Geotechnical engineering is now a fundamental component of construction projects. The fourth and final volume of this book presents a range of retaining structures, alongside soil reinforcement and improvement techniques and processes. Applied Geotechnics for Construction Projects 4 first presents the concept of thrust-fall, then goes on to examine the behavior of retaining structures and their design and justification methods. A variety of practical applications for retaining structures are then considered, covering gravity walls, sheet pile curtains, in advance shoring excavations and retaining diaphragm walls. The book goes on to study soil reinforcement and improvement techniques, a subject that the author has dedicated thirty-five years to researching and teaching: from reinforced earth, in situ soil nailing, micropiles, in situ soil compaction, stone columns and rigid inclusions to "soil-cement" and "lime cement" columns. This book ends with a comprehensive and practical discussion of the behavior of underground structures; covering the concepts of convergence-confinement, stress evolution and subsidence estimation. Each chapter of this fourth volume is illustrated with concrete examples and measurements of retaining structures, soil reinforcement and soil improvement from construction sites. The result is a combination of geotechnical expertise and lessons learned from experience, both of which are highly valuable in the field of applied geotechnics for construction projects.