SUN Mengmeng, WU Libo, YANG Qiuning, LI Hongbo, LIU Huiyang, YANG Jiawei

(School of Civil and Hydraulic Engineering, Ningxia University, Yinchuan 750021, China)

Abstract

Objective Loess with large pores is easy to sink after immersion, and its mechanical properties are easy to change under the action of freeze-thaw cycles, which seriously affects the strength and stability of soil. In seasonal frozen soil area, the use of coal gangue to improve loess can not only reduce the cost, but also solve the problems of large coal gangue pile, wide distribution and environmental pollution. Moreover, the use of coal gangue to improve loess can realize the resource utilization of industrial solid waste, and reduce the cost of engineering construction, while taking into account the problem of environmental protection.

Methods The particle size and composition of loess and coal gangue were tested to analyze the reaction mechanism of coal ganguemodified loess. The unconfined compressive strength test, direct shear test, consolidation compression test and collapsibility test were carried out on the modified loess of coal gangue with different mass fractions. By analyzing the unconfined compressive strength, shear strength, cohesion, internal friction angle, compression coefficient and collapsibility coefficient of coal gangue improved loess specimens, the optimum mass fraction of coal gangue was determined. Using loess raw material as control group, the freeze-thaw cycle test of coal gangue with optimum mass fraction was carried out. To analyze the mechanical properties of the optimal specimens after freeze-thaw cycle, the unconfined compressive strength test and direct shear test were carried out.

Results and Discussion When the mass fraction of coal gangue is 20% and the curing period is 28 days, the unconfined compressive strength of the improved loess is 585 kPa, the shear strength is 287 kPa, the compression coefficient is about 0. 19 MPa^-1,the cohesion of the improved loess is 63. 755 kPa, the internal friction angle is 29. 646 °, and the collapsibility is eliminated.The reaction between coal gangue and loess is sufficient, and the cementation between the reaction products and soil particles is strengthened. Meanwhile, the reaction products fill the pores of loess, making the soil structure more dense. In the freeze-thaw cycle test of the optimum specimen with 20% coal gangue, the unconfined compressive strength of the optimum specimen decreases gradually with the increase of the number of freeze-thaw cycles. When the number of freeze-thaw cycles is 11, the loss rates of unconfined compressive strength, shear strength and cohesion are 26. 9%, 7. 4% and 18. 6%, respectively. In contrast, the loss rates of unconfined compressive strength, shear strength and cohesion of unimproved loess are 35. 8%, 9. 6% and 24. 3%, respectively. The influence of freeze-thaw cycles on internal friction angle is small. Therefore, coal gangue-modified loess has better freeze-thaw resistance.

Conclusion Although the activity of coal gangue is low and the strength of improved loess slowly, the collapsibility and freeze-thaw resistance of coal gangue improved loess can be significantly improved. Therefore, when coal gangue is added into loess, the strength and the freeze-thaw resistance of loess can be improved and the collapsibility of loess can be eliminated. In conclusion,coal gangue improved loess is suitable as a foundation material of loess in seasonal frozen soil area.

Keywords:coal gangue; improved loess; mechanical property; freeze-thaw resistance

Get Citation:SUN M M, WU L B, YANG Q N, et al. Mechanical and freeze-thaw resistance properties of loess improved by coal gangue[J].China Powder Science and Technology, 2023, 30(2): 24-35.

Received: 2023-07-10,Revised:2023-11-20,Online:2024-01-13。

Funding Project:国家自然科学基金项目,编号:41961011;宁夏重点研发计划(引才专项)项目,编号:2019BEB04010。

First Author:孙萌萌(1997—),男,硕士生,研究方向为煤基固废的资源化利用。 E-mail: 562994064@qq.com。

Corresponding Author:武立波(1978—),女(满族),副教授,博士,硕士生导师,研究方向为环境岩土工程及煤基固废的建筑资源化利用。E-mail: wulibo@nxu.edu.cn。

DOI:10.13732 / j.issn.1008-5548.2024.02.003

CLC No: TB4; TU444                  Type Code:A