Development of the fastening design of the underground structure immersed in water-satureted soils of St. Petersburg, from floating up

摘要

The practice of design shows that the need to develop explanations, recommendations and examples of calculations to go with the essential requirements of the building rules. The author has set the task to simplify the use of the requirements for the design and construction of soil bases for cylinder open caissons. The objective of the work is to develop the fixing design of an underground structure of 24 m in diameter and 15.6 m in height, immersed in an antifriction jacket below the groundwater level to depth of 16,8 m, to prevent it from floating up. The article describes the geological structure and soil characteristics of St. Petersburg, a characteristic feature of which is the presence of groundwater horizons in the soils, complicating underground constraction. Recommendations and explanations are given as to how to forecast the forces of friction at the point of contact between the structure and the water-saturated soils. The constractive scheme of securing embedded structure from floating up has been developed. The methods of calculation and design of additional loads and ground anchors is described in detail. The results of calculation and analysis have been performed to verify the probability of the open caisson floating up due the action of the hydrostatic load. The main types of construction work are cementation of the antifriction cavity, building on the perimeter of the well of a reinforced collar rigidly connected with the front shaft, providing a sandy backfill as additional load for the well, anchoring the bottom of the well using vertical ground anchors. The paper may be of interest to designers working in the area of the design of underground structures.