International Journal of Civil Engineering and Technology (IJCIET) Volume 9, Issue 7, July 2018, pp. 20112027, Article ID: IJCIET_09_07_214 Available online at http://iaeme.com/Home/issue/IJCIET?Volume=9&Issue=7 ISSN Print: 0976-6308 and ISSN Online: 0976-6316
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INVESTIGATION OF THE MASS MOVEMENT IN VARANDHA REGION, WESTERN GHAT OF MAHARASHTRA USING GEOSPATIAL TECHNIQUE
Dattatraya J. Khamkar PhD Scholar, Civil and Environmental Engineering Department, VJTI, Mumbai-400019, Maharashtra, India
Sumedh Y. Mhaske Associate Professor, Civil and Environmental Engineering Department, VJTI, Mumbai-400019, Maharashtra, India
ABSTRACT Verandha Ghat Section is connecting shield-plateau region with Konkan Coastal Belt (KCB) through Bhor Ghat area. Therefore, it is considered as a lifeline of Bhor (in Pune district) and Mahad (Raigarh District of Konkan), of western Maharashtra corridor. Geologically, this region belongs to Ambenali and Mahabaleshwar – Poladpur formation. The area shows thick flows of the Deccan Trap basalt of Upper Cretaceous to Eocene age. All the rock flows of this formation, exposed along this highway are in the form of rock cutting along the Pandharpur-Mahad Maharashtra State Highway -70, in the 74 km Ghat section from Bhor (part of Sahyadri Uplands, from Pune district) onwards and before Mahad (part of Konkan Coastal Belt from Raigarh district) of Maharashtra, are highly susceptible for landslide activity. A detailed exploration was carried out on all along the road section started from Bhor city and it extends up to the Varandah village, at the foot hill of Sahyadri, in Konkan region. In the present context, detailed investigations of the mass movement were carried out to prepare the map of highly vulnerable locations, in the study area. The remedial measures are suggested to minimize the severity of landslide. Key words: Konkan, Landslide, Mass Movement, Sahyadri, Verandha, Western Ghat. Cite this Article: Dattatraya J. Khamkar and Sumedh Y. Mhaske, Investigation of the Mass Movement in Varandha Region, Western Ghat of Maharashtra Using Geospatial Technique. International Journal of Civil Engineering and Technology, 9(7), 2018, pp. 2011-2027. http://iaeme.com/Home/issue/IJCIET?Volume=9&Issue=7
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1. INTRODUCTION Mass movement is one of the most important processes which can cause enormous changes on the surface of the earth. It is a process, in which sudden downward movement of rock / or loose sediments lead to the formation of slopes. Such movements of slope forming material cause extensive damage to life and property, in which the communication networks such as Highway, Railway, Canals, Tunnels etc. will be generally affected. In most of the time, these processes become most active in the rainy season. They affect at least 15 percent part of India- an area which exceeds 0.49 million km2 (ndma.gov.in). These are the unpredictable natural phenomenon, which causes property and living loss of life. Generally, such process is defined as the probability of occurrence of landslides within a specific period of time and within a given area (Varnes, 1984). While, in according to Schidegger (1994), landslides are the probability, that reasonably stable condition may opaque abruptly. Afterward, Guzetti et al (1999) preferred the definition to include the area, volume and velocity of the expected landslides. The complete hazard assessment and mapping work should be based on where, when, and how large a landslide will occur. An increasing socio-economic interaction between the Konkan Coastal belt and Plateau region has resulted in an increase in the density the lines of communication, by traversing through the Ghat section, which is highly susceptible for mass movements, especially in rainy season. Such activities some at local and regional scale produce large-scale hazard along the ghat section roads. Resulting, highway traffic jam takes place. The term the Western Ghats geographically includes a chain of hill range which trending roughly North-South and run parallel to the west coastline of India. The Sahyadri escarpment is a steep, high-rise west facing, which varying elevation ranging from 500 to 1500m and having regional slopes of wells over 17° (Peshwa and Kale,1987). Rock falls and landslides are localized in those parts of the Ghats with slopes exceeding 35° and the part which directly comes base of the scarp is suffering from slope failure problems. Slope stability studies by various leading workers in this field, for example, Terzagi (1950), Morgenstem and Sangrey (1978) among numerous others indicate that the stability of any slope is primarily dependent upon the Slope angle; Physical properties of the material underlying the slope, e.g. shear strength (s); cohesive strength and the angle of int saturated samples yield weaker strength characteristics while the dry, unaltered samples are considerably stronger. According to Parthsarthi and Shah (1981), the compressive strength of Deccan Trap basalts recorded varying from 