Strength Properties of Lignin Modified Silty Soil After Dry-Wet Cycles

By adding lignin into silty soil, a new lignin-modified silty soil was proposed to overcome the disadvantages of silty soil such as low strength and poor dry–wet cycle performance, and to solve the problem of resource utilization of solid waste lignin. In order to study the shear strength and dry–wet cycle performance of lignin-modified silty soil, direct shear tests and X-ray diffraction tests were conducted on the modified soil samples with different lignin content after dry–wet cycles. The effects of lignin content 0, 2%, 5%, 8%, 12%, 15% and dry–wet cycles 0, 1, 2, 3, 4 times on the shear strength of lignin-modified silty soil were studied. The experimental results showed that lignin incorporation could significantly improve the shear strength and dry–wet cycle resistance of the modified soil. Under a certain number of dry–wet cycles, the shear strength and cohesion of the modified soil increased first and then decreased with the increase of lignin content, and the internal friction angle increased linearly at first and then remained unchanged. The highest shear strength, cohesion and internal friction angle were found when the lignin content was 8%. The shear strength, cohesion and internal friction angle of the modified soil decreased with the increase of the number of dry–wet cycles. When lignin content was 8%, the strength loss rate of the modified soil after dry–wet cycles was the lowest. When the lignin content was 8%, the content of quartz, calcite and dolomite was the highest, the content of clay minerals was higher, and the content of albite was the lowest, which was the direct cause for improving the strength of modified soil and its dry–wet cycle performance. The results showed that when lignin content was 8%, the modified soil had obvious advantages in improving shear strength and dry–wet cycle performance. © 2024 Sichuan University. All rights reserved.