Deep Foundations

Currently designers and constructors often face the challenges of implementing projects of high-rise buildings and unique structures due to the fact that the foundation has relatively deformed grounds whereas the load on the foundation is often enormous and it can reach 1000 kPa.

At the same time the high-rise structure engages a huge amount of ground directly under the foundation as well as behind the excavation wall of the building under construction. All this leads to the necessity to consider the complex task of interaction of the elements of the “basis - foundation - structure” system (hereinafter - the system) and take into account the non-linear soil behavior of the foundation under heavy loads. However, the existing regulations on the classification of bases and foundations do not include an entire set of peculiarities of this interaction, which leads to various negative factors such as: the increase of the costs of the design and construction, the increase of the lead-time of the design and even to the cancellation of construction due to a number of reasons.

In this article we pay attention to important factors that affect the design of high-rise foundations that allow us to take into account soil behavior under such heavy loads during the interaction with other foundations. The consideration of these factors will make it possible to most reliably describe the initial basic stress state, its transformation during construction and as a result to obtain adequate forecast values of shifts and stresses in the basis.

1. Soil Tests Adequate for the Complex under Design
The application of adequate basic soil models to estimate the stressstrain behavior (SSB) under loads and unloads makes it possible to most accurately assess the change of stresses and strains during all stages of high-rise construction: pit digging and unloading of the basis, re-loading to the natural state and over-loading beyond the natural stress. Among the modern models of soils that are used in the world we can point out a soil model with an increasing stiffness (Hardening soil).

It is quite versatile and it can relatively precisely describe the behavior of the soil with both good and poor mechanical properties. The distinguishing feature of this model is its non-linearity throughout the entire load range and change of soil modulus e (MPa) during loading and unloading. In cases, when there can be little deformations (multilayer erecting pits for underground construction, tunneling, etc.), we may apply the model of hardening soil small strain. It considers much greater hardening of the basis within the range of little deformations.

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Written by: Zaven Ter-Martirosyan, Doctor of Engineering, Professor;
Armen Ter-Martirosyan, Doctor of Science, Associate Professor;
Vitaly Sidorov, Doctor of Science, Associate Professor;
Federal State Budgetary Educational Institution of Higher Professional Education
“Moscow State University of Civil Engineering”;
“Geotechnics” Research and Educational Center at MSUCE