1000 and 2600 kg/sq.cm. Their observation again confirms that the saturated and/or weathered samples are considerably weaker. Simple estimates of slope stability would, therefore, suggest that the horizontally stratified, completely unaltered, compact basaltic flows of traps should sustain perfectly stable slopes with inclinations exceeding 30°. The slope failures noted in along the highway in the Ghat section invariably fall in the rock- fall rock-topple category in the classification of Varnes (1978). Therefore, it may be concluded that the slope failures observable in the Western Ghats are due to a combination of factors which are induced as a consequence of the mass-wasting of the trappean rocks. Ansari and et al. (2016) focused on risk consequence analysis for rock fall locations along SH-72of Maharashtra. Singh and et al. (2010) have done the static and dynamic analysis of a landslide of the Amiyan area, near Kathgo dam, Nainital, Uttarakhand. A comparative analysis has been carried out on the basis of factor of safety of slope. Savoikar and Choudhury [2010] considered the effects of cohesion and fill amplification on seismic stability of municipal solid waste landfills. Liquefaction of soil is generally occurs in loose cohesionless
http://iaeme.com/Home/journal/IJCIET 2012 [email protected] Dattatraya J. Khamkar and Sumedh Y. Mhaske saturated soil when pore water pressure increases suddenly due to induced ground motion and shear strength of soil decreases to zero and leading the structure situated above to undergo a large settlement , or failure. Mhaske and Choudhury [2010] have developed a methodology for preparation of soil liquefaction susceptibility map of the entire Mumbai city during earthquake using GIS.
2. STUDY AREA The study area is a part of Sahyadri Uplands, which is present between Konkan Coastal Belt bounded to the Arabian Sea in the West and shield - plateau region in the east. It is next to the Bhor, a southwestern boundary of Pune District. The proposed study area is located in Bhor region of Pune district of Maharashtra along SH-70. The area under investigation falls in the - economic interaction between the Konkan Coastal belt and Plateau region has resulted in increase in the density, the lines of communication, by traversing through the Ghat section, which is highly susceptible for mass movement especially in rainy season. Such activity some at local and regional scale produce large- scale hazard along the ghat section roads resulting, highway traffic jam takes place. Location Map of the study area is shown in Fig. 1.
Figure 1 Location Map of the study area
2.1. Geology and Geomorphology As stated above, the study area of Ghat section is a part of Deccan Volcanic Provinces (DVP) which formed in Upper Cretaceous to Lower Eocene period. Lithologically, these volcanic igneous rocks are massive (non-vesicular), some time presence of empty cavities (vesicular) / filled gas cavities with secondary minerals (Amygdales), and fine textured. The flows two types of characters, i.e. nonvesicular-compact basalt flows are thick, regular, and extensive and are shows plain tops and bottoms. While, the amygdaloidal basalt flows are thin, irregular, less extensive, chaotic flows and absence of plain tops and bottoms. These individual flows are separated by thin, bands of red / green tachylitic basalt. When they expose to the atmosphere, they rapidly give a response to the weathering action and converted into small fragments, resemble like baked soil and after some period, the baked soil starts to convert into the fine textured clay.
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At places, the rock shows different divisional planes, viz. columnar (vertical), sheet (horizontal) and irregular (both consistent and inconsistent) type. The block type of joint is comparatively less. These joints are open at the surface at the top portion. As the study area is a part high relief zone of Sahyadri Upland. Therefore, it shows a high rate of precipitation, comparative to the low relief areas of plateau region (Pune District Gazetteer). Therefore, during rain, water seeps through these joints and encircle the nucleus of the. Resulting, separate, isolated blocks are formed. During every rainy season, fine developed loose sediment was washing out and the gaps between two blocks were washing out. In this way, the gaps between two blocks were increased and such blocks become unsupported. In this way, they started to dislodge, in the form of mass movement activity in this area. This formation covers nearly 85% part of Maharashtra state and hence the continuous area of plateau having rocks of trap formation (Gupte, 2005). While the southward extension of the basalt traps origin can be traced a little beyond Maharashtra. Layers of such basalt rock have almost horizontal deposition except for some local deviation. They have a tendency to form flat-topped plateaus and therefore, these are referred to as plateau basalt. This structured base is subjected to denudation agencies producing a landscape that contains many small and big rivers.
