Bull 207 Thanh et al. Bull. Iraq nat. Hist. Mus. December, (2018) 15 (2): 207-223 ROCK SLOPE FAILURE BLOCKS AND THEIR RELATION TO TECTONIC ACTIVITY: A CASE STUDY IN 3B HIGHWAY, XUATHOA AREA, BACKAN PROVINCE, VIETNAM Phi Truong Thanh * Phi Hong Thinh ** and Nguyen Viet Ha *** * Hanoi University of Natural Resources and Environment, Hanoi, Vietnam ** University of Transport and Communications, Hanoi, Viet Nam *** Hanoi University of Mining and Geology, Hanoi, Viet Nam *Corresponding author: thanhgislab@gmail.com Received Date: 22 October 2018 Accepted Date: 24 December 2018 ABSTRACT This paper presents the results of the slope failure analyses from fracture distributions and their relation to tectonic activity; the analytical results have indicated that the phenomena of plane failure, wedge failure and toppling failure can occur at almost of the survey sites within the study area. The statistical data show that the fracture orientation mainly develop in the E-W, N-S and NW-SE due to the influence of tectonic activity. The occurrence of them together with the rock slope surface orientation has formed plane failure on the slope surface of the 3B highway in the E-W direction and the types of wedge failure and toppling failure on the slope surface of the highway in the N-S and NW-SE direction. Keywords: Fracture, Plane failure, Toppling failure, Wedge failure, 3B highway. INTRODUCTION The slope failure occurs quite commonly along roads in the mountainous provinces of Vietnam; their occurrence is not only affects economic activities but also threatens the lives of people, impact negatively on the environment. The cause of the slope failure is mainly due to the imbalance of rock mass on the slope surface along with the occurrence of storms and underground water (Do and Nguyen, 2013). At present, the slope failure along the road is one of the most important problems that the localities in the mountainous provinces of Vietnam are facing; the slope failure researches in Vietnam have been conducted since the early 2000s. However, they are almost project; there are very few papers published at this time. After that, most studies were conducted on the basis of processing satellite image, terrain, geomorphology, etc. to build the zoning map and forecast risk of landslide (Truong et al., 2011; Nguyen et al., 2012; Tran et al., 2013; Bui et al., 2016; Nguyen, 2016). From the other hand, the above studies do not take into account the relationship between landslide and fracture, caused by tectonic activity in the Earth’s crust, while the other studies on the relationship between fractures and failure have also considered by Wittke (1965), Muller (1968), Markland (1972), Hocking (1976), Haines and Terbrugge (1991). Some studies specifically addressed the landslide related to the tectonic movement (Youd, 1978; Harp and Noble, 1993; Harp et al., 2003). Recently, the other authors of Vietnam have http://dx.doi.org/10.26842/binhm.7.2018.15.2.0207 208 Rock Slope Failure Blocks and their Relation developed the Block Theory of Goodman and Shi (1985) to analyze slope failure based on fracture orientation and slope surface direction (Nguyen and Phi, 2014). The aim of this paper is to analyse the results of the relationship between the formation of failure blocks on the slope surface and tectonic activity along the 3B highway in Xuathoa area, Backan province, Vietnam by using Hoek and Bray’s application (2004). MATERIALS AND METHODS Materials Data sources used are the fracture orientations, which selected from 33 survey sites on the slope surface along the 3B highway in Xuathoa area, Backan province, Vietnam. The collection data were measured randomly using compass at each survey