"Вестник МГСУ"

Subject: an analytical solution to the problem of interaction of the pile and the raft plate with the surrounding soil taking into account the possibility of expansion of the pile’s shaft is given. Closed solutions are obtained for determination of stresses in the pile’s shaft and in the soil under the raft plate. We take into account the effect of prestress of the base after compaction on formation of stress-strain state during construction and operation of structures. These solutions are relevant for compaction piles made of crushed stone or soil-cement piles whose stiffness is comparable with the stiffness of the surrounding soil. Research objectives: determination of the average strength and deformation parameters of weak soils subjected to transformation using the piles of finite stiffness made of loose gravel material and soil-cement material; comparative analysis of the obtained results with the data of in situ tests on a construction site. Materials and methods: when solving the problem of interaction between the pile and the surrounding soil with the expansion of pile’s shaft, analytical solutions based on well-known expressions of classical soil mechanics and solid mechanics are used. Experimental studies were carried out on a certified laboratory equipment and with the help of field methods regulated by the existing design codes. Results: the presented technique of improving mechanical parameters of soils and the method of their calculation in the transformed foundation allow us to determine the average characteristics of strength and deformability of the entire foundation. These techniques are necessary for analysis of the transformed foundation by two types of limit states in the process of designing the structure by analytical and numerical methods. Conclusions: the resulting dependencies and the proposed techniques for designing reinforcement of the base with the help of pile-drains are used on real construction sites. We present the results of large-scale tests at the experimental site for construction of a large energy facility in Russia as well as at the housing construction site in the Central region of the Russian Federation.

Interaction between long piles and the adjacent soil has a spatial and temporal nature. This phenomenon is based on a set of non-linear and rheological properties of soils. Distribution of lateral forces between the surface and the pile toe is heavily dependent on the above properties. The process of formation of the stress-strain state around the pile can demonstrate decaying, constant or progressive velocity depending on the rheological processes in the soil that may be accompanied by hardening and softening processes at one and the same time. These processes may be caused by destruction and restoration of ties between clay soil particles, soil compaction and de-compaction. Predominance of the process of hardening leads to damping, while predominance of the process of softening causes progressive destruction. Description of this multi-component process depends on the rheological model of the soil. This research is based on the modified rheological model originally designed by Maxwell. The authors consider solutions to the problem of quantification of the stressstrain state of soil around the pile and their interaction. This research makes it possible to project motion patterns of long piles over the time and evaluate the limit of their long-term bearing capacity.