"Вестник МГСУ"

Subject: friction piles are calculated by the first and second group of limit states. The article describes a new method for friction pile design by the second group (by settlement) of limit state in relation to the pile foundations of buildings and structures in the urban area and in the design of extensions to existing buildings in which the value of settlement is limited or unacceptable. A new method of piles settlement calculation is different from existing method by the Building Code SP 24.13330.2011. The method is based on a new approach of the pile behavior in soil base, which is different from the existing regulations and science papers. Research objectives: the new method of pile settlement calculation is presented with the purpose of clarifying the calculation of pile bearing capacity unlike an existing method in the Building Code (SP 24.13330.2011). The basis of the design is a new idea of the pile behavior in the soil base, which differs from the existing approaches. Materials and methods: the method consists in the formation of the pile settlement only as a result of pile shortening from the compressive force by the deformation of the pile material. Results: the design equation is presented for calculation the pile settlement caused by the pile material deformation. The condition for determining the pile length is presented, which provides the pile settlement only due to the pile material deformation. Conclusion: such approach of the pile settlement calculation is necessary for the design of extensions to existing buildings, as well as new structures near existing buildings, in which the settlement value is already close to the ultimate value of settlement. The article presents the examples of pile settlement calculations obtained by various methods (including the method of the Building Code SP 24.13330.2011) for comparison of the results. The article can be used in the piles design and in the formation of new design standards for pile foundations of structures and machines.

Introduction. Reviewed the features of the work of the pile on Permian claystones with the help of numerical and field experiments, analytical calculations. Materials and methods. Numerical modeling was performed in the Plaxis 3D and Midas GTS NX software packages. Full-scale tests of driven piles are made in accordance with the requirements of GOST 20276-2012. The obtained results are compared with the results of analytical calculations according to SP 24.13330.2011. Results. The scientific novelty of the investigation consists in a comparative analysis of the results of numerical modeling of the interaction of a driving pile with claystones with the results of field tests and analytical calculations. Finite element analysis in software package Plaxis 3D using Hardening Soil model shows higher values of settlement (up to 6 times) in relation to stabilized settlement of full-scale pile tests. Calculations in the software package Midas GTS NX showed overestimated values of pile settlements in relation to full-scale pile tests (13-24 times). Analytical calculations in accordance with SP 24.13330.2011 also showed overestimated (up to 3 times) values of the maximum pile settlement in relation to the stabilized settlement during full-scale pile tests. Conclusions. The calculations by the finite element method in the package Plaxis 3D and Midas GTS NX, by the analytical method according to SP 24.13330.2011, show overestimated values of settlement in relation to the stabilized settlement of piles on claystones. Using the Linear-Elastic model for claystones in numerical calculations in Plaxis 3D provides a value close to the settlement of full-scale pile. However, the use of this model is not fully justified for claystones due to the presence of residual deformations and the nonlinear character of pile settlement during loading. Necessary to correct the existing numerical and analytical methods for calculating pile foundations on claystones. It is necessary to continue the work on the further generalization of the experience of arranging piles on weathered claystones in order to evaluate the long-term work of not only a single pile, but also a pile foundation.

Effective method of strengthening of foundations of existing buildings by pre-stressed shells is considered in the paper. Advantages of the proposed strengthening method, its production technology and pre-conditions of its analysis are also presented. Presently, strengthening of ground foundations and foundations of buildings and structures is a relevant civil engineering challenge. It is driven by high intensity of restructuring and modernization of buildings and alteration of geological engineering conditions of the areas that are being built up. One of effective methods of strengthening of foundations of existing buildings represents arrangement of pre-stressed concrete shells with conventional steel or metal-free reinforcement. If compared with injection-based technologies, the proposed reinforcement method reduces the cost of construction work by 1.5 times, on average. Therefore, the per-unit cost of shell-based reinforcement of foundations is under 500 Russian roubles per 1 sq. m. of the building floor area. It is noteworthy that no restrictions are imposed on the operation of the building in the course of the above reconstruction, as the secluded backyard is the sole area that accommodates supplementary construction operations.

The paper provides a definition of and a solution to the problems of interaction between long piles and the soil body as part of the slab-pile foundation with the due account for the interval between the piles, the length of piles and their correlations, as well as the nonlinear properties of soil identified by analytical and numerical methods through the application of Plaxis-2d software.
It is proven that the above properties produce a substantial impact onto the stress-strain state of soils that interact with the pile and the grid, and the impact values make it possible to assess the rigidity of the slab-pile foundation that is needed to solve the problems of the multiplicity of piles as well as the problems of distribution of the total load between the piles and the grid.