site (Map1, Tab.1). Table (1): Location of the survey sites, number of fractures and rock slope surface orientation. No. Survey sites Longitude (Degree) Latitude (Degree) Slope surface orientation Fracture number Geological age 1. BK-01 105.879951 0 22.081889 0 140/70 73 D1ml1 2. BK-15 105.898139 0 22.093861 0 345/65 127 D2-3th 3. BK-17 105.899778 0 22.094222 0 250/75 103 D1-2nq2 4. BK-21 105.898444 0 22.097167 0 280/75 23 D2-3th 5. BK-26 105.898944 0 22.098833 0 320/75 116 D2-3th 6. BK-27 105.899944 0 22.099750 0 350/70 122 D2-3th 7. BK-28 105.901100 0 22.099820 0 356/75 96 D2-3th 8. BK-30 105.901944 0 22.099500 0 370/75 137 D2-3th 9. BK-34 105.905417 0 22.100694 0 370/75 96 D2-3th 10. BK-35 105.906417 0 22.101083 0 325/75 105 D2-3th 11. BK-41 105.913028 0 22.104194 0 350/75 188 D2-3th 12. BK-50 105.922694 0 22.104278 0 340/75 136 D2-3th 13. BK-52 105.924500 0 22.102583 0 90/75 113 D1-2nq2 14. BK-53 105.925222 0 22.101278 0 45/60 135 D1-2nq1 15. BK-57 105.929083 0 22.098167 0 15/75 71 D1ml2 16. BK-58 105.930028 0 22.098083 0 60/80 90 D1ml2 17. BK-59 105.930444 0 22.097250 0 80/80 79 D1ml2 18. BK-61 105.930500 0 22.095722 0 115/70 165 D1ml2 19. BK-62 105.930639 0 22.094944 0 10/75 76 D1ml2 20. BK-63 105.931833 0 22.094833 0 350/75 65 D1ml2 21. BK-66 105.933472 0 22.095083 0 30/75 104 D1ml2 22. BK-68 105.934306 0 22.093944 0 65/70 120 D1ml2 23. BK-69 105.935058 0 22.092972 0 60/70 103 D1ml2 24. BK-72 105.935472 0 22.092083 0 50/70 70 D1ml2 25. BK-74 105.937444 0 22.092250 0 25/70 119 D1ml2 26. BK-75 105.940556 0 22.091333 0 210/70 99 D1-2nq1 27. BK-76 105.942167 0 22.091028 0 210/70 128 D1-2nq1 28. BK-78 105.943917 0 22.090889 0 180/70 152 D1-2nq1 29. BK-79 105.944944 0 22.090917 0 210/70 155 D1-2nq1 30. BK-80 105.945583 0 22.091242 0 260/75 158 D1-2nq1 31. BK-81 105.946000 0 22.089056 0 230/70 172 D1ml2 32. BK-82 105.947000 0 22.088500 0 145/75 215 D1ml2 33. BK-83 105.947806 0 22.087750 0 190/75 102 D1ml2 209 Thanh et al. Map (1): Geological map, minimized from scale 1: 200.000 and survey locations. (Followed by Nguyen et al. (2000)) Where: D2-3th: Tam Hoa formation: polymictic conglomerate, gritstone, lay shale and limestone bearing; D1ml2: Mia Le Formation: clayish siltstone, marlaceous shale; D1-2nq1: Na Quan formation: marlaceous shale; D1-2nq2: Na Quan formation: Shale interbedded with gram. Method of slope failure analysis The analyses of plane failure, wedge failure, toppling failure and circular failure were carried out by Hoek and Bray’s application (2004), based on the fracture orientation; the analytical results will indicate the types of plane failure, wedge failure, toppling failure and circular failure on the rock slope surface as shown in the figures below. 210 Rock Slope Failure Blocks and their Relation Plate (1): (A) plane failure, (B) wedge failure, (C) circular failure, (D) toppling failure ( Followed by Hoek and Bray (2004)). Diagram (2): (A) Plane failure, (B) wedge failure and (C) toppling failure (Followed by Hoek and Bray (2004)). RESULTS AND DISCUSSION Results The slope failure analysis and their relation to tectonic activity were conducted according to Hoek and Bray’s application (2004) at 33 survey sites with 3813 fracture orientations along the 3B highway in Xuathoa area, Backan province, Vietnam (Map. 1). The slope failure analysis at each survey site was conducted with the input parameters as the fracture orientation measurement, slope surface orientation and friction angle. In this case, the friction angle for the marlaceous shale is determined to be 25 0 ; the analytical results indicated that almost survey sites can occur plane failure, wedge failure and toppling failure, such as the survey site BK-82 (Diag. 2). In this status, the number of fractures that can occur plane failure is 32, wedge failure is 45 and toppling failure is 21. 