LANDSLIDE HAZARD ESTIMATION IN THAKTHING VENG ROAD SECTION, AIZAWL, MIZORAM

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International Journal of Civil Engineering and Technology (IJCIET) Volume 9, Issue 4, April 2018, pp. 298 307, Article ID: IJCIET_09_04_033 Available online at http://www.iaeme.com/ijciet/issues.asp?

1 International Journal of Civil Engineering and Technology (IJCIET) Volume 9, Issue 4, April 2018, pp , Article ID: IJCIET_09_04_033 Available online at ISSN Print: and ISSN Online: IAEME Publication Scopus Indexed LANDSLIDE HAZARD ESTIMATION IN THAKTHING VENG ROAD SECTION, AIZAWL, MIZORAM Rahul Verma Department of Mining & Geological Engineering, BIUST John Blick Department of Geology, Mizoram University, Aizawl, Mizoram ABSTRACT Landslides that often occur along highways and inhabited areas, around Mizoram, create one of the most problematic situations faced in the region. One of the landslide prone zones Thakthing road section, lies in the southern parts of the state capital Aizawl. This section is situated along NH-54 Aizawl-Lunglei highway. For the present investigation, an attempt has been made in the area to understand the slope instability (SI) and Landslide Hazard Zonation (LHZ) based on Bureau of Indian Standards (BIS) (Part 2) :1998. Thematic layers for Landslide Hazard Evaluation Factors (LHEF) rating for different causative inherent and external parameters are lithology, structure, slope morphology, hydrological condition, land use/cover, rainfall and seismicity. Each factor is assigned a value called LHEF. Finally, Total Estimated Hazard (TEHD) has been calculated by adding the total LHEF score. Slope facet in an area can be categorized into five classes of relative hazard zones. According to the classification of TEHD, any section having TEHD > 8.00, falls under "Very High Hazard" Zone (VHH).Since, the TEHD calculated for the Thakthing section scores 8.30 and accordingly the section falls in Very High Hazard Zone. Landslide preventive measures immediately needed for the very section include-, filling and grouting of weaker zones, meshing in the most vulnerable patches, construction of retaining walls, evacuation of vulnerable buildings. Key words: LHEF; TEHD, LHZ, BIS, Meshing, Retaining Wall. Cite this Article: Rahul Verma and John Blick, Landslide Hazard Estimation In Thakthing Veng Road Section, Aizawl, Mizoram, International Journal of Civil Engineering and Technology, 9(4), 2018, pp editor@iaeme.com

2 Landslide Hazard Estimation In Thakthing Veng Road Section, Aizawl, Mizoram 1. INTRODUCTION Mizoram is a landlocked state in North East India whose southern part shares 722 kilometers long international borders with Myanmar and Bangladesh, and northern part shares domestic borders with Manipur, Assam and Tripura. It lies from 21 o 56 N to 24 o 31 N, and 92 o 16 E to 93 o 26 E. The tropic of cancer runs through the state nearly at its middle. In the northern part of the state, the capital of Mizoram Aizawl is located. The city is situated on a ridge, varying in height between 800 m to 1188 m above mean sea level. It can be easily approachable through NH-54 from Guwahati via Shillong and Silchar (Assam) and by air from Kolkata, Guwahati and Imphal. Geologically, Mizoram constitute a part of the Assam - Arakan geosynclinal basin (Nandy, 1972 [1], 1980[2] & 1982 [3]). The Mizoram Hills (Lushai Hills) are an integral part of the Indo- Myanmar mobile belt. Landslide are closely associated with the tectonically active Himalayan regions, and can be considered as the most common natural hazards which lead to damage in the road sector and residential areas in the hilly terrains ( Gurugnanam B et al., 2012[4]).Tectonic movements within this mobile belt are expressed in the rocks in form of faults and shear zones. The rocks of Aizawl represent the Surma Group. The lithology contains thickly bedded sandstones, shale, and mudstones of various Stratigraphic horizons (Tiwari and Kumar, 1996 [5]). The rock have a regional dip towards east in the northern area of Aizawl, and due west in the southern portion of the city. The entire region receives heavy from May to September and the average annual rainfall is 253 cm. The combined impact of lithology, structure, slope, relief, hydrological condition and external factors (seismicity and rainfall) in the state of Mizoram have caused severe damage due to landslide in the state. (Lallianthanga, R.K & Lalbiakmawia, F [6], Verma, R.2013 [7], Verma, R a [8] & b [9]; Rao, Ch.U.B. & Verma, R [10], John Blick & Verma, R [11]). The study section Thakthing Veng Road Section lies in the southern parts of Aizawl town and its exact coordinates are 23 42'47.36"N & 92 43'12.99"E.(left bottom boundary), 23 42'47.48"N 92 43'13.37"E (left top boundary), 23 42'44.91"N 92 43'11.26"E (right top boundary ) and 23 42'44.42"N 92 43'10.23"E (right bottom boundary), with an elevation of ft. It is situated on the Aizawl-Lunglei road (NH-54). Figure.1 shows the exact location on the sketch, Google Earth and Google map of the study section editor@iaeme.com