2.2. Environment / Climate In general, the weather over the region during the whole year varies with the season. This is the most important factor influencing land use, cropping pattern, economic activity as well as distribution and density of human being. It also affects transportation network and the settlement pattern. Essentially, the climate of the study region is of a tropical monsoon type and it saw variations during the year. The north-south orientations of Sahyadris, as well as northeast orientation of Balaghat and Mahadeo ranges, determine the climatic conditions of the region. The proximity of the Sahyadri to the Arabian Sea restricts the coastal climate to a narrow strip on the west coast of Konkan that stands in sharp contrast to the continental climate over the entire region. Sahyadri runs across nearly at right angle to the monsoon streams forming an important climatic divide. Naturally, the windward slopes of Sahyadris and its crest gets sufficient rainfall while to the eastward of Ghat section, rainfall decreases rapidly over a short distance. The monsoon dominated climatic characteristics of the region has four seasons, which, over rest of India are the same one, these are, (I) The Cold Weather Period (December to February), (II) The Hot Weather Period (March to May), (III) South- West Monsoon Period (June to September) and (IV) Post-Monsoon Period (October to November). Annual percentage contribution of rainfall in each month and season at all stations is shown in Table 1. Annual rainfall trend at Akluj and Bhor station is shown in Fig.2. Seasonal rainfall trend at Bhor station is shown in Fig. 3. This study reveals significant changes in seasonal and annual rainfall in Nira river basin of Maharashtra, Central India during past 104 years. Significant increasing trends are detected in annual rainfall at 10% significance level for the Akluj and Bhor stations. Seasonal rainfalls in the basin have increased especially during the monsoon and post-monsoon seasons. The analysis shows that larger anthropogenic trends are embedded in the climate data in the baseline period. It is possible that climatic changes taking place after 1960 might have affected the rainfall pattern in the basin which needs further investigations (Murumkar and Singh, 2014). The analysis of rainfall data and findings shall be useful for irrigation and agricultural managers and may play an important role in managing water resources in the basin.
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Table 1 Annual percentage contribution of rainfall in each month and season at all stations (Source: Murumkar and Arya, 2014).
Month Akluj Baramati Bhor Malsiras Jan 0.45 0.70 0.12 0.82 Feb 0.65 0.16 0.05 0.18 Mar 1.88 0.36 0.22 0.47 Apr 3.94 1.11 1.17 1.64 May 13.60 5.05 2.69 3.80 Jun 13.46 16.78 15.59 17.52 Jul 13.44 10.79 1.29 12.85 Aug 11.84 10.84 22.03 11.50 Sep 16.78 30.09 12.40 27.43 Oct 9.12 17.11 1 8.17 15.96 Nov 2.19 5.36 2.79 5.66 Dec 1.26 1.05 0.50 1.60 Seasons Winter 2.22 1.92 0.67 2.60 Summer 16.37 6.51 4.07 5.91 Monsoon 48.65 38.41 71.91 41.88
Figure 2 Annual rainfall trend at Akluj and Bhor station (Source: Murumkar and Arya, 2014).
Figure 3 Seasonal rainfall trends at Bhor station (Source: Murumkar and Arya, 2014).
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3. MATERIAL AND METHOD APPLIED A detailed exploration was carried out to find out the past- history and present conditions of the Varandah Ghat section, i.e. along the Maharashtra State Highway-15 (MSH-15), on the Deccan plateau which cutting the Sahyadri escarpments along its route line. Another aim of this field exploration was to compare the landslides occurred in the Ghat section with landslides in the adjacent region such as Yelvandi river basin, with respect to different environmental factors which are responsible for the same. These factors include, lithology, texture, structural characters, slope, the rate of weathering, the intensity of rainfall, climatic variations, geomorphology, and tectonic activity, which leads to the mass movements. For the present study, the investigation work has been divided into three categories, i.e. Pre-field, field and lab investigations. Flowchart of the methodology is shown in Fig. 4.
