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Chapter:
1. SUMMARY REPORT OF GEOLOGICAL FIELD WORK
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:
2. Write an essay about any one of Geological hazards and ir mitigation measures in context of Nepal.
Nepal lies in the central part of the Himalayan belt. Because of its location characterized by a rugged topography, very high relief, variable climate conditions, complex geological structures with active tectonic processes and continued seismic activities, Nepal is prone to natural disasters. Obviously, the country requires a strong coping strategy and DRM to minimize the negative effects of natural disasters. But various human interventions have hastened the occurrences of natural disasters. Due to this, the vulnerable groups, mainly the poor and the marginalized people from the rural and urban areas, are facing economic hardships and bearing all kinds of burden. Insufficient knowledge on DM, emerging climate risks, low literacy rates, inadequate physical infrastructure, poor forecasting facilities and unplanned settlements have worsened the situation. Frequent problems related with the livelihoods have hit the vulnerable people the most. Agriculture is the hardest hit sector.
Nepal is one of the 20 most disaster-prone countries in the world. The data on human mortality for the period 1971-2007 show more than 27,000 deaths, 50,000 injuries, 3,000 missing and approximately 5 million affected people. More people are killed by disasters in Nepal than in any other country in South Asia.One of such disasters is an earthquake.
Earthquake is a physical phenomenon caused by the release of seismic waves from the interior of the earth on its surface. The earthquake produces the seismic waves, which are detected by a sensitive instrument called seismograph, by means of seismometer.
Earthquake is caused by faulting and folding in the crust due to tectonic activities.The mechanism of earthquake is well defined by the Elastic Rebound Theory.The earth is a dynamic body,the plates on the earth are moving continuously,due to which the rocks, at the plate boundaries, are continuously undergoing deformation. During the process of deformation of a plate, a great amount of stress is gradually exerted on the rock. When the stress exceeds the elastic limit, a fracture is developed.But the friction along the fracture resist the movement for a certain time, when the stress exceeds the frictional resistance also, the block moves along a fault plane i.e, an accumulated energy is suddenly released and it travels through the earth shaking the earth's crust for a period of time.This concept of earthquake is called 'Elastic Rebound Theory'.
The earthquake may also occur due to collapse of subterrain cavities and underground mines. The ground may shake due to large scale blasting and the use of heavy machines as well as passing trains and tanks.Big landslides and avalanches are also responsible for ground tremor. Other reason may be the volcanic eruption and collapse of volcanic terrain.
Some of the effects of earthquake can be listed below:
Destruction of Various civil engineering structures like dams, bridges, tunnels etc.
Creation of irregularities and cracks on earth's surface.
Causes of landslides along hill slopes
Changes in courses of river due to faulting across them.
Formation/deformation of lakes, springs, and waterfalls.
Submarine earthquakes may cause Tsunamis.
Subsidence of land mass.
Cracking of gas and water pipes.
Soil liquefaction.
Heavy loss of life and property.
Seismic areas are places which experience earthquakes frequently. The civil engineers must think of making his construction immune to earthquakes. The difficulties in achieving these objectives are:
the exact place of earthquake (this is important because the epicenter region will be worst affected and hence needs maximum protection).
the magnitude of an earthquake (this is important because the cost of construction increases with increases in safety required).
the duration of earthquake (this is important because the extent of the damage will be more if duration is more).
the direction of movement of the ground at the time of earthquake.
The above mentioned factors are crucial because unless they are known, assessment of probable damage due to earthquake to civil engineering structures is not possible.
Some of the civil engineering considerations in seismic areas are:
In seismic areas, the civil engineering Structures like buildings, bridges, dams,etc should be made resistant to earthquake damage.
structures should be designed in such a way that there will be no damage in a minor quake, and avoidance of serious damage or collapse in a major shake.
Seismic risk should be limited to socio-economically accepted levels.
