Slope stability analysis in hard rocks and prediction of ... - Paas.com.pk

Pakistan Journal of Science (Vol. 63 No. 4 Dec, 2011) 

SLOPE STABILITY ANALYSIS IN HARD ROCKS AND PREDICTION OF LANDSLIDE 

ALONG KHEWRA CHOHA SAIDDEN SHAH ROAD, SALT RANGE PAKISTAN 

M. S. Khan, I. Ahmad * , S. R. Ahmad ** and M. A. Qadri *** 

Department of Geological Engineering, University of Engineering and Technology, Lahore Pakistan. 

* 

College of Earth and Environmental Sciences, Punjab University, Lahore, 

** 

Institute of Geology, Punjab University, Lahore, 

*** 

Department of Geological Engineering, University of Engineering and Technology, Lahore 

Corresponding author e-mail: msaleemkhan1984@yahoo.com 

ABSTRACT: Landslides and slope failure in hard rocks are different compared to soft geological 

formations. A number of failures in hard rocks such as plane failure, wedge failure and toppling take place 

depending on the geology and tectonic setup of the area. Often the controlling factors are determined with scan 

line methodology and physical characterization of rock types. Limestone formation outcropped in the form of 

vertical cliff along Khewra-Choha Saidden Shah road has been analyzed with respect to its slope stability and to 

find out the probable mode of failure. The results indicate that in the study area there is threat of failure of 

vertical cliffs through toppling and the predicted direction of the failure is from north east to south west. 

Estimate based on physical inspection shows that probable landslide can cause severe damage and blockage of 

the road. It is suggested that few outer vertical blocks posing high risk should be removed through controlled 

blasting to avoid the expected failure otherwise which may cause a great hazard 

Keywords: Limestone, vertical cliffs, columnar joints, slope failure, toppling. 

INTRODUCTION 

The study area is located between 7-9 

kilometer from Choha Saidden Shah towards Khewra 

along Khewra-Choha Saidden Shah road (Fig.-1). This 

road is one of important link road in the Salt Range 

which passes through the mountainous area. It is very 

regularly used for transportation of minerals such as 

salt, coal, limestone, gypsum and many other minerals 

being mined in the area. The high slopes and 

outcropped rocks in vertical cliffs have special interest 

for tourists and local population visiting Khewra Salt 

Mine Tourist area. 

Analysis of the rock slope stability has been 

studied by a number of researchers who also suggested 

remedial measures (Lim, and Yang, 2004; Kumsar, et 

al., 2000; Bye and Bell, 2001; Hammah and Curran, 

1998; and Sameeni, 2009). Kumsar, et al. (2000) have 

reported dynamic and static stability assessment of rock 

slopes against wedge failure, “The test performed on 

model wedges under static and dynamic loading 

conditions are described and the existing limiting 

equilibrium methods are extended to take into the 

account dynamic effects. The applicability and validity 

of the presented method are checked through model test 

carried out under well controlled conditions and by 

actual cases studied by the authors, both in Turkey and 

Japan”. 

Bye and Bell (2001) has studied the open pit 

with respect to the slope stability and described, 

“Sandsloot open pit is located on the northern limb of 

the Bushveld Igneous Complex. It is the largest open pit 

platinum mine in the world. Three major joint sets have 

been recognized at Sandsloot, which are related to the 

regional tectonic history. They have an important influence 

on slope stability in the open pit, notably in terms of planar 

and wedge failure”. 

Fig. 1 Location map of the study area with probable 

direction of failure 

Identification and applications of joint sets are 

very important to analyze the stability of an area. The task 

of identifying and isolating joint sets or subgroups of 

discontinuities existing in data collected from joint surveys 

232


is not a trivial issue and is fundamental to rock 

engineering design (Hammah and Curran, 1998). 

In addition to the identification of joint sets 

and their orientation, the physical characterization of 

the outcropped rock in the slopes is very important. It 

also includes identification of the rock type, its 

weathering grade, roughness of the joints and water 

condition along the joint planes. This study has been 

carried out to analyze the slopes and to predict the 

possible failure mode in limestone formation making 

vertical cliffs which are located along Khewra-Choha 

Saidden Shah road in tectonically fragile zone of Salt 

Range, Pakistan. 