Figure 4 Flowchart shows the methodology used for the work. Pre-field Investigations study is carried out with the help of available previous literature, topographic maps and google images of the study area. Based on this work various thematic maps such as location, geology, base, relief, drainage, slope, land-use and land-cover and landslide hazard zonation map were studied. The Contour, DEM, Slope, Drainage and Geomorphic maps were prepared on the basis of Survey of India Toposheet no. E43H12, E43H16 on the scale of 1:50000. ASTER- USGS derived 30-meter-resolution digital elevation models of the study area. The topographical map was geo-referenced in the GIS environment and the Varandha Ghat road, landslide locations
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were digitized using the ArcGIS software (version 10.1). For Land cover assessment; Landsat 8 satellite image used to classify land use and land cover of the study area. Landsat 8 Panchromatic (12/02/2015) multispectral images have been applied. Field Investigations study is carried out to get the following information. Initial point of the survey and their RL Details of the each locality Position (Latitude-longitude), Elevation details of each locality. Degree of the slope Type of vegetation Types of rock Texture and structure present in the rock. Details of the previous records of the mass movement of the area. Recording of the panoramic view of the mass movement by using camera and video camera. Drawing of the stratigraphic section. Rate of weathering of the flows of different varieties of basalt.
4. FIELD OBSERVATIONS As stated above, the study area is a part of the Western Ghats, which declared as World Heritage by UNESCO and Government of India for many reasons such as the presence of very rare, endangered species of plants and animals, geomorphic features, Natural features, cultural heritage and eco-tourism point of view. Mostly, during the rainy season, the roads in area is present in between Khandala- Lonawla Hill station at North and Panchgani- Mahabaleshwar, at the south extension. Therefore, by knowing the importance of the same, a detailed field exploration is carried out along the Bhor-Mahad Highway, Via. Varandha Ghat. During the survey, each important previous mass movement locations along the left and right side of the road is systematically encountered and mapping is carried out with the help GPS (Garmin E-Trex-30). Their details, such as nature, type, extension, dimension, causes of mass movements, etc. observations were carried out. Details of the Field Observations in the Varandha ghat section is given in Table-2.
Table 2 Details of Field Observations Loc Location/ Latitude/ Slope/ Type of Type of Prev- Type of Types of Weatherin Chan- atio Arrival Longitude/ Height/ Vegetation Rock ious Joints flow g condition ces of n Point Elevation Length land- sliding No. slide 1 Venupuri S-90° Moderately Vascular Yes Sheet Joint Vascular Deeply High Bus Stop H-20 ft dense basalt with and Basalt with weathered A-316 Ele.-741 m L-50 ft zeolitic lava Irregular zeolitic lava Moderately matrix matrix weathered 2 Venupri S-45° Moderately Red Yes Irregular Red Deeply Very near H-30 ft dense Tachylatic Joint Tachylatic weathered High bridge Ele.-721 m L-75ft. Bassalt Bassalt A-320 3 Kondri S-90° Scanty Compact Yes Irregular Compact Low High Bus Stop H-60 ft Bassalt Joint Bassalt Moderately A-323 Ele.-733 m L-50 ft weathered