Design, construction and maintenance is done taking in consideration of the possible seismic loads. The structures do not necessarily have to be extremely strong or expensive but have to be properly designed to withstand the seismic effects while sustaining an acceptable level of damage.
The epicenter region, probable magnitude and duration of earthquake, direction of movement of the ground at the time of the earthquake are not possible to predict. This brings difficulty in achieving the objective. Proper assessment is necessary to incorporate the required safety factor in producing earthquake-resistant designs .
3. Discuss briefly on Geomechanical classification of Rock mass (RMR).
The mass of rock interrupted by discontinuities with each constitute discrete block having intact rock properties is known as Rock mass.
Rock mass are heterogeneous because of different rock type ,presence of discontinuities, and varying degrees of weathering.The Stability and deformability of rock is dependent on the strength and the deformability of the rock mass. Bedding Planes, foliation, joints,faults,and fault zones are all forms of discontinuities.
Rock mass= Intact Rock + Discontinuities
During the the feasibility and preliminary design instead of a project, when very little detailed information on the rock mass and its stress and hydrologic characteristics is available, the use of rock classification scheme can be of considerable benefit. Different classification system place different emphases on the various parameter, and it is recommended that at least two method be used at any site during the early stage of a project.
Rock Mass Classification is the process of placing a rock mass into groups or classes on defined relationships (Bieniawski, 1989) and assigning a unique description (or number) to it on the basis of similar properties/characteristics such that the behavior of the rock mass can be predicted. The Rock mass classification system at
Terzaghis Rock mass classification
Rock quality designation index (RQD)
Geomechanical classification/ RMR classification
Rock tunneling quality index(Q-index)
Geomechanical classification/ RMR classification
Bieniawski published the details of a rock mass classification called the geomechanics classification and widely known as rock mass rating (RMR) system.This system combines the most significant geologic parameters and represent them with one overall comprehensive index of Rock quality, which is used for the design and construction of exhibition in rock, such as tunnels, mines and foundations.
The following 6 parameters are used to classify a rock mass using RMR system.
Uniaxial compressive strength of rocks,
RQD,
Spacing of discontinuities,
Condition of discontinuities,
Orientation of discontinuities,
Groundwater conditions.
According to Bieniawski (1993), the objectives of rock mass characterization and classification are:
to identify the most significant parameters influencing the behavior of a rock mass;
to divide a particular rock mass formation into a number of rock mass classes of varying quality;
to provide a basis for understanding the characteristics of each rock mass class;
to derive quantitative data for engineering design;
to recommend support guidelines for tunnels and mines;
to provide a common basis for communication between engineers and geologists;
to relate the experience on rock conditions at one site to the conditions encountered and experience gained at other
Advantage of Rock mass Classification System:
Classification of rock mass improves the quality of site investigations by calling for a systematic identification and quantification of input data. A rational, quantified assessment is more valuable than a personal (non-agreed) assessment. Classification provides a checklist of key parameters for each rock mass type (domain) i.e. it guides the rock mass characterization process. Classification results in quantitative information for design purposes and enables better engineering judgment and more effective communication on a project (Bieniawski, 1993). A quantified classification assists proper and effective communication as a foundation for sound engineering judgment on a given project (Hoek, 2007). Correlations between rock mass quality and mechanical properties of the rock mass have been established and are used to determine and estimate its mechanical properties and its squeezing or swelling behavior.
Disadvantages of rock mass classification:
According to Bieniawski (1993), the major pitfalls of rock mass classification systems arise when:
using rock mass classifications as the ultimate empirical cook book, i.e. ignoring analytical and observational design methods;
using one rock mass classification system only, i.e. without cross-checking the results with at least one other system;
using rock mass classifications without enough input data;
using rock mass classifications without full realization of their conservative nature and their limits arising from the database on which they were developed.
Some people are of the opinion that
natural materials cannot be described by a single number,
other important (often dominating) factors are not considered
results of rock mass classification are prone to misuse (e.g., claims for changed conditions)