3 Rahul Verma and John Blick 2. MATERIAL AND METHOD For the present study area, Bureau of Indian Standards (BIS) (Part 2) :1998 [12] method is applied for the estimation of maximum LHEF rating for different causative factors for macrozonation viz. lithology, structure, slope morphology, relative relief, hydrological condition, land use/cover and external factors (seismicity and rainfall). A landslide hazard zonation (LHZ) map divides the land surface into zones of varying degrees of stability, based on the estimated significance of causative factors in inducing instability. Landslide Hazard Evaluation Factors (LHEF) rating scheme, which also follows an empirical approach, takes into consideration individual and net effect of all inherent causative factors responsible for slope instability (SI). This technique accounts for inherent causative factors (whose effect in inducing instability can be studied or assessed on slope) responsible for SI and accordingly rates them depending on their influence in inducing instability. Hazard probability of a facet usually depends on combined effect of all inherent parameters, which can vary from facet to facet. Anbalgan, et al., 2008 [13], have successfully worked on the LHEF for application in similar mountainous terrains 3. GEOLOGY AND STRUCTURE The geology of the area of Thakthing road section consists of sandy shales which are thinly bed and fractured, soft shale, silty shale, and an intercalation of siltstone and shale at the bottom (Plate. I- E). Lithology or rock type is an important factor in controlling slopes stability; it controls the nature of weathering and erosion for a rock slope (R Anbalagan et al., 2008 [13]). It can be observed that the rocks dip uniformly due southwest, varies from 32 o 39 o with an elevation of 3499 ft above mean sea level. At the base of the section, irregular and thinly bed of shales are present along the road. The E-W set of joints varies from 60 o 88 o and its opening differ from 3 15 mm. Persistence can be crudely quantified by observing the trace lengths of discontinuities on exposed surfaces. The persistence of joint sets control large scale sliding or down steeping failure of slope. The spacing of adjacent joints largely control the size of individual blocks of intact rock. It controls the mode of failure (Plate. I- A). A close spacing gives low mass cohesion and circular or even flow failure. It also influences the mass permeability. It is observed that most of the persistence of joints sets varies from 3 7 m (Plate. I- F). The shortest spacing between two joints measured 3m and the longest measured 9m. Based on International Society for Rock Mechanics (ISRM) classification of discontinuity persistence, it falls under Medium Persistence (3 10 m). Intersection of bedding planes and nearly sub vertical joint planes is a common feature of the very road section (Plate. I-E &F) and has imparted a blocky nature to the rock, mainly sandstones. Shale, being very fragile, has easily crumpled into tabs. Further, the dilation of asperities, has led to the wedge Formation (Plate. I- C). Similar feathers have been observed in the Kulikawn-Ngaizel road section (Verma, R a [8]). Landslide is closely associated with the geo-physical factors like lithology, slope, geological structure and relative relief. It is pertinent to note that landslide activity is mostly confined to the inhabited parts of the district. The intensification of human activities, encroachment on vulnerable land, uncontrolled settlement and rampant expansion of roads are the main causes of landslide within the district. A number of fractures and wedges are also present that run across a thinly bed of the intercalation of siltstone and shale that gradually result and happen in a conditions for sliding of rock blocks along existing joints at slope or excavation opening are governed by the shear zones (Plate. I-G & H) developed on the sliding rock discontinuities. Figure.2 shows the geological map of the Thakthing Road section editor@iaeme.com

