SCIENTIFIC EVIDENCE FOR WALLS FASTENING TECHNOLOGIES OF WORKING TRENCH BY THE SPECIAL METHOD « SLURRY WALL » FOR SHALLOW SUBWAYS ’ STATIONS

Dep. «Construction of Mines and Underground Structures», Donetsk National Technical University, Artem St., 58, room 414, Donetsk, Ukraine, 83001, tel. +38 (062) 301 03 23, e-mail borshevskiy@gmail.com, ORCID 0000-0002-7194-8785 Dep. «Tunnels, Bases and Foundations», Dnipropetrovsk National University of Railway Transport named after Academician V. Lazaryan, Lazaryan St., 2, Dnipropetrovsk, Ukraine, 49010, tel. +38 (050) 708 50 69, e-mail petrenko1937@mail.ru, ORCID 0000-0002-5902-6155 Dep. «Tunnels, Bases and Foundations», Dnipropetrovsk National University of Railway Transport named after Academician V. Lazaryan, Lazaryan St., 2, Dnipropetrovsk, Ukraine, 49010, tel. +38 (066) 290 45 18, e-mail tutkin@mail.ru, ORCID 0000-0003-4921-4758 Dep. «Tunnels, Bases and Foundations», Dnipropetrovsk National University of Railway Transport named after Academician V. Lazaryan, Lazaryan St., 2, Dnipropetrovsk, Ukraine, 49010, tel. +38 (098) 768 49 21, e-mail jaksson777@rambler.ru, ORCID 0000-0002-4529-7384 Dep. «Tunnels, Bases and Foundations», Dnipropetrovsk National University of Railway Transport named after Academician V. Lazaryan, Lazaryan St., 2, Dnipropetrovsk, Ukraine, 49010, tel. +38 (096) 992 15 81, e-mail murzilka891@mail.ru, ORCID 0000-0002-6077-1689


Introduction
Owing to the dynamic growth of the population in the cities and a tendency of the perspective transport infrastructure solution with using of underground space, there is a task in the solution of a number of questions, belonging to area of underground construction.The building of the underground facilities, which is being built by the open method, requires a detailed design and protection from excessive strain of fastening construction, and daily surface around the working trench.The progressive method of fixing of the working trench slopes is the special method of a construction "slurry wall".
This method of the construction of working trench has several disadvantages, namely: the emergence of excessive deformations and displacements in the system of wall-array local occurrence of extreme stress [2].
The question is to strengthen the design on the finite element model, which is a prototype of the working trench of the shallow subway's station using the additional fastening by means of strut rail.

Purpose
Numerical justify fixing technology and selection of optimal variant, creating graphs comparing of fastening for idealized cases and finding methods to prevent undue strain and stress in the wall.

Methodology
It is build the finite element models that reflect the working trench for the shallow subway's station, with four ways of fastening "slurry wall" for achieve this task, and also the calculation and analysis of the stress-strain state structures and fastening elements by means of FEM complex calculation is conducted.

Findings
The analysis of the stress-strain state and movement of various fundamental soil nailing system and comparing of the given results.It is built the tables and resulting graphs behavior and state of construction fasteners, change its settings and parameters surrounding the array on the basis of researches.

