To the question of concrete creep in the soil environment

Abstract

Introduction. Concrete creep coupled with specific soil properties represent a problem for the analysis of reinforced concrete structures in geotechnical engineering. The mission of this research is to make a problem statement and to outline its potential solutions.
 Materials and methods. In the course of the research, the finite element method was applied and the review of works, covering various problem aspects, was performed.
 Results. Concrete creep in respect of a diaphragm wall is most vividly manifested in deflections and stresses in struts; as for piles, concrete creep is manifested by the longitudinal axial force distribution along the length. The co-authors have demonstrated that is necessary to single out the excavations device under bentonite slurry protection from the viewpoint of the construction technology. In this case, a 5–10 mm thick water-saturated filter cake is formed at the contact between soil and concrete. The filter cake retains its permanent water penetrability at some level that depends on pressure and injection time; therefore, concrete in trench cannot be considered isolated from filtration water flows. Following the concrete mix casting into the trench, water saturated filter cake is consolidated, and this enables the authors to make a conclusion about its resistance to vapour penetration.
 Conclusions. If water saturation is equal to Sr > 0.5–0.6 and if excavation works are performed under the protection of the bentonite slurry, relative air humidity of soil RH can be considered to be equal to 100 %, and if water saturation Sr < 0.5–0.6, RH needs to be analysed. Identification of concrete moisture content depending on relative air humidity, the groundwater filtration flow and influence of the filter cake at the contact between ground and concrete make it possible to take account of the effect of soil conditions on concrete creep.

Taking into account technological features of the diaphragm wall for deep pits

“…For the cost-effective design of pit enclosure structures and assessing the impact of construction on the surrounding buildings in the corner zones, it is necessary to perform calculations in a three-dimensional formulation of the problem. It is also advisable to take into account the nonlinear work of concrete, since it was found that the creep of concrete affects the distribution of forces in depth and leads to a decrease in the flexural stiffness of reinforced concrete structures [8].…”

Determination of the Bending Moment in the Diaphragm Wall by Inclinometric Observations

“…To determine the values of the actual bending moments that occur in the diaphragm wall in the ground, it is also necessary to correctly determine the stiffness of the structure (Sapin and Diakonov 2019). At the same time, it is necessary to take into account the non-linear nature of the work of reinforced concrete, since when the moment of cracking is exceeded, the rigidity of the structure drops significantly [12,13]. In accordance with this, it is necessary to plot the relationship between the bending moment acting on the wall and its stiffness (EI).…”

Boundary conditions for the problem of moisture transport in concrete

“…The boundary conditions for the model of moisture transport in saturated concrete according to Darcy's law will be water pressure at the contact with structure, and environmental relative humidity for unsaturated concrete under to the Bažant-Najjar model. Since soil is the environment for such structures as piles or diaphragm walls, it is necessary to take into account the relative humidity of soil environment [17]. Then the boundary conditions at soil contact with the geotechnical structures can be characterized by such parameters as temperature, the pore pressure and the relative humidity of the environment.…”