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Loc Location/ Latitude/ Slope/ Type of Type of Prev- Type of Types of Weatherin Chan- atio Arrival Longitude/ Height/ Vegetation Rock ious Joints flow g condition ces of n Point Elevation Length land- sliding No. slide 4 Ramdas S-90° Scanty Compact Yes Irregular Compact Fresh In Swami H-65 ft Bassalt Joint Bassalt future Vidyalaya Ele.-743 m L-80 ft A-326 5 Ayush S-85° Moderately Red Yes , Irregular Red Deeply Medi- Garden H-40 ft dense Tachylatic Creep Joint Tachylatic weathered um before Ele.-743 m L-350 ft Bassalt, Bassalt, Hirdoshi Compact Compact A-332 Bassalt Bassalt 6 Near S-75° Moderately Red Yes Vertical Compact Fresh Very bridge H-45 ft dense Tachylatic columnar Tachylatic High Hirdoshi Ele.-705 m L-70 ft Bassalt joint Bassalt A-334 7 Near S-85° Dense Red Yes Irregular Red Moderately High bridge H-70 ft Tachylatic Joint Tachylatic weathered Hirdoshi Ele.-705 m L-400 ft Bassalt Bassalt A-336 8 Near S-85° to Moderately Compact Yes Vertical Compact Deeply High bridge ' 90° dense Bassalt and Sheet Bassalt weathered Hirdoshi 35" H-40 ft Joint A-338 Ele.-701 m L-150 ft 9 Near S-85° Moderately Red Yes Columnar R.T.B Deeply High bridge TO 90° dense Tachylatic Jointed Compact weathered Hirdoshi 34" H-40 ft Basalt, Bassalt A-344 Ele.-696 m L-70 ft Compact Bassalt 10 Near S-85° Moderately Compact Yes Irregular Compact Deeply High bridge H-35 ft dense Bassalt Joint Bassalt weathered Hirdoshi 36.2" L-60 ft A-349 Ele.-733 m 11 Right side S-85° Moderately Red Yes Irregular D.W. C.B Deeply High bridge H-35 ft dense Tachylatic Joint R.T.B weathered Hirdoshi Ele.-733 m L-60 ft Bassalt A-349 12 Near S-75° Moderately Compact Yes , Irregular D.W. C.B Deeply High temple H-40 ft dense Bassalt Falling Joint C.B weathered Hirdoshi Ele.-734 m L-100 ft Fresh Fresh A-351 C.J. C.B 13 Before S-85° Scanty Red Yes , Columnar Red Deeply High Mahad 46 H-50 ft Tachylatic Falling Jointed Tachylatic weathered km 15.5" L-200 ft Bassalt, Sheet Joint Bassalt, Fresh Near Ele.-739 m Compact Compact temple Bassalt Bassalt Hirdoshi A-350 14 Before S-70° Scanty Compact Yes , Irregular Compact Fresh Very Mahad 46 E 73* H-55 ft Bassalt, Falling Joint Bassalt, High km 0.18" L-100 ft C.G.C.B. C.J.C.B. Near Ele.-740 m temple Hirdoshi A-355 15 Kurkunj S-85° Moderately Tachylatic Yes, Irregular Tachylatic Fresh High A-357 E 7 H-45ft dense Bassalt, sliding Joint Bassalt, Ele.-728 m L-400ft Compact Compact Bassalt. Bassalt.
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Loc Location/ Latitude/ Slope/ Type of Type of Prev- Type of Types of Weatherin Chan- atio Arrival Longitude/ Height/ Vegetation Rock ious Joints flow g condition ces of n Point Elevation Length land- sliding No. slide 16 Karunjgan S-85° Moderately Compact Yes, Irregular Compact Fresh High bus stop 34" H-40ft dense Bassalt falling Joint Bassalt After Ele.-678 m L-200ft Crossing River A-359 17 Karunjgan S-80° Scanty D.W.C.B Yes, Irregular D.W.C.B Fresh High bus stop H-40ft P.C.B sliding Joint P.C.B After Ele.-614 m L-400ft Compact Compact Crossing Bassalt Bassalt River A-363 18 Karunjgan S-80° Moderately D.W.C.B Yes Irregular MWCB Fresh High bus stop H-35ft dense P.C.B Joint Fresh After 11.4" L-80ft C.B Compact Crossing Ele.-710 m Bassalt River A-365 19 A-371 S-90° Moderately Tachylatic Yes Irregular Tach. B, Deeply High H-35 ft dense Compact sliding Joint CB Weathered Ele.-711 m L-400ft Bassalt 20 A-373 S-85° Dense Compact Yes Irregular I.J.C.B and Moderately High H-40ft Bassalt Joint Compact -deeply Ele.-776 m L-100ft Bassalt weathered
(Index: CB-Compact Basalt, CPB-Compact porphyritic basalt, I.J.C .B-irregular jointed compact basalt, CJCB-Columnar Jointed Compact Basalt, RTB-Red Tachylitic basalt , MWCB-Moderately weathered compact basalt, DWCB-Deeply weathered compact basalt, PCB- Porphyritic compact basalt S-Slope, H-Height, L-Length).
5. DATA LAYERS AND CLASSIFICATION OF MASS MOVEMENT The different data layers are prepared for the study of landslide of the selected area.
