Soil with high liquid limit is often encountered in southern China, which is unsuitable for direct use as embankment fill. Current soil reinforcement methods entail high carbon emissions, necessitating mitigation for a low-carbon future. In this study, a reconstituted soil is reconstituted to simulate the soil with high liquid limit from the site of the reconstruction and expansion project for the Zhangshu-Ji'an Highway in Jiangxi, China. This reconstituted soil was reinforced using steel slag, varying in grain sizes and employing two mixing methods. The mechanical characteristics of the pure and reinforced soil were examined by a series of monotonic and cyclic triaxial tests. The results indicate that decreasing the grain size of steel slag increases the monotonic shear strength and leads to a decrease in the permanent strain under cyclic loading, regardless of the mixing methods. The reduction in grain size of steel slag increases the total frictional surface area, thereby enhancing soil strength and resistance to deformation. Compared to the samples by uniform mixing with the steel slag, the samples by layered mixing results in a greater shear strength and a more significant permanent strain, because the concentrated steel slag grains and reconstituted soil particles produce greater friction and more significant compressibility, respectively. Overall, smaller grains of the steel slag by uniform mixing are more effective for reinforcing weak soil with high liquid limit, as it provides a higher monotonic strength and a lower permanent deformation, and reduces rapid energy dissipation under cyclic loading, compared to layered mixing.

This paper performs the strength properties of bio-enzyme improved high liquid limit soil (HLLS) treated with 4% (by weight) content of cement or lime cured for 28 days. A series of consolidated undrained (CU) triaxial tests and unconfined compressive (UC) strength tests were conducted on plain soil (untreated by cement or lime), cement-treated and lime-treated HLLS specimens improved with different bio-enzyme content (i.e., 0%, 0.2%, 0.4%, 0.6% and 0.8% by weight) to investigate the effect of bio-enzyme content on the strength properties of tested soil. The results indicate that the stress-strain relationship of bio-enzyme improved plain soil specimens exhibit strain-hardening behavior and ductile failure mode. The other specimens exhibit strain-softening behavior and brittle failure mode. Adding 0.6% bio-enzyme, the values of undrained shear strength of CS specimens are about 1.7 times, 1.8 times, and 1.9 times of LS specimens at sigma 3 = 100 kPa, 200 kPa and 300 kPa. The residual strength is about 40.5% on average the peak strength for CS specimens, and 37.0% for LS specimens. The cohesion c increased 258.6% and 220.7%, and the internal friction angle phi increased 38.57% and 39.05% for CS and LS specimens respectively. The UC strength of CS specimen is 1.69 times that of LS specimen. The magnitudes of CU strength, UC strength, cohesion and internal friction angle of three types of soil specimens followed the same increase trend when the bio-enzyme content increased from 0 to 0.6%, and peak values can be observed at 0.6% bio-enzyme content. The use of bio-enzyme to improve the strength behavior of HLLS treated with cement or lime is an innovative and attractive solution in geotechnical engineering. The effectiveness of bio-enzyme in improving the strength of HLLS treated with cement or lime was studied based on a laboratory investigation.Adding cement or lime in HLLS provided a significant increase in strength and strength parameters at a certain bio-enzyme content, where the treatment effect of cement is better than that of lime.The bio-enzyme content of 0.6% can achieve the most economical effect on enhancing the strength and the strength parameters of HLLS improved by 4% cement or lime.