A Geological overview of Ramban to Banihal Highway, Jammu and Kashir

Report on a Geological Overview of Ramban to Banihal Highway Project, Jammu and Kashmir

1.       Introduction:

Ramban to Banihal highway project is a most difficult part of NH-1A (NH-44) due to very rough topography with a steepest terrain on Jammu to Srinagar highway, this is vital for providing connectivity between Ramban to Banihal. The Geological condition is very complex in this section due to past tectonic activity. The total length of the project is 36 km from Km 151+000 and ended at Km 187+000, including 06 major bridges, 21 minor bridges and 6 Tunnels.

2.       Geology of the Project area:

During the field work it has been observed, from Ramban to Banihal metamorphic rocks are exposed along the project highway. These exposed rocks have undergone moderate to high temperature and pressure condition due to Murree thrust, Makarkote thrust and Panjal thrust. At some places, intrusion of granitic rock have been observed near Panthal and khuninallah area. Two local thrusts have been encountered named as Digdole and Magarkote thrust, at Digdole and north of Ramsu respectively. From Ramban to Banihal, there are numerous Shear zone/seams are present which generate rockfalls and slides along the highway on steep hill slopes in the project area. The area from where project highway starts km.151+000 is highly sheared and fractured.

Stratigraphic sequence of the project area (Bhat, et al.,1999)

 The rocks of Salkhala group are exposed along the highway, comprises foliated slate, phyllite, quartzitic phyllite dolomite form 151+00 to up to km. 169+00. Salkhala group is divided to salkhala formation, Ramban formation, sinchua formation and Baila-Gamir formation. Ramban formation comprises slate, phyllite, dolomite and quartzite, highly jointed and sheared at some places (At T1 and T2 tunnel) due to effect of Panjal thrust as well as Muree thrust. Muree thrust separates murree group of rocks to metamorphic rock near Ramban  which is parallel to the Chenab river. Ramban formation is tectonically overlain by salkhala formation near Digdole. The Granitic rocks are exposed near Khuni nallah next to Digdole ut to Magarkote. Further next to Magarkote km.169+000, the rocks of Ramsu formation are exposed along the highway comprise a highly compressed unit of phyllite and phyllitic slates, quartzite. Ramsu formation is separated tectonically from salkhala formation by Makarkote thrust at km. 170+000.  It is recorded unfossiliferous till date. The rocks of Ramsu formation are exposed between Makarkote to Sherbibi along the project highway. Ramsu formation has micro folds due to thrusting activity over salkhala formation. Further from Km. 181+000 to up to end of the project 187+000, the rocks of Chamalwas formation are exposed which comprises greenish grey slate, quartzite, metasandstone and metasiltstone which is uncomfortably overlain by syringotheris limestone. The Chamalwas formation is also unfossiliferous like Ramsu formation.

Lothological Strip Chart along Highway

1.       Structures, Bridge, Retaining walls foundation and Tunnels:

As we have know this area falls under the youngest mountain chain of the world and most difficult zone of Jammu to Srinagar highway due to its geomorphology and geological complexity. The lithology of the project area is metamorphic sequence which is fresh to highly weathered in nature shows intense shearing, fracturing and folding at at some locations (Ramban, Digdol and Ramsu, Nachilana area).

Mom Passi, Highly Steep Terrain with Complex Geology

 There is need to design and execute the foundation work of structure carefully.  During execution of shallow open cast foundation of bridges, geological logging of the foundation area needs to be carried out properly and if found any shear zone/seams should be treated by dental treatment as per the standard (IS:11973, 12070). At some places the nature of rock strata is noticed as poor to very poor rock (Class C, highly jointed, weathered with open joint). Such foundation location should be noticed carefully and foundation improvement to be carried out before laying the PCC by fully grouted anchoring or cyclic grouting method, if required as per IRC or IS standard (from Seri to Battery Chasma MNB at km.153+900,156+070 and 157+970, MJB 161+300).

The foundation which will be cast over a steep slope, the edge distance, frustum of bearing etc. should be checked as per IS 1904,13063 and IRC 78-2000. Excavation for open foundations should be done after taking necessary safety measures for which guidance may be taken from IS: 3764.The foundation protection work related to structures on a steep hill slope noticed carefully at the time of design and execution and kinematic analysis and further modeling needs to be carried out to check the stability of foundation as per the site condition and codal provision. The area from Maroge to Makarkote is the steepest area of the project so special attention needs to be required in this area (Bridge at 153+900,160+300 and 169+060).

