International Journal of Civil Engineering and Technology (IJCIET) Volume 10, Issue 04, April 2019, pp. 341-350, Article ID: IJCIET_10_04_036 Available online at http://www.iaeme.com/ijciet/issues.asp?JType=IJCIET&VType=10&IType=04 ISSN Print: 0976-6308 and ISSN Online: 0976-6316 © IAEME Publication Scopus Indexed ENGINEERING-GEOLOGICAL ZONING OF THE ROUTE OF TECHNOLOGICAL TUNNEL DESIGNED UNDER COMPLEX STRUCTURAL AND TECTONIC CONDITIONS Lange Ivan Department of hydrogeology and engineering geology, St. Petersburg Mining University, 2, 21st Line, Vasilyevsky Island, 199106, Russia Lebedeva Yana Department of hydrogeology and engineering geology, St. Petersburg Mining University, 2, 21st Line, Vasilyevsky Island, 199106, Russia, ABSTRACT The paper deals with the route of the designed tunnel and its main technical characteristics. The paper presents specific features of engineering-geological conditions of the territory of its location, as well as the analysis of the impact of structural and tectonic conditions on the state and properties of rocks, enclosing the tunnel structure. Forecast of the risk of inrush formation while performing mining workings, based on calculations of the enclosing rocks stability, have been made. Taking into account the degree of fracturing, rock inrush formation and water inflows value, a scheme of engineering-geological zoning of the designed tunnel route has been developed. Keywords: tunnel, structural and tectonic conditions, flysch formation, fracturing, inrush formation, stability of rocks, engineering-geological zoning. Cite this Article: Lange Ivan and Lebedeva Yana, Engineering-Geological Zoning of the Route of Technological Tunnel Designed Under Complex Structural and Tectonic Conditions, International Journal of Civil Engineering and Technology, 10(04), 2019, pp. 341-350 http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=10&IType=04 I. INTRODUCTION Currently, the operation of oil industry enterprises is represented by a consistent implementation of the production cycle stages, from the development of fields and oil production to petroleum products sales to the end consumer. The inescapable link in this cycle http://www.iaeme.com/IJCIET/index.asp 341 editor@iaeme.com Lange Ivan and Lebedeva Yana is the transportation of petroleum refinery products, which is the most frequently carried out using the main pipeline systems [4-8, 25, 26]. In connection therewith, for the delivery of exported petroleum products, by one of oil processing plants, the construction of main product pipelines, located in the technological tunnel of total length greater than 4.0 km, was designed. The territory of the tunnel route is located in the southern part of Russia and is confined to a large geological structure - the Semigorskaya anticline, the structure of which comprises flysch deposits of Cretaceous period - interbedding of marls, sandstones and limestones, rarely, mudstones, crumpled into isoclinal folds. One of the reasons for the intensive folding of rocks is the high seismic activity of the territory under consideration (intensity 8 on the MSK-64 scale), with about 16 tectonic disturbances, intersecting its profile - from normal faults to reverse-thrust faults. Thus, the complex structural and tectonic conditions predetermined the formation of the enclosing rocks fracturing [17, 18, 19]. 