211 Thanh et al. Diagram (3): The analytical results according to Hoek and Bray’s application (2004) at the survey site BK-82; (A) Plane failure, (B) Wedge failure, (C) Toppling failure. Similarly, the analysis is also considered for total other survey sites along the 3B highway in Xuathoa area, Backan province, Vietnam (Maps: 2-4 and Tabs: 2-4). Plane failure Table (2): The statistical results of the number and percentage of fractures at the survey sites can occur plane failure along the 3B highway in Xuathoa area, Backan province, Vietnam. No. Survey sites Number Percentage (%) No. Survey sites Number Percentage (%) 1 BK-01 8 10.96 18 BK-61 7 4.24 2 BK-15 35 27.56 19 BK-62 23 30.26 3 BK-17 18 17.48 20 BK-63 14 21.54 4 BK-21 5 21.74 21 BK-66 34 32.69 5 BK-26 7 6.03 22 BK-68 29 24.17 6 BK-27 43 35.25 23 BK-69 21 20.39 7 BK-28 18 18.75 24 BK-72 32 45.71 8 BK-30 57 41.61 25 BK-74 18 15.13 9 BK-34 18 18.75 26 BK-75 19 19.19 10 BK-35 25 23.81 27 BK-76 14 10.94 11 BK-41 69 36.70 28 BK-78 45 29.61 12 BK-50 45 33.09 29 BK-79 13 8.39 13 BK-52 29 25.66 30 BK-80 29 18.35 14 BK-53 19 14.07 31 BK-81 16 9.30 15 BK-57 13 18.31 32 BK-82 32 14.88 16 BK-58 24 26.67 33 BK-83 10 9.80 17 BK-59 33 41.77 212 Rock Slope Failure Blocks and their Relation Map (2): The survey sites can occur plane failure according to analyzing fracture orientations along the 3B highway in Xuathoa area, Backan province, Vietnam. Wedge failure Table (3): The statistical results of the number and percentage of fractures at the survey sites can occur wedge failure along the 3B highway in Xuathoa area, Backan province, Vietnam. No. Survey sites Number Percentage (%) No. Survey sites Number Percentage (%) 1 BK-01 5 6.85 18 BK-61 51 30.91 2 BK-15 9 7.09 19 BK-62 0 0.00 3 BK-17 4 3.88 20 BK-63 35 53.85 4 BK-21 6 26.09 21 BK-66 40 38.46 5 BK-26 7 6.03 22 BK-68 50 41.67 6 BK-27 24 19.67 23 BK-69 9 8.74 7 BK-28 10 10.42 24 BK-72 28 40.00 8 BK-30 19 13.87 25 BK-74 16 13.45 9 BK-34 6 6.25 26 BK-75 39 39.39 10 BK-35 20 19.05 27 BK-76 39 30.47 11 BK-41 52 27.66 28 BK-78 24 15.79 12 BK-50 8 5.88 29 BK-79 29 18.71 13 BK-52 56 49.56 30 BK-80 58 36.71 14 BK-53 55 40.74 31 BK-81 27 15.70 213 Thanh et al. 15 BK-57 44 61.97 32 BK-82 45 20.93 16 BK-58 07 7.78 33 BK-83 20 19.61 17 BK-59 14 17.72 Map (3): The survey sites can occur wedge failure according to analyzing fracture orientations along the 3B highway in Xuathoa area, Backan province, Vietnam. Toppling failure Table (4): The statistical results of the number and percentage of fractures at the survey sites can occur toppling failure along the 3B highway in Xuathoa area, Backan province, Vietnam. No. Survey sites Number Percentage (%) No. Survey sites Number Percentage (%) 1 BK-01 13 17.81 18 BK-61 7 4.24 2 BK-15 5 3.94 19 BK-62 6 7.89 3 BK-17 4 3.88 20 BK-63 3 4.62 4 BK-21 0 0.00 21 BK-66 0 0.00 5 BK-26 1 0.86 22 BK-68 10 8.33 6 BK-27 3 2.46 23 BK-69 6 5.83 7 BK-28 5 5.21 24 BK-72 2 2.86 8 BK-30 4 2.92 25 BK-74 4 3.36 9 BK-34 9 9.38 26 BK-75 10 10.10 10 BK-35 7 6.67 27 BK-76 12 9.38 214 Rock Slope Failure Blocks and their Relation 11 BK-41 2 1.06 28 BK-78 09 5.92 12 BK-50 10 7.35 29 BK-79 17 10.97 13 BK-52 1 0.88 30 BK-80 20 12.66 14 BK-53 7 5.19 31 BK-81 20 11.63 15 BK-57 1 1.41 32 BK-82 21 9.77 16 BK-58 7 7.78 33 BK-83 14 13.73 17 BK-59 5 6.33 Map (4): The survey sites can occur toppling failure according to fracture orientations along the 3B highway in Xuathoa area, Backan province, Vietnam. 