results suggested reductions in the thickness of the base layer by using geogrids of up to 18%. The improvement by geogrids was shown to be less for increasing base layer thickness. The results indicated that the method underpredicted the required base thickness to support the applied traffic loads.
The fourth paper presented by Rabiei et al., (2022) assesses the improvements achieved in erosion resistance for BC formed on medium–coarse silica sand. Specimen groups were inoculated with Nostoc sp. and Calothrix sp., incubated for 32- or 48-day periods and then tested using an erosion function apparatus. Compared with untreated sand, inoculated specimens had a significantly greater erosion resistance that increased with the incubation period, with Nostoc inoculum producing greater reductions in erodibility coefficients (45–75%) compared with Calothrix (16–67%). This paper concludes by encouraging cyanobacteria inoculation as an eco-friendly, cost-benefit and effective technique for mitigating land degradation.
Finally, Sivakumar et al., (2022) describes the results of a comprehensive laboratory investigation involving the assessment of cement/lime treatments for improving the geotechnical characteristics of three different soft clays: kaolin, sleech and Belfast clay. The evolution of the small-strain shear stiffness was progressive, and all soils exhibited a steady increase in stiffness, the rate of which reduced as the curing period approached 7 days. When allowed access to water, strength and stiffness increased, although at a much-reduced rate. The stress–strain behaviour of kaolin also changed from ductile when untreated to highly brittle as the curing period approached 90 days.