2. RESEARCH METHODOLOGY The analysis of the results of geological survey performed in respect to the designed tunnel route witnesses in favor of a high heterogeneity of the flysch strata depending on the position, in sectional view, of discontinuous faults (fig.1). Figure 1 – Section of the designed tunnel route. The revealed heterogeneity consisted in the difference in the degree of fracturing of the enclosing rocks. Quantitative assessment of the disintegration of rocks was performed by the rock quality designation (RQD) and the fracture index Mj. According to regulatory documents, the RQD parameter is defined as the ratio of the total length of the intact core samples of more than 10 cm in length, to the length of the drilled interval in the well. At the same time, the fracture index describes the number of cracks per 1 meter of the measurement line perpendicular to the main fracture system or systems. According to the numerical values of these parameters, rocks are divided into five groups by the degree of fracturing – from very weakly fractured (Mj <1.5; RQD 90 ÷ 100%) to very highly fractured (Mj > 1.5; RQD 0 ÷ 25%) [2,3]. According to this classification, a comparative assessment of the degree of fracturing of the enclosing rocks both within and outside zones of tectonic disturbances have been conducted by the staff members of the Department of hydrogeology and engineering geology of Saint Petersburg Mining University. The results of the assessment performed are given in table 1. http://www.iaeme.com/IJCIET/index.asp 342 editor@iaeme.com Engineering-Geological Zoning of the Route of Technological Tunnel Designed Under Complex Structural and Tectonic Conditions Table 1. Characteristics of the degree of fracturing of flysch rocks within and outside zones of tectonic disturbances (referring to the above-mentioned section of the tunnel route). Age K2an K2nt2 K2nt1 K2kr K2an K2nt2 K2nt1 K2kr The total The total length of number of The drilled Core RQD, Fracture index interval recovery, the intact cracks per Rock family % Mj length, m m core interval, samples, m pcs. Within zones of tectonic disturbances Flysch interbedding 2.2 2.0 0.5 22.5 38 19.0 of marls and sandstones Flysch interbedding of marls, 4.5 4.5 0.6 13.3 20 4.4 sandstones, limestones and mudstones Flysch interbedding 26.5 26.1 3.1 11.6 385 14.8 of marls and sandstones Flysch interbedding 9.0 9.0 1.3 14.1 157 17.4 of marls and sandstones Flysch interbedding of marls, 9.0 9.0 0.7 7.9 240 26.7 sandstones and mudstones Outside zones of tectonic disturbances Flysch interbedding 72.0 72.0 60.9 84.7 375 5.2 of marls and sandstones Flysch 274.5 274.3 221.2 80.6 1243 4.5 interbedding of marls, sandstones, 177.0 177.0 137.8 77.9 1108 6.2 limestones and mudstones Flysch interbedding 149.0 149.0 119.2 80.0 921 6.2 of marls and sandstones Flysch interbedding of marls, 63.0 63.0 48.0 76.2 517 8.2 sandstones and mudstones Degree of fracturing* Very highly fractured Very highly fractured Very highly fractured Very highly fractured Very highly fractured Weakly fractured Weakly fractured Weakly fractured Weakly fractured Weakly fractured Note: When assessing the degree of fracturing, the RQD parameter was taken as the basis. Table 1 shows, that in terms of the core quality, by RQD parameter, the enclosing rocks within zones of tectonic disturbances were characterized as very highly fractured, and outside http://www.iaeme.com/IJCIET/index.asp 343 editor@iaeme.com Lange Ivan and Lebedeva Yana the said zones as weakly fractured. Fracture systems, characterized by a northwest and northeast strike, are associated with regional faults and complicated by smaller fractures of different directions [10-13, 22-28]. Intensive and multidirectional disintegration of the enclosing rocks caused the formation therein of a free aquifer of Upper Cretaceous deposits, the level of which is above the design reference marks of the tunnel and varies from 1.0 m to 76.0 m. To assess the impact of groundwater on the construction works performance, calculations of possible water inflow into the designed tunnel [9, 14-16, 20, 21] have been made. On the basis of the hydrodynamic scheme, chosen by the production company, the staff members of the Department of hydrogeology and engineering geology of Saint Petersburg Mining University made calculations using the formula [3,4]: Q k hS , Ф Where k is the filtration coefficient of rocks, m/day; h is the average depth of the filtration flow, m; S is the water level above the tunnel line, m; Ф is the