Construction and Geotechnics

The methods for determining the parameter of design resistance of foundation soil R for shallow foundations of reconstructed (restorable) buildings built on sandy and clayey soils are considered. It is established that during the long-term operation of buildings and structures such soils are compacted, and their properties usually improve. For the conditions of reconstruction and restoration of buildings, the parameter R is commonly referred to as the design resistance of compacted foundation soil Rup . The known methods of determination of Rup parameter published in works of Russian scientists for the last 50 years (since 1971) have been analyzed by the authors. The most effective among the considered methods is the engineering method (1997) that takes into account not only the improvement of soil properties under the foundations but also their weakening (deterioration) caused by watering of these soils during the period of the buildings operation. This method of determining Rup is based on the recommendations for the calculation of R according to SP 22.13330.2016, which includes additions that take into account the changes in the above soil characteristics. The scope of the method applies to clays, loams and sandy loam from hard to flowable (plastic) consistency. In order to design shallow foundations in various cases of reconstruction and restoration of buildings on sandy and clay soils, it is necessary to further develop the methods of determining the parameter Rup .

A comparative assessment of the long steel shell-pile bearing capacity is carried out in conditions of deep bedding of dense soils on the example of the Crimean bridge. The soil column is represented by six layers of soil only the last sixth layer of which located at a depth of 62 m has a high bearing capacity. Three design schemes are considered, taking into account soil resistance along the outer side surface and under the lower end of the pile, along the outer and inner side surfaces of the pile, as well as along the outer side surface and under the lower end of the pile, taking into account the soil core and self-locking effect. The results of calculating the bearing capacity of the steel pile-shell for each of the design schemes are presented in tabular and graphical form. Conclusions are drawn about the nature of the change in the soil resistance forces with the depth of the pile immersion both along its outer and inner lateral surfaces as well as under its lower end. The depth at which the soil core formation begins as well as the depths within which the soil is compacted and self-locking inside the pile cavity has been established. In this case the pile begins to work as a pile with a closed lower end and a further increase in its bearing capacity occurs due to the frictional forces of the soil along the outer lateral surface. A comparison is made of the bearing capacity values calculated for each of the three design schemes with the partial value of the ultimate resistance according to immersion data with actual (measured) residual failures based on the results of field tests with dynamic load.

The research goal is to formulate and solve the problem of distributing the external load between piles with widening and a low grillage as part of a strip foundation in a flat setting and comparing the results obtained with experimental data. The design model of Flaman (the plane problem) and Boussinesq (the spatial problem) about the force applied on the surface and Melan's solution about the force applied inside the soil half-space are taken as the initial design models. An analytical calculation method was proposed, as a result of solving the problem. This method, with sufficient accuracy for practical purposes, allows to define the bearing capacity of the foundation on piles with widening and to estimate the distribution of the load between the piles and the grillage as part of the strip foundation. The proposed approach to solving the problem of load distribution between the grillage and piles with widening is important for design of strip foundations.

Nowadays, the role of the majority of professional engineering communities, unfortunately, is devalued in Russia. It does not lead to the required development of engineering activities due to the disunity of individual specialists the lack of motivation to coordinated decision of professional issues, the lack of participation in the general professional labor market, the impossibility of direct communication with leaders in a particular field of knowledge, etc. The number of members in professional society with significant work experience is constantly decreasing. Professional communities that have not been able to build the structure of their work and become interesting for specialists usually disappear or have a formal status. The paper describes the successful world experience of the professional communities existence, considers the basic principles of the activities of such communities as: ASCE (American Society of Civil Engineers) and BGA (British Geotechnical Association). The success of these communities is evidenced by the fact that ASCE has unified a global community of engineers since 1852, with more than 150,000 members. The BGA has functioned since 1949 with over 60 collective members representing the UK's proponent geotechnical agencies. The advantages of membership in these societies for both professional engineers and students are given, including: rapid career growth supported by the community; active participation in the life of society, based on individual and social benefits; establishing personal contacts and obtaining first-hand information on topics of interest; great benefits or free membership for students; a large amount of events held under the auspices of ASCE and BGA , etc.

Phosphogypsum is a waste obtained by binding calcium in the process of sulfuric acid decomposition of phosphate raw materials in the production of phosphorus fertilizers. The article presents the results of complex laboratory studies of more than 500 samples of calcium sulfate hemihydrate and dihydrate. Calcium sulfate dihydrate (CaSO4·2H2O) is a solid fine-crystalline substance of white or gray color with the inclusion of large aggregates. Deformability, strength properties and permeability of calcium sulfate dihydrate were determined on specially prepared samples with a relative compaction of 0.95; 0.90 and 0.80 by the methods used in engineering and geological surveys. The internal friction angle, cohesion and coefficient of permeability have values typical for silty sands and sandy loam, and the compressibility characteristics are significantly lower due to the solubility of matter. This material is characterized by subsidence and suffusion sediment characteristic of carbonate rocks (dolomite, limestone). Calcium sulfate hemihydrate (CaSO4·0.5H2O) - a loose earthy mass of white or gray color, as the process of hydration and the appearance of cementation bonds turns into a semi-rocky technogenic soil of low strength. The characteristics of calcium sulfate hemihydrate were determined on the undisturbed samples taken from the dump after 1 and 6 months, 1, 5 and 10 years after storage. These characteristics are comparable to construction gypsum materials from lower grades. It is recommended to use calcium sulfate dihydrate as ground material when carrying out water-protective measures and neutralizing the acids contained in it, the use of calcium sulfate hemihydrate is significantly limited by its setting time.

The paper presents comparison of results of calculations of position, sizes and shapes of plastic deformation areas carried out on the basis of use of Coulomb plasticity condition and solution of elastic-plastic problem and mixed problem of elasticity theory and ground plasticity theory which resulted, among other things, in graphs of dependence of depth of plastic zones development on value of intensity of external influence. Calculations have been executed at three values of coefficient of side pressure of ground about = 0.37; 0.54; 0.72 for uniform strip load (no die), and for absolutely rigid die under condition of full sticking and under condition of no friction on ground-stamp contact. As a result, it was found that the plastic regions corresponding to the "Coulomb" solution differ essentially from similar regions based on elastic-plastic (mixed) solutions. Their sizes, with the same intensity of loading, are larger, their rate of development into the deepening of the base is higher than that of the alternative ones, and when the load reaches the maximum permissible value, they merge under the punch and form a single sickle-shaped area. In the case of "Coulomb" plastic areas, their shape and rate of development into the foundation in the initial stages of loading are rather strongly dependent on the value of soil side pressure coefficient. In the case of "mixed" solution, the "velocity" of this process is practically independent of the value of coefficient o. If we use the condition of closing of plastic regions in the foundation under load as the criterion for determination of the maximum permissible value of intensity of external action, then in "Coulomb" regions this value will be substantially lower than in alternative ones for all considered values of the coefficient of lateral pressure of soil.