The authors propose new analytical and numerical solutions to develop an advanced method
of assessment of the stress-strain state of unsaturated clay soils exposed to external loading.
The research findings demonstrate that the stress-strain state of the soil exposed to distributed
loading in the half-space b = 2a is complex and homogeneous. It depends on the percentage of saturation and on the excessive pore pressure based on the saturation percentage. At the interim
stage, when the pore water is squeezed towards drainage borders, the area that has a maximal
pore pressure in its centre, travels downwards. Consequently, the alteration of excessive pore pressure
in the course of time is dramatic in layers of soil between drainage surfaces. This finding was
obtained through the employment of analytical and numerical solutions.
It is noteworthy that the diagram of stress distribution ƒ = (ƒ1+ƒ2+ƒ3)/3 and z alongside z axis
below strip b = 2a demonstrates damping. This is the reason why the strip exposed to loading and
excessive pressure is limited in its dimensions. Besides, the authors have proven that the surface
soil settlement is caused by shear and 3-dimensional deformations of the soil exposed to the loading
alongside b = 2a strip. Therefore, s = sg + sv, and any settlement increase sg doesn't depend on the
excessive pore pressure, as it occurs concurrently with loading.

This article gives an overview of the analytical methodology for assessing the environmental safety in construction, the existing government programs in energy saving, and the analysis of the actual state of the investigated problem, proposed a method of assessment of environmental safety efficiency criteria of a city. The analysis is based on the data on housing and communal services of the City of Moscow. As a result of the consideration of the government programs and methods of assessing the environmental security in construction the conclusion was made that none of the programs reviewed and non of the methods include consideration of the relationship between environmental parameters of environmental security and energy efficiency (indicators of them are considered separately from each other). In order to determine the actual state of environmental safety analytical review was performed of energy efficiency programs of the government in Moscow and the methods of assessing the environmental safety of a construction. After considering a methodology for assessing the environmental safety of a construction, the author proposes to use the model for determining the indicator of efficiency of the city to ensure the environmental safety of the processes of life-support of the city, which takes into account the dependence of the parameters of environmental safety and energy efficiency. The author describes the criteria for selecting thr data on energy and environmental efficiency of the city. The article shows the sequence to identify the criteria for determining the indicator of efficiency of the city. In the article the author presents the results of ecological assessment of Moscow on the energy-ecological efficiency model, using the model defined performance indicators of the city to ensure environmental safety processes of life support of the city. The model takes into account the dependence of environmental safety parameters, environmental and energy efficiency. The correlation analysis of the effectiveness of the city of Moscow, the graphs for the regression assessment models of the data are described. The coefficient of efficiency indicators correlation of city support and the coefficient of life safety in the city are calculated. Performance indicator for Moscow in 2009-2012 is defined, which reflects the dependence of the processes of life support and life sustenance of the city. The proposed approach to the assessment of environmental safety may be used in the development of governmental programs on energy saving, as well as in the preparation of regulatory documents.

The article presents the formulation and analytical solution to a quantification of stress strain state of a two-layer soil cylinder enclosing a long pile, interacting with the cap. The solution of the problem is considered for two cases: with and without account for the settlement of the heel and the underlying soil. In the first case, the article is offering equations for determining the stresses of pile’s body and the surrounding soil according to their hardness and the ratio of radiuses of the pile and the surrounding soil cylinder, as well as formulating for determining equivalent deformation modulus of the system “cap-pile-surrounding soil” (the system). Assessing the carrying capacity of the soil under pile’s heel is of great necessity. In the second case, the article is solving a second-order differential equation. We gave the formulas for determining the stresses of the pile at its top and heel, as well as the variation of stresses along the pile’s body. The article is also formulating for determining the settlement of the foundation cap and equivalent deformation modulus of the system. It is shown that, pushing the pile into underlying layer results in the reducing of equivalent modulus of the system.

When a long pile is interacting with the soil, the combined force applied to the pile head is distributed among the side face and the pile toe inhomogeneously. The toe gets not more than 30 % from the general force, which doesn’t let using the reserves of the bearing capacity of relatively firm soil under the fifth pile. Account for the depth of the pile toe and the dead load of the soil allows increasing the bearing capacity of the soil under the pile toe and decrease the pile settlement in general. For the quantitative estimation of these factors it is necessary to solve the task on the interaction of the rigid long pile with the surrounding soil, which includes under the pile toe, which is absolutely rigid round stamp.The article presents the formulation and analytical solution to a quantification of the settlement of a circular foundation with the due account for its depth, basing on the development of P. Mindlin’s studies as well as the interactions between a long rigid pile and surrounding soils, including under pile toe.It is proposed to compare the estimated value of stresses under the heel of pile with the initial critical load for the round foundation to check the condition that the estinated value is less than the intial critical one.