At Tunnel 1, 2 and 6 the rock mass is noted as highly jointed and moderate to high weathered slate/phyllite/schist rock including Dolomite. Which belongs near to class C as per the rock mass classification, so proper attention is to be required to design the portal face and tunnel support system based on assumed and field parameters. 

Highly Jointed and Sheared Granitic Schist at Panthal Tunnel Portal

The rock strata at Tunnel 3, 4 and 5 is better with compare to tunnel l, 2 and 6 known as granite/ granitic gneiss (eccept few meter sheared zone at panthal). The Rock strata of this stretch belongs to class A-B of the rock mass classification, moderately jointed and fresh in nature except Panthal bridge location where poor quality of rock mass is observed up to few meters along the tunnel axis both side from center of nallah. At this location weathering and shearing effect have been observed on right bank of panthal nallah up to few meters inside the hill slope. During excavation of tunnel a detail geological mapping including 3-D face logging should be carried out after every cycle of excavation on a scale 1:100 or 200 and if found any deviation in designed data to be communicated to designer to improve the support system and value engineering. The over breaking should be noticed carefully and blast design updated accordingly. Blast design is exercised properly in each type of rock mass for tunneling work as well as for cut slope excavation works.

2.       Road Cut Slope Stability Or Slope Protection works:

As the terrain of the project is through the mountainous region, various protection works, such as revetment walls, rock net and special slide protection works to be required to stabilize the slope. The slope protection works will be mainly soil slope, soil-rock slope and rock catch type. 

Highly Steep Cut Slop required correct Protection measures

For a soil slope, soil nailing, revetment wall (180+000 to 184+000) or stone masonry walls can be used to protect the slope including bioengineering method such as hydro seeding to control surface erosion by quick vegetation development. For highly fractured rock mass, the revetment wall can be applied to protect the slope as per the site condition, if the height of the wall is more than 6 meters the strength parameters to be carried out for the wall foundation (Ramban formation, Ramsu formation and soil strata). Where the slope is stable but surface instability is occurred  due to shooting stone with deferent size of rock pieces, rock net and rock catch fence to be installed as per site condition and contract agreement (Battery chasma to panthal nallah, khuni nallah and magarkot area). In the special protection works such as planer, wedge and toppling failure (Km.170+000 to 178+000 and Km.186+000 to 187+000 ), we can stitched the jointed rock mass by  fully grouted rock anchoring, dowelling with or without shotcrete as per site condition but detail  kinematic slope stability analysis (day lighting case)  should be carried out to check the failure mechanism and FOS. Further we can confirm these results with continuum and discontinuum modeling in details if required. (Digdole,khuni nallah,panthal, Magarkot, Sherbibi and 186+000 location).

The Slope geometry, rock type and shear strength parameters should be checked properly in the field with design and drawing before executing the work of cut slope and if found any deviation in rock type, class and cut slope angle, protection measures must be updated accordingly.  During the cut slope activity at km183+600 to 184+600 and 177+300 (SB), mass movement (creep movement) has been observed due to excessive cut height, toe cutting of the slope, needs to be protected.

3.       Major Landslide at Highway:

Several landslides have been encountered at Ramban to Banihal project highway, named and chanaige as follows:

·         Seri Landslide                                       Km.151+300

·         Landslide at Khuni nallah               Km.162+800

·         LandSlide at Panthal Bridge        Km. 168+600

·         Ramsu landslide                            Km. 172+600

·         Landslide at  Ratanbas               Km. 176+100        

                                                                                               

Landslides are natural phenomena and occurred due to natural forces as well as manmade activity like improper excaation. As we know this area exists in zone IV on earthquake zonation map of India. The topography of this area is very roughed and geologically very complex in nature. When the degree of weathering (physical, chemical and biochemical) is increased and strength parameter of rock mass is decreased as the time passes away. When the shear strength parameters of the rock mass are reached at peak value due to natural or manmade forces, slope fails in continuum or discontinuum materials. Most of landslides of the project area are governed by discontinuities except Seri landslide. The material at Seri Slide is highly crushed and seems to continuum in nature. A brief description of major slides along the alignment and  location view is being presented below:

·         Seri Landslide:   landslide is encountered at Km 151.050 and occurred in sheared and highly crushed rock mass (slate and phyllite) which is continuum in nature.The rock mass fails during monsoon seasons due to decrease in shear strength parameters of rock mass while pore water pressure increased (saturated condition).