Originality and practical value
In solving task in hand was analyzed and investigated the behavior of fixing construction and its stress-strain state, found the space and plots of fixing construction which require further elaboration, investigation and resolution measures to strengthen the construction and consolidation items.
During the construction of underground facilities with using a special method "slurry wall" the question that has to be answered is in a fast selection of optimal parameters, elements and ways to consolidate its walls from excessive strain, stabilize the soil mass around working trench, minimizing the value of its deformation and prevent landslides with the expectation gravity load in the construction of working trench.
Developments of finite element model for calculation the dimensional mountings of "slurry wall".
For calculation the stress-strain state of the fixing construction of the working trench by means of strut rail is used finite-element model which is a section of working trench of length 7 m.The square size of the finite element is taken 0.5 m.
As it is considered the part of the construction, which has the extensive sizes, it is necessary to impose the relocation ban of the appropriate sides: the relocation prohibition along the global axes X, Y, Z, for a basis, and in X, Y directions, on extreme edges, that lying in the YoZ and XoZ planes accordingly [4].
For strut rail fixing two options are selected: 1. Alternative mounting by means of help of one row strut rail, as shown in Fig. 1, and in the form of a pipe with a diameter of 1 000 mm and thick wall of 10 mm; 2. Option fixing with two rows of strut rail, as it is shown in Fig. 1b, in the form of pipes with a diameter of 1 000 mm and a wall thickness of 10 mm; Strut rail in the submitted models are represented as finite element of square section.For faithful calculation results by means of VC SCAD, it is given elastic modulus, principal moment of inertia section area of pipe and composite unit weight in accordance with section [8,13].
It is developed models and calculation of a homogeneous soil mass for a more detailed analysis and idealized stress-strain state of fixing construction [6,7].It allowed reflecting the real action of one given type of the soil on construction of a barrier.
The calculation was conducted with using parameters that numerically reflect the properties of the material and ground mounting sections and values through their elastic modules, the proportion of materials and Poisson's ratio for each type of rigidity [3,5].The soils surrounding the array presented in a variety of similar species, such as sandy, loam, clay and sand.
The diagram (Fig. 2, a, b) shows the placement of designated models of rigidity, which correspond to the actual placement of fixing construction in the working trench with one and two rows of strut rails, respectively.
These numerical characteristics of the soil and the materials fastening elements are summarized in the Table 1.For further calculation of construction for strength, that carried on concrete that is used to crack the maximum normal stresses arising in the "slurry wall" along the global Z-axis [10,14].
The obtaining of normal stresses allows considering multi-axial stress in elements of model and more precisely to clarify behavior of construction in case of interaction it with the environmental array executions and caused by its loadings [6].
It is the initial data for calculating finiteelement models of attachment.
The calculation for working trench, slopes consolidation of which are presented in the form of "slurry wall" attached to one and two tiers of strut rails.Each of these models is the section of working trench length of 7 m [11].
For comparing four finite-element models of a special method of working trench slopes fixing by means of "slurry wall" without any additional fixing with the help of strut rails are constructed.The rigidness is appropriated to these models, the similarly provided in  fixing-array and to define points the application of points of additional coupling in the form of strut rails.The following number 0-1, 0-2, 0-3, and 0-4 for environmental arrays in the form of sandy loam, loam, clay and sand respectively is assigned to these models.
It is analyses the stress-strain state of working trench mounting with the help of "slurry wall" without additional fasteners.
The software package SCAD Office 11.5 was used to calculate the construction of stress-strain state.The scheme of the distribution of normal stresses along the Z-axis, available in wall and it is visible section of their maximum values, and these values are extreme at 10 m from the top "slurry wall" are given on Fig. 3. Data retrieved of tensile stresses in concrete allow picking up reinforcement for the given construction.By means of results it is revealed the trouble spots which need the additional fixing and gains for introduction into service.The maximum expanding and compression stresses which arose in construction when using the environmental array in the form of sandy loam, loam, clay and sand are defined.These data allow calculating fixing construction reinforcements.
In the analysis of horizontal relocation it was revealed that the maximum relocation of "slurry wall", are watched at the level of top of a retaining wall.All these data are provided in table 2. During the study the calculation of the finiteelement models mount slopes of the working trench with using a special method "slurry wall" without any additional mounting was conducted.The resulting diagrams clearly reflect the processes in the surrounding array and the "slurry wall" [10,14].
Considering the data provided in Table 2 it is possible to draw a conclusion that "slurry wall" has the considerable margin of safety, but this system doesn't satisfy a boundary condition of horizontal relocation of the wall top in case of model with loam makes the maximum value of 24,10 cm.So it is necessary to enter additional systems of fixing in the form of executions of the same kind at the level of 1, 5 m from wall top.It will allow compensating relocation, arisen in system without additional fixing [10].
It is analysis of the stress-strain state of working trench mounting with "slurry wall" with additional support in the form of the one row of strut rails.
In models that have been developed and calculated using the finite element method with the introduction of a number of strut rail clearly displayed behavior change "slurry wall".These changes consist in reducing the horizontal movement of the wall with the array of local and extra stress at the site of attachment to the strut rail fence [12,15].
The diagram (Fig. 4) shows movement isofield of fastening systems along the X-axis of the global maximum values of displacement and stress: for walls -at the bottom of the working trench and third of the height of the wall from the bottom of the working trench, respectively; and contiguity strut rail at the "slurry wall".The results are summarized in Table 3.The largest equivalent stress and horizontal displacement observed in the variant with the surrounding array, which is presented in a sandy loam and smallest values of these parameters are observed in the array, in the form of sand.By means of results it is revealed trouble spots which need additionally fixing and gains for introduction into service.The maximum expanding and compression stresses which arose in construction when using an environmental array in the form of sandy loam, loam, clay and sand are defined.These data allow calculating the fixing construction of reinforcements.
It can be concluded that the introduction of additional spacer model led to reduction of stress in concrete construction "slurry wall" and reduce the horizontal displacement at the top of the working trench.However, at the bottom of the pit horizontal displacement values increased significantly as a result of "slurry wall" "rotation" around the strut rail.In this case it is advisable to introduce an additional row of strut rail vertically, to reduce the expression of this phenomenon.
It is analysis of the stress-strain state of working trench mounting with "slurry wall" with additional support in the form of two rows of strut rails.
In the above models for analysis and comparison have been introduced additional second tier of strut rails.This event allowed significantly reduces the horizontal displacement system mounting and reduce its domestic efforts [14,16].The results of models calculation with the help of finite element method are shown in Table 4.These results show that the introduction of the additional second row of strut rails allowed reducing the horizontal displacements up to 25% compared to the variants of working trench mounting slopes with using the optional mounting as one row of strut rail.However, there were local extreme tensions at the site of attachment of the second strut rail row.Following to this, efforts for strengthening the places of strut rail attaching point enter the additional reinforcement.