In the article the problem of designing pile foundations on claystones is reviewed. The purpose of this paper is comparative analysis of the analytical and numerical methods for forecasting the settlement of piles on claystones. The following tasks were solved during the study: 1) The existing researches of pile settlement are analyzed; 2) The characteristics of experimental studies and the parameters for numerical modeling are presented, methods of field research of single piles’ operation are described; 3) Calculation of single pile settlement is performed using numerical methods in the software package Plaxis 2D and analytical method according to the requirements SP 24.13330.2011; 4) Experimental data is compared with the results of analytical and numerical calculations; 5) Basing on these results recommendations for forecasting pile settlement on claystone are presented. Much attention is paid to the calculation of pile settlement considering the impacted areas in ground space beside pile and the comparison with the results of field experiments. Basing on the obtained results, for the prediction of settlement of single pile on claystone the authors recommend using the analytical method considered in SP 24.13330.2011 with account for the impacted areas in ground space beside driven pile. In the case of forecasting the settlement of single pile on claystone by numerical methods in Plaxis 2D the authors recommend using the Hardening Soil model considering the impacted areas in ground space beside the driven pile. The analyses of the results and calculations are presented for examination and verification; therefore it is necessary to continue the research work of deep foundation at another experimental sites to improve the reliability of the calculation of pile foundation settlement. The work is of great interest for geotechnical engineers engaged in research, design and construction of pile foundations.

Underground construction in dense urban areas requires solving many problems, the most important of which is to prevent excessive additional deformations of the bases, which surround the area of the construction of buildings and structures.In order to prevent deviant strains different methods are used in engineering practice. In the recent years our country began to use a very popular abroad method of compensation grouting, which is currently one of the most effective methods of protecting the land-based facilities from the influence of underground facilities. This method has another important advantage, which allows using it rather for stabilizing yield of buildings and structures continuing for various reasons (geological, technological, etc.), or for lifting them if the settlement has exceeded the standard value.The method involves injection of a slowly hardening compensation grouting solution of a definite viscosity, which has a mineral base (suspension), into the foundation soil of the structure, the settlement of which should be controlled or compensated.

Subject: the “load”-“deformation” dependence and phases of the stress-strain state of claystones and sandstones. Research objectives: perform stamp and pressuremeter tests, analyze results of field tests and create recommendations for the design and calculation of foundations on claystones and sandstones. Materials and methods: in this article the field methods of testing of claystones and sandstones are considered. Stamp and pressuremeter tests were performed, the “load - settlement” dependence was obtained and phases of the stress-state for claystone and sandstone were identified. The design strength of the soil for the drill pile buried in claystones and sandstones by more than 0.5 m was determined. Results of field tests are processed by mathematical statistics methods in accordance with GOST 20522-2012. The obtained results are analyzed and compared with the previous results of tests on foundations. Results: the scientific novelty of this work consists in revealing the regularities in the formation of the stress-strain state in claystones and sandstones under the action of the load in various directions. The deformation mode and development of phases of the stress-strain state in claystones and sandstones differ significantly from modern clays and sands. In 58 % of the stamp tests, the loss of the bearing capacity of the base, composed of claystones and sandstones, was observed only after reaching the load of 3.0 MPa. In 19 % of the stamp tests, the deformations sharply increased already at the load level of 0.6…2.2 MPa, which is characteristic of less stable varieties of claystones and sandstones. In 23 % of the experiments, the vertical deformations of sandstones and claystones had a linear character for the entire “load”-“settlement” graph and the phase of soil bearing capacity loss was not achieved. A similar picture was observed when performing pressuremeter tests: the phase of bearing capacity loss was not achieved for claystones at a maximum horizontal pressure of 0.85 MPa and for sandstones - at a maximum horizontal pressure of 1.0 MPa, and the deformations of the soil were predominantly linear, which is typical for compaction phase and phase of local shears. Conclusions: claystones and sandstones have high values of design strength and can be a reliable low-compressible base for buildings and constructions with loads from 0.2 to 0.3 MPa. Calculations can be made using the theory of a linearly deformed soil when designing the foundations of buildings and constructions on claystones and sandstones. However, it should be taken into account that this observation is valid for one-time loading, since claystones and sandstones have residual deformations associated with the destruction of cementation bonds between soil particles. It is rational to use in calculations of foundations on claystones and sandstones the values of the strength parameters of the soil obtained in laboratory or field tests with soaking, taking into account the possible deterioration of the properties of these soils.