215 Thanh et al. The analytical results of percentage of plane failure, wedge failure and toppling failure in the Tables 2 to 4 are plotted in Diagram (3). Diagram (3): The graph of fracture percentage can occur the plane failure, wedge failure and toppling failure at each survey site along the 3B highway in Xuathoa area, Backan province, Vietnam. The slope failure analysis is conducted based on the statistical percentage of fracture orientations which can occur the plane failure, wedge and toppling failure at each survey site along the 3B highway in Xuathoa area, Backan province, Vietnam. In Diagram (3), the fracture percentage lies within the region that can occur the plane failure varies slightly among the survey sites; the largest percentage value belongs to the survey sites: BK-27, BK- 30, BK-41, BK-59, BK-72 and BK-78. Similarly, the intersection percentage of the conjugate fractures lies within the region that can occur the wedge failure varies slightly from survey sites BK-01 to BK-50, from BK-72 to BK-83 and the largest change at the survey sites: BK-52, BK-53, BK-57, BK-63, BK-66, BK- 72, BK-75, BK-80; the fracture percentage lies within the region can occur the toppling failure varies slightly at total survey sites along the 3B highway in Xuathoa area, Backan province. The comparison results among the three types of failures in Diagram (3) indicate that the survey sites from BK-01 to BK-50 and from the survey sites BK-69 to BK-83, the fractures can occur plane failure and wedge failure together. However, the fracture percentage can occur the wedge failure is smaller than the fracture percentage that can occurs the plane failure, particularly for the survey sites from BK-78 to BK-83, the plane failure, wedge failure and toppling failure can occur together. Discussion The 3B highway belongs to Xuathoa area, Backan province, Vietnam cut through the ancient rock of the Devon system with the main component is marlaceous shale (Nguyen et al., 2000). These rocks were severely broken due to the tectonic activities of the Indian- Australian Plate move toward the north and the Pacific Plate move toward the west, forming the compressed and extended area (Phung et al., 1996). Some the other research results 216 Rock Slope Failure Blocks and their Relation suggested that the northeastern region of Vietnam, including the 3B highway in Xuathoa area, Backan province (Map 5) occurs two major phases of tectonic activity in the Cenozoic era (Nguyen, 1991; Phung et al., 1996). The early phase was determined as occurrence from Eocene to late Miocene period and late phase occurs during the Pliocene - Quaternary period (Vu, 2002). The first tectonic phase caused the left-lateral motion of the NW-SE fault system and the late phase caused the right-lateral motion of this fault system. The left-lateral motion of the Red River Fault System was the results of the India-Eurasia plate collision (Tapponnier et al.,1986) and it occurred during within 30 Ma to 5.5 Ma, corresponding to the Oligocene-Miocene period, from analytical results of the seismic data (Rangin et al., 1995). The another analytical result of seismic profiles in the north area of the Red River sedimentary basin also identified one phase of left-lateral motion that occurred about before 21 Ma within the Song Lo and Song Chay river fault zone, belong to the Red River Fault System (Nguyen, 2003). Besides, the study also indicated one different tectonic activity phase with the NE-SW compression direction, caused the inversion of NW-SE trending fault during 10.5 k.y - 5.5 k.y. In addition, the analyzing geological structure of Oligocene sedimentary rocks on Bach Long Vi island also determined three maximum compression phases: E-W, NE-SW and NW-SE during the Cenozoic era (Phung et al., 2007). Recently, the analyzing tributaries of the Red River Fault