coefficient, calculated by the formula: Ф 2h S 1 l rd 1 y1 rd ln 2 y1 rh , Where l is the calculated tunnel route length, m; rd is the cone of depression radius of effect, m; rh is the tunnel radius, m; y1 is the aquifer thickness in the calculated interval, m; The calculation results showed, that within the selected section of the route (see Fig.1), the value of water inflow into the tunnel varies from 163.8 to 228.4 m3/day (Table 2). Table 2. Water inflow values within the selected section of the tunnel route (within and outside zones of tectonic disturbances). Age K2an K2nt2 Water inflow to the Average Water level 100th interval, Depression depth of the above the Rock family Ф coefficient m3/day radius rd, m filtration tunnel line flow h, m S, m Within zones of tectonic disturbances Flysch interbedding 956.5 103.1 73.8 10.2 223.1 of marls and sandstones Flysch interbedding of marls, sandstones, 975.4 100.1 75.8 10.3 219.9 limestones and mudstones http://www.iaeme.com/IJCIET/index.asp 344 editor@iaeme.com Engineering-Geological Zoning of the Route of Technological Tunnel Designed Under Complex Structural and Tectonic Conditions K2nt1 K2kr Flysch interbedding of marls and sandstones Flysch interbedding of marls and sandstones Flysch interbedding of marls, sandstones and mudstones 871.8 95.1 69.8 9.3 214.3 1003.3 108.1 75.8 10.7 228.4 Outside zones of tectonic disturbances K2an K2nt2 K2nt1 K2kr K2kr Flysch interbedding of marls and sandstones Flysch interbedding of marls, sandstones, limestones and mudstones Flysch interbedding of marls and sandstones Flysch interbedding of marls, sandstones and mudstones 786.5 114.1 71.8 8.7 187.5 767.8 111.6 70.8 8.5 185.5 762.5 109.6 70.8 8.4 184.1 683.9 85.1 69.8 7.2 163.8 680.8 78.1 59.8 7.2 194.0 According to the data of table 2, the largest values of water inflow were obtained for rocks within zones of tectonic disturbances, wherein the values of water inflow outside the said zones are lower. The presence of highly fractured, water-flooded rocks, confined to zones of tectonic disturbances, cast doubt on their stability when driving the designed tunnel. It is highly likely that, during construction in the specified zones, rock inrush formation may occur. To forecast this process development, calculations were made using the formula by N.S. Bulychev [1]: 𝑆=𝑓∙ 𝐾𝑀 ∙ 𝐾𝑅 ∙ 𝐾𝑊 , 𝐾𝑁 ∙ 𝐾𝑡 ∙ 𝐾𝐴 ∙ 𝐾𝛼 where 𝑆 is the empirical parameter of stability; 𝑓 is the rock-hardness ratio according to M.M. Protodiakonov; 𝐾𝑀 and 𝐾𝑁 are the coefficients accounting for the impact by the degree of fracturing of rocks and the number of fracture systems, respectively; 𝐾𝑅 is the coefficient, http://www.iaeme.com/IJCIET/index.asp 345 editor@iaeme.com Lange Ivan and Lebedeva Yana depending on the relief of walls; 𝐾𝑊 is the coefficient, depending on the hydration of rocks; 𝐾𝑡 is the coefficient, assessing the degree of unfilled cracks opening; 𝐾𝐴 and 𝐾𝛼 are the coefficients, depending on the nature of cracks filler and on the angle α between the axis of mines and the main direction of the crack, respectively. Depending on the parameter of stability S, the rocks are divided into five groups according to their susceptibility to inrush formation: I - completely stable (> 70); II - stable (5-70); III medium stability (1-5); IV - unstable (1-0.05); V - highly unstable (<0.05). The results of calculations for the resistance of rocks to inrush formation are given in Table 3. Table 3. The results of calculations for the resistance of rocks to inrush formation within the specified section of the route (within and outside zones of tectonic disturbances). Age Rock family Hardness coefficient f 𝑲 𝑴 𝑲𝑵 Coefficients 𝑲𝑹 𝑲𝑾 𝑲𝒕 𝑲𝑨 𝑲𝜶 Parameter S Class of stability Within zones of tectonic disturbances Flysch interbedding of K2an marls and sandstones Flysch interbedding of marls, K2nt2 sandstones, limestones and mudstones 4 0.5 6.0 0.5 0.8 1.0 1.0 1.0 0.13 Unstable 5.8 2.5 6.0 0.5 0.8 1.0 1.0 1.5 0.64 