Biochar application, as a kind of soil amendment, significantly influences soil physical and mechanical properties. This study revealed the effects of biochar application on the physical and mechanical properties of a clay-type soil at different irrigation levels. Soil was treated with three levels of biochar application: B0 (0 t ha(-1)), B1 (25 t ha-(1)) and B2 (50 t ha b(-1)), and three levels of irrigation: T0 (1.2 pan evaporation Ep), T1 (1.0 Ep) and T2 (0.8 Ep). The results indicated that other treatments reduced the soil bulk density compared with the control treatment (CK) (B0T1). Compared to CK, the highest reduction in soil bulk density was 18%. Irrigation did not improve the soil bulk density and porosity at the same biochar application in the short term. Biochar enhanced the stability of the soil aggregates. Compared to CK, the largest MWD (mean weight diameter) was enhanced by 9%. The addition of biochar and decreasing irrigation could decrease soil cohesion. The addition of biochar and increasing irrigation could increase the soil internal friction angle. The soil cohesion first increased and then decreased as the soil water content increased. According to the fitting formula, the soil cohesion was found to be minimum at B2T2, which was a decrease of 39% compared to B0T1. At the same irrigation level, the soil internal friction angle decreased with increasing soil water content. Soil penetration resistance showed a decreasing trend with the application of biochar. The more irrigation there is, the larger the soil penetration resistance.

Problem Statement. . The necessity to review, revise, and supplement existing building regulations in the field of engineering surveys and design is driven by the increasing significance of hydrogeological research. This is in response to the growing trend of urban development on territories (mainly within urban agglomerations) that were previously considered unsuitable for construction due to adverse engineering-geological conditions. The issue becomes particularly relevant against the backdrop of Russia's armed military aggression against Ukraine, which necessitates deeper underground space utilization to construct reliable shelters for protecting civilians from missile and bomb attacks. Under these conditions, new and stricter requirements arise for the content and quality of engineering surveys, design solutions, as well as for measures related to the engineering preparation and protection of territories and individual objects from hazardous geological processes. The aim of this study is to highlight the significance and objectives of engineering-hydrogeological surveys in construction and to propose recommendations for improving the state of survey and design activities in the context of large-scale reconstruction in Ukraine. Research Methodology. . The research involves the systematization and generalization of both domestic and international experience in conducting engineering-geological surveys for construction. Special attention is paid to identifying areas where hydrogeological studies should be prioritized. To formulate requirements and suggestions for improving the regulatory framework in the field of engineering surveys and design, the study analyzes various manifestations of flooding processes. Additionally, the impact of groundwater in various physical states on the strength and deformation properties of soils, as well as the initiation and intensification of hazardous engineering-geological processes, is investigated. Results. The study presents the scientific foundations for improving the regulatory framework in the field of engineering surveys for construction, according to modern requirements. Special emphasis is placed on enhancing the role of hydrogeological research in deepening underground space utilization within urban agglomerations. It is noted that with the expansion of the interaction sphere between projected structures and the geological environment, the influence of groundwater on engineering-geological conditions intensifies, leading to a deterioration in the properties of specific soils and the activation of engineering-geological processes. Scientific Novelty. For the first time, a theoretical justification is provided for the concept of mandatory inclusion of hydrogeological studies in the scope of engineering-geological surveys, even in cases where groundwater is absent within the interaction sphere of the designed structure and the geological environment. Based on the study and systematization of flooding processes, the stages of predicting changes in engineering-hydrogeological conditions have been improved. Practical Significance. The theoretical findings can be used to enhance the regulatory framework in the field of engineering surveys, particularly for developing requirements regarding the content and quality of hydrogeological research. This will improve the reliability of designed buildings and structures while also reducing the risks of hazardous engineering-geological processes emerging or intensifying.