# Performance Study of Black Shale Modified Soil for Road Use Based on Eshelby-Mori-Tanaka Theory
## 6 Conclusions  
This paper explores the strength characteristics of black shale gravel bodies with cement and clay admixtures through indoor experiments, and assesses their suitability for roadbed filling. Based on the Mori-Tanaka equivalent stress principle, a strength characterization relationship for black shale modified soil is established. The conclusions are as follows:  
1. Cement-soil is used to improve the strength of black shale gravel. When the cement content is 10% to 30%, the optimal moisture content is 18.2\(\sim\)19.4%, the maximum dry density is 1.66\(\sim\)1.71 g/cm\({}^{3}\), and the maximum unconfined compressive strength is 2.0-4.0 Mpa. The optimal moisture content, maximum dry density, and maximum unconfined compressive strength increase with the increase in cement content. 2. The elastic modulus of black shale modified soil is positively correlated with the cement content. Based on economic principles and highway specifications, the experimentally used black shale modified material is suitable for the subbase of medium to light secondary and below-secondary highways. The optimal mixing ratio is M\({}_{\text{shale}}\):M\({}_{\text{clay}}\):M\({}_{\text{cement}}\) = 70:21:9. The unconfined compressive strength of the material under 7-day curing is 1.36 MPa. 3. For the optimally mixed black shale modified soil, cement hydration is nearly complete before 14 days, and the strength stabilizes around two weeks. The repeated \"drying and soaking\" environment is the most unfavorable for this modified soil, followed by prolonged immersion. Before entering the elastic-plastic deformation stage, the lateral deformation of the modified soil specimens is not significant. Afterward, lateral deformation develops rapidly. 4. The relationship between the strength of black shale modified soil and the content of cement, black shale gravel, and the strength of the soil can be expressed as follows: \([\sigma]=[\sigma](1+\gamma\frac{\eta}{\Gamma-m})(a^{\prime}m^{3}+b^{\prime}m ^{2}+c^{\prime}m+1)\). Using this strength relationship, the impact of the mix ratio on the strength of the modified soil can be accurately predicted. The contributions of all the authors to this manuscript are as follows: 1. [PERSON]: The person in charge of the research group, proposes the research topic, formulates a detailed research plan, is responsible for coordinating all the work of the research, providing research funds and supporting equipment, and revising the paper. 2. [PERSON]: Perform the experimental tasks involved in this study, collect and sort out experimental data and analyze experimental results, and write the main chapters of the paper. 3. [PERSON]: summarize the latest research results, theories and prac  
Figure 17: Measured value and fitting value. tical experience in related fields, construct the theoretical framework of this research, and revise the paper. **4**. [PERSON]: Revised and improved the experimental plan, guided [PERSON] and [PERSON] to conduct experiments, and analyzed the experimental results. **5**. [PERSON]: Revised and improved the experimental plan, guided [PERSON] and [PERSON] to conduct experiments, and revised and proofread the papers. **6**. [PERSON]: Assist [PERSON] to carry out experiments, collect and sort out experimental data. **7**. [PERSON]: Organize the experimental data and proofread the paper. All authors have read and agreed to the published version of the manuscript. This work is founded by the National Natural Science Foundation of China Youth Program No. 51908065 and No. 52008038, the Science and Technology Progress and Innovation Program Project of the Hunan Provincial Department of Transportation No. 201938, the Scientific Research Project of the Hunan Provincial Department of Education No. 20B010, 21C0219, the Hunan Natural Science Youth Foundation No. 2021J40579, and the Open Fund for Changsha University of Science and Technology Bridge Engineering No. 15 KC03. Not applicable. The data presented in this study are available on request from the corresponding author.