The need to analyze clays of the Lower Cambrian and the Upper Vendian as the crackblock structure, taking into account the influence of micro- and makrojointing of rocks in the calculation of stability, is indicated. The influence of sample size of the Upper Vendian clays on the value of cohesion and modulus of total deformation, depending on the level of stress and strain conditions, was analyzed. The influence of microcracks on the mechanical properties of clays is recommended to study under laboratory conditions, makrocracks – through field testing or calculation method.
Engineering-geological and hydro-geological features of rent of St. Petersburg are considered. It is noted that at designing buildings for different purposes, in order to ensure their long-term stability it is necessary to analyze the possibility of their transformation the main components of underground space (rocks, underground water, gas, microbiota, underground structures) under the influence of natural and technogenic factors. Examples of transformation of sand-clay soils under the influence of physical and chemical conditions change and activization of microbial activity in underground space are given. The case of transition of a heavy construction to a pre-emergency condition because of mistakes in engineering research and incorrect assigning of computative parameters is analyzed.
The history of high-rise construction is considered summarily. The main features of high-rise buildings and difficulties connected with theirs engineering and construction especially with underground space development and deep excavations in soft water saturated soils are characterized. Territorial construction guides «Residential and social high-rise buildings» prevail in Saint-Petersburg are analyzed in the context of recommendations for reliable basement choice. Brief description of Pre-Quanernary clays (Upper Vendian clays and Lower Cambrian clays) as basement for high-rise constructions are given. It is placed emphasis that the main feature of Pre-Quaternary clays is zone sequence of physical and mechanical properties and fissuring in depth. Physical and mechanical properties of Upper Vendian clays, Lower Cambrian clays and glacial clays are given. In addition, it is confirmed that glacial soils is not recommended to use as a basement for high-rise buildings.
In the paper specificity of geotechnical engineering conditions in the local zone of the right river Neva bank are considered. The influence of underground topographies of Pre-Quaternary soils roof formed by paleovalleys on the specificity of engineering geological profile is analyzed. Influence of tectonic faults on physical and mechanical properties of Upper Kotlin clays (Upper Vendian) which it is planned to use as the basis for high-rise constructions is considered. Negative influence of Low Kotlin (Upper Vendian) pressure water-bearing horizon on clay properties in the construction foundation and structural materials is investigated.
Opportunities of radical breeds of sedimentary cover usage in St.-Petersburg as the basis of high-altitude buildings are considered in the paper in compressed form. Influence of a underground relief of a radical breeds roof of late Vendian, generated by buried bottomlands, on feature of an engineering-geological cut of the basis is analyzed. The generalized parameters of jointing and physic mechanical properties of top-kotlin clay of late Vendian and early Cambrian clay adjournment are resulted, allowing to estimate bearing ability of these soils. Recommendations whenever possible uses of various types of the bases depending on an engineering-geological cut are given.
The construction site of the «Baltiyskaya Zhemchyzhina» multifunctional complex is characterized by rather complicated engineering-geological, hydrogeological and geoecological conditions due to the presence of a deep paleovalley on the site territory, unstable clayey soils and sand lenses with high water head as well as highly polluted ground water. The paper studies possibilities of confined water breakout during the initial stage of construction works depending on the excavation depth and position of the piezometrical surface. Calculations have been done based on the assumption that waterproof bearing block works in shear under the pressure of the confined water. The most dangerous zones in term of possible breakouts have been mapped. These forecasts were conformed during construction works and foundation ditch excavations at the «Baltiyskaya Zhemchyzhina» construction site.