MATERIALS AND METHODS 

Field geological survey was carried out to 

collect data by adopting scan line methodology along 

the critical section of Khewra-Choha Saidden Shah 

road. The survey indicated that two geological 

formations, Tobra and Sakesar Limestone are exposed 

in the study area The Sakesar Limestone forms vertical 

cliffs and susceptible to slope stability problem which 

can be further classified into, massive limestone, 

nodular limestone and argillaceous limestone. 

Measurements of dip, strike and dip direction 

(continuous sampling).was recorded at every 

discontinuity. To analyze and determine the possible 

failure mode, the DIPS Software (2005) was used. 

Fig. 2. A view of possible landslide section with 

predicted toppling block. 

RESULTS AND DISCUSSION 

The geology of the study area is 

predominantly composed of limestone belonging to 

Sakesar Limestone Formation of Eocene age. Shah 

(2009) reported the Sakesar Limestone as, “the unit 

consists dominantly of limestone with subordinate marl. 

The limestone through out its extent is cream coloured 

to light grey, nodular usually massive with considerable 

development of the chert nodules in upper part. The 

formation is widely distributed in Salt Range and the 

Surgher Range. In the Salt Range its thickness varies 

between 70 m and 150 m.” 

Generally there are 5-6 feet thick alternate 

beds of nodular and massive limestone. The top most 

massive bed is more than 10 feet thick. The bedding 

planes contain filling of argillaceous material which is 

weathered and eroded. The formation is making vertical 

cliffs of more than 80 feet high nearby road side in the 

study area. Open vertical columnar joints are very 

common in Sakesar Limestone and at places these 

joints are up to 2 feet wide in upper horizon (Fig.-2). 

Fig. 3. Contour plot of data indicating the concentration 

areas. 

The exercise performed on the basis of 51 

discontinuities readings of joints and bedding planes from 

the study area are utilized for analysis of slope stability. 

The field data is used to develop contour concentration 

(Fig.-3). On the basis of contour concentration weighted 

average planes are generated, which are given in the form 

of rosette plot (Fig.-4). There are 4 numbers of major joint 

sets present which contribute towards probable slope 

failure in various rocks outcropped in the area. 

233


The analysis made with software (Dips, 2005) clearly 

indicates toppling failure in the outcropped formation 

which is given in Figure-5. The orientation of the 

predicted landslide failure is from north east to south west. 

Hence the high risks blocks (Fig.-2) are capable to block 

and severely damage the road. 

Fig. 4 Rosette plot of data high lighting the orientation of toppling region 

Fig. 5. Estimate of the toppling risk region with probable failure plans. 

Conclusion: Four joint planes have been identified in 

the study area which is responsible for slope failure. 

The stereographic analysis has indicated that failure in 

the vertical cliff through toppling is expected. It is 

suggested to immediately adapt precautionary measures 

such as removal of toppling region under high risk through 

control blasting to avoid possible hazard. 

Acknowledgement: The facilities for field visits and 

testing were provided by the University of Engineering and 

Technology, Lahore which is greatly acknowledged. 

234


REFERENCES 

Bye, A. R. and F. G. Bell, Stability assessment and 

slope design at Sandsloot open pit, South 

Africa. International Journal of Rock 

Mechanics and Mining Sciences 38, 449–466 

(2001) 

Hammah, R. E. and F. G. Curran, J. H. Fuzzy Cluster 

Alogrithm for the Automatic Identification of 

joint sets. Int. J. Rock Mech. Min. Sci. 35, 

(7):889-905 (1998). 

Kumsar, H., O. E. Aydan, and R., Ulusay. Dynamic and 

Static Stability Assessment of rock slopes 

against wedge failures. Rock Mech. Rock Engg. 

33 (1):31-51 (2000). 

Lim, S.S. and H.S. Yang. An analysis of plane failure of 

rock slopes by quantified stereographic projection. 

Int. Jou. of Rock Mech. and Min Sci. 41 (3): 3A 

05 (2004): 

Sameeni, S.J,. The Salt Range: Pakistan’s unique field 

museum of geology and paleontology. Carnet de 

Geology/Notebook on Geology- Book 2009/03 

(CG2009_03), chapter 6 (2009). 

Shah, S.I. Stratigraphy of Pakistan (Memoirs of the 

Geological Survey of Pakistan). Published by 

Geological Survey of Pakistan, Vol. 22, (2009). 

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