The design of parts of machines, mechanisms, structures and foundations, particularly in the aerospace industry, is closely related to the definition of the stress state of the body. The accuracy of determining the stress state is the key to optimizing the use of materials. Therefore, it is important to develop methods to achieve such goals. In this work, the second main spatial problem of the elasticity theory is solved for a layer with a longitudinal cylindrical cavity with periodic displacements given on the surface of the layer. The solution of the problem is based on the generalized Fourier method for a layer with a cylindrical cavity. To take into account periodic displacements, an additional problem is applied with the expansion of the solution for a layer (without a cavity) in the Fourier series. The general solution is the sum of these two solutions. The problem is reduced to an infinite system of linear algebraic equations, which is solved by the reduction method. As a result, the stress-strain state of the layer on the surface of the cavity and isthmuses from the cavity to the boundaries of the layer was obtained. The conducted numerical analysis has a high accuracy for fulfilling the boundary conditions and makes it possible to assert the physical regularity of the stress distribution, which indicates the reliability of the obtained results. The method can be applied to determine the stress-strain state of structures, whose calculation scheme is a layer with a cylindrical cavity and a given periodic displacement. Numerical results make it possible to predict the geometric parameters of the future structure.

This article deals with the casting of concrete and reinforced concrete pipes by vibro-vacuum technique. The existing techniques are investigated, the shortcomings are revealed and the solutions to major issues with the improved techniques were offered. Improvement of a technological process of concrete and reinforced concrete pipes production is an important and current task. Development of such technologies should ensure the required supporting capacity reducing the cost of pipeline construction thereof. In this article the existing ways of molding concrete and reinforced concrete pipes have been evaluated. Their engineering deficiencies in terms of labour-intensity and obtaining the products with increased physical and mechanical characteristics have been identified. The offered solution addressing the problems has been identified, namely, the casting of concrete pipes by vibro-vacuum technique. Pilot studies have confirmed that this method makes it possible to achieve the sufficiently high physico-mechanical characteristics of the products. Tensile strength of vibro-vacuum pipes is 40% higher than that of pipes obtained by layer-by-layer axial compaction.

A new method was established to estimate the ultimate load, which is utilized in the assessment of pile test. In the present study twenty five reports of failure test piles (28.5 x 28.5 cm in dimensions, 12 m in depth and the working load was 40 ton) of Um-Alqura Mosque project were studied in according to their loading and settlement. The (mean ± SD) of the pile settlement for each load of all piles studied were determined, and the results obtained were utilized to generate the equation that correlates between the load and settlement using (4th degree polynomial fit graph). The equation obtained was applied to estimate the ultimate load for the maximum settlement (10% of the pile diameter). The estimated ultimate load (130 ton) in the present study was compared with the ultimate load (132 ton), which was determined previously using (Fellenius and Decourt presentation, 2001). The deviation between the ultimate load of the previous and the present method was (1.5%), but the present method depends on two working load, so it saves time and efforts and suitable to implement in the assessment of the test pile.