Seri Landslide

Deep seated failure has not been observed but it is a large slide. For the protection measure we can used gabion wall or reinforced wire mess grid at this location with bioengineering method such as seeding root mat or hydro seeding as per the site condition.  Location of all current slide https://www.google.com/maps/d/edit?hl=en&mid=1kG4dcr-_JQQmJybqIu45ttv3rmrH942Z

https://www.google.com/maps/d/edit?mid=1kG4dcr-_JQQmJybqIu45ttv3rmrH942Z&usp=sharing

·         Khuni nallah Landslide:  Khuni nallah landslide is located at Km 166+200 just before the bridge. This landslide is governed by discontinuity. It is occurred due to road widening/toe cutting with a combination of planar, wedge failure within the rock mass.

Landslide near Khuni Nallah

The rock type of this area noted as phylitic, granite dipping towards the highway (daylight at some location). For control measures of this landslide we can use rock catch fence with rock net. As we have observed, this landslide produces different size of rock boulders so that the rock catch fence to be design after knowing the trajectory path and kinetic energy of the detached boulders. 

·         Panthal Nallah  Landslide: 

This landslide is located just after the Panthal  bridge at km 168+700. The area is noted as moderately jointed granitic gneiss with steep slope. The nature of this slide is governed by kinematic mechanism and required slope

Landslide at Panthal Nallah

 protection as trimming of the slope, rock netting with rock bolting. The stone masonry wall, revetment wall can be used at the bottom of the slope. Before finalizing the rock net kinematic analysis should be carried out to know the mode of failure and protection works to be decided and executed accordingly.

·         Ramsu Landslide:   This landslide is located at km 172+600. It is most prominent landslide in the project area and occurred due to widening of existing road and complex mechanism of failure due to Magarkote thrust. The rock type of this area is noted as highly compress sequence of Phyllite, carbonaceous slate, dolomitic and siliceous limestone including quartzite of Ramsu formation. 

Ramsoo Landslide

This area is highly sheared, fractured and folding to Makarkote thrust. For the control measure of this landslide we can use reinforced gabion wire mesh grid at the bottom of the slope. Loose rock pieces/rock boulders must be removed by trimming and rock net to be used with geo-mat from top of the slope (crown) up to the gabion wall top. The rock bolting can be used to improve the shear parameters of the rock mass but before finalizing special protection a detail kinematic analysis of the slope, slope 2-D face logging, and subsurface parameter of rock mass needs to be carried out.

·         Landslide at Ratanbas:   This landslide is located at Km. 181+400 near Ratanbas area. It is occurred due to planar and wedge failure in carbonaceous slate and phyllite. Rock mass is moderately weathered.  

Landslide at Ratanbas area

Slope failure is occurred along closely spaced and steeply dipping joints as a planar and wedge mechanism due to the intersection of adversely-oriented joint planes. For control measure of this landslide first we can need to redesign the slope face geometry and remove all loose materials from rock slope then we can use rock bolting with rock net and shotcreting. A detail analysis should be carried out before finalizing special protection measures as 2-D slope face logging, subsurface parameter of rock mass.

1.      Conclusion:

As we have noted that the topography of this section is extremely rugged including steep hill slope. The area is witnessed two major thrusts known as Digdole and Makarkote which is tectonically active till date. It is also noticed mostly length of the project covered by slate, phyllite and schistose rock mass wherever these rocks are highly weathered and jointed at places may leads to problems in both cases, slope protection as well as structures foundation stability. Special attention is to be required during execution of cut slope excavation, tunnel portal face as well as foundation excavation. At Seri,Ramsoo and Ratanbas  landslide locations, we can also go for square half tunnel with inclined roof top but the applicability of this type of structure is a matter of technical and financial discussion. These types of structures are successfully adopted in the country for highway protection from unexpected fall, avalanche landslide on highway. At the location of Maroge, Digdole and Makarkote bridge, foundation will be on a steep slope, an excessive excavation will be required to layout the foundation on steep slope, is not good for foundation stability. So we can go for pile foundation in rock on steep slope, if required. The tunnel 3,4 and 5 will be executed as rock type seems fair to good but special attention will be required for execution of Tunnel 1,2 and 6.