Unstable Flysch interbedding of K2nt marls and sandstones 5.4 0.5 6.0 0.5 0.8 1.0 1.0 1.0 0.18 Unstable Flysch interbedding of marls and sandstones 3.0 0.5 6.0 0.5 0.8 1.0 1.0 1.5 0.07 Unstable Flysch interbedding of marls, sandstones, limestones and mudstones 3.0 0.5 6.0 0.5 0.8 1.0 1.0 2.0 0.05 Unstable 1 K2kr Outside zones of tectonic disturbances Flysch interbedding of K2an marls and sandstones 4.0 4.5 6.0 0.5 0.8 1.0 1.0 1.0 1.2 Medium stability Flysch interbedding of 5.8 4.5 6.0 0.5 0.8 1.0 1.0 1.5 1.2 Medium stability K2nt2 http://www.iaeme.com/IJCIET/index.asp 346 editor@iaeme.com Engineering-Geological Zoning of the Route of Technological Tunnel Designed Under Complex Structural and Tectonic Conditions marls, sandstones, limestones and mudstones Flysch interbedding of K2kr marls and sandstones Flysch interbedding of K2kr marls, sandstones and mudstones K2nt1 5.4 3.0 6.0 0.5 0.8 1.0 1.0 1.0 1.0 Medium stability 3.0 3.0 6.0 0.5 0.8 1.0 1.0 1.0 0.6 Unstable 3.0 2.5 6.0 0.5 0.8 1.0 1.0 1.0 0.5 Unstable According to the data obtained, as shown in Table 3, within zones of tectonic disturbances, the S parameter varies from 0.05 to 0.64 (unstable rocks), outside zones of tectonic disturbances - from 0.5 (unstable) to 1.2 (medium stability). The presence of unstable rocks outside zones of tectonic faults can be generally explained by complex structural and tectonic conditions of the region, associated with high water encroachment by water of the Upper Cretaceous horizon. 3. RESULTS AND DISCUSSION The results of the assessment of flysch rocks fracturing, the values of possible water inflow, as well as the enclosing strata resistance to the inrush formation were used as the basic criteria for drafting a scheme of engineering-geological zoning of the tunnel route (Figure 2). The designed tunnel route zoning makes it possible to substantiate a safe method of tunneling and a technology of work performance [28]. In total, three zones along the tunnel route were selected by the presence of favorable conditions for the mining workings implementation (Table 4). Table 4. Basic criteria of engineering-geological zoning within the selected section of the route. Basic criteria * Number and name of Water inflow The presence of the engineeringDegree of the rocks value, m3/day tectonic geological zone fracturing disturbances I – Conditionally favorable No Weakly fractured Less than 200 II – Unfavorable Yes Weakly fractured III – Very unfavorable Yes Very highly fractured More than 200 Class of stability of rocks Medium stability Unstable Unstable Note: *In case of the difference in criteria within one zone, the class of stability of rocks was taken as the basis. http://www.iaeme.com/IJCIET/index.asp 347 editor@iaeme.com Lange Ivan and Lebedeva Yana Figure 2 - Scheme of engineering-geological zoning of the designed tunnel route (section). Engineering-geological zones: I – conditionally favorable; II – unfavorable; III – very unfavorable. It is worth noting, that according to the scheme of engineering-geological zoning, the main part of the selected section of the route is characterized as unfavorable and very unfavorable. Referring to the entire route of the designed tunnel, the total length of such zones exceeds 3.5 km (over 80% of the total length of the tunnel). 4. CONCLUSIONS The following conclusions can be made from the results obtained: When designing a tunnel under complex structural and tectonic conditions, it is necessary to take into account the seismicity of the territory under consideration and the specific features of its geological structure, determining the mode of occurrence of rocks, the presence of discontinuous faults, the nature of the enclosing strata disintegration. Prior to the designed tunnel construction implementation, a comprehensive engineeringgeological assessment of the state and properties of rocks should be performed. 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