4 Landslide Hazard Estimation In Thakthing Veng Road Section, Aizawl, Mizoram

5 Rahul Verma and John Blick 4. SLOPE MORPHOLOGY Slope morphology or surface topography greatly affects the stability of slopes with regard to both surficial erosion and mass wasting. Topographic parameters normally considered in estimating soil erosion losses and calculating short-term mass stability includes inclination and length of slope. The Thakthing section of the slopes can be genetically categorizes into secondary slopes formed by processes tending to decrease relief. Secondary slopes evolve from the erosion and modification of primary slopes (formed by processes that tend to promote relief). The topography follows the dip direction which is toward southwest. Near the crown portion of the slide, the topographic slope is greater than that of the dip of the bed. The slope along the edge of the crown measures about 62 o or more but the bed rock angle dips lesser which measures mostly 32 o 39 o. The slopes of the upper parts of the section measure under very steep slope (46 o 65 o ) and the lower parts dip mostly 34 o 47 o. Figure.3 represents the slope morphology of the study area. 5. HYDROLOGICAL CONDITION The generation of surface run-off is a critical triggering mechanism for debris flows. This runoff occurs both on saturated and unsaturated soil conditions and provides water to debris material that have accumulated in channels, thus increasing the pore pressure within the debris mass which initiates the debris flow. In such circumstances, the maximum fluid pressure that can be generated in the debris mass is controlled by the infiltration capacity of the soil and the geometry of the slope (gradient, shape and roughness). Hydrological condition immediately editor@iaeme.com

6 Landslide Hazard Estimation In Thakthing Veng Road Section, Aizawl, Mizoram prior to the landslide of the Thakthing section is shown in Figure 4. Most of the top shale layer is under the condition of damp and dry. The lower parts of the intercalation of siltstone and shale beds are in almost dry and is also observed in a condition of dripping near the edge of the right flank. 6. LAND USE COVER Land use and land cover pattern is one of the important parameters governing slope stability. Vegetation has major role to resist slope movements, particularly for soil slopes. The study area of Thakthing section is densely populated, buildings are usually located by constructing local cut slopes and flat terraces with on vegetation or grass cover that enhances not only the action of weathering and erosion but also adds to the natural weight of the slope as surcharge due to weight of civil structures and hence to instability of the slopes. Few buildings are located at the top, which are in high risk zone. (Plate. I- B) editor@iaeme.com