5.1. DEM- Digital Elevation Model of Varandha Ghat
Figure 5 Digital Elevation Model of Varandha Ghat. A Digital Elevation Model (DEM) is a digital representation of topography, i.e. an elevation map. In this m
http://iaeme.com/Home/journal/IJCIET 2019 [email protected] Investigation of the Mass Movement in Varandha Region, Western Ghat of Maharashtra Using Geospatial Technique different class of height is shown in different colour. Faint Green colour shows the lowest of 23 to 459 meters above sea level. While the highest class in white colour is 1,110 to 1,418 meter above sea level. Most of the Varandha Ghat road area covered under the 869 m to 460 m height of the terrain. Most of the landslides are spotted in this area. Digital Elevation Model of Varandha Ghat is shown in Fig.5.
5.2. Slope Analysis of Varandha Ghat As slope plays a dominant role in landslides, as the construction of Varandha Ghat road has caused profile alteration. The degree of slope gently decreases towards the confluence region of water the body. This map shows the slope of the terrain in Degree. It is represented by different shades of brown colour. White colour shows the flat terrain where the dark brown colour shows the mountainous or hilly areas. Most of the landslides spotted on 12° to 60° slope area. Slope Map of Varandha Ghat is shown in Fig. 6.
Figure 6 Slope Map of Varandha Ghat
5.3. Land use / Land Cover of the Study Area Land Use/ Land Cover play an important role in environmental assessments and issues. Identifying, delineating and mapping land cover is important for global monitoring studies, resource management, and planning activities. Land use Map of Varandha Ghat is shown in Fig.7.
Figure 7 Land use Map of Varandha Ghat.
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This map is divided into 4 categories which are as follows: Barren Land: 59.62% land in of the whole study area is covered with barren Land where no activities are carried out. In this map barren land is shown with the light brown colour. Vegetation: Total of 34.89% land is covered by vegetation. In the map, it is shown by Green colour. Water: Out of total study area, around 5.48% of the land is covered by water bodies. It is shown in the Blue colour. Varandha Ghat Road: This road passes through the whole study area from West to east direction. Barren land is largely observed in this study area but equally dominated by Agricultural practices. A lot of Open or Barren lands are present where no human or natural activities are being carried out.
5.4. Zonation of a Mass Movement On the basis of the field inferences, the mass movements and their intensity observed at different locations in the study area are divided into several categories, such as Very Low, Low, Moderate, high and Very High Susceptible Zones (GSI, 2005). Table 3. shows susceptible zonations table (GSI, 2005). Susceptible zonations are shown in Table-3. (GSI, 2005).
Table 3 Susceptible zonation table (GSI, 2005). Sr. No TEH(GSI, 2005) Zone 1 > 4.9 Very Low Susceptible Zone (VLSZ) 2 4.91-7.0 Low Susceptible Zone (LSZ) 3 7.1 -8.4 Moderate Susceptible Zone (MSZ) 4 8.41-10.5 High Susceptible Zone (HSZ) 5 >10.5 Very High Susceptible Zone (VHSZ)
5.5. Mass Movement and their Category It is observed that, most of the mass movements occurred in the study area is belonging to active and most active category while very few (only one) case is come under the dormant and no any area is found with the absence of mass movement. Therefore, on the basis of this one can conclude that nearly each and every area in the study area is very active for a mass movement activity. Locations of different category landslides in the study area are shown in Table-4.. Locations of different category landslides in the study area are shown in Fig. 8.
Table 4 Locations of different category landslides in the study area. Sr. No Category Location 1 No Mm Nil 2 Dormant Mm 02 3 Active Mm 5,6,12,14,16,17,18,19,20, 21,22,23,24,25,26. 4 One very large active Mm 1,3,4,7,8,9,10,11,13,15,27, 28. (Index: Mm--Location numbers).
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Figure 8 Locations of different category landslides in the study area.
5.6. Slope and Mass Movement The slope is one of the important and most responsible factors for the formation and to decide the type of mass movements. A slope facet is a part of an inclined surface having a consistent slope direction and its inclination which delineated by geomorphic features such as gullies, river, ridges, interlocked spurs and slope etc. (Singh et. al., 2011). This factor is prepared by using Survey of India toposheet. On the basis of slope studies, it clearly indicates that most of the mass movement prone region is present in the area which geomorphologically bounded by Escarpment/cliff, Steep Slope. While very little mass movement activity is observed in moderate to gentle slope area. In short, the number of mass movement increases with increase in the stiffness of the slope. Analysis of slope and its relation with mass movement activity is shown in Table- 5.