System from Quaternary alluvial fans, river valley on Landsat and SPOT satellite images, detailed topographical maps and field observation determined right-lateral offsets of stream channels range between 150 and 700m (Phan et al., 2012). This is the results of the stress state of N-S compression direction; E-W extension direction caused the right lateral strike-slip along the Red River Fault System and probably, began in the Pliocene time. The tectonic phase also was clearly visible on the Red River Fault System and the Dien Bien Phu fault from the analyses of Landsat and SPOT satellite images (Lacassin et al., 1994; Phan et al., 2012). The Phan et al. (2012) analyses also recognized that Cao Bang - Tien Yen (CB-TY) fault which is located in the NE of the Red River Fault System is right lateral strike-slip fault, results from the N-S compression direction using Landsat and SPOT satellite images, aerophotographs and 1:50.000 scale topographic maps. The relation to dextral strike-slip motion of the Red River Fault System in the episode of Pliocene-Quaternary also confirmed in study of Witold (2013). The result of tectonic-geomorphic studies indicated that the amount of Quaternary dextral offset of the Red River Fault System in Vietnam, calculated from offset and deflection of the tributary valleys of the Red River, ranges between 400m and 5.3km. The axis of maximum horizontal compression associated with dextral slip of the fault zone were aligned from NNW-SSE to N-S. Similarly, the Kasatkin et al. (2014)’s study indicated that predominantly sinistral strike slip of Red River Fault System formed as a result of ENE regional compression (80°) during the Oligocene-Miocene period and dextral strike slip of the Red River Fault System formed as a result of NNW regional compression 330-350° during the Pliocene-Quaternary. 217 Thanh et al. Map (5): Trajectories of the maximum compressive stress within the Indochina Peninsula during the Oligocene (a) and at the present time (b). The legend in the Map (5) is described as follows: (1) trajectories of the maximum compressive stress are directly related to the Indo-Eurasian plate collision (a) and its far-field effects (b); (2) faults and directions of displacement (arrows); (3) zone of continental collision; (4) subduction zone; (5) extension structures; (6) spreading zones; (7) current position of the land; Red River Fault System (RRFS); Cao Bang - Tien Yen fault (CB-TY) (Kasatkin et al., 2014). The failure blocks on rock slope surfaces are formed by the intersection of fractures, faults in different directions and rock slope surfaces. The fractures, faults are the result of tectonic activities in the earth’s crust. Initially, the rock blocks are formed by the intersection among fractures in steady status; after being excavated, they lose their equilibrium status and can slide on the rock slope surface, causing plane failure, wedge failure or toppling failure. The statistical data in the study area showed that the fracture orientations, which collected at survey sites developed in three main directions: E-W, NW-SE, N-S (Diag. 4). 218 Rock Slope Failure Blocks and their Relation Diagram (4): The contour graph and rose graph of 3813 fractures at 33 survey sites along 3B highway in Xuathoa, Backan province, Vietnam. The percentage value of fracture direction of the total survey sites is recorded in Table (5) and Diagram (5). Table (5): The percentage value of the fracture direction at the total survey sites along 3B highway in Xuathoa area, Backan province, Vietnam. No Orientation (Degree) Percentage (%) No Orientation (Degree) Percentage (%) 1 0-10 4.38 10 271-280 6.08 2 11-20 5.51 11 281-290 6.03 3 21-30 3.80 12 