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The worship places in India are usually situated in and around the hilly regions and/or mountainous area and a number of devotees used to visit the holy places in every area for worship. The stability slopes upon which these worship places are located in the hilly and mountainous region are always a major concern. Moreover, heavy precipitation, weathering conditions, seismic disturbances and human activities could cause problem to the stability of such slopes. The effect of slope instability could cause delay in traffic, loss of life of the devotees at pilgrim sites and the loss of the properties. The Saptashrungi gad temple (SGT) situated on basaltic hills belongs to Deccan volcanic and is one among the 51 Shakti Peeths and the most holy place for pilgrims. In this research, the slope stability analysis at SGT hill is assessed using Phase 2, a finite element program along the two parikrama paths: Parikrama Path 1 (or the Badi Parikrama Path “BPP”), and Parikrama Path 2 (or the Chhoti Parikrama Path “CPP”). On the basis of extensive field work, topographic survey, complex geology, orientations of joint sets, hill slope faces and geotechnical conditions, the study area has been divided into eight zones (Zone#01 to Zone#08), and eighteen topographic profiles (AA′ to RR′) are taken from these eight zones for detailed slope stability analysis. The analysis helps to identify the potentially vulnerable slope and zone of instability.

Natural slopes are omnipresent on earth surfaces with slope inclination varying from near zero to almost vertical. Also, man-made slopes can be created by excavation activities such as building, roadways, railways and highways. The failure of these slopes occurs whenever an imbalance takes place between shear strength and shear stress in the ground and causes enormous loss of life as well as properties. The triggering factors for slope failure could be linked to heavy precipitation, weathering conditions, seismic disturbances and human activities [

Stability analysis of rock slopes is carried out to assess the safe and economical design of slopes and/or to assess the equilibrium conditions of the slopes. The method selected for stability analysis depends on site condition and potential mode of failure with special consideration given to strength, weakness and limitation of each methodology. The main objectives of these stability analyses are: 1) to investigate the potential failure mode; 2) to determine slope stability conditions; and 3) to design safe and economical slopes. In present time, n-number of slope stability analysis tools are available for rock slope as well as rock-soil mixed slopes; these range from limit equilibrium technique (simple infinite slope) to sophisticated couple finite distinct codes or couple distinct element codes. However, these slope stability methods can be discussed under three categories such as conventional, numerical and probabilistic [

Kinematic analysis and limit equilibrium techniques come under conventional slope stability methods. Numerical methods of analysis for rock slope stability investigation can be divided into three methods: 1) continuum modeling; 2) discontinuum modeling; and 3) hybrid modeling. Continuum method used in stability analysis includes finite element methods (FEM) and finite difference method (FDM), which is applicable for the slopes comprised of massive to soil-like or heavily fractured rock masses. In discontinuum modelling, rock slope is considered as discontinuous rockmass by considering it as an assemblage of rigid or deformable blocks with discontinuities represented explicitly (having specific attitude and position). Several variations of the discrete-element methodology exist as: 1) distinct element method (DEM); 2) discontinuous deformation analysis (DDA); and 3) particle flow codes (PFC) [

In this research, the slope stability analysis at SGT hill is assessed using Phase 2 [

hill slope faces and geotechnical conditions, the study area has been divided into eight zones (Zone#01 to Zone#08), and eighteen topographic profiles (AA′ to RR′) are taken from these eight zones for detail slope stability analysis (

Representative rocks samples have been collected from the study area and the samples have beed tested in the laboratory as per the established standard procedures. The experiments were done to estimate the essential input parameters for slope stability analysis (point load strength index, uniaxial compressive strength, tensile strength, slake durability index, young modulus, Poisson’s ratio, density and porosity) of rocks.

The study helps to identify the stability of the slopes using FEM method at SGT hill that is further used to define economical protection measures.

The Saptashrungi Gad Temple (SGT) lies in Vani village of Nashik district, Maharashtra, India. The SGT hill situated on the top of the hill range known as Saptashrungi. SGT is a holy place for the pilgrims and every year large number of devotee used to come for Devi Darshan and to perform parikrama along both the parikrama paths. The study area is located between latitude 20˚23'05" - 20˚23'55" and longitude 73˚54'05" - 73˚54'30" and comes within the topo-sheet no. 46H/15 allocated by the Survey of India (SOI). The study area can assess through the National Highway (NH)-3 and then by a State Highway (SH)-17 to reach SGT hill located near the village of Vani (

The residual hill ranges and the intermediate valleys are well developed on a tableland surface, forming the main geomorphic element of the landscape in the area. About, 60 million years ago, the outpouring of basic lava through fissures formed horizontally bedded basalt over large regions. Variations in their composition and structure have resulted in massive, well-jointed steel-grey cliff faces alternating with structural benches of vesicular amygdaloid lava, all of which contribute to the pyramidal-shaped hills and crest level plateau or mesas. The area exposes thick pile of basaltic flows with a number of basic and rare acid intrusive belongs to Deccan Volcanic of Upper Cretaceous to Lower Eocene age of Sahyadri Group. The entire lava flow has been separated into three formations viz. Salher Formation, Lower Ratangarh Formation and Upper Ratangarh Formation in ascending order of the Sahyadri group (

The SGT hill is extensively investigated for structural parameters and found that the study area has multi- oriented joint patterns with three sets plus random orientations at the majority of the locations. In addition,

wedge failures were noticed throughout the hill as shown in shown in

Field observations help to identify the geological conditions of the study area along with the degree of weathering, joint orientations and slope stability problems. Also, representative rock samples collected during field investigations for the determination of physico-mechanical properties in the laboratory as per the methods suggested by ISRM [

Finite element models are computer based program, tries to characterize the mechanical behavior of a rockmass with a set of initial conditions, i.e. boundary, in-situ stresses and water conditions. The models divide the rockmass into zones and each zone comprising material model and properties. The role of material model is to describe how the material behaves (stress/strain relations). The factor of safety (FOS) defined as the ratio of actual shear strength to the minimum shear strength required to prevent slope failure. The logical way to compute FOS with finite element method is to reduce the shear strength until the collapse occurs and termed as shear strength reduction (SSR) technique first introduced by Reference [

over limit equilibrium slope stability is two folds: i) SSR automatically identify the critical slip surface and no need to specify the shape of the sliding surface, and ii) SSR technique automatically satisfy translational and rotational equilibrium, which has not available in some of the limit equilibrium techniques.

Moreover, it is required to artificially truncating the infinite extent of a real problem domain to include the immediate area of interest in slope stability analysis. To overcome this difficulty Reference [_{cm}), the rockmass deformation modulus (E_{m}) and the rockmass constants (m_{b}, s and a) using Roclab program based on generalized Hoek-Brown failure criterion [

where _{b} = value of the Hoek-Brown constant m_{i} for the rockmass, given by,

s and a = constant factors, depending on the rock mass properties, given by:

Geological strength index (GSI) value can be obtained by comparing the quantitative GSI chart with the condition of the exposed rock mass identified by visual inspection [

During the extensive field visit, it has been found that the SGT hill was highly jointed and deformed with more than three joint sets (

Slope stability for SGT hill was performed along 18 profiles (AA′ to RR′) distributed in eight zones. The Phase 2 program has been used to do the FEM simulations. Uniform mesh with 6 node triangular and approximately 1500 mesh elements was constructed to divide the slope geometry. Also, plain strain analysis type with Gaussian elimination solver has been used with maximum number of iterations as 500 and tolerance as 0.001. Phase 2 can allow the user to choose if the material can behave like an elastic and/or plastic material for slope stability analysis. So, for the present study plastic material type has been chosen, indicating that the material can yield/fail. Initial element loading is set to gravity field stress and body force (both in-situ stress and material self-weight is applied).

A) Zone#01

The zone#01 comprises of four profiles EE′, FF′, GG′ and HH′. The profile HH′ is along the temple. The FEM analyses have been shown in

B) Zone#02

Profiles CC′ and DD′ come in zone#02 with FOS > 2.0, suggested stable slopes respectively. The maximum total displacement is >1.0 cm for CC′, whereas, for DD′, greater than 1.5 cm.

C) Zone#03, Zone#04 and Zone#05

Parameters | Values | Parameters | Values |
---|---|---|---|

Unit Weight (kN/m^{3}) | 27.80 | Young’s Modulus (kPa) | 23.34E6 |

Cohesion (kPa) | 1061 | Poisson’s Ratio | 0.264 |

Friction Angle (˚) | 30.00 | Tensile Strength (kPa) | 43.00 |

Each zone comprises of a single profile, i.e. profiles BB′, AA′ and RR′ respectively. The analyses indicate a stable slope condition with FOS 2.36 for profile BB′, 1.75 for profile AA′ and 1.59 for profile RR′ respectively. In addition, among the three profiles, BB′ has least maximum total displacement with value less than 0.001 mm (

D) Zone#06

The results of the numerical analysis for profile PP′ and QQ′ are shown in

concentrated at the top portion of the hill (only 35% of the total slope height), suggested no sign of instability.

E) Zone#07

This zone comprises of profiles MM′, NN′ and OO′ and the results shown in

F) Zone#08

The left zone of SGT hill has profiles II′, JJ′, KK′ and LL′. Among the four profiles, two profiles II′ and JJ′ has FOS >2.5 (

The FEM analyses provide the FOS, shear strain and total displacement pattern along the slope profiles. Magnitude of above parameters has been on the safe side, with FOS values range from 1.59 to 4.84, the maximum shear strain varies from 0.0003 to 0.0017 and the maximum total displacement varies from 0.0008 cm to 2.40 cm (

The critical slope profiles have been identified as EE′ and FF′ of Zone#01, AA′ of Zone#04 and RR′ of Zone#05. The FOS of these profiles was in between 1.50 - 2.00, indicates safer slope conditions with the minor requirement of repairment of the slopes. However, profile RR′ shows maximum total displacement of about 1.0 cm, indicating a chance of failure if the strength of the material further decreases.

The FOS between 2.00 to 2.5 were obtained for profile HH′ of Zone#01, CC′ of Zone#02, BB′ of Zone#03, QQ′ of Zone#06 and NN′ of Zone#07. As per visual observations during field survey and numerical analysis, these slopes were safe. However, numerical analysis of section HH′ of Zone#01 showed the maximum total displacement >1.0 cm which indicates a chance of failure, if strength of material decreases. Other slopes such as DD′, II′, JJ′, MM′, OO′, SS′, KK′, LL′ and PP′ of respected zones were identified as very safe as per numerical analysis.

Although finite element analyses provide majority of slopes are stable in nature; however, given that rockfall is a frequent happening at the SGT hill, 2D and 3D rockfall studies have been performed at SGT hill [

The present study deals with the study of the slope stability using the FEM method at SGT hill. It is concluded

Zone | Profile No. | Profile | FOS | Strain | Maximum Total Displacement (cm) |
---|---|---|---|---|---|

#01 | P1 | EE¢ | 1.75 | 0.00072 | 0.3000 |

P2 | FF¢ | 1.90 | 0.00090 | 0.4700 | |

P3 | GG¢ | 4.84 | 0.00030 | 0.1800 | |

P4 | HH¢ | 2.00 | 0.00140 | 1.1000 | |

#02 | P5 | CC¢ | 2.13 | 0.00145 | 1.4000 |

P6 | DD¢ | 2.61 | 0.00170 | 1.7000 | |

#03 | P7 | BB¢ | 2.26 | 0.00043 | 0.0008 |

#04 | P8 | AA¢ | 1.75 | 0.00063 | 0.3000 |

#05 | P9 | RR¢ | 1.59 | 0.00104 | 0.9500 |

#06 | P10 | PP¢ | 3.06 | 0.00077 | 0.6650 |

P11 | QQ¢ | 2.20 | 0.00162 | 2.4000 | |

#07 | P12 | MM¢ | 2.85 | 0.00048 | 0.2550 |

P13 | NN¢ | 2.34 | 0.00038 | 0.5000 | |

P14 | OO¢ | 2.79 | 0.00051 | 0.3600 | |

#08 | P15 | II¢ | 2.69 | 0.00143 | 1.2400 |

P16 | JJ¢ | 2.63 | 0.00060 | 0.3400 | |

P17 | KK¢ | 3.07 | 0.00060 | 0.3000 | |

P18 | LL¢ | 3.04 | 0.00090 | 0.5700 |

The color code is based on the values of maximum total displacement for less than and greater than 1.

that the advertently field investigation/survey is the foremost and very important exercise to understand the conditions and the nature of the slopes. Keep this in mind during field observations; every location has been carefully investigations. Vulnerable slopes were identified using lithological nature and characteristics of the discontinuities in different parts of the SGT hill that helps to categorize the study area into eight zones. The FEM analysis indicates that FOS varies from 1.59 to 4.84 representing stable slope. The maximum shear strain varies from 0.0003 to 0.0017. The maximum total displacement varies from 0.0008 cm to 2.40 cm. However, for section CC′, DD′, HH′, II′ and QQ′, the maximum total displacement is greater than 1.0 cm and any local or global disturbance may cause decrease in material strength, ultimately resulting in localized slope failures.

The fracture pattern identified during the field visit indicated the problem of rockfall, which had been reported by References [

Mohammad KhalidAnsari,MashudAhmad,RajeshSingh,Trilok NathSingh, (2016) Slope Stability Assessment of Saptashrungi Gad Temple, Vani, Nashik, Maharashtra, India—A Numerical Approach. World Journal of Engineering and Technology,04,103-115. doi: 10.4236/wjet.2016.41010