Examples of the Construction of Deep Excavation Ditches in Weak Soils

The information about the engineering- geological conditions in the central part of St Petersburg, which are characterized by deep thickness of weak water saturated soil, is given. The examples of underground space in three constructed buildings in St. Petersburg are considered. The depth of each considered space exceeded 12 m and that required the usage of modern and nonstandard construction and technological methods for protection of the ditch walls. The wall protection were done by sheet piles, by “Wall in ground” method, and “jet grouting”, the soil excavation was carried out by traditional method or “Top -down” method.The basic constructive schemes and technological methods of excavating ditches, test results of deformation of the protection walls during excavation of the ditch and the settlements of the neighboring buildings are given.