291-300 6.43 4 31-40 3.25 13 301-310 6.06 5 41-50 3.38 14 311-320 5.80 6 51-60 4.20 15 321-330 6.71 7 61-70 5.61 16 331-340 7.79 8 71-80 6.48 17 341-350 7.87 9 81-90 4.67 18 351-360 5.95 219 Thanh et al. Diagram (5): The graph of percentage value of the fracture direction of the total survey sites along 3B highway in Xuathoa area, Backan province, Vietnam. The intersection of the different fracture orientations and the slope surface along the 3B highway in Xuathoa area, Backan province, Vietnam have formed a series of blocks that can occur plane failure, wedge failure and toppling failure. In the direction of E-W, the survey sites BK-27, BK-30, BK-41, BK-59 và BK-72 clearly reflect that high plane failure potential may occur in the E-W orientation fracture system; in the direction of NW-SE, the survey sites BK-52, BK-53, BK-57, BK-63, BK-66, BK- 68, BK-72, BK-75, BK-80 clearly reflect that the high wedge failure potential can occur in the NW-SE orientation fracture system. The analytical results of this study also indicate the relationship between the fracture orientation, which formed due to the tectonic activity and the direction of the rock slope surface and the formation of the types of failure blocks. CONCLUSIONS By analyzing 3813 fracture orientations at 33 survey sites on the marlaceous shale belong Devon formation, along the 3B highway in Xuathoa area, Backan province, Vietnam, the analytical results have also indicated that the phenomena of plane failure, wedge failure and toppling failure can occur at almost survey sites within the study area. The statistical data also show that the fracture orientation mainly develop in the E-W, N-S and NW-SE due to the influence of tectonic activity; the occurrence of them together with the rock slope surface direction has formed the type of plane failure for the 3B highway in the E- W direction and the type of wedge failure and some toppling failure for the 3B highway in the N-S and NW-SE direction. The results of this study have important significance in planning the highway design and tunnel construction; because, this way will be excavating in the next time. ACKNOWLEDGEMENTS This research is supported by the project of “Research on the application of Block Theory to assess the risk of slope failure along the highway. Case study from km 0 to km 80 on the 3B highway”, Code: TNMT.2018.03.18 of Ministry of Natural Resources and Environment, within the time 2018-2020. 220 Rock Slope Failure Blocks and their Relation LITERATURE CITED Bui, T. V., Nguyen, S. H. and Nguyen, H. T. 2016. 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December, (2018) 15 (2): 209-223 دراسة للطريق السريع : المنحدر الصخري وعالقتها بالفعالية البنائية التكتونية فشل بلوكات منطقة كزاثوا ، مقاطعة باكان ، فيتنام 3ب ***و نكوين فيت ها** ، في هونغ ثن*في ترونغ ثان جامعة هانوي للمصادر الطبيعية والبيئة ، هانوي ، فيتنام* فيتنام جامعة االتصاالت والنقل ، هانوي ،** ولوجي والمناجم ، هانوي ، فيتنامجامعة هانوي للجي*** 24/12/8102: تاريخ القبول 22/01/8102: تاريخ االستالم الخالصة التكتوني؛ يعرض البحث نتائج تحاليل فشل الميل من توزيعات الكسر وعالقتها بالنشاط وقد أشارت النتائج التحليلية إلى أن ظواهر الفشل بالمستوى االفقي والعمودي واإلخفاق في 3للطريق السريع ب االنقالب يمكن أن تحدث في مواقع المسح تقريباً داخل منطقة الدراسة .منطقة كزاثوا ، مقاطعة باكان ، فيتنام غرب –الكسر يتطور بشكل أساسي باتجاه شرق تشير البيانات اإلحصائية إلى أن اتجاه .جنوب شرقي -جنوب و شمال غربي–و باتجاهات شمال تحدث ظواهر الفشل الثالثة بسبب تأثير النشاط التكتوني البنائي للقشرة االرضية مع اتجاه سطح االنحدار الصخري بتكوين مستوى ضعف وفشل على سطح المنحدر للطريع غرب، و بانواع فشل عمودية وتدية ومنقلبة على سطح –باتجاه شرق ب3السريع .جنوب شرقي -جنوب و شمال غربي–المنحني للطريق السريع باتجاهات شمال