The Impact of the Unsupported Excavation on the Boundary of the Active Zone in Medium, Stiff and Very Stiff Clay

Deep excavation adjacent to existing buildings with shallow foundations and/or old wall bearing buildings represents a big challenge to the geotechnical engineer. The restriction of the lateral movement of the soil underneath those building represents the primary objective for any excavation support system. The previous research resulted in many excavation support systems including; soldier pile walls, sheet pile walls, secant piles, tangent piles, diaphragm walls, etc. These techniques may be cost-effectively for large and important projects but they are not for small projects which represent the majority. The main objective of this research is to study the stability of excavation sides in medium, stiff and very stiff clay soils either with or without a minimum safe lateral horizontal distance to the adjacent building. A parametric study was carried out to determine the minimum horizontal distance, H, for selected excavation depths, de, ground water depth, dw, and surcharge stress (q) underneath the neighboring buildings. The research outcomes showed that a significant saving can be achieved by excavation in very stiff clay excavation to a relatively large depth up to 9 m without retaining system. While for stiff and medium clay soils, a horizontal distance should be left beside the neighbored buildings depending on the magnitude of the surcharge stress, q.