Prepared by: Assistant Lecturer Lina Hussein Ali Rapporteur of the Civil Engineering Department – College of Engineering – Al-Mustaqbal University Geotechnical engineering is one of the fundamental branches of civil engineering. It is concerned with studying the behavior of soil and rock and their interaction with various engineering structures. Its importance stems from the fact that all civil engineering structures, regardless of their size and purpose, depend directly or indirectly on the ground on which they are constructed. Therefore, understanding the geotechnical properties of soil is a critical factor in ensuring the success, safety, and sustainability of a project. Engineering experience has demonstrated that many cases of structural failure are not necessarily caused by errors in structural design, but rather by geotechnical problems resulting from inaccurate assessment of soil properties or inadequate investigation. The rapid pace of urban development and the growing trend toward constructing high-rise buildings, bridges, dams, tunnels, and large-scale infrastructure projects have increased the importance of geotechnical investigations. These investigations have become an essential component of the planning, design, and construction stages. Therefore, this article aims to highlight the pivotal role of geotechnical engineering in achieving the stability of civil engineering structures and ensuring their safe long-term performance. Concept of Geotechnical Engineering Geotechnical engineering is the branch of engineering concerned with studying the physical, mechanical, and hydraulic properties of soil and rock and analyzing their behavior under the influence of various loads. Its primary objective is to provide the scientific basis required for the safe and efficient design of engineering structures. Its applications include the design of foundations, retaining walls, slopes, earth dams, and tunnels, as well as soil improvement and the treatment of geo-environmental problems. Geotechnical engineering relies on a range of field and laboratory tests used to determine the engineering properties of soil, such as density, moisture content, cohesion, angle of internal friction, compressibility, permeability, shear strength, and other essential properties required for design. Importance of Geotechnical Investigations in Civil Engineering Projects Ensuring the stability of civil engineering structures begins with conducting a geotechnical site investigation. This process includes drilling boreholes, collecting soil samples, and performing appropriate tests to determine the nature and characteristics of the underlying soil layers. The results of these investigations provide essential information that helps engineers understand soil behavior under expected loads and assess potential risks. Geotechnical investigations contribute to: Determining the bearing capacity of soil under structural loads. Estimating the expected settlement of structures. Selecting the appropriate type of foundation. Assessing the stability of slopes and excavations. Investigating the effects of groundwater on structures. Proposing soil improvement methods when necessary. Without these investigations, a project may be exposed to serious problems such as differential settlement or ground failures.