## 4 Conclusions  
The main objectives of the present study were to explore the multiple mechanical and engineering properties of mudstone improved with the increasing density or addition of 4% and 8% dry cement. Thus, mudstone clods with three grain sizes (grains that passed through #4, #4-3/4\", or >3/4\" sieves) were examined. Three methods (compaction, kneading, and static) and six dry density levels were used to prepare specimens. Two cement content levels were also applied. The following conclusions are drawn.  
1. For the compaction tests, specimen moisture content was controlled and unconfined compression strength increased with \(\gamma_{\text{d}}\). The compaction method produced specimens with the highest strength. In contrast, the clods with grain sizes larger than 3/4\" exhibited the lowest strength. The clad effect was similar with the results of the triaxial permeability test. The hydraulic gradient k values of mudstone clods ranged between \(10^{-4}\) and \(10^{-7}\) cm/sec, indicating low permeability or no permeability and that the hydraulic gradient k values of mudstone increased in relation to clods.
2. The mudstone specimen formula yielded E\({}_{50}\) = 47.699 q\({}_{\text{u}}\) and R\({}^{2}\) = 0.8708, while the mudstone-cement formula yielded E\({}_{50}\) = 69.397 q\({}_{\text{u}}\) and R\({}^{2}\) = 0.9693. By comparing our study with those that used formulas proposed by other researchers, we found that the differences between coefficients could be attributed to the material added and specimen preparation methods.
3. The triaxial CU and UU test results were used to calculate shear strengths through the application of the Mohr-Coulomb formula. For mudstone supplemented with  
Figure 20: CBR values and swelling ratio for treated soils: (**a**) CBR versus \(\gamma_{\text{d}}\); (**b**) Swelling ratio versus compaction (times).  
cement paste, its \(\rm q_{u}\) values increased 7- to 10-fold and shear strength values increased 2- to 3-fold. Thus, the choice of the strength testing method is vital for geotechnical consideration.
4. The results from the one-dimension compression test indicate that the addition of cement for soil improvement is effective in inhibiting consolidation settlement. In addition, an increase in the number of compactions and amount of cement added led to a decrease in the swelling ratio according to the CBR test results. Therefore, an increase in compactions and cement addition are good ways to improve the property of mudstone.
5. Taken together, our study demonstrates the application of engineering techniques and the addition of small amounts of cement. This method not only adheres to low-carbon and environmental protection requirements, but also verifies the feasibility of using compacted mudstone as an engineering material.  
Project administration, D.H.; Experimental and analysis, D.H.; Supervision, D.H.; Writing--original draft preparation and editing, D.H; Validation; C.H.; Writing--review, C.H. All authors have read and agreed to the published version of the manuscript.  
Not applicable.  
All data is available upon request.  
CPCI Co. in Taiwan supplied materials to support the experiment's requirements throughout. All experimental works were performed in the geotechnical laboratory in NKUST, whose assistance is appreciated. The copy editing assistance provided by [PERSON] is also appreciated.  
The authors declare no conflict of interest.