Table 5 Analysis of slope and its relation with mass movement activity. Sr. Slope Category Location Number of Number of landslides No locations D A VA 1 Esc/Cl (>85°) 1,3,4,7,8,9,10,11,13,15, 12 03 07 02 24, 27. 2 Ss(45-85°) 12,14,17,18, 23,24, 25,26 08 02 04 02 3 Moderately 16,17, 21,22,23, 05 - 04 01 (25°-45°) Ss 4 Gs (<15°-25°) 5,6,18, 19, 20 05 - 04 01 5 Very Gs (<15°) 02 01 - - 01 (Index: Esc/Cl- Escarpment/cliff, Ss-Steep Slope, Gs-Gentle Slope, D-Dormant landslide, A-Active landslide, VA-More than one landslide or one very active landslide, 1,2-Location numbers).
5.7. Rock Type and Mass Movement As stated above in the geology of the area point, the study area is a part of Deccan Volcanic provinces of Sothern India, which consists of thick and thin flows of different varieties of basalts In this, the proportion of compact and amygdaloidal is predominant than vesicular, tachylitic and volcanic breccias. As per as the intensities of mass movements in particular varieties of Deccan Trap at different locations is concerned, most of such processes are observed in compact basalt and tachylitic basalt. In compact basalt, high intensities is observed because of the presence of different types of joint and fracture plane while in
http://iaeme.com/Home/journal/IJCIET 2022 [email protected] Dattatraya J. Khamkar and Sumedh Y. Mhaske tachylitic basalt is due to the washing of deeply weathered material of tachylitic by quick response to weathering action, removal of baked soil-like material produces weak cavities and resulting movement of overburden material takes place by dislodging/ un supporting activity. While very few mass movements are observed in amygdaloidal basalt and volcanic breccias due to the absence of weak planes. Intensities of mass movements in particular varieties of Deccan Trap at different locations are shown in Table-6.
Table 6 Intensities of mass movements in particular varieties of Deccan Trap at different locations. Sr. No. Types of divisional planes Locations No 1 Compact bassalt 3,4,8,9,10,12,13,14,15,6,17,18,19,20,21,22, 22 23, 24, 25, 26, 27, 28. 2 Amygdaloidal basalt 1,2. 2 3 Vesicular bassalt Nil 0 4 Tachylitic bassalt 5,6,7,9,11,13,15,19,24 9 5 Volcanic breccia 1 1
5.8. Nature of Rock and Mass Movement To understand the different lithology and their response to the mass movements, the study area was investigated properly. It is clearly observed that, maximum mass movements were observed in fresh to slightly weathered rock then moderately weathered and then deeply weathered basalt. While such movements are found rarely in loose, sandy soil over bed rock. Lithological characters at different locations are shown in Table-7.
Table 7 Lithological characters in different locations. Sr. Various litho units in the Locations. Number of Number of landslides No. study area locations D A VA 1 Slightly weathered basalt 1,3,4,7,8,9,10,11,1 12 02 08 02 3,15, 24, 27. 2 Moderately weathered 12,14,17,18, 23,24, 08 02 04 06 basalt 25,26 3 Moderately-deeply 16,17, 21,22,23, 05 - 05 - weathered basalt 4 Deeply weathered basalt 5,6,18, 19, 20 05 01 03 01 5 Sandy soil over bed rock 02 01 - - 01 6 Poorly compacted loose Nil - - - - material (debris)
5.9. Rock Structure and Mass Movement Similarly, the different divisional planes/joints observed in the basalts at various locations were also carefully noted during the survey. Most of the time, the joints are responsible for the movements of loose materials. Because, through the unjointed, homogenous basalt no mass movement is observed. While contradictory to this, the irregular jointed compact basalt is highly prone for the mass movement because of the high intensity of divisional planes which spread throughout the particular flows. The columnar joints are also shown considerable tendency than the sheet jointed basalt. Characteristics of the divisional planes occurred in the different locations are shown in Table-8.
