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.

This study aims to explore the performance of lime-treated soil for repairing the lime soil of the earthen city wall of Kaifeng and to standardize the construction technology of lime-treated soil. The research comprehensively considered factors such as carbonation time, lime particle size, aging conditions, and lime content, and conducted various tests and analyses including triaxial mechanical properties, surface crack analysis, particle size distribution, pH measurement, composition analysis, and electron microscopy on different samples. The results indicate that the significant effect of high-concentration CO2 carbonation enhances the chemical reactions of lime soil, and an appropriate carbonation process can strengthen the bonding and density between soil particles. Under the maintenance condition of 5 % CO2, with increasing carbonation time, the crack ratio, average crack length, and average crack width of the samples decreased. Cohesion and internal friction angle of the samples exhibited an initial increase followed by a decrease, while shear strength of the samples increased by 22.93 %-75.09 %. The lime particle size has a critical impact on the formation of cracks in lime soil. With increasing lime particle size, the crack ratio, average crack length, and average crack width of the samples increased. Cohesion and internal friction angle of the samples gradually increased with increasing lime content. The increase in crack ratio, average crack length, and average crack width during natural curing of lime-treated soil samples was proportional to the lime content. Appropriate carbonation time, smaller lime particle size, and curing conditions with 5 % CO2 contribute to improving the particle size distribution of lime-treated soil samples, reducing surface cracks, and enhancing performance. However, prolonged carbonation may lead to larger lime particle size, resulting in rough and loose particles, disorganized arrangement of CaCO3 crystals, and the inability to form a cross-linked network skeleton, causing a reduction in shear strength of the samples. These research findings provide important theoretical basis and construction technology guidance for the application of lime-treated soil combined with CO2 carbonation in repairing earthen city walls.