Conclusions
By results of these conducted researches the analysis of change of the intense deformed status of construction of slopes fixing is made.The solution of these tasks was shown that it didn't lead to introduction of one vertical row of strut rails to significant improvement of indexes and led to the origin of additional tension and extreme relocation at the level of excavation bottom.It shows that with big depths of working trenches it is necessary to enter additional vertical rows of strut rails in the course of carrying out the soil development for shallow subways' stations and other underground engineering constructions [1].
According to the movements it is built the dependency diagrams of elastic modulus and horizontal displacements wall-soil system for each case of working trench fixing.The diagrams are built for extreme values of displacements at the excavation bottom (except option without additional fasteners) and shown in Fig. 5.The data of relocation for a graphics of fixing option of the working trench without strut rails are used for the level of working trench top [16].
This diagram shows efficiency of additional fixing introduction of two vertical rows of strut rails and the changing of deformations value with change of elastic modulus of an environmental array.
The graphs of functions are represented as power function and performance with reliability approximation equal to about 1, which is confirming the existence of power dependence of the elasticity modulus and movement in the system [9].
According to the given results of calculations it is possible to make the following conclusions.
The method of introducing of the additional rows of strut rails in the fastening construction has been achieved the reduction of the horizontal displacement at the excavation bottom.And to reduce the value of the main stress concrete construction "slurry wall", which is allowing arguing about the effectiveness of using this method in any geological conditions, presented by soils with unstable grounds [7].

Fig. 1 .Fig. 2 .
Fig. 1.The finite element model with additional fastening "slurry wall" by means of: a -one row of strut rail; b -two rows of strut rail

Fig. 3 .
Fig. 3.The scheme of the voltages in the "slurry wall" without the additional fastening.

Fig. 4 .
Fig. 4. The scheme of movements along the global X-axisAccording to the attained results it is shown that the design has significant reserves of strength for the first group of limiting states.However, it does not satisfy the condition of horizontal displacement (second boundary condition) in different types of soils.The largest equivalent stress and horizontal displacement observed in the variant with the surrounding array, which is presented in a sandy loam and smallest values of these parameters are observed in the array, in the form of sand.

Fig. 5 .
Fig. 5.The dependence graph of the horizontal displacements of the array from the elasticity modulus