7 Rahul Verma and John Blick

8 Landslide Hazard Estimation In Thakthing Veng Road Section, Aizawl, Mizoram 7. EISMICITY AND RAINFALL Triggering factors like seismicity and rainfall may initiate slope movements and are accordingly called as triggering factors. The study area falls under maximum intensity of seismicity Zone- V. Zone of high intensity of seismicity may result slope stability to instability with different phenomena. Similarly, the annual precipitation of the study area falls under high zone (253 cm). Debris flows, shallow slips and deep-seated rotational and translational slides are among the most common of landslide types triggered by rainfall as there are always chances of sudden pore water pressure built up in slopes following a heavy spell of rain and this may also induce slope instability. 8. RESULT AND DISCUSSION Based on Bureau of Indian Standards (BIS) (Part 2):1998 [12], each parameters has been assigned a numerical values for different weightage for all the themes. The Total Estimated Hazard (TEHD) is calculated by adding Landslide Hazard Evaluation Factor (LHEF) ratings obtained for individual inherent parameters and for external parameters (rainfall and seismicity). The internal parameters are (i) Lithology/Weathering/Soil type (ii) Structure (parallelism between slope and discontinuity, relation between dip of the discontinuity and slope, dip of discontinuity and depth of the soil cover). (iii) Slope (iv) Relative Relief (v) Land Use Cover/ Land Use pattern (vi) Hydrological conditions (dry, damp, wet or dripping and flowing ).The external parameters are Seismicity ( 0,02 for Zone II to 0.50 for Zone V) and Rainfall ( 0.02 for < 50 cm for > 150 cm).the maximum assigned values for external factors is Maximum ratings of LHEF for lithology/weathering condition/soil type, is 2. In case of totally weathered section, a corrected value of 4 is assigned. The lithology of the study area (shale, siltstone and intercalation of siltstone- shale) falls under Type- III (Fair) and has been assigned to a value of The LHEF ratings for structure can be categorized into three sub types viz. (a) Parallelism between slope and discontinuity, (b) relation between slope inclination and dip, (c) amount of dip of discontinuity (d) Depth of the over burden/soil cover. Rating for relationship of parallelism between slope and discontinuity (joints) falls under category IV i.e o (unfavorable) and has been assigned to a value of For relationship between slope inclination and dip, the area is in a very favorable condition ( 100 o ) and has been assigned a score of The amount of dip of discontinuity of the area is >80 o (very unfavorable) assigning to a value of maximum rating Hence the total LHEF for structure sums up to The slope of the study facet is 65 o and thus the assigned value for Slope is 2.0.Relative relief of the facet of the area is in moderate (50 100m) and has been assigned to For land use/cover, the study area is densely populated (highly urbanized) with inadequate drainage on the slopes and hence assigned a LHEF of The hydrological condition of the area is unfavorable; most of the shale layer is damp and has been assigned to The seismic zonation of the area falls in Zone-V (highly unfavorable condition) indicates maximum intensity of seismicity assigning maximum rating The annual precipitation of the study area falls under high zone (253 cm). Zone of high annual precipitation has been assigned to the maximum rating 0.50 as well. Hence the total assigned ratings for external factors seismicity and rainfall sum up to The Thakthing landslide is a case of slope instability (SI), resulted due to combined effect of individual inherent parameters and external parameters like excess rainfall, intersection of bedding and sub vertical joint planes leading to the formation of wedges. Most of the area is in damp condition which makes the soft sandy shale loosening and altering the slope stability. Heavy rainfall, has led to the distortion of massive rock faces by weathering activity, invariably causes widening of existing fractures and thus leading to failure. Due to improper drainage of editor@iaeme.com

Rahul Verma and John Blick surface water runoff and poor sewage system, water percolates immediately through the top sandy soil and the whole area become water bearing horizon in the rainy season,

9 Rahul Verma and John Blick surface water runoff and poor sewage system, water percolates immediately through the top sandy soil and the whole area become water bearing horizon in the rainy season, which leads to the loosening of the water bearing shale layer, as a result, the higher parts of the slope above the water bearing horizon (top soil) become less stable and subside and finally collapse under the influence of gravitational force. The heavy rainfall, has led to the distortion of siltstone - shale intercalation by weathering activity, invariably causes widening of existing fractures and thus leading to failure. Prominent lithology comprising of intercalation of shale and siltstone overlain and underlain by shale, presence of a set of vertical joints, slope morphology, fractures and shear, resulting into growth of blocks and wedges are the main triggering factors. 9. CONCLUSION AND RECOMMENDATION Total Estimate Hazard (TEHD) is calculated by adding Landslide Hazard Evaluation Factor (LHEF) ratings for individual inherent parameters and external parameters. The final TEHD value of instability is calculated facet wise by adding all assigning values of inherent and external parameters. LHZ map on meso-scale of the study area is prepared from corrected TEHD values of the facets. On the basis of range of TEHD values, all slopes facets in an area can be categorized into five classes of relative hazard zones. For the Thakthing section, the calculated value of TEHD stands 8.30 and accordingly the section falls in Very High Hazard Zone (Table.1) editor@iaeme.com

10 Landslide Hazard Estimation In Thakthing Veng Road Section, Aizawl, Mizoram Situation demands immediate preventive measures such as meshing, filling and grouting, treatment of the discontinuities, improvement in the drainage and sewage, people s awareness about landslide hazard and demolition of high risk building and evacuation of urban population settlements at the top. ACKNOWLEDGEMENTS The authors extend their heartfelt thanks to the Department of Science & Technology, for providing financial assistance in form of major research project on landslide studies. The authors are also thankful to the Principal, Pachhunga University College and the Vice Chancellor of Botswana International University, for providing infrastructure and laboratory facilities. REFERENCES [1] Nandy, D.R., 1972: Style of Folding in the Mio Pliocene of Tripura and Mizoram area and possible rock of Basement Dislocation Fabrics. Misc. Publ. G.S.I., 31, pp [2] Nandy, D.R., 1980: Tectonic Pattern in N-E. India., Ind. Journal. Earth Sci. 7(I), pp [3] Nandy, D.R., 1982: Geological Set Up of The Eastern Himalayas and the Patkai - Naga - Arakan - Yoma (India - Myanmar) Hill Ranges in relation to the Indian Plate movement. MSC. Publ. G.S.I., 41, pp [4] Gurugnanam.B., and M. Arunkumar 2012: Assessment Of Influenciable Land use / Land cover For Landslides Study - A Remote Sensing And GIS Approach, International Journal of Remote Sensing & Geoscience (IJRSG), Volume 3, Issue 1, Jan. 2014,pp [5] Tiwari, R.P., and Kumar, S., 1996: Geology of the Area around Bawngkawn, Aizawl Dist. Mizoram, India: in the Geological Assoc. and Research Centre, Misc. Publ. No. 3, pp [6] Lallianthanga, R.K & Lalbiakmawia, F. 2013: MIRSAC, Aizawl, Mizoram, Landslide Hazard Zonation of Aizawl district, Mizoram, India using Remote sensing and GIS techniques. Publ. IJRSG, Vol 2, [7] Verma Rahul, 2014 (a): Ngaizel Landslide, Aizawl, Mizoram, India: A Case of Wedge Failure. Publ. AARJMD, Vol. 1, June, 2014, ISSN: [8] Verma, R (b): Landslide Hazard in Mizoram: Case Study of Laipuitlang Landslide, Aizawl. International Journal of Science and Research (IJSR), ISSN (Online): , Impact Factor (2012): 3.358; June [9] Ch.Udaya Bhaskara Rao and Verma, R. (2017). Micro-Zonation of Landslide Hazards Between Aizawl City and Lengpui Airport, Mizoram, India, Using Geoinformatics, International Journal of Basic & Applied Sciences IJBAS-IJENS Vol:17 No:05, Oct.2017 pp 7-17, ISSN: (Online), Indexed in Scopus. [10] John Blick and Verma, R. 2018: Classification of Tlangnuam Landslide, Aizawl, Mizoram in Asian Academic Research Journal, Feb pp ISSN X. [11] BIS, 14996, 1998: Preparation of Landslide Hazard Zonation Maps in Mountainous Terrains: Guidelines, Part.II, Macro Zonation (BIS, New Delhi). [12] Anbalgan, R, Chakraborty, D. & Kohli, A., 2008: Landslide Hazard Zonation (LHZ) Mapping on Meso-Scale for Systematic Town Planning In Mountainous Terrain. Publ. JSIR, Vol. 67, 2008, pp [13] Verma, R. 2013: Landslide hazard in Aizawl Township, Mizoram" in Edited Vol. Landslides and Environmental Degradation in Hilly Terrains. Editor. R.A.Singh, ISBN. No Gyanodaya Pub, Nanital, Uttarakhand, pp editor@iaeme.com

Landslide hazard zonation (LHZ) mapping on meso-scale for systematic town planning in mountainous terrain

Journal of Scientific & Industrial Research 486 Vol. 67, July 2008, pp. 486-497 J SCI IND RES VOL 67 JULY 2008 Landslide hazard zonation (LHZ mapping on meso-scale for systematic town planning in mountainous