Rainwater harvesting (RH) techniques, specifically the implementation of Bio-pore Infiltration Holes (BIH), have been investigated as cost-effective and practical methods for managing surface runoff and mitigating flood risks. This study aimed to evaluate the infiltration rates of BIH in secondary forest and agricultural moorland areas, providing a basis for sustainable soil and water conservation practices. A survey methodology was employed to assess infiltration rates using the Horton equation model applied to circular holes with a depth of 50 cm. Soil samples were collected from the vicinity of the BIH for analysis of physical properties at the Soil Science Laboratory, Faculty of Agriculture, Tadulako University. A 4-inch diameter PVC pipe, inserted 30 cm into the soil, was used to measure water infiltration, with water levels recorded up to 60 cm. The findings indicated that infiltration rates in both secondary forest and agricultural lands were moderate. The physical characteristics of the soil, including its texture and organic carbon content, were identified as suboptimal, which constrained the efficiency of waste absorption through the infiltration process. The soil texture in both land types was classified as sandy according to USDA standards, making it susceptible to erosion, which is directly related to the infiltration capacity and the potential for soil transport during erosion events. The carbon organic content was relatively low, at 2.50% in secondary forest land and 1.17% in agricultural land, indicating medium-level criteria for organic content. To enhance soil conservation and flood mitigation, it is recommended that efforts be made to increase organic material content through compost application and post-flood land rehabilitation. Expanding the use of BIH in high-risk flood areas is advocated to effectively reduce and control surface runoff.

The substitution of cement with coal gangue powder (CGP) offers significant potential for energy conservation, emission reduction, and environmental sustainability. To optimize the mechanical properties of coal gangue cement paste, a modified response surface methodology (RSM) model was developed, incorporating grinding parameters as independent variables and compressive strength as the response variable. The feasibility of the model was validated through coefficient estimation, variance analysis, and fitting statistics. The analysis revealed that milling speed was the most significant factor influencing the compressive strength at 20% substitution, while the ball-to-material ratio predominantly affected the strength at 50% substitution. An increase in milling speed was observed to significantly broaden the particle size distribution, with larger particles (15.14$\mathrm{\mu m}$ to 275.42$\mathrm{\mu m}$) serving primarily as micro-aggregates, and smaller particles (0.32$\mathrm{\mu m}$ to 15.14$\mathrm{\mu m}$) functioning as fillers within ultra-fine pores. Scanning Electron Microscopy (SEM) further corroborated these findings. Numerical optimization based on the RSM model identified optimal grinding parameters: a ball-to-material ratio of 1.40, a milling time of 0.843 hours, and a milling speed of 300 rpm. These parameters are recommended to achieve the target compressive strengths of 25 MPa at 20% CGP substitution and 10 MPa at 50% CGP substitution. This study provides a cost-effective and feasible approach for the utilization of coal gangue in cementitious materials, contributing to the advancement of sustainable construction practices.