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Table 8 Characteristics of the divisional planes occurred in the different locations. Sr. No Types of divisional planes Locations
1 Unjointed rock compact basalt Nil 2 Columnar jointed compact basalt 6,7,8,13,21,27,28 3 Sheet jointed compact basalt 1,7,27. 4 Irregular jointed compact basalt 1,2,3,45,,7,10,12,14,15,16,17,18,19,20, 21,23, 24, 25, 27. 5 Block jointed compact basalt 21
6. RESULT AND DISCUSSION According to Thigale and Umarikar (2007), mountainous topography, heavy rainfall, tectonic setting, seismic history and anthropogenic changes were factors conducive for bringing slopes on the threshold of equilibrium and in-equilibrium. In this, rains before the episode ensured displacement of air from pores by percolated water through regolith up to basalt, thereby increasing pore-water pressure and weight of the slopes. Therefore, the heavy rains during the episode acted as a triggering mechanism that ultimately caused land sliding. They studied six locations such as; Dasgaon, Jui, Rohan, Turil, Gothe and Kondvite, where, the hydrothermal anomaly generated during the episode, was unique, where no reports of occurrence of such a phenomenon in the past, except the landslide that caused forest fire in a remote area of the Los Padres National Forest, California (Allen et.al, 2005). According to Mizutani et.al. (1976), Singh (1988) and Arora (1988), origin of the hydrothermal anomaly can be explained applying dilatancydiffusion mechanism, which suggests that as the groundwater under the effect of stress is forced through the pores or newly created cracks, the streaming potential is produced which in turn induces electric current along the pattern of groundwater flow. Then they found that the rainwater, while percolating from regolith into the upper vesicular portion of lobes of compound basalt, flows through the pores and newly developed cracks produce streaming potential through electro-kinetic effect. Having reached the critical point, energy was released bursting the rock and giving rise to a fountain of dust and steam, leaving behind a narrow but deep depression, and ultimately triggering landslides. Schematic cross-section explaining the landslide process. (Inset) Cross-section of typical hummocky lobe of compound flow is shown in Fig. 9.
Figure 9 Schematic cross-section explaining the landslide process. (Inset) Cross-section of typical hummocky lobe of compound flow (Source: Thigale and Umarikar, 2007).
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It is clear the delineation of the vulnerable zones will be more helpful for the sustainable construction activities, implementation of protection measures thus to prevent the nature of Ghat Section cutting and various types of failure which described as above, during the rainy season. Therefore, continuous efforts should be taken to stabilize road cutting to prevent the various types of mass movements.
7. CONCLUSIONS Mass movements are not an uncommon phenomenon in Western Ghat area. Especially, during the rainy season, along the Bhor-Mahad State highway faces number of unusual mass movement incidents such as rock fall, landslides and creep movements through which big blocks, rubbles, soil mixed boulders slides and spread along the road, affected the road traffic jam problems, causes large scale damages road constructions and human lives. Through this shortcut way, which connecting upper Plateau region and Konkan Coastal Belt, vehicle carries huge traffic thousands of passengers and goods. The highway has deep cut along its rout with mostly untreated, unsafe slopes and presence extreme climatic conditions. Another important is that, a lot of construction activities day to day are going on in the hilly terrain, which is partially responsible to cause the jerk in the rock along the road cutting section. Such activities help for the movements of loose material towards the sloppy area. For the prevention of such mass movements, there is need of ground improvement techniques for the stability of slopes. As it is a highly vulnerable region especially in a rainy season as per as the mass movements are concerned. The controlled measures are as follows. i. Continuous contour trenches should be constructed along the stiff slope areas. ii. As the total part of the Ghat section is rocky escarpment of Sahyadri hill ranges and covered with thin-moderate vegetative cover. Therefore, there is need of plantation of trees along the ghat section road. iii. Berms step-like terraces should construct to restrict the movement and quick, in-situ deposition of loose, transferred sediments. iv. In case of highly jointed and fractured rock cliffs along the road side, they should stabilize by giving bolting-netting-grouting treatment. v. To avoid the movements of loose sediments towards highway track side, guard wall should be constructed parallel to the road along the difficult, movement prone terrain area. vi. Geosynthetic net should be provided on the highly jointed /deeply weathered portion of the surface to avoid the sliding of the sediment. vii. easy alarm. viii. Patrolling in the weaker section ghat section is required during the rainy season. ix. Awareness in the mind of people from Bhor portal and Konkan portal. Unless otherwise the evaluation is properly made on stability factors, the vulnerability is going to be high in future due to increase in traffic and developments. Therefore, by keeping all these views in the mind, there is need of implementation of above-suggested measures and further, detail investigations to stabilize the mass movements in this area.
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