"Вестник МГСУ"

The parametric analysis of the stress state of a transversally isotropic rock mass near a pressurized hydraulic tunnel of a box-shaped form is carried out. Pressurized hydro-technical tunnels of box-shaped cross-section are widely used in the field of hydraulic engineering construction and are one of the complex, labor-intensive and expensive types of structures that make up the main structures of waterworks, melioration systems and water supply systems. As a culvert and water supply facilities they are built underground if the open excavation is impossible or not economical, or when the tunnel runs through a densely populated or densely built-up area, or when landslides, screes, rockfalls are possible. Violation of integrity of the rock mass, in particular, caused by tunneling, modifies the stress-strain state (SSS) of the rock mass, which leads to appearance of tensile stresses in some places, and in some cases, to significant compressive stresses. If these stresses exceed the design strengths of rock to tension and compression, respectively, then the collapse of the working roof and buckling of the side walls and the bottom of the tunnel may occur. Subject: analysis of the stress state of transversally isotropic rocks near the pressurized hydraulic tunnel of horseshoe cross-section caused by the internal head of water. Research objectives: determination of real values of circumferential stresses along the development contour. Materials and methods: solution of the problem of plane deformation of the theory of elasticity for a transversely isotropic medium containing tunnel excavation cannot be obtained by analytical methods, and therefore the stress-strain analysis was carried out by the finite element method using the ANSYS software package, MCE. Results: determination of stresses along the development contour, construction of diagrams and graphs showing the effects of the anisotropy conditions and Poisson’s ratio. The tangential stresses along the contour of hydraulic tunnel development for various values of deformation modulus and Poisson’s ratio are determined, which makes it possible to estimate the strength of the rock mass for different tunnel depths. The analysis of a long hydro-technical tunnel, laid in a strong, transversally isotropic rock, is reduced to the problem of plane deformation of the theory of elasticity for a transversely isotropic medium containing tunnel excavation. The size and type of the finite element suitable for analysis were determined in advance based on the solution of the test problem. Conclusions: it is necessary to determine the physical and mechanical properties of rocky soils more accurately, paying special attention to elastic characteristics; calculations should be performed taking into account the anisotropy of elastic properties.

A sustained pace of construction of dams and dikes using water resources and intensive development of underground space in the construction of buildings and structures require ensuring anti-seepage measures. For efficient stoppage of fluid flow a variety of methods are applied such as cement and grout curtains, teeth, core walls including ones made of soil-cement mixtures performed by the method of diaphragm wall. The following characteristics are the main selection criteria of the material composition for a diaphragm wall : permeability, strength, deformability, efficiency. Clay-cement-concrete (CCC) is one of the materials satisfying all the above characteristics. The influence of the components used to prepare CCC mixtures on its strength and deformation characteristics was the main objective of the performed study. In order to solve the task, the formulas of CCC used at the objects of hydroengineering construction have been considered. For analyzing the influence of the components of CCC on its characteristics, the dependences of compression strength and deformation modulus of CCC on water-cement and water-astringent ratios have been built. The dependence of compression strength of CCC on the cement/bentonite ratio was built as well. The analysis of the dependences defined that the compression strength of CCC depends primarily on water-cement ratio and the amount of cement used in the composition. The increase in the value of water-cement ratio and water-astringent ratio leads to monotone decrease of the compression strength of CCC and the deformation modulus of CCC. Change of the quantitative content of one or more components of CCC composition allows controlling physical-mechanical characteristics of the anti-seepage element which is an important advantage of clay-cement-concrete. The performed analysis of the influence of CCC formula on its physical and mechanical properties can be used to select the optimal composition of CCC when solving specific hydroengineering tasks.

In design of hydraulic structures seepage-control components are used; for installation thereof the cut-off wall method is often applied. Previous studies demonstrated that the reliable operation of the wall (diaphragm) depends much on properties of the material of which it is made. The article considers the results of calculations of stress-strain state of the earth dam 39 m of height, with the seepage-control component in a form of a diaphragm installed using the cut-off wall method. During the research the properties of the wall material varied. It was revealed in the course of works that tensile stresses resulting from bending strains when the wall takes on the hydrostatic pressure are of serious hazard to the diaphragm. Such stresses are problematic for designs of seepage-control diaphragms (cut-off walls) in earth dams made of stiff materials. The more stiff the material the higher the risk of showing of tensile stresses. When using the material with the deformation modulus less than 1000 MPa the tensile stresses do not show because they are compensated by compression under action of the wall’s own weight. If a reinforced concrete is used as the wall material, the appearing tensile stresses will exceed the tensile strength of the reinforced concrete and will not be able to be taken even by reinforcing bars. It is recommended to use clay cement concrete with the deformation modulus not higher than 1000 MPa. It was concluded that a non-ground diaphragm installed in the earth dam body using the cut-off wall method can be a reliable seepage-control component because it is installed after the dam construction completion and does not exercise significant deformations from ground fill settlements. A stress-strain state of the thin-walled non-ground diaphragm in the earth dam body is determined by deformations of the fill containing it. Intrinsic wall stiffness influences weakly on the stress-strain state of the earth dam.

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.

The article covers the problem of parameters that underlie the choice of mechanical properties of the clay stone used as the foundation material in Perm. The object of this study is the clay stone of the early Permtric modulus, effective cohesion intercept and angle of internal friction constitute tian age. Mechanical properties, including the deformation modulus, oedomehe subjects of the study. The authors enumerate the following tasks:1) description of geological conditions of the two sites of experiments in Perm,2) development of the methodology of identification of strength and deformation properties of the clay stone in the laboratory (oedometry testing and shear box testing of water saturated and water free samples) and on site (cone penetration tests, pressuremeter tests) according to the Russian technical regulations,3) experiments aimed at identification of mechanical properties of the clay stone,4) analysis and comparison of mechanical properties of the clay stone using various methods,5) provision of conclusions and recommendations concerning mechanical properties of upper layers of the clay stone in Perm.A lot of attention is paid to the analysis of results of cone penetration tests, pressuremeter and laboratory tests. The study has revealed a significant effect of test methods on the resulting values of strength and deformation properties of the local clay stone.

Introduction. Modern nondestructive techniques of wave analysis can be applied for the rapid preliminary geotechnical soil assessment. One of these techniques is Multichannel Analysis of Surface Waves (MASW) which allows to obtain velocities profile of shear waves and an initial shear modulus for upper section at minimal duration and labor costs. But for soil deformation properties assessment it is required a deformation modulus obtained by means of direct technique of plate load test. The purpose of the performed study is assessment of the correlation between plate load test deformation modulus and initial shear modulus obtained via wave analysis. Materials and methods. Plate load tests were carried out for various plates and moduli of deformation were calculated. Deformation modulus adjustment factors were applied to perform a comparative analysis of different sizes plates at 5000 cm2 plate. Wave analysis was carried out by the active method of MASW. Results. During comparative analysis a correlation coefficient was evaluated for two cases: the deformation modulus was determined strictly according to GOST 20276-2012; deformation modulus was determined for the loading interval 0.050-0.125 MPa. In the first case “correlation coefficient-unit weight” indicative dependence was observed. The regression equations for the both cases was presented. Conclusions. Correlation between two types of tests was performed by results of in-situ tests. The proposed empirical regression equation allows to obtain the value of the deformation modulus on the basis of wave analysis data and to perform rapidly a soil foundation geotechnical assessment for the future construction.