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.
When calculating of the moisture transport in concrete of such geotechnical structures as a pile or diaphragm wall, contact with soil is forming the special boundary conditions. If the soil is in the full saturated state, then the Darcy’s law should be used to solve the problem, the boundary condition for which is the water pressure. Otherwise, the Bažant- Najjar model is used, for which the boundary condition is the relative humidity of soil environment at a certain temperature. The soil environment temperature is unique characteristic for each construction area. For Moscow region, the weighted arithmetic mean temperature to the depth of 60 m is 7.3°C. It is proposed to calculate the relative humidity of the soil environment according to the Kelvin capillary condensation equation, in which the suction is calculated using the Mualem-van Genuchten hydraulic model from the degree of saturation. Two well- known sets of hydraulic parameters of the Mualem-van Genuchten model, compiled on the HYPRES and the HYDRUS-1D database from the European soil map texture classes and the USDA textural soil classification respectively, were compared with the measurement results for soil samples classified according to Russian the GOST 25100. The experimental data showed a good approximation to the calculation with a set of parameters obtained on the basis of the HYPRES database. At the same time, the solution with the HYDRUS-1D parameter set showed a poor correlation.
Introduction. The analysis of moisture fields in a diaphragm wall is needed to determine such rheological parameters of concrete as creep and shrinkage deformations. Materials and methods. In the paper, the main solution was obtained by expansion into the trigonometric Fourier series using data on diffusion properties of materials identified by reviewing the studies. Results. By solving the problem of moisture transport in the diaphragm wall, taking into account filter cake, the authors found out that the relative humidity in the concrete pore space decreases extremely slowly over time. Linear distribution is achieved only 48 years after the excavation of the diaphragm wall. At a depth of 20 cm, humidity dropped to 92 % on day 365 and to 82 % after 3 years. In the 6th year, the drying of concrete by the atmospheric air affects the boundary with filter cake and continues until the 48th year, when the relative humidity of concrete takes a steady value of 69 %. Conclusions. The analysis of the accurate solution shows a strong effect of filter cake on the drying rate of the diaphragm wall. Low diffusion permeability of filter cake accelerates the drying of concrete. Given that the coefficient of diffusion of filter cake is 15.6 ∙ 10–8 m2/day, its effect manifests itself in deep layers after 3 years. Relative humidity of air in a trench is more significant for near-surface areas.
Engineering calculations in the spatial formulation, as well as the results of field observations, show a significant decrease in lateral displacements of the foundation pit retaining walls in the area of the corner zones. At the same time, in design practice, a large number of decisions are made on the basis of calculations in a flat formulation. For pits with a depth of more than 10 m, the influence of corner zones can make a significant contribution to the reduction of movements and, as a result, internal forces in the retaining walls and restraint systems. The underestimation of the corner effect leads to an increase of the retaining structures construction cost. This article presents the results of FEM calculations studies of the monolithic reinforced concrete wall functioning in the corner zones of pit in sandy soils. As a result, it was revealed that the movement of the diaphragm wall in the area of the corner zones of the foundation pit is influenced by such factors as: the pit depth, the angle between retaining walls, and the stiffness of the retaining wall and struts. At the same time, the properties of the sand and the stiffness of the retaining wall and struts do not affect the distribution of displacements in the corner zones.
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