SUMMARY REPORT OF GEOLOGICAL FIELD WORK
Submission Date: 04.03.2076
Report by:Sagar Acharya
Rollno: PUR074BCE066
IOE PURWANCHAL CAMPUS,DHARAN
INTRODUCTION:
PREVIEW OF THE STUDY TOUR:
The geology study tour arranged by our respected geology faculty teacher,Champak babu, under the support of our respected head of department, along with our cr Mr. Prajwal Bhandari, was arranged on 4th of shrawan,in order to accustom knowledge about the geological structures, their engineering significance,and to analyse the failure mechanism by stereographic projection.
This field visit gave us a wider aspect about all the geological concepts covered in our class sessions. We consisting of approximately 46 students were taken to field visit location by our campus bus.The time duration being one evening was spent in learning basic theoretical knowledge and one morning was spent in geological field study in Basantapur,about 90-100 km from dharan in eastern hill of Nepal.
OBJECTIVE OF THE STUDY TOUR:
To study the rock slope stability along the under construction highway.
To underestand different types of failure (plane failure,wedge failure, and toppling failure) that generally occurs in a rock mass.
To study and analysis of discontuinities data for failure mechanism by stereographic projection/ using Stereonet.
METHODOLOGY:
Kinematics Methods:
Kinematic methods are based on the principle of kinematics which deals with the geometric condition that is required for the movement of the rock block over the discontinuity plane, without considering any forces responsible for the sliding The commonly used kinematic method to determine possible mode of failure was initially proposed by Markland and later it was redefined by Hocking.
For kinematic check stereographic projections are used.The stereographic projection is a methodology used in structural geology and engineering to analyze orientation of lines and planes with respect to each other. A standardized mapping system known as stereonets are used to project different lines and planes in stereographic projections. Stereonets are circular graphs used for plotting planes based on their orientations in terms of dip direction (direction of inclination of a plane) and dip (inclination of a plane from the horizontal).
On a stereo-net, the representative great circles for all preferred discontinuity planes, present on the given slope, are plotted. Also, great circle for slope face and friction circle, corresponding to the friction angle of the discontinuity plane, are plotted. The zone demarcated by the friction circle and the slope face is designated as sliding envelope. If any great circle of a discontinuity plane, having strike nearly parallel to the slope face, falls within this sliding envelope, kinematic condition is satisfied.
Thus, we have following cases:
Plane failure:When the joints, bedding or foliation planes dip parallel to the slope with an angle equal or less than the hill slope, plane failure occurs.
Wedges Failure:When Slope Failure > plunge angle of the block > angle of friction along the failure plane, then wedge failure occurs.
Toppling Failure:Steep dipping of discontinuities parallel to the slope face and dipping into it steeply causes toppling failures.
Hoek and Bray further redefined the kinematic condition for plane mode of failure by introducing two more general conditions;
the strike difference between the slope face and the potential failure surface must be nearly parallel (±20°) and
there must be lateral release surfaces on either sides of the sliding block which must not provide any resistance to the sliding.
Kinematic check is the first step to proceed for other analytical techniques.
Empirical methods:
In past several empirical methods based on rock mass classification systems have been developed. The important slope classification systems are;
Classification proposed by Selby (1980),
Slope Mass Rating (SMR) (Romana, 1985),
Modified Slope Mass Rating (MSMR) (Anbalagan et al., 1992),
Slope Stability Probability Classification (SSPC) (Hack, 1998) and
rock mass classification system for slopes proposed by Liu and Chen (2007).
SMR classification, proposed by Romana can be used to assess the stability condition of a rock slope. SMR utilizes Bieniawskis rock mass rating (RMR), the relationship between parallelism of slope and discontinuities, dip amount of the discontinuity and relation between the slope inclination and dip of the discontinuity. Also, mode of excavation is considered in SMR.
Anbalagan modified SMR by considering wedge mode of failure as a separate case. For stability analysis of slope, having plane mode of failure, both SMR and MSMR classifications can be utilized.
Hack proposed SSPC to classify the rock mass and to define its in situ stability condition with probability of failure to occur. The SSCP accounts for discontinuity relations with the slope, degree of weathering and the shear strength of the slope material. In SSPC the exposed rock mass is characterized to represent in its imaginary un-weathered and undisturbed state for which suitable corrections for weathering and excavation disturbance are made.
Further, Liu and Chen proposed a classification system for the assessment of rock slope stability. In this classification geological, geometric and environmental factors were considered. By combining Fuzzy Delphi method and Analytic Hierarchy Process, a model to estimate the rock mass quality was developed.
Effectiveness of stability analysis techniques:
Each of the methods available for plane failure analysis has certain advantage and limitations . Thus, selection of these methods will depend on governing parameters involved in the analysis, complexity of the geological conditions, hydrologic and geometric parameters, purpose for which the slope stability has to be assessed, computational capacity and the capability of an evaluator.
Kinematic methods have a merit that they are simple in their application. These methods will only suggest the potential for failure and do not provide slope stability condition in quantitative terms. However, these methods are essential before application of other quantitative methods. Further, empirical methods can be applied over large area to investigate slope stability condition, in general. For simple cases such as uniform planar discontinuities these methods can be applied directly. However, for complex cases, involving variable slope geometric and geologic conditions, these empirical methods cannot be applied.
FIELD OBSERVATION AND RESULT:
Joint Number | Strike | Dip direction | Dip amount | Remarks |
1 | S75E/N75W | N15E | 39 | J1 |
2 | N25W/S25E | N65E | 82 | J1 |
3 | N50E/S50W | S40W | 60 | J3 |
Strike | dip | Dip amount | Remarks |
N-S | east | 70 | Hill slope |
CONCLUSIONS:
Thus as a conclusion of the two day geological tour to the Gupha pokhari , we realized the engineering geology has wide scope in civil engineering field and is very much important in both theoretical and practical point of view. Since this region has various geological features, different types of mass movement activities like slope failure, landslides, and a under construction road, it has proved that it is oned of the best site for our geological studies as per our objectives and we were able to explore it to its maximum depth though to explore any geologically important place to totally is impossible.
We are now, able to identify different type of mass movement activities, its cause and nature, slope stability measurement for stability analysis through stereonet analysis. It is better to say that
Engineering geological tour for a civil engineer is one of the most essential aspect for his skill, practical knowledge about the field and in overall career development.
Inspite of this,this Geological tour to Tinjure can be more fruitful. We were not able to achieve all our objectives as per our syllabus. We were unable to visit an underconstruction hydropower site due to some difficulties like weather condition, transportation difficulties, time limit and much importantly the interest of students towards the natures beauty instead of visiting hydropower sites.However, we enjoyed a lot at that place.
Some Important Memories